Survival of Class III Amalgam and Composite Restorations in Primary Cuspid Teeth
by
Edwin Ka Meng Kenneth Chan
A thesis submitted in conformity with the requirements for the degree of Master of Science in Paediatric Dentistry
Faculty of Dentistry University of Toronto
© Copyright by Edwin Ka Meng Kenneth Chan 2018
ii
Survival of Class III Amalgam and Composite Restorations in
Primary Cuspid Teeth
Edwin Ka Meng Kenneth Chan
Master of Science Paediatric Dentistry
Faculty of Dentistry University of Toronto
2018
Abstract
Objective: The aim of this retrospective cohort study was to determine the survival of class III
amalgam and composite restorations in primary canines. Methods: A chart review was done on
patients seen at the University of Toronto’s pediatric dental clinic between 1999 and 2017.
Results: The median survival time of amalgam and composite was approximately 4.5 years and
3.8 years respectively. There was no significant difference between the clinical survival of
amalgam and composite (log-rank test: p=0.09, Wilcoxon: p=0.31). Amalgam was significantly
less likely to fail due to recurrent caries versus composite (p<0.01). Conclusion: In this study,
both amalgam and composite restorations had similar survival when used as a restorative
material for class III restorations in primary canines.
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Acknowledgments
I would like to thank my thesis supervisor Dr. Paul Andrews for always being available and for
his continual support throughout not only this project, but also my education. Also, I am grateful
for the valuable expertise, feedback and direction provided by my committee members Dr. Amir
Azarpazhooh, Dr. Keith Titley and Dr. Michael Sigal. Lastly, thank you Junmin Yang for all
your help and sharing your knowledge on statistical analysis.
A special thank you to my family for supporting me throughout the many years, thank you for
always being there for me.
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Table of Contents
Acknowledgments .......................................................................................................................... iii
Table of Contents ........................................................................................................................... iv
List of Tables ................................................................................................................................ vii
List of Figures .............................................................................................................................. viii
List of Appendices ......................................................................................................................... ix
List of Abbreviations ...................................................................................................................... x
1 Introduction ................................................................................................................................ 1
2 Literature Review ....................................................................................................................... 2
2.1 Amalgam ............................................................................................................................. 2
2.1.1 History ..................................................................................................................... 2
2.1.2 Composition ............................................................................................................ 3
2.1.3 Setting Reaction and Properties .............................................................................. 3
2.1.4 Use of Amalgam ..................................................................................................... 4
2.2 Composite ........................................................................................................................... 5
2.2.1 History ..................................................................................................................... 5
2.2.2 Composition ............................................................................................................ 6
2.2.3 Polymerization and Properties ................................................................................ 6
2.3 Determining Restoration Longevity ................................................................................... 7
2.3.1 Differences in Primary and Permanent Teeth ......................................................... 8
2.3.2 Evaluation Criteria .................................................................................................. 9
2.4 Class III Cavity ................................................................................................................. 10
2.4.1 Cavity Preparation Types ...................................................................................... 10
2.5 Class III Longevity ........................................................................................................... 13
2.5.1 Primary Teeth ........................................................................................................ 13
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2.5.2 Permanent Teeth ................................................................................................... 15
2.6 Comparison of Class II Restorations ................................................................................ 20
2.6.1 Primary Molars ..................................................................................................... 20
2.6.2 Permanent Molars ................................................................................................. 22
3 Objectives ................................................................................................................................. 28
4 Materials and Methods ............................................................................................................. 28
4.1 Design ............................................................................................................................... 28
4.2 Sample Size ....................................................................................................................... 31
4.3 Data Analysis .................................................................................................................... 32
5 Results ...................................................................................................................................... 33
5.1 Descriptive Data ................................................................................................................ 33
5.2 Survival Curves ................................................................................................................. 39
5.2.1 Amalgam Survival Curve ..................................................................................... 39
5.2.2 Composite Survival Curve .................................................................................... 41
5.3 Amalgam versus Composite ............................................................................................. 43
5.4 Influence of Variables ....................................................................................................... 44
5.5 Reason for Failure ............................................................................................................. 47
5.6 Reliability Between Evaluators ......................................................................................... 47
5.7 Reliability Between Pre-tests ............................................................................................ 48
5.8 Radiographic Evaluation ................................................................................................... 48
5.8.1 Association Based on Radiographic Interpretation ............................................... 50
5.8.2 Association Based on Chart Data ......................................................................... 51
6 Discussion ................................................................................................................................ 54
6.1 Potential Limitations ......................................................................................................... 59
6.2 Future Directions .............................................................................................................. 61
7 Conclusions .............................................................................................................................. 61
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References ..................................................................................................................................... 63
Appendices .................................................................................................................................... 78
vii
List of Tables
Table 1. Demographic characteristics of restorations ................................................................... 34
Table 2. Clinical characteristics .................................................................................................... 36
Table 3. Survival probability of amalgam class III restorations ................................................... 39
Table 4. Survival probability of composite class III restorations ................................................. 41
Table 6. Patient demographic and health factors influence on survival ....................................... 45
Table 6. Clinical condition and setting factors influence on survival ........................................... 45
Table 7. Hazard ratio for levels of material, age and surface ....................................................... 46
Table 8. Relative risk of amalgam compared with composite being due to defective restoration,
necrosis and recurrent caries ......................................................................................................... 47
Table 9. Kappa between evaluators for radiographic radiolucencies ........................................... 47
Table 10. Kappa between pre-tests for radiographic radiolucencies ............................................ 48
Table 11. Range of follow-up periods for post-operative radiographs ......................................... 49
Table 12. Radiographic evaluation ............................................................................................... 50
Table 13. Location of radiolucency if related to caries ................................................................ 50
Table 14. Location of radiolucency if related to procedural technique ........................................ 51
Table 15. Location of radiolucency if chart data indicated failure due to a defective restoration 51
Table 16. Location of radiolucency if chart data indicated failure due to recurrent decay .......... 52
viii
List of Figures
Figure 1. Frontal view of a four year-old child's smile ................................................................... 1
Figure 2. Conventional preparation as described by Piyapinyo and White .................................. 11
Figure 3. Modified preparation as described by Piyapinyo and White ......................................... 11
Figure 4. Conventional class III cavity preparation on the distal aspect of the upper right primary
canine ............................................................................................................................................ 13
Figure 5. Modified class III cavity preparation with a dovetail on the distal aspect of the upper
right primary canine ...................................................................................................................... 13
Figure 6. Copy stand and camera for digitizing film radiographs ................................................ 31
Figure 7. Amalgam Kaplan-Meier survival curve ........................................................................ 39
Figure 8. Composite Kaplan-Meier survival curve ....................................................................... 41
Figure 9. Amalgam versus composite survival curves ................................................................. 44
Figure 10. Right maxillary canine AR at 521 day follow-up in adequate condition .................... 53
Figure 11. Right mandibular canine CR at 464 day follow-up in adequate condition ................. 53
Figure 12. Right maxillary canine AR at 586 day follow-up with caries-related radiolucency
involving the cavosurface margin and gingival wall .................................................................... 53
Figure 13. Left mandibular canine CR at 322 day follow-up with caries-related RL involving
cavosurface margin, gingival and axial wall ................................................................................. 53
Figure 14. Left mandibular canine AR at 1289 day follow-up with procedural-related RL
requiring replacement involving cavosurface margin and gingival wall ...................................... 53
Figure 15. Left mandibular canine CR at 1274 day follow-up with procedural-related RL
involving cavosurface margin ....................................................................................................... 53
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List of Appendices
Appendix A. Personal consent form……………………...………………………….………...78
x
List of Abbreviations
AFR Annual failure rate
AR Amalgam restorations
ASA American Society of Anesthesiologists
Bis-GMA Bisphenol A-glycidyl methacrylate
BPA Bisphenol A
CI Confidence interval
CQ Camphoriquinone
CR Composite restorations
dmfs Decayed missing filled surfaces for primary teeth
EDMA Ethylene glycol dimethacrylate
ENT Ear, nose and throat
GA General anesthesia
HR Hazard ratio
LA Local anesthesia
MMA Methyl methacrylate
MST Median survival time
N2O Nitrous oxide
N2O+midaz Nitrous oxide and oral midazolam
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NECAT New England Children’s Amalgam Trials
NHS National Health System
PPD 1-phenyl-1,2-propanedione
RCT Randomized control trials
RL Radiolucency
RMGI Resin-modified glass ionomer
RR Relative risk
SD Standard deviation
TEGDMA Triethylene glycol dimethacrylate
UDMA Urethane dimethacrylate resin
USPHS United States Public Health Service
VLA Visible light activated
°C Degrees Celsius
γ-MPTS γ-methacryloxypropyltriethoxysilane
% Percent
1
1 Introduction
Dental caries or tooth decay is described by the United States Surgeon General’s report as the
most common chronic disease of children, stating it is “five times more common than asthma
and seven times more common than hay fever” (U.S. Department of Health and Human Services,
2000). Its effect on children is particularly concerning since it has shown to have a negative
effect on sleep, school performance, learning, behavior, eating, nutrition and growth (Acs,
Lodolini, Kaminsky, & Cisneros, 1992; Blumenshine, Vann, Gizlice, & Lee, 2008; Clarke et al.,
2006; Edelstein, Vargas, Candelaria, & Vemuri, 2006; Vargas, Macek, Goodman, & Wagner,
2005).
Amalgam restorations (AR) and composite (CR) restorations are the two major materials of
choice for direct intra coronal restorations in both the primary and permanent dentition. Although
amalgam was considered the standard in the past, there has been a steady shift to the use of
composite since its invention (Berthold, 2002; Sunnegårdh-Grönberg, van Dijken, Funegård,
Lindberg, & Nilsson, 2009). This change is most perceptible in the anterior region where
cosmetics is more of a concern. However, the use of amalgam in the anterior dentition continues
to be presented as an acceptable restorative option. It is included in didactic teaching and in
textbooks such as Sturdevant's art & science of operative dentistry (2014). Furthermore, a
particular situation where esthetics is no longer a concern is the restoration of the distal aspect of
canines. The curvature of the dental arch and the presence of an individual’s lips makes this
region difficult or even impossible to visualize (see Figure 1).
Figure 1. Frontal view of a four year-old child's smile
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In terms of affordability, AR continue to be the more affordable material (Beazoglou et al., 2007;
B. Wilson, 1991). Lastly, the longevity of each restorative material is an important consideration.
One study has estimated that 60% of restorative or operative work is the replacement of failed
restorations (Mjör, 1989). The literature available on the longevity of amalgam or composite in
primary anterior teeth is minimal and is mainly based on expert opinion (Council on Clinical
Affairs AAPD, 2017). To the best of our knowledge, no previous published literature has
compared the outcomes of intra coronal primary anterior canine amalgam versus composite resin
restorations. Thus, the aim of this retrospective cohort study is to determine the survival of class
III amalgam and composite restorations in primary canines at the University of Toronto’s
pediatric dental clinic.
2 Literature Review
2.1 Amalgam
2.1.1 History
Dental amalgam became popular during the 19th century as a restorative material when silver
coins were mixed with mercury. However, dental amalgam has been documented to have been
used as early as the Tang Dynasty in China between 618-907 A.D. and may have been used even
earlier (Bjørklund, 1989; Czarnetzki & Ehrhardt, 1990). The initial composition of a dental
amalgam formed of bismuth, lead and tin, had a melting point of 100°C. The addition of
mercury lowered the melting point to approximately 68°C (Hanson & Pleva, 1991). The
popularization of amalgam was in part due to the work of G.V. Black. He described the
properties of an amalgam composed of silver, tin, gold and zinc, as well as the principles of
cavity design (G. V. Black, 1895, 1896).
While it is the most commonly used dental material for the restoration of posterior teeth, it has
declined in use during the last decade (Beazoglou et al., 2007). This can be attributed to an
increased importance given to esthetics and the controversy surrounding mercury and dental
amalgams. The latter concern has been the topic of a number of papers that have studied and
have not found any correlation between dental amalgam’s mercury release and effect on the
nervous system, renal system, nor any other medical concerns (ADA Council on Scientific
3
Affairs, 1998; Bellinger et al., 2006; Bellinger et al., 2008; Brownawell et al., 2005; DeRouen,
Martin, Leroux, & et al., 2006; Saxe et al., 1999). However, some small studies have found a
higher mercury concentration in urine when dental amalgams are present (Bellinger et al., 2006;
Bellinger et al., 2008; Evens et al., 2001; Gabrio et al., 2003; Trepka et al., 1997).
Mercury can exist in its elemental, organic or inorganic form. The release of mercury from
dental amalgams occurs as a vapor or as an inorganic ion. Thus, the greatest risk of mercury
release occurs during the placement or removal of the restoration. The uptake of mercury is most
significant during inhalation as absorption of inorganic mercury through skin or the
gastrointestinal tract is poor. To reduce any risk, proper burnishing, isolation and disposal is
recommended (Van Noort, 2013).
2.1.2 Composition
The mixture of a metal and mercury (Hg) forms an amalgam. In dentistry, these metals are often
silver (Ag), tin (Sn), copper (Cu) and zinc (Zn). The alloy in amalgam capsules can have
different sizes and shapes which will alter the handling and physical properties of the material.
Lathe-cut particles of the alloy is made by machining a solid ingot, whereas spherical particles
are created by spraying melted alloy into an inert atmosphere where the droplets harden into
small spherical pellets. The latter particle shape provides a greater ease of condensation and
lowers the mercury required due to its lower surface area to volume ratio. Whereas in the past
amalgam was mixed by hand, manufacturers today sell the material in capsules. The capsule
contains mercury and the alloy separated by a membrane. During preparation, the membrane is
broken and the two components mix during trituration to form the final product.
2.1.3 Setting Reaction and Properties
The mixing of the alloy Ag3Sn (γ or gamma) and mercury (Hg) forms three phases: γ + Ag2Hg3
(γ1) + Sn7Hg (γ2). The γ phase and the γ1 phase have similar hardness, while the γ2 is softer. The
tensile strength of γ2 is weaker than the other two phases as well. Corrosion of amalgam occurs
readily when used as a dental restorative material. These corrosion products are what produces a
4
good marginal seal, but the formation of an oxidation cell in a gap can cause breakdown in the
amalgam’s properties (Ben-Amar, Cardash, & Judes, 1995; Van Noort, 2013). Because the γ2
phase is more electronegative, it is the phase most responsible for the corrosion process. The
final composition of the phases is dependent on the mercury in the final composition, where
larger amounts of mercury will produce larger amounts of the weaker phases. Consequently,
high copper amalgams were developed to reduce the γ1 and γ2 phases. The initial reaction is
followed by another reaction: γ2 + Ag-Cu → Cu6Sn5 + γ1. The addition of copper causes very
little γ2 phase being formed reducing the amount of corrosion. High-copper content amalgams
have shown to have less creep, higher compressive strength, less marginal breakdown and less
dimensional changes (Van Noort, 2013).
The expansion or contraction of an amalgam depends on its composition. In general, there is an
initial contraction as Hg mixes with the alloy. Afterwards, an expansion of the material occurs
with the formation of γ1 crystals. This is more likely if a sufficient quantity of Hg is available.
Modern formulations which contain lower Hg to alloy ratios and smaller particle sizes will often
show a net contraction of the material (Van Noort, 2013).
2.1.4 Use of Amalgam
The use of amalgam is based on its historical success, ease of use, longevity, strength and
affordability (Heymann et al., 2014). Amalgam has been shown to reduce microleakage due to
self-sealing from corrosion products at the cavosurface margin (Guthrom, Johnson, & Lawless,
1983). It has better dimensional stability when placed in the presence of moisture versus
composite (Oliva & Lowe, 1987). Dental amalgams have demonstrated superior antibacterial
properties when compared to composite (Beyth, Domb, & Weiss, 2007). The reported
disadvantages of amalgam include: it is not tooth-colored, does not bond to the tooth and
requires a preparation that is retentive. Due to esthetic concerns, the use of amalgam in the
anterior region has been often limited to the distal of the cuspid teeth.
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2.2 Composite
2.2.1 History
Epoxy resins were first described as a potential dental restorative material by Bowen (1956). At
the time, methyl methacrylate (MMA) was the main monomer used, but it had many faults
including shrinkage, low stiffness and a high thermal expansion coefficient (Bowen, 1963;
Paffenbarger, Nelsen, & Sweeney, 1953). As a result, bisphenol A-glycidyl methacrylate (Bis-
GMA) was developed and demonstrated less shrinkage than MMA (Bowen, 1963, 1982).
Roughly at the same time, Buonocore had detailed acid etching and micromechanical bonding of
enamel (M. Buonocore, Wileman, & Brudevold, 1956; M. G. Buonocore, 1955). Presently, CR
have gained popularity, are increasingly selected by patients and the time allotted in the dental
curriculum to its instruction has increased (Burke et al., 2003; C. D. Lynch, McConnell, &
Wilson, 2007; Pair, Udin, & Tanbonliong, 2004; Varughese, Andrews, Sigal, & Azarpazhooh,
2016).
Bisphenol A (BPA), a xenoestrogen, is released from CR by salivary enzymatic hydrolysis or
can be present as an impurity as most dentin bonding resins are made of BPA derivatives
(Fleisch, Sheffield, Chinn, Edelstein, & Landrigan, 2010). A xenoestrogen is a compound that
demonstrates estrogen-like properties. Xenoestrogens have been established as endocrine
disrupting chemicals that can be involved at high enough doses in alterations to fertility, growth
and development and increases cancer rates in wildlife and humans (Choi, Yoo, & Lee, 2004).
BPA can be detected in saliva for up to three hours after the insertion of a composite restoration
(Fung et al., 2000). A study done in children and adolescents that measured urinary BPA levels
concluded that dental composites are not a measurable source of BPA after placement
(Maserejian et al., 2016). Their research demonstrated that the transient increases in urinary BPA
concentration, were no longer detectable in the samples taken at approximately 14 days and 6
months after placement. However, they did notice a larger increase in one participant who had 8
surfaces restored at the visit and decided to exclude this participant in their conclusion. While,
the authors described the latter as an outlier, children with high caries risk can often have greater
than 8 surfaces restored in one visit. In particular, children seen under general anesthesia (GA)
with early childhood caries can receive over 8 surfaces restored during their treatment visit. To
limit BPA released, it is recommended to remove the unpolymerized monomer found in the
6
oxygen inhibited layer on the surface with pumice on a cotton ball or a rubber cup on a slow-
speed handpiece (Rueggeberg, Dlugokinski, & Ergle, 1999).
2.2.2 Composition
Resin-based composite materials are formed by three main components: a resin matrix, a filler
and a coupling agent. The resin matrix is a monomer such as Bis-GMA, urethane dimethacrylate
resin (UDMA), ethylene glycol dimethacrylate (EDMA) and triethylene glycol dimethacrylate
(TEGDMA). Fillers are used in composites to reduce shrinkage, reduce the thermal expansion
coefficient, improve mechanical properties, incorporate a radiopaque element and control
esthetic features such as colour, translucency and fluorescence (Van Noort, 2013). The filler used
determines the classification of the composite depending on the nature and the size of the filler
(Van Noort, 2013). Traditional composites contain glass fillers between 10-20µm, have a poor
surface finish and are dull in appearance. Microfilled resins contain colloidal silica fillers
between 0.01-0.05µm. The small particle size allows a polished and smooth finish, but the
quantity of filler that can be used is limited due to the high surface area. Smaller particle sizes
have a higher surface to volume ratio to form bonds with monomer molecules, which will
increase the viscosity and decrease the flow of the composite resin. Hybrid composites contain
large fillers between 15-20µm and a small amount of colloidal silica sized between 0.01-0.05µm.
Small-particle hybrid composites have filler particles between 0.1-6.0µm. Lastly, a silane
coupling agent is used to bond the resin and filler to each other. The most common silane is γ-
methacryloxypropyltriethoxysilane (γ-MPTS).
2.2.3 Polymerization and Properties
Initially, the polymerization of composite would occur after mixing two pastes, one of which
would contain an activator that would polymerize the material. Ultraviolet light activated
composites paved the way for visible light activated (VLA) composites. Currently, VLA
composites often use camphoriquinone (CQ) or 1-phenyl-1,2-propanedione (PPD) as the UV
activator compound. These two activators are photosensitive initiators that are responsible in
starting the polymerization process. The advantage of PPD is that it does not have the
7
undesirable yellowing effect of CQ (Cook & Chong, 1985; Park, Chae, & Rawls, 1999; Silami,
Mundim, Garcia, Sinhoreti, & Pires-de, 2013).
During polymerization of composite, a 1.5-5% shrinkage occurs as the material undergoes
volumetric contraction (Ferracane, 2005). The change in volume can potentially lead to a
decreased bond strength or the formation of gaps between the restoration and the tooth surface
(Ferracane & Mitchem, 2003; Van Ende, Mine, De Munck, Poitevin, & Van Meerbeek, 2012).
To minimize these effects, it has been suggested to control the stress development within the
restoration by the design of the cavity preparation, use of bases under the restorations, rubber
dam isolation to control moisture and finally the placement of the resin in small increments
(Carvalho, Pereira, Yoshiyama, & Pashley, 1996; Fleisch et al., 2010).
Composite resin is an esthetic restorative material that has acceptable strength and sealing
characteristics (Lambrechts, Willems, Vanherle, & Braem, 1990). However, it is more technique
sensitive than amalgam and requires a well isolated dry field (Burrow et al., 1995; Fundingsland,
Aasen, Bodger, & Cernhous, 1992). In fact, it is suggested that composites are not the materials
of choice if patient cooperation or isolation are not satisfactory (Antony, Genser, Hiebinger, &
Windisch, 2008).
2.3 Determining Restoration Longevity
After meta-analyses and systematic reviews, randomized control trials (RCTs) are considered the
strongest form of scientific evidence. Some authors argue that a controlled research environment
does not necessarily mirror a dental practice, especially when technique-sensitive materials are
involved (Anusavice, 1989; Tyas, 1991). A material’s success may not reflect those
demonstrated in a controlled setting, since restorations are not always placed consistently in
clinical practice under the same conditions with uniform cavity preparation. Alternative study
designs are occasionally done in a general practice, but this may not necessarily be better as there
is limited time for dentists to conduct research and thresholds for replacement can vary (Drake,
Maryniuk, & Bentley, 1990). Certain authors argue there is no incentive to produce more than an
acceptable standard quality of care (Drake et al., 1990). The result is studies with short follow-up
8
times. The situation is further confounded due to inconsistencies in the definitions of restoration
success or failure between studies or even within studies.
Determining the true clinical performance of a restorative material is difficult as there are many
variables that are difficult to control or record that may influence the materials performance over
time. Prospective studies over an extended time period lead to issues such as a greater number of
participant dropouts, difficulty with recruitment, expense, changes in materials that are available,
patient representation, clinician’s change in diagnostic ability or replacement criteria (Jokstad,
Bayne, Blunck, Tyas, & Wilson, 2001; Mackert & Wahl, 2004).
Retrospective studies are based on a review of charts which can then be combined with a recall
examination of the patients for evaluation of the restoration’s performance. However, because it
relies on previous documentation, there may be missing information or little information on the
conditions of placement or reason for replacement (Jokstad et al., 2001). In fact, replacements
may not always be due to failure (Anusavice, 1989). The advantage of this type of study is that a
large number of restorations are easily evaluated to determine their success or failure, while a
disadvantage is the lack of control over the placement technique and material selection (Mackert
& Wahl, 2004).
Replacement studies are perhaps a weaker form of evidence for longevity studies, since there is a
lack of consistency in recorded information. Since the time until replacement is being recorded,
the actual time frame may reflect clinical practice quite well, but the reasons for replacement and
evaluation criteria are often not clear. Also, many of these studies do not include the
demographic characteristics of the patients, nor the clinical details such as the setting the
restoration was placed in or the patient’s level of cooperation.
2.3.1 Differences in Primary and Permanent Teeth
Primary or deciduous teeth are different than permanent or succedaneous teeth. Primary teeth
have a thinner enamel and dentin layer, there is greater amount of organic matter and less
mineral salts in the enamel. The prismless layer present in primary teeth does not respond well to
acid etching, dentin is less mineralized and has been described as being more reactive to acid
etching than permanent teeth, and lower bond strengths have been reported (Lee, 2002; Skalerič,
9
Ravnik, Cevc, & Schara, 1982; P. Wilson & Beynon, 1989). While there is some available
literature of the two materials being evaluated, this review will contain sections on the two
materials being used in permanent teeth due to the limited availability of evidence based
literature on the subject of longevity on class III restorations. Consequently, the literature
published regarding permanent teeth cannot be directly correlated to primary teeth. Thus, the
clinical data presented later in this review must be judiciously evaluated as to its pertinence.
2.3.2 Evaluation Criteria
A number of authors have used the United States Public Health Service (USPHS) evaluation
criteria for dental restorations, also called the Ryge criteria (Ryge & Snyder, 1973). However,
numerous studies use their own modified version of the Ryge criteria to appraise restorations in
their studies which makes a direct comparison between studies more difficult. The criteria
evaluated are based on visual and tactile inspection. Colour match, anatomic contour, marginal
discolouration, marginal integrity, secondary caries, surface texture and gross facture are
evaluated on an Alfa, Bravo, Charlie and occasionally Delta ranking scale. The system describes
the factors for each score, however the scores remain as subjective observations of various
characteristics. Alfa and Bravo scores are considered as a restoration being satisfactory, whereas
any score of Charlie or Delta is considered as unsatisfactory. This can differ from one paper to
another as authors will modify the number of rankings or the definitions for each criterion. The
criteria are not always applied in the manner it was originally suggested, where it was
recommended that two independent non-operators be calibrated to 80% reproducibility.
The FDI World Dental Federation criteria for evaluation of direct and indirect restorations is a
proposed improvement over Ryge’s criteria (Reinhard Hickel et al., 2007). Each criterion is
divided into 5 categories ranging from clinically excellent to clinically poor; where the latter is
when replacement is necessary. Three broad categories are further subdivided. In the esthetic
properties category, the characteristics evaluated are the following: surface luster, surface
staining, colour stability and translucency and anatomic form. The functional properties category
includes the following: fractures and retention, marginal adaptation, wear, contact point,
radiographic examination and patient’s opinion. Lastly, biological properties are considered
including: postoperative sensitivity and tooth vitality, recurrence of caries, erosion and
10
abfraction, tooth integrity (cracks), periodontal response, adjacent mucosa, oral and general
health.
Comparative studies between amalgam and composite are generally at risk for bias as it is
impossible to blind the evaluators, randomization generally does not occur and many studies
have short follow-up periods. Finally, many studies claim they followed the restorations for a
certain time period but then do not provide actual data for the mean, range of follow-up periods
or number of teeth in each time period.
2.4 Class III Cavity
The class III cavity involves a carious lesion in the interproximal region of an anterior tooth (G.
Black, 1917). The restoration of anterior primary teeth has been described by Shah, Lee, and
Wright (2004) to be a challenge due to their small size, proximity of the pulp, thin enamel, lack
of surface area for bonding and child cooperation.
There is very little literature available for class III restorations in both the primary and permanent
dentition. This is reflected in the American Academy of Pediatric Dentistry’s (AAPD) restorative
dentistry guideline (2017) which states there is no data to support amalgam’s use as a class III
restoration material and there is “expert opinion” level of evidence to support the for the use of
composites. Expert opinion is defined by the AAPD as being based on retrospective trials, case
reports, in vitro studies and opinions from clinical researchers.
2.4.1 Cavity Preparation Types
An in vitro study done by Piyapinyo and White (1998) evaluated 15 extracted primary central
incisors with a conventional (triangular) class III preparation versus 15 incisors that were
prepared with a modified class III design by adding a 0.5mm labial reduction (see Figure 2 and
3). The cavity preparations were filled with a composite resin Herculite XRV (Kerr
Manufacturing Co., Romulus, MI). The two groups were thermocycled and then tested for failure
under a load via a pin. The mean failure load of the restoration group that had the labial
reduction (92.2±13.6N) was significantly higher than the conventional preparation group
11
(45.6±9.8N) (p<0.001). However, this data is based on in vitro results with a small sample size
which do not always correlate with clinical significance. Also, the measure of the mean failure
loads relied on the failure at the position of the pin head described to be a size 17 silk pin, which
is not representative of the forces that a restoration would endure in vivo.
Figure 2. Conventional preparation as described by Piyapinyo and White
Figure 3. Modified preparation as described by Piyapinyo and White
Another in-vitro study compared the placement of a bevel on the cavosurface margin of class III
resin-based composite restorations and found a bevel resulted in less microleakage (Hoelscher,
Gregory, Linger, & Pink, 2000). However, as mentioned before, in-vitro results do not always
lead to similar meaningful clinical significance. The effect of a bevel was investigated in a study
that found that while beveled enamel margin class V cavity preparation resulted in better
12
retention at 6 months, after three years there was no significant difference (Baratieri, Canabarro,
Lopes, & Ritter, 2003). Another clinical assessment over 11 years compared 52 pairs of
permanent anterior teeth with or without beveling of a conventional preparation and found no
overall difference (Qvist & Strøm, 1993). They did notice beveled restorations had more
marginal discoloration and marginal discrepancies at 2 and 6 years respectively, but this was not
found at the 11-year follow-up. Also, a meta-analysis done on anterior composite restorations
found bevels to have no significant influence on the survival of the restoration (Heintze,
Rousson, & Hickel, 2015).
Various class III preparations were tested to evaluate their effect on tensile failure load for
composite restorations (Asl Aminabadi et al., 2014). Four groups of 24 preparations each were
verified: conventional (A), labial surface bevel (B), conventional with air abrasion (C) and labial
surface bevel with air abrasion (D). They found significant differences between groups A and C
(P = 0.003), groups A and B (P < 0.001), groups A and D (P < 0.001), groups B and C (P =
0.028), groups B and D (P = 0.027), and also groups C and D (P< 0.001). However, the mean
tensile failure load was 20.66±7.99N for group A, 42.04±19.68N for group B, 28.69±11.90N for
group C and 54.23±7.41N for group D. The recorded tensile failure loads indicated a larger
standard deviation (SD) for group B, which may signify a large variation in technique or material
quality. More importantly, when the SDs are taken into account there is overlap of force needed
for failure between groups A and B, A and C, B and C, B and D. Also, if the range between
minimum and maximum force required until failure for each group is taken, then all four groups
overlap with each other. Consequently, when there is variation within an in-vitro study that
indicates the tensile failure load for each preparation was not regularly different, its application
clinically may vary even more; where there is more variation in technique and environment in
which the restoration is placed.
Trairatvorakul and Piwat (2005) studied slot versus dovetail class III restorations in primary
teeth that were restored with a composite resin Herculite XRV. They had 36 matched pairs and
evaluated them for up to 24 months using an adapted version of Ryge’s criteria and found no
difference in the clinical characteristics between the two designs. They state that while not
statistically different slot preparation exhibited a 90.9% optimal rating versus 86.4% for dovetail
counterparts. They note in their selection criteria that the patient had to be cooperative and with a
small to medium size caries lesion in the middle third and the depth had to be confined to the
13
dentinoenamel junction. Rathnam, Nidhi, Shigli, and Indushekar (2010) found no statistical
difference after 12 months in 50 pairs of anterior primary teeth with class III slot and dovetail
preparations. As a result, both these papers recommend the use of a slot preparation to avoid
removing unnecessary tooth structure. Despite their closing remarks, it cannot be concluded that
these two preparation types are comparable since both these studies have small samples and short
follow-up, one can postulate that failures may differ, or become more evident with longer
follow-up.
The studies that have compared different class III cavity preparation types are infrequent and it is
difficult to conclude from the existing literature if placing a dovetail and/or bevel is of any
advantage to the performance or long-term survival of the restoration. Moreover, the literature
above concerns CR and not AR. Since, this author could not find any comparative studies
between conventional (see Figure 4) and dovetail (see Figure 5) preparations for class III AR.
Figure 4. Conventional class III cavity
preparation on the distal aspect of the upper
right primary canine
Figure 5. Modified class III cavity
preparation with a dovetail on the distal
aspect of the upper right primary canine
2.5 Class III Longevity
2.5.1 Primary Teeth
In an effort to regroup as much evidence as possible, the following review includes studies that
have included class III AR or CR as a subset of their study. But, the review will focus on
pertinent aspects of the described literature.
Part of a study done in 1986 (Atkins Jr, Rubenstein, & Avent) reported a 10.0% failure after 3 of
30 class III CR were done on primary teeth. They state that no additional mechanical retention
14
such as a labial or lingual dovetail lock was done. This failure rate is described at a short follow-
up period of 6 months. A study of a 1071 glass-ionomer and amalgam restorations as class I, II,
III and V restoration over a three-year period in children treated within the Public Dental Health
Service in Demark by 14 dentists reported that 2 of 14 class III or V AR in primary teeth failed
after three years (Qvist, Laurberg, Poulsen, & Teglers, 1997). The sample concerning class III
restorations is small and cannot be differentiated from the number of class V restorations as they
were combined in the same category. The latter group published an article regrouping several of
their papers and estimated a 75% survival time of 3.5 years for class III/V restorations (Qvist,
Poulsen, Teglers, & Mjor, 2010). The survival time estimate is based on a sample size of 77, but
it is unclear if the group is a combination of only composite and GI or includes amalgam as well.
A university-based study in Iran studied the survival of anterior restorations in three to five year
old children (Ajami, Ebrahimi, Makarem, Movahhed, & Motamedi, 2012). A total of 94 teeth
were restored, 17% were glass-ionomer, 42.6% compomer and 40.4% composite. The nine-
month retention rate for a compomer was 95%, 21% for composite and 12.5% for glass-ionomer.
The distribution of restorations was 21.3% class III, 29.8% class IV, 5.3% class V and 43.6%
were a combination of class IV and V restorations. Follow-up ranged from one to nine months
with a mean of only 5.5±0.3 months. The sample size is relatively small and is divided into
different materials used for a variety of types of cavity preparations. There was no breakdown to
see if there was a relative equal distribution of materials used per cavity type. Also, the majority
of restorations were likely larger restorations. Since, almost half the included restoration types
were what the authors called a combination of a class IV and V preparation.
A Fuji resin-modified glass ionomer (GC, Tokyo, Japan) was compared to Solare composite
(GC, Tokyo, Japan) by Priyank et al. (2016). 40 teeth were restored with each material and were
evaluated using Ryge’s criteria. They do not state who was involved with placement or
evaluation of the restorations. After 12 months both groups were evaluated to have a 100%
success rate. This is a short-term follow-up, with a small sample size and there is a risk of bias as
the authors did not explain who was involved with evaluating the restorations.
Pedrotti et al. (2017) evaluated the survival of resin-based composite restorations in primary
teeth in a university-based setting. The authors included 212 restorations from 76 children who
were considered to be high caries risk. The restorations were followed up to six years. The
15
restorations were clinically evaluated using the FDI criteria by two calibrated examiners. The
mean survival time was 4.3 years (95% CI: 4.0-4.6), the survival at six years was 35.3% and the
estimated annual failure rate was 18.8%. They did not document cavity preparation type, but
they did document that half the restorations (49.5%) were 1 surface restoration, whereas the
remaining restorations involved 2 or more surfaces. Moreover, only 29 teeth (or 13.7%) of the
total restorations were done on anterior teeth, hence the reader cannot be certain if class III
restorations were included. Most likely due to the small sample size, the authors did not estimate
survival for the anterior restorations separately. Thus, the mean survival time is probably more
representative of the survival of a posterior composite restoration in a primary tooth.
2.5.2 Permanent Teeth
An investigation done in permanent teeth evaluated 303 anterior restorations placed in 27
patients (van Dijken, 1986). This means that there was an average of 11 anterior teeth restored
per patient. Seven different composite restorative materials composed of various particle filler
types were used. 183 of the total restorations (60.4%) were class III and the rest were class IV or
V restorations. The main reason for replacement was recurrent caries and the cumulative
frequency of replacement varied between 14.8 and 55.1% depending on the material used. As the
authors mention, this sample of individuals are at high caries risk where almost each individual
had all their anterior teeth restored. Also, considering the number of individuals and the number
of materials used there is less variability or randomization, which consequently increases the risk
of bias.
Class III restorations were investigated as part of a study on the survival of anterior resin
composites in a general dentist practice (Van Noort & Davis, 1993). 14 dentists restored 2399
class III restorations over 5 years. The survival at five years was 62.9%. They note that there was
a large spread in performance between the dentists with the upper limit being 87.5% and the
lower limit being 37.0%. Also, they describe the probability of survival depending on the
material used ranged from 70.4±2.9% to 56.3±2.9%, but do not state if the materials with lower
success was associated with the dentist(s) that had lower success. The study states they did not
set criteria for which patients the dentists chose to include for the study, nor did they try to
16
standardize technique, nor did they calibrate the dentists as to deciding when a restoration was to
be replaced.
A study compared a macrofilled composite, microfilled composite and silicate cement over 10
years (Jokstad, Mjor, Nilner, & Kaping, 1994). One dentist placed 131 restorations in 57
patients, they were evaluated by two trained dentists, although they do not state if the operator
was involved in the evaluation. Survival curves were established, where visual interpretation of
the curve would estimate that the macrofilled resin had an approximate 95%, microfilled 80%
and silicate cement 40-45% survival at 10 years. The authors do not define clearly what was
considered a failure, but do state that an “unacceptable USPHS rating did not automatically
result in restoration replacements” and that the dentist practiced a treatment philosophy that
“advocates observation and preventive measures rather than immediate operative intervention”.
This comment can lead the reader to believe the survival curve is an estimate of success, as
failure was not always considered even if the restoration had an undesirable USPHS rating.
A study by Millar, Robinson, and Inglis (1997) evaluated a hybrid composite material Opalux
(ICI Dental, Macclesfield, Cheshire), which is no longer available, using the USPHS criteria.
They included 25 class III, 3 class IV and 16 class V restorations and followed up at 3 months,
then at 1, 2, 3 and 8 years. At 8 years, they found a 73% survival. While, they did follow-up on
the restorations for 8 years, the sample was relatively small. In addition, the three authors placed
and evaluated the restorations, which increases the risk of bias.
Three related articles were published at a three, five and six-year follow-up period (van Dijken,
1996, 1999, 2001). They placed 154 class III restorations in 50 patients to compare a compomer,
a resin-modified glass ionomer and a hybrid light-cure resin composite. These restorations were
evaluated on a yearly basis with modified USPHS criteria. At six years, 141 restorations were
evaluated, 16 (11.2%) were deemed unacceptable. The composite showed better colour match
and the RMGI had a higher surface roughness. It is unknown who was involved as an operator or
as an evaluator. Also, there is no mention of reliability or percent agreement tests being done.
The same first author was involved with another paper which compared an oxalic acid cavity
conditioning to a phosphoric acid etch technique when used in combination with two different
bonding systems and found no difference (van Dijken, Olofsson, & Holm, 1999). Of the 163
class III restorations and 12 class IV restorations, 95% were considered acceptable when
17
evaluated with modified USPHS criteria. The paper did not state if the two evaluators were
involved as operators.
Demirci and his colleagues published various articles following the performance of Dyract
(Dentsply de Trey, Konstanz, Germany), a polyacid modified resin composite at different time
intervals. The first study evaluated 61 restorations from 30 patients placed by the same operator.
They were assessed at a one-year period using the modified Ryge criteria and reported a 98.4%
retention rate (Demirci & Ucok, 2001). The same sample is followed-up in another study after a
three-year recall period, where 62 restorations had a retention rate of 96.7% (Demirci, Ersev, &
Ucok, 2002). Finally, at a five-year follow-up, the authors describe a 94.6% cumulative retention
rate for the restorations. They reported that one restoration was replaced due to pulpitis and five
due to recurrent caries (Demirci, Ersev, Sancakli, & Topcubasi, 2006). The restorations were
evaluated by two-calibrated evaluators at yearly intervals, but it is not clear if the operator was
involved as one of the evaluators. Another study compared composite resins and the same
compomer as the previous study (Demirci, Yildiz, & Uysal, 2008). The pretreatment of the
compomer restorations were divided into two groups. One group has a phosphoric acid etch that
was used and the other a non-rinse conditioner. 32 patients were recruited and had three
restorations each for a total of 96 restorations. There was a 96.4% retention for each group at
two-years. All restorations were placed by the same operator and evaluated by two calibrated
evaluators. As above, it is unknown if the operator and evaluator were the same person.
A five-year retrospective that included 83 restorations from 36 patients evaluated the five-year
performance of CR (Nikaido et al., 2006). Amongst this sample were nine class III restorations;
where one was replaced and one was evaluated as being clinically unacceptable. While the
follow-up period is acceptable, it is difficult to infer any conclusion concerning the class III
restorations due to the small sample size.
A study by Loguercio et al. (2007) evaluated a microfilled composite Durafill VS (Heraeus
Kulzer, Hanau, Germany), a hybrid composite Filtek Z250 (3M ESPE, St Paul, MN) and a
nanofilled composite Filtek Supreme (3M ESPE, St Paul, MN) as class III restoration materials.
They used an adapted version of the USPHS criteria. After a year follow-up, they found that all
of the the 114 restorations were acceptable (Alfa or Bravo). The procedure was done by two
18
operators and evaluated by two different independent evaluators. This is a short follow-period
and further studies with longer follow-ups will be explored in this section.
Baldissera et al. (2013) stated they had a 10.5% failure rate from their sample of 219 combined
class III and IV restorations over a 10-year period. The annual failure rate was 0.5% for
Herculite XR (Kerr, Orange, CA) and 1.8% for Charisma (Heraeus Kulzer, Hanau, Germany).
The restorative procedures were done under rubber dam by one operator and evaluated by
separate evaluators using the FDI criteria, but did not include radiographic interpretation. Also,
they do not breakdown the difference between results for class III or IV restorations.
A study evaluated a two-step adhesive self-etch adhesive over three years in class III cavities
with or without the additional step of using a phosphoric acid etchant (Ermis, Temel, Cellik, &
Kam, 2010). They had 38 patients and a single operator conducted a paired-tooth design. They
found that there was a significant difference where the group that received the additional etch
had less marginal discoloration. Concerning longevity, they were able to follow-up on 80 of the
102 restorations due to patients not coming for their recall. 100% success was reported for both
groups at three years using the modified Ryge criteria with two independent evaluators. While
this is not a large sample it adds to the body of literature available. Also, they could have tested
the potential benefit of using an extra etch step before the two-step adhesive by running an in-
vitro test to verify microleakage. While, they did find a difference clinically, a small sample of
participants who know they are being evaluated may induce some bias regarding hygiene which
could have resulted in less chance of discoloration.
A group studied composite restorations placed between 1995 and 2005 at Nagasaki University
Hospital (Kubo, Kawasaki, & Hayashi, 2011). 277 of the 545 restorations were class III
restorations. 124 of the restorations were done by the first author and the remaining 153
restorations were placed by 23 different dentists. The class III restorations had a total 10 year
survival of 76.9%. Survival time was defined as the age when the restoration was replaced,
repaired or tooth extracted. Consequently, this is largely based on the first author’s replacement
rates since a faulty or missing restoration (if not repaired or replaced) would not be included as a
failure.
A study conducted in Brazil evaluated CR placed by undergraduate students over a three-year
period in 256 teeth, which included 134 class III restorations (Moura et al., 2011). Two
19
calibrated examiners assessed the quality of the restorations. 91.8% of class III were satisfactory,
0.8% unsatisfactory, 6.0% lost, 1.5% fractured. Satisfactory was defined as Alfa or Bravo scores
using an adapted version of the modified USPHS criteria. They found more restorations were
lost “due to limited adhesiveness”, which they explain may be due to the operators’ lack of
experience working with adhesive techniques.
Heintze et al. (2015) completed a meta-analysis on composite restorations in permanent anterior
teeth. Their objective was to “verify whether specific material classes, tooth conditioning
methods and operational procedures influence the result for Class III and Class IV restorations”.
They included 21 studies, 14 studies were on class III restorations, 6 for class IV restorations and
a study on diastema closure was included in the class IV group. Using a linear mixed model
statistical analysis, they concluded the estimated overall median success rate after 10 years for
class III composite restorations was 95% and for class IV restorations 90%. The above estimate
has been cited in other papers, but their estimate based on their statistical model was largely
influenced by shorter term studies that have higher success rates than long term studies. For
example, the first of two studies they included that described results at a follow-up greater than
10 years was by Qvist and Strøm (1993) which stated that there was a cumulative 84% survival
rate at 11 years or 89% at 10 years for class III restorations. The second study was by Van
Dijken and Pallesen (2010) which states they had 25.6% fractured restorations at 9.9 years for 43
composite restorations. The latter study evaluated uniquely class IV restorations. The only two
studies that discuss results at approximately 10 years have lower estimates than the model the
paper extrapolated. The result obtained was likely influenced by the survival of other included
studies that all had less than five-years follow-up. Hence, the quoted survival is most likely
overestimated. In addition, there is a potential risk of bias in the publication, as the first author is
a researcher for Ivoclar Vivadent AG (Schaan, Liechtenstein).
A systematic review by Demarco et al. (2015) aimed to study the long-term performance of
composite restorations in anterior teeth. They included 17 studies with at least a three-year
follow-up that studied class III, class IV, direct veneers or full-coverage build-ups. Overall,
direct anterior restorations had a 0 to 4.1% annual failure rate (AFR). They concluded that class
III restorations overall had generally lower AFR versus other types of direct restorations,
although the study with the highest AFR of 4.1%, was one that involved class III restorations
(Smales & Hawthorne, 1996). In the latter study, they examined the records of 100 patients and
20
restorations placed by 20 dentists. They found no statistical difference in glass-ionomer versus
composite restorations placed as class III restorations. The reported survival was 85% for glass-
ionomers and 72% for composites at 10 years. There were 50 GI vs 284 CR that were done for
the class III restorations. They mention that they censored failures that were caused by reasons
unrelated to the restoration itself. But, they did not explain if the definition was defined for the
dentists or if it was each individual dentist who interpreted a successful versus failed restoration.
The systematic reviews and meta-analyses that have been done are not strict in inclusion criteria.
The studies they included have different methodologies, materials, evaluation criteria, patient
populations, etc. The authors who attempt to review the literature are left with a choice of
defining strict inclusion and exclusion criteria or including more studies. Because of the lack of
data, many choose to include more studies in an effort to infer or provide more of an overall
view of the results practitioners should expect on the subject. However, this type of methodology
for systematic reviews and meta-analyses may result in an unreliable conclusion if the studies
included are of low quality or at high risk of bias.
2.6 Comparison of Class II Restorations
There are currently no comparative studies in the literature assessing both the survival of class III
amalgam and composite restorations. Hence, this review will discuss the available literature that
compares these materials for the class II restorations. The latter involves the interproximal
surface of posterior teeth. This review does not discuss studies that do not compare the two
materials and will focus on amalgam and composite outcomes if the review includes other
materials.
2.6.1 Primary Molars
The survival rates of primary molar restorations placed by dentists and students at the University
of Leeds was studied (Papathanasiou, Curzon, & Fairpo, 1994). The population consisted of
children who attended the dental hospital between February 1, 1989 and January 31, 1991. A
third or 355 records were chosen at random from the 1065 who attended the clinic during this
21
time period. 604 restorations from 128 patients met the study’s criteria and were included. While
they documented the number of surfaces they did not breakdown their analysis to compare
similar restoration types. They observed a significant difference between the survival curves
(p=0.0001). The median survival time was more than five years for both amalgam and stainless-
steel crowns (SSCs). The five-year survival estimate was 68% for SSCs and 60% for amalgams.
The median survival time for composite was 32 months and the four-year survival estimate was
40%. The survival curve for composite did not continue past approximately 50 months, whereas
the amalgam curve had data up to approximately 60 months.
A study based on the New England Children’s Amalgam Trials (NECAT) evaluated longevity of
amalgam versus compomer and composite restorations (Soncini, Maserejian, Trachtenberg,
Tavares, & Hayes, 2007). Their findings for primary and permanent molars will be presented in
this section. The NECAT was a randomized controlled clinical trial that assigned 6 to 10-year-
old children to receive amalgam or composite/compomer restorations and followed them for five
years. They used the set of restorations placed by the dentist J.A.S., where 954 amalgam and
1088 compomer restorations were placed in primary posterior teeth (in 461 children) and 509
amalgam and composite restorations were placed in permanent posterior teeth. The follow-up
average length was 2.8±1.4 years for primary tooth restorations and 3.4±1.9 years for permanent
tooth restorations. Permanent teeth were evaluated regarding repair or replacement, but primary
teeth were only evaluated for replacement. The evaluation of primary teeth restorations lacks
detail, if a tooth was extracted rather than repaired, it would not have been recorded as a failure
despite the condition of the restoration. Conversely, in the permanent restoration group,
composites were more likely to be repaired for marginal defects versus amalgams which would
be replaced. The replacement rate was 4.0% for amalgams and 5.8% for compomers in primary
teeth. The replacement rate was 10.8% for amalgams and 14.9% for composite in permanent
teeth; whereas the repair rate was 0.4% for amalgams and 2.8% for composites. In addition, the
study evaluated replacement of restorations that were due to recurrent caries. In primary teeth,
3.0% of compomers were replaced due to recurrent caries versus the 0.5% of amalgam
restorations (p=0.002). In permanent teeth, they did not run an analysis to compare the likelihood
of replacement due to recurrent caries for composite versus amalgam restorations. They did not
find a difference in the replacement rate. But, the study mentions that composites were seven
times more likely to require repair (AR: 2.8%, CR: 0.4%; p=0.02).
22
Qvist et al. (2010) combine the results of three previous studies and the latest results from a
fourth (Qvist, Laurberg, Poulsen, & Teglers, 2004a, 2004b; Qvist, Manscher, & Teglers, 2004).
The combination of these studies included 398 amalgam, 406 glass-ionomer, 805 resin-modified
glass-ionomer, and 674 composite restorations in primary teeth. The maximum follow-up period
was 7-8 years in the first three studies and five years in the most recent sample. Restorations
were considered failures if they were repaired or replaced. The authors were assessing their own
operative work which puts them at risk for bias. Also, the study was prompted by the mercury
ban in many Scandinavian countries in 2008 and the study sought to “determine which
restorative material would be the best alternative(s) to amalgam in primary teeth”. The latter can
result in bias, since the goal was to find a suitable replacement material. The combination of the
four studies results found 75% survival estimates for class II restorations at 4.0 years for CR, 3.8
years for AR, 3.8 years for RMGI, and 1.4 years for GI; the latter was significant, where
p=0.000.
2.6.2 Permanent Molars
A systematic review aimed to study the longevity of posterior permanent teeth restorations. They
searched the literature for class I or II restorations made of amalgam, composite resin, glass
ionomer and cast gold (Downer, Azli, Bedi, Moles, & Setchell, 1999). Eight of 58 selected
articles were judged to be adequate in quality. They concluded that the articles suggest that 50%
of restorations regardless of type could be expected to survive between 10 and 20 years. An
included study was by Hawthorne and Smales (1997) which published a median survival time
(MST) of 16.72±1.37 years for composite and 22.5±1.07 for amalgam. Another included study
by Bentley and Drake (1986) estimated a 72.0% survival for amalgam and 55.9% for composite
at ten years. The authors’ final conclusion was that it was difficult drawing conclusions based on
the vast differences in methodologies between studies. Many studies had imperfections and those
that were sound often did not indicate if the unit of analysis was an individual person or
restoration. They acknowledge that designing investigations in this subject is difficult, but better
comparative studies are needed.
Chadwick et al. (1999) published a review initiated for the National Health System (NHS)
Centre for Reviews and Dissemination located in York, United Kingdom. The final conclusion
23
was “dental amalgam is the direct restorative material with the longest duration and from the
perspective of the NHS is of lower cost”. They describe that longevity estimates for amalgam
were shorter when they were reported from comparative studies versus when reported without
comparison and suggest the possibility of publication bias. Their study identified several
weaknesses which are outlined in a summary by Jokstad (2002). Examples provided are the
following: use of percentage instead of actual numbers, use of confusing outcome scales such as
the USPHS scale, lack of baseline information, tooth type, cavity type, clinician’s experience,
definition of failure and evaluator characteristics. The use of the USPHS scale has been
described as confusing as it is not consistently used by different studies and it uses subjective
observations of certain parameters (Chadwick et al., 2001). Many studies use these factors as a
way to determine longevity or failure, which he describes as a strategy that may be inappropriate.
On the other hand, N. J. Opdam, Bronkhorst, Roeters, and Loomans (2007) argue that the
difference found in comparative studies is due to the environment (e.g. academic settings), where
they explain operators are more often strictly trained in the techniques being evaluated and
restorations are placed in patients with greater dental motivation.
A cross-sectional study done via survey of dentists in Finland aimed to study and analyze
changes over a five-year period (Forss & Widstrom, 2001). 659 of 1229 dentists responded to
their questionnaire. They asked respondents from private practices to answer questions on
patients and their restorations from one ordinary working day or based on three days if they
worked in a health center. The median age of failed amalgam restorations was 10.5 years in
patients aged 20 to 39 years old and 13.5 years in patients over 40 years old. The median age of
failed composite restorations was 4 years in patients aged 20 to 39 years old and 5.8 years in
patients over 40 years old. This type of study gives a snapshot in time and may be biased due to
the low response rate. However, if the sample is representative of the population, which cannot
be assumed, then the results can be interpreted as a good representation of the survival of the
restorations based on dentists’ perceptions of failure in Finland.
A review published a couple years later aimed to determine annual failure rates in stress bearing
posterior cavities (R. Hickel & Manhart, 2001). They do not describe any inclusion or exclusion
criteria of how they selected which studies to include. The tables they include that describe
which articles they reviewed have varying study designs, methodologies, and report longevity in
different manners. Also, the studies include class I and II restorations, which the authors do not
24
differentiate between when they report their findings. The reported annual failure rate was 0 to
7% for amalgam restorations and 0 to 9% for composites. The reasons reported for failure of
amalgams are secondary caries, fracture, cervical overhang and marginal ditching. High copper
amalgams are reported as having higher survival rates. The composites in the 1970s and 1980s
were reported to have failed usually due to poor wear resistance which led to degradation, loss of
anatomic form and loss of interproximal contacts. However, during the period the review was
written, the main reasons for failure were fractures, marginal deterioration, discoloration, and
marginal opening with secondary caries.
N. J. Opdam et al. (2007) evaluated charts retrospectively from two general dentists to determine
the longevity of AR and CR in the Netherlands. They evaluated class I and II restorations placed
between 1990 and 1997 in premolar and molars. Success or failure was determined by whether
the restoration was replaced or not. Thus, the study was based mainly on the two dentists’
clinical judgement. Operator 1 placed 502 amalgams and 1470 composites, whereas operator 2
placed 410 amalgams and 485 composites. Observing the number of restorations placed, it is
possible that operator 1 or their patients had a preference for composite and that some bias could
be introduced. The proportion of restorations 3 to 5 surfaces was compromised of 66% of
amalgams for operator 1 and 51% for operator 2. Whereas for composites, multi-surface
restorations of 3 surfaces or more comprised of 39% and 19% respectively for operator 1 and 2.
The descriptive results may indicate that there was a greater proportion of large amalgam
restorations versus composite restorations in the sample used to calculate survival. Interestingly,
the cox regression analysis found a significant effect of the number of surfaces restored on
survival. The survival rates for each material at 10 years was 82.2% for composite and 79.2% for
amalgam. However, the findings may be biased based on sampling. The first author with other
authors published a study evaluating the repair of restorations (N. J. Opdam, Bronkhorst,
Loomans, & Huysmans, 2012). It included 133 AR that needed repair where 57% were due to
fracture and 113 CRs that needed repair where 62% were due to caries. The annual failure rates
9.3% for AR, 5.7% for CR after 4 years and was significantly different (p=0.001). Restorations
that were repaired due to fracture had a lower survival than restorations that were repaired due to
caries (p=0.006).
Bernardo et al. (2007) studied participants in the Casa Pia Study of the Health Effects of Dental
Amalgams in Children. The latter was a randomized clinical trial that assessed the safety of low
25
level mercury exposure attributable to dental AR. There were 472 individuals between 8 and 12
years old and they were assigned randomly to receive a restoration in either material type. Oral
hygiene and prevention programs were initiated during follow-up visits. Restorations needing
replacement were quantified as failures and were evaluated by the study’s dentists. It is unclear if
the study dentists were amongst the 14 dentists who were involved with placing the restorations.
Mean annual failure rate was from 0.16 to 2.83% for amalgam and between 0.94 to 9.43% for
composite at seven years. They found that restorations of 4 surfaces or more had the lowest
survival rates (50.0%) and that amalgam restorations performed better in large restorations
versus composites. Secondary caries was the main reason of failure for both materials. They
found the relative risk was 3.5x greater in composites for secondary caries, which was
statistically significant (p<0.0001).
N. Opdam, Bronkhorst, Loomans, and Huysmans (2010) published an article that evaluated the
performance of large class II amalgam and composite restorations in relation to the patient’s
caries risk. They included 3, 4 or 5 surface restorations. In one of the author’s general practice,
restorations placed before 1994 were almost always with amalgam, whereas there was a shift
towards composite during the 1994/1995 period. They chose to exclude any restorations done
during the transition period. This may lead the reader to believe that the study was based on
records that most likely did not have the material type written down if they had to exclude the
transition years to ensure they recorded the restoration as the appropriate type. While there could
have been a learning curve initially for composite, this may have been discounted as they
eliminated restorations placed during the transition years. Moreover, composites placed were
done when the clinician had more experience versus the amalgams that were placed which could
have influenced the results. In 273 patients, 1202 amalgams were placed between 1983 and
1993, while 747 composites were place between 1996 and 2003. The results they found were that
restorations in the high-risk group had significantly lower survival rate after 12 years (p<0.01).
The two materials showed comparable performance at 5 years (p=0.18), but composite showed
higher survival rate at 12 years (p=0.013). The AFR of amalgam was 1.68% for composite and
2.41% for amalgam at 12 years. Large composite restorations showed a higher survival in the
low-risk group for 3 surface restorations (p=0.03) and the combined 4 and 5 surface restoration
group (p=0.02). Amalgam showed better survival for three-surface restorations in high-risk
patients (p=0.03), but this was not statistically significant in 4 or 5 surface restorations (p=0.69).
26
A practice-based study conducted from 2001 to 2004 included a total of 4030 class II
restorations (Kopperud, Tveit, Gaarden, Sandvik, & Espelid, 2012). 27 dentists from the Public
Dental Health Service in Norway participated in the study. Composite was used for 3286
restorations (81.5%), compomer for 510 (12.7%), amalgam for 184 (4.6%) and glass-ionomer
cement for 50 (1.2%). Amalgam restorations were significantly better in survival compared with
composite restorations (p=0.02). The mean annual failure rate was calculated to be 1.6% for
amalgam compared with 2.9% for resin-composite restorations. Cox-regression analyses were
significant for the following factors affecting survival negatively: young patient age, high
previous caries experience, deep caries, saucer-shaped preparation technique (vs traditional class
II preparation). The sample groups are largely favoured towards the use of composite. Also, this
is a practice-based study which means the technique and evaluation criteria were left up to the
participating dentist. This may mimic the restorative material’s performance as a replacement
study in a general practice in Norway. Another practice-based study was designed as a cross-
sectional longitudinal cohort study (McCracken et al., 2013). 226 practitioners mainly from the
United States contributed reports of 6218 restorations from 3855 patients with a mean follow-up
of 17.6±9.2 months. Teeth that were repaired or replaced were considered as failures. This study
included class I (n=1716), class II (n=1960), anterior class III or IV (n=878), buccal (n=991),
large 4 or more surfaces (n=114) and other (n=173) restorations. The failure rates between
amalgam and composites was not significantly different, but no numerical values are described
and the study had a very short follow up time period.
A Cochrane review was done comparing composites and amalgams for permanent posterior
teeth. Their review excluded studies with follow-up less than three years and selected
comparative randomized control trials (RCT). Seven trials were included but were judged to be
at high risk for bias. They described that there was a high risk of bias because the evaluators
could not be blinded as to the restorative material type. This risk of bias will always remain as
there is no easy way to mask an evaluator’s ability to tell what material was used while still
maintaining their ability to evaluate the restoration’s status. Their conclusion states the
following: “There is low-quality evidence to suggest that resin composites lead to higher failure
rates and risk of secondary caries than amalgam restorations. This review reinforces the benefit
of amalgam restorations and the results are particularly useful in parts of the world where
amalgam is still the material of choice to restore posterior teeth with proximal caries” (Rasines
27
Alcaraz et al., 2014). A systematic review and meta-analysis that evaluated posterior composite
and amalgam restorations came to a similar conclusion after including 8 studies, but caution of
its conclusions due to only 2 RCTs being included (Moraschini, Fai, Alto, & Dos Santos, 2015).
They estimated a 92.8% mean rate of survival for amalgams and 86.2% for the composite resins
at a mean follow-up of 55 months. The relative risk in favour of amalgams for secondary caries
was 0.23 (95% CI: 018–0.30, p<0.00001). They conclude with the following statement: “The
results of this review suggest that posterior composite resin restorations still have less longevity
and a greater number of secondary caries when compared to amalgam restorations”. A study by
Heintze and Rousson (2012) conducted a meta-analysis on class II restorations similar in design
to their study on anterior restorations (as previously discussed). The first author was the head of
preclinical research for Ivoclar Vivadent, which can introduce a source of bias. Their study had
broader inclusion criteria, as they included 59 studies, such as only requiring a minimum of 20
restorations. The search time included studies between 1966 and 2011. Their conclusion was that
hybrid and microfilled composites were equal to amalgam. However, macrofilled composites
and compomers demonstrated more shortcomings such as greater wear and fractures. They also
explain that for best results, the use of enamel etching with 37% phosphoric acid reduced the
occurrence of marginal discoloration versus when no etch was used. The former is currently
considered a standard of practice (Eliades, Eliades, & Watts, 2005). The statistical analysis used
a linear model to characterize the deterioration process of the restorations. The conclusions of
this last meta-analysis are probably not as representative of the performance of the two materials
due to its inclusion of a vast amount of literature with different methodologies that were used as
well as mixed statistical models.
The studies above have shown that there is a lack of literature describing the survival of not only
class III restorations, but anterior restorations in general. Articles that do exist are difficult to
interpret, since these studies often fail to subcategorize the restorations as primary or permanent
teeth or do not describe the type of cavity preparation used for the restoration. Also, there were
not any articles found that discussed the longevity of anterior primary AR. The comparison in
performance of amalgam and composite is therefore based on the literature available for class II
restorations. This project seeks to add to the body of literature in order to provide more
information regarding the outcomes of amalgam restorations versus composite restorations as
direct restorative materials for class III restorations in primary canine teeth.
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3 Objectives
The primary aim of this thesis was to evaluate the survival of class III amalgam and composite
restorations in primary canines.
Secondarily, the survival curves of class III amalgam restorations were compared to composite
restorations in primary canines to determine if there was a difference between the two materials.
The null hypothesis was that there was no significant difference between the survival curves of
the two materials.
The final aim was to determine if other factors such as sex, age, insurance, American Society of
Anesthesiologists (ASA) physical status classification, tooth number, arch, side, number of
surfaces, surface types, GI base, isolation, setting, behavior, decayed missing filled surfaces
(dmfs) status, operator, brushing frequency, toothpaste use, flossing, diet and pulp treatment
affected survival time. The null hypothesis was that each factor did not influence the survival of
the class III restoration.
4 Materials and Methods
4.1 Design
The research protocol was approved by the Health Sciences Research Ethics Board of the
University of Toronto (reference number: 33787). A retrospective chart review of all patients
with class III restorations involving the distal aspect of primary canines was conducted. Due to
the low risk of the retrospective chart review, specific patient consent was not required for this
study. Furthermore, permission to access the data is part of the Faculty of Dentistry’s “Patient
consent form: for collection, use and disclosure of personal information” signed by patients or
their parents (see Appendix A).
The patients included in this study were searched for in the AxiUm, version 6.03 (Exan Group,
Port Coquitlam, BC), database used at the University of Toronto’s dentistry clinics. The search
included patients between November 1, 1999 and February 28, 2017. Patients that had the distal
aspect of a primary canine restored with either composite or amalgam and at least one follow-up
29
were included. The codes included in the search are those corresponding to the Canadian Dental
Association’s Uniform System of Codes and List of Services (CDA-USC&LS): 21111, 21112,
21113, 23411, 23412 and 23413. The inclusion criteria for the patient charts to be obtained were:
a primary canine restored with a class III amalgam and/or composite restoration, patient has had
at least one follow-up visit following the restoration of their primary canine. The treatment must
have been conducted between November 1, 1999 and February 28, 2017. Exclusion criteria
comprises of any patient who does not meet the inclusion criteria and/or has periodontal disease.
Clinical or absolute failure included: recurrent decay, loss or fracture of the restoration,
replacement of restoration, symptoms related to the tooth (pain on function, mobility,
necrosis/infection), loss of tooth (extraction). Recurrent or secondary caries was defined as a
“new lesion at the margin of existing restorations” (Mjör & Toffentti, 2000) and did not include
new carious lesions that did not involve the existing restoration. Success was defined as intact
restoration without new caries at the last time of follow-up or if the tooth has exfoliated naturally
without any of the failure criteria having been charted prior to its exfoliation. In this study, the
criterion determined for success defined the survival of the restoration.
The latter was collected using Epi Info version 7.2.1.0 (Centers for Disease Control and
Prevention, Atlanta, GA) on a password protected computer.
The material used to restore the tooth was chosen after giving the option between composite and
amalgam to the patient/parent(s), since they are both indicated materials for class III restorations
on the distal aspect of primary canines. After verbal consent was obtained, the treatment was
provided in the university dental clinics by undergraduate or graduate students with or without
the additional use of an inhalation/oral sedation agent or general anesthesia. The multitude of
operators (dental students and residents) that placed the restorations were not standardized.
However, the didactic teaching received by the operators has been consistent throughout the
years. The standardization and quality of the restoration is controlled by the supervising clinical
staff at the time of treatment. Amalgam restorations done in the children’s clinic or in the
surgicenter were with Permite (SDI, Bayswater, VIC), an admix amalgam. Composite
restorations were etched with a 37% phosphoric acid, the resin-modifed glass ionomer (RMGI) if
used was Vitrebond (3M ESPE, St Paul, MN) or Ionoseal (Voco, Briarcliff Manor, NY), the
adhesive used was Adper Scotchbond Multi-purpose (3M ESPE, St Paul, MN) or Scotchbond
30
Universal (3M ESPE, St Paul, MN) or Brush & Bond (Parkell Inc., Edgewood, NY). The
composite used was Herculite XR (Kerr Corporation, Orange, CA) or Herculite XRV (Kerr
Corporation, Orange, CA) or Spectrum TPH (Dentsply, York, PA) or TPH Spectra (Dentsply,
York, PA) or Filtek Supreme (3M ESPE, St Paul, MN).
Demographic, clinical and radiographic data were obtained from the chart review on an
anonymous basis. Data collected included: sex (male or female); age (years); insurance type
(private, public or none); American Society of Anesthesiologists (ASA) physical status
classification (I – normal healthy patient, II – a patient with mild systemic disease, III – a patient
with severe systemic disease); review of systems involved (central nervous system,
cardiovascular, hematologic, respiratory, endocrine, renal, hepatic, musculoskeletal, ears nose
and throat [ENT], dermatology, immunologic, psychiatric and/or past surgery or hospitalization);
birth history (full term [37 weeks to 41 weeks and 6 days], preterm [<37 weeks], post-term [≥42
weeks]); delivery (vaginal or cesarean); immunizations up to date (yes or no); medications (yes
or no); allergy (yes or no); brushing frequency (0, 1, 2, >3 times/day); toothpaste (non-
fluoridated toothpaste, fluoridated toothpaste, unknown type of toothpaste, no toothpaste used);
flossing (yes or no); diet (low or high in simple carbohydrates); decayed missing filled surfaces
[dmfs] (numerical score).
Clinical characteristics recorded were the following: tooth number (53, 63, 73, 83); arch (maxilla
or mandible); side (left or right); surface (distolingual, distobuccal, distolinguo-bucal, distal);
liner/base (yes or no); pulp treatment (pulpotomy or pulpectomy); isolation (rubber dam or
cotton roll); setting (general anesthesia [GA], local anesthesia [LA], nitrous oxide [N2O], nitrous
oxide and oral midazolam [N2O+midaz]); behavior (Frankl scale: definitely positive, positive,
negative, definitely negative); operator (dental student or pediatric dentistry resident), recent visit
type (emergency visit, follow-up, recall, restorative visit); clinical failure (yes or no); reason of
failure (defective restoration [fracture or missing], necrosis/infection, recurrent caries); follow-up
period (date of insertion to last follow-up date [days]).
Available radiographs were kept on the same password-protected computer. Size 0 or 2
periapical and bitewing radiographs had been taken with Kodak analog film or by CS 7600
phosphor storage plates (Carestream Health Inc, Rochester, NY). Analog films were digitized
using a Nikon COOLPIX 995 on a stand with a Vistek LP-100 light panel as seen in Figure 6.
31
The settings of the camera were shot in macro mode, fine quality (3:2), f3.8. The distance from
the camera lens to the table was set at 5.25 inches.
Figure 6. Copy stand and camera for digitizing film radiographs
Radiographic follow-up was calculated as the days between the date of insertion to the date of
the last available radiograph. Two pretests were done with evaluator PA and EC to establish the
reliability of the radiographic criteria. Radiographs were evaluated as a yes or no evaluation for
the following criteria: caries-related radiolucency, procedural-related radiolucency, missing
restoration, inadequate anatomic contour. Also, the location of the radiolucency was assessed as
being present at the: cavosurface margin, gingival wall, axial wall and/or incisal wall.
4.2 Sample Size
A power calculation was performed using MedCalc Statistical Software version 15.8 (MedCalc
Software, Ostend, Belgium). In a parallel group design, with a confidence interval of 95%
(α=0.05) and a power of 0.8 (β=0.2), to detect a 20% difference (60-80%) between the survival
of amalgam and composite restorations, a sample size of 172 restorations was calculated.
32
The patients included in this study was determined by the inclusion criteria as stated earlier using
the billing codes in AxiUm version 6.03 (Exan Group, Port Coquitlam, BC); which is estimated
to be greater than the minimum sample needed. All data was included as the power calculation
was based on the expected difference to be detected, but a larger sample would allow the
detection of a smaller difference should it have occurred. Furthermore, not every patient would
have had a follow-up appointment or have a post-operative radiograph. Hence, a greater sample
would allow for a sufficient amount of radiographic data to be collected for analysis.
4.3 Data Analysis
The dataset was analyzed with SAS 9.4 (SAS Institute Inc., Cary, NC). Descriptive statistics
were done to summarize the number of observations found for each category. Continuous
variables were described as a mean with its standard deviation.
A Kaplan-Meier survival analysis was performed to produce a graph and a life table.
Comparison survival curves were analyzed with the log-rank and Wilcoxon test. The log-rank
test is better than the Wilcoxon at detecting differences between groups at later points in time
and has the most power when the hazards ratio is constant over time. Conversely, the Wilcoxon
test is more powerful than the log-rank test at detecting differences between groups at early
points in time, but can be biased if the censoring pattern is different between the two groups.
Also, the influence of factors (such as gender, patient age, operator level, treatment modality,
tooth position, etc.) were analyzed to see if they affected survival time with a cox regression
model. In order to determine if there were possible confounders in either group, regression
analysis will consider the possible influence of independent variables on the survival curves. An
adjusted hazards ratio was calculated with the Cox proportional hazard frailty model. Lastly,
relative risk (frailty model) of an amalgam versus a composite restoration failing due to recurrent
caries, necrosis/infection or being a defective restoration was assessed.
The radiographic analysis consisted of descriptive statistics and Pearson-chi square or Fisher’s
exact tests to test for association. Association was verified to determine if the locations of the
radiolucencies (RL) were likely to be located in certain areas when judged to be caries-related or
33
procedural-related. The same association tests were then used to determine if there was an
association with the chart documented reason of failure.
Beforehand, using a set of 19 radiographs, the principal investigator (E.C.) was evaluated for
reliability between two separate tests done at a two-week interval. Moreover, the reproducibility
of the measurements was tested against another clinician (P.A.) using Cohen’s kappa coefficient.
The measurements evaluated will be described in section 5.6.
5 Results
5.1 Descriptive Data
833 patient charts (1482 teeth) were identified through the database. After reviewing the charts,
603 patient files (1101 teeth) were selected as meeting the established inclusion criteria.
57.5% of the patients were male and 42.5% female. Over 90% of patients had insurance
coverage, where 70.0% of the patients being recipients of government-funded insurance. 87.9%
of the restorations were placed in teeth of healthy patients classified as being ASA I. The
remaining restorations were placed in patients who were ASA II (11.6%) and ASA III (0.5%).
The system most likely to be affected was the respiratory system. 89.6% patients were born full-
term and 70.4% through vaginal delivery.
Almost all patients reported that their immunizations were up to date, 11.9% responded that they
were taking medications and 8.8% had at least one allergy. See Table 1 for further demographic
characteristics.
34
Table 1. Demographic characteristics of restorations
Variable Total N (%)
Sex Male 347 (57.5)Female 256 (42.5)
Insurance type Private 119 (21.0)Public 397 (70.0)None 51 (9.0)
ASA classification ASA I 530 (87.9)ASA II 70 (11.6)ASA III 3 (0.5)
Systems Central nervous system 19 (3.2)Cardiovascular 9 (1.5)Hematology 1 (0.2)Respiratory 63 (10.5)Endocrine 5 (0.8)Renal 5 (0.8)Hepatic 0 (0)Musculoskeletal 3 (0.5)ENT 2 (0.3)Dermatology 19 (3.2)Immunology 0 (0)Psychology 0 (0)Past surgery or hospitalizations 34 (5.6)
Birth history Full term 206 (89.6)Pre term 23 (10.0)Post term 1 (0.4)
Delivery Vaginal 138 (70.4)Cesarean 58 (29.6)
Immunizations Not up to date 7 (1.2)Up to date 568 (98.8)
Medications Yes 72 (11.9)No 531 (88.1)
Allergy Yes 53 (8.8)No 550 (91.2)
35
Between November 1, 1999 and February 28, 2017, 602 patients were included in this study for
a total of 1101 restorations. The restorations done are well distributed amongst the four primary
canines with a quarter of the restorations done for each cuspid. There were 403 amalgam and 698
composite restorations placed.
The average age at placement of the class III restorations was approximately 5.8 years old.
76.8% of respondents stated that their child brushed twice a day with or without help and 0.7%
or five patients were documented as not brushing daily. 87.8% of patients used fluoridated
toothpaste when brushing, 6.6% were unsure of the type of toothpaste used, 4.2% used non-
fluoridated toothpaste and 1.4% stated they did not use toothpaste when brushing. Lastly, 89.9%
of patients had a diet high in simple carbohydrates. The average dmfs score of patients was
44.9±18.8.
72.2% of amalgams that were placed included the distolingual surface, 16.4% distolinguo-
buccal, 6.5% distal and 5.0% distobuccal surfaces. In composites, 39.5% of the restorations
included the distolinguo-buccal surfaces, 33.8% the distolingual surface, 21.9% distobuccal and
4.7% distal surface. The use of a liner/base was more common when a composite was used, as it
was used beneath 35.7% of composites. Whereas, a RMGI liner/base was used beneath amalgam
restorations 4.0% of the time. A pulpotomy or pulpectomy was done in 2.0% of all the teeth
restored. A rubber dam was used for approximately 98.3% of the restorations.
The restorations were done when the patient was under general anesthesia in 58.3% of cases,
22.1% using non-pharmacologic management (local anesthetic without additional pharmacologic
behavior management), 19.1% with the adjunct of nitrous oxide and 0.5% with nitrous oxide and
an oral premedication. The proportion of amalgams done were 40.5% under GA, 30.8% with LA
only, 28% with nitrous oxide and 0.8% with nitrous oxide and an oral premedication. 68.6% of
composites were done under GA, 17.1% with LA only, 13.9% with N2O and 0.4% with N2O and
an oral premedication.
Behavior was documented amongst the patients that did not receive treatment under GA. 56.1%
of the latter patients were recorded as a being ‘definitely positive’ or a 4 on the Frankl scale,
23.0% were ‘positive’ or a 3 on the scale, 12.0% were ‘negative’ or a 2 on the scale and 8.8%
were ‘definitely negative’ or a 1 on the scale.
36
The restorations were mainly placed by residents in the graduate Pediatric dentistry program
(90.2%). The last recorded appointment where the restoration was assessed was a recall
appointment in 41.4% of cases, a follow-up appointment in 36.5% instances, a restorative visit
20.2% of cases and an emergency visit in 1.9% of cases.
The overall failure percentage without taking time in consideration, was 13.9% for amalgam
restorations, 17.0% for composite restorations and was 15.9% overall. An estimated 3.2% (13 of
403) amalgams had recurrent caries, whereas 10.0% (70 of 698) composites had recurrent caries.
Amongst the 56 recorded failures of teeth restored with amalgam, 5 did not have a documented
reason. Amongst the 119 recorded failures of teeth restored with composite resin, 7 did not have
a documented reason. The next percentages are presented out of the recorded data. The reason
for failure for composite was due to a defective restoration in 33.9% of instances (38 of 112),
3.6% due to the tooth becoming necrotic and 62.5% due to recurrent caries. 70.6% of amalgams
failed due to a defective restoration (36 of 51), 3.9% due to the tooth becoming necrotic and
25.5% due to recurrent caries. Altogether, of the failed restorations, 45.4% restorations failed due
to a defective restoration (74 of 163), 3.7% due to the tooth becoming necrotic and 50.9% due to
recurrent caries.
The average follow-up time for both groups was similar, where the mean was 13.0±15.8 months
for both groups. The range of follow-up time was between one day and 10.9 years. The
breakdown of restorations and their respective follow-up period, as well as further clinical
characteristics are outlined in Table 2.
Table 2. Clinical characteristics
Variable Amalgam Composite p-value† Total N(%) N(%) N(%)Age at insertion (years) [mean±SD] 5.9±1.7 5.7±1.9 0.22 5.8±1.8Number of restorations 403 698 1101Brushing frequency*
0 4 (1.3) 1 (0.2) 0.17 5 (0.7)1 51 (17.0) 67 (15.3) 118 (16.0)2 222 (74.0) 344 (78.7) 566 (76.8)>3 23 (7.7) 25 (5.7) 48 (6.5)
Toothpaste* Non-fluoridated toothpaste 7 (3.3) 14 (4.9) 0.29 21 (4.2)Fluoridated toothpaste 185 (86.5) 252 (88.7) 437 (87.8)Unknown type of toothpaste 19 (8.9) 14 (4.9) 33 (6.6)
37
Variable Amalgam Composite p-value† TotalNo toothpaste used 3 (1.4) 4 (1.4) 7 (1.4)
Flossing* Yes 33 (15.4) 43 (17.1) 0.62 76 (16.3)No 181 (84.6) 208 (82.9) 389 (83.7)
Diet* Low in sugar 19 (8.3) 36 (11.4) 0.23 55 (10.1)High in sugar 211 (91.7) 279 (88.6) 490 (89.9)
dmfs (mean±SD)* 42.4±19.5 46.2±18.1 <0.01 44.9±18.8Tooth number
53 86 (21.3) 187 (26.8) 0.05 273(24.8)63 93 (23.1) 183 (26.2) 276(25.1)73 116 (28.8) 174 (24.9) 290 (26.3)83 108 (26.8) 154 (22.1) 262 (23.8)
Arch Maxilla 179 (44.4) 370 (53.0) 0.01 549 (49.9)Mandible 224 (55.6) 328 (47.0) 552 (50.1)
Side Left 209 (51.9) 357 (51.2) 0.82 566 (51.4)Right 194 (48.1) 341 (48.8) 535 (48.6)
Number of surfaces 1 26 (6.4) 33 (4.7) <0.01 59 (5.4)2 311 (77.2) 389 (55.7) 700 (63.6)3 66 (16.4) 276 (39.5) 342 (31.1)
Surface Distolingual 291 (72.2) 236 (33.8) <0.01 527 (47.9)Distobuccal 20 (5.0) 153 (21.9) 173 (15.7)Distolinguo-buccal 66 (16.4) 276 (39.5) 342 (31.1)Distal 26 (6.5) 33 (4.7) 59 (5.4)
Liner/base Yes 16 (4.0) 249 (35.7) <0.01 265 (24.1)No 387 (96.0) 449 (64.3) 836 (75.9)
Pulp treatment Pulpotomy 5 (1.2) 11 (1.6) 0.67 16 (1.5)Pulpectomy/RCT 1 (0.3) 4 (0.6) 5 (0.5)
Isolation* Rubber dam 337 (98.5) 547 (98.2) 0.70 884 (98.3)Cotton roll 5 (1.5) 10 (1.8) 15 (1.7)
Setting GA 162 (40.5) 478 (68.6) <0.01 640 (58.3)LA 124 (31.0) 119 (17.1) 243 (22.2)Nitrous oxide 111 (27.8) 97 (13.9) 208 (19.0)Nitrous oxide and midazolam 3 (0.7) 3 (0.4) 6 (0.6)
Behaviour* Definitive positive 109 (30.9) 101 (15.6) <0.01 210 (21.1)Positive 44 (12.4) 42 (6.5) 86 (8.6)Negative 24 (6.5) 21 (3.3) 45 (4.4)
38
Variable Amalgam Composite p-value† TotalDefinitive negative 21 (5.9) 12 (1.9) 33 (3.3)
Operator Student 34 (8.4) 74 (10.6) 0.24 108 (9.8)Resident 369 (91.6) 624 (89.4) 993 (90.2)
Recent visit type Emergency visit 9 (2.2) 12 (1.7) <0.01 21 (1.9)Follow-up 113 (28.0) 289 (41.4) 402 (36.5)Recall 177 (43.9) 279 (40.0) 456 (41.4)Restorative visit 104 (25.8) 118 (16.9) 222 (20.2)
Clinical failure Yes 56 (13.9) 119 (17.1) 0.17 175 (15.9)No 347 (86.1) 579 (82.9) 926 (84.1)
Reason of failure Defective restoration (fracture or missing)
36 (70.6) 38 (33.9) <0.01 74 (45.4)
Necrosis/infection 2 (3.9) 4 (3.6) 6 (3.7)Recurrent caries 13 (25.5) 70 (62.5) 83 (50.9)
Follow-up period (mean±SD) [months] 13.5±16.0 12.7±15.6 0.38 13.0±15.8Number of restorations with follow-up
<30 days 92 (22.8) 214 (30.7) 0.19 306 (27.8)30-60 days 31(7.7) 47 (6.7) 78 (7.1)61-180 days 52(12.9) 70 (10.0) 122 (11.1)181-365 days 65 (16.1) 106 (15.2) 171 (15.5)366-730 days 81 (19.9) 124 (17.8) 205 (18.5)731-1095 days 44 (10.9) 72 (10.3) 116 (10.5)1096-1460 days 23 (6.0) 36 (5.2) 59 (5.5)1461-1825 days 13 (3.2) 19 (2.7) 32 (2.9)>1825 days 2 (0.5) 10 (1.4) 12 (1.1)
Range of follow-up period (days) 1 - 3989 2 - 3671 1 - 3989† Pearson’s chi-squared test or Fisher’s exact test for categorical variables, and Student’s t-test for continuous variables. *Data collected is based on available information from charts (some patients were missing data).
39
5.2 Survival Curves
5.2.1 Amalgam Survival Curve
The Kaplan-Meier survival curve for amalgam class III restorations can be seen in Figure 7.
Figure 7. Amalgam Kaplan-Meier survival curve
The median survival time (MST) is described as the time at which an individual restoration has a
50% chance of exceeding. The MST for amalgam is 4.5 years. Further estimates for the
likelihood of survival can be found in Table 3.
Table 3. Survival probability of amalgam class III restorations
Time (days) Probability of survival Failure rate Standard error0 1.00 0.00 0.0014 0.99 0.01 0.0021 0.99 0.01 0.0028 0.99 0.01 0.0141 0.99 0.01 0.0143 0.98 0.02 0.01
40
Time (days) Probability of survival Failure rate Standard error70 0.98 0.02 0.0191 0.97 0.03 0.01111 0.97 0.03 0.01114 0.96 0.04 0.01140 0.96 0.04 0.01154 0.95 0.05 0.01159 0.94 0.06 0.01194 0.94 0.06 0.01226 0.93 0.07 0.02245 0.93 0.07 0.02277 0.93 0.07 0.02287 0.92 0.08 0.02288 0.92 0.08 0.02292 0.91 0.09 0.02315 0.91 0.09 0.02342 0.90 0.10 0.02345 0.90 0.10 0.02347 0.89 0.11 0.02365 0.88 0.12 0.02385 0.88 0.12 0.02400 0.87 0.13 0.02459 0.87 0.13 0.02475 0.86 0.14 0.02490 0.85 0.15 0.02546 0.85 0.15 0.03553 0.84 0.16 0.03594 0.83 0.17 0.03604 0.82 0.18 0.03630 0.81 0.19 0.03667 0.80 0.20 0.03670 0.80 0.20 0.03686 0.79 0.21 0.03735 0.78 0.22 0.03737 0.77 0.23 0.03748 0.76 0.24 0.03764 0.75 0.25 0.04836 0.74 0.26 0.041006 0.72 0.28 0.041007 0.71 0.29 0.041027 0.69 0.31 0.041039 0.68 0.32 0.041204 0.66 0.34 0.051212 0.63 0.37 0.051222 0.61 0.39 0.051582 0.54 0.46 0.081678 0.47 0.53 0.103989 0.00 1.00 .
41
5.2.2 Composite Survival Curve
The Kaplan-Meier survival curve for composite class III restorations can be seen in Figure 8.
Figure 8. Composite Kaplan-Meier survival curve
The MST for composite is 3.8 years. Further estimates for the likelihood of survival can be found
in Table 4.
Table 4. Survival probability of composite class III restorations
Time (days) Probability of survival Failure rate Standard error0 1.00 0.00 0.007 1.00 0.00 0.0011 1.00 0.00 0.0014 0.99 0.01 0.0018 0.99 0.01 0.0025 0.99 0.01 0.0027 0.99 0.01 0.0049 0.99 0.01 0.0053 0.98 0.02 0.0163 0.98 0.02 0.01
42
Time (days) Probability of survival Failure rate Standard error126 0.98 0.02 0.01128 0.98 0.02 0.01132 0.97 0.03 0.01137 0.97 0.03 0.01146 0.97 0.03 0.01147 0.97 0.03 0.01160 0.96 0.04 0.01167 0.96 0.04 0.01193 0.96 0.04 0.01195 0.95 0.05 0.01212 0.95 0.05 0.01218 0.95 0.05 0.01221 0.94 0.06 0.01224 0.94 0.06 0.01225 0.93 0.07 0.01238 0.93 0.07 0.01281 0.93 0.07 0.01285 0.92 0.08 0.01287 0.92 0.08 0.01294 0.92 0.08 0.01296 0.91 0.09 0.01301 0.91 0.09 0.01305 0.91 0.09 0.01308 0.90 0.10 0.02317 0.90 0.10 0.02322 0.89 0.11 0.02328 0.89 0.11 0.02331 0.89 0.11 0.02343 0.88 0.12 0.02357 0.87 0.13 0.02368 0.87 0.13 0.02369 0.86 0.14 0.02371 0.85 0.15 0.02378 0.85 0.15 0.02412 0.84 0.16 0.02419 0.84 0.16 0.02425 0.83 0.17 0.02428 0.83 0.17 0.02450 0.83 0.17 0.02467 0.82 0.18 0.02476 0.82 0.18 0.02490 0.81 0.19 0.02492 0.81 0.19 0.02502 0.80 0.20 0.02524 0.80 0.20 0.02546 0.79 0.21 0.02555 0.79 0.21 0.02573 0.78 0.22 0.02575 0.77 0.23 0.02581 0.77 0.23 0.02
43
Time (days) Probability of survival Failure rate Standard error585 0.76 0.24 0.02595 0.76 0.24 0.03603 0.76 0.24 0.03623 0.75 0.25 0.03638 0.75 0.25 0.03644 0.74 0.26 0.03669 0.74 0.26 0.03682 0.73 0.27 0.03705 0.72 0.28 0.03725 0.72 0.28 0.03728 0.71 0.29 0.03735 0.71 0.29 0.03737 0.70 0.30 0.03747 0.69 0.31 0.03749 0.69 0.31 0.03752 0.68 0.32 0.03838 0.67 0.33 0.03894 0.66 0.34 0.03908 0.66 0.34 0.03923 0.65 0.35 0.03925 0.64 0.36 0.03939 0.64 0.36 0.03944 0.63 0.37 0.03953 0.62 0.38 0.031035 0.62 0.38 0.031042 0.61 0.39 0.031058 0.60 0.40 0.031084 0.59 0.41 0.031101 0.58 0.42 0.041107 0.57 0.43 0.041108 0.56 0.44 0.041148 0.55 0.45 0.041155 0.54 0.46 0.041163 0.53 0.48 0.041257 0.51 0.49 0.041513 0.49 0.51 0.041603 0.46 0.54 0.051733 0.43 0.57 0.061864 0.37 0.63 0.073671 0.00 1.00 .
5.3 Amalgam versus Composite
Figure 9 is the representation of both Kaplan-Meier curves. The survival curves of both materials
are not significantly different (Log-rank: p=0.09, Wilcoxon: p=0.31). The hazard ratio (HR) at a
95% confidence-interval is 0.76 (0.55, 1.05).
44
Figure 9. Amalgam versus composite survival curves
5.4 Influence of Variables
Patient demographic and health factors were tested to determine their potential influence on the
survival functions (see Table 5).
Age was found to influence survival (Log-rank: p<0.01, Wilcoxon: p=0.01). However, sex (Log-
rank: p=0.87, Wilcoxon: p=0.83), insurance type (Log-rank: p=0.29, Wilcoxon: p=0.41), ASA
classification (Log-rank: p=0.08, Wilcoxon: p=0.59), brushing frequency (Log-rank: p=0.34,
Wilcoxon: p=0.71), toothpaste use (Log-rank: p=0.21, Wilcoxon: p=0.16), flossing frequency
(Log-rank: p=0.53, Wilcoxon: p=0.86), dmfs score (Log-rank: p=0.24, Wilcoxon: p=0.50), high-
sugar diet (Log-rank: p=0.94, Wilcoxon: p=0.89), did not significantly affect survival.
45
Table 5. Patient demographic and health factors influence on survival
p-value for Log-rank test p-value for Wilcoxon test Sex 0.87 0.83Age <0.01 0.01Insurance 0.29 0.41ASA classification 0.08 0.59Brushing 0.34 0.71Toothpaste 0.21 0.16Flossing 0.53 0.86dmfs 0.24 0.50Diet 0.94 0.89
Clinical condition and setting factors influence on survival were tested (see table 6). Number of
surfaces was found to be a significant factor in survival when tested with the Log-rank analysis
(p=0.04), but not with Wilcoxon analysis (p=0.05). Tooth number (Log-rank: p=0.93, Wilcoxon:
p=0.23), arch (Log-rank: p=0.72, Wilcoxon: p=0.08), side (Log-rank: p=0.77, Wilcoxon:
p=0.50), surfaces involved (Log-rank: p=0.06, Wilcoxon: p=0.05), GI base (Log-rank: p=0.18,
Wilcoxon: p=0.21), pulp treatment (grouped) (Log-rank: p=0.97, Wilcoxon: p=0.53), isolation
type (Log-rank: p=0.37, Wilcoxon: p=0.29), setting (Log-rank: p=0.83, Wilcoxon: p=0.19),
behavior (Log-rank: p=0.05, Wilcoxon: p=0.06), operator (Log-rank: p=0.47, Wilcoxon: p=0.47)
did not significantly affect survival.
Table 6. Clinical condition and setting factors influence on survival
p-value for Log-rank test p-value for Wilcoxon test Tooth number 0.93 0.23Arch 0.72 0.08Side 0.77 0.50Number of surfaces 0.04 0.06Surfaces 0.06 0.05GI base 0.18 0.21Pulp treatment (grp) 0.97 0.53Isolation 0.37 0.29Setting 0.83 0.19Behavior 0.05 0.06Operator 0.47 0.47
Factors with potential to affect survival were entered into the Cox proportional hazard frailty
model as the adjustment and the significant ones were kept in the final model. The final model
adjusted for age, number of surfaces and surface types. However, number of surfaces and
46
surfaces demonstrated collinearity, thus only surface types was kept. The HR adjusted for age
and surface types was 0.77 (95% CI: 0.54, 1.09; p=0.14).
The effects of these factors are that a child aged less than five years old is 2.09 times more
frequently per unit time to fail versus a child who is older than seven years old (95% CI: 1.25,
3.90; p<0.01). Similarly, a child between five to seven years old is 2.06 times more frequently
per unit time to fail versus a child who is older than seven years old (95% CI: 1.24, 3.43;
p=0.01). The HR for a child less than five years old was not found to be significantly different
than a child between five to seven years old (HR: 1.01 [95% CI: 0.73, 1.39], p=0.95).
The effect of surface type showed an increased likelihood of failure for a disto-lingual (DL)
restorations versus a distal (D) restorations which was not statistically significant (HR: 2.15
[95% CI: 0.87, 5.36], p=0.10). The HR showed a 2.47 greater likelihood of a distolinguo-buccal
(DLB) versus distal restoration failing, which was not statistically significant (95% CI: 0.99,
6.16; p=0.05),
The HR for a disto-buccal (DB) versus distal restorations (p=0.30), disto-lingual versus
distolinguo-buccal restorations (p=0.44), disto-buccal versus distolinguo-buccal restorations
(p=0.10), disto-lingual versus disto-buccal restorations (p=0.30), were all not statistically
significant.
The various levels are summarized in Table 7.
Table 7. Hazard ratio for levels of material, age and surface
Factor Level HR 95% CI p-value Material Amalgam vs. composite 0.77 0.54 1.09 0.14 Age 0-5 vs. >7 2.09 1.25 3.90 <0.01
5-7 vs. >7 2.06 1.24 3.43 0.01 0-5 vs 5-7 1.01 0.73 1.39 0.95
Surface DL vs. D 2.15 0.87 5.36 0.10 DB vs. D 1.67 0.63 4.39 0.30 DLB vs. D 2.47 0.99 6.16 0.05 DL vs. DLB 0.87 0.61 1.24 0.44 DB vs. DLB 0.67 0.42 1.09 0.10 DL vs. DB 1.29 0.79 2.10 0.30
47
5.5 Reason for Failure
The likelihood of failure of an amalgam class III restoration versus a composite was quantified
using relative risk frailty model calculations. There was no difference in the RR of amalgam
restoration failing versus a composite restoration due to it becoming defective (p=0.07), nor due
to the tooth becoming necrotic (p=0.83). However, an amalgam restoration was significantly less
likely to fail due to recurrent caries with a RR of 0.35 (95% CI: 0.19, 0.65; p<0.01). See Table 8.
Table 8. Relative risk of amalgam compared with composite being due to defective
restoration, necrosis and recurrent caries
Reason of Clinical Failure Relative Risk 95% CI p-value
Defective Restoration 1.52 (0.97, 2.38) 0.07
Necrosis/Infection 0.83 (0.15, 4.53) 0.83
Recurrent Caries 0.35 (0.19, 0.65) <0.01
5.6 Reliability Between Evaluators
The kappa value between E.C. and P.A. is summarized in Table 9. Level of agreement is based
on Landis and Koch’s criteria (1977). There was perfect level of agreement for identifying
missing restorations. There was almost perfect level of agreement for identifying procedural-
related requiring replacement and axial wall RL. The level of agreement was substantial for
identifying the following RLs: procedural-related, inadequate contour, cavosurface margin and
gingival wall. Caries-related and incisal wall RL had a moderate level of agreement between
evaluators.
Table 9. Kappa between evaluators for radiographic radiolucencies
Kappa (95% CI) p-value Level of Agreement
Caries-related 0.46 (0.30, 0.90) 0.04 Moderate
Procedural-related 0.61 (0.14, 1.00) <0.01 Substantial
Procedural-related requiring replacement
0.83 (0.50, 1.00) <0.01 Almost perfect
Inadequate contour 0.79 (0.51, 1.00) <0.01 Substantial
Cavosurface margin 0.67 (0.33, 1.00) <0.01 Substantial
48
Kappa (95% CI) p-value Level of Agreement
Gingival wall 0.78 (0.50, 1.00) <0.01 Substantial
Incisal wall 0.56 (0.13, 1.00) 0.01 Moderate
Axial wall 0.83 (0.50, 1.00) <0.01 Almost perfect
Missing restoration 1.00 (1.00, 1.00) <0.01 Perfect
5.7 Reliability between Pre-tests
The kappa value between pre-tests is summarized in Table 10. There was perfect level of
agreement for identifying procedural-related RL, procedural-related RL requiring replacement,
cavosurface margin RL, gingival wall RL, incisal wall RL, axial wall RL and missing
restorations. There was a substantial level of agreement for caries-related RL. Lastly, there was
fair level of agreement for evaluating the inadequate contour criterion.
Table 10. Kappa between pre-tests for radiographic radiolucencies
Kappa (95% CI) p-value Level of agreement
Caries-related 0.63 (0.27, 0.97) <0.01 Substantial
Procedural-related 1.00 (1.00, 1.00) <0.01 Perfect
Procedural-related requiring replacement
1.00 (1.00, 1.00) <0.01 Perfect
Inadequate contour 0.28 (-0.16, 0.72) 0.21 Fair
Cavosurface margin 1.00 (1.00, 1.00)) <0.01 Perfect
Gingival wall 1.00 (1.00, 1.00) <0.01 Perfect
Incisal wall 1.00 (1.00, 1.00) <0.01 Perfect
Axial wall 1.00 (1.00, 1.00) <0.01 Perfect
Missing restoration 1.00 (1.00, 1.00) <0.01 Perfect
5.8 Radiographic Evaluation
355 of the 1101 restorations had a post-operative radiograph of adequate diagnostic quality. 138
radiographs of AR and 217 of CR were included. The mean radiographic follow-up period was
20.5±13.2 months. The mean follow-up was 20.8±12.6 months for AR and 20.3±13.5 months for
49
CR. The range of follow-up was 7 to 1733 days for ARs and 7 to 2185 days for CR. The detailed
ranges can be found in Table 11. The mean age was 6.0±1.6 years old for AR and 5.9±2.3 for
CR.
Table 11. Range of follow-up periods for post-operative radiographs
Number of restorations that had follow-up AR CR Total <30 days 3 5 8 30-60 days 0 0 0 61-180 days 8 11 19 181-365 days 25 60 85 366-730 days 59 69 128 731-1095 days 28 44 72 1096-1460 days 7 17 24 1461-1825 days 8 8 16 >1825 days 0 3 3
The clinical failure (based on the chart review that involved the clinician’s clinical and
radiographic interpretation at that time) set of data for charts with available radiographs included
a cumulative failure of 18.8% (or 26 failures for AR): 14 due to defective restorations, 2 due to
necrosis/infection and 10 due to recurrent caries. The latter clinical data was not available to the
radiographic evaluator at the time of analysis for this section. The clinical failure for the
radiographic set of CR was 40.1% (or 87 failures): 24 due to a defective restoration, 3 due to
necrosis/infection and 60 due to recurrent caries.
Radiographic evaluation is described below in Table 12. 30 of 138 (21.7%) AR were judged to
be failures based only on radiographic interpretation. Failure was defined when the restoration
was missing, caries-related RL was present or procedural-related RL requiring replacement. 95
(43.8%) of CR were considered failures based on radiographic interpretation.
11.6% of AR were missing, 7.2% had caries-related RL, 5.8% had procedural-related
radiolucency, 3 of the latter were significant enough to warrant replacement based on
radiographic interpretation alone. 13.8% of CR were missing, 23.5% had caries-related RL,
32.3% had procedural-related RL and 19 of the latter were significant enough for replacement.
50
Table 12. Radiographic evaluation
AR CR TotalMissing 16 30 46Caries-related RL 10 51 61Procedural-related RL 8 70 78Procedural-related RL requiring replacement 3 19 22Inadequate contour 17 28 45Cavosurface margin RL 13 99 112Gingival wall RL 13 106 119Axial wall RL 3 51 54Incisal wall RL 2 39 41Failure 30 95 125
5.8.1 Association Based on Radiographic Interpretation
The radiographic evaluation criteria were categorized depending if there was a caries-related
radiolucency (Table 13) or a procedural-related radiolucency (Table 14). The association
between caries-related RL and procedural-related RL was done with the RL location
(cavosurface, gingival, axial, incisal) stratified by restoration type and with stratification.
100% of the 10 ARs evaluated to have a caries-related RL involved the cavosurface margin and
90% involved the gingival wall. 98% of the 51 CR evaluated to have a caries-related RL
involved the cavosurface margin and the gingival wall. Both, AR and CR had a statistically
significant association between caries-related RL and the cavosurface margin (p<0.01), as well
as the gingival wall (p<0.01).
Table 13. Location of radiolucency if related to caries
Amalgam Composite TotalCavosurface margin 10* 50* 60*
Gingival wall 9* 50* 59*
Axial wall 0 18 18†
Incisal wall 1 15 16*
* p<0.01 assessed by Pearson Chi-Square test or Fisher’s exact test. † p=0.01 assessed by Pearson Chi-Square test or Fisher’s exact test.
50% of the 8 AR evaluated to have procedural-related RL involved the gingival wall, 37.5% the
cavosurface margin and axial wall. 70% of the 70 CR evaluated to have a procedural-related RL
involved the cavosurface margin, 80% the gingival wall, 47.1% the axial wall and 34.3% the
51
incisal wall. AR had a statistically significant association between procedural-related RL and the
cavosurface margin (p=0.04), the gingival wall (p<0.01) and the axial wall (p<0.01). CR had a
statistically significant association between procedural-related RL and the cavosurface margin
(p<0.01), gingival wall (p<0.01), axial wall (p<0.01) and incisal wall (p<0.01).
Table 14. Location of radiolucency if related to procedural technique
Amalgam Composite TotalCavosurface margin 3† 49* 52*
Gingival wall 4* 56* 60*
Axial wall 3* 33* 36*
Incisal wall 1 24* 25*
* p<0.01 assessed by Pearson Chi-Square test or Fisher’s exact test. † p=0.04 assessed by Pearson Chi-Square test or Fisher’s exact test.
5.8.2 Association Based on Chart Data
The Pearson Chi Square test and Fisher’s exact test was used to verify association between the
location of the radiolucency observed by E.C. and the reason for failure documented in the
patient chart. Table 15 summarizes the location of a radiolucency among the 14 available post-
operative radiographs for AR and 24 available radiographs for CR that were documented in the
patient’s chart as having failed due to a defective restoration.
Table 15. Location of radiolucency if chart data indicated failure due to a defective
restoration
Amalgam Composite TotalCavosurface margin 0 9 9Gingival wall 0 8 8Axial wall 0 6 6Incisal wall 0 4 4
* p>0.05 for each location as assessed by Pearson Chi-Square test or Fisher’s exact test.
No radiolucency was found for the set of radiographs based on AR. The location of the
radiolucency for the 24 CR involved the cavosurface margin in 37.5% cases, the gingival wall in
33.3% cases, the axial wall in 25.0% cases and the incisal wall in 16.7% of cases. No association
was found between a clinically defective restoration and any of the four possible locations of the
radiolucency.
52
Table 16 summarizes the location of a radiolucency among the 10 available post-operative
radiographs for AR and 60 available radiographs for CR that were documented in the patient’s
chart as having failed due to recurrent decay.
Table 16. Location of radiolucency if chart data indicated failure due to recurrent decay
Amalgam Composite TotalCavosurface margin 6 39 45Gingival wall 6 40 46Axial wall 0 17 17Incisal wall 0 13 13
* p≥0.05 for each location as assessed by Pearson Chi-Square test or Fisher’s exact test.
60.0% of the available post-operative radiographs for AR that failed due to recurrent decay had a
radiolucency located at the cavosurface margin and/or the gingival wall. 66.7% of the CR
evaluated in the clinical chart as having recurrent decay involved the gingival wall, 65.0% the
cavosurface margin, 28.3% the axial wall and 21.7% the incisal wall. No association was found
between a restoration with recurrent caries and any of the four possible locations of the
radiolucency.
53
Figure 10. Right maxillary canine AR at 521 day follow-up in adequate condition
Figure 11. Right mandibular canine CR at 464 day follow-up in adequate condition
Figure 12. Right maxillary canine AR at 586 day follow-up with caries-related radiolucency involving the cavosurface margin and gingival wall
Figure 13. Left mandibular canine CR at 322 day follow-up with caries-related RL involving cavosurface margin, gingival and axial wall
Figure 14. Left mandibular canine AR at 1289 day follow-up with procedural-related RL requiring replacement involving cavosurface margin and gingival wall
Figure 15. Left mandibular canine CR at 1274 day follow-up with procedural-related RL involving cavosurface margin
54
6 Discussion
Comparison to other results is difficult as there is very little literature on the subject. Study
designs are different, materials continuously change and evaluation criteria of the materials is not
constant from one study to another. Also, amongst the studies available in the literature, failure
rates are reported either as mean annual failure rate, annual failure rate, median survival time, or
other metrics which makes direct comparisons difficult. Median survival time may be preferable
as it is not influenced by short follow-up or changes in survival rate.
This current study found a median survival time of amalgam and composite was approximately
4.5 years and 3.8 years respectively. While, they do not categorize by cavity preparation type,
Pedrotti et al. (2017) found the mean survival time of the anterior composites in primary teeth to
be 4.3 years (95% CI: 4.0-4.6). This is similar to our median survival time for composite. Qvist
et al. (2010) published a 75% survival estimate of 3.5 years for class III/V restorations combined
in primary teeth, but the material type in unclear.
In the context of this study design, the HR using the Cox proportional frailty model was 0.77.
The direction of the effect can further be evaluated through the 95% CI limits of 0.54 and 1.09.
The CI suggests a potentially important clinical implication as the direction of the effect may
point to less risk for failure when using amalgam, as a non-statistically significant result does not
automatically mean that there was no effect (McCormack, Vandermeer, & Allan, 2013; Singh,
Kelley, & Agarwal, 2008). A narrower CI, possibly achieved through greater power may have
shown a different statistical result. Future randomized controlled trials may elucidate a more
clear effect when comparing the two materials. Due to the inclusion of the null-value, no
statistical significant difference was found between the survival of AR and CR, which may
contradict the comparative meta-analyses or Cochrane review done in posterior restorations
(Moraschini et al., 2015; Rasines Alcaraz et al., 2014). However, past studies have compared
these two materials describing similar survival (Mair, 1998; N. J. Opdam et al., 2007), or better
performance of amalgam (Collins, Bryant, & Hodge, 1998; Tate, Ng, Needleman, & Acs, 2002;
Van Nieuwenhuysen, D'Hoore, Carvalho, & Qvist, 2003). Composite has been found by Opdam
et al. (2010) to have a higher survival rate in a low risk group, and a lower survival rate in a
high-risk patient. Consequently, depending on the setting, inconsistent results have been
reported.
55
The incidence of recurrent caries found in this study is similar to the incidence described in the
literature which is between 0 and 4.9% for amalgams and 0 and 12.7% for composites (Bernardo
et al., 2007; Kopperud et al., 2012; Mannocci, Qualtrough, Worthington, Watson, & Pitt Ford,
2005; Nedeljkovic, Teughels, De Munck, Van Meerbeek, & Van Landuyt, 2015; Sachdeo, Gray,
Sulieman, & Jagger, 2004; Soncini et al., 2007; M. Wilson, Cowan, Randall, Crisp, & Wilson,
2002). The incidence of recurrent caries has been associated with caries risk. This study did not
report low versus high caries risk. The descriptive data of the sample in the study can be
considered as being high risk. The sample had a high mean dmfs index, a high proportion were
on a government-assisted insurance program and a there was a high self-reported high-sugar diet.
Previous studies have shown that socioeconomic status (SES) can affect the survival of
restorations, where people of lower SES are more at risk for failure versus those who are in a
higher bracket (Correa et al., 2013). In addition, caries risk or a high DMFT index (decay-
missing-filled teeth) is not only associated with higher risk for recurrent caries, but are at higher
risk for replacement of the restoration (Christopher D Lynch, Frazier, McConnell, Blum, &
Wilson, 2011; N. Opdam et al., 2010; Trachtenberg, Maserejian, Tavares, Soncini, & Hayes,
2008; Van de Sande et al., 2013). The main reason of amalgam failure in the present study was
due to fracture, which is similar to the finding of N. J. Opdam et al. (2012), but they found that
most failed amalgams were due to a tooth fracture and not the fracture of the restoration.
Similar to this study’s findings, many studies have found that recurrent caries is one of the main
reasons for failure of composites (Bernardo et al., 2007; Chrysanthakopoulos, 2011; Collins et
al., 1998; Gordan et al., 2012; Kopperud et al., 2012; Nedeljkovic et al., 2015; N. J. Opdam et
al., 2007; Palotie & Vehkalahti, 2012; Soncini et al., 2007). Replacement of a restoration that
presents with recurrent decay is to prevent the deleterious effects of caries progression which
may lead to pulpal involvement, non-restorability and ultimately the premature loss of the tooth.
Arguably, if a patient is considered at high risk of caries, the use of amalgam may be considered
as the preferred material choice. Other authors have argued that signs of marginal leakage
observed clinically as a brown or black marginal staining are more easily detected around tooth-
colored restoration, versus amalgams. Thus, are interpreted as recurrent caries (Dennison &
Sarrett, 2012; Mjör & Toffentti, 2000). However, it is important to recognize that a marginal
stain is indicative of a significant marginal leakage and a loss of adequate seal.
56
The bacteria surrounding and under composite has been found to be higher in number, greater
diversity and to have a significantly higher proportion of streptoccus mutans versus amalgams
(Heinrich, Bernhardt, Splieth, & Meyer, 2017; Svanberg, Mjor, & Orstavik, 1990). A favourable
environment for these bacteria leads to a cariogenic biofilm. Furthermore, the resin-based
restorations have been shown to undergo hydrolytic and enzymatic degradation. Enzymatic
degradation can involve salivary, bacterial or dentinal enzymes. It has been found that bacteria
such as streptococcus mutans can produce an esterase that can also take part in the degradation
of the resin (Bourbia, Ma, Cvitkovitch, Santerre, & Finer, 2013; Li et al., 2014).
This study did not find an influence of a large number of potentially confounding factors.
Whereas, Eidelman, Faibis, and Peretz (2000) have reported that the quality of restorations done
under general anesthesia were better quality than those performed under conscious sedation.
Because this was a university-based study, there is consistency in the fact that ideal conditions
are taught, highly recommended and generally enforced in the clinical setting. The high usage of
a rubber dam indicates that practitioners aimed to have proper isolation, which is key to the
success of composite materials. Knibbs and Plant (1990) published a survey that reported the
main reason for unsatisfactory glass-ionomer cement restorations in primary teeth performed by
general dentists was moisture contamination. However, the necessity of rubber dam has shown a
variety of results, where some studies show better results and others find no difference when
isolating with a rubber dam (Raskin, Michotte-Theall, Vreven, & Wilson, 1999; Smales, 1992,
1993; van Dijken & Horstedt, 1987). A Cochrane review “found some very low-quality
evidence, from single studies, suggesting that rubber dam usage in dental direct restorative
treatments may lead to a lower failure rate of the restorations, compared with the failure rate for
cotton roll usage” (Wang et al., 2016). Nevertheless, the frequent use of rubber dam in this study
does indicate there was a concerted effort to avoid salivary contamination during the operative
procedure.
This study did not find that behavior or setting influenced the survival of the materials. A study
by Eidelman et al. (2000) found that treatment outcomes were better for children who received
treatment under general anesthesia compared to those who received treatment under sedation.
They found a significant difference in the number of successful restorations for marginal
adaptation, anatomical form and no secondary caries. They analyzed restorations performed
57
under sedation and found that restorations per tooth done on children whose behavior was
recorded as being Frankl 1+2 had significantly more recurrent caries than those for children
categorized as 3+4. However, they did not find a statistical difference when comparing failure of
restorations for the sedation groups when calculated per child. In this study, each score was
categorized differently and not combined. However, there was no statistical difference in the
percent failure based on sedation group by Frankl’s behavioral scale. The latter is similar to their
“per child” result.
This study did not find a difference in survival based on the education level of the operator,
similar to a study done on amalgams that found experience of general dentists did not influence
length to replacement (Bailit, Chiriboga, Grasso, Damuth, & Willemain, 1979). However, other
studies have found that the level of the operator training and experience can significantly affect
the success of a restoration where experienced dentists had better results (Bernardo et al., 2007;
Demarco, Correa, Cenci, Moraes, & Opdam, 2012; Maupomé et al.). On the other hand, one
study on composites did find that younger graduates had the best results after placement of
composite restorations (Hawthorne & Smales, 1997). A possible explanation is that a recently
graduated student is more disciplined in the rigor required in technique and isolation versus a
practitioner that has been out of school for a longer time period and perhaps is less disciplined
due to the lack of supervision. Also, the year of the resident was not subcategorized and the data
of a first year resident was in the same category of a third year resident. Arguably, the latter
should have more experience versus a dental student or a first-year. Despite this, the multitude of
operators could mimic a private practice environment and how these materials might perform in
a multitude of general practices where individuals may have different degrees of clinical ability.
Although this study identified different age groups as being at risk for failure, other studies have
shown the influence of age on the survival of restorations as well (Bernardo et al., 2007; Hunter,
1985; Pallesen, van Dijken, Halken, Hallonsten, & Höigaard, 2014; Soncini et al., 2007).
Different reasons that could influence the survival is the difference in caries risk that changes
with age, younger children needing help for oral hygiene, dietary habit changes and changes in
cooperation during treatment.
While this study did not find an effect or did not test for the effect, the following factors have
been found by other studies to have an effect of the longevity of a restoration: site of the
58
restoration, size of the restoration, sex, socio-economic characteristics, oral hygiene, salary
structure and frequency of changing the dentist (Atchison & Schoen, 1990; Davies, 1984; Dolan,
McNaughton, Davidson, & Mitchell, 1992; Eriksen, Bjertness, & Hansen, 1986; G. Maryniuk,
1990; G. A. Maryniuk & Kaplan, 1986; Mjör, 1985; Qvist, Thylstrup, & Mjör, 1986).
The radiographic analysis was done without the evaluator having access to clinical data to avoid
any bias during the interpretation of the films. The radiographs that were available represented a
larger clinical failure, which indicates that radiographs were most likely to be available when
failure occurred. Thus, only quantitative descriptive statistics were done because the
radiographic set was not necessarily representative of the sample. Also, procedural-related RL
were chosen to be described instead of procedural-related RL requiring replacement, as the
descriptive statistics in the latter category would be very limited for the AR. The location of
caries-related RL can be explained by interproximal caries usually developing gingival due to the
contact point. Also, leakage can occur in this area because contamination is more likely to occur
in this area during placement and the thinner thickness of enamel at the cervical margin may
result in a weaker bond strength. Lastly, bacterial accumulation (as most children in this study
did not floss) and the gingival crevicular fluid can contribute recurrent caries in the region. On
the other hand, radiographs of procedural-related RL indicated the involvement of more walls
than caries-related RL. In CR, the RL can be due to a layer of adhesive that is too thick which
results in a well-defined radiolucent contour around the entirety of the restoration (Hardison,
Rafferty-Parker, Mitchell, & Bean, 1989). A thinner layer can be obtained with an air-syringe to
minimize this radiographic appearance. The discrepancy in the documented RL found for the
radiographic set in Table 14 and 15 demonstrates that a lot of CR show a radiolucent border
around the restoration that are present, but are not indicative of a carious process. The number of
procedural-related RL can be minimized with an appropriate technique. The procedural error in
AR can most probably be attributed to inadequate insertion and compaction (Summitt, Robbins,
Hilton, Schwartz, & dos Santos Jr, 2006). In terms of radiographic interpretation, a study argues
that the radiopacity of the restorative material can affect the performance of the evaluator
(Espelid, Tveit, Erickson, Keck, & Glasspoole, 1991). They found that recurrent carious lesions
are more difficult to detect next to a material of high radiopacity such as amalgam. An
alternative that has been proposed is the use of cone-beam computed tomography, however due
to the much higher dose of radiation versus conventional techniques it goes against the ALARA
59
principle; which mandates keeping radiation doses “as low as reasonably achievable”
(Charuakkra et al., 2011; Murat, Kamburoğlu, Isayev, Kurşun, & Yüksel, 2013).
To our knowledge, this is the first study to research the longevity of amalgam and composite
class III restorations in primary canines. This provides additional evidence to the body of
literature and thus can provide information to educators, clinicians and patients on the possible
performance of these materials. As previously discussed, the comparison of amalgam and
composite restoration’s risk of failure showed a potential effect that can be described as a
possible smaller risk of failure for amalgam, or as being equivalent to composite as the null value
is included within the upper limit. The latter can be taken into careful consideration by a
clinician when discussing the advantages and disadvantages of the use of these materials to
patients. Also, it can perhaps serve as an argument for the continued teaching of class III distal
amalgams for canines in dental schools as done previously. Moreover, the results indicate that
amalgam is less likely to fail due recurrent caries than composite, which can guide clinicians and
patients to consider the use of amalgam in a high caries-risk population. Previous studies have
discussed the cost-effectiveness of amalgam over composite restorations (Mjör, 1992; Tobi,
Kreulen, Vondeling, & Amerongen, 1999). Thus, from a public-health cost perspective, there
may be an advantage for public-funded programs to advocate for amalgam restorations as both
materials may perform similarly or amalgam might have less risk of failure.
6.1 Potential Limitations
There was a large standard deviation for the mean follow-up period because a large number
patients were lost after an initial one-month post-operative follow-up after a general anesthesia;
where the patients return to their community dentist after treatment. This can potentially
introduce the possibility of attrition bias. The latter is not unprecedented, since children who
have received dental treatment under general anesthesia have been found not to return for follow-
up (Berkowitz, Moss, Billings, & Weinstein, 1997; Eidelman et al., 2000; O'Sullivan & Curzon,
1991). But, the Kaplan-Meier survival curves are designed to censor data and take into account
patients who are lost to follow-up. However, low-rates of follow-up can introduce a risk of bias
in the sample, where those parents and children more likely to return are those who have noticed
a problem with the restoration. Alternatively, those who do not return for a follow-up visit may
60
do so as they do not have concerns. Another consideration that could have influenced these
results is that this study entered data as individual restorations. Thus multiple entered teeth from
the same individual could possibly skew the results if the individual is at high risk for restoration
failure. In addition, this study documented a failure if there was documentation that there was a
fault such as recurrent caries or a fracture even if the restoration did not have an ideal contour
and was not replaced.
A systematic review found that smaller restorations lasted longer than larger restorations
(Downer et al., 1999). Consequently, the results could be skewed if there was a bias for one
material over the other for larger cavity preparations. Because this was a retrospective study, the
size of the restoration cannot be evaluated and is unknown.
Different cavity preparations were done on the teeth, while surfaces and tooth number were
documented, the presence or absence of a dovetail or bevel was generally not written in the
clinical notes. However, the influence of a class III cavity preparation is still debated as in vitro
and in vivo results vary in conclusion and the literature available is extremely limited (Atkins Jr
et al., 1986; Baratieri et al., 2003; Heintze et al., 2015; Hoelscher et al., 2000; Piyapinyo &
White, 1998; Rathnam et al., 2010; Trairatvorakul & Piwat, 2005; Waggoner, 2015).
The types of materials used was determined from the purchase order history applicable to the
study time period. However, because a certain proportion of the clinical notes did not include the
material used, in the context of this study, these authors could not ascertain as to when each
material was used and could not unquestionably verify the effect a different material might have
had on the survival curves. In addition, establishing survival for a specific material is practical
from a controlled protocol point of view, but not always practical afterwards as materials
constantly change, and by the time studies are published, they may no longer be available.
The definition of failure was defined earlier, but the documentation relied on the provider’s
clinical notes. The challenge is that in a retrospective study, the clinicians are not calibrated, nor
given guidelines. However, given that this is a university-based study, students or residents are
taught techniques that should remain consistent. Also, clinical demonstrators will verify
preparations and insertions. While the university sets standards for its students, the
documentation of a failure either must be mentioned or is only assumed once the restoration is
reported as replaced. This author hopes that there was consistency, but studies have shown that
61
there is variation amongst dentists and even disagreement within the same dentist evaluating the
same entity at different occasions (Elderton & Nuttall, 1983; Kay & Knill-Jones, 1992). Despite
the fact the survival curves do not represent a standardized protocol done in a controlled
environment, they may mimic the expected survivability on average in a multitude of dental
offices considering the number of practitioners involved with the placement and evaluation of
the placed restorations (Allander, Birkhed, & Bratthall, 1990; Mjör, 1997). Furthermore, it has
been argued that clinical studies with a rigorous study protocol is not representative of dentistry
outside of a research setting and does not allow the findings to be generalized to a general
practice (Jokstad et al., 2001).
6.2 Future Directions
This study adds to the paucity of literature on this subject. However, prospective studies with
randomized allocation and standardized treatment and evaluation protocols are recommended.
This would provide more objective and reproducible results. Moreover, standardized evaluation
criteria could be developed as different authors tend to modify the USPHS criteria for their own
use and few use the FDI criteria; which can make comparison difficult. Multicenter studies
would test the performance of materials in different study populations and permit the evaluation
of potential factors affecting survival.
7 Conclusions
In this retrospective chart review, the median survival time of amalgam and composite was
approximately 4.5 years and 3.8 years respectively in this high caries risk population of children.
Radiographic analysis showed caries-related RL were significantly associated for involving the
gingival wall and cavosurface margin for both AR and CR. Post-operative radiographs showed
RL related to procedural technique for AR involved the gingival wall, axial wall and cavosurface
margin. Whereas, for CR, the gingival wall, axial wall, incisal wall and cavosurface margin were
involved.
62
There was no statistically significant difference between the clinical survival of amalgam and
composite. Restorations placed in children between 0-5 years old were significantly more likely
to fail than when placed in a child over 7 years old. Additionally, when placed in a child between
5-7 years old, the restoration was more likely to fail than when placed in a child over 7 years old.
Composite restorations were statistically more likely to fail from recurrent decay than amalgam
restorations.
63
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Appendices
Appendix A: Patient consent form
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