J. Dent. 1987; 15: 67-72 Printed in Great Britain 67

Microleakage of dentine-bonded posterior composite restorations

M. A. Fayyad* and A. C. C. Shot-tall Department of Conservative Dentistry, The Dental School, Birmingham

KEY WORDS: Composite, Posterior, Microleakage

J. Dent 1987; 15: 67-72 (Received 27 June 1986; accepted 30 September 1986)

ABSTRACT This in vitro investigation assesses the marginal leakage of extensive class II preparations that had been restored with light-cured posterior composite materials using dentine- bonding agents or glass-ionomer cement linings. The restored teeth were immersed in a marker dye solution while being subjected to thermal cycling treatment and, after sectioning the restorations, dye penetration at the restoration/tooth interface was assessed and quantified using digital imaging microscopy.

Microleakage was observed at the cervical wall of all the restorations and was more extensive when the cervical cavity margin was located below the cemento+namel junction. The use of a glass-ionomer cement lining significantly reduced the extent of cervical marginal leakage in this situation. Continued development of dentine-bonding agents and/or composite resin restoratives is required before a satisfactory marginal seal can be guaranteed when using these materials in the restoration of extensive cavities in posterior teeth.

INTRODUCTION

A good marginal seal between tooth and restoration is required to minimize cavomarginal discolouration and the risk of secondary caries formation. Microbial micro- leakage has also been identified as a major factor in the pulpal reaction to composite resin restorations (BrBnnstrBm, 1984). In recent years there has been a marked increase in the use of resin-based materials in the restoration of posterior teeth. This situation has arisen because of an increased demand for aesthetic dentistry and, to a lesser extent, because of a growing concern about the possible risk of mercury toxicity associated with the use of silver amalgam restorations. In addition, manufacturers have produced composite resin materials specifically designed for the restoration of posterior teeth.

While the acid-etch technique can afford a good marginal seal for composite resin restorations placed in enamel-bonded cavities, greater demands are made on marginal seal when these materials are used in extensive cavities, especially in posterior teeth. The larger size of

* Present address: Department of Conservative Dentistry, University of Jordan, Amman, Jordan.

these cavities leads to greater dimensional changes on either polymerization of the restoration or consequent to thermal fluctuation. Also, because the restorations are more complex in shape, volume changes will tend to flex the restoration and so stress the marginal seal (Forsten et al., 1982). In many posterior cavities removal of caries or existing restorations results in a gingival floor situated below the cemento-enamel junction. In this situation the use of acid-etch technique may lead to an increase in the magnitude of contraction gap formation at the cervical wall of approximal composite resin restorations (Br&mstr(im et al., 1984).

Recently, materials and techniques have been developed in order to offset the problems created by a lack of adhesion between composite resin restoratives and dentine cavity surfaces. Many dentine-bonding agents have been introduced in the past few years and the manufacturers often claim a very strong bond between adhesive, composite resin and dentine. In addition, a technique for sealing the cervical dentine wall of a cavity with glass-ionomer cement before acid-etch bonding of the composite resin restoration to the glass-ionomer cement and the etched enamel cavity walls has recently been described (McLean et al., 1985).

68 J. Dent. 1987; 15: No. 2

The purpose of the present in vitro investigation was to evaluate the marginal seal of two commercially available composite resin restorative materials when used in conjunction with dentine-bonding agents or glass-ionomer cement bases in the restoration or extensive class II MOD cavities in molar teeth.

MATERIALS AND METHODS

Forty caries- and defect-free extracted human molar teeth were used in this investigation. An MOD cavity was prepared in each tooth using a cylindrical diamond bur (Hi Di 546 Cylindrical Diamond Bur, Ash Instrument Division, Dentsply Ltd, Gloucester GLl 5 SG, UK) in an air-turbine handpiece operated with water spray. All cavity margins were finished to a cavosurface angle of 90-110” using tungsten carbide burs (Beaver 331L Tungsten Carbide Bur, Beaver Dental Products Ltd, Morrisburg, Ontario, Canada). Each bur was discarded

The prepared teeth were randomly assigned to four groups, each of 10 teeth, for etching, bonding and restoration ( Table I). In all four groups the enamel cavity walls were acid-etched with a phosphoric acid gel (Stratford Cookson Company, Newman, GA 30246, USA) applied for 60 s, washed thoroughly with water and the cavity preparations were dried with compressed air before restoration. The restorative procedures adopted for the four groups are described below.

Group A

After acid-etching of enamel cavity walls, light-cured Scotchbond (3M Dental Products, 225-55 3M Center, St Paul, MN 55144, USA) was applied in two layers to enamel and dentine cavity surfaces (each layer was blown with compressed air after placement) before curing for 10 s with a Luxor light-activating unit (Imperial Chemical Industries PLC, Pharmaceutical Division, Macclesfield, Cheshire, UK). A metal matrix band was then placed

Table I. Materials evaluated and restorative technique

Experimental group

Cavity surface treatments

Bonding/lining materials

Restorative material

D

A Acid-etch enamel cavity walls

Polyacrylic acid con- ditioning of dentine cavity walls Acid-etch enamel cavity walls and glass- ionomer cement lining

Acid-etch enamel cavity walls

Gluma Cleanser applied to dentine cavity walls

Acid-etch enamel cavity walls

Scotchbond (enamel and dentine cavity walls)

P-30

Ketac-Bond (dentine cavity walls)

P-30

Scotchbond (enamel and glass-ionomer cement lining)

Clearfil New Bond (enamel and dentine cavity walls)

Gluma Bond (dentine cavity walls) Clearfil New Bond (dentine cavity walls) Clearfil New Bond (enamel and dentine cavity walls)

Clearfil Ray

Clearfil Ray

after the preparation of live cavities. In each tooth the cervical wall of one proximal box was located 1 f 0.25 mm above the cemento-enamel junction (enamel side), while the cervical wall of the other proximal box was located 1.0 f 0.25 mm below the cementHname1 junction (cementum side). The occlusal width of each cavity was made equal to half the intercuspal width and the pulpal floor was extended 1 mm into dentine. The mesiodistal width of the cervical wall of each proximal box was made equal to the diameter of the cylindrical diamond bur (1.3 mm). Following preparation the cavities were washed with an air/water spray and dried with compressed air before restoration.

before applying and polymerizing P-30 (3M Dental Products) light-cured composite in layers according to the manufacturer’s instructions. Each increment was cured for 20 s using the Luxor light applied from the occlusal surface and each proximal box was given an additional 10 s irradiation with the light applied from the proximal surface after removal of the matrix band.

Group B

The prepared dentine cavity surfaces were treated with a 25 per cent (v/v) polyacrylic acid solution applied to 30 s on a cotton wool pledget. The preparations were washed

Fayyad and Shortall: Microleakage of restorations 69

well with water and dried with compressed air before lining all the dentine cavity surfaces with a fast-setting radiopaque glass-ionomer cement (Ketac Bond, ESPE, D-803 1 Seefeld/Oberbay, FR Germany) lining material. After waiting for 4 min any excess cement was removed from the enamel cavity walls and the cement was finished to a feather edge at the cavosurface margin of the proximal box extended below the cemento-enamel junction. The enamel cavity walls and the glass-ionomer cement lining were then etched for 60 s with phosphoric acid gel before restoration, as in group A.

Group C

Following acid-etch pretreatment of enamel cavity walls, Clearfil New Bond (Cavex Holland BV, Keur & Sneltjes Dental Mfg. Co., Harmenjansweg 19-21 Haarlem, Holland) was mixed and applied to unetched dentine and etched enamel cavity walls and blown dry with compres- sed air. After the bonding agent had lost its glossy surface the cavities were restored with Clearfil Ray (Cavex Holland BV) light-cured composite packed and polymer- ized incrementally as described for the P-30 composite material.

Group D

The prepared dentine cavity surfaces were treated by scrubbing for 30 s with a cotton wool pledget saturated with Gluma Cleanser (Bayer Dental, D-5090, Leverkusen, FR Germany) before rinsing the cavities with water. The cavities were briefly blown dry with air before applying Gluma Bond (Bayer Dental) to prepared dentine cavity surfaces and spreading it with a compressed air jet. Cleatil New Bond was then mixed and applied to dentine cavity surfaces and air blown dry. After allowing the material to polymerize, any excess was removed from the enamel cavity walls before acid-etching the enamel and restoration as described for group C.

The preparations were slightly over-filled and the excess composite resin was removed after 15 min using tungsten carbide finishing burs (Komet 500 274 072 016 Tungsten Carbide Finishing Bur, GEBR. Brasseler GmbH & Co., KG Lemgo, FR Germany), and composite finishing discs (Dr H v Weissenfluh Ltd. Ch-6925 Gentilino, Switzerland). The restored teeth were then placed in distilled water at 37 “C for 1 week before thermal cycling. To prevent dye penetration in areas other than at the exposed margins the root apices were sealed with a cold-cure acrylic resin material and the teeth were sealed with two applications of nail varnish leaving 1 mm around the restoration margins free of the varnish. The restored teeth were exposed to changes in temperature by means of a temperature-cycling machine to simulate temperature changes in the mouth (Kidd et al., 1978). Each cycle consisted of 4 min in a 37 “C neutral bath, 1 min in a 15 “C cold bath, 4 min again at 37 “C, and 1 min in a 45 “C hot bath. Cycling continued for 24 h, giving a

total of approximately 150 cycles. During cycling the teeth were immersed in a 1 per cent solution of methylene blue dye sealed in plastic bags, and following cycling the teeth were sectioned longitudinally in a mesiodistal direction through the middle of the restorations using a water-cooled diamond-bladed sectioning apparatus.

The sectioned restorations were examined with a stereomicroscope (Wild M3Z Stereozoom Microscope, Wild Heerbrugg Ltd, CH-9435, Heerbmgg, Switzerland) and the extent of dye penetration (measured along the cavity/restoration interface) was recorded and quantified by using an image analysis apparatus (Imagan, Semi- Automatic Image Analysis System, Graphic Information Systems, Technical Development Centre, Lomond House, Almondvale, Livingston, Scotland) linked to the microscope by a viewing tube (Drawing Tube M3/7A/ 7S/8 with mirror attachment, E Leitz (Instruments) Ltd, 48 Part St, Luton LUl 3HP, UK). The extent of dye penetration was assessed separately for each proximal box (above or below the cementc+enamel junction) of each restoration and both halves of each restoration were assessed for the extent of dye penetration, resulting in 160 proximal box assessments in total. An assessment was also made of the percentage of sections in each group which demonstrated dye penetration past the amelo- dentinal junction on the enamel side of the specimens.

RESULTS

The average length of dye penetration (measurements in mm), standard deviation and number of observations recorded for each group are shown in Table II.

Students r test was used to analyse the data. On the enamel side of the specimens no statistically significant difference in dye penetration was found between groups A and B, A and C, and B and D. A statistically significant difference in dye penetration was found between groups A and D (P < O*OOS), B and C (P < O*OS), and C and D (P < O+lOS).

Dye penetration in the cementurn side differed signifi- cantly between groups A and B (P < O*OOl), A and C (P < O*OS), A and D (P < O.OOl), B and C (P < 0.001) and C and D (P < OXlOl). No statistically significant difference was found between groups B and D on this side.

With the exception of procedure B, dye penetration measurements were significantly lower in the enamel side than in the cementum side. On the enamel side all of the group A and B specimens exhibited dye penetration past the amelo-dentinal junction. Two specimens in group C and four specimens in group D had either no dye penetration or dye penetration that did not reach the amelo-dentinal junction on this side of the specimens. Thus, 80 per cent of the sections in group C and 60 per cent of the sections in group D exhibited dye penetration beyond the amelo-dentinal junction.

70 J. Dent. 1987; 15: No. 2

Tab/e I/. Measurements of dye penetration along the enamel side and cementum side of class II MOD composite resin restorations

Experimental group

A

B

c

D

Bonding/lining materials

Scotchbond

Scotchbond/Ketac Bond

Clearfil New Bond

Gluma Clearfil New Bond

Extent of dye penetration (mm)

Restorative material

P-30

P-30

Enamel side Cementum side

Mean s.d. n Mean s.d. n

3.1 1.4 20 9.3 1.9 20

2.1 2.2 20 2.7 2.2 20

Clearfil Ray 3.5 1.8 20 6.2 3.1 20

Clearfil Ray 1.6 1.6 20 2.9 1.9 20

DISCUSSION

Shortall (1982) has reviewed the techniques which have been developed to assess the marginal seal of resin-based restorations and the permeability of the tooth/restoration interface, Dye penetration tests afford a simple and relatively inexpensive method of making such an assess- ment. However, the results obtained may be influenced by factors such as the nature (chemical composition, molecular size) of the dye marker substance and the precise experimental method employed (whether dye immersion occurs coincident with or follows after thermal cycling procedures). Dye penetration tests simply indicate the presence of a marginal gap and do not predict any possible adverse clinical consequences. The use of bacteria or sugar molecules to study marginal leakage are methods which offer more direct clinical relevance, given the role played by these substances in secondary caries formation and pulpal pathology (Fayyad, 1984; Shortall et al., 1985). Fayyad (1984) has demonstrated a correlation between the results of bacterial and dye penetration test methods when assessing the marginal leakage characteristics of several resin-based restorative materials.

The method of using digital imaging microscopy to record the actual length of dye penetration (in mm) along the cavity/restoration interface allows a more objective assessment to be made of the extent of marginal leakage in comparison to traditional methods of dye marker assess- ment where qualitative judgements have been made for the depth and path of tracer penetration. Previous investigations have assigned numerals to specific points of dye ingress (such as the amelo-dentinal junction) and data analysis has assumed equality between the unit scores for dye penetration. Even with standardized cavity preparation technique, however, cervical enamel thickness varies between experimental samples (Retief et al., 1982).

The restored teeth were not subjected to dye immersion or thermal cycling for a 1 week period after restoration, as it has been shown that teeth restored with acid-etched

mesio-occluso-distal composite resin restorations continue to undergo significant intercuspal dimensional changes fdr up to 1 week after polymerization of the restoration (Causton et al., 1985).

The finding that all but one restorative technique (group B) resulted in more extensive marginal leakage on the cementum side as compared to the enamel side of the restorations confirms the findings of Gross et al. (1985), and emphasizes the need for more secure bonding to cervical enamel and dentine in order to provide a reliable marginal seal for posterior approximal composite resin restorations. While bevelled cavity margins have been recommended for class II restorations of composite resin by some authors, the adequacy of this method bf cavity margin finishing may be questioned for a number of reasons (Ehmford and Derand, 1984; Boksman and Jordan 1985). Bevelling of occlusal cavity margins results in a wider functional occlusal surface for the restoration, makes precise ‘finishing’ more difficult, and creates problems with thin sections of marginal excess which may be prone to fracture under occlusal loading. Bevelling of proximal and cervical enamel cavosurface margins in extensive class II cavities can lead to difficulties with effective isolation, can create problems in regard to matrix placement and stabilization and may hinder accurate reproduction of existing tooth contours. Extensive cervical bevelling may also eliminate any remaining enamel available for bonding with the acid-etch technique. The cavity dimensions and cavity margin location employed in the current investigation represent those which a dentist might be expected to .deal with in the replacement of an extensive class II amalgam restoration.

The use of a glass-ionomer cement lining of exposed dentine cavity surfaces resulted in a significant reduction in dye penetration at the tooth/restoration interface on the cementum side of the restoration in comparison to the other experimental procedures. The value of using a polyacrylic acid conditioning agent on exposed dentine cavity surfaces to improve adhesion of the glass-ionomer cement has already been established (Powis et al., 1982).

Fayyad and Shot-tall: Microleakage of restorations 7 1

The glass-ionomer cement used in the current study was developed especially for use with the acid-etch technique of composite resin restoration (McLean et al., 1985).

An interesting finding noted with the sectioned group B restorations was the presence of dye marker at the glass- ionomer/composite interface. The extent of dye uptake at this interface could be quite marked in relation to the degree of marginal leakage (as assessed by dye penetra- tion at the restoration/dentine interface) exhibited on the same section. No attempt was made to quantify this phenomenon in the current investigation, but further work is in progress to ascertain its clinical relevance. Different acid types, concentrations and application times are being investigated in order to determine the most effective regimes for pretreatment of glass-ionomer lining materials, while still permitting a short interval between cement placement and acid-etch pretreatment. It is perhaps not surprising that dye penetration was noted at this interface as it represents only a mechanical and not a physico- chemical bond (McLean et al., 1985).

The restorative procedure adopted in group D was based on the experimental finding reported by Munksgaard et al. (1985) that the use of Gluma followed by Clearfil Bond prevented marginal contraction gap formation in 29 out of 30 cavities restored with a light-cured restorative resin. It should be noted, however, that the cylindrical dentine cavities employed in that investigation were much smaller than those of the current study and bonding to dentine cavity walls was not complicated by the presence of acid-etched enamel around most of the filling periphery. When acid-etch technique prevents contraction gap formation at the occlusal enamel margins of class II cavities, then a larger contraction gap may be expected at the cervical wall devoid of enamel (Brlnnstr6m et al., 1984).

Also, it is known that dentine adhesives have much less effect on contraction gap formation when used with highly filled restorative resins (Hansen, 1986), as employed in the current study, in contrast to the less heavily filled restorative resin used in the study by Munksgaard et al. (1985). While the restorative procedure adopted in group D resulted in restorations with the best marginal seal on the enamel side of the preparation, dye penetration on the cementum side was significantly greater for this experi- mental group. This restorative procedure was complicated by the number of steps involved in the bonding treatment and by the limited access available for scrubbing the exposed dentine surfaces with cotton wool pledgets soaked in Gluma Cleanser.

CONCLUSIONS

1. Extension of the cervical cavity wall of class II composite resin restorations below the cementc+enamel margin will result in more extensive marginal leakage for these restorations.

2. Use of a glass-ionomer cement lining of exposed dentine cavity surfaces can significantly reduce the marginal leakage on proximal box preparations located below the cemento-enamel margin. However, the inter- face between the acid-etched glass-ionomer and the composite resin may be a weak link.

3. None of the restorative procedures/materials tested resulted in restorations free from marginal leakage.

4. The increasing use of composite resin restorative materials in extensive class II cavities suggests the need for the continued development of these materials in order to overcome the problems posed by marginal leakage.

Acknowledgements

The authors would like to express their gratitude to Professor D. S. Shovelton for his help and encouragement during the course of this study. The image analysis equipment used in this investigation was provided through a grant (GL 3009) made available to one of the authors from the Endowment Fund Medical Research Committee of the Central Birmingham Health Authority.

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72 J. Dent. 1987; 15: No. 2

Powis D. R., Folleras T., Merson S. A. et al. (1982) Shortall A. C. (1982) Microleakage, marginal adaptation Improved adhesion of a glass-ionomer cement to enamel and composite resin restorations. Br. Dent. J. 153, and dentine. J. Dent. Res. 61, 1416-1422. 223-231.

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Correspondence should be addressed to: Mr A. C. C. Shortall, Department of Conservative Dentistry, The Dental School, University of Birmingham, St Chad’s Queensway, Birmingham, B4 6NN, UK.

Forthcoming Articles A method of clinical evaluation of bulk fracture of amalgam restorations Ph. L. M. Lemmens, G. J. J. M. Straetmans, M. C. R. B. Peters and H Letzel.

Indirect dental laminate veneers-an overview G. G. Toh. J. C. Setoos and A. R. Weinstein.

The mechanical strength and microstructure of all-ceramic crowns I’. Piddock, P. M. Marquis and H. J. Wilson.

Denture bases: the effects of various treatments on clarity, strength and structure J. G. Robinson, J. F. McCabe and R. Storer.

Quantification of hydrogen gas released from polyvinylsiloxane impression ,materials in contact with die stone materials J. McCrossan, S. W. Sharkey, G. McR. Smith and R. A. Anderson.

The effect on marginal leakage, in vitro, of curing composite material at elevated temperatures with or without marginal etching of the cavity G. J. Pearson and C. M. Longman.

Characterization of aluminium radiopacity standards for restorative materials D. C. Watts.

Corrosion rate studies: measurements of corrosion rates of some non-precious dental alloys in artificial saliva L. Wiegman-Ho and J. A. A. Ketelaar.

The effect of social class on the prevalence of caries, plaque, gingivitis and pocketing in 1 1-lZyear-old children in South Wales P. M. H. Dummer, M. Addy, R. Hicks, A. Kingdon and W. C. Shaw.