implant complications

8/12/2019 implant complications

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The International Journal of Oral & Maxillofacial Implants 69

Mechanical and Technical Risks in Implant TherapyGiovanni E. Salvi, PD, Dr Med Dent 1 /Urs Brgger, Prof Dr Med Dent 2

Purpose: To systematically appraise the impact of mechanical/technical risk factors on implant-supported reconstructions. Material and Methods : A MEDLINE (PubMed) database search from 1966 to

April 2008 was conducted. The search strategy was a combination of MeSH terms and the key words:design, dental implant(s), risk, prosthodontics, fixed prosthodontics, fixed partial denture(s), fixed den-

tal prosthesis (FDP), fixed reconstruction(s), oral rehabilitation, bridge(s), removable partial denture(s),overdenture(s). Randomized controlled trials, controlled trials, and prospective and retrospectivecohort studies with a mean follow-up of at least 4 years were included. The material evaluated in each

study had to include cases with/without exposure to the risk factor. Results: From 3,568 articles, 111were selected for full text analysis. Of the 111 articles, 33 were included for data extraction after

grouping the outcomes into 10 risk factors: type of retentive elements supporting overdentures, presence of cantilever extension(s), cemented versus screw-retained FDPs, angled/angulated abutments,bruxism, crown/implant ratio, length of the suprastructure, prosthetic materials, number of implants

supporting an FDP, and history of mechanical/technical complications. Conclusions: The absence of a metal framework in overdentures, the presence of cantilever extension(s) > 15 mm and of bruxism,the length of the reconstruction, and a history of repeated complications were associated withincreased mechanical/technical complications. The type of retention, the presence of angled abutments, the crown-implant ratio, and the number of implants supporting an FDP were not associatedwith increased mechanical/technical complications. None of the mechanical/technical risk factors hadan impact on implant survival and success rates. INT J ORAL MAXILLOFACIMPLANTS 2009;24( SUPPL):6985

Key words: clinical studies, oral implants, prosthodontics, risk factors

Medical interventions involving surgical proce-

dures for the insertion of devices such as stents,hip or knee prostheses, orthopedic devices, or dentalimplants are associated with risk. Before undergoingsuch interventions, the risks for failure or complica-tions and chances of survival or success need to becarefully weighed by patients and professionals. Aqualitative description of risk would relate a greateroverall risk to a greater loss and greater likelihoodthat an event occurs.

In medicine, a risk factor is a variable associated

with an increased risk of disease or infection. Risks arecorrelational and not necessarily causal. Risk factorsare evaluated by comparing the risk of those exposedto the potential risk factor to those not exposed. Forthe purpose of the present review, mechanical andtechnical risks were defined as follows:

Mechanical risk: Risk of a complication or failure of a prefabricated component caused by mechanicalforces.

Technical risk:Risk of a complication or failure of thelaboratory-fabricated suprastructure or its materials.

Mechanical and technical risks play a major role inimplant dentistry.They may lead to increased rates of repairs and remakes, and to a waste of time andfinancial resources, and may even affect the patientsquality of life.

During treatment planning, constellations knownto be associated with increased risk should beavoided. Risks associated with different treatmentoptions must also be related to the financial conse-quences, especially when considerable price differ-ences exist between the prosthetic options.

1 Vice Chairman and Graduate Program Director in Periodontology,Department of Periodontology, School of Dental Medicine,

University of Bern, Bern, Switzerland.2 Chairman, Division for Fixed Prosthodontics, School of DentalMedicine, University of Bern, Bern, Switzerland.

The authors reported no conflict of interest.

Correspondence to: Prof Urs Brgger, Division for Fixed Prostho-dontics, School of Dental Medicine, University of Bern, Freiburg-strasse 7, CH-3010 Bern, Switzerland. Fax: +41 31 632 4931.Email: [email protected]

This review paper is part of the Proceedings of the Fourth ITI Consen- sus Conference, sponsored by the International Team for Implantol- ogy (ITI) and held August 2628, 2008, in Stuttgart, Germany.


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A series of systematic reviews were launched toestimate and compare the failure/complication ratesto be expected with various types of fixed recon-structions on teeth and implants. 18 With some of thereconstructions, considerably increased rates of fail-ures were estimated to occur over 10 years of func-tion 6: fixed dental prostheses (FDPs) with cantileverextensions on teeth (19.6%), combined tooth-implant-supported FDPs (22.3%), and resin-bondedFDPs (35.0%).

The protocols of the systematic reviews mentionedabove were designed to include publications report-ing on the prosthetic failure and complication rateswith a particular design of a reconstruction, ie,full-archFDPs on implants/teeth, short-span FDPs on implantsand teeth,and single crowns,over at least 5 years.

Excluding multiple other factors that may mask acorrelation with a particular risk factor seems to bedifficult when combining data from cohort studies

being performed at various centers. According to thedefinition of risk factormentioned above, long-termstudies that evaluated and compared the risk of those patients/reconstructions exposed to a certainrisk factor to those not exposed to that risk factor inthe same environment are of particular interest.

Therefore, the aim of this review was to systemati-cally screen the literature for information answeringthe following focused question: Which mechanical/technical risk factors have an impact on implant-sup-ported reconstructions?

MATERIALS AND METHODS

Search StrategyA search in the MEDLINE (via PubMed) database from1966 up to and including April 2008 was performed.Publications in English,German, French, and Italian inpeer-reviewed journals were considered; abstractswere excluded. The search strategy applied was acombination of MeSH terms and free text words,including the following key words: design , dental implants/risk , prosthodont ics , fixed prosthodontics ,

fixed partial denture(s) , fixed reconstruction(s), oral rehabilitation, bridge(s), removable partial denture(s),and overdenture(s).

A complementary manual search from 1986 up toApril 2008 was carried out in the following journals: Journal of Oral Rehabilitation , Journal of Prosthetic Dentistry , International Journal of Prosthodontics , Inter-national Journal of Periodontics & Restorative Dentistry ,Clinical Oral Implants Research, and International Jour-nal of Oral & Maxillofacial Implants . In addition, thereference lists of articles selected for inclusion in thisreview were screened.

Selection CriteriaRandomized controlled trials (RCTs), controlled trials,and prospective and retrospective cohort studieswith a mean follow-up time of at least 4 years wereincluded. The material evaluated in one study had toinclude cases with the risk factor and cases withoutexposure to the risk factor.

The following inclusion criteria were used:

Mean follow-up time 4 years At least five patients included Studies on fully and partially edentulous patients Studies on fixed and/or removable implant-sup-

ported dental prostheses Studies on fixed dental prostheses with cantilever

extension(s) Studies on implant-supported single-unit crowns Studies on implant- and/or tooth-implant-sup-

ported reconstructions

Studies on cylindrical and/or cylindrical-conicalsolid-screw implants

Clinical examination at the follow-up visits Detailed information on the characteristics of the

implants and their supported reconstructions

The following exclusion criteria were used:

Animal studies in vitro studies Studies based on patients records, surveys, ques-

tionnaires,or interviews

Studies focusing exclusively on finite elementanalysis (FEA) Studies focusing exclusively on implant length

and/or diameter Studies focusing exclusively on patient-centered

outcomes Reviews Case reports Abstracts

Validity Assessment Two reviewers (UB and GES) screened ti tl es and

abstracts identified through the search for possibleinclusion. The discrepancies were resolved by discus-sion.Publications of potential interest were obtained inorder to evaluate the full text. Both reviewers screenedthe included publications independently using theinclusion criteria. Again, any disagreement wasresolved by discussion between the two reviewers.

Data ExtractionCollectively, the outcome variables included:

70 Volume 24, Supplement, 2009

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Salvi/Brgger

Implant-related mechanical and technical risk fac-tors

Abutment-related mechanical and technical risk factors

Suprastructure-related mechanical and technicalrisk factors

Depending on the presence or absence of a spe-cific mechanical or technical risk factor, survival andsuccess rates of implants, abutments, and relatedsuprastructures were extracted from the publica-tions. Survival was defined as presence of theimplant, abutment, and/or its suprastructure in situ inits original extension at follow-up examination withor without complications. Success was defined aspresence of the implant, abutment, and/or supras-tructure in situ without any mechanical or technicalcomplications during the entire follow-up period.

From the included papers, the following informa-

tion was extracted: the number of patients examined,the mean age of the patients, the mean observationtime, the number of implants restored, the implantsystem used, the designs of the reconstructionsunder examination, and the study design applied.Finally, the major findings related to harm to thesuprastructure, prosthetic components of theimplant systems, peri-implant tissues, implants, andresults of statistical analyses were noted andgrouped according to potential risk factors.

RESULTSOf the 3,568 titles resulting from the online search,111 were selected for full text review after readingthe abstract. From the 111 full-text articles, 33 wereincluded for data extraction. Two additional articleswere included based on a manual search (Fig 1).

The data from 35 publications were grouped accord-ing to 10 risk factors identified after screening the lit-erature:

Type of retentive elements supporting overden-tures

Cantilever extension(s) on fixed dental prostheses(FDPs)

Cemented versus screw-retained FDPs Angled/angulated abutments Bruxism Crown-to-implant ratio Length of the suprastructure Prosthetic materials Number of implants supporting an FDP History of mechanical/technical complications

Retentive Elements of Overdentures(Tables 1 and 2)Eight studies dealing with mandibular overdenturesin which the allocation of patients to different treat-ment groups was performed in a randomized man-

ner were identified (Table 1). Naert et al compared 12patients with Dolder bars to 12 patients with ballattachments and 12 patients with magnets. 9 At 5years, the highest retention measured by means of adynamometer amounted to 1,240 g in the bar group,followed by 567 g in the ball attachment group, andonly 110 g in the magnet group. 9 When questionsabout prosthesis stability and cleaning comfort wereranked on a scale from very bad (1) to excellent (9),mean rankings were statistically significantly lower inthe magnet group compared to the ball and bargroups. Patient satisfaction related to chewing com-fort and phonetics did not change significantly overthe 5 years. In the magnet group, however, a signifi-cant decrease in general satisfaction and in satisfac-tion with denture stability was noted ( P < .03).

In a later publication by Naert et al, 10 unfortu-nately no detailed information related to prostheticcomplications over 10 years of observation was pre-sented. Similar failure rates for the implants werenoted in the three groups of overdentures.

Gotfredsen et al found less frequent events forpatients receiving ball attachments (19 cases, 0.6events per year) than for patients receiving a round

Potentially relevantpublications identified from

the online search (n = 3,568)

Potentially relevant full-textarticles retrieved for detailed

evaluation (n = 111)

Publications included basedon the MEDLINE database

search (n = 33)

Publications excluded on thebases of title and abstract

evaluation (n = 3,457)

Publications excluded on thebasis of full-text evaluation

(n = 78)

Publications included basedon the manual search (n = 2)

Publications included in the present systematic review

(n = 35)

Fig 1 Selection process used to identify the included publications.


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T a b l e 1

R a n d o m i z e d C o n t r o l l e d T r i a l s w

i t h E d e n t u l o u s

M a n d i b l e s R e s t o r e d w

i t h V a r i o u s O v e

r d e n t u r e D e s i g n s o n D i f f e r e n t I m p l a n t S y s t e m s : R e s u l

t s a f t e r

5 a n d 1 0 Y e a r s o f O b s e r v a

t i o n

M e a n

M e a n

N o . o f

a g e ,

o b s e r v a t i o n

N o . o f

I m p l a n t

O v e

r d e n t u r e

T y p e o f

S u m

m a r y

S t u d y

Y e a r

p a t i e n t s

y ( r a n g e )

t i m e

i m p l a n t s

s y s t e m

d e s i g n

s t u d y

o f r e s u l t s

N a e r t e t a l 1 0

1 9 9 9

3 6

6 3

. 7 ( 3 6 8

5 )

6 0 m o

7 2

N o b e l B i o c a r e

1 2 D o l d e r b a r

P r o s p e c t i v e

R e t e n t i o n o f d e n t u r

e : b a r > b a l l > m a g n e t

1 2 m a g n e t

r a n d o m i z e d

R e d u c

t i o n o f r e t e n t i o n i n % o f o r i g i n a l v a l u e

s i m i l a r

1 2 b a l l

R C T

C o m p l i c a t i o n s : m

a g n e t > b a l l > b a r

M o r e h y p e r p l a s i a w

i t h b a r

M o r e u l

c e r s w

i t h b a l l

S a t i s f a c t i o n : c o m f o r t w

i t h s t a b i l i t y s i g n i f i c a n t l y r e d u c e d w

i t h m a g n e t

N o r i s k f a c t o r f o r i m p l a n t l o s s

G o t f r e d s e n e t a l 1 1

2 0 0 0

2 6

6 4 ( 5 2 7

8 )

6 0 m o

5 2

A s t r a T e c h

1 1 r o u n

d b a r


C o m p l i c a t i o n s p e r y e

a r p e r p a t i e n t 1

. 0 f o r b a r , 0

. 6 f o r b a l l

1 9 b a l l

r a n d o m i z e d


R C T

M e i j e r e t a l 1 2

2 0 0 4

9 0

5 4

. 0 ( 3 8 7

7 )

6 0 m o

1 8 0

3 0 I M Z

A l l D o l d e r b a r

R a n d o m i z e d


5 6

. 6 ( 3 5 7

9 )

3 0 N o b e l B i o c a r e ( 9 0 )

( e n v e l o p e )

5 2

. 8 ( 3 8 7

4 )

3 0 S t r a u m a n n

R C T

T i m m e r m a n e t a l 1 5

2 0 0 4

1 1 0 / 1 0 3

3 9 8

7

8 . 3

y

2 7 4

S t r a u m a n n

3 6 b a l l

R a n d o m i z e d

S a t i s f a c t i o n w

i t h r e t e n t i o n , s t a b i l i t y d e c r e a s e d w

i t h b a l l

3 7 b a r o n

R C T

N o d i f f e r e n c e i n c h a n g e o f s a t i s f a c t i o n

2 i m p l a n t s

T w o i m p l a n t s w

i t h b a r b e s t s o l u t i o n

3 7 b a r o n

N R

4 i m p l a n t s


2 0 0 0

6 1

5 9 1 1

5 y

1 2 2

2 9 I M Z

6 1 r o u n

d b a r s

C o m p u t e r i z e d

M u l

t i p l e p r o s t h e t i c r e v i

s i o n s

3 2 N o b e l B i o c a r e w

/ A c k e r m a n n

b a l a n c i n g

P r e c i s i o n a t t a c h m e n t s y s t e m

i n t h e o v e r d e n t u r e w

i t h f r e q u e

n t

c l i p s

f r a c t u r e s a n d l o o s e n i n g s

I m p l a n t s u r v i v a

l : I M Z 9 3 % ; N

o b e l B i o c a r e 8 6 %

V i s s e r e t a l 1 6

2 0 0 5

6 0

N R

6 0 m o

1 8 0

I M Z

3 0 t w o i m p l a n t s


T e n d e n c y f o r m o r e p r o s t h e t i c a f t e r c a r e w i t h t w o i m p l a n t s a n d b a r

a n d b a r , 3 0 f o u r

c o m p a r a t i v e

M o r e s o f t t i s s u e c o m p l i c a t i o n s w

i t h f o u r i

m p l a n t s a n d b a r

i m p l a n t s a n d b a r

N o d i f f e r e n c e i n s a t i s f a c t i o n



2 0 0 4

6 1

5 9 1 1

1 2 0 m o

1 2 2

2 9 I M Z

6 1 r o u n

d b a r s

R a n d o m i z e d

V e r y h i g h i n c i d e n c e s o f t e c h n i c a l / p r o s t h e t i c c o m p l i c a t i o n a n d

5 5 1 2

3 2 N o b e l B i o c a r e w

/ A c k e r m a n n

c o m p u t e r - m o d e l f a i l u r e s

c l i p s

R C T

M e a s u r e d b y c l i n i c a l i m p l a n t p e r f o r m a n c e s c o r e : s i m i l a r s c o r e s f o r

t h e t w o s y s t e m s


N a e r t e t a l 1 0

2 0 0 4

3 6

6 3

. 7 ( 3 6 - 8

5 ) 1 2 0 m o

7 2


1 2 D o l d e r b a r


N o m o r e i n f o r m a t i o n o n t e c h n i c a l p r o s t h e t i c c o m p l i c a t i o n s

1 2 m a g n e t

r a n d o m i z e d

c o m p a r e d t o N a e r t e t a l 1 9 9 9

1 2 b a l l

R C T


N R = n o

t r e p o r t e

d ;

R C T = r a n

d o m

i z e

d c o n

t r o

l l e d t r i a l .


Salvi/Brgger


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bar (11 cases, 1.0 events per year). 11 Over 5 years, 48complications/repairs were observed in the ball groupand 53 in the bar group.Mainly during the first year of function, there were statistically significantly morecomplications/repairs in the bar group. However,some of the technical complications were related tothe devices needed for radiographic standardization.

Meijer et al 12 followed overdentures with Dolderbars on three different implant systems (IMZ, NobelBiocare, and Straumann). Over 5 years, there was noeffect on the implants and no information was pre-sented on prosthetic aspects. In an earlier report bythe same group comparing overdentures on IMZ andNobel Biocare implants, multiple prosthetic revisionswere noted. 13

When the same patients were followed over 10years, 14 the 56 surviving overdentures with roundbars and Ackermann clips required 256 prostheticactions, including replacement of broken abutments

and loose clip screws, placement of new bars or goldcylinders and new or fastening clips, relining of max-illary or mandibular dentures, repair of denture basesor teeth, readjustment of occlusion, and provision of new maxillary and mandibular dentureswith noobvious difference between the IMZ and Nobel Bio-care groups.A clinical implant performance scale wasused to score the events.With a mean score of 1.3 forthe IMZ group and 1.2 for the Nobel Biocare group,the clinical outcomes appeared to be similar.

Three types of overdenture designs were com-pared comprehensively using a computerized ran-

dom allocation procedure.15

Thirty-six overdentureswere attached to two ball anchors,37 to a bar on twoimplants, and 37 to a bar on four implants. Generalsatisfaction with phonetics, esthetics, and social func-tioning remained high. The score reflecting satisfac-tion with retention and stability of the overdenturedecreased significantly in the group with two ballattachments.

Comparing 30 overdentures with bars on twoimplants to 30 overdentures with bars on fourimplants, Visser et al 16 found a tendency for morebiological complications with four implants but a

higher need for prosthetic aftercare on two implants(not statistically significant).Six additional studies were found in which over-

dentures with different attachment systems werecompared longitudinally. In these studies, allocationof the groups was not performed using randomiza-tion (Table 2).

Forty-nine patients with maxillary and mandibularoverdentures were followed over 62 months (range12 to 106 months). 17 When patients received over-dentures either on ball anchors or on a round bar, theoverdentures that were not reinforced with a metal

framework were at high risk of fracturing. In the bargroup, 30 of 36 patients required denture repairs. Inthe maxilla, 25% of the originally placed implantswere lost compared to none in the mandible. Theamount of bone anchorage in relation to the leverarm was higher in the lost implants (mean leverarmbone anchorage ratio of 1.3) than in all implantsplaced (a mean lever armbone anchorage ratio of about 1).

Over an observation period of 5 to 15 years (mean9.3 years), 119 patients with implant-supported over-dentures were monitored at regular intervals. 18 Therate of prosthetic maintenance per patient over 5years was similar for the resilient and rigid types of fixation applied. However, the characteristics of thecomplications differed. Whereas resilient attach-ments had more complications with retainers, moredenture base resin fractures, mucosal hyperplasia,and denture relines, the rigid support attachments

had more fractures of bar extensions and neededretightening of female parts. It was obvious that rigidfixation was an advantage, since less time wasrequired for services.The time to the first change of acomponent was not significantly different forresilient versus rigid attachments.

The amount of aftercare in patients with overden-tures was assessed cumulatively up to 8 years byNedir et al. 19 The percentage of overdentures remain-ing free from complications was 57% for the bardevices but only 24% for overdentures with ballanchors ( P < .04); 1.5 events per year were noted in

the ball attachment group, whereas 0.9 events peryear per patient occurred in the bar group.Anatomical, morphologic, and prosthetic variables

are considered to be of importance when selecting aparticular implant position. Oetterli et al 20 evaluatedthe casts and clinical parameters of 90 edentulouspatients, each one with two intraforaminal implantssupporting an overdenture. The angle between thevirtual axis connecting both implants and the man-dibular hinge axis was measured on mounted casts. The suppor ting surface was identified between bentclip bars and U-shaped extension bars. Seventy

patients could be evaluated clinically after 5 years. The positions and retention mechanism of mandibu-lar implants supporting an overdenture had littleinfluence on the clinical parameters assessed. Nodata related to technical/mechanical complicationswere reported.

The long-term function (10-year life table) of over-dentures was compared to the clinical outcome withfull-arch fixed prostheses in a study including 233patients receiving 163 overdentures and 95 fixed full-arch prostheses. 21 The survival rates for overdentureson Dolder bars were 87.5% for the maxilla and 97.7%


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for the mandible. Survival of full-arch prosthses was96.4% in the maxilla and 100% in the mandible.Over-dentures on milled bars had a 94.7% survival rate inthe maxilla, and overdentures on ball anchors in themandible had a 98.8% survival rate.

One study reported a dramatic incidence of implant loss (27% over 4 to 6 years), remakes of over-dentures (50%), and relinings (30%). 22 Handling suchfrequent catastrophic events would be highlyimpracticable in daily clinical practice.

Fixed Dental Prostheses (FDP) with CantileverExtension(s) (Table 3)In four papers, the presence of a cantilever extensionas a potential risk for technical/mechanical complica-tions was assessed. In the oldest report, dramaticallyhigher failure rates with cantilever extensions > 15 mmwere noted. 23 In 25 patients, 24 edentulous mandiblesand four edentulous maxillae were restored with full-

arch fixed bilateral cantilever prostheses on five to siximplants. The prostheses were grouped into thosewith a cantilever length of > 15 mm and those with 15 mm (range 5 to 22 mm). The prostheses werefollowed from 20 to 80 months. Of the 28 prostheses,12 had to be remade.Practically all of those were orig-inally designed with cantilever extensions > 15 mm.

Comparing 24 FDPs with cantilever extensions to26 FDPs without cantilever extensions over 5 years in45 consecutive patients, Wennstrm et al 24 did notfind any negative effect on the peri-implant condi-tions. The six technical complications noted were not

related to the cantilever extensions.Romeo et al 25 collected clinical and radiographicdata from 42 FDPs with a cantilever extension and 137FDPs without a cantilever extension. The cumulativesurvival rates of the implants reached 94.4% with therisk cantilever extension and 96.5% without the risk cantilever extension, as assessed in a 7-year life tableanalysis.Radiographic success was defined as absenceof bone loss > 1 mm during the first year of loadingand 0.2 mm/year thereafter. Clinical success, definedas absence of probing pocket depths > 3 mm, wasobserved in 76.3% of cases with cantilever extensions

and in 73.8% of cases without cantilever extensions.Nedir et al 19 presented data on consecutivepatients treated with implant-supported removableor fixed prostheses and single crowns on implants.Seventeen of the fixed reconstructions had a can-tilever extension and 228 did not. Up to 8 years fol-low-up, the authors found technical complications inabout 30% of the reconstructions with cantileverextensions but in only 8% of the reconstructionswithout cantilever extensions.

Romeo et al 26 collected radiographic and clinicalinformation on fixed dental prostheses in 49 partially

edentulous patients. Fifteen of the FDPs had a distalcantilever extension and 34 a mesial cantileverextension. After a mean follow-up of 4 years, no neg-ative effects related to the presence of the mesial orthe distal cantilever extension were found.

Cemented Versus Screw-Retained Dental

Prostheses (Table 4)In a prospective randomized study, 12 cemented and12 screw-retained crowns were constructed onimplants to replace missing lateral incisors. 27 Fouryears after loading, no differences in peri-implantconditions and no prosthetic complications werenoted.

In two other reports, similar rates of complicationswere noted over 5 years with cemented and screw-retained crowns and FDPs. 19,28 It should be noted,however, that the group with cemented reconstruc-tions was considerably larger in both studies. The

screw-retained reconstructions in the study by DeBoever et al 29 demonstrated twice as many complica-tions as the cemented ones: 29/127 cemented (22.8%)and 26/45 screw-retained (57%) reconstructionsdemonstrated technical/mechanical complications(P < .001). In 21 of the 26 interventions, however, onlyretightening was required.

Angled/Angulated Abutments (Table 5) Two studies focusing on the potentially negativeinfluence of nonparallel implants requiring the place-ment of angled abutments were found.In a report by

Sethi et al,30

misangulations ranged from 0 to 45degrees. Of 3,101 implants, 264 implants with anabutment angulation of > 15 degrees were com-pared to 352 implants with a more axial abutment ( 15 degrees). Over 10 years, the angulation had noeffect on the probability of survival of the implants.However, no information on mechanical/technicalcomplications was available.

A more sophisticated method of analyzing angleswas presented by Koutouzis and Wennstrm in2007. 31 Standardized photographs were taken of themaxillary and mandibular study casts in occlusion

and then with guide pins in place. Thus, within thesuperimposed image, the inclination of the implantsin relation to the occlusal plane was obtained. Finally,interimplant inclinations in both mesiodistal andbuccolingual directions were obtained. Axialimplants were defined as ranging from 0 to 4degrees and nonaxial implants from 12 to 30degrees. The 36 axial and 33 nonaxial implantsyielded similar bone remodeling over 5 years, asassessed in radiographs. Moreover, there was noincreased risk of mechanical/technical complicationsassociated with tilted implants. 31


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T a b l e 3

E x t

e n s i o n

M e a n

M e a n

N o . o f

a g e , y


N o . o f

I m p l a n t

D e s i g n s o f

S t u d y

S t u d y

Y e a r

p a t i e n t s ( r a n g e )

t i m e

i m p l a n t s

s y s t e m

r e c o n s t r u c

t i o n

d e s i g n

F i n d i n g s

W e n n s t r m

e t a l 2 4

2 0 0 4

4 5

5 7 1 0

. 3

5 y

1 3 0

A s t r a T e c h

2 4 F D P s w

i t h e x t e n s i o n

C o n s e c u t i v e

6 c o m p l i c a t i o n s i n 5 y

n o t r e l a t e d t o p r e s e n c e o f e x t e n s i o n

6 2 8

. 5

2 6 F D P s w

i t h o u t e x t

e n s i o n

p a t i e n t s

N o i n f l u e n c e o n p e r i - i m p l a n t c o n d i t i o n

m o

S h o r t F D P s

S h a c k l e t o n e t a l 2 3

1 9 9 4

2 5

N R

2 0 8

0 m o

N R


2 8 f u l l - a r c h p r o s t h e s e s

5 - y

s u r v i v a

l

L e n g t h > 1

. 5 c m

d r a m a t i c a l l y m o r e f r a c t u r

e s

w i t h e x t e n s i o n s

1 2 / 2 8 r e m a k e s

1 . 5

c m a

n d > 1

. 5 c m

N o i n f l u e n c e o n i m p l a n t l o s s

R o m e o e t a l 2 5

2 0 0 4

N R

N R

4 y

a f t e r

3 7 9

S t r a u m

a n n

4 2 F D P w

i t h e x t e n s i o n s

3 . 8

y s u r v i v a

l


l F P w

i t h e x t e n s i o n s ( 9 4

. 4 % )

l o a d i n g

1 3 7 F D P w

i t h o u t e x t e n s i o n s


l F P w

i t h o u t e x t

e n s i o n s

( 9 6

. 1 % )

N e d i r e t a l 1 9

2 0 0 6

N R

N R

8 - y

l i f e t a b l e

N R

S t r a u m

a n n

1 7 w

i t h e x t e n s i o n s


2 9

. 4 % c o m p l i c a t i o n s v e

r s u s

7 . 9 %

2 2 8 w

i t h o u t e x t e n s i o n s

P

2 . 0

B l a n e s e t a l 3 5

2 0 0 7

8 3

N R

6 ( 5 1

0 ) y

1 9 2

S t r a u m a n n

8 : 0 0 . 9

9


N o i n f l u e n c e o n b o n e l o s s

1 3 3 : 1 1 . 9

9

p a t i e n t s


5 1 :

2

N R = n o

t r e c o r d e

d ;

C : I = c r o w n - t o - i m p

l a n t r a

t i o ;

F D P =

f i x e

d d e n

t a l p r o s t

h e s i s .

T a b l e 8

L e n g t h o f R e c o n s t r u c t i o n

M e a n

N o . o f

M e a n a g e ,


N o . o f

I m p l a n t

S t u d y

Y e a r

p a t i e n t s

y ( r a n g e )

t i m e ( r a n g e )

i m p l a n t s

s y s t e m

T y p e o f s t u d y

D e s i g n o f r e c o n s t r u c

t i o n

F i n d i n g s

D e B o e v e

r e t a l 2 9

2 0 0 6

1 0 5

2 5 8

6

6 2

. 5 2 5

. 3

2 8 3

S t r a u m a n n

C o n s e c u t i v e p a t i e n t s

8 0 S C

2 5 % o f S C h a d c o m p l i c a t i o n s

m o

3 9 t w o c o n n e c t e d c r o w n s

3 5 % o f t w o c o n n e c t e d c r o w n s h a d

3 8 3 - t

o 4 - u

n i t F D P

c o m p l i c a t i o n s

4 4 % o f 3 - t

o 4 - u n i t F D P h a d c o m p l i c a t i o n s

,

P 1 /2 of the implantlength.

Pooling wide ranges of biological and technicalcomplications in the same category may mask clini-cally important differences between groups. 43

In 2006, Nedir et al grouped prosthetic complica-tions of overdentures into foreseeable and nonfore-seeable events. 19 Change of female parts of thespherical attachment, change of the clip, and relining

were categorized as foreseeable. Mechanical reten-tion problems, repair and replacement of the over-denture, and complications of the opposing completedenture were unforeseeable complications in theoverdenture group. For the fixed restoration group,complications were graded as minor or major. A frac-ture was considered major if it affected esthetics,caused the metal framework to be visible, resulted ina missing interproximal contact point, or caused thepatient to complain of tongue- or masticatory-relateddiscomfort. Major fractures resulted in a prosthesisremake;minor fractures did not lead to remakes.

In a series of systematic reviews on complicationand failure rates reported with various types of reconstructions on teeth and implants, the extracteddata were listed as the estimated event rates per 100reconstructions per year, considering the actualexposure time and assuming no change in the long-term risk intensity. 6 Statistically significantlyincreased failures rates were calculated for cantileverFDPs on teeth and tooth-implantsupported FDPscompared to FDPs on teeth without extension,implant-supported FDPs, and single crowns onimplants over 10 years. In addition,statistically signifi- T

a b l e 1 1

C o m p l i c a t i o n s L e a d i n g t o F a i l u r e s

M e a n

N o . o f

M e a n a g e ,


N o . o f

I m p l a n t

D e s i g n o f r e c o n s t r u c

t i o n /

S t u d y

Y e a r

p a t i e n t s

y ( r a n g e )

t i m e ( r a n g e ) i m p l a n t s

s y s t e m

m a t e r i a l s u s

e d

T y p e o f s t u d y

F i n d i n g s

P a r e i n e t a l 4 3

1 9 9 7

1 5 2

5 5

. 7 ( 1 4 9

0 )

4 . 2

y

3 9 2

B r n e m a r k

5 6 S C o n i m p l a n t s


O f 3 0 f a i l u r e s w

i t h r e c o n s t r u c

t i o n s

,

1 6 8 F D P o n i m p l a n t s

1 5 h a d m a j o r s o - c a l l e d r e t r i e v a

b l e

c o m p l i c a t i o n s b e f o r e

O d d s r a t i o 3

. 5 5 ; P

< . 0

0 1

B r g g e r e t a l 4 4

2 0 0 5

8 9

5 8

. 9 ( 2 8 8

8 )

1 0

1 6 0

S t r a u m a n n

6 9 S C o n i m p l a n t s


L o s s o f r e t e n t i o n l e a d i n g t o t e c h n i c a l

( 8 1

2 ) y

( 2 4

3 3 F P D s I - I

f a i l u r e ; O

d d s r a t i o 1 7

. 6 ( 3

. 6 8

6 . 4

) ;

t e e t h )

2 2 F P D s I - T

P 15 degrees for the abutments and theprosthesis had any effect on the outcome. Thepatient risk factor bruxism resulted in significantlyincreased event rates in two studies, in trends forhigher rates in two studies, and in no difference in

one report.From a retrospectively assessed cohort of 368

patients with 838 endosseous implants, 19 caseswere selected in which there were technical/mechanical complications such as implant fractures,abutment fractures, screw loosening, occlusal wear,or damage to the prosthesis. 46 The 19 patients wereevaluated for sleep bruxism using polysomnographicanalysis. Most of the bruxism episodes occurred dur-ing light sleep and did not cause arousal, and thepatients were unaware of the nocturnal parafunc-tional habits. Bruxism was reported to have contin-

ued despite the fact that all these patients wereprovided with a nightguard.Crown-to-root ratio, material aspects, and the

number of implants placed were not identified as risk factors for increased failure/complication rates. Thecomplexity of a reconstruction, expressed as thenumber of units, was identified as a risk in only onestudy, and having had a previous complication wasidentified as a risk in two.

The implant length in relation to the height of thesuprastructure as well as the number of implantsneeded to physically support an FDP and assure its

function are risk factors related to the quality andquantity of the osseointegration and the torqueneeded to disrupt the chemical and histologicbonding between the supporting bone and theimplant surface.

Efforts to improve osseointegration in implantdentistry by modifying the surface characteristics,such as the topography and chemistry, have led tomuch more reliable clinical results compared to theoriginal machined implants when using shorter andfewer implants. 47,48

Limitations/Critical Remark The fact that some of the mechanical/technical char-acteristics evaluated were not identified as true risk factors in this review does not mean that they arenot, in fact, risks.Limitations of the study designs, toomany uncontrollable variables, small number of sub- jects, etc,may have hidden the actual facts in some of the studies.


16/17

CONCLUSIONS

Mandibular overdentures: Independent of theretentive element system used, patients requiredmultiple prosthetic services during the observationperiod (six RCTs). Technical/mechanical complica-tions occurred more frequently with a ball attach-ment than with a bar retentive system (one RCT).With respect to retention,patients were most satis-fied with a bar retentive system, followed by ballanchors, and least satisfied with magnets (oneRCT). Metal frameworks protected overdenturesfrom fractures (one consecutive case study).

The presence of cantilever extensions was notassociated with increased mechanical/technicalrisks for implants supporting short-span FDPs(three consecutive case studies).

The presence of cantilever extensions > 15 mm wasassociated with an increased risk of full-arch FDP

fracture compared with the presence of cantileverextensions 15 mm (one consecutive case study).

No increased mechanical/technical risks for FDPswere observed in three of four studies (oneprospective, one retrospective, and one consecu-tive case study) comparing screw-retained versuscemented reconstructions.

The presence of angled/angulated abutments wasnot associated with increased mechanical/techni-cal risks for implant-supported FDPs (one consec-utive case study).

Increased mechanical/technical risks for FDPs

were observed in bruxers in four of five studies(two retrospective and two consecutive case stud-ies) comparing bruxers and nonbruxers.

The crown-to-implant ratio was not associated withimplant loss and marginal bone loss of implantssupporting FDPs (2 consecutive case studies).

Increased mechanical/technical risks for FDPswere observed in 1 study (consecutive cases) com-paring 3- to 4-unit FDPs with single crowns anddouble crowns.

Increased mechanical/technical risks for FDPswere observed in two studies (consecutive case

studies) comparing FDPs with and without a his-tory of complications. Regarding the survival/success rate of the implant,

none of the 10 listed mechanical/technical riskshad an influence.

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