Q U I N T E S S E N C E I N T E R N AT I O N A L
PROSTHODONTICS
Michael Korsch
Retrospective analysis of loosening of cement-retained vs screw-retained fixed implant-supported reconstructions Michael Korsch, DDS1/Winfried Walther, DDS2 Objective: The cementation of fixed dental prostheses (FDPs) on implants involves the risk of undetected excess cement. If a zinc oxide–eugenol cement (ZEC) is used as the luting material, this risk appears to be lower, as the excess cement will dissolve in the peri-implant sulcus. However, using a ZEC on a general basis conflicts with the manufacturers’ classification of a ZEC as a temporary luting material. To evaluate the clinical safety of ZECs, the present study investigated whether more ZECretained reconstructions than screw-retained reconstructions loosen over time. Method and Materials: In a retrospective observational study, the frequency of FDP loosening was investigated. For this purpose, data from patients who had been fitted with FDPs on two or more than two posterior implants were investigated. The study compared screw-retained (n = 59) vs cement-retained (n = 40) FDPs on implants over an observation period of 3.5 years after reconstruction incorpora-
tion. All cement-retained FDPs had been cemented with a temporary ZEC. Results: The prevalence of reconstruction loosening was significantly lower for cement-retained FDPs when a ZEC (10%) was used than it was for screw-retained FDPs (29%); four screw-retained FDPs and one cementretained FDP developed major complications. The survival rate of the reconstructions within the observation period was 97% for screw-retained FDPs and 100% for cement-retained FDPs (not significant). Conclusion: The prevalence of cementretained FDP loosening was significantly lower than that of screw-retained FDPs. Cementing FDPs on implants using a temporary cement does not necessarily lead to a higher number of loosened reconstructions. Permanent cementation with ZEC appears to be justified. (Quintessence Int 2015;46:583–589; doi: 10.3290/j.qi.a34077)
Key words: cement-retained, fixed dental prostheses, loosening, screw-retained, TempBond
Fixed dental prostheses (FDPs) on implants can be retained with either screws or cement. Many publications have compared these two retention methods.1-4 Compared with cemented dental prostheses, screw1
Head of Oral Surgery, Dental Academy for Continuing Professional Development, Karlsruhe, Germany; and Clinic of Operative Dentistry, Periodontology and Preventive Dentistry, University Hospital, Saarland University, Homburg, Germany.
2
Professor, Director, Dental Academy for Continuing Professional Development, Karlsruhe, Germany.
Correspondence: Dr Michael Korsch, Dental Academy for Continuing Professional Development, Lorenzstrasse 7, 76135 Karlsruhe, Germany. Email: [email protected]
VOLUME 46 • NUMBER 7 • JULY/AUGUST 2015
retained prostheses have a better marginal fit,5,6 and make it easier to remove the suprastructure. The disadvantages of screw retention are inferior primary retention, limited esthetics,7 and the risk of screw loosening at the level of the abutment.8 As the laboratory costs are higher for screw-retained reconstructions, they are more expensive to fabricate.7,8 The survival rates of screw-retained and cement-retained FDPs seem to essentially be the same.2,9 The frequency of suprastructure loosening in the case of screw-retained and cemented FDPs has been
583
Q U I N T E S S E N C E I N T E R N AT I O N A L Korsch/Walther
a Figs 1a and 1b
b Prefabricated abutments.
investigated in several studies, with contradictory results.1,8,9 Both temporary and permanent cements are offered for the cementation of implant-supported restorations. These cements mainly differ based on their retentiveness.10,11 Therefore, temporary cements offer the benefit of easy removal of the suprastructure. TempBond (Kerr), as one of the zinc oxide–eugenol cements (ZECs), is classified as a temporary cement, and in scientific studies it demonstrates significantly lower retentiveness than permanent cements.10,12 Excess cement left in the peri-implant sulcus after cementation favors the formation of a biofilm,13,14 which increases the risk of cement-induced peri-mucositis and peri-implantitis.15-18 The cementation of suprastructures with TempBond also seems to lead to excess cement.19,20 However, there are indications that ZECs dissolve in contact with fluid21,22 so that excess cement will not remain in the peri-implant sulcus for any length of time. The material properties of TempBond appear to make this material the ideal luting agent for the cementation of FDPs on implants. Nevertheless, its classification as a temporary cement limits this indication. The present retrospective study was conducted to investigate whether more FDP loosening occurs compared to screw retention when TempBond is used. Moreover, the intention was to clarify whether permanent cementation with TempBond is justifiable.
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c Fig 1c Screw-retained FDP with two implants on prefabricated abutments.
a
b
Fig 2a Prefabricated customized abutments.
Fig 2b Cement-retained FDP with two implants on prefabricated customized abutments.
METHOD AND MATERIALS In a retrospective observational study, the frequency of FDP loosening was investigated. For this purpose, data from patients who had been fitted with FDPs on two or more than two posterior implants were investigated. A total of 89 patients with 204 Astra Tech implants (Astra Tech Dental) that were prosthetically restored in the clinic of the Karlsruhe Dental Academy for Continuing Professional Development in the period from January 2006 to September 2010 with implant-supported FDPs in the posterior region were followed up. Between January 2006 and December 2008, the FDPs were screwed onto prefabricated abutments (Fig 1). From December 2008, all FDPs were cemented (Fig 2).
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Table 1
Sex, age, number of implants per patient and in relation to the type of FDP (at patient level)
Descriptor
Patients with screw-retained FDPs
Male
36
Patients with cement-retained FDPs 19
Female
16
18
Total
52
37
Mean age at time of prosthetic reconstruction (years)
63.5
65.4
2.3
2.3
Mean number of implants per patient
Table 2
Screw- vs cement-retained FDPs (at reconstruction level)
Descriptor
Screw-retained FDPs
Cement-retained FDPs
FDPs with 2 implants
57
36
2
4
59
40
FDPs with more than two implants Total
The reasons for changing the method of retention were the limited esthetics and higher laboratory costs of screw-retained vs cemented FDPs on implants. All FDPs (screw-retained and cemented) in the study period had a metal framework veneered with ceramic material. TempBond was the luting agent used for the cemented FDPs. In the treatment data analysis, loosening of the implant-supported restoration (screw loosening or decementation) over a period of 3.5 years after insertion was investigated. The data were compiled based on the patients’ medical records. In addition, all of the patients were asked over the telephone whether any loosening that was not treated by this clinic but by an external dentist had occurred after reconstruction insertion. Loosening after the period of 3.5 years was not evaluated.
Inclusion and exclusion criteria Patients met the inclusion criteria if they had undergone fixed prosthodontic therapy with Astra Tech implants in the posterior region between January 2006 and September 2010. Implant-supported restorations in the anterior region were excluded. FDPs with two or more implants were included, and single-tooth crowns on implants were excluded. Other requirements for inclusion were complete documentation of all technical
VOLUME 46 • NUMBER 7 • JULY/AUGUST 2015
implant characteristics (implant system and location) and continuous treatment by the clinic (at least once per year) since placement of the restoration. Patients with incomplete documentation or patients who could not be contacted by telephone were excluded.
Patients Over the evaluation period, 93 patients were treated; four patients were excluded because of incomplete documentation. Thus, 89 patients who met the inclusion criteria were evaluated, representing 96% of the originally treated patient population. Between March and April 2014, the included patients were interviewed over the telephone and asked whether they had undergone other therapies in addition to the documented renewed denture fixation. The 89 patients were divided into two groups depending on the type of denture retention. The groups were further subdivided based on FDPs with two implants or more than two implants (Tables 1 and 2).
Evaluation of the reconstruction level For the analysis of the reconstruction level, every implant was weighted inversely to the total number of implants per reconstruction.
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Table 3
Loosening of the reconstruction in relation to the type of FDP (at reconstruction level)
Descriptor
Screw-retained FDPs
Cement-retained FDPs
Statistical test
Loosening within 3.5 years after prosthetic reconstruction
17 (29%)
4 (10%)
χ2 = 4.622; P < .032
Average time of onset of loosening after prosthetic reconstruction (years)
1.6
1.4
NS
FDPs with two implants
17 (30%)
3 (8%)
χ2 = 4.241; P < .039
1 (25%)
NA
FDPs with more than two implants
0 (0%)
NA, not applicable; NS, not significant.
Table 4
Further loosening of the reconstruction in relation to the type of FDP (at reconstruction level)
Descriptor
Screw-retained FDPs
Cement-retained FDPs
Statistical test
FDPs with two implants loosening twice
5 (9%)
1 (3%)
NS
FDPs with two implants loosening three times
2 (4%)
0 (0%)
NA
NA, not applicable; NS, not significant.
Statistical method Data were compiled in Excel and analyzed with IBM SPSS Statistics 21 on Windows XP (Microsoft). The statistical methods included cross-tabulations with chisquared analysis for categorical data. The means were compared by t tests.
RESULTS The evaluation of the telephone interviews showed that seven patients had undergone treatment outside the clinic during the observation period, although these treatments included emergency measures only. All cases of reconstruction loosening were treated in the clinic.
FDP loosening based on reconstruction level Within the first 3.5 years after prosthetic restoration, screw-retained FDPs loosened significantly more often than cemented FDPs (screw-retained FDPs, 17 [29%]; cemented FDPs, 4 [10%]; χ2 = 4.622; P < .032) (Table 3). On average, screw-retained restorations loosened after 1.7 years, whereas cement-retained restorations loosened after 1.4 years. In the subgroups of FDPs with two implants, the difference was also significant (screwretained, 17 [30%]; cemented, 3 [8%]; χ2 = 4.241; P < .039). In the subgroup of screw-retained FDPs with more than two implants, loosening did not occur at all,
586
and one (25%) of the cement-retained FDPs loosened. Given the low number of cases, no statistical evaluation was performed for this subgroup. Bivariate analysis showed significant association between loosening of reconstructions and type of FDP. In a multivariate logistic regression the effect of type of FDP was independent of age of patient and sex. There were no significant associations with patient sex and age of patient and loosening of reconstructions. Within the observation period of 3.5 years, six FDPs with two implants loosened twice (Table 4) (screwretained FDPs, 5 [9%] loosenings; cemented FDPs, 1 [3%]). None of the FDPs with more than two implants loosened more than once, and two (4%) screw-retained FDPs with two implants loosened three times, but none of the cemented FDPs showed further loosening. No further loosening occurred for screw-retained FDPs. Major complications (Fig 3) developed in four (7%) screw-retained FDPs with two implants (three abutment fractures, one implant fracture). In two cases of abutment fracture, the prefabricated abutment was replaced, and the reconstruction was saved. Only one cemented FDP with two implants (1%) developed a major complication (screw fracture). The screw was replaced, and the suprastructure was saved. Neither the cemented nor the screw-retained FDPs with more than two implants developed any major complications. The
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Q U I N T E S S E N C E I N T E R N AT I O N A L Korsch/Walther
a Fig 3a
b Prefabricated abutment fracture.
Table 5
Fig 3b
Implant fracture with prefabricated abutment.
Survival rates of FDPs
Descriptor
Screw-retained FDPs
Cement-retained FDPs
Statistical test
Survival rate of FDPs with two implants
55 (96%)
36 (100%)
NS
4 (100%)
NS
Survival rate of FDPs with more than two implants
2 (100%)
NS, not significant.
survival rate (Table 5) was 97% for the screw-retained (two implants, 96%; more than two implants, 100%) and 100% for the cemented restorations (two implants, 100%; more than two implants, 100%).
DISCUSSION In addition to screw-retention, cementation is a frequently used method for retaining fixed restorations on implants. Both methods pose a risk of reconstruction loosening after incorporation of the dental restoration.1,2,23 The retrospective follow-up examination presented here compared the frequency of loosening of implant-supported screw-retained FDPs vs cemented FDPs. A total of 89 patients with 99 reconstructions on 204 implants were followed up over a period of 3.5 years after insertion of the reconstruction. Over this period, the number of screw-retained FDPs that loosened was almost three times the number of loosened cement-retained FDPs (29.3% vs 10%, respectively). This difference was significant. Nissan et al1 noted a similarly significant prevalence of loosened restorations on prefabricated abutments over an average observa-
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tion period of 5.5 years. In addition, in the study of Nissan et al,1 ZEC was also used for the cementation of the FDPs and the screws were also inserted from the occlusal on prefabricated abutments. For cemented FDPs only one screw is needed for the fixation of the abutment on the implant, whereas screw-retained FDPs require two screws to fix the suprastructure. In the case of cemented FDPs this reduces the possibility of preloaded stress and screw loosening,8 and presumably explains the difference in the prevalence of reconstruction loosening in the present study. One advantage of the present study was that exactly identical types of restorations (fixed FDPs with two or three abutments) were compared with one another. The two types of restorations only differed in terms of fixation (screw-retention vs cementation). Moreover, only FDPs placed on Astra Tech implants in the posterior region were selected. Based on these criteria of inclusion and exclusion, any unwanted effect of the type of restoration, implant region, or implant system on the result could be avoided. A weakness of the study was that the different types of fixation were not
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applied at the same time but one after the other. This may have influenced the results. In addition, only one type of fixation was applied per patient. In a prospective study, Nissan et al1 used a split-mouth design and could thus make sure that in all patients both types of fixation were applied at the same time. As already mentioned, the results were similar to those presented herein. In dentistry, it is general practice to differentiate between temporary and permanent cements. This classification is also made in the manufacturers’ product descriptions and refers to the cementation of toothsupported dental restorations. In this clinical application, it is not only necessary to produce a secure hold of the restoration but also to counteract crown margin caries; however, implant-supported dental prostheses differ. The differentiation between permanent and temporary cement applied to the natural tooth cannot be transferred to this type of reconstruction. Many studies that compare the retentiveness of temporary versus permanent cements are in vitro studies.10,12 They do not prove any clinical relevance regarding retentiveness to the frequency of reconstruction loosening. A lower degree of retentiveness makes it easier to remove the suprastructure and is therefore of benefit from this particular point of view;22 thus, access to the implants can be gained without any major risk in cases of periimplant treatment. Compared with screw-retained FDPs, cementretained FDPs on implants may lead to undetected excess cement in the peri-implant sulcus.16 In the current literature, it has been repeatedly shown that excess cement affects the peri-implant tissue.16,17 This excess favors peri-implant inflammation15 and may cause bone loss or even implant failure.18,24 A ZEC was used in the present study. Presumably, excess cement is also present when ZEC is used, but apparently it dissolves in contact with the sulcular fluid in the periimplant tissue. In vitro studies have shown that ZECs demonstrate signs of dissolution after a short time in contact with artificial saliva.25 In the present study, the survival rate of reconstructions within the observation period of 3.5 years was more than 96% in all subgroups.
588
The 5-year survival rate reported in the literature for both screw-retained and cemented FDPs is approximately 95%.23,26,27 Whereas serious biologic complications are more likely to develop in connection with cemented FDPs, screw-retained FDPs are mainly causing technical problems.23 Technical complications, such as reconstruction loosening and major complications, also predominated with screw-retained FDPs in the present study. With regard to peri-implant bone loss, however, the results in the literature are contradictory when screw-retained and cemented FDPs are compared.1,23 A closer examination of these studies shows that different cements were used. It cannot be excluded that the type of cement used has a greater effect on the peri-implant bone than the method of retention (screw-retention vs cementation). For some years an increasing number of luting cements containing methacrylate have been used. In a clinical observational study it could be shown that implant-supported restorations cemented with ZEC developed significantly less peri-implant inflammation and bone loss than those cemented with a methacrylate cement.22 The present study could demonstrate that using a temporary ZEC does not cause more reconstruction loosening than screw-retention of FDPs. In view of the fact that ZEC obviously leads to less peri-implant inflammation than methacrylate-based cements it appears to make sense to consider using ZEC for permanent cementation.
CONCLUSION The use of a temporary ZEC does not necessarily lead to an increase in denture loosening based on comparisons between cement-retained dental prostheses and screw-retained dental prostheses. Provided that an appropriate cement is used, revision treatment of the prosthesis is an easier technique. In addition, the problem of excess cement remaining in the sulcus is counteracted. The use of ZECs for the permanent cementation of FDPs on implants therefore appears to be a responsible treatment option.
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REFERENCES 1. Nissan J, Narobai D, Gross O, Ghelfan O, Chaushu G. Long-term outcome of cemented versus screw-retained implant-supported partial restorations. Int J Oral Maxillofac Implants 2011;26:1102–1107. 2. Wittneben JG, Millen C, Bragger U. Clinical performance of screw- versus cement-retained fixed implant-supported reconstructions: a systematic review. Int J Oral Maxillofac Implants 2014;29(Suppl):84–98. 3. Gotfredsen K, Wiskott A, Working G. Consensus report - reconstructions on implants. The Third EAO Consensus Conference 2012. Clin Oral Implants Res 2012;23(Suppl 6):238–241. 4. Clelland NL, Yilmaz B, Seidt JD. Three-dimensional image correlation analyses for strains generated by cement and screw-retained implant prostheses. Clin Implant Dent Relat Res 2013;15:271–282. 5. Keith SE, Miller BH, Woody RD, Higginbottom FL. Marginal discrepancy of screw-retained and cemented metal-ceramic crowns on implants abutments. Int J Oral Maxillofac Implants 1999;14:369–378. 6. Guichet DL, Caputo AA, Choi H, Sorensen JA. Passivity of fit and marginal opening in screw- or cement-retained implant fixed partial denture designs. Int J Oral Maxillofac Implants 2000;15:239–246. 7. Lee A, Okayasu K, Wang HL. Screw- versus cement-retained implant restorations: current concepts. Implant Dent 2010;19:8–15. 8. Michalakis KX, Hirayama H, Garefis PD. Cement-retained versus screwretained implant restorations: a critical review. Int J Oral Maxillofac Implants 2003;18:719–728. 9. Sherif S, Susarla HK, Kapos T, Munoz D, Chang BM, Wright RF. A systematic review of screw- versus cement-retained implant-supported fixed restorations. J Prosthodont 2014;23:1–9. 10. Garg P, Gupta G, Prithviraj DR, Pujari M. Retentiveness of various luting agents used with implant-supported prostheses: a preliminary in vitro study. Int J Prosthodont 2013;26:82–84. 11. Covey DA, Kent DK, St Germain HA Jr, Koka S. Effects of abutment size and luting cement type on the uniaxial retention force of implant-supported crowns. J Prosthet Dent 2000;83:344–348. 12. Nejatidanesh F, Savabi O, Ebrahimi M, Savabi G. Retentiveness of implantsupported metal copings using different luting agents. Dent Res J (Isfahan) 2012;9:13–18. 13. Busscher HJ, Rinastiti M, Siswomihardjo W, van der Mei HC. Biofilm formation on dental restorative and implant materials. J Dent Res 2010;89:657–665. 14. Obst U, Marten SM, Niessner C, Hartwig E, Korsch M, Walther W. Diversity of patients microflora on orthopaedic and dental implants. Int J Artif Organs 2012;35:727–734.
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15. Korsch M, Robra BP, Walther W. Predictors of excess cement and tissue response to fixed implant-supported dentures after cementation. Clin Implant Dent Relat Res 2015;17(Suppl 1):e45–e53. 16. Wilson TG Jr. The positive relationship between excess cement and periimplant disease: a prospective clinical endoscopic study. J Periodontol 2009;80:1388–1392. 17. Korsch M, Obst U, Walther W. Cement-associated peri-implantitis: a retrospective clinical observational study of fixed implant-supported restorations using a methacrylate cement. Clin Oral Implants Res 2014;25:797–802. 18. Callan DP, Cobb CM. Excess cement and peri-implant disease. JIACD 2009;1:61–68. 19. Wadhwani C, Hess T, Pineyro A, Chung KH. Effects of abutment and screw access channel modification on dislodgement of cement-retained implantsupported restorations. Int J Prosthodont 2013;26:54–56. 20. Wadhwani C, Pineyro A, Hess T, Zhang H, Chung KH. Effect of implant abutment modification on the extrusion of excess cement at the crown-abutment margin for cement-retained implant restorations. Int J Oral Maxillofac Implants 2011;26:1241–1246. 21. Yanikoglu N, Yesil Duymus Z. Evaluation of the solubility of dental cements in artificial saliva of different pH values. Dent Mater J 2007;26:62–67. 22. Korsch M, Robra BP, Walther W. Peri-implantitis associated with type of cement: A retrospective analyze of different types of cement and their clinical correlation to the peri-implant tissue [epub ahead of print 2 Sep 2014]. Clin Implant Dent Relat Res doi: 10.1111/cid.12265. 23. Sailer I, Muhlemann S, Zwahlen M, Hammerle CH, Schneider D. Cemented and screw-retained implant reconstructions: a systematic review of the survival and complication rates. Clin Oral Implants Res 2012;23(Suppl 6):163– 201. 24. Gapski R, Neugeboren N, Pomeranz AZ, Reissner MW. Endosseous implant failure influenced by crown cementation: a clinical case report. Int J Oral Maxillofac Implants 2008;23:943–946. 25. Yanikoglu N, Yesil Duymus Z. Evaluation of the solubility of dental cements in artificial saliva of different pH values. Dent Mater J 2007;26:62–67. 26. Buser D, Janner SF, Wittneben JG, Bragger U, Ramseier CA, Salvi GE. 10-year survival and success rates of 511 titanium implants with a sandblasted and acid-etched surface: a retrospective study in 303 partially edentulous patients. Clin Implant Dent Relat Res 2012;14:839–851. 27. Sherif S, Susarla SM, Hwang JW, Weber HP, Wright RF. Clinician- and patientreported long-term evaluation of screw- and cement-retained implant restorations: a 5-year prospective study. Clin Oral Investig 2011;15:993–999.
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PROSTHODONTICS
Michael Korsch
Retrospective analysis of loosening of cement-retained vs screw-retained fixed implant-supported reconstructions Michael Korsch, DDS1/Winfried Walther, DDS2 Objective: The cementation of fixed dental prostheses (FDPs) on implants involves the risk of undetected excess cement. If a zinc oxide–eugenol cement (ZEC) is used as the luting material, this risk appears to be lower, as the excess cement will dissolve in the peri-implant sulcus. However, using a ZEC on a general basis conflicts with the manufacturers’ classification of a ZEC as a temporary luting material. To evaluate the clinical safety of ZECs, the present study investigated whether more ZECretained reconstructions than screw-retained reconstructions loosen over time. Method and Materials: In a retrospective observational study, the frequency of FDP loosening was investigated. For this purpose, data from patients who had been fitted with FDPs on two or more than two posterior implants were investigated. The study compared screw-retained (n = 59) vs cement-retained (n = 40) FDPs on implants over an observation period of 3.5 years after reconstruction incorpora-
tion. All cement-retained FDPs had been cemented with a temporary ZEC. Results: The prevalence of reconstruction loosening was significantly lower for cement-retained FDPs when a ZEC (10%) was used than it was for screw-retained FDPs (29%); four screw-retained FDPs and one cementretained FDP developed major complications. The survival rate of the reconstructions within the observation period was 97% for screw-retained FDPs and 100% for cement-retained FDPs (not significant). Conclusion: The prevalence of cementretained FDP loosening was significantly lower than that of screw-retained FDPs. Cementing FDPs on implants using a temporary cement does not necessarily lead to a higher number of loosened reconstructions. Permanent cementation with ZEC appears to be justified. (Quintessence Int 2015;46:583–589; doi: 10.3290/j.qi.a34077)
Key words: cement-retained, fixed dental prostheses, loosening, screw-retained, TempBond
Fixed dental prostheses (FDPs) on implants can be retained with either screws or cement. Many publications have compared these two retention methods.1-4 Compared with cemented dental prostheses, screw1
Head of Oral Surgery, Dental Academy for Continuing Professional Development, Karlsruhe, Germany; and Clinic of Operative Dentistry, Periodontology and Preventive Dentistry, University Hospital, Saarland University, Homburg, Germany.
2
Professor, Director, Dental Academy for Continuing Professional Development, Karlsruhe, Germany.
Correspondence: Dr Michael Korsch, Dental Academy for Continuing Professional Development, Lorenzstrasse 7, 76135 Karlsruhe, Germany. Email: [email protected]
VOLUME 46 • NUMBER 7 • JULY/AUGUST 2015
retained prostheses have a better marginal fit,5,6 and make it easier to remove the suprastructure. The disadvantages of screw retention are inferior primary retention, limited esthetics,7 and the risk of screw loosening at the level of the abutment.8 As the laboratory costs are higher for screw-retained reconstructions, they are more expensive to fabricate.7,8 The survival rates of screw-retained and cement-retained FDPs seem to essentially be the same.2,9 The frequency of suprastructure loosening in the case of screw-retained and cemented FDPs has been
583
Q U I N T E S S E N C E I N T E R N AT I O N A L Korsch/Walther
a Figs 1a and 1b
b Prefabricated abutments.
investigated in several studies, with contradictory results.1,8,9 Both temporary and permanent cements are offered for the cementation of implant-supported restorations. These cements mainly differ based on their retentiveness.10,11 Therefore, temporary cements offer the benefit of easy removal of the suprastructure. TempBond (Kerr), as one of the zinc oxide–eugenol cements (ZECs), is classified as a temporary cement, and in scientific studies it demonstrates significantly lower retentiveness than permanent cements.10,12 Excess cement left in the peri-implant sulcus after cementation favors the formation of a biofilm,13,14 which increases the risk of cement-induced peri-mucositis and peri-implantitis.15-18 The cementation of suprastructures with TempBond also seems to lead to excess cement.19,20 However, there are indications that ZECs dissolve in contact with fluid21,22 so that excess cement will not remain in the peri-implant sulcus for any length of time. The material properties of TempBond appear to make this material the ideal luting agent for the cementation of FDPs on implants. Nevertheless, its classification as a temporary cement limits this indication. The present retrospective study was conducted to investigate whether more FDP loosening occurs compared to screw retention when TempBond is used. Moreover, the intention was to clarify whether permanent cementation with TempBond is justifiable.
584
c Fig 1c Screw-retained FDP with two implants on prefabricated abutments.
a
b
Fig 2a Prefabricated customized abutments.
Fig 2b Cement-retained FDP with two implants on prefabricated customized abutments.
METHOD AND MATERIALS In a retrospective observational study, the frequency of FDP loosening was investigated. For this purpose, data from patients who had been fitted with FDPs on two or more than two posterior implants were investigated. A total of 89 patients with 204 Astra Tech implants (Astra Tech Dental) that were prosthetically restored in the clinic of the Karlsruhe Dental Academy for Continuing Professional Development in the period from January 2006 to September 2010 with implant-supported FDPs in the posterior region were followed up. Between January 2006 and December 2008, the FDPs were screwed onto prefabricated abutments (Fig 1). From December 2008, all FDPs were cemented (Fig 2).
VOLUME 46 • NUMBER 7 • JULY/AUGUST 2015
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Table 1
Sex, age, number of implants per patient and in relation to the type of FDP (at patient level)
Descriptor
Patients with screw-retained FDPs
Male
36
Patients with cement-retained FDPs 19
Female
16
18
Total
52
37
Mean age at time of prosthetic reconstruction (years)
63.5
65.4
2.3
2.3
Mean number of implants per patient
Table 2
Screw- vs cement-retained FDPs (at reconstruction level)
Descriptor
Screw-retained FDPs
Cement-retained FDPs
FDPs with 2 implants
57
36
2
4
59
40
FDPs with more than two implants Total
The reasons for changing the method of retention were the limited esthetics and higher laboratory costs of screw-retained vs cemented FDPs on implants. All FDPs (screw-retained and cemented) in the study period had a metal framework veneered with ceramic material. TempBond was the luting agent used for the cemented FDPs. In the treatment data analysis, loosening of the implant-supported restoration (screw loosening or decementation) over a period of 3.5 years after insertion was investigated. The data were compiled based on the patients’ medical records. In addition, all of the patients were asked over the telephone whether any loosening that was not treated by this clinic but by an external dentist had occurred after reconstruction insertion. Loosening after the period of 3.5 years was not evaluated.
Inclusion and exclusion criteria Patients met the inclusion criteria if they had undergone fixed prosthodontic therapy with Astra Tech implants in the posterior region between January 2006 and September 2010. Implant-supported restorations in the anterior region were excluded. FDPs with two or more implants were included, and single-tooth crowns on implants were excluded. Other requirements for inclusion were complete documentation of all technical
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implant characteristics (implant system and location) and continuous treatment by the clinic (at least once per year) since placement of the restoration. Patients with incomplete documentation or patients who could not be contacted by telephone were excluded.
Patients Over the evaluation period, 93 patients were treated; four patients were excluded because of incomplete documentation. Thus, 89 patients who met the inclusion criteria were evaluated, representing 96% of the originally treated patient population. Between March and April 2014, the included patients were interviewed over the telephone and asked whether they had undergone other therapies in addition to the documented renewed denture fixation. The 89 patients were divided into two groups depending on the type of denture retention. The groups were further subdivided based on FDPs with two implants or more than two implants (Tables 1 and 2).
Evaluation of the reconstruction level For the analysis of the reconstruction level, every implant was weighted inversely to the total number of implants per reconstruction.
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Table 3
Loosening of the reconstruction in relation to the type of FDP (at reconstruction level)
Descriptor
Screw-retained FDPs
Cement-retained FDPs
Statistical test
Loosening within 3.5 years after prosthetic reconstruction
17 (29%)
4 (10%)
χ2 = 4.622; P < .032
Average time of onset of loosening after prosthetic reconstruction (years)
1.6
1.4
NS
FDPs with two implants
17 (30%)
3 (8%)
χ2 = 4.241; P < .039
1 (25%)
NA
FDPs with more than two implants
0 (0%)
NA, not applicable; NS, not significant.
Table 4
Further loosening of the reconstruction in relation to the type of FDP (at reconstruction level)
Descriptor
Screw-retained FDPs
Cement-retained FDPs
Statistical test
FDPs with two implants loosening twice
5 (9%)
1 (3%)
NS
FDPs with two implants loosening three times
2 (4%)
0 (0%)
NA
NA, not applicable; NS, not significant.
Statistical method Data were compiled in Excel and analyzed with IBM SPSS Statistics 21 on Windows XP (Microsoft). The statistical methods included cross-tabulations with chisquared analysis for categorical data. The means were compared by t tests.
RESULTS The evaluation of the telephone interviews showed that seven patients had undergone treatment outside the clinic during the observation period, although these treatments included emergency measures only. All cases of reconstruction loosening were treated in the clinic.
FDP loosening based on reconstruction level Within the first 3.5 years after prosthetic restoration, screw-retained FDPs loosened significantly more often than cemented FDPs (screw-retained FDPs, 17 [29%]; cemented FDPs, 4 [10%]; χ2 = 4.622; P < .032) (Table 3). On average, screw-retained restorations loosened after 1.7 years, whereas cement-retained restorations loosened after 1.4 years. In the subgroups of FDPs with two implants, the difference was also significant (screwretained, 17 [30%]; cemented, 3 [8%]; χ2 = 4.241; P < .039). In the subgroup of screw-retained FDPs with more than two implants, loosening did not occur at all,
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and one (25%) of the cement-retained FDPs loosened. Given the low number of cases, no statistical evaluation was performed for this subgroup. Bivariate analysis showed significant association between loosening of reconstructions and type of FDP. In a multivariate logistic regression the effect of type of FDP was independent of age of patient and sex. There were no significant associations with patient sex and age of patient and loosening of reconstructions. Within the observation period of 3.5 years, six FDPs with two implants loosened twice (Table 4) (screwretained FDPs, 5 [9%] loosenings; cemented FDPs, 1 [3%]). None of the FDPs with more than two implants loosened more than once, and two (4%) screw-retained FDPs with two implants loosened three times, but none of the cemented FDPs showed further loosening. No further loosening occurred for screw-retained FDPs. Major complications (Fig 3) developed in four (7%) screw-retained FDPs with two implants (three abutment fractures, one implant fracture). In two cases of abutment fracture, the prefabricated abutment was replaced, and the reconstruction was saved. Only one cemented FDP with two implants (1%) developed a major complication (screw fracture). The screw was replaced, and the suprastructure was saved. Neither the cemented nor the screw-retained FDPs with more than two implants developed any major complications. The
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a Fig 3a
b Prefabricated abutment fracture.
Table 5
Fig 3b
Implant fracture with prefabricated abutment.
Survival rates of FDPs
Descriptor
Screw-retained FDPs
Cement-retained FDPs
Statistical test
Survival rate of FDPs with two implants
55 (96%)
36 (100%)
NS
4 (100%)
NS
Survival rate of FDPs with more than two implants
2 (100%)
NS, not significant.
survival rate (Table 5) was 97% for the screw-retained (two implants, 96%; more than two implants, 100%) and 100% for the cemented restorations (two implants, 100%; more than two implants, 100%).
DISCUSSION In addition to screw-retention, cementation is a frequently used method for retaining fixed restorations on implants. Both methods pose a risk of reconstruction loosening after incorporation of the dental restoration.1,2,23 The retrospective follow-up examination presented here compared the frequency of loosening of implant-supported screw-retained FDPs vs cemented FDPs. A total of 89 patients with 99 reconstructions on 204 implants were followed up over a period of 3.5 years after insertion of the reconstruction. Over this period, the number of screw-retained FDPs that loosened was almost three times the number of loosened cement-retained FDPs (29.3% vs 10%, respectively). This difference was significant. Nissan et al1 noted a similarly significant prevalence of loosened restorations on prefabricated abutments over an average observa-
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tion period of 5.5 years. In addition, in the study of Nissan et al,1 ZEC was also used for the cementation of the FDPs and the screws were also inserted from the occlusal on prefabricated abutments. For cemented FDPs only one screw is needed for the fixation of the abutment on the implant, whereas screw-retained FDPs require two screws to fix the suprastructure. In the case of cemented FDPs this reduces the possibility of preloaded stress and screw loosening,8 and presumably explains the difference in the prevalence of reconstruction loosening in the present study. One advantage of the present study was that exactly identical types of restorations (fixed FDPs with two or three abutments) were compared with one another. The two types of restorations only differed in terms of fixation (screw-retention vs cementation). Moreover, only FDPs placed on Astra Tech implants in the posterior region were selected. Based on these criteria of inclusion and exclusion, any unwanted effect of the type of restoration, implant region, or implant system on the result could be avoided. A weakness of the study was that the different types of fixation were not
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applied at the same time but one after the other. This may have influenced the results. In addition, only one type of fixation was applied per patient. In a prospective study, Nissan et al1 used a split-mouth design and could thus make sure that in all patients both types of fixation were applied at the same time. As already mentioned, the results were similar to those presented herein. In dentistry, it is general practice to differentiate between temporary and permanent cements. This classification is also made in the manufacturers’ product descriptions and refers to the cementation of toothsupported dental restorations. In this clinical application, it is not only necessary to produce a secure hold of the restoration but also to counteract crown margin caries; however, implant-supported dental prostheses differ. The differentiation between permanent and temporary cement applied to the natural tooth cannot be transferred to this type of reconstruction. Many studies that compare the retentiveness of temporary versus permanent cements are in vitro studies.10,12 They do not prove any clinical relevance regarding retentiveness to the frequency of reconstruction loosening. A lower degree of retentiveness makes it easier to remove the suprastructure and is therefore of benefit from this particular point of view;22 thus, access to the implants can be gained without any major risk in cases of periimplant treatment. Compared with screw-retained FDPs, cementretained FDPs on implants may lead to undetected excess cement in the peri-implant sulcus.16 In the current literature, it has been repeatedly shown that excess cement affects the peri-implant tissue.16,17 This excess favors peri-implant inflammation15 and may cause bone loss or even implant failure.18,24 A ZEC was used in the present study. Presumably, excess cement is also present when ZEC is used, but apparently it dissolves in contact with the sulcular fluid in the periimplant tissue. In vitro studies have shown that ZECs demonstrate signs of dissolution after a short time in contact with artificial saliva.25 In the present study, the survival rate of reconstructions within the observation period of 3.5 years was more than 96% in all subgroups.
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The 5-year survival rate reported in the literature for both screw-retained and cemented FDPs is approximately 95%.23,26,27 Whereas serious biologic complications are more likely to develop in connection with cemented FDPs, screw-retained FDPs are mainly causing technical problems.23 Technical complications, such as reconstruction loosening and major complications, also predominated with screw-retained FDPs in the present study. With regard to peri-implant bone loss, however, the results in the literature are contradictory when screw-retained and cemented FDPs are compared.1,23 A closer examination of these studies shows that different cements were used. It cannot be excluded that the type of cement used has a greater effect on the peri-implant bone than the method of retention (screw-retention vs cementation). For some years an increasing number of luting cements containing methacrylate have been used. In a clinical observational study it could be shown that implant-supported restorations cemented with ZEC developed significantly less peri-implant inflammation and bone loss than those cemented with a methacrylate cement.22 The present study could demonstrate that using a temporary ZEC does not cause more reconstruction loosening than screw-retention of FDPs. In view of the fact that ZEC obviously leads to less peri-implant inflammation than methacrylate-based cements it appears to make sense to consider using ZEC for permanent cementation.
CONCLUSION The use of a temporary ZEC does not necessarily lead to an increase in denture loosening based on comparisons between cement-retained dental prostheses and screw-retained dental prostheses. Provided that an appropriate cement is used, revision treatment of the prosthesis is an easier technique. In addition, the problem of excess cement remaining in the sulcus is counteracted. The use of ZECs for the permanent cementation of FDPs on implants therefore appears to be a responsible treatment option.
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15. Korsch M, Robra BP, Walther W. Predictors of excess cement and tissue response to fixed implant-supported dentures after cementation. Clin Implant Dent Relat Res 2015;17(Suppl 1):e45–e53. 16. Wilson TG Jr. The positive relationship between excess cement and periimplant disease: a prospective clinical endoscopic study. J Periodontol 2009;80:1388–1392. 17. Korsch M, Obst U, Walther W. Cement-associated peri-implantitis: a retrospective clinical observational study of fixed implant-supported restorations using a methacrylate cement. Clin Oral Implants Res 2014;25:797–802. 18. Callan DP, Cobb CM. Excess cement and peri-implant disease. JIACD 2009;1:61–68. 19. Wadhwani C, Hess T, Pineyro A, Chung KH. Effects of abutment and screw access channel modification on dislodgement of cement-retained implantsupported restorations. Int J Prosthodont 2013;26:54–56. 20. Wadhwani C, Pineyro A, Hess T, Zhang H, Chung KH. Effect of implant abutment modification on the extrusion of excess cement at the crown-abutment margin for cement-retained implant restorations. Int J Oral Maxillofac Implants 2011;26:1241–1246. 21. Yanikoglu N, Yesil Duymus Z. Evaluation of the solubility of dental cements in artificial saliva of different pH values. Dent Mater J 2007;26:62–67. 22. Korsch M, Robra BP, Walther W. Peri-implantitis associated with type of cement: A retrospective analyze of different types of cement and their clinical correlation to the peri-implant tissue [epub ahead of print 2 Sep 2014]. Clin Implant Dent Relat Res doi: 10.1111/cid.12265. 23. Sailer I, Muhlemann S, Zwahlen M, Hammerle CH, Schneider D. Cemented and screw-retained implant reconstructions: a systematic review of the survival and complication rates. Clin Oral Implants Res 2012;23(Suppl 6):163– 201. 24. Gapski R, Neugeboren N, Pomeranz AZ, Reissner MW. Endosseous implant failure influenced by crown cementation: a clinical case report. Int J Oral Maxillofac Implants 2008;23:943–946. 25. Yanikoglu N, Yesil Duymus Z. Evaluation of the solubility of dental cements in artificial saliva of different pH values. Dent Mater J 2007;26:62–67. 26. Buser D, Janner SF, Wittneben JG, Bragger U, Ramseier CA, Salvi GE. 10-year survival and success rates of 511 titanium implants with a sandblasted and acid-etched surface: a retrospective study in 303 partially edentulous patients. Clin Implant Dent Relat Res 2012;14:839–851. 27. Sherif S, Susarla SM, Hwang JW, Weber HP, Wright RF. Clinician- and patientreported long-term evaluation of screw- and cement-retained implant restorations: a 5-year prospective study. Clin Oral Investig 2011;15:993–999.
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