Sailer Et Alsystematic Review of Ceramic Implant Abutments

Sailer et alSystematic review of ceramic implant abutments

Discussion parts I and II

This systematic review of the literature indicated no significant differences in the performance of ceramic and metal abutments. Ceramic abutments exhibited similar survival and complication rates as metal abutments when supporting implant-borne crownsand FDPs. Furthermore, atendency toward fewer technical and esthetical complications was observed with ceramic abutments. Consequently, ceramic abutments can be considered to be a valid alternative to metal abutments.

Systematic reviews have increasingly been used to summarize the cumulative information on the optimal treatment, which is most appropriately given in RCTs (Egger et al. 2001). For the present review, three RCTs comparing ceramic and metal abutments were available. The remainingstudieswereprospectiveand retrospective cohort studies. The shortest follow-up period of all included studies was three years. A 3-year observation period is rather short and consequently no final conclusions can be drawn on the performance of ceramic compared with metal abutments. In fact, ceramics as brittle materials are prone to fracture due to fatigue over time (Rekow & Thompson 2007). For definitive conclusions on their performance, long observation periods are therefore needed. Unfortunately, very few studies have been published on ceramic abutments, although the first ceramic abutments were introduced in 1993 (reports on Prestipino and Ingber’s ceramic abutments in this review were published between 2001 and 2009). These studies had maximum observation periods of 4

years. In contrast, the observation periods in the studies of metal abutments ranged from 3 to 8 years. The mean follow-up of 3 years was, hence, a necessary compromise.

Implant survival

The analyses performed in this systematic review estimated a 96.4% implant-infunction survival rate for implants supporting ceramic or metal abutments for a follow-up of 5 years. In previous systematic reviews of implant-borne single crowns (Jung et al. 2008a) and FDPs (Pjetursson etal. 2004), 5-year implant survivalratesof 96.8% and 95.4%, respectively, were reported.

One further review of the incidence of biological and technical complications in implant dentistry (Berglundh et al. 2002) reported a 2.06–2.5% rate of implant loss

during 5 years of single crown function. The respective rate for implants lost during 5-year support of FDPs was 2.49–3.07% (Berglundh et al. 2002). In the present review the mean estimated rate for implant failure during 5 years of loading with single crowns or FDPs was slightly higher, with 3.6% (95% CI: 2.5–5.1%). Overall, the results of the reviews are in agreement.

Abutment survival

The survival rate of ceramic abutments was 99.1% after an estimated follow-up of 5 years. The corresponding survival rate of metal abutments was 97.4%. Most encouragingly, in the present review no significant differences in the survival rates of ceramic and metal abutments were found.

Metal abutments exhibit high survival rates due to the excellent physical proper-

ties of metal (Andersson et al. 1998). Metals are ductile, which enhances their tolerance toward small defects or cracks. Ceramics, in contrast, are delicate materials due to their brittleness. Because of this brittleness they do not withstand tensile forces or surface defects and cracks very well. Fracture occurs when the tensile forces exceed the limits determined by the fracture toughness (Rekow & Thompson 2007). Improvements in the field of ceramics have encompassed the development of the high-strength ceramics alumina and zirconia, which exhibit increased fracture toughness. Very promising survival rates of implant abutments made out of both alumina and zirconia have been reported (Andersson et al. 2001; Glauser et al. 2004; Canullo 2007). Among all dental ceramics zirconia exhibits the highest fracture toughness (Lu¨thy 1996). One recent RCT of zirconia and titanium abutments showed that this ceramic can be used as an abutment material even in posterior regions of the jaws with success similar to metal (Zembic et al. 2009). Besides its successful application as an abutment material, zirconia has been demonstrated to exhibit a very promising performance as a framework material for tooth-borne FDPs in areas with high loading (Raigrodsky et al. 2006; Sailer et al. 2007; Molin & Karlsson 2008; Tinschert et al. 2008).

In summary, high-strength ceramic abutments yielded excellent survival rates when supporting implant-borne fixed reconstructions. Their survival resembled that of metal abutments. It has to be considered, though, that this evidence was derived from five studies reporting on 166 ceramic abutments and 18 studies reporting on 4807 metal abutments. Furthermore, the ceramic abutments had been followed up for 3.7 years, whereas the metal abutments had been followed up for

4.8 years.

Technical complications

No significant differences in the technical outcomes occurred at ceramic and metal abutments.

Moreover, with the exception of abutment fractures, the present review showed a trend for fewer technical complications with ceramic abutments. It has to be considered, though, that the majority of the

data on ceramic abutments were obtained from anterior and premolar regions, where lower occlusal forces are assumed.

Fracture of the abutment seldom occurred with either type of abutment, despite the differences in fracture resistance. Its cumulative incidence was only 0.3%.

Problems with the abutment screws were most frequently reported as a technicalcomplication. They encompassedeither fracture or loosening of the abutment screw. Abutment screw fracture solely occurred at metal abutments at an estimated 5-year rate of 0.8%. It might be hypothesized that with ceramic abutments, frac-

ture of the abutment itself would occur before fracture of the abutment screw (Tripodakis et al. 1995). During occlusal loading of an implant-borne reconstruction, the region around the abutment screw head is the area of the highest torque and stress concentrations. This area has been demonstrated to be the most critical region for the stability of ceramic abutments in laboratory studies (Tripodakis et al. 1995; Att et al. 2006a, 2006b). High tensile forces occurring in this region during function were the most frequent origin of fracture of the ceramic

...