A Comparison of Zirconia CAD/CAM and Conventionally Fabricated Single Implant Abutments and Restorations in the Esthetic Zone: a Randomized Controlled Clinical Trial.

Introduction

Long-term prospective studies demonstrate a high success rate of Straumann implants in partially or fully edentulous patients both with early and conventional loading (Salvi et al. 2004, Lambrecht et al. 2003, Cochran et al. 2002, Weber et al. 2000, Buser et al. 1997). Before the introduction of CAD/CAM technology to the field of implant dentistry in the beginning of 1990's (Priest 2005), the available approach for restoring single dental implants was either with stock or cast custom abutments and a ceramo-metal crowns. In spite of the satisfactory results that this conventional treatment approach has achieved, several disadvantages have been recognized. First, non tooth-colored abutments possess the problem of bluish appearance of overlying tissue in cases of thin gingival biotype (Barclay et al. 1996, Prestipino and Ingber, 1996). Second, with stock abutments ideal emergence profile can not be achieved (Daftary 1997), a disadvantage that was reduced with the use of custom abutments. However, custom abutments present other disadvantages including possible imprecision of fit due to inaccuracies associated with impression, waxing, investing and casting procedures and the negative effect of the gold alloy on the peri-implant mucosal barrier as demonstrated by Abrahamsson in 1998 (Abrahamsson et al 1998 ).

The introduction of CAD/CAM technology to implant dentistry was meant to provide higher quality restorations. Since its introduction, the use of this technology in the production of implant ceramic frameworks and crowns especially in esthetic regions has been rapidly expanding because of the promising esthetic, biologic, and mechanical properties. Alumina as well as Zirconia abutments are characterized by good tissue compatibility (Abrahamsson et al. 1998). In a study by Barclay et al in 1996 it was found that plaque accumulation scores for ceramic-coated transmucosal elements were significantly lower than those recorded in titanium transmucosal elements (Barclay et al. 1996). These results suggest that the further development of a ceramic implant transmucosal collar may assist plaque control at the soft tissue-implant interface and may favorably influence the tissues in this region (Barclay et al. 1996). Other studies documented no significant differences in plaque accumulation and microbial colonization between titanium and ceramic abutment samples (Andersson et al. 2003, Rasperini et al. 1998). The bacterial colonization of Zirconia ceramic surfaces was recently studied in vitro and in vivo (Rimondini et al. 2002). The authors found that, overall, Zirconia ceramic surfaces developed for implant abutments accumulate fewer bacteria than commercially pure titanium, and may therefore be considered as a promising material for abutment manufacturing (Rimondini et al. 2002). A comparison of the recorded superficial soft tissue responses to titanium and ceramic surfaces of transmucosal elements of implants revealed no significant differences between both groups (Barclay et al. 1996, Andersson et al. 2001). Almost no marginal bone loss was recorded, indicating a stable bone situation both at ceramic and titatium abutments on single-tooth implants (Andersson et al. 2001). However, it seems to be that the peri-implant soft tissues adjacent to titanium and ceramic surfaces may differ in features that are not apparent when routine clinical parameters are used (Barclay et al. 1996).

Because of their specific mechanical properties, all-ceramic restorations demonstrate a lower fracture resistance than ceramic restorations supported by metal substructures. The ceramic abutments on implants are more sensitive to fracture and to handling procedures than the titanium abutments (Andersson et al. 2001). However, advances have been made in the fabrication of high-strength all-ceramic abutments for anterior implants (Yildirim et al. 2003). The hardness of the Zirconium ceramic also allows it to undergo conventional prophylaxis with ultrasonic scalers without alteration of its surface quality of abutment (Marzouk, 1996). Moreover, Zirconia has a flexural strength and fracture toughness almost twice as high as alumina (Glauser et al. 2004, Yildirim et al. 2003).

Currently very limited number of clinical studies is present supporting the clinical viability of CAD/CAM ceramic restorations (Henriksson 2003, Canullo 2007) and no reports were found on the performance of CAD/CAM ceramic implant restorations in comparison to conventional implant restorations.