Original study - ZZI 02/2012

A retrospective study on the incidence of chipping of zirconia-based and metal-ceramic implant-supported single crowns and splinted crowns*

S. Schwarz1, C. Schröder1, W. Bömicke1, A. J. Hassel1, P. Rammelsberg1

Aim: To compare the influence of chipping on the survival and success rates of implant-supported single crowns and splinted crowns within a retrospective study design.

Material and methods: 161 patients (50.8 % male, mean age 55.2 years) received 232 cemented implant-supported single crowns and 14 splinted crowns. 179 crowns and twelve splinted crowns had a metal framework (gold alloy). The other 53 single crowns and two splinted crowns were all-ceramic (zirconia framework and glass-ceramic veneer material). A total of 54.7 % of the single crowns and 50 %
of the splinted crowns were fixed by semipermanent
cementation.

Results: During the implant-observation period of in mean 2.8 years (standard deviation 1.4) one implant was lost, resulting in a survival rate of 99.6 %. Seven further implants had clinical signs of moderate peri-implantitis and bone loss, so the success rate was 96.9 %. During the superstructure-observation period of in mean 2.2 years (standard deviation 1.4) a total of 78.2 % of the single crowns and 91.7 % of the splinted crowns made of metal-ceramic, and 69.8 % of the single crowns and 50 % of the splinted crowns made of all-ceramic had no technical complication at all. The most common complication, fracture of the veneer material, occurred significantly more often on all-ceramic restorations (p < 0.001). A total of ten single crowns had to be remade, resulting in survival rates of 98.3 % (metal-ceramic) and 88.7 % (all-ceramic). The survival rates of the splinted crowns were 100 % in both groups.

Conclusion: Chipping was found to be more frequent for all-ceramic implant-supported single crowns, the survival and complication rates were significantly lower. The survival rates for splinted crowns were the same in both groups, no failures occurred. Nevertheless, within the limitations of this retrospective study, zirconia-based suprastructures veneered with glass ceramic cannot be generally recommended.

Keywords: dental implants; all-ceramic; metal-ceramic; chipping; zirconia

Introduction

Treatment of single-tooth gaps using implant-supported restorations has become established in the past few years as a preferred treatment concept. The main advantage of this concept is the conservation of healthy adjacent tooth structure. Metal-ceramic crowns are the standard restoration with this treatment. Clinically, crowns are both screw-retained and cement-retained [3, 11, 14].

All-ceramic crowns have gained in importance in recent years, which is due on the one hand to their high biocompatibility and on the other hand to possible aesthetic advantages. Tooth-supported, all-ceramic crowns produce impressively good results clinically. In a prospective study by Marquardt and Strub the survival rates of pressed lithium disilicate crowns (IPS Empress 2, Ivoclar Vivadent GmbH, Ellwangen, Germany) after five years was 100 %. [7] In a review involving 34 studies Pjetursson et al. also reported high, but material-dependent five-year survival rates of all-ceramic crowns between minimum 87.5 % (simple glass ceramic) and maximum 96.4 % (densely sintered aluminium oxide ceramic) [10].

The higher masticatory forces, which can occur with implant-support restorations [6], limit the use of these materials in implant prosthetics. The material technology properties of fracture toughness and fracture resistance are inadequate, particularly when used in the posterior region. The introduction of yttrium-reinforced zirconia as a framework material should address this problem. Particular characteristics of zirconia are its high flexural strength and high fracture strength, which are exceptional for a brittle ceramic [8]. The principle of the high fracture toughness of polycrystalline zirconia is based on the phase transformation of the individual crystallites under the influence of mechanical loading (yttrium-stabilized tetragonal zirconia polycrystalline, i. e. Y-TZP) [13].

Clinical studies into zirconia-based single crowns with glass-ceramic veneering, however, are rare in the literature. Cehreli et al. investigated 15 tooth-supported single crowns (Cercon base) over a period of two years [4]. One crown fractured and the survival rate was 93.3 %. The incidence of chipping was not reported. In another study by Örtorp et al. 168 zirconia crowns (Nobel Procera, Nobel Biocare), which were also tooth-supported, were studied over a period of three years. There were also no incidences of framework fractures; chipping occurred with a frequency of 2 % (four crowns) [9]. To date, there are no clinical studies in the literature on zirconia-based single crowns with a glass ceramic veneer.

The aim of this retrospective analysis was, therefore, to evaluate the frequency of chipping on implant-supported single crowns and splinted crowns fitted in the Department of Prosthodontics, University of Heidelberg. All-ceramic, zirconia-based superstructures with glass-ceramic veneering and metal-ceramic restorations were included in the analysis. The null hypothesis was that the survival and complication rates of implant-supported all-ceramic single crowns and splinted crowns are equivalent to those of metal-ceramic restorations.

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