To restore oral functions in patients with missing teeth, single-tooth implants are a well-documented treatment option. Along with high survival rates, aesthetic factors have become an important clinical outcome variable for evaluating treatment success of implant-supported restorations. Thus, the selection of restoration materials should be based on proper optical characteristics in addition to biocompatibility and sufficient strength of materials. Abutments and crowns based on zirconia are one of the most recent alternatives to metal abutments and metal-ceramic crowns. To date, only few comparative studies have reported on aesthetic, biological, biomechanical and patient-reported outcomes of implant-supported single-tooth restorations of various biomaterials.
The aim of the present thesis was to investigate the clinical performance of zirconia-based implant-supported single-tooth restorations and to estimate long-term biomechanical results of zirconia-based versus metal-based restorations. The aim of study I was to analyse the mode of fracture and number of cyclic loadings until veneering fracture of zirconia-based all-ceramic restorations compared to metal-ceramic restorations. The aim of study II was to test the reliability and validity of six aesthetic parameters used at the Copenhagen Dental School to assess the aesthetic outcome of implant-supported restorations. The aims of study III and IV were to compare the influence of different abutment and crown materials on biological, biomechanical and technical, and professional- and patient-related aesthetic outcomes of implant-supported single-tooth restorations.
In the first study, the most frequent fracture mode was the veneering fracture, which was more severe at the all-ceramic than at the metal-ceramic restorations. Furthermore, more loading cycles until veneering fracture were registered at the metal-ceramic than at the all-ceramic restorations.
In study II, the overall intra- and inter-observer agreements for the six aesthetic parameters were substantial and moderate, respectively. The mucosal discolouration score had the highest intra- and inter-observed agreement. The six aesthetic parameters had a highly significant correlation to the corresponding VAS scores; thus, each parameter was found to be valid.
In study III and IV, all implants survived and the marginal bone loss was generally low. No significant differences in the mPlI and mBI at restorations of different abutment materials and in the marginal bone loss at restorations with zirconia and titanium abutments were recorded. In study III, the marginal bone loss at restorations with gold alloy abutments was significantly higher than at restorations with zirconia abutments. In study III and IV, the marginal adaptation of crowns was
7
significantly less optimal at the all-ceramic than at the metal-ceramic crowns. The loss of retention was the most frequent biomechanical complication and was mostly registered at the posterior regions. The veneering fracture was slightly more frequent at the all-ceramic than at the metal-ceramic crowns. The crown colour match was significantly better at all-ceramic versus metal-ceramic crowns, while no significant difference in the other aesthetic parameters between various restoration materials were observed. The patient-reported satisfaction with aesthetic outcomes was not significantly different at restoration of various materials, and it was not significantly correlated to the professional-reported aesthetic outcomes.
Conclusion: The biological outcome variables were similar at the different abutment materials; however, the marginal bone loss was higher at the gold alloy compared to the zirconia and titanium abutments. The biomechanical and technical outcome variables were more optimal at the metal-ceramic than at the zirconia-based all-ceramic restorations. The six aesthetic parameters used in our studies were feasible, reliable and valid, which make them useful for quality control of implant-supported single-tooth restorations. The use of these aesthetic parameters indicated no remarkable difference in aesthetic outcome of restorations with various abutments materials, but the all-ceramic crowns provided a better colour match than the metal-ceramic crowns. The patients did not notice difference in the aesthetic results of restorations of various materials.