Clinical performance of metal-free polymer crowns after 3 years in service

Objective To investigate the influence of location and preparation design on the survival and complication rate of metal-free polymer crowns within a prospective clinical study. Methods After randomization, a total of 114 (68 posterior and 46 anterior) single crowns were prepared, either with a chamfer finishing line or with a shoulder combined with occlusal reduction of at least 1 mm. Build-ups were made with a composite material, using the corresponding dentin adhesive. After making impressions with polyether material, polymer crowns were manufactured on stone dies and adhesively luted with resin cement. Follow-ups were scheduled after 1 month, 1 year, 2 years and 3 years. Documentation included failures and other complications, as well as ratings of esthetic and functional performance. After 3 years, data from 100 single crowns were statistically evaluated. Results Within a minimal observation period of 3 years, 10 complications occurred, including 3 total fractures, 3 partial fractures and 3 decementations. Only 4 crowns (3 total fractures +1 partial fracture) had to be replaced, whereas 2 partial fractures could be repaired and all loosened crowns could be recemented. Kaplan–Meier survival analysis did not show any influence of location or preparation design on the complication rate. Esthetic and functional evaluation by the patients revealed a high acceptance of single polymer crowns, indicated by medians of 9–10 on a 10-point-scale. Conclusion Within the 3 year observation period, it can be concluded that 0.5 mm chamfer and shoulder preparation ensure that the stability of metal-free polymer crowns for anterior and posterior teeth is acceptable. Long-term stability and wear behavior has still to be evaluated.