A practice-based clinical evaluation of the survival and success of metal-ceramic and zirconia molar crowns: 5-year results

This practice-based study evaluates the survival and success of conventionally luted metal-ceramic and zirconia molar crowns fabricated by using a prolonged cooling period for the veneering porcelain. Fifty-three patients were treated from 07/2008 to 07/2009 with either metal-ceramic crowns (MCC) or zirconia crowns (ZC). Forty-five patients (26 female) with 91 restorations (obser-vational period: 640 +/- 48 months) participated in a clinical follow-up examination and were included in the study. Estimated cumulative survival (ECSv), success (ECSc) and veneering ceramic success (ECVCSc) were calculated (Kaplan-Meier) and analysed by the crown fabrication technique and the position of the restoration (Cox regression model) (P < 005). Five complete failures (MCC: 2, ZC: 3) were recorded (5-year ECSv: MCC: 976%, (95% confidence interval (95%-CI): [93%; 100%]/ZC: 940%, (95%-CI): [87%; 100%]). Of the MCCs (n = 41), 850%, [95%-CI: (77%; 96%)] remained event-free, whereas the ECSc for the ZCs (n = 50) was 743% (95%-CI): [61%; 87%]. No significant differences in ECSv (P = 051), ECSc (P = 043) and ECVCSc (P = 036) were detected between the two fabrication techniques. Restorations placed on terminal abutments (n = 44) demonstrated a significantly lower ECVCSc (P = 0035), (5-year VCF-rate: 148%) than crowns placed on tooth-neighboured abutments (n = 47), (5-year VCF-rate: 43%). In the present study, zirconia molar crowns demonstrated a 5-year ECSv, ECSc and ECVCSc comparable to MCCs. Irrespective of the fabrication technique, crowns on terminal abutments bear a significantly increased risk for VCFs. Clinical investigations with an increased number of restorations are needed.