Objectives: In this clinical trial, 180 veneer restorations (VRs) were evaluated. The purpose of the study was to collect survival data and to find possible relations between survival and (1) 'type of VR', (2) 'preparation design', (3) 'operator' and (4) the patient-related variables 'tooth-type' and 'vitality of the tooth'.
Methods: The restorations were provided by seven dentists in 1 12 patients on central and lateral maxillary incisors. Experimental variables were: 'type of VR' (either direct resin composite (DC), indirect resin composite (IC) or porcelain (P)), 'preparation design' (with and without incisal overlap) and 'operator'. Failures were recorded at two levels: absolute failure (need for new restoration) and relative failure (need for repair). Survival was defined at three levels: (1) survival of original restoration (Sr, endpoints: 'absolute' failures), (2) functional survival (Sf, endpoints: 'relative' failures) and (3) overall survival (SO, endpoints: both 'absolute-' and 'relative failures').
Results: The variable 'type of VR' showed significant influence on Sf and So but not on Sr. Sf and So rates of P, IC and DC were, respectively: Sf-P, 94%; So-P, 94%; Sf-IC, 94%; So-IC, 90%; Sf-DC, 80%; So-DC, 74%. VRs on vital teeth showed a significantly better survival than VRs on non-vital teeth at all survival levels.
Conclusions: Preparation of the incisal edge for incisal coverage is considered to be unnecessary to assure or improve the strength of VRs. Veneers on non-vital teeth showed higher risk to fail than veneers placed on vital teeth. Porcelain veneers showed the best overall survival.