An in vitro assessment of the strength of porcelain veneers dependent on tooth preparation

The treatment of teeth using veneer restorations combines aesthetic and fun ctional improvements with a low destructive technique. Different kinds of t ooth preparation techniques are described in the literature for this kind o f restoration. This in vitro study aimed to examine the influence of the in cisal preparation on the loadability of teeth restored with porcelain lamin ate veneers. Thirty-six selected mandibular incisors were randomly assigned to three groups with 12 teeth per group. In the first group, only the faci al surface was prepared. In the second group, the preparation included a ro unded incisal edge and a distinct chamfer lingually. The third group served as an unprepared control. Empress(R) veneers were then fabricated and ceme nted with a low viscous luting composite material. After 120 days storage i n Ringer's solution, the specimens were loaded incisally to the point of fa ilure. Statistical analysis of the results showed significant differences b etween the series (P = 0.0103). Group 2 (with preparation of the incisal ed ge) exhibited the lowest fracture resistance (466 +/- 99 N) (N, mean forces ). When prepared only facially, the teeth restored with Empress(R) veneers reached the strength of unprepared teeth. Compared with the biting force de scribed for incisors in the literature, the in vitro loadability reached in this investigation seems to jusitify the clinical use of both preparation designs tested.