All-ceramic partial coverage premolar restorations. Cavity preparation design, reliability and fracture resistance after fatigue.

PURPOSE

To investigate the effects of different cavity preparation designs on the reliability and fracture resistance of partial coverage restorations (PCR) which were luted adhesively to natural premolars after exposure to a mastication simulator.

METHODS

80 caries-free, extracted human maxillary premolars were randomly divided into two control groups (A, B) and three test groups (C-E) consisting of 16 specimens each. Group A served as a control group with no preparation. The specimens of Groups B to E were prepared as follows: Group B: MOD inlay, Group C: PCR (palatal), Group D: PCR (palatal and buccal), Group E: complete veneer. Using pressed ceramic IPS e.max Press (VP 1989), 64 all-ceramic restorations were fabricated and luted adhesively. The 80 specimens were subjected to 1.2 million mastication (F= 49 N) and 5500 thermal cycles at 5 degrees C and 55 degrees C in a mastication simulator. Subsequently, all test specimens were loaded occlusally until fracture using a universal testing machine. The statistical analysis included the unpaired Wilcoxon rank sum test and box plots.

RESULTS

All the specimens withstood the masticatory simulation. The following mean fracture strength values (N) (minimum/maximum) were recorded: Group A: 1446 (417/2404), Group B: 1351 (657/2096), Group C: 837 (346/1472), Group D: 963 (481/1691), Group E: 1361 (900/2211). The fracture strength values of Groups A, B and E were statistically significantly higher (P < 0.05) than those of Groups C and D. Inlays and complete veneers made of IPS e.max Press reached fracture strength values corresponding to those of natural premolars.