CUSP REINFORCEMENT BY BONDING OF AMALGAM RESTORATIONS

The purpose of the present study was to assess the effectiveness of se veral adhesives in bonding amalgam in order to recover tooth stiffness . A non-destructive experimental methodology was adopted, using strain gauges bonded to the midbuccal surfaces of 40 teeth, with sequential evaluation of loaded intact, prepared and restored stages of the same tooth. Continuous strain measurement as a function of the applied load was acquired by A/D equipment and a data acquisition programme. The s train-force behaviour of the sound teeth under nonaxial force up to 97 .5 N served as the baseline. The five experimental groups (8 X 5) cons isted of control (no adhesive) and four different adhesives. One-way a nalysis of variance with repeated measures was calculated for the defo rmation ratio, relative stiffness and recovery values. Reductions in t ooth structure by cutting a mesio-occlusal-distal preparation, width o ne-third intercuspal distance, resulted in 39-52% loss of buccal cusp stiffness. Non-bonded amalgam produced negligible increase (5%) in the stiffness recovery values of the buccal cusps. The adhesives splinted the cusps together, thereby decreasing cuspal flexure and increasing relative stiffness values. Recovery values obtained ranged from 39% to 61%. Assuming that cusp fracture occurs as a result of brittle tooth structure fatigue, amalgam adhesives may contribute to the strengtheni ng of weakened cusps. (C) 1998 Elsevier Science Ltd. All rights reserv ed.