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.