EFFECT OF MASTICATORY CYCLES ON TOOTH COMPRESSION AND RESULTANT LEAKAGE OF AMALGAM RETROFILLS

This study was carried out to investigate the effect of changes in too th structure due to masticatory cycles on amalgam retrofillings perfor med to different cavity depths, Forty upper maxillary first molars wer e tested, In the obturated palatal root apical amalgam was inserted to different depths (1.5 and 3 mm), Eight casts were built, each having four sample molars, To block the teeth, the vestibular roots were embe dded in resin (palatal root was left free), The eight remaining retrof illed teeth served as controls and were not submitted to occlusal forc es, A mechanical device to simulate masticatory cycles subjected the t eeth to 500,000 to three million cycles, Leakage was assessed from dye penetration observations, The values of microleakage were analyzed an d compared, and strain gauges were used to assess structural modificat ions to the tooth, The leakage of all retrofilled obturations increase d in correlation with the number of masticatory cycles, At three milli on cycles, root length compression was 0.3 +/- 0.02%, Leakage was sign ificantly less for the deeper cavity preparations at all stages, This in vitro study suggests a significant effect by root compression due t o masticatory loads on the leakage of retrofilled amalgam obturations.