Resistance to fracture of teeth with various preparations for amalgam

Advances in dental instrumentation and materials have allowed for increasingly conservative preparations when treating teeth for dental caries. Research has shown that some materials, properly used, can restore teeth to their pre-prepared strength. At the present time, the longevity of these materials is unknown, requiring clinicians to remain committed to conservative methods of tooth preparation. The purpose of this study is to compare the resistance to fracture of teeth prepared with occlusal, mesio-occlusal-distal (MOD) and mesial/distal slot preparations against unprepared control teeth.

Thirty-two non-carious, non-restored human maxillary premolar teeth were divided into three experimental groups and a control group with eight teeth in each. After preparation, the teeth were loaded to fracture on an Instron Universal Testing Machine, and the results were compared using an Analysis of Variance (ANOVA) followed by Tukey's Studentized Range Test (P < 0.05). Fracture patterns were compared by chi-square analysis at the 0.1 level of probability.

There was no significant difference in fracture resistance among the experimental groups, but all were less resistant to fracture than the unprepared control group. The MOD and occlusal groups demonstrated a tendency towards vertical fracture while the mesial-distal slot and unprepared groups tended to a more limited fracture of a single cusp.

Any preparation appears to decrease a tooth's resistance to fracture. Conservative preparation design may affect fracture pattern and enhance options for subsequent restoration.