Influence of depth of mesio-occlusodistal preparation and mechanical cycling on fracture resistance of restored premolars.

The purpose of this in vitro study was to evaluate the influence of depth (3.0 vs 5.0 mm) of mesio-occlusodistal (MOD) cavity preparation and mechanical cycling on fracture resistance of maxillary premolars restored with resin-based composite (RBC). Seventy premolars were randomly divided into 7 groups (n = 10): NP, no cavity preparation (control); MOD3, 3.0-mm-deep MOD preparation, not restored; MOD3R, 3.0-mm-deep MOD preparation restored with RBC; MOD5, 5.0-mm-deep MOD preparation, not restored; MOD5R, 5.0-mm-deep MOD preparation restored with RBC; MOD3RC, 3.0-mm-deep MOD preparation restored with RBC and subjected to mechanical cycling; and MOD5RC, 5.0-mm-deep MOD preparation restored with RBC and subjected to mechanical cycling under the same conditions as MOD3RC. All specimens were tested using a universal testing machine, resulting in the following mean (SD) values: NP, 224.65 (35.66) kgf; MOD3, 58.92 (15.48) kgf; MOD3R, 95.58 (13.88) kgf; MOD5, 68.06 (10.12) kgf; MOD5R, 98.49 (13.16) kgf; MOD3RC, 83.68 (14.39) kgf; and MOD5RC, 54.25 (11.56) kgf. Analysis of variance and Tukey test showed no statistically significant difference among MOD3, MOD5, and MOD5RC; between MOD5 and MOD3RC; or among MOD3R, MOD5R, and MOD3RC (P > 0.05). MOD3RC had significantly greater fracture resistance than MOD5RC (P < 0.05). NP had the highest fracture resistance of all groups (P < 0.05). The results showed that the depth of the cavity preparation only influenced fracture resistance after mechanical cycling of the specimens.