Influence of the shape core on custom cast dowel and core removal by ultrasonic energy.

The aim of this study was to assess the influence of the shape of custom cast dowel and cores on their removal by the use of ultrasound technique. Twenty-four single-rooted bovine teeth were prepared and had cast dowel fixed with zinc phosphate cement. The teeth were randomly divided into two groups: group I- received custom cast dowel and cores made without the coronal portion anatomy, simulating removal this portion with a bur, and group II- received cores that reproduced the coronal anatomy. Both were treated with an ultrasound device in two three-minute cycles (US). The force necessary for dowel removal was determined using a mechanical test machine. In the second stage of the study, the custom cast dowel and cores were again cemented and no ultrasound vibration was used on them (C). Data were submitted to the two-way anova (2 x 2) and Tukey test (P < 0.05), resulting in decreased tensile strength values (Kgf): GIC (49.85 +/- 11.10); GIIC (48.22 +/- 11.09); GIIUS (32.36 +/- 6.21) and GIUS (8.0 +/- 7.52). It was concluded that the shape of the core without the anatomic coronal portion facilitated removal of intra-radicular retention only when associated with the use of ultrasound.