Influence of specimen preparation on ultimate tensile strength of dentin

Objectives: To investigate if the mode of preparation of microtensile dentin specimens affects their ultimate micro-tensile cohesive strength (μTCS). Methods: Extracted human third molars that had been stored in distilled water for no longer than one month were selected and divided into three experimental groups. Group 1: Molars were sectioned parallel to their long axis in two perpendicular directions in order to obtain 1.3 x 1.3 mm dentin beams. Only beams located above the pulp chamber were selected. They were placed into the chuck of a lathe and were slightly ground forming an hour-glass cylindrical shape with a little groove marked in order to induce the fracture. Group 2: Dentin beams were prepared as described above but using water cooling. Group 3: 0.8 x 0.8 mm dentin beams from above the pulp chamber were selected. Each beam was tested in tension. From the three groups, specimens with areas between 0.5 and 0.7 mm² were selected and the results were analysed (one way ANOVA and SNK (p<0.05)). Results: Mean μTCS (SD), in MPa, and number of specimens are shown in Table, per groups. Same superscript indicates no significant difference in μTCS caused by the mode of preparation.

Conclusions: The use of a non-trimming mode of preparation of the dentin specimens was related with higher ultimate tensile cohesive strength values. When specimens were trimmed, water cooled ones yielded higher results, although this effect was not statistically significant.