Effect of cervical dentine thickness on hardness reduction of outer dentine following intracoronal bleaching

Aim: Dental bleaching could adversely affect dentine hardness. The aim of the present study was to evaluate the effect of cervical dentine thickness on hardness reduction of outer dentine following intracoronal bleaching.
Materials and methods: Thirty-six intact anterior teeth were selected and the root segments were separated 2 mm below the cementoenamel junction. Using a diamond fissure bar, dentine substrate was removed so that cervical dentine thickness in one part of the separated tooth was twice that in the other half. A resin-modified glass-ionomer cement plug was placed in 2-mm thickness from the apical side. Teeth were randomly divided into three groups (n = 12) to be treated with bleaching agents containing 35% hydrogen peroxide, sodium perborate, and distilled water in the control group. Vickers hardness numbers were measured for outer and inner dentine in each tooth sample. Data were analysed using Mann-Whitney U tests.
Results: The mean Vickers hardness number between the two dentine thicknesses showed a statistically significant difference only in the sodium perborate bleaching group (P = 0.000). The mean Vickers hardness number of inner dentine was significantly higher in the small dentine thickness in comparison to the large dentine thickness (P = 0.000). The mean Vickers hardness number of outer dentine was significantly higher in the large dentine thickness in comparison to the small dentine thickness (P = 0.000).
Conclusions: Within the limitations of this laboratory study, even in the presence of an orifice barrier, removal of excessive dentine from the root canal walls during root canal preparation could increase the damaging effect of bleaching materials on outer dentine microhardness.