Effect of different intracoronal bleaching agents on tubule radius, microhardness and mineral content of crown dentin exposed to irrigation solutions

Hydrogen peroxide 35% (HP), carbamide peroxide 37 % (CP) and sodium perborate (SP) are the most common intracoronal bleaching agents used in internal bleaching which has become an important treatment modality in discolored teeth after regenerative procedures. Similar dimensioned 240 dentin sections were obtained from 60 intact human mandibular molar crowns. Samples were randomly divided into 2 groups according to the root canal irrigation exposure. Half of the samples (120) were exposed to root canal irrigants (10 ml NaOCl %2,5 for 20 minutes, 3 ml EDTA %17 for 3 minutes). Then samples were further divided into 6 sub-groups (n=20) according to the bleaching agents used: SP, CP, HP, SP+CP, SP+HP and no bleaching as a negative control group. Samples were treated with respective bleaching agents, then they were isolated with PTFE tape and stored for 2 weeks. On day 7, bleaching agents were renewed. All samples were stored at 25°C in saline. Vickers microhardness values were measured before and after the bleaching procedure. Samples were inspected under SEM for tubule radii and mineral content. Data was statistically analyzed. Irrigation alone did not influence the microhardness values of samples (p > .05). Treatment with SP, SP+CP, CP, and SP+HP significantly increased the microhardness values of samples regardless of the final irrigation regimen (p < .05). Microhardness values of irrigated/SP + CP treated samples were statistically higher than not-irrigated/SP + CP treated samples (p < .05). There was no significant difference among the bleached groups in terms of tubule radii except the HP group, although irrigated samples had significantly increased radii (p < .05). There was no significant increase in mineral values( Ca, P and Ca/P) of the bleached test subgroups when compared with non-bleached control groups (p > .05) but all surface mineral values were statistically higher among irrigated samples .