Effects of the Ratio between Pigment and Bleaching Gel on the Fracture Resistance and Dentin Microhardness of endodontically treated Teeth

Fracture strength and hybrid layer formation of endodontically-treated teeth after dental bleaching photoactivated with violet LED

OBJECTIVE

To evaluate in vitro the effect of dental bleaching using high concentration hydrogen peroxide (HP) photoactivated with violet LED on fracture strength and hybrid layer formation.

METHODS

forty endodontically-treated bovine teeth were randomized into four groups (n = 10): C - Control, HP - 35% hydrogen peroxide, HP-BL - 35% hydrogen peroxide photoactivated with blue LED, HP-VL - 35% hydrogen peroxide photoactivated with violet LED. Three bleaching sessions with an interval of 7 days between them were performed. After 10 days of the last bleaching session, the dental crowns were restored and submitted to the fracture strength test. Five specimens from each group were used to evaluate the hybrid layer formation by scanning electron microscope (SEM) images. One-way ANOVA and Kruskal-Wallis test were used for parametric and non-parametric data, respectively. Significance level of 5% was adopted to all the tests.

RESULTS

No differences on fracture strength among the groups were observed (p > 0.05). HP and HP-BL showed alterations on hybrid layer formation compared to C group (p < 0.05), but not for HP-VL (p > 0.05). No differences on hybrid layer formation were observed among HP, HP-VL and HP-BL groups (p > 0.05).

CONCLUSION

Dental bleaching, photoactivated or not, did not affect the fracture strength of endodontically-treated teeth. Regardless of the protocol used, hydrogen peroxide altered the hybrid layer formation at some level when the restoration was placed after 10 days of the last bleaching session.

Effect of non-vital tooth bleaching photoactivated with blue or violet LED on color and microhardness

BACKGROUND

To evaluate the efficacy of non-vital dental bleaching protocols using 35% hydrogen peroxide photoactivated with violet LED on color and microhardness of endodontically treated teeth.

METHODS

Forty specimens were selected and randomized into 4 groups (n = 10): C - Control, HP - 35% hydrogen peroxide, HP + BL - 35% hydrogen peroxide + blue LED, HP + VL - 35% hydrogen peroxide + violet LED. Three bleaching sessions were performed for each group. Color analysis was performed 7 days after each bleaching session. Two-way repeated measure ANOVA and Bonferroni test were used to evaluate the effect of different bleaching protocols and evaluation times on the dependent variables (∆E and ∆L). Dentin microhardness was measured 24 hours after the third bleaching session. Data were evaluated by ANOVA and Tukey's test at a significance level of 5%.

RESULTS

Differences on ∆E and ∆L were verified after the first and second bleaching sessions (p < 0.05) and showed stability after the third one, for all the groups. No differences were observed among HP, HP + BL, and HP + VL groups, regardless of the evaluation time (p > 0.05). HP and C showed the greatest and smallest reduction in dentin microhardness (p < 0.05), respectively. No difference between HP + BL and HP + VL protocols (P > 0.05) was observed.

CONCLUSIONS

High concentration hydrogen peroxide (35%) photoactivated with violet LED bleached endodontically treated teeth effectively. However, the same protocol negatively affected the dentin microhardness, but not in the same level of 35% HP solely used.