Effectiveness and Relapse of Tooth Whitening During Orthodontic Therapy: A Six-Month in vitro Assessment

Objective: This in vitro study evaluated the effectiveness and relapse of whitening performed during active orthodontic treatment in comparison to whitening performed in non-bracketed teeth. Materials and Methods: Eighty human premolar teeth extracted for orthodontic reasons were randomly divided into four groups: (1) control, (2) bleached without brackets, (3) brackets without bleaching, and (4) brackets with bleaching. The teeth in Groups 3 and 4 were bonded using metal brackets and teeth in Groups 2 and 4 were fitted for single-unit customized bleaching trays. Whitening procedures were then performed on teeth in Groups 2 and 4 with 10% carbamide peroxide for 8 hr/day for 14 days. Upon completion of the whitening procedure, brackets were removed from all bonded teeth, followed by the removal of the adhesive resin excess on the tooth surface. Quantitative tooth shade measurements were taken for all teeth with a digital spectrophotometer (L*a*b* system) at baseline, post-whitening, one month post-whitening, and six months post-whitening. Results: significant mean differences of ΔE* where found between Group 2 and Group 4, p-value < 0.001. After the tooth whitening procedure, both groups were significantly lighter than at baseline and also significant decreases in a* and b* values were observed. Higher differences were shown in Group 2 with a mean ΔE* value of 8.02 post-whitening, while in Group 4 the mean ΔE* value was 4.00 post-whitening when compared to the baseline. Group 2 and Group 4 also showed statistically significant differences at one month and six months after the tooth whitening process (ΔE*, Δa* and Δb*), p < 0.05. Long-term evaluation, showed a relapse for the lightness (ΔL*) in both groups at six months post-whitening when compared to baseline. However, the teeth in Group 2 showed to be lighter six months post-whitening, while the teeth in Group 4 went back to their initial brightness when compared to baseline. Conclusions: Nightguard vital bleaching technique using 10% carbamide peroxide was effective, lightened the shade of teeth even when the whitening is performed during active orthodontic treatment. However, the long-term stability may not be achieved when teeth are whitened with orthodontic brackets.