The influence of the renewal or the single application of the peroxide gel on the efficacy and tooth sensitivity outcomes of in-office bleaching-A systematic review and meta-analysis.

OBJECTIVE: To answer the question: "Does the peroxide gel application regimen (single application vs. renewal) influence the efficacy and the tooth sensitivity outcomes of in-office tooth bleaching?" METHODS: The search was done in Pubmed, Cochrane, LILACS, Scopus, Web of Science, and EMBASE in February 2021 (updated in July 2021). Randomized clinical trials (RCT) comparing the single application vs. the renewal protocols of HP were included. The meta-analyses were performed for the objective (ΔEab ), subjective (ΔSGU) color changes, and absolute risk of tooth sensitivity (TS). Heterogeneity was evaluated using Q test (I2 ). Cochrane Collaboration tool assessed the risk of bias (RoB). The GRADE evaluated the certainty of evidence. RESULTS: Five RCT studies remained. Two studies showed high RoB, and three presented some concerns. No significant differences were observed between the protocols in terms of the ΔEab , ΔSGU, and TS. ΔEab exhibited substantial heterogeneity (I2  = 87%), while ΔSGU (I2  = 60%) and the TS (I2  = 62%) presented a moderate one. The certainty of evidence was considered low or very low, depending on the variable response and the evaluation time. CONCLUSION: The application regimen (single vs. renewal of HP) did not impact color change or the absolute risk of TS. CLINICAL SIGNIFICANCE: The renewal of bleaching gel during the in-office appointment may not be necessary. However, there is at least a low certainty of evidence. Because of this, further randomized clinical trials with appropriate methodology on this topic are encouraged.

Effects of dental bleaching protocols with violet radiation on the color and chemical composition of stained bovine enamel.

OBJECTIVES: To evaluate the bleaching efficacy of a violet radiation (VR) combined or not with bleaching gels on the color and mineral content of stained teeth. MATERIAL AND METHODS: Enamel/dentin blocks were obtained and stained (n = 50) with coffee, red wine, tobacco smoke, or were left non-stained. The stained or not-stained blocks (n = 10) were distributed into five bleaching groups (n = 10): VR, CP (37 % carbamide peroxide), VR/CP, HP (35 % hydrogen peroxide), and VR/HP. Color (ΔE00, ΔL, Δa, and Δb) and whiteness index (ΔWID) changes were evaluated after staining and after bleaching using a spectrophotometer. Calcium (Ca), phosphorous (P), and Ca/P contents (in wt%) were measured after bleaching using energy-dispersive X-ray spectroscopy (EDS). Data was statistically analyzed (α = 0.05) using two-way ANOVA and Tukey tests (ΔE00, ΔWID, ΔL, Δb, wt%) or Kruskal-Wallis and Dunn tests (Δa). RESULTS: VR alone caused higher colorimetric changes on coffee, tobacco and red wine-stained groups compared to non-stained enamel (p < 0.05). VR/CP exhibited higher colorimetric changes compared to CP in coffee and non-stained groups. The VR/CP, HP and VR/HP groups exhibited no change differences (p > 0.05). No differences were observed for the wt% of Ca, P and Ca/P between the groups. CONCLUSIONS: The violet radiation was more effective in bleaching stained rather than non-stained teeth. VR combined with 37 % carbamide peroxide was as effective as the HP agent. Besides, no adverse effects could be observed in the enamel mineral content, regardless of the bleaching protocol tested, according to the EDS semi-quantitative analysis.