| Summary: | Objective: To test the hypotheses that blue light accelerates whitening through either (1) direct photobleaching or (2) photon-assisted oxidation using sequential longitudinal bleaching. Methods: Thirty extracted human tooth samples having natural life accumulated color were divided over five groups: A. 9h light + 10h 6% H2O2 gel + 6h light & 6% H2O2 combined; B. 9h 6% H2O2 gel + 10h light + 6h light & 6% H2O2 combined; C. 11 h light & 6% H2O2 combined; D. 8.45h 25 %H2O2 gel + 10h of light only + 6h light & 25% H2O2 combined E. 10.45 h light & 25 %H2O2 combined. Blue light (456nm) was used at 190 mW/cm2. Color change (ΔE) was measured over time, and reported after 48h color stabilization. Results: Groups A, B and D reached saturation in the first phase (at 9h) at a ΔE of 4.3 ± 0.7, 4.9 ± 1.3 and 10.9 ± 2.2, respectively. Groups C and E achieved in the same time a significantly higher ΔE of 14.2 ± 1.7 and 15.6 ± 1.9, respectively. Subsequently adding the opposite single modality to groups A, B and D for 10h did reach an end stage at 8.1 ± 1.3, 8.8 ± 1.8 and 10.8 ± 1.4 ΔE, respectively. The final 6h treatment combining light and H2O2 showed in these groups a statistically significant step in ΔE reaching 12.9 ± 1.4, 10.7 ± 2.5 and 15.3 ± 1.7, respectively. Conclusions: Blue light significantly increases bleaching rate and final achievable ΔE.This sequential whitening study provides a first indication that this enhanced bleaching is the result of the hypothesized light mechanisms acting in parallel to hydrogen peroxide bleaching. Clinical significance: This study shows that blue light can accelerate whitening, within the limits of an in-vitro model. The findings help the clinician explain to their patients that in light accelerated whitening the light not merely accelerates the bleaching process, but that it attacks more stain compounds than peroxide alone does.
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