Efficacy and Characterization of Violet LED Light for In-office Bleaching

Objectives: This study evaluated color and morphology of tooth submitted to violet LED light (LED) associated or not with 35% hydrogen (HP) or 37% carbamide peroxide (CP) and analyzed light irradiance and light transmission (LT) through enamel.
Methods: Bovine crowns were stained with black-tea solution for 24h and submitted to (n=10): LED; LED with HP (LED/HP); LED with CP (LED/CP); HP; CP or remained untreated (C). Bleaching with LED consisted of twenty 1-min irradiations; bleaching with HP or CP was carried out for 30min, and all gel-containing protocols were performed in three appointments and LED in 10 sessions. Samples were stored in artificial saliva (AS) among intervals and C remained in AS. Color alteration (ΔE) was determined using a spectrophotometer, after staining (T_s), after bleaching (T_b), 7 (T₇) and 14 (T₁₄) days elapsed from bleaching. Data were analyzed (ANOVA, Tukey test, α=5%) and enamel morphology was observed under scanning electron microscopy (SEM, n=3). LED irradiance was evaluated at 0 and 8mm from the light source and LT was determined through 1.0mm thick enamel samples (n=5), by means of a fiberoptic spectrometer and a spectral radiometer, respectively.
Results: LED/HP and LED/CP were similar (p>0.05) and exhibited higher ΔE than LED (p<0.05), regardless the evaluation time. LED/CP promoted higher ΔE than CP (p<0.05), irrespective to time. Morphological alterations promoted by HP and CP were not affected by LED application, and LED irradiance decreased 50% at 8 mm-tip to target distance, after twenty irradiations. In addition, LT though 1mm-thick enamel was reduced in 97.7%.
Conclusions: Violet LED bleaching with HP or CP was more effective than violet LED alone; still, LED enhanced CP efficacy. Furthermore, violet LED is unable to deliver power and propagate into 1-mm thick enamel and LED irradiance decreased at the end of bleaching therapy.