Blue Light Bleaches Additional Classes of Chromophores in Tooth Whitening

Objectives: The merits and mechanisms of visible light accelerated whitening (LAW) are still controversial. Two mechanisms of LAW are hypothesized:
- Photo bleaching (light only).
- Photon-assisted oxidation (light and oxidizers).
In order to study LAW mechanisms, extracted human teeth are bleached separating hydrogen peroxide, blue light and the combination in time, using long treatment times to obtain end stage whitening levels for each modality.
Methods: Treatment groups (n=6):
A. 9h light only + 10h 6% H₂O₂ gel only + 6h light & 6% H₂O₂ combined
B. 9h 6% H₂O₂ gel only + 10h light only + 6h light & 6% H₂O₂ combined.
C. 10 h light & 6% H₂O₂ combined (Philips Zoom! Whitespeed LED Accelerator).
DeltaE (±SD) was measured over time using spectroscopy.
Results: Groups A & B reached saturation in the first 9h at a DeltaE of 4.3±0.7 and 4.9±1.3, respectively. Group C did achieve in the same time a DeltaE of 14.2±1.7, a statistically significant improvement. Subsequently adding the opposite single modality to groups A and B for 10h did reach an end stage for these modalities at 8.1±1.3 and 8.8±1.8 DeltaE, respectively. The final 6h treatment combining light and H₂O₂ showed in both groups a statistically significant step in DeltaE, reaching 12.9±1.4 and 10.7±2.5, respectively.
Conclusions: Only a sub-section of the naturally occurring chromophores in teeth can be addressed with H₂O₂ alone. LAW bleaches two additional classes of chromophores:
- Chromophores susceptible to light only, but not to oxidation by H₂O₂.
- Chromophores resistant to either H₂O₂ alone, or light alone, but susceptible to combining H₂O₂ and light.
The total efficacy of LAW is therefore the sum of H₂O₂ oxidation, photo bleaching and photon-assisted oxidation, leading in this extracted tooth study to a 2.9 fold increase in DeltaE of LAW over 6% H₂O₂ alone.