Design Principles for Oxidative Tooth Whitening: The Addition of Light
The influence of light in enhancing oxidation processes has been well known for centuries – the process is called photooxidation. This process is responsible for the degradation of polymers in industrial applications (e.g., automobile dashboards) as well as fading of dyes in various plastic products.
Some authors have reported improvements in whitening efficiency with the use of various light activation systems.85 However, it is fair to say that the performance of light activated bleaching has been controversial. Some light activated in-office bleaching systems have been criticized for patient tolerability and efficacy in improving bleaching performance.86-96 It is likely that some of the original light activated systems were not fine-tuned for the proper intensity or wavelengths to activate bleaching and may have relied on simple heating to enhance bleaching. Oxidation reactions are quite sensitive to temperature – although heat activation may negatively influence the response of dental pulps.97-99
Overall, light sources can act to enhance oxidative processes; this is the principle of photooxidation. Certainly, technological advancements in the field of marketed light activated systems have become more fine-tuned in choice of wavelength and intensity. In addition, most of the light activated systems have been employed in office settings where short-term high-efficacy bleaching is carried out at ultra-high concentrations of peroxide. Under these conditions it may be difficult to readily observe any improvements in whitening performance. It is possible that the acceleration of whitening with bleach is better suited to application in lower-concentration bleaching settings, including recently introduced light activated home tooth bleaching.
In photo-oxidation (light enhanced) molecules absorb light energy, once a stain molecule absorbs a sufficient amount of energy its electrons reconfigure and it becomes easier for the peroxide to remove them from the molecule, rendering it colorless. For light to be effective peroxide has to be in close proximity to the stain molecule. For this reason, it is best to optimize and protect diffusion time to the chromogen stain first before applying the light (i.e., apply light at the end of the treatment, after diffusion).