How peroxide interacts with enamel proteins and porosity

The three parts of the process

Tooth whitening with peroxide-based materials is described as a dynamic process. It involves movement of the agent into the tooth, interaction with stain molecules, and micromorphologic alterations on the surface and within the structure that affect optical properties.

Kwon and Wertz described it this way: the process involves diffusion of the whitening material to interact with stain molecules and also involves micromorphologic alterations on the surface and changes within the tooth that affect its optical properties.

The interaction is not limited to stain molecules. It is an affinity-based process that also accompanies effects on sound enamel and dentin structures.

The job of the peroxide is to oxidize organic chromogens so they become less colored. At the same time, the molecule does not ignore the organic fraction that remains in mature enamel.

What a 2025 study measured

A 2025 paper by Eric and colleagues examined how hydrogen peroxide treatments affect enamel porosity and protein structure, and tracked shade and hardness over time. They incubated extracted teeth in 30 % hydrogen peroxide or distilled water, then measured shade, microhardness, surface area, and protein conformation.

In the short term, HP treatment significantly increased lightness. One week after treatment some of the initial gains in tooth lightness were partially lost. Hardness decreased in the bleached group. HP treatment increased enamel surface area and reduced its average pore size. Proteins from HP-treated teeth mostly adopted a non-random conformation and had smaller average protein sizes.

HP treatment lightened tooth shade and significantly reduced enamel microhardness over time. This could be related to changes in surface area and porosity caused by denaturalization of the enamel proteins. HP induced denaturation of enamel proteins, resulting in increased enamel porosity and reduced microhardness. These changes could help explain clinical complications observed with these treatments such as increased sensitivity.

This is an in-vitro study on extracted teeth using a high concentration. It does not describe at-home products or claim that every protocol produces the same degree of change. It does show that peroxide can alter the organic matrix that remains in enamel, and that the resulting porosity and hardness shifts can be measured.

The longer literature on surface effects

Not every study finds the same degree of change. Joiner’s 2007 review concluded that the majority of studies indicate that peroxide containing products and solutions have no significant deleterious effects on enamel and dentine surface morphology and chemistry, surface microhardness, subsurface enamel and dentine microhardness or ultrastructure.

Contrasting studies often have methodological limits or use particularly low-pH solutions in which acid erosion can dominate the observed changes.

The two pictures are compatible. Most properly buffered, time-limited exposures do not produce large, lasting mineral loss. At the same time, the organic fraction can be altered, surface area can increase, and optical properties can shift for reasons beyond simple chromogen bleaching. Partial rebound of lightness within a week is consistent with ongoing surface reorganization and with the reformation of the acquired pellicle that binds new chromogens.

What this means after a session

A typical session is ten minutes. During that window the gel is in contact with the enamel surface. After the session ends, residual gel and any loosened surface film are still present. The temporary increase in accessible surface area means chromogens from the next beverage can bind more readily until the pellicle stabilizes and mechanical cleaning removes the outer film.

The practical consequence is mechanical and temporal, not a claim that the enamel has been permanently altered. Clear the surface after the session. Avoid immediate high-chromogen or acidic drinks while the outer film is reforming. Brush and floss as usual later in the day; the goal is to keep the new shade position from being covered by a fresh pellicle loaded with pigments.

Sensitivity that appears during or after a session is often discussed in the literature as related to peroxide reaching the pulp or to transient changes in the outer layers. The findings link the porosity and protein changes to that clinical observation. It does not diagnose a condition or prescribe a treatment. If sensitivity is more than a short zinger, the standard advice is to pause and speak with a dentist.

Limits of the evidence

The Kwon and Wertz review and the Joiner review are literature syntheses. The Eric study is a controlled in-vitro experiment on extracted teeth. None of them is a clinical trial of a specific at-home kit. Optical improvement and any hardness or porosity shifts are measured under laboratory conditions that do not fully replicate saliva flow, pellicle formation, or daily mechanical cleaning.

What the sources do show is that whitening is not a pure surface bleach of external stains. Peroxide diffuses, interacts with organic material including residual enamel proteins, and can leave measurable temporary changes in porosity and hardness that coincide with the shade change. Those changes help explain why shade can drift and why surface care after each session matters.

The same sources also show that the majority of studies find no large deleterious effect on mineral structure when pH and exposure are controlled. The distinction between temporary organic and porosity shifts and lasting mineral damage is the one the literature continues to draw.

References

1. Kwon SR, Wertz PW. Review of the mechanism of tooth whitening. Journal of Esthetic and Restorative Dentistry. 2015;27(5):240-257. https://doi.org/10.1111/jerd.12152 https://pubmed.ncbi.nlm.nih.gov/25969131/
2. Joiner A. Review of the effects of peroxide on enamel and dentine properties. Journal of Dentistry. 2007;35(12):889-896. https://doi.org/10.1016/j.jdent.2007.09.008 https://pubmed.ncbi.nlm.nih.gov/17964705/
3. Eric J, Ciobanu O, Abdallah MN, et al. The effect of hydrogen peroxide treatments on dental enamel porosity and protein structure and its long-term implications on tooth hardness and optical properties. Journal of Dentistry. 2025;156:105714. https://doi.org/10.1016/j.jdent.2025.105714 https://pubmed.ncbi.nlm.nih.gov/40132790/