Dynamic Model of Hydrogen Peroxide Diffusion Kinetics into the Pulp Cavity

Aim: To measure the time course hydrogen peroxide penetration into the pulp cavity and evaluate short-term tooth color changes after bleaching. Materials and methods: Twenty extracted human canineswere sectioned, pulp tissue removed and the cavity enlarged. Teeth were painted with nail varnish to leave a 6-mm diameter circle on the buccal surface. Baseline color was measured spectrophotometrically. Teeth were randomized into a control group (n = 10) treated with 30 μl of glycerin base and a bleaching group (n = 10) exposed to 30 μl of 40% hydrogen peroxide for 1 hour. A linear low densitypolyethylene wrap was placed to prevent evaporation of the material. Acetate buffer was placed into the cavity and replenished every 10 minutes and placed into plastic tubes. Hydrogen peroxide amount was estimated spectrophotometrically using leukocrystal violet and horseradish peroxidase. Specimen color was remeasured immediately after bleaching, 1 hour, 1 day 1, 2 and 6 weeks postbleaching. Color change was measured per Commission Internationale de l'Eclairage methodology. Mann-Whitney procedure was used to assess baseline color measurements and total hydrogen peroxide penetration amount. Friedman's test was used to assess within group differences for color change and hydrogen peroxide penetration. Results: There was significantly greater hydrogen peroxide penetration in the bleaching group (p < 0.05).Hydrogen peroxide penetration levels were constant throughout the 1-hour evaluation periodin the bleaching group. The groups showed no difference at baseline with respect to any of L*a*b color measurements (p > 0.05). The postbleaching color measurement showed an increase of change in overall color (δE) and lightness (δL) up to 1 week followed by a gradual stabilization up to 6 weeks. Conclusion: This dynamic model provided information about the time course diffusion kinetics into the pulp cavity, demonstrating constant penetration of hydrogen peroxide into the pulp cavity during a 1-hour bleaching session. Clinical significance: A prolonged application of 40% hydrogen peroxide bleaching materialfor 1 hour produces constant penetration of hydrogen peroxide into the pulp cavity in vitro.