Dynamic Model of Hydrogen Peroxide Diffusion-Kinetics into the Pulp Cavity

Objectives: To measure the time course hydrogen peroxide penetration into the pulp cavity, and evaluate tooth color changes after bleaching over different time periods. 

Methods: 20 extracted human canines were sectioned above the CEJ, pulp tissue removed and cavity enlarged. Teeth were painted with nail varnish to leave a 6mm diameter circle on the buccal surface. Baseline color was measured spectrophotometrically; 25μl acetate buffer was added into the cavity. Teeth were randomized into a control group (n=10) treated with 30μl glycerin base and an experimental group (n=10) exposed to 30μl 40% hydrogen peroxide for 1 hour. A linear low density polyethylene wrap was placed to prevent evaporation of material. Acetate buffer was removed from the cavity and replenished every 10 minutes and placed into tubes. Hydrogen peroxide amount was estimated spectrophotometrically using leucocrystal violet and horseradish peroxidase. Specimen color was re-measured immediately after bleaching, 1hour, 1 day and 1week post-bleaching. 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.

Results: The groups showed no difference at baseline with respect to any of L*a*b color measurements (p>0.05); there was significantly greater hydrogen peroxide penetration in the experimental group (p<0.05). Hydrogen peroxide penetration levels were constant throughout the one-hour evaluation period in the experimental group. The post-bleaching color measurement showed an increase of the overall color change (ΔE) up to one week in the experimental group and an initial increase followed by a decrease at one week in the control group. 

Conclusions: This dynamic model provides information about the time course diffusion kinetics into the pulp cavity, demonstrating constant penetration of hydrogen peroxide into the pulp cavity during a one-hour bleaching session.

Acknowledgement: Bleaching materials were kindly provided by Ultradent Products, Inc.