Enhanced Protective Effect of Ion-Releasing S-PRG Coatings Containing Theobromine

Objectives: This study investigated protective effects of tooth coatings materials containing theobromine and/or a Surface Pre-Reacted Glass (S-PRG) filler (PRG Barrier Coat™, Shofu Inc.), by measuring acid buffering and hardness changes of enamel and dentin in artificial saliva.
Methods: 1) Materials: Four tooth coating materials – containing [i] S-PRG filler, [ii] S-PRG filler and 5.0% theobromine, [iii] silica filler and 5.0% theobromine and [iv] silica filler, were used.
2) pH measurement: Disks cured coating materials for each group (n=5) were incubated in buffered lactic acid (pH 4.0) for 1-6 day, and pH was monitored.
3) Hardness: Extracted human molars were prepared with flatened enamel and root dentin surfaces. Tooth coatings were applied to flattened surfaces, and light cured (n=5 per group). These specimens were placed in artificial saliva for 4 weeks. Specimen hardness was tested at three sites of coated enamel and dentin using Rockwell superficial hardness, before and after placing in artificial saliva. Data were evaluated by one-way ANOVA and Fisher’s PLSD test (α=0.05).
Results: After 6 days, the buffer pH for each group was; [i]: 6.80±0.07, [ii]: 6.86±0.05, [iii]: 3.74±0.06, [iv]: 3.64±0.04. Mean percent change (Δ%) in hardness (enamel/dentin) for each group were; [i]: 2.64±0.36/3.56±1.12, [ii]: 5.56±2.30/7.39±1.57, [iii]: 3.34±1.00/5.34±0.94, [iv]: -1.32±2.14/0.72±1.68, [control (uncoated)]: -1.51±1.93/0.36±1.28. Hardness increased significantly (p<0.05) with all but groups [iv] and control.
Conclusions: The coating materials containing S-PRG filler neutralize lactic acid, while the buffer pH shifted to lower values with the materials without S-PRG filler. Both theobromine and S-PRG filler increase enamel and dentin hardness, with greater increase observed when S-PRG and theobromine are combined. The ability of theobromine to increase HAp crystalline size may provide an added protective benefit for ion-releasing/remineralizing, topical treatments.