A Study for Tooth Bleaching via Carbamide Peroxide-Loaded Hollow Calcium Phosphate Spheres

Abstract

The objective of this study was to investigate if a prolonged bleaching effect of carbamide peroxide-loaded hollow calcium phosphate spheres (HCPS) can be achieved. HCPS was synthesized via a hydrothermal reaction method. Carbamide peroxide (CP) was-loaded into HCPS by mixing with distilled water as solvent. We developed two bleaching gels containing CP-loaded HCPS: one gel with low HP concentration as at-home bleaching gel, and one with high HP concentration as in-office gel. Their bleaching effects on stained human permanent posterior teeth were investigated by measuring the color difference before and after bleaching. The effect of gels on rhodamine B degradation was also studied. To investigate the potential effect of remineralization of using HCPS, bleached teeth were soaked in phosphate buffer solution (PBS) containing calcium and magnesium ions. Both bleaching gels had a prolonged whitening effect, and showed a strong ability to degrade rhodamine B. After soaking in PBS for 3 days, remineralization was observed at the sites where HCPS attached to the teeth surface. CP-loaded HCPS could prolong the HP release behavior and improve the bleaching effect. HCPS was effective in increasing the whitening effect of carbamide peroxide and improving remineralization after bleaching process.

Keywords: calcium phosphate; remineralization; spheres; tooth bleaching.

Figure 1

SEM images and XRD pattern of hollow calcium phosphate spheres synthesized by hydrothermal method. (A) Spheres dried at 60 °C for 2 h after synthesis; (B) Spheres loaded with hydrogen peroxide for 2 h; (C) X-ray diffraction pattern of (A), which indicates that the composition of spheres is magnesium substituted calcium phosphate.

Figure 2

Hydrogen peroxide release profiles from (A) CP-loaded HCPS and (B) modified CP-loaded HCPS. (A) 0.5 g spheres, 2.475 g CP, and 9.5 mL water were mixed with stirring for 2 h at room temperature; (B) 0.5 g spheres, 2.475 g CP, 0.5 g 35% HP (total mole ratio of HP: urea = 1.2:1), and 9.5 mL water mixed with stirring for 2 h at 9 °C.

Figure 3

Example of the effect of 45 min bleaching in-office and 24 h after bleaching procedure and wet storage (digital camera).

Figure 4

Examples of bleaching effect after 45 min bleaching by at-home bleaching gel.

Figure 5

Rhodamine B degradation profile (average and standard deviation) via (A) at-home gel and (B) in-office gel. Each 0.5 g gel was placed in 10 mL 0.5 M rhodamine B solution for 250 min. For each gel, n = 3.

Figure 6

Morphology of bleached teeth surface after being rinsed in 2 mL phosphate buffer solution (PBS) at 37 °C for 0 days (A,C) and 3 days (B,D). (A,B) and (C,D) were bleached by at-home gel and in-office gel, respectively.