Basic Research for New Tooth Whitening Applied the Powder Jet Deposition

Abstract

The powder jet deposition (PJD) process is used for creation of hydroxyapatite (HA) layers on human teeth. The fabricated HA layers showed excellent microstructural and mechanical properties in vitro and in vivo. Titanium dioxide (TiO 2) changed the whiteness of the layers because of the selective reflection of light. This raises the possibility that TiO 2-HA layer deposition may improve new whitening treatment for discolored teeth. For the development of new tooth whitening by PJD, the microstructural and mechanical properties of the TiO 2-HA layers, particularly the effects of thermal stress, the color change obtained, and the color stability of the layers after thermal cycling were evaluated. Materials and Methods: The microstructural properties of the TiO 2-HA layers, namely surface thickness and roughness were evaluated from scanning electron microscopy (SEM) images and three-dimensional profiles. The mechanical properties were evaluated by micro-Vickers hardness and bonding strength tests. For color differences and stability, the CIE L*a*b* color system was used, and ΔE* values were calculated before and after the fabrication of the TiO 2-HA layers. For visual color evaluation, images of specimens were taken with a digital camera. Furthermore, these material properties and color differences were evaluated before and after 500 thermal cycles (5-55 °C). Results and Discussion: The TiO 2-HA particles were packed densely in the layers, the maximum thickness of layers was about 60 µm. There were no significant differences in surface roughness, hardness, or bonding strength before and after the thermal cycling. Moreover, these properties were equivalent to those of HA layers fabricated by PJD. The TiO 2-HA layers had increased L* and decreased b* parameter compared with those of the enamel substrates, and the color difference ΔE* was about 6.7 units, indicating that TiO 2-HA layers whitened the color of the treated tooth. Furthermore, it was confirmed from digital camera images that TiO 2-HA layers showed visually perceptible level of whiteness. This color was maintained even after thermal cycling. Conclusion: The fabrication of TiO 2-HA layers by PJD may be a suitable new whitening treatment for discolored teeth.