Evaluation of Enamel Acid Resistance and Whitening Effect of the CAP System

Abstract

This study aimed to compare the effectiveness of a novel professional tooth-strengthening system and a conventional caries-prevention method that involved the use of high fluoride concentrations, to determine whether the system has a whitening effect. Bovine tooth-enamel samples were treated with fluoride gel (conventional APF method) or a mixture of citric acid gel, calcium phosphate (α-TCP), and fluoride gel, referred to as the CAP system; these treatments were performed to generate an acid-resistant layer on the enamel surface. For the evaluation of the acid resistance, a cyclic experiment, involving a 1-h remineralization and a 24-h acid treatment, was conducted thrice after the treatments. The height profiles were observed using a 3D-measuring laser microscope and the hardness was evaluated by Vickers hardness test. The morphological changes in the surface and cross-section of the enamel were observed by scanning electron microscopy. To evaluate the whitening effect, the enamel was ground until the color of the underlying dentin was recognizable; the CAP system was applied once, and the color change was measured using a color difference meter. As a result, it was confirmed that an acid-resistant layer was formed on the tooth surfaces treated with the CAP system, and a whitening effect was obtained.

Improved Enamel Acid Resistance Using Biocompatible Nano-Hydroxyapatite Coating Method

“…Soares et al performed a micro-energy dispersive X-ray fluorescence analysis after applying nHAp and APF gels to the enamel and found that the nHAP-treated group had higher calcium and phosphorus contents than the APF group [ 31 ]. The coatings in our study are consistent with those observed in previous studies; moreover, the thickness in the BioHap group was greater than those observed in previous studies ( Figure 4 f) [ 24 , 31 , 32 , 33 ]. The coating layer is expected to physically protect the tooth surface from acid, and it has been reported to suppress tooth demineralization [ 37 , 38 ].…”

“…In addition, the Ld in the BioHap group was approximately half of that in the control group ( Figure 7 b). The demineralization pattern in the APF group is consistent with those observed in previous studies; however, localized demineralization under the coating layer, such as that in the BioHap group, has not been observed in previous studies [ 24 ]. The CMR image of the BioHap group quantitatively clarified that demineralization did not extend to deep layers in the BioHap group; instead, it was observed just below the coating layer and enamel surface.…”

“…2020-105060 and 2020-117423, Figure 1 F). Previous studies that have employed combinations of α-TCP and fluoride have reported the formation of very thin coatings of 1–2 μm on the enamel surface layer, but the thick coating layer in this study has not been observed [ 24 , 31 , 32 , 33 ]. Thus, the small particle size and large surface area of BioHap might affect the formation speed and thickness of the coating layer.…”

“…With respect to the formation mechanism of the coating layer, Miki et al considered that the calcium ions released from α-TCP mix with citric acid combined with fluoride ions to precipitate CaF 2 [ 24 ]. Huang et al reported that calcium phosphates, such as dicalcium phosphate dihydrate and octacalcium phosphate, are produced along with CaF 2 [ 29 , 40 ].…”

“…The method employed by Miki et al was used to apply BioHap to the tooth surface enamel [ 24 ]. After ionizing some crystals on the surface by applying citric acid gel (5% citric acid, 0.01% malic acid, 5% glycerin, 3% tamarind gum, pH 3.0; AIWA Co., Ltd., Osaka, Japan), BioHap (25 g, BIOAPATITE Inc., Shiga, Japan) and citric gel were mixed in a 1:2 weight ratio and applied to the surface ( Table 1 ).…”