Effect of a dentifrice containing different particle sizes of hydroxyapatite on dentin tubule occlusion and aqueous Cr (VI) sorption

Abstract

Background: Dentin hypersensitivity is a common negative oral condition that can be treated with dentifrice containing hydroxyapatite (HA). The study evaluated the effect of nano-HA dentifrice on plugging the dentinal tubules for an anti-sensitivity reaction compared to a dentifrice containing common-sized particles. Also, the adsorption capacity of different particle sizes of HA mixed in a dentifrice and which is the optimal particle size was considered.

Methods: Fourty premolar dentine discs and fourty molar dentine discs were randomly divided into 4 groups: distilled water group, ordinary dentifrice group and 80, 300 nm HA dentifrice group. Each dentin disc was brushed with a dentifrice twice daily at 7600 rpm under 100 g force for 2 mins for 7 consecutive days and divided into two parts, half of the dentin disc was detected by the scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), the other half was brushed with distilled water and observed by SEM. One milliliter dentifrice solution (80 nm HA dentifrice, 300 nm HA dentifrice, ordinary dentifrice) was added to 50 ml potassium dichromate solution for 1, 14, and 28 d. The residual Chromium (Cr⁶⁺) concentration in the supernatant was measured by the diphenylcarbon phthalocyanine hydrazine method. The elemental constitution in the precipitate was detected by EDS. The Kruskal-Wallis test was used to analyze surface mineralization and different plugging rates of dentinal tubules. The absorption capacity of dentifrices were also evaluated by the Kruskal-Wallis test.

Results: The plugging rate in the HA dentifrice group was higher than that in the ordinary dentifrice group, and the 80 nm HA dentifrice group showed the best result. The atomic percentages of Ca and P of 80 nm dentifrice group on the surface of dentinal tubules were the highest. The 80 nm HA dentifrice group showed the best adsorption and stable effect of Cr⁶⁺, followed by the 300 nm HA dentifrice group. The 300 nm HA dentifrice and the ordinary dentifrice showed desorption phenomenon.

Conclusions: The dentifrice containing HA, especially the 80 nm HA dentifrice, exerts good dentinal tubule occlusion and surface mineralization effect. This dentifrice was also a good adsorbent of Cr⁶⁺.

Keywords: chromium ion; dentifrice; dentin hypersensitivity; heavy metal ion; nano-hydroxyapatite.

Figure 1

Dentinal tubule occlusion of dentine discs after treatment with a dentifrice for 7 days (SEM, 5000×).

Figure 2

Dentinal tubule occlusion treated by mechanical brushing with distilled water for 7 days (SEM, 5000×).

Figure 3

The plugging rates of dentinal tubules treated with a dentifrice for 7 days (Molar group: χ²=59.430, P=0.000; Premolar group: χ²=57.147, P=0.000; *P<0.05).

Figure 4

Dentinal tubules after mechanical brushing with distilled water for 7 days (Molar group: χ²=52.585, P=0.000; Premolar group: χ²=56.314, P=0.000; *P<0.05).

Figure 5

Atomic percentages of calcium and phosphorus in dentin in the molar group (Ca: χ²=33.244, P=0.000; P: χ²=33.518, P=0.000; *P<0.05).

Figure 6

Atomic percentages of calcium and phosphorus in dentin in the premolar group (Ca: χ²=33.637, P=0.000; P: χ²=33.855, P=0.000; *P<0.05).

Figure 7

Adsorption capacity of a dentifrice. (A) Adsorption capacity of a dentifrice for Cr⁶⁺ at 1 day. (B) Adsorption of Cr⁶⁺ by the 80 nm HA dentifrice at 1, 14, and 28 days. (C) Adsorption of Cr⁶⁺ by the 300 nm HA dentifrice at 1, 14, and 28 days. (D) Adsorption of Cr⁶⁺ by an ordinary dentifrice at 1, 14, and 28 days.

Figure 8

EDS spectra before and after dentifrice adsorbed Cr⁶⁺. The horizontal axis represents the value of the voltage (keV) at which different elements can be excited. The findings comparing between before/after diagrams for each group showed that there was chromium in the powder which was further confirmed that the HA dentifrice could adsorb Cr⁶⁺.