Abstract
Many revolutionary approaches are on the way pertaining to the high occurrence of tooth decay, which is an enduring challenge in the field of preventive dentistry. However, an ideal dental care material has yet to be fully developed. With this aim, this research reports a dramatic enhancement in the rehardening potential of surface-etched enamels through a plausible synergistic effect of the novel combination of γ-polyglutamic acid (γ-PGA) and nano-hydroxyapatite (nano-HAp) paste, within the limitations of the study. The percentage of recovery of the surface microhardness (SMHR%) and the surface parameters for 9 wt% γ-PGA/nano-HAp paste on acid-etched enamel were investigated with a Vickers microhardness tester and an atomic force microscope, respectively. This in vitro study demonstrates that γ-PGA/nano-HAp treatment could increase the SMHR% of etched enamel to 39.59 ± 6.69% in 30 min. To test the hypothesis of the rehardening mechanism and the preventive effect of the γ-PGA/nano-HAp paste, the surface parameters of mean peak spacing (Rsm) and mean arithmetic surface roughness (Ra) were both measured and compared to the specimens subjected to demineralization and/or remineralization. After the treatment of γ-PGA/nano-HAp on the etched surface, the reduction in Rsm from 999 ± 120 nm to 700 ± 80 nm suggests the possible mechanism of void-filling within a short treatment time of 10 min. Furthermore, ΔRa-I, the roughness change due to etching before remineralization, was 23.15 ± 3.23 nm, while ΔRa-II, the roughness change after remineralization, was 11.99 ± 3.90 nm. This statistically significant reduction in roughness change (p < 0.05) implies a protective effect against the demineralization process. The as-developed novel γ-PGA/nano-HAp paste possesses a high efficacy towards tooth microhardness rehardening, and a protective effect against acid etching.
Highlights
Dental enamel, the hardest tissue of the human body, comprises nanoscale hydroxyapatite (HAp) forming the major mineral portion [1,2], with a parallel arrangement of enamel prisms [3,4,5]
To prepare the tooth-repairing paste, 0.27 g γ-polyglutamic acid (γ-PGA) was first dissolved in 5 mL DI water, 0.50 g nano-HAp was added to the solution and stirred overnight
The microhardness of the sound sample was found to be 361.16 ± 9.21 Vickers hardness number (VHN), which reduced to 218.41 ± 6.87 VHN after acid-etching
Summary
The hardest tissue of the human body, comprises nanoscale hydroxyapatite (HAp) forming the major mineral portion [1,2], with a parallel arrangement of enamel prisms [3,4,5]. Tooth decay, including dental caries and dental erosion caused by demineralization in an acidic environment, can lead to the destruction of the nanostructure of enamel [6,7]. In order to assist the tooth repair, the reversibility of progressive deterioration could be mediated by a remineralization process under external sources of calcium and phosphate ions, promoting ion deposition into the decayed enamel crystal cavity. This approach, when carried out in clinically relevant conditions, might result in a significant contribution towards dental research [15,16,17]
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