Protection, remineralisation and tubule occlusion of dentine by desensitising toothpastes

Abstract

Enamel is one of the strongest and highly mineralised tissues in the human body and it protects the underlying dentine. The high mineral content of the enamel makes it susceptible to erosive wear via dissolution of the ions in low pH. Loss of the minerals also softens the enamel, making it vulnerable to further damage by mechanical and chemical challenges in the oral environment. The loss of enamel or gum recession along the gum lines exposes the dentine, causing dentine hypersensitivity (DH). Active ingredients such as bioactive glasses, arginine and calcium silicate have been used in toothpastes to treat DH by depositing a layer over the dentine and occluding exposed tubules. As well as providing relief against sensitivity, these layers could protect the dentine against chemical and mechanical challenges. The first aim of this study was to investigate the ability of 5 different layers formed on dentine to protect the tissue against these challenges. The layers were formed following brushing with 5 commercially available toothpastes containing chloro calcium phosphosilicate, fluoro calcium phosphosilicate, calcium sodium phosphosilicate, arginine with calcium carbonate, and calcium silicate with sodium phosphate. 60 bovine dentine discs were divided into 6 groups and were manually brushed twice a day for two minutes over 7 days with one of the toothpastes or artificial saliva as a control. In vitro techniques such as nanoindentation, nano scratch, scanning electron microscopy, nuclear magnetic resonance, X-ray-diffraction, Fourier-transform infrared spectroscopy, energy-dispersive x-ray, and Raman spectroscopy were used to characterise the layers. Acid resistivity of the layers was also investigated by immersion in 1 wt% citric acid (pH 3.1) for two minutes. Results showed that all 5 active ingredients formed a protective layer onto the dentine surface, these layers were chemically and structurally similar to hydroxyapatite with higher hardness and Young’s modulus compared to the control dentine. Calcium silicate with sodium phosphate formed the hardest layer with a hardness of 0.88 GPa compared to control dentine (0.55 GPa), however, it did not perform well under acid challenge. Arginine with calcium carbonate formed the second hardest layer with superior resistance to acid challenge, highest hardness/modulus ratio, elastic recovery, and lowest scratch penetration depth. This layer also had the highest average crystal size and crystallinity index. Therefore it would offer the best protection to the dental tissue. Tubule occlusion is one of the most widely accepted methods in treating DH. Current techniques such as focused ion beam, scanning electron microscopy or hydraulic conductance that are used to determine tubule occlusion in vitro do not provide the depth of occlusion, are limited in terms of the volume of dentine tested or extremely time consuming and expensive. The second aim of this study was to use a unique serial blockface scanning electron microscopy (SBF-SEM) to overcome these limitations and to determine the level of tubule occlusion and mineralisation by Sensodyne® Repair and Protect and Rapid Relief toothpastes containing calcium sodium phosphosilicate (CSPS) and stannous fluoride (SnF2) respectively. Bovine dentine discs (n=6) were randomly divided into two treatment groups, one for each toothpaste (n=3). Discs were halved with one half treated with toothpaste and one as a control. 600 slices with a thickness of 60 nm were cut by a diamond knife in a microtome and the surface was imaged by a backscattered electron detector after each slice. CSPS occluded 100% of the tubules at the surface compared to 83% for SnF2. No tubules were occluded in the control group. CSPS also significantly reduced the diameter of the tubule opening, while no significant change was seen in the SnF2 group. Both materials resulted in a greyscale value increase around the tubules with CSPS significantly higher than SnF2. Therefore CSPS may provide better relief against DH and help with mineralisation due to a superior occlusion percentage and increased dentine mineralisation.

More information

Identifiers

ORCID for Robert Wood: orcid.org/0000-0003-0681-9239

Catalogue record

Export record