Diffusive transport within dentinal tubules: An X-ray microtomographic study

Three-dimensional visualization of dentine occlusion based on FIB-SEM tomography

The occlusion of dentinal tubules has become a rapid and effective method for treating dentin hypersensitivity. Accurate evaluation of dentin occlusion is critical to illustrate the efficacy of oral care products and to optimize dental therapy in the clinics, which is limited by the conventional two-dimensional (2-D) characterization methods. Here, we demonstrate the visualization of the dentin occlusion via three-dimensional (3-D) characterization using a focused ion beam-scanning electron microscopy (FIB-SEM) tomography. Using the "Slice and View" approach, the material used for occluding dentin tubules is imaged with a very high-resolution voxel (10 nm × 10 nm × 20 nm) from 2-D SEM images and then reconstructed into a 3-D volume, which presents the mode of action of toothpaste for treating dentin hypersensitivity. Meanwhile, quantitative analysis of the depth of occlusion is successfully obtained. This work validates the feasibility of FIB-SEM tomography in the analysis of dentin occlusion within the complicated networks of dentine tubules at the nanoscale, and provides a novel approach to facilitate the research and development of oral care products.

Applications of scanning electron microscopy and focused ion beam milling in dental research

The abilities of scanning electron microscopy (SEM) and focused ion beam (FIB) milling for obtaining high-resolution images from top surfaces, cross-sectional surfaces, and even in three dimensions, are becoming increasingly important for imaging and analyzing tooth structures such as enamel and dentin. FIB was originally developed for material research in the semiconductor industry. However, use of SEM/FIB has been growing recently in dental research due to the versatility of dual platform instruments that can be used as a milling device to obtain low-artifact cross-sections of samples combined with high-resolution images. The advent of the SEM/FIB system and accessories may offer access to previously inaccessible length scales for characterizing tooth structures for dental research, opening exciting opportunities to address many central questions in dental research. New discoveries and fundamental breakthroughs in understanding are likely to follow. This review covers the applications, key findings, and future direction of SEM/FIB in dental research in morphology imaging, specimen preparation for transmission electron microscopy (TEM) analysis, and three-dimensional volume imaging using SEM/FIB tomography.

A comparative evaluation of the efficacy of two novel desensitising dentifrices

A comparison of the desensitising efficacy of two commercially available dentifrices with different modes of action was conducted in a randomised, examiner-blind, two-arm, parallel group, 8-week, longitudinal clinical study. Dentifrice A, (Sensodyne Multi Action Iso-Active), contained 50000 ppm KNO(3) and 1450 ppm fluoride as NaF. Dentifrice B, Colgate Sensitive Pro-Relief, contained a combination of 80000 ppm arginine, bicarbonate, calcium carbonate, and 1450 ppm fluorine as NaMFP. Subjects (N = 110), stratified into two groups (N = 55), brushed twice-daily for 60 s, over an 8-week period. Sensitivity status, compliance, and safety were determined at 1, 2, 4, and 8 weeks. A fixed-effects ANCOVA statistical model was applied to the Intent-To-Treat population using a two-sided 5% significance level. After 8 weeks, the treatment groups using Dentifrice A and Dentifrice B exhibited mean reductions from baseline of 49% and 45% in air sensitivity visual analogue scale (VAS) score, 61% (both) in examiner-based Schiff Sensitivity score, and clinically significant reductions in tactile pain threshold; all reductions were statistically significant (P < 0.0001). Both treatment groups also exhibited significant reductions across all sensitivity measures at 1, 2, and 4 weeks (P ≤ 0.0059, Dentifrice A; P ≤ 0.0137, Dentifrice B).

Multi-component bioactive glasses of varying fluoride content for treating dentin hypersensitivity

OBJECTIVE

Dentin hypersensitivity (DH) is a commonly occurring dental condition, and bioactive glasses (BG) are used in dentifrice formulations for treating DH by forming a surface layer of hydroxycarbonate apatite (HCA) on the tooth, thereby occluding exposed dentinal tubules. Fluoride-containing BG, however, form fluorapatite, which is more stable toward acid attack, and provide a more sustainable option for treating DH.

METHODS

Melt-derived multi-component BG (SiO(2)-P(2)O(5)-CaO-CaF(2)-SrO-SrF(2)-ZnO-Na(2)O-K(2)O) with increasing CaF(2)+SrF(2) content (0-32.7 mol%) were prepared. Apatite formation, occlusion of dentinal tubules in dentin discs and ion release in Tris buffer were characterized in vitro over up to 7 days using X-ray diffraction, infrared spectroscopy, scanning electron microscopy and inductively coupled plasma emission spectroscopy.

RESULTS

The fluoride-containing bioactive glasses formed apatite from as early as 6h, while the fluoride-free control did not form apatite within 7 days. The glasses successfully occluded dentinal tubules by formation of apatite crystals and released ions such as fluoride, strontium and potassium.

SIGNIFICANCE

Fluoride significantly improved apatite formation of the BG, allowing for treatment of DH by occlusion of dentinal tubules. The BG also released therapeutically active ions, such as strontium and fluoride for caries prevention, zinc for bactericidal properties and potassium, which is used as a desensitizing agent in dentifrices.