Simulation of Non-Carious Cervical Lesions by Computational Toothbrush Model: A Novel Three-Dimensional Discrete Element Method.

Non-carious cervical lesions (NCCLs) are saucer-shaped abrasions of a tooth. NCCLs can form due to various etiologies, including toothbrushing wear, acid erosion, and mechanical stress. Owing to this complex interplay, the mechanism of NCCLs in tooth abrasion has not been established. This study aims to develop a numerical method using a computational toothbrush to simulate NCCLs. The forces acting on the teeth and the amount of abrasion generated were evaluated. The discrete element method using in-house code, connected particle model, and Archard wear model were applied for brushing. In the toothbrush model, 42 acrylic tufts were fixed into a toothbrush head. The teeth models with enamel properties comprised four flat plates and two grooves to simulate the anterior teeth and NCCLs. The brushing speed and depth for one cycle were established as simulation parameters. The force applied within the ununiform plane was concentrated on several bristles as the toothbrush passed through the interproximal space. The brushing force (depth) had a greater effect on tooth abrasion than the brushing speed. Toothbrushing abrasion was mainly concentrated in the interproximal space. Therefore, forceful tooth brushing can cause NCCLs from the interproximal space to the cervical area of the tooth.

Effect of B2O3 on the removal of phosphate ions from an aqueous solution in borosilicate glasses.

Recently, it was found by the authors of this study that glasses of a special composition have an ability to remove some hazardous ions from waste solutions. In the present study, a SiO(2)-B(2)O(3)-CaO-Na(2)O glass system has been chosen to remove phosphate ions from an aqueous solution. Several glasses with different amounts of B(2)O(3) in the SiO(2)-B(2)O(3)-CaO-Na(2)O glass system have been prepared, and these glasses have been reacted with a solution containing 155 ppm of phosphate ions. A silica-rich layer is first formed on the glass surface by leaching Na(+) and Ca(2+) ions from the glass, and then the Ca(2+) and PO(4)(3-) ions in the solution have been uptaken on the silica-rich layer to precipitate hydroxyapatite crystals. In this manner, the phosphate ions could be removed from the solution. The efficiency of removing the phosphate ions was found to depend strongly on the B(2)O(3) contents. With increase of B(2)O(3) contents in the glass, more Ca(2+) ions can be leach out of the glass, promotes the precipitation of hydroxyapatite. Therefore, the removal efficiency increases with increased B(2)O(3) content. The phosphate ion removal efficiency was also sharply enhanced by increasing the surface area of the glasses and decreasing the pH of the solution.