In vitro effects of acid challenge on incisal/occlusal cupping/cratering

Statement of problem. The cause of occlusal/incisal cupping/cratering (depressed dentin surrounded by elevated rims of enamel) has been postulated to be primarily the effect of acid on exposed dentin. It is hypothesized that abrasion, bruxism, attrition, and stress-corrosion may play a secondary role in lesion formation. The primary cause and sequence of occlusal/incisal cupping/cratering remain scientifically controversial. Purpose. The purpose of this in vitro study was to determine the effects of acid on human enamel, mantle dentin, and peritubular dentin in the creation of incisal/occlusal cupping/cratering. This study was designed to visually illustrate the role of acid in the formation of cupping/cratering. Material and methods. A soft compact toothbrush was tested using both high relative dentin abrasivity (RDA)- and low-RDA dentifrices and water only (nonabrasive) on extracted human teeth. Seventeen specimens of 4 teeth each (68 teeth) were subjected to horizontal brushing with a 1:1 dentifrice-to-water slurry or water only. Twelve of these 17 specimens, a total of 48 teeth, were subjected to acid challenge. Each of these 12 specimens were brushed for 500 strokes after each acid challenge for a total of 150 000 strokes and 300 acid immersions. Half the specimens were acid challenged for 5 minutes and the other half for 10 minutes between brushings. Results. No visible loss of tooth structure was noted in the control specimens brushed in water only. The control specimens brushed in a 1:1 slurry of toothpaste/water demonstrated incisal/occlusal cupping/cratering. The acid-challenged specimens brushed in water only demonstrated enamel and peritubular dentin loss with elevated rims and/or plateaus of mantle dentin, the opposite of occlusal/incisal cupping/cratering. All specimens brushed with the higher abrasive dentifrice demonstrated visible wear of enamel, mantle, and peritubular dentin, culminating in occlusal/incisal cupping/cratering. Surprisingly, those acid-challenged specimens brushed with the lower abrasive toothpaste demonstrated visible wear of the enamel and peritubular dentin, resulting in elevated rims and/or plateaus of mantle dentin. Conclusions. Acid affects both the enamel and the mineralized component of dentin. This study demonstrated that incisal/occlusal cupping/cratering occurring in worn dentition can be caused by the use of dentifrice alone. Acid challenge affects the inorganic components of tooth structure but not the organic components and so does not cause the dentinal cupping/cratering of the incisal/occlusal surfaces of the human dentition.