Ultrasonication versus Toothbrushing Abrasion of Short-Time Eroded Enamel

Objective: To quantify and compare the amount of demineralised enamel removed by ultrasonication and toothbrushing abrasion of short-time eroded samples. Methods: Thirty bovine enamel samples were demineralised in hydrochloric acid (pH: 2.1) for 60 s. The demineralised layer was subsequently removed stepwise by ultrasonication in water for 5, 30, 60 and 120 s (n = 10) or by brushing with destilled water (n = 10) or toothpaste slurry (n = 10) with 50 strokes each step. By measuring baseline and post-treatment values of Knoop indentation length (5 indentations each sample), the median amount of enamel loss was calculated from the change in indentation depth. Results: Curve fitting method yielded an exponential relationsship between enamel loss and ultrasonication time (y = 231.07e^-0.042x, R² = 0.97). Thereby, up to 60 s ultrasonication, wear of demineralised samples was significantly increased and plateaued thereafter to 240 nm. Also, the relationship between enamel abrasion and toothbrushing strokes could be expressed as exponential function: y = 461.38e^-0.0095x(R² = 0.95) for destilled water and y = 573.53e^-0.0089x(R² = 0.98) for toothpaste slurry. For toothbrushing with destilled water, abrasion plateaued after 250 strokes and neared to 423 nm. Abrasion values of brushing treatment with toothpaste slurry approximated to 540 nm after 300 strokes. Conclusion: Toothbrushing abrasion leads to higher enamel loss of eroded enamel than ultrasonication. From the mathematical model of toothbrushing abrasion, it is calculated that the acid softened zone of short-time eroded enamel removable by toothbrushing amounts to 423 to 540 nm.