Early stages of enamel erosion analysis

Objective:   The aim of this study was to evaluate early stages and evolution of dental enamel erosion with hydrochloric acid simulating gastroesophageal reflux episodes using Atomic Force Microscope (AFM). Method: Five ground flat, polished bovine enamel slabs (4X4X2mm) were selected. Enamel surface area was exposed to 0.1mL of 0.01M hydrochloric acid  (pH=2) at 37°C in five different exposure intervals: control (without acid exposure); 10s, 20s, 30s and 40s of acid exposure. After this, the exposed area was analyzed through AFM measuring the roughness, superficial area and morphological surface. Data were analyzed qualitatively.  Results:  it can be observed that until 30s (Rrms = 12.5 nm) the development speed of the roughness was 0.3nm/s, higher exposure revealed a pronounced decline in speed (0.04nm/s), measuring Rrms = 12.9nm at 40s, corresponding to 7.5  times lower rate.  Surface area (SA) increased 13.950nm²/s until 20s, for higher exposures it was observed decrease in speed (1.350nm²/s -  10.3 times lower rate), verifying SA = 4.40 μm_² at 30s and  SA = 4.43μm_² at 40s.  In surface morphology, it was observed that control sample presented smaller hydroxyapatite  crystals (22nm), after 40s the crystals size was ≈ 60nm.  Conclusion:  It can be concluded that short periods were able to cause enamel demineralization (erosion) in different speeds, which decreased with increase of exposure time to hydrochloric acid.