Erosive/abrasive Process on Dentin With Gaseous and Liquid Hydrochloric Acid

Objectives: The aim of this in vitro study was to evaluate the effect of hydrochloric acid (HCl) in liquid or gaseous form on dentin with or without toothbrushing.
Methods: Forty ground flat, polished human root dentin slabs (4x3x2mm) were isolated with composite resin. Half of the specimen surface was exposed to erosive/abrasive challenges and the other half of the surface was used as control. The specimens were submitted to initial erosive challenge with liquid HCl (pH=1.2, 37^oC, 3x/day, 20s) and surface images were obtained using 3D confocal laser microscopy (OLS 4000). The specimens were divided into four groups according to the challenge (n=10): Group 1: liquid HCl (pH=1.2, 37^oC, 0.3%, 20s, 6x/day for 5 days), Group 2 liquid HCl (same protocol G1) + Abrasion, Group 3: gaseous HCl (pH=1.2, 37^oC, 20s, 6x/d for 5 days) and Group 4: gaseous HCl (same protocol G3) + Abrasion. The abrasive challenge protocol (G2 and G4) was performed with electric toothbrush between the 3rd and 4th erosive cycle (liquid and gas) and after the last erosive challenge for 10s, 2x/day, 200g load. The volume loss (V) and the step (S) were analyzed using laser scanning confocal microscope. Data were analyzed by one-way ANOVA and Tukey test (α = 5%).
Results: It was observed that both response variables presented similar behavior: G1 (V:12.86±0.63; S:19.08±0.39) and G2 (V:14.42±1.24; S:20.88±1.54) showed higher volume loss (µm³/µm²) and step (µm) with significant difference (p<0.05) from G3 (V:5.55±0.92; S:10.91±0.63) and G4 (5.69±1.46; S:11.09±1.06).
Conclusions: The erosive process by liquid was more intense than by gas. When the abrasive process was associated with erosion, wear on dentin was more pronounced only on the erosion by liquid.