Erosive Potential of Citric and Hydrochloric Acids With Acquired Enamel Pellicle

Objectives: To compare the erosive potential of hydrochloric acid (HCL) (mimicking gastric juice and intrinsic acids), citric acid (mimicking dietary acids) and a water control. The effect of acquired enamel pellicle (AEP) on protection against erosion by citric acid and HCL was also investigated.
Methods: Human polished buccal molar enamel samples (n=200) were randomly divided into five groups: water (control), citric acid (0.3%, pH 3.2), citric acid with saliva, HCL (0.01M, pH 2.2) and HCL with saliva, with 8 ml of solution per sample, at various time points (n=10) (30 s, 60 s, 120 s and 300 s). Stimulated whole mouth saliva was collected and samples immersed for 24 h prior to acid exposure. Non-contact surface profilometry (NCSP) and knoop microhardness (KHN) were used. Data were normally distributed for both measurements, so 2-way ANOVA, Sidak's and Tukey's post-hoc tests were applied (α=0.05).
Results: Mean (SD) KHN at 30 s exposure to citric acid were 55.1(3.0) and 46.2(2.8), at 300 s they were 116.0(5.5) and 95.3(2.7), with and without AEP (p<0.0001). For HCL at 30 s exposure they were 66.0(2.3) and 52.5(4.7) and at 300 s they were 123.6(3.4) and 109.5(4.4), with and without AEP (p<0.0001).
Mean (SD) step height for 30 s exposure to citric acid were 0.08 (0.04) and 0.16(0.1) with and without AEP (p>0.05). At 300 s, they were 1.4 (0.4) and 2.21(0.9) with and without AEP (p<0.01). For HCL at 30 s exposure they were 1.88(0.9) and 0.54 (0.2) and at 300 s they were 6.73(0.5) and 4.5 (0.8) with and without AEP (p<0.0001).
Conclusions: Presence of AEP increased KHN change for both acids. Interestingly, presence of AEP reduced tissue loss for citric acid groups but resulted in increased tissue loss for HCL groups.