Evaluation of optical coherence tomography in detecting initial enamel erosion bin vitro and in vivo studies / Azwatee Abdul Aziz

Introduction: Enamel erosion is a problem of increasing clinical concern and early detection is difficult. A reliable tool that is able to detect minute changes on the enamel surface is indispensable. Optical Coherence Tomography (OCT) has significant potential for non-invasive, non-ionizing detection of the earliest signs of enamel erosion. Hence, the overarching goal of this study is to assess the potential of OCT to detect initial enamel erosion that could be used in clinical trials and oral health survey. Aims: For the in vitro study, to evaluate the effect of early dental biofilm on OCT backscattered intensity, and to evaluate the effect of dental water-jet on acid-induced softened human enamel surfaces. For the in vivo study, to explore the utility of OCT in detecting initial enamel erosion, in vivo. Methods: In vitro study, 80 enamel specimens were prepared, exposing 2 x 4mm2 window. At baseline (t1), specimens were subjected to acid challenge (citric acid for 30 min) and divided into four groups; (1) Control (immersed in de-ionised water for 3-days), (2) 1-Day_Biofilm, (3) 2-Day_Biofilm, and (4) 3-Day_Biofilm. Specimens from group 2, 3 and 4 were inoculated to produce early laboratory-cultivated biofilm for 1, 2 and 3 days, respectively. All specimens were then subjected to water-jet (WJ) for 20 sec. Swept Source OCT (SS-OCT) was used to scan the specimens at baseline (t1), post-erosion (t2), with biofilm (t3) and post-WJ (t4) time points. Surface Microhardness (SMH) was measured at t1 and t2. Repeated measures ANOVA was used to compare the data between time points, within each group. The in vivo study involved a two-phase (A and B) study with 22 subjects. In Phase-A, subjects were instructed to swish a total of 250 ml orange juice for 10 min, three times per day with three-hour interval for three consecutive days. In Phase B, the same protocol was followed with an addition of gum chewing for 15 min iv after each swishing. OCT measurements were taken before and after each swishing, totalling of six time points per day (t1 � t6). Data was analysed using repeated measures ANOVA and paired t-test. The level of significance was set at p<0.05 for all studies. Results: The in vitro results showed statistically significant increase (p<0.05) in Supra?surface integrated reflectivity (IRbiofilm) between t2 and t3 for all groups. Subsurface integrated reflectivity (IRsub) results showed significant decrease (p<0.05) in 2-Day Biofilm group, however, a significant increase (p<0.05) was shown in 3-Day Biofilm group, between t2 and t3. Results also showed a significant reduction in SMH (p<0.05) at t2, however, the reduction in enamel thickness (D) was not statistically significant. IRbiofilm mean values showed no significant differences at t4 (p>0.05) amongst all groups. The in vivo results revealed that there was a statistically significant increase in IR after repeated acid challenge (p