The effects of repeated etching cycles on enamel loss, relative attenuation coefficient, surface roughness and esthetics outcomes of resin infiltration on demineralized enamel: an in vitro study / Dayang Fadzlina Abang Ibrahim

ntroduction: Resin infiltration is used to mask enamel opacities and the recommended etching cycles are three. However, anecdotal evidence suggests that favorable esthetics outcomes can be obtained by increasing the etching cycles. Objectives: The purpose of this study was (i) to determine the incremental and total enamel loss when enamel surfaces are exposed to multiple etching cycles using 15% HC1, (ii) to assess the relative attenuation coefficient after various etching cycles and resin infiltration treatment, (iii) to compare changes of surface roughness between the various etching cycle groups at multiple treatment stages and (iv) to compare the esthetics outcomes of various etching cycle groups at multiple treatment stages. Methodology: On the buccal surface of ninety healthy premolars, an artificial demineralization was created. The teeth were separated into nine groups (n=10), with each group undergoing one additional etching cycle up to a total of nine cycles. Each group underwent seven stages of evaluation that include at baseline, after demineralization, after etching, after resin 1 treatment, after resin 2 treatment, post resin 7 days and post resin 28 days. The teeth were scanned using optical coherence tomography (OCT) and enamel loss was quantified using a custom written MATLAB program. Resin infiltration was performed twice, first for 3 minutes (Resin 1) and again for 1 minute (Resin 2). All teeth were examined for baseline surface roughness using a profilometer (Ambios XP-200) before being treated to a pH cycling regime for 7 and 28 days. Esthetics changes was assessed using a Minolca spectrophotometer. Data were analyzed with one-way ANOVA and two-way ANOVA. Result: There was no significant difference in incremental enamel loss between each group with a mean depth of 6.801 ± 0.606%. However, there is a significant total enamel loss of more than 33% found at seven etching cycles and above. A two-way ANOVA revealed that there was a statistically significant interaction between the effects of the relative attenuation coefficient on the different stages and various etching groups, F(24, 216) = 2.184, p = 0.006. There was a significant interaction between the different stages and various groups of etching cycles on surface roughness, F(48, 126) = 3.48, p <0.001 .There was also a significant interaction between the different stages and various groups of etching cycles on color changes, (F(4, 126) = 1.177, p = 0.045). The esthetics outcome of the two applications of resin infiltration is comparable to the baseline (sound tooth) and found to significantly mask the demineralized lesions at 4 etching cycles and beyond. Conclusion: Repeated etching for the purpose of resin infiltration is acceptable and capable of improving esthetic outcomes. However, this study recommends that etching should not be repeated more than seven cycles to prevent excessive enamel loss. After eight rounds of etching, resin infiltration penetration nearly matched that of healthy enamel. The results showed that demineralized lesions treated with resin infiltration showed low surface roughness comparable to sound enamel, indicating the treatment efficacy of resin infiltration for demineralized enamel lesions. This study revealed that resin infiltration produced favorable esthetics results after more than 5 etching cycles. The esthetic outcome and surface roughness remain unchanged for up to 28 days.