Statistical analysis
The quantitative data obtained in the present study was entered in MS Excel spreadsheet (Microsoft, WA, USA) for further statistical analysis using SPSS v. 26 (IBM statistics, IL, USA).Paired samples dependent t-test was used to analyse statistically significant differences (if any) between the: 1) PLM pH (at baseline) and the pH of the PLM after inclusion of Perspex® coated varnishes; 2) Ra at baseline and post-erosive cycles by SPA/AFM; and 3) Ca/P ratio at baseline and post-erosive cycles for all treatment groups challenged by either of the PLM.One-way ANOVA with Bonferroni post-hoc test was performed to identify differences between the treatment groups at each baseline and post-erosive cycle for characterizations of Ra (by SPA/AFM) and Ca/P ratio by SEM-EDX with relevant computed mean difference (modulus of the difference between baseline and post-erosive cycle determined variable).Two-way ANOVA with Bonferroni post-hoc test (at all levels) was used to analyse the effect of Factor 1: treatment groups; and Factor 2: time points (0 min, 30 min, 1 h, and 4 h) on the determined pH of the PLM. Further, factor interaction analysis was undertaken to estimate interaction-based changes on the PLM pH determined with respective treatment groups and different time-points.For all statistical tests, the level of significance was set at 