fluoride

SMHR test was used to assess the changes in mineralization status of enamel specimens using a Wilson 2100 Hardness tester. SMHR was determined by measuring the length of the indentations of enamel specimens. An increase in the indentation length compared to the baseline indicates softening while decrease in the indentation length represents rehardening of enamel surface. Percent SMHR was calculated from indentation values of enamel specimens at baseline (B), after in-situ hardening (R) and after first erosive challenge (E1) using formula: \[(E1-R)/ (E1-B)\]\*100.

Surface microhardness recovery (SMHR) test was used to assess the changes in mineralization status of enamel specimens using a Wilson 2100 Hardness tester. SMHR was determined by measuring the length of the indentations of enamel specimens. An increase in the indentation length compared to the baseline indicates softening while decrease in the indentation length represents rehardening of enamel surface. Percent SMHR was calculated from indentation values of enamel specimens at baseline (B), after in-situ hardening (R) and after first demineralization challenge (D1) using formula: \[(D1-R)/ (D1-B)\]\*100.

To evaluate fluoride content, plaque samples were collected from the interproximal surfaces of the posterior teeth of participants using a standardized approach. Plaque fluid fluoride were calculated using a micro analytical method and in comparison to a standard fluoride curve constructed on the same day of the analysis. AUC was determined from 0-4hours using trapezoidal rule and natural log transformation was applied due to failure of assumption of normal distribution of data.

The examiner assessed the participant's response to an evaporative air stimulus for each tooth using the Schiff Sensitivity Scale which was scored as follows - 0: Participant did not respond to air stimulation; 1: Participant responded to air stimulus but does not request discontinuation of stimulus; 2: Participant responded to air stimulus and requested discontinuation or moves from stimulus; 3: Participant responded to stimulus, considered stimulus to be painful, and requested discontinuation of the stimulus. A reduction in Schiff Sensitivity score will be indicative of an improvement in sensitivity.

The Bleeding Index was performed by a single examiner using a color coded periodontal probe. The probe was engaged approximately 1 millimetre (mm) into the gingival crevice. A moderate pressure was used whilst sweeping from interproximal to interproximal along the sulcular epithelium. The BI scoring system used is as follows: 0= No bleeding after 30 seconds; 1= Bleeding upon probing after 30 seconds; 2= Immediate bleeding observed

MGI was assessed on facial and lingual surfaces at two sites on each tooth (papillae and margin). The scoring of the MGI was performed under dental office conditions using a standard dental light for illuminating the oral cavity. Compressed air, water and mouth mirrors were available to each examiner. This procedure was performed by a single examiner. The MGI scoring system is as follows: 0 = absence of inflammation; 1 = mild inflammation; slight change in color, little change in color; little change in texture of any portion of the marginal or papillary gingival unit; 2 = mild inflammation; criteria as above but involving the entire marginal or papillar gingival units; 3= moderate inflammation; glazing, redness, edema, and/ or hypertrophy of the marginal or papillary gingival unit; 4 = severe inflammation; marked redness, edema and/or hypertrophy of the marginal or papillary gingival unit, spontaneous bleeding, congestion, or ulceration

Enamel specimens were exposed to dietary erosive challenge and set of five indentations within each specimen was measured. Decrease in the indentation length compared to the baseline indicates hardening of enamel surface. Enamel specimens were exposed to second erosion challenge to determine NER which compared the indentations values of enamel specimens at baseline (B), first erosive (E1) and second erosive challenge (E2). Percent NER was calculated by formula: \[(E1-E2)/ (E1-B)\]\*100. Smaller the negative NER, better is treatment regimen in imparting resistance to enamel.