Effect of two different fluoride varnishes on enamel de-mineralization and re-mineralization: an in vitro study

Introduction:
Interdental stripping, mechanical grinding of the proximal tooth surface, is a common practice to reduce mesiodistal diameter for orthodontic management of minor crowding and tooth shape or size disharmony.

Objectives:
The aim of the study was to evaluate the effectiveness of Duraphat and Clinpro varnishes in protecting stripped enamel and re-mineralizing initial enamel lesion.

Material and methods:
Sixty-six stripped and sixty-six de-mineralized proximal surfaces of human premolars were covered with acid-resistant nail varnish, except for 3 × 4 mm enamel windows, and were assigned to group 1 (stripped enamel) and group 2 (initial enamel lesion), respectively. Each group was equally divided into 3 sub-groups (n = 22) according to varnish treatment for exposed windows: sub-group A (no varnish treatment, control), sub-group B (Duraphat varnish), and sub-group C (Clinpro varnish). Before each varnish application to its respective sub-groups, baseline Vickers micro-hardness test for each sub-group was done. All specimens were subjected to de-mineralizing solution for 10 days. Vickers micro-hardness for each sub-group was measured again at exposed enamel windows, and two specimens from each sub-group were examined under SEM.

Results:
High statistically significant difference in micro-hardness was found between control sub-groups (228.2 ± 14.2 and 158.6 ± 13.3) and their respective sub-groups treated with either Duraphat (351.3 ± 15.2 and 281.5 ± 16.8) or Clinpro varnish (350.6 ± 15.4 and 280.4 ± 16.4), respectively (p = 0.000). No statistically signifi­cant difference was found in comparison between Duraphat and Clinpro sub-groups, or between treated sub-groups and their respective baseline values (p > 0.05). Under SEM, protective layer of crystals was observed in treated sub-groups, while honeycomb-like de-mineralized enamel and variable sizes of porosities were seen in control sub-groups.

Conclusions:
Both varnishes protect stripped enamel and re-mineralized initial enamel lesion.