The effect of iontophoresis delivery of fluoride in stannous fluoride desensitizing toothpaste on dentin permeability in human extracted teeth

Abstract

This study aimed to determine the effect of iontophoresis delivery of fluoride in stannous fluoride (SnF₂) toothpaste on dentin permeability in human extracted third molars. For dentin permeability test, 26 dentin specimens were randomly divided into 4 groups; SnF₂ without-iontophoresis (n = 10), SnF₂ with-iontophoresis (n = 10), no SnF₂ without-iontophoresis (n = 3), and no SnF₂ with-iontophoresis (n = 3). The hydraulic conductance of dentin (HD) was measured after smear layer removal, immediate treatment, 7 days, and acid challenge. The other 26 specimens were also prepared under these different conditions to assess degree of dentinal tubule occlusions using scanning electron microscopy (SEM). Percentage decrease of HD in SnF₂ without-iontophoresis after immediate treatment, 7 days and acid challenge were 38.38 ± 13.61, 56.92 ± 17.22 and 33.07 ± 23.57%. The corresponding values in SnF₂ with-iontophoresis were 42.16 ± 14.49, 62.35 ± 15.67 and 50.01 ± 12.60%, respectively. There was a significant difference between without- and with-iontophoresis groups after acid challenge (p < 0.05). For SEM, after 7 days, SnF₂ with-iontophoresis showed deeper dentinal tubule occlusion (p < 0.05) and more resistance to acid challenge than SnF₂ without-iontophoresis. No significant change was observed in groups of no SnF₂ treatment. Cathode iontophoresis could enhance the effect of SnF₂ toothpaste in decreasing dentin permeability and increasing resistance to acid challenge.

Figure 1

Mean (± 1 SD) percentage decreases of hydraulic conductance of dentin after (A) no stannous fluoride treatment; (B) stannous fluoride treatment, without (black column) and with (gray column) iontophoresis at immediate treatment, 7 days and acid challenge. The same lowercase letter represents no significant change among the times of treatment. *Statistically significant difference between without and with iontophoresis (p < 0.05, 2-way repeated measures ANOVA and Tukey test).

Figure 2

(A–I) Scanning electron micrographs of cross sectional views of human dentin (original magnification × 2000). (A) Treated with 17% EDTA; (B) treated with distilled water for 7 days; (C) applied with distilled water and cathode iontophoresis for 7 days; (D–F) applied with stannous fluoride without iontophoresis; (G–I) applied with stannous fluoride and cathode iontophoresis at (D,G) immediate treatment, (E,H) 7 days and (F,I) acid challenge.

Figure 3

(A–K) Scanning electron micrographs of longitudinal views of human dentin (original magnification × 5000). (A) Treated with 17% EDTA; (B,C) immediate treatment of stannous fluoride, (B) without iontophoresis and (C) with iontophoresis, the dentinal tubules were partially blocked with deposits (blue arrows); (D–H) 7 days of stannous fluoride treatment, (D,E) without iontophoresis and (F–H) with iontophoresis, all dentinal tubules were occluded with deposits at dentin surfaces (blue arrow), granular precipitates (yellow arrow) at the depth of 50 µm, bundle precipitates (orange arrow) at the depth of 130 µm, and small granules (green arrow) at the depth of 250 µm from dentin surfaces; (I–K) after acid challenge of (I) without iontophoresis and (J,K) with fluoride iontophoresis, red arrows showing precipitates still remained within dentinal tubules.

Figure 4

Mean (± 1 SD) depths of dentinal tubule occlusion after stannous fluoride treatment, without (black column) and with (gray column) iontophoresis at immediate treatment and 7 days. The same lowercase letter represents no significant change after 7 days. *Statistically significant difference between groups (p < 0.05, 2-way ANOVA and Tukey test).