title: Effect of fluoride on artificial caries lesion progression and repair in human enamel: regulation of mineral deposition and dissolution under in vivo-like conditions.
abstract: OBJECTIVE
  This study was carried out to determine in vitro the effect of fluoride on (1) the demineralization of sound human enamel and (2) the progression of artificial caries-like lesions, under relevant oral conditions.
  
  
  METHODS
  Thin sections of sound human enamel were exposed to solutions undersaturated with respect to tooth enamel to a degree similar to that found in dental plaque fluid following sucrose exposure in vivo, containing fluoride concentrations (0-0.38ppm) found in plaque fluid. Mineral changes were monitored for 98 days, using quantitative microradiography. The effect of fluoride (1.0-25.0ppm) on the progression of artificial caries-like lesions was similarly studied.
  
  
  RESULTS
  Fluoride concentrations of 0.19ppm and greater were found to prevent the demineralization of sound enamel in vitro. However, significantly higher concentrations of fluoride (25.0ppm) were required to prevent further demineralization of artificial caries-like lesions. Demineralizing solutions with intermediate fluoride concentrations (2.1-10.1ppm) induced simultaneously remineralization in the outer portion of the lesion and demineralization in the inner portion. Simultaneous remineralization and demineralization were also observed in hydroxyapatite pellets.
  
  
  CONCLUSIONS
  Our results show that the observed effect of fluoride on enamel demineralization is not solely a function of bulk solution properties, but also depends on the caries-status of the enamel surface. A mechanistic model presented indicates that, in comparison to sound enamel surfaces, higher concentrations of fluoride are required to prevent the progression of artificial caries-like lesions under in vivo-like conditions since the diffusion of mineral ions that promote remineralization is rate-limiting.
authors.affiliation: Health Care Products Research Laboratories, Kao Corporation, 1-3, Bunka 2 chome, Sumidaku, Tokyo 131-8501, Japan. hyamazaki@forsyth.org
authors.forename: Hajime
authors.initials: H
authors.lastname: Yamazaki
authors.forename: Amy
authors.initials: A
authors.lastname: Litman
authors.forename: Henry C
authors.initials: HC
authors.lastname: Margolis
mesh_terms: D000704:Analysis of Variance; D002327:Cariostatic Agents / Q000494:pharmacology*; D003731:Dental Caries / Q000517:prevention & control; D003743:Dental Enamel / Q000737:chemistry / Q000187:drug effects*; D005459:Fluorides / Q000494:pharmacology*; D006801:Humans; D008954:Models, Biological; D017001:Tooth Demineralization / Q000517:prevention & control*; D014089:Tooth Remineralization
chemical_list: D002327:Cariostatic Agents; D005459:Fluorides