title: Changes in composition and enamel demineralization inhibition activities of gallic acid at different pH values.
abstract: BACKGROUND
  Gallic acid (GA) has been shown to inhibit demineralization and enhance remineralization of enamel; however, GA solution is highly acidic. This study was to investigate the stability of GA solutions at various pH and to examine the resultant effects on enamel demineralization.
  
  
  METHODS
  The stability of GA in H2O or in phosphate buffer at pH 5.5, pH 7.0 and pH 10.0 was evaluated qualitatively by ultraviolet absorption spectra and quantified by high performance liquid chromatography with diode array detection (HPLC-DAD). Then, bovine enamel blocks were subjected to a pH-cycling regime of 12 cycles. Each cycle included 5 min applications with one of the following treatments: 1 g/L NaF (positive control), 4 g/L GA in H2O or buffered at pH 5.5, pH 7.0 and pH 10.0 and buffers without GA at the same pH (negative control), followed by a 60 min application with pH 5.0 acidic buffers and a 5 min application with neutral buffers. The acidic buffers were analysed for dissolved calcium.
  
  
  RESULTS
  GA was stable in pure water and acidic condition, but was unstable in neutral and alkaline conditions, in which ultraviolet spectra changed and HPLC-DAD analysis revealed that most of the GA was degraded. All the GA groups significantly inhibited demineralization (p < 0.05) and there was no significant difference of the inhibition efficacy among different GA groups (p > 0.05).
  
  
  CONCLUSIONS
  GA could inhibit enamel demineralization and the inhibition effect is not influenced by pH. GA could be a useful source as an anti-cariogenic agent for broad practical application.
authors: State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University , Chengdu , PR China.
authors: Jingyang
authors: J
authors: Zhang
authors: Xuelian
authors: X
authors: Huang
authors: Shengbin
authors: S
authors: Huang
authors: Meng
authors: M
authors: Deng
authors: Xincheng
authors: X
authors: Xie
authors: Mingdong
authors: M
authors: Liu
authors: Hongling
authors: H
authors: Liu
authors: Xuedong
authors: X
authors: Zhou
authors: Jiyao
authors: J
authors: Li
authors: Jacob Martien
authors: JM
authors: Ten Cate
mesh_terms: D000818:Animals; D002021:Buffers; D002118:Calcium / Q000032:analysis; D002327:Cariostatic Agents / Q000627:therapeutic use*; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D003743:Dental Enamel / Q000737:chemistry / Q000187:drug effects*; D005707:Gallic Acid / Q000627:therapeutic use*; D006863:Hydrogen-Ion Concentration; D010710:Phosphates / Q000737:chemistry; D012969:Sodium Fluoride / Q000627:therapeutic use; D013056:Spectrophotometry, Ultraviolet; D017001:Tooth Demineralization / Q000517:prevention & control*; D014089:Tooth Remineralization; D014867:Water / Q000737:chemistry
chemical_list: D002021:Buffers; D002327:Cariostatic Agents; D010710:Phosphates; D014867:Water; D005707:Gallic Acid; D012969:Sodium Fluoride; D002118:Calcium
keywords: demineralization; enamel; gallic acid; polyphenol; stability