title: Physical chemical effects of zinc on in vitro enamel demineralization.
abstract: OBJECTIVE
  Zinc salts are formulated into oral health products as antibacterial agents, yet their interaction with enamel is not clearly understood. The aim was to investigate the effect of zinc concentration [Zn(2+)] on the in vitro demineralization of enamel during exposure to caries-simulating conditions. Furthermore, the possible mechanism of zinc's action for reducing demineralization was determined.
  
  
  METHODS
  Enamel blocks and synthetic hydroxyapatite (HAp) were demineralized in a range of zinc-containing acidic solutions (0-3565ppm [Zn(2+)]) at pH 4.0 and 37°C. Inductively coupled-plasma optical emission spectroscopy (ICP-OES) was used to measure ion release into solution. Enamel blocks were analysed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), and HAp by X-ray diffraction (XRD) and neutron diffraction (ND).
  
  
  RESULTS
  ICP-OES analysis of the acidic solutions showed a decrease in [Ca(2+)] and [PO4(3-)] release with increasing [Zn(2+)]. FTIR revealed a α-hopeite (α-Zn3(PO4)2.4H2O)-like phase on the enamel surfaces at >107ppm [Zn(2+)]. XRD and ND analysis confirmed a zinc-phosphate phase present alongside the HAp.
  
  
  CONCLUSIONS
  This study confirms that zinc reduces enamel demineralization. Under the conditions studied, zinc acts predominantly on enamel surfaces at PO4(3-) sites in the HAp lattice to possibly form an α-hopeite-like phase.
  
  
  CONCLUSIONS
  These results have a significant implication on the understanding of the fundamental chemistry of zinc in toothpastes and demonstrate its therapeutic potential in preventing tooth mineral loss.
authors.affiliation: Barts and The London School of Medicine and Dentistry, Queen Mary University, Dental Physical Sciences Unit, Centre for Oral Growth and Development, London E1 4NS, United Kingdom. Electronic address: n.mohammed@qmul.ac.uk.
authors.forename: N R
authors.initials: NR
authors.lastname: Mohammed
authors.affiliation: Barts and The London School of Medicine and Dentistry, Queen Mary University, Dental Physical Sciences Unit, Centre for Oral Growth and Development, London E1 4NS, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Mneimne
authors.affiliation: Barts and The London School of Medicine and Dentistry, Queen Mary University, Dental Physical Sciences Unit, Centre for Oral Growth and Development, London E1 4NS, United Kingdom.
authors.forename: R G
authors.initials: RG
authors.lastname: Hill
authors.affiliation: Barts and The London School of Medicine and Dentistry, Queen Mary University, Dental Physical Sciences Unit, Centre for Oral Growth and Development, London E1 4NS, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Al-Jawad
authors.affiliation: GlaxoSmithKline Consumer Healthcare, St George's Avenue, Weybridge, Surrey KT13 0DE, United Kingdom.
authors.forename: R J M
authors.initials: RJ
authors.lastname: Lynch
authors.affiliation: Barts and The London School of Medicine and Dentistry, Queen Mary University, Dental Physical Sciences Unit, Centre for Oral Growth and Development, London E1 4NS, United Kingdom.
authors.forename: P
authors.initials: P
authors.lastname: Anderson
mesh_terms: D002118:Calcium / Q000032:analysis; D055598:Chemical Phenomena; D003743:Dental Enamel / Q000187:drug effects*; D004058:Diffusion; D017886:Durapatite / Q000032:analysis / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008422:Materials Testing; D033363:Neutron Diffraction; D010710:Phosphates / Q000032:analysis / Q000737:chemistry; D013054:Spectrophotometry, Atomic; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D017001:Tooth Demineralization / Q000378:metabolism / Q000503:physiopathology*; D014961:X-Ray Diffraction; D015032:Zinc / Q000737:chemistry / Q000494:pharmacology*; D017967:Zinc Compounds / Q000032:analysis / Q000737:chemistry
chemical_list: D010710:Phosphates; D017967:Zinc Compounds; C043952:zinc phosphate; D017886:Durapatite; D015032:Zinc; D002118:Calcium
keywords: Caries; Demineralization; Enamel; Hopeite; Hydroxyapatite; Mineralized tissue; Zinc