title: Discolouration of glass-ionomer cement at different fluoride concentration levels.
abstract: BACKGROUND
  Although application of professionally applied Acidulated Phosphate fluoride (APF) gel is effective in prevention of dental caries, APF-induced discolouration and/or surface degradation of dental restorations has been reported. However, no publication has reported a dose-response effect of APF gel on Glass Ionomer Cement (GIC) restorations in vivo and/or human teeth. Therefore, this study aimed to examine the discolouration effect of APF gel at various concentration levels on GIC restorations of human teeth in vitro.
  
  
  METHODS
  Seventy extracted human teeth were used. Each was restored with GIC and then topically applied with a different dilution of APF gel. Change of shade and/or colour of restorations was assessed by a trained examiner.
  
  
  RESULTS
  GIC discolouration was detected on 4 (5.71%) and 23 specimens (32.86%) after the first and the second APF applications, respectively. The discolouration rate increased with APF gel concentration on the second application (χ2=38.314, df=1, p<0.001) but not the first ( χ2=2.352, df=1, p=0.125). Discolouration of GIC restorations was more likely to form under application of a higher concentration of APF gel (OR=1.099, 95%CI=1.052, 1.148), a higher concentration of fluoride (OR=1.001, 95%CI=1.000, 1.001) and/or a lower pH value (OR=0.002, 95%CI=0.000, 0.039).
  
  
  CONCLUSIONS
  Discolouration of GIC was associated with concentration and frequency of APF gel application in extracted natural human teeth in vitro. Increasing discolouration rates were related to increased fluoride concentration and increasing acidity of APF gel. Further investigation is indicated.
authors.forename: Eric
authors.initials: E
authors.lastname: Wang
authors.affiliation: JCU School of Medicine and Dentistry, PO Box 6811, Cairns, QLD 4870, Australia; Tel: +61 7 4232 1297, +61 7 4232 1920; e-mail: boyen.huang@jcu.edu.au.
authors.forename: Boyen
authors.initials: B
authors.lastname: Huang