title: Storage of polyacid-modified resin composites ("compomers") in lactic acid solution.
abstract: OBJECTIVE
  The aim of this study was to determine the interaction of four polyacid-modified resin composites with aqueous lactic acid solutions, and to compare changes with those for a glass-ionomer cement and a conventional resin composite.
  
  
  METHODS
  For each material, namely Compoglass F, Dyract AP, Hytac and Ana Compomer, plus AquaCem (glass-ionomer cement) and Pekafil (conventional composite resin), five cylindrical specimens of 4 mm diameter x 6 mm height were prepared and weighed. They were stored individually in 2.0 cm3 of 0.02 mol l-1 lactic acid solution for 1 week then the pH was determined and the specimens reweighed. The lactic acid solution was replenished, and the specimens were stored for a further week, after which the pH and specimen weights were again measured. This was repeated at 1 week intervals until the specimens were 6 weeks old. Differences were analysed by ANOVA followed by Newman-Keuls post hoc analysis.
  
  
  RESULTS
  All four polyacid-modified composites increased the pH of the solutions at all time intervals by at least 0.26 pH units (significant to at least p < 0.01). This effect was similar to that of the glass-ionomer (but significantly less, p < 0.05) while significantly greater (p < 0.05) than that for the composite, Pekafil, which, by contrast, had no effect on pH. The observed rise in pH reduced significantly over time (ANOVA, p < 0.05). After 1 week, all pH changes were accompanied by net reductions in specimen mass, indicating susceptibility to acid erosion. Hytac was significantly more resistant to this erosion than the other materials; conversely, it had the least effect on solution pH.
  
  
  CONCLUSIONS
  These results show that polyacid-modified resin composites neutralise lactic acid in vitro but suffer erosion in the process.
authors.affiliation: Dental Biomaterials Department, Guy's King's St Thomas' Dental Institute, King's College London, UK. john.nicholson@kcl.ac.uk
authors.forename: J W
authors.initials: JW
authors.lastname: Nicholson
authors.forename: B J
authors.initials: BJ
authors.lastname: Millar
authors.forename: B
authors.initials: B
authors.lastname: Czarnecka
authors.forename: H
authors.initials: H
authors.lastname: Limanowska-Shaw
mesh_terms: D000704:Analysis of Variance; D020770:Compomers / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry; D004356:Drug Storage; D005899:Glass Ionomer Cements / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000737:chemistry*; D018709:Statistics, Nonparametric
chemical_list: D020770:Compomers; D003188:Composite Resins; D005899:Glass Ionomer Cements; D019344:Lactic Acid