title: Critical pH in resting and stimulated whole saliva in groups of children and adults.
abstract: OBJECTIVE
  The concentrations of calcium and phosphate in saliva have significant influence on the protective mechanisms of dental hard tissues within the oral environment. A lower calcium concentration means: 1) a lower thermodynamic driving force for hydroxyapatite precipitation at normal oral pH; 2) a higher driving force for hydroxyapatite dissolution at low pH; 3) a lower critical pH. The aims of this study were to: 1. determine the calcium and phosphate concentrations 2. calculate the critical pH for enamel and 3. determine the driving forces for demineralization and remineralization in a group of children and adults.
  
  
  METHODS
  In this comparative study, calcium and phosphate concentrations were measured in the resting and stimulated saliva of child and adult volunteers using a spectrophotometric system used in routine blood analysis. Salivary flow rates were also measured in each group.
  
  
  RESULTS
  The calcium concentrations were lower in children than adults, but the phosphate concentrations were not significantly different. The critical pH was significantly higher for children than adults in both resting and stimulated saliva. Therefore, the thermodynamic driving forces for; (1) demineralisation at low oral pH, is greater, and (2) for remineralisation at normal oral pH, is lower, in children compared to adults.
  
  
  CONCLUSIONS
  The results of this study show that from thermodynamic considerations alone, there is increased risk of demineralization in children compared with adults.
authors.affiliation: Department of Oral Growth and Development, Queen Mary, University of London, UK. p.anderson@mds.qmw.ac.uk
authors.forename: P
authors.initials: P
authors.lastname: Anderson
authors.forename: M P
authors.initials: MP
authors.lastname: Hector
authors.forename: M A
authors.initials: MA
authors.lastname: Rampersad
mesh_terms: D000328:Adult; D002118:Calcium / Q000032:analysis; D002648:Child; D003747:Dental Enamel Solubility; D017886:Durapatite / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D010710:Phosphates / Q000032:analysis; D010812:Physical Stimulation; D012016:Reference Values; D012307:Risk Factors; D012463:Saliva / Q000737:chemistry* / Q000378:metabolism; D018709:Statistics, Nonparametric; D017001:Tooth Demineralization / Q000503:physiopathology
chemical_list: D010710:Phosphates; D017886:Durapatite; D002118:Calcium