title: Time-related Changes in pH, Buffering Capacity and Phosphate and Urea Concentration of Stimulated Saliva.
abstract: OBJECTIVE
  To quantify changes in pH, buffering capacity and hydrogen carbonate, phosphate, protein and urea concentrations of stimulated saliva which occur during a 30-min measurement delay after saliva collection. The correlation between time-related chemical changes and changes of salivary pH and buffering capacity was assessed in order to explain the observed changes in salivary pH and buffering capacity.
  
  
  METHODS
  Stimulated saliva samples were collected from 30 volunteers after inducing salivation by chewing a piece of parafilm. Measurements of salivary variables were made immediately after saliva collection and again 30 min later, during which time the specimens were exposed to the atmosphere in collection cups at room temperature.
  
  
  RESULTS
  Postponement of measurements resulted in a significant increase in pH and a significant decrease of buffering capacity, phosphate and urea concentration. The results suggest that the time-related pH increase could primarily be attributed to loss of dissolved carbon dioxide from saliva, and confirm the importance of hydrogen carbonate in the neutralisation of hydrogen ions, but they do not support the principle of catalysed phase-buffering for the hydrogen carbonate buffer system in saliva. A decrease in phosphate and urea concentration affects salivary buffering capacity.
  
  
  CONCLUSIONS
  This study emphasises the importance of the standardisation of measurement time when measuring salivary pH, buffering capacity, phosphate and urea concentrations following the collection of saliva in order to obtain comparable results. It also provides a partial explanation of the mechanisms underlying the observed changes of pH and buffering capacity over time.
authors.forename: Lea
authors.initials: L
authors.lastname: Vuletic
authors.forename: Kristina
authors.initials: K
authors.lastname: Peros
authors.forename: Stjepan
authors.initials: S
authors.lastname: Spalj
authors.forename: Dunja
authors.initials: D
authors.lastname: Rogic
authors.forename: Ivan
authors.initials: I
authors.lastname: Alajbeg