Saliva performs a multiplicity of roles within the oral cavity. Regrettably, its importance is usually not appreciated until it is absent. Salivary dysfunction is a common problem and is frequently undiagnosed, at least in part, because the patient’s symptoms are not a reliable indicator of salivary gland function. Patients will rarely be aware of diminished output until the resting flow rate is less than half the normal rate. The functions of saliva include -
• lubricating the oral tissues for swallowing and speech,
• assisting the sense of taste by acting as a solvent for ions and through proteins such as gustin,
• maintaining health of the oral mucosa through growth factors to promote wound healing, and cystatins to inhibit destructive enzymes e.g. cysteine proteases,
• assisting in digestion through amylase and lipase,
• dilution and clearing of material from the oral cavity,
• buffering acids from dental plaque,
• buffering weak acids from food and drink e.g. wine or black cola soft drinks,
• buffering short term exposure to strong acids e.g. reflux and vomiting,
• serving as a reservoir for the ions calcium, phosphorus, and fluoride used in remineralisation,
• controlling oral microflora through immunological (IgA), enzymatic, peptide and chemical mediators.
Salivary flow is stimulated by the taste and mastication of food. The increased flow will lead to a raised pH with an increase in bicarbonates and, therefore, an increase in buffering capacity. Calcium and phosphate levels will also rise and this will influence the balance between demineralisation and remineralisation of tooth structure. There will also be an improved clearance of food debris due to more rapid movement of the salivary film as well as greater activity of the antimicrobial mechanisms available from saliva. Reductions in the quantity of salivary secretions or changes in the properties of saliva are responsible for a host of related oral and dental problems which impact directly upon quality of life.
Saliva flow rates in healthy patients,
• resting flow rate for pooled saliva = 0.3-0.4 mL/minute.
• less than 0.1 mL/minute = xerostomia.
• stimulated flow rates = 1-2 mL/minute,
• less than 0.7 mL/minute = pathology.