Dry mouth, or oral dryness, is a complex and quite commoncondition, reported with a varying prevalence of 10-80 %, expressed as a physiological deficiency with or without perceived dysfunction. This condition can severely affect oral health, oral function andquality of life.This thesis is based on four studies:Study I is a systematic review of the scientific literature and anevaluation of the quality of the evidence for diagnostic methods used to identify oral dryness. The literature included publications during the time period January 1966 to February 2011.Results and conclusions: The database searches resulted in 224 titles and abstracts. A total of 18 original studies were judged relevant and interpreted for this review. When evaluating the included studies witha quality assessment tool for diagnostic accuracy, many of the studiesexhibited shortcomings. The most common shortcomings were that the patient selection criteria were not clearly described and the test or reference methods were not described in sufficient detail. Seven of the included studies presented their results as a percentage of correct diagnoses. The evidence for the efficacy of clinical methods to assess oral dryness is sparse and improved standards for the reporting ofdiagnostic accuracy are needed in order to assure the methodological quality of studies. Furthermore, a global consensus regarding theterminology of oral dryness is needed in order to facilitate diagnostic procedures, choice of treatment and research design. Salivary dysfunction has mainly been described as being related to low salivary flow rate but the correlation between salivary flow rate and symptoms has shown to be weak. This suggests that not onlyquantity as a parameter, but also qualitative parameters of saliva,are needed to be included as factors of importance in evaluatingthe perception of oral dryness. The protective functions of salivaare performed both through and within the bulk liquid phase ofsaliva, but maybe more implicit through saliva components beingdynamically associated as a thin intermediary film on all surfacesexposed in the oral cavity. For instance, examples of qualitativeprotective functions of surface associated saliva would be the film- forming capacity and rheological characteristics of saliva. Today thereis a lack of clinical diagnostic methods that systematically combine individual’s perception of saliva and tests of protective functions of saliva, which in combination may identify individuals at risk andneed of directed preventive regimens.The overall aim of this thesis was to evaluate scientifically reported diagnostic methods in use to identify oral dryness and to exploremethods for clinical monitoring of protective functional characteristicsof salivary films Study II surveyed the occurrence of subjective and objective oraldryness in two populations, one randomly selected group and onedental care-seeking group. The relationship between subjectiveand objective oral dryness to clinical parameters was analyzed and individuals were designated into one of four groups depending onthe occurrence of subjectively described and /or clinically measured oral dryness.Results and conclusions: No association between subjective oraldryness and flow rates of unstimulated and stimulated saliva wasfound in either of the two populations studied. Individuals identified with subjective oral dryness or objective oral dryness presented to a greater extent a history of oral rehabilitation compared to individualswho showed no indications of oral dryness. Results and conclusions: Individuals with subjective oral drynessexhibited lower values for saliva viscosity and elasticity, whencompared to the other groups. Additionally, the amount of salivaassociated to a germanium prism was the lowest measured in thisgroup, even if the total protein concentration was not extremely low. These test results in combination with a moderate decrease in surfacetension after 600 s may be indicative of a lower film forming capacityof saliva from individuals expressing subjective oral dryness.