18 Chapter 1 measures only the whole saliva secretion, but this flow rate does not provide information on the extent of the moisturizing effect of saliva. For this reason, hyposalivation and xerostomia are not correlated per se [23, 41]. Moreover, the sensation of a dry mouth is not only related to the reduction in salivary secretion rate, but possibly also to the unequal thickness of the saliva film on both soft and hard oral tissue surfaces [23]. The salivary film thickness could influence the moisturizing effect of saliva, and consequently the surface over which saliva is spread can influence the salivary film thickness and possibly also its moisturizing effect. An important gap in the scientific literature is a dry-mouth questionnaire which explores the perceived dryness at various intra-oral locations, specifically various mucosal surfaces such as the tongue or palate. And, although, a large number of studies have shown that the salivary film is not equally distributed within the oral cavity [33, 42-49], a questionnaire to determine dryness at specific oral locations is still lacking. For this reason, it is envisaged that a questionnaire to determine dryness at specific oral locations could increase our understanding about the distribution of saliva in the oral cavity and the relation with perceived dryness. Additionally, such a new questionnaire could even contribute to determining the cause of oral dryness in specific patient groups. In addition, as the (size of) surface area plays a role in the distribution of saliva, measurement of the oral surface areas could be an important additional tool during the diagnosis of oral dryness. Nowadays, various interventions are available to relieve oral dryness. The reasons that affect the use of dry-mouth interventions by patients are not fully understood yet. In previous research it was shown that age, gender and the presence of a dental prothesis could affect the use of dry-mouth interventions in Sjögren’s syndrome patients [50]. However, it is still unclear whether the severity of intra-oral dryness could also affect the use of drymouth interventions. For this reason, factors that affect the choice of dry-mouth interventions will be further explored. Aimand outline of the thesis The overall aimof this thesiswas to improve the current, available diagnostic tools for drymouth by developing a newmethod for measuring the perceived dryness at specific various intra-oral locations and to investigate the effect of intra-oral surface areas on the distribution of saliva within the oral cavity. Additionally, the use of dry-mouth interventions by various dry-mouth patients will be investigated to understand which factors affect the use of these interventions. In this thesis, eight research chapters are divided into three main themes:
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