125 Salivary film thickness and MUC5B levels 2010mm2 [15, 16, 50]. In these studies, the palatal surface areas were determined using foil impressions taken from stone models, while another study used CBCT imaging and digital analysis [15, 16, 50]. Apparently, all methods used so far reveal comparable and representative results as their surface areas are in the same range. In addition, the technique presented in the current study, using an intra-oral scanner, adds up to this line of methods as it had very good reproducibility, as indicated by the excellent range of the ICC. However, future studies, which investigate and compare the validity and the reliability of various methods including the intra-oral scanner for measuring the intra-oral surface area, seem warranted. The pattern of salivary film distribution over intra-oral locations found in the current study was comparable with the distribution of the salivary film in healthy volunteers reported previously [2, 11–14, 18–21]. Also, comparable patterns were seen in the current study, as the tongue and/or the floor of the mouth had the thickest salivary film, while the anterior palate had the thinnest salivary film. The reason why the tongue has the highest level of wetness is probably because of its anatomical location near the caruncle of the Wharton’s ducts [2, 13, 18]. Here, saliva from the many minor glands in this region and the nasopalatine glands as well as the secretions of the submandibular and sublingual glands is collected [2]. Besides, the von Ebner’s glands, with their ducts opening into the sulci of the circumvallate and foliate papillae, produce serous saliva that contributes to the moistening of the tongue [51, 52]. In contrast, several factors make the anterior palate more susceptible to having a thinner salivary film than other intra-oral locations: lack of hard palatal salivary glands, and evaporation, especially during speaking and breathing [18, 53, 54]. Moreover, gravity forces part of the excreted saliva to pool on the floor of the mouth between swallowing episodes. As a consequence, the palate can be moistened less sufficiently [2]. Two previous studies investigated MUC5B levels at various intra-oral locations in healthy controls [11, 14]. However, different techniques were used in these studies compared to our study: Firstly, SDS-PAGE was performed on the eluted Sialopapers with subsequent PAS staining. Then, software analysis was used, scanning lanes of PAS-stained mucin glycoprotein bands, and analysed for colour intensity, gauging the amount of mucin [11, 14]. In contrast, we applied ELISA using an antibody, i.e. F2, to specifically measure MUC5B levels. However, it seemed difficult to compare our findings to those of Chaudhury et al. [11] because they expressed the MUC5B levels in MUC5B glycan/protein proportion. In contrast, we calculated arbitrary units/volume of fluid on Sialopaper [11]. In the study by Pramanik et al., contradictory results compared to our study 6
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