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BACKGROUND Quantitative clinical assessment tests for oral function have become popular in patient assessment, however, their comparability remains unclear. OBJECTIVE To assess the reliability and comparability of pairs of different instruments for measuring maximum tongue pressure (MTP), chewing function (CF), and maximum lip force (MLF), and to analyze the influence of subjects' characteristics on the applied instruments. METHODS Each pair of instruments, as well as a single device measuring the maximum voluntary bite force (MBF) was assessed across 26 healthy volunteers. The respective pairs of devices were compared using Bland-Altmann plots and linear regression analysis. Furthermore, the influence of age, occlusal support zones, number of functional occlusal units, MBF, MTP, and MLF were investigated as predictors on CF using a generalized estimating equations model. RESULTS Neither the two assessments of CF, nor of MLF were correlated to each other, but there was a significant correlation between the assessments of MTP. Hue-Check gum was able to demonstrate a significantly higher CF in younger compared to older individuals (p=0.004) and individuals with high numbers compared to low numbers of occlusal units (p<0.001). Those differences could not be demonstrated with the Vivident chewing gum. CONCLUSION The absolute values of MTP assessed by the two applied devices cannot directly be compared, although normalized values may be directly comparable. Moreover, our observations suggest that the Hue-Check gum was able to discriminate the effects of age and the number of occlusal units on CF. Our observations suggest that the two gums cannot be used interchangeably.