Comparison of smartphone-camera and conventional flatbed scanner images for analytical evaluation of chewing function.

Abstract

The two-colour mixing test is a quick method to assess chewing function (CF). The use of smartphone cameras for acquiring images may help in further simplifying the process. This study evaluated the reliability of smartphone-camera images of chewing gums to assess CF. Five test samples of a bicoloured chewing gum were produced by a single fully dentate adult volunteer. The specimens were flattened to 1-mm thick wafers. The two sides of the wafers were digitised with a conventional flatbed scanner (control) and were photographed 20 times using 8 different smartphones. The images were assessed optoelectronically to obtain the variance of hue (VoH) and subjectively by visual assessment (SA) using a categorical scale (SA1-SA5). Spearman's correlation and regression models were used for statistical analyses. The intra-group variability for SA1-SA3 was <1% for all smartphones, but significantly higher than controls for SA4 and SA5 (smartphone: SA4=5.57%; SA5=8.76%; control: SA4=2.5%; SA5=0.79%). VoH was progressively lower from SA1 to SA5 for all imaging devices (r>-.97; P<.001). VoH comparisons between control and smartphone images revealed significant differences for the individual SA categories, and however, the magnitude of differences was small and non-significant when the full range of SA levels were considered. The linear mixed model regression showed significant effects for all the smartphones (P<.001) and SA levels (P<.001) in relation to the flatbed scanner values. Smartphone cameras may be used to evaluate colour mixture for a bolus-kneading test, however, the precision is lower with higher degrees of colour mixing.