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

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.