A novel method for assessing oral mixing ability based on the spatial clusters quantified by variogram

Background: The two-colour chewing test (TCCT) has been widely used for assessing oral mixing ability, a critical component of masticatory performance. Most studies focused on quantifying the evenness of colour distribution. It remained unknown if the variation of colour clustering was a valid index of oral mixing ability. Objective: The study aims to investigate the oral mixing ability based on the spatial clusters quantified by variogram. Methods: Fifty older people (15 male/35 female, age: 66.0 ± 7.8 years) were assessed for the TCCT and the colour-changeable chewing gum test (CCGT). For the CCGT, we quantified the degree of colour change (ΔE). For the TCCT, the highest peak in colour histogram (HP), the standard deviation of colour values (SDC) and the range of variogram from colour spatial distribution (VARG) were quantified. The participants were grouped according to the contacts of posterior teeth, as assessed by Eichner Index (EI). Results: Highest peak, SDC and VARG showed statistically significant differences between the EI groups (two-tailed independent t test P <.05). Higher VARG (ie a lower degree of clustering) was significantly negatively correlated with ΔE (r = −.36, one-tailed P <.01). The binary logistic regression revealed that among the spatial indices (HP, SDC and VARG), only VARG achieved statistical significance in prediction to the EI group. Eliminating other indices was insignificant to the model performance. Conclusions: Our results show that the averaged cluster sizes, quantified by variogram, are a valid index for quantifying the TCCT. Compared with other spatial indices, it had the best predictability to the condition of posterior contact.