Validity and reliability of the mixing ability test as masticatory performance outcome in children with spastic cerebral palsy and children with typical development: A pilot study

Background: The mixing ability test (MAT) as an outcome measure of masticatory performance is largely used in studies with adults, but not yet with children. Objective: This study aimed to test the construct validity and the test-retest reliability of the MAT in children with spastic cerebral palsy (CP) and children with typical development (TD). Method: The results of the MAT were correlated with tongue movements, mandible movements, relative muscle contraction and clinical observation measured with ultrasound, 3D kinematics, electromyography (EMG) and relevant items of the mastication observation and evaluation (MOE) instrument, respectively. Moreover, the between-groups effect was tested. Test-retest reliability was calculated with an intra-class correlation coefficient (ICC) and standard error of measurement (SEM). Results: Twenty-one children (seven children with spastic CP and 14 children with TD) participated in this study. The MAT scores showed moderate to good correlations with some variables of the tongue movements, horizontal mandible movements and occlusion duration, relative muscle contraction of the left temporalis and all six MOE items (−0.80 < r < 0.49). The MAT scores were significantly higher for children with CP (mean 22.6; SD 2.4) compared to children with TD (mean 19.9; SD 1.9). The test-retest reliability had an ICC of 0.7 and a SEM of 1.16 (±5% of the mean score). Conclusion: These results indicate that the MAT is suitable and complementary to ultrasound, 3D kinematics, EMG and observation to compare the masticatory performance between children with CP and children with TD, with an acceptable test-retest reliability.