It is well known that mastication has a significant influence on mandibular growth and development, but the mechanism behind this effect has not yet been clarified. Furthermore, no studies have examined the effects of changes in mastication on the three-dimensional (3D) morphometry of the mandible. The aim of the present study was to investigate the influences of changes in mastication on mandibular growth and morphology. Twenty-five 3-week-old (at the time of weaning) imprinting control region mice were randomly divided into three groups: mice fed a hard diet (HD), mice fed a soft diet (SD), and mice alternately fed hard and soft diets (HSDs) every week for 4 weeks. The morphometry of the mandible was analysed using 3D microcomputed tomography (muCT). Statistical analysis was undertaken using a t-test. muCT analysis showed that the condylar width was significantly greater in the HD group than in the SD group after 1 week. After 4 weeks, mandibular length was significantly longer and ramus height was greater in the HSD group than in the other two groups. Bone volume was significantly less in the SD group than in the other two groups after 4 weeks. These findings suggest that changes in mastication markedly affect mandibular condylar cartilage growth and mandibular morphology. It is considered that dietary education at an early age is important in order to prevent disruption of the development of the mandible.