The temporomandibular joint (TMJ) showed characteristic anatomy and functions contrast to the other joints. In particular, children or young adolescent with the progressive temporomandibular disorder (TMD) showed remarkable changes in their mandibular growth and occlusion. The purpose of this study was to elucidate the functional and biomechanical causes for the maxillofacial deformities of TMD. A typocranial experiment was performed using a plastic skull model by simulating the mandibular movement after condylectomy. The directional forces of masticatory and suprahyoid muscles were reproduced on the typocranial skull model by elastics connecting between mandible and adjacent bony structures. Resultantly, the mandible of unilaterally or bilaterally condylectomized mandible was rotated downward and backward by the activation of masticatory and suprahyoid muscles. When unilaterally or bilaterally condylectomized mandible was activated by masticatory, suprahyoid and perioral muscles, the mandible was less rotated downward and backward than the cases activated by masticatory and suprahyoid muscles only. In the typocranial experiment after unilateral condylectomy the mandible was rapidly deviated toward the affected side, but this deviation was much reduced when the mandible was intensely supported by perioral muscles. By the compensatory response against the overload of TMJ due to the mandible body resection the typocranial experiment also produced the deepening of antegonial notch by the increased force of mylohyoid and perioral muscles. These findings suggest that after condylectomy the posterior fibers of mylohyoid and perioral muscles become hypertrophic and induce the characteristic mandibular deformities, i.e., deepening of antegonial notch and bowing of posterior ramus, which are similar to the mandibular changes in the progressive TMD.