The purpose of this investigation was 1) to analyze horizontally the growth changes of dentofacial pattern in mandibular prognathism before treatment, and to evaluate the influence of treatment by comparing the mean changes occured during treatment periord with the general tendency of the growth changes, and 2) to detect the factors influencing the severity of mandibular prognathism, and to find the differences of response to treatment among mandibular prognathisms of various intensity. Two hundred and thirty-one cases including seventy-two males and one hundred and fifty-nine females, ranging from age 4.67 years to age 27 years, of anterior cross bite and mandibular prognathism were selected for roentgeno-cephalometric study. These cases were classified into five age groups and four skeletal types, by males and females respectively, according to the chronological age and the apical base relationship before treatment. All these cases showed negative overjet before treatment and showed positive overjet after treatment. The lateral headplates taken before and after treatment were used for tracing and analysis. Areas studied were relative to the craniofacial skeletal pattern and the denture pattern. Several findings were observed : 1) The flexion of the cranial base (∠BaSN) showed no significant difference among various age groups in the average before treatment, and revealed no significant change after treatment. 2) Dimensional increment of S-N, S-Ba, Pns-Ans, Go-Me, and Ar-Gn during treatment periord were regarded as contribution of the growth. 3) In the skeletal pattern, ∠SNA, ∠SNAns, ∠PP-SN, gonial angle, Ar-Go, and Ar-Ba remained stable during treatment period. 4) No evidence of growth activation on anteroposterior dimension of the maxilla was noted although maxillary dentition had been treated on the basis of labial expansion. Dimensional growth of the mandibular body and effective length of the mandible did not seem to be retarded in spite of the fact that the retraction force had been applied on the mandible during treatment period. 5) The position of the mandible was found to be shifted backward and downward as relative to the cranial base under the influence of the treatment. Skeletal discrepancy between the maxilla and the mandible was found being corrected to a certain degree mainly by this positional change of the mandible. 6) Axial inclination of the incisors was found to be affected most markedly by treatment. The maxillary incisor was tipped labially and the mandibular incisor was tipped lingually by the treatment. 7) Dimension and the flexion of the cranial base did not seem to be correlative with severity of mandibular prognathism. Undergrowth and retrusion of the maxilla seemed to play only a small part in the severity of mandibular prognathism. 8) However, summation of the dimensional factors and positional factors of the mandible would affect the severity of mandibular prognathism more conspicuously. 9) Contrary to the expectation and the ordinary concept, it was found that the cases of severer mandibular prognathism would tend to have a smaller gonial angle and a smaller mandibular plane angle in the average. 10) It was revealed that the more the mandible protruded, the more the maxillary incisor inclined labially and the more the mandibular incisor inclined lingually before treatment. The tilting up anteriorly of the occlusal plane and the increasing of the overbite would associate with this. 11) The more the mandible protruded before treament, the more it would be retruded by the treatment. It does'nt necessarily mean that the mandible was easier to be retruded by the treatment when it had been more protruded. It would rather mean that it was more necessary to retrude the mandible in the severer mandibular prognathism although there exist a limitation of the retrusion. 12) The more the mandible protruded before treatment, the less the maxillary

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