Abstract: Objective: To describe the dental form and basal bone arch form of skeletal Class Ⅱ malocclusion patients by transforming 3D image data to 2D plane and establishing a mathematical model. Methods: CBCT data of 30 patients with skeletal Class Ⅱ malocclusion were selected. Occlusion plane with mathematical algorithm by dental form point (Fa) and basal bone arch form point (Ba) was determined. 3D image data was transformed to 2D plane with Software Matlab 7.0. Results: The mathematical model describing the dental arch and basal bone arch form of skeletal ClassⅡ malocclusion was established: 1) dental arch: maxillary Y=41.01[1- (2X/61.08)2]0.73; mandibular Y=37.35[1- (2X/59.55)2]0.717; 2) basal bone arch: maxillary Y=29.15[1- (2X/65.63)2]0.721; mandibular Y=30.91[1- (2X/79.19)2]1.24. Conclusion: A function equation which has high fitting degree with the dental form and basal bone arch form of the skeletal Class Ⅱ malocclusion patients was established. The function equation and the measurement data from it can guide further research

Key words: Skeletal class Ⅱ malocclusions, Dental arch, Basal bone arch, Mathematical model, 2D projection