Objective: To study the stability of SN (anterior cranial base) length and the ability to evaluate upper lower jaws, and study the inner skeletal structure mechanism.
Methods: Interrelated angles, SN length, maxillary and mandible length were measured, the ratios between SN and maxillary and mandible length were compared with normal standard data, the data between mixed and permanent dentition groups were compared.
Results: No significant difference was found on SN length between anterior crossbite patients and normal sample. Significant difference was found between crossbite and normal data on the ratio of SN and maxillary length and mandible length. Based on evaluation of SN length, the crossbite can be divided into three types of skeletal structures including normal maxilla and longer mandible, short maxilla and normal mandible, short maxilla and longer mandible, the longer mandible is a main factor.
Conclusion: With the advantage of stability, SN can be used to evaluate maxilla and mandible, and decide the skeletal mechanics of crossbite individually and accurately.