Cephalometric assessment of sagittal jaw base relationship prior to orthognathic surgery: the role of anterior cranial base inclination.

In a cephalometric study, 71 presurgical lateral radiographs of patients suffering from malpositions of 1 or both jaws were analyzed to assess the influence of cranial base inclination on anteroposterior cephalometric angles. Angles SNA and SNB, as well as the angle between sella-nasion (SN) and Frankfort horizontal (FH), were measured. To verify the true sagittal position of the jaws, SNA and SNB were related to a corrected normal anterior cranial base inclination (mSNA, mSNB). Two geometric models were calculated and examined. The application of the first and second models for SNA and SNB resulted in different estimations of the sagittal jaw position in 46% and 38% of the presented patients, respectively. Linear regression analysis demonstrates that FH may not be substituted for SN as a reference line in anteroposterior measurements, but underlines that a correction with regard to anterior cranial base inclination is beneficial. According to the results of the second model, the most valuable reference line appears to be located approximately halfway between SN and FH. Considering the frequent coincidence of jaw malposition and cranial base dysmorphia, cranial base-related cephalometric parameters should be interpreted carefully.