The relation between pogonion advancement and posterior maxillary impaction

Controversy exists about the relation between the amount of posterior maxillary impaction and pogonion (P) advancement. The aims of the current study were to (1) propose a formula to predict the amount of P advancement due to posterior maxillary impaction surgery, (2) predict the amount of posterior maxillary impaction by means of a formula to achieve the best facial harmony, and (3) identify the compatibility between proposed formulas and the actual resultant mandibular position after posterior maxillary impaction surgery. For obtaining the formulas, 2 cephalograms were taken from 1 patient in centric occlusion and rest position. Afterward, mandibular rotational center was obtained by superimposing the cephalograms; by the help of which the 2 formulas were obtained. To check the reliability of the formulas, 10 patients with the mean age of 21 +/- 1.5 years who had undergone posterior maxillary impaction were selected. The presurgical and postsurgical cephalograms of patients were obtained. These cephalograms were superimposed to find the center of mandibular rotation. Pearson correlation coefficient test was used to evaluate the relation between the suggested formulas and the clinical data. This test showed that there were significant correlations between maxillary impaction and P advancement in both the formulas and clinical evaluation. This correlation (r) was 0.993 (P < 0.001) based on formulas and r = 0.806 (P < 0.005) based on tracing. This study showed that the amounts of anterior facial height reduction and P advancement were almost the same, and the anterior facial height was reduced 1.5 times more than the amount of maxillary impaction.