The use of linear and angular measurements of maxillo-mandibular anteroposterior discrepancies

OBJECTIVES: To extend the assessment of the clinical significance of the measurement of the anteroposterior discrepancy between maxilla and mandible on the bisector of the palatal plane to mandibular plane angle to a large group of randomly selected patients of both sexes, and to verify the correlation of this measurement to well established angular and linear assessments of anteroposterior discrepancy. DESIGN: Retrospective analysis of pre-treatment lateral cephalometric radiographs. SETTING AND SAMPLE POPULATION: The Laboratory of Functional Anatomy of the Stomatognathic Apparatus at Milan University, Italy. Three hundred and six orthodontic patients (165 males, 141 females) aged between 6 and 50 years. EXPERIMENTAL VARIABLE: ANB angle; corrected ANB* angle which compensates for the position of the maxilla and rotation of the mandible relative to the cranial base; Wits appraisal; MM-Wits: linear distance between the projections of A and B points on the bisector of the palatal plane to mandibular plane angle. RESULTS: The MM-Wits distance was significantly correlated to two angles (ANB and ANB*), as well as to the Wits appraisal. All the correlations performed did not show sex- or age-characteristic patterns. The correlation to the corrected ANB* was the best among the three, with a correlation coefficient of 0.915, MM-Wits (mm) = 1.497 x ANB* (degrees) -6.784. From the correlation, reference values for the new measurement have also been estimated, and found to be between -0.65 and -6.85 mm for skeletal Class I individuals. CONCLUSION: It is recommended that the diagnosis of orthodontic anomalies should be performed taking into consideration more than a single anteroposterior appraisal.