The 'Wits' appraisal - its skeletal and dento-alveolar background.

The AB/Occlusal Plane angle (‘Wits’ appraisal) was measured on lateral cephal-ometric radiographs of 25 boys and 25 girls aged between ten and fourteen years. All the subjects were orthodontically untreated and had either a Class I or Class II malocclusion. During the period of the investigation the distance AB ¯ increased by 0.59 mm/year and the AB–Occ decreased by 0.29 mm/year with a resultant increase in the AB/FOP value of 0.20 mm/year. In consequence the ‘Wits’ appraisal was found not to be constant in time. A statistically significant correlation was found between the distance AB ¯ and the angle ANS–PNS/MGo which means that, on average, high angle cases show a greater ‘Wits’ distance than low angle cases. The method error of measuring the ‘Wits’ appraisal by dropping perpendiculars from point A and B to the occlusal plane was 1.21 mm. Calculation of the distance by a formula based on its geometrical parameters gives a slight but insufficient improvement in the method error. A means of reducing the method error and eliminating vertical influences on the ‘Wits’ appraisal is discussed.