Floating norms for individualising the ANB angle and the WITS appraisal in orthodontic cephalometric analysis based on guiding variables

PURPOSE: The sagittal skeletal relationship of maxilla and mandible (skeletal class) can generally be determined via lateral cephalograms (ANB angle or Wits appraisal) by comparing measurements to empirical norms based on the respective population mean. However, values differing from these empirical norms also enable a therapeutically desired, normal class I occlusion depending on individual craniofacial pattern, thus requiring floating norms based on guiding variables. As available regression equations consider only few predictor variables and are not up-to-date regarding a contemporary patient collective, the aim of this study was to establish improved and extended regression equations for individualising the ANB angle and Wits appraisal. METHODS: This retrospective, cross-sectional multicentre study was based on 71 Caucasian male and female subjects of any age with normal dental occlusion. We cephalometrically analysed digitised pretreatment lateral radiographs and performed multiple linear regression analyses to identify suitable skeletal predictor variables for individualising the ANB angle and Wits appraisal. RESULTS: Inter- and intrarater reliability tests showed mostly perfect measurement concordance. Both original regression equations by Panagiotidis/Witt and Järvinen could be updated for a contemporary population with new regression coefficients. The equation for individualising the ANB could be further optimised in its prediction reliability by adding the skeletal predictor variables NL-NSL, NSBa, facial axis (Ricketts) and index (Hasund), whereas the recalculated Wits equation could not be further improved by additional guiding variables. CONCLUSIONS: The improved regression formulae for individualising the ANB angle and Wits appraisal should help to improve the assessment of sagittal skeletal class in clinical orthodontic practice.