Validity of the Cervical Vertebral Maturation Method for Prediction of Mandibular Growth Peak

Background: Determination of residual growth potential is an important part of treatment planning in dentofacial orthopaedics. Utilisation of periods of accelerated growth during treatment may help to enhance a patient’s dental and skeletal outcomes; and a variety of skeletal maturation methods have been proposed to date. Cervical vertebral maturation (CVM) has been popularised as a method of skeletal maturation as the cervical vertebrae (C2-C4) can be seen on routine lateral cephalograms taken for orthodontic treatment. Most of the currently accepted methods of CVM are qualitative and subjective. Hence, there is a need for a quantitative and non-subjective method for vertebral maturation assessments in the field of orthodontics. The aims of the present study were to: firstly, analyse the morphometric changes in C2-C4 with growth; and secondly, to test the validity of the assumptions underlying the CVM method, and its relationship to observed changes in mandibular length during growth. Methods:This study was a retrospective longitudinal study of a unique collection of radiographs from the Toronto-Burlington Growth Study, housed in the American Association of Orthodontists Foundation (AAOF) Craniofacial Growth Legacy Collection. Lateral cephalograms of 25 participants from ages 10 to 16-years were downloaded and scaled according to the guidelines set by the AAOF curators. Sixty-three mandibular and cervical landmarks were identified and analysed to answer the following research questions: (1) Are the vertebral shape changes consistent with the stages described by the CVM method? (Baccetti et al., 2005); (2) How do the morphometric shapes of C2, C3 and C4 change with growth?; (3) Does the maximum change in mandibular length actually occur between the stages described as CS3 and CS4?; (4) At what chronological age does peak mandibular growth occur?; (5) How does mandibular length relate to gender, chronological age and cervical stage?; and (6) Can the mandibular growth peak be reliably predicted using a quantitative shape analysis?. Reproducibility was tested by repeating cervical staging after two weeks and landmark identification after four weeks. Point distribution methods were used to describe the morphometric templates of the vertebrae in relation to chronological age and timing of peak mandibular growth. Mixed model analysis was used to determine the relationship between mandibular length, sex, CVM stage and chronological age. Results:High agreement was seen between repeated assessments, with low mean standard deviations calculated for the x- and y-coordinates in repeat landmarks (0.3mm and 0.4mm respectively). The reliability of CVM staging was high (84%). Weighted and unweighted kappa values were 0.89 and 0.80 respectively. In all cases, the difference between two determinations was no more than one category. This study demonstrated: Firstly, that quantitative assessment of vertebral shapes are consistent with the qualitative descriptions used by the CVM methods except for the sequential appearance of concavity in the inferior border of C2 to C4. Secondly, morphometric changes of C2-C4 during growth were consistent with the CVM descriptions. However, morphometric templates of vertebral shapes were similar before and during mandibular growth peak; and changes were only detectable after the growth peak had passed. With chronological age, morphometric vertebral shape changes varied between sexes. Thirdly, mandibular length changes were not significantly associated with CVM stages after adjusting for chronological age. Mixed model analysis showed that mandibular length was found to relate most significantly to chronological age, and to a marginal extent to gender. Peak mandibular growth occurred at a mean age of 11.7 years in females (95% C.I = 11.1-12.3) and 12.8 years in males (95% C.I = 12.1-13.5). Conclusions: The present study used quantitative and morphometric assessments of vertebral shape to assess mandibular growth in relation to currently accepted CVM methods, sex and chronological age. Quantitative shape descriptions were consistent with qualitative CVM descriptions in most cases. However, morphometric changes of the second to fourth cervical vertebrae are poorly related to mandibular growth rate. Chronological age represents a better predictor of mandibular growth peak than cervical stage