Introduction: This investigation aims (1) to compare the timing and magnitude of peak growth velocity (PGV) of cervical vertebrae (CV) 3 and 4 with those of maxillomandibular complex and (2) to determine the optimal timing for orthodontic treatment based on CV morphological changes among skeletal class II Caucasian males. Methods: A longitudinal sample of 46 males with skeletal class II relationship (ANB>4.0) between 9-20 years of age was collected from the Burlington Growth Center (Toronto, Canada). For each subject, lateral cephalometric radiographs were traced to assess vertebral, maxillary and mandibular dimensional changes at age 9, 12, 14, 16 and 20. At the same time hand-wrist x-rays were evaluated for Skeletal Maturation Index (SMI). Descriptive statistics were done and, using SMI as the independent variable, general box plot graphs were generated for growth velocities of maxillary and mandibular cephalometric measures, and height(H), width(W), height/width ratio(H/W) of CV 3 and 4.
Results: Both CV3 and CV4 H PGV occurred at the similar timing, SMI 8-9. The velocities of the CV3 and CV4 W, however, were relatively constant with no identifiable peak. CV3 and CV4 H/W displayed a general sigmoidal growth curve with a value between 0.60-0.65 corresponding to SMI 4. The maxillary and mandibular sagittal PGV occurred around SMI 5-9 and SMI 6-7, respectively, while vertical PGV of the maxilla (SMI 8-9) and mandible (SMI 9) occurred later in development and to a much smaller magnitude.
Conclusions: The PGV of H, H/W changes of CV3 and CV4 coincide with different aspects of craniofacial growth. CV3 and CV4 H seems to be a promising indicator of maxillary and mandibular vertical growth. The CV3 and CV4 H/W at SMI 4, which is 0.62, may be of critical value in predicting the major growth peaks of maxillomandibular complex among skeletal class II Caucasian males.