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The influence of the spheno occipital synchondrosis fusion on craniofacial form Fortanely, Beatriz Ellen


Introduction: Growth of the facial skeleton is integrated to growth of the cranial base. This relationship is highlighted in patients with craniosynostosis syndromes in whom premature fusion of cranial base synchondroses, including the spheno-occipital synchondrosis (SOS), is associated with severe midface deficiency. Objectives: To evaluate the relationship between SOS fusion and craniofacial morphology in non-syndromic individuals – specifically midface projection and skeletal Class III phenotype. Methods: 250 pre-treatment cone-beam computed tomography images were studied from a collection of orthodontic patients’ records, aged 5-11 years (M = 99, F = 151, average age = 8.77 years). SOS fusion was scored using a 6-stage SOS fusion scale utilizing InVivoDental (v6). 3D Slicer (v4.10.2) was used to place three-dimensional landmarks. Error analysis was performed by repeat landmarking of 12 volumes (mean error = 0.23 mm). X, Y, Z coordinates for landmarks were used to determine linear and angular craniofacial measurements. Geometric morphometric (GM) analyses were used to describe facial shape variation. Results: There is a large variation in SOS fusion stage, with older children tending to have a higher fusion stage than younger children. While SOS stage is correlated with subject age, no statistically significant relationships were noted in the age of SOS stages between the Skeletal Class I, II, and III groups for males or females. There were no statistically significant findings of SOS stage as it relates to age or the linear and angular craniofacial measurements in this study, except A Point – Nasion – B point angle being decreased in SOS stage 3 compared to SOS stage 2. The GM analyses suggests that SOS stage, sex, and skeletal class do correlate with craniofacial morphology. Conclusions: This data suggests that younger children with early fusion of the SOS may display a skeletal pattern which is similar to a skeletal Class III morphology. SOS stage is more closely correlated to facial morphology differences of increased mandibular length and transverse facial width. Maxillary projection is also found to be correlated with sex and skeletal class. Further investigation is needed to assess how fusion of the SOS may affect orthodontic and orthopedic treatments for midface deficiency.

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