Mandibular Spatial Reorientation and Morphological Alteration of Crouzon and Apert Syndrome.

BACKGROUND: From infancy to adulthood, the mandible develops increased ramus height, prominence of the chin, and laterally widened gonial angles. In Crouzon and Apert syndromes, both relative retrognathia and prognathic jaws have been reported. Growth is influenced by a variety of factors, including the growth and relative position of the skull base, functional coordination, and the spatial influence of the laryngopharynx. Thus, this study aimed to explore in detail the evolution of the mandible in both syndromes and its relationship with the entire facial structure and skull base. METHODS: One hundred twenty-three preoperative computed tomographic scans (Crouzon, n = 36; Apert, n = 33; control, n = 54) were included and divided into 5 age subgroups. Computed tomographic scans were measured using Materialise software. Cephalometrics relating to the mandible, facial structures, and cranial base were collected. Statistical analyses were performed using t test and statistical power analysis. RESULTS: In Crouzon syndrome, the angle between the cranial base and gnathion was increased prior to 6 months of age by 10.29 degrees (P < 0.001) and by adulthood to 11.95 degrees (P = 0.003) compared with normal. After 6 months of age, the distance between bilateral mandibular condylions (COR-COL) was narrower by 15% (P < 0.001) in Crouzon syndrome compared with control subjects. Before 6 months of age, Apert COR-COL decreased 16% (P < 0.001) compared with control subjects and 13% (P = 0.006) narrower than Crouzon. During 2 to 6 years of age, Apert mandibular ramus height caught up to, and became longer than, Crouzon by 12% (P = 0.011). The nasion-sella-articulare angle of the Apert skull was 5.04 degrees (P < 0.001) less than Crouzon overall. CONCLUSIONS: In Crouzon syndrome, the changes of the spatial relationship of the mandible to the cranial base develop earlier than the mandibular shape deformity, whereas in Apert syndrome, the spatial and morphological changes are synchronous. The morphological changes of the mandible are disproportional in 3 directions, initially significant shortening of the mandibular width and length, and, subsequently, reduced height. Crouzon has more shortening in mandibular height compared with Apert, reflecting the more shortened posterior cranial base length. The narrowed angle between the mandible and the posterior cranial base in Apert skulls is consistent with the more limited nasopharyngeal and oropharyngeal airway space.