Mandibular form in a rabbit model of familial nonsyndromic coronal suture synostosis

Nonsyndromic coronal suture synostosis produces predictable and well-documented morphologies of the cranial vault with anteroposterior growth restrictions and mediolateral compensatory growth. The potential effects of nonsyndromic coronal suture synostosis on mandibular form are not as clear, however. This study was designed to evaluate whether coronal suture synostosis is associated with alterations in mandibular form by using a familial rabbit model of coronal suture synostosis. To assess this potential relation, the following hypothesis was tested: mandibular form in rabbits with coronal suture synostosis is significantly (P < 0.05) different from that seen in normal rabbits. The cleaned and dried mandibles of 33 adult New Zealand white rabbits were used (12 from normal rabbits, 13 from rabbits with delayed-onset synostosis, and 8 from rabbits with complete coronal suture synostosis). Seven anatomical landmarks on the mandible were located and digitized in three dimensions: anterior molar on the alveolus, posterior molar on the alveolus, coronoid process, anterior pole of the condyle, condylar process, angular process, and mandibular angle. To describe the mandibular condyle, the distance from the anterior pole to the posterior pole of the condyle was measured with digital sliding calipers, as was the distance between the medial and lateral poles. A shape ratio was then created using the dividend of these sums. Statistical analyses of mean form differences between mandibles were executed using Euclidean distance matrix analysis. Statistical analyses of the mandibular condyle linear and shape measurements were analyzed using one-way ANOVA in the three groups. Results showed that complete coronal suture synostosis is associated with significant (P < 0.05) differences in mandibular form compared with that of normal rabbits but that mandibular form in rabbits with delayed-onset synostosis does not differ from that of normal rabbits (P > 0.05). In particular, distances involving the coronoid process in rabbits with coronal suture synostosis were significantly different, paralleling previous work in human patients with coronal synostosis. There are no intrinsic condylar linear or shape differences between any of these groups, however. The form difference noted is most likely secondary to the synostosed coronal suture and may reflect alterations in the cranial base or masticatory musculature in this rabbit model.