[Decision strategies in orthognathic surgery. Part 1: The predominance of functional factors in the choice of osteotomy sites. A theoretical study].

Most of the scientific papers concerning facial osteotomies are focused on the surgical procedures. However, the most important thing to consider is how to go to the right indication and not how to do it. By an only morphological approach, as we can do with dental casts and cephalometric studies, it is obvious that we forget the functional factors. They nevertheless are essential to consider. Their knowledge permits understanding the physiopathology of the deformity and avoiding the postsurgical relapses. The main five factors concern: the dentoalveolar corridor, between tongue and orbicularis oris muscle, the facial bone growth modeling by functional matrix, the relations between upper incisors, lower incisors and lips, the posterior airway and the rest position of the tongue, the vertical muscular balance. Surgery has to normalize the abnormal function which is at the origin of the abnormal morphology. For this reason, maxillary surgery is better than mandibular surgery for the correction of a Class III deformity. Moreover, the transversal and vertical dimensions are always to be considered at the light of the functional parameters. Most of cases of dentofacial deformities are to be treated by bimaxillary osteotomies, including often transversal and/or vertical modifications. When the anatomical sites of these surgical procedures are determined, then we have to make an aesthetic facial profile simulation to validate the total amount of the bone displacements (cf. Part 2).