Orthognathic Surgery and Craniofacial Deformities
Orthognathic Surgery and Craniofacial Deformities
This domain covers the surgical correction of dentofacial deformities, including mandibular prognathism (class III), retrognathia (class II), vertical maxillary excess, and asymmetries. You must know the pre-surgical orthodontic phase, the surgical procedures (BSSO, Le Fort I osteotomy, genioplasty), and the post-surgical care. Also, understand craniofacial syndromes (cleft lip/palate, Crouzon, Apert) and their management. Key concepts include cephalometric analysis, model surgery, and virtual surgical planning.
Traps: Questions often test the complications of BSSO: inferior alveolar nerve injury (most common), relapse, and unfavorable fractures. Another trap is the timing of cleft lip repair (rule of 10s: 10 weeks, 10 lbs, 10 g/dL hemoglobin) and cleft palate repair (9-12 months). Also, know that Le Fort I osteotomy can be used for maxillary impaction or advancement; BSSO for mandibular advancement or setback.
Rule of thumb: For orthognathic surgery, always perform pre-surgical orthodontics to decompensate the dentition. Use rigid internal fixation for stability. For cleft lip, the Millard rotation-advancement technique is common.
Worked example: A patient with mandibular prognathism (class III) undergoes BSSO setback. Post-operatively, they develop numbness of the lower lip. This is likely due to inferior alveolar nerve stretch or injury. Most cases resolve spontaneously within 6 months.