The Definitive Treatment Plan
Treatment planning should only be undertaken after a thorough history and clinical examination of the patient, together with an analysis of the radiographs and study casts.
Planning the Maxillary Move
The key to successful surgery is to place the maxilla and the decom-pensated maxillary incisors in the optimum anteroposterior and vertical position in relation to the upper lip and face. The mandible is then placed in a Class I incisor relationship to the maxilla.
The profile of the seated patient is assessed with the Frankfort plane horizontal to decide the horizontal anteroposterior movement of the maxilla.
Changes of the naso-labial angle can be predicted with a moist cotton roll or soft pink wax. The frontal view is assessed by:
i) The ratio of the cephalometric upper to lower facial height — 45:55%.
ii) The incisor exposure with the lips parted at rest — will decide the vertical movement of the maxilla. Aesthetic exposure may vary from 1 to 4 mm. This is inversely proportional to the upper lip length which ranges from 18-24 mms.
iii) Excessive or unaesthetic incisor exposure is corrected with appropriate maxillary impaction.
iv) Where the upper lip is unduly short, the patient can show a greater amount of incisor. If not, the resulting midfacial appearance will be disproportionately small in the vertical dimension.
v) Rarely the patient has marked dento-alveolar hypoplasia and shows little or no incisor with a normal lip length. This is corrected with an inferior movement of the maxilla.
vi) Horizontal as well as vertical maxillary movements will affect the incisor exposure. Advancing the maxilla will lead to greater incisor exposure which will need to be adjusted for when considering the vertical move.
vii) Coronal occlusal cants and midline rotations must also be corrected.
viii) Moving the maxilla will also affect the nose. Vertical impaction widens the alar base and forward movements will elevate the nasal tip. Depending upon the initial appearance these changes may or not be desirable. If not, then a record should be made to provide a “cinch suture” across the lateral alar cartilages or to reduce the anterior nasal spine at the time of surgery.
ix) The inherent inaccuracy of the planning and surgical technique and the eye’s inability to perceive small anatomical changes, determine that units of horizontal advancement should be no less than 3 mm. This also facilitates planning as a 3 mm minor advancement; a 6 mm/>