Prediction of mandibular autorotation.
OBJECTIVE
The purpose of this investigation was to test the hypothesis that the mandible rotates around the same point during maxillary impaction surgery as during initial jaw opening. This point, called the center of mandibular autorotation (CAR), could then be used to predict mandibular position and to decide whether only maxillary impaction would be needed to correct the occlusion and the facial profile.


METHODS
Preoperatively, two lateral cephalograms were obtained from a consecutive series of 20 patients who underwent maxillary impaction without concomitant mandibular ramus osteotomy. One cephalogram was taken with the mandible in centric relation using a wax bite wafer and another with a jaw opening of 10 mm using a fabricated acrylic bite block with the mandible manipulated to its most retruded position. The CAR was calculated before and after jaw opening using the Rouleaux method on the lower incisor and gonion point. A third lateral cephalogram was taken within 2 days postoperatively. The postoperative lower incisal point was then transferred to the first cephalogram using cranial base superimposition.


RESULTS
When the preoperative and postoperative distances between CAR and incisal point were compared, there was no significant difference between these distances, proving the hypothesis.


CONCLUSIONS
The method used is a practical and precise way to determine the center of mandibular autorotation on an individual basis. The center of rotation during initial jaw opening is the same as during impaction surgery.
Nadjmi
N
N
Department of Surgery, General Hospital St John, Bruges, Belgium.
Mommaerts
M Y
MY
Abeloos
J V
JV
De Clercq
C A
CA
D000180:Acrylic Resins; D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D016302:Centric Relation; D002508:Cephalometry; D002680:Chin / Q000033:anatomy & histology; D003766:Dental Occlusion; D005260:Female; D005544:Forecasting; D006801:Humans; D007180:Incisor / Q000033:anatomy & histology; D007574:Jaw Relation Record / Q000295:instrumentation / Q000379:methods; D008046:Lip / Q000033:anatomy & histology; D008297:Male; D008310:Malocclusion / Q000601:surgery; D008334:Mandible / Q000033:anatomy & histology* / Q000502:physiology; D008437:Maxilla / Q000601:surgery*; D009666:Nose / Q000033:anatomy & histology; D011446:Prospective Studies; D012399:Rotation; D014885:Waxes
D000180:Acrylic Resins; D014885:Waxes