INTERNAL CALVARIAL BONE DISTRACTION IN RABBITS WITH EXPERIMENTAL CORONAL SUTURE IMMOBILIZATION - EFFECTS OF OVERDISTRACTION

This study was designed to assess the effects of over-distraction of a n experimentally immobilized coronal suture using an internal applianc e on craniofacial growth in rabbits. Fifty-three, 1.5-week-old rabbits were used. Markers were placed on either side of the calvarial suture s. Thirty-nine rabbits had bilateral coronal suture immobilization usi ng methyl methacrylate; 14 rabbits served as normal controls. At 6 wee ks of age, the 39 immobilized rabbits were randomly assigned to four g roups: (1) immobilized controls (n = 14); (2) suturectomy (n = 6); (3) suturectomy with distraction (n = 9);and (4) suturectomy with overdis traction (n = 10). Lateral head radiographs were taken at 1.5, 6, 12, and 18 weeks of age. Results revealed that, by 18 weeks of age, rabbit s with overdistraction exhibited significant compensatory growth abnor malities in the cranial vault, midface, and anterior cranial base comp ared with the other groups. Results indicate that overdistraction may contribute to craniofacial anomalies through altered growth vectors an d compressive tension-stress forces at adjacent sutures and suggest th at it may be important to keep ''pace'' with the growing coronal sutur e and neurocapsular matrix during distraction to reestablish normal cr aniofacial morphology.