FRONTONASAL SUTURE EXPANSION IN THE RABBIT USING TITANIUM SCREWS

Purpose: This study investigated the ability to use titanium screws to provide stable skeletal points in the growing craniofacial region of the rabbit for suture expansion, These screws provided sites for direc t application of external forces to alter growth and anatomic form. Ma terial and Methods. Twenty-one rabbits (30 days old) were divided into three groups: control (n = 9), experimental (n = 9), acid sham (n = 3 ), Four four-holed AO/ASIF commercially pure titanium craniofacial pla tes were contoured into an L-shape with a 90 degrees angle at the midp oint. The plates were placed bilaterally in the frontal and nasal bone sites and secured with 2.0-mm diameter, 4-mm long, commercially pure titanium screws in both the sham and experimental groups, After 4 week s of healing, a spring mechanism with a distraction force of 55 g was activated between ipsilateral plates and across the frontonasal suture s bilaterally in the experimental group for 5 weeks. No force was appl ied between the plates in the sham group. A preliminary evaluation of the bone-implant interface and the changes in the sutures was done his tologically. Morphologic changes were measured using cephalometric rad iographs and direct anatomic measurements. Results: The experimental g roup showed a significant increase in growth across the frontonasal su ture in comparison with the sham group (P < .05). In addition, an incr ease in the length of the nasal and frontal bones in the expanded grou p was observed in comparison with the control and sham groups (P < .05 ). Histologically, a mixture of woven and lamellar bone was seen in th e suture region and lamellar bone was seen in the screw-bone interface . Conclusion: This study indicates that titanium screws in the develop ing rabbit skull can provide stable sites for the direct application o f external forces, producing secondary changes in skeletal mrophology. This laboratory model provides a useful system for the further study of growth modification using such external mechanical forces.