ORIGINAL ARTICLE Effect of ultrasound on rabbit mandibular incisor formation and eruption after mandibular osteodistraction Tarek H. El-Bialy, BDS, MS, PhD, a Abd El-Moneim Zaki, BChD, DDR, MScD, PhD, b and Carla A. Evans, DDS, DMSc c Tanta, Egypt, and Chicago, Ill Therapeutic ultrasound is known to enhance bone-fracture healing. The purpose of this article was to study the effect of therapeutic ultrasound on mandibular incisor development and eruption in 15 skeletally mature male New Zealand white rabbits undergoing mandibular osteodistraction. The surgical cuts were made anterior to the molars and consequently transected the mandibular incisors. The animals were divided into 3 groups of 5 rabbits each. Group I received ultrasound on both sides of the mandible every other day. Group II received ultrasound on the left side of the mandible every day. Group III did not receive ultrasound. Ultrasound was given for 20 minutes per application. Mandibular incisor eruption was measured directly on the rabbits and on lateral head radiographs. The animals were killed 4 weeks after surgery, and dissected mandibular specimens that contained the incisor segments were evaluated histologically. The lengths of the tooth segments increased in the ultrasound-treated animals, compared with the controls (group III). However, the rabbits in group II had greater increases in length of the mandibular incisor segments than those in group I. Histologic examination showed that the newly formed tissues at the distraction site and at the cut ends of the incisor segments consisted of osteodentin-like tissue and cementum. Thus, therapeutic ultrasound combined with distraction enhanced mandibular incisor growth and eruption. (Am J Orthod Dentofacial Orthop 2003;124:427-34) D istraction osteogenesis is a biologic process that leads to bone formation between 2 bony segments that are mechanically separated at a constant rate. Distraction osteogenesis has been used since the beginning of the 20th century 1 ; it enables the clinician to lengthen and widen bone and fill in gaps between bones without the need for bone or soft tissue grafts. 2 Knowing that soft tissue mass and bone in- crease with distraction osteogenesis is useful in treating hemifacial microsomia, a condition in which part of the face is underdeveloped. 3 The appropriate rate of dis- traction osteogenesis has been a long-standing contro- versy. It has been reported that there was no clinical difference between the outcomes of mandibular distrac- tion osteogenesis in rabbits at rates of 1 and 3 mm per day, but there was fibrous union in the middle of the distraction gap in rabbits distracted at a fast rate. 4 Tooth eruption is the process of migration of the partially developed tooth from its site of development within bone to its functional position in the oral cavity. Theories of tooth eruption have evolved from studies of tooth development. 5 Although there is no unequivocal proof that validates any of these theories, there is considerable evidence that links the periodontal liga- ment to the eruption of teeth. In 1923, Eidmann 6 pointed out that significant pressure due to cellular proliferation provides sufficient force to account for the eruption of teeth. Many objections have been raised to refute the theory that cellular proliferation is the mech- anism responsible for tooth eruption. Yet cellular pro- liferation might be considered one of many factors operating to cause tooth eruption. 5 Ten Cate et al 7 reported a cellular basis for the connective tissue remodeling that takes place during physiologic tooth movement. They suggested that the fibroblast can synthesize and degrade collagen simultaneously, thereby controlling collagen remodeling in the peri- odontal ligament. They also suggested that this cellular basis of connective tissue remodeling will have a direct significance for orthodontic tooth movement once con- a Assistant lecturer, Department of Orthodontics, Tanta University, Tanta, Egypt; former resident, Department of Orthodontics, University of Illinois at Chicago. b Professor of oral biology, University of Illinois at Chicago. c Professor and head, Department of Orthodontics, University of Illinois at Chicago. Reprint requests to: Dr Carla A. Evans, 801 S Paulina St, M/C 841, Chicago, IL 60612-7211; e-mail, caevans@uic.edu. Submitted, October 2002; revised and accepted, January 2003. Copyright © 2003 by the American Association of Orthodontists. 0889-5406/2003/$30.00 + 0 doi:10.1016/S0889-5406(03)00408-6 427