Biomechanical and Histomorphometric Analyses of Monocortical Screws at Placement and 6 Weeks Postinsertion
Maxillofacial screws are increasingly being used in orthodontics to provide anchorage for tooth movement. The objective of this study was to determine the biomechanical stability as well as the bone tissue response of screws at 6 weeks postinsertion in a canine model. Seven skeletally mature male dogs received 102 screws (2 × 6 mm or 2 × 8 mm) at predetermined sites. Twenty screws became loose or were lost during the 6-week undisturbed healing period. Forty-eight screws were randomized for mechanical testing and 34 for histology. Peak pullout strength was recorded and ∼80-μm sections were examined for histomorphometric parameters. Statistical analyses were conducted by analysis of variance and Tukey-Kramer method. Mean ± SE peak pullout strengths for the various sites ranged from 153.5 ± 37.6 N to 389.3 ± 32.5 N with no significant (P < .05) differences at immediate placement and 6 weeks postinsertion. Bone contact ranged from 79% to 95%. Histomorphometric analyses indicated higher bone formation rate in the mandible than in the maxilla and a gradient of decreasing turnover with increasing distance from the screw interface. These results provide the clinical orthodontist with an estimate of the holding power of these screws and an understanding of early biological healing response associated with self-drilling screws.Abstract
and 2. Figure 1. Epifluorescent micrograph (×100) of screw-supporting bone in the maxillary posterior region. Note the periosteal (top) and endosteal callus, both of which have incorporated the calcein bone label. The intracortical passage is spanned by 1 pitch of the screw. Figure 2. Epifluorescent micrograph (×40) of screw-supporting bone in the mandibular mid region. Osteonal remodeling typical of bone healing is evident. Modeling response of the periosteal and endosteal callus is very limited. The intracortical passage is spanned by 3 pitches of the screw. Intimate bone adaptation is seen at 6 weeks postinsertion
Contributor Notes
S. S. Huja, DDS, PhD, is an assistant professor in the Section of Orthodontics, College of Dentistry, The Ohio State University, 4088 East Postle Hall, 305 West 12th Avenue, Columbus, OH 43210 (huja.1@osu.edu). Address correspondence to Dr Huja.
J. Rao, DDS, is a graduate student in the Section of Orthodontics, College of Dentistry, The Ohio State University, Columbus, Ohio.
J. A. Struckhoff, DDS, MS, is in private practice in Cincinnati, Ohio, and is a former graduate student in the Section of Orthodontics, College of Dentistry, The Ohio State University, Columbus, Ohio.
F. M. Beck, DDS, MA, is an associate professor in the Department of Oral Biology, College of Dentistry, The Ohio State University, Columbus, Ohio.
A. S. Litsky, MD, ScD, is an associate professor in the Departments of Orthopaedics and Biomedical Engineering, College of Medicine and College of Engineering, The Ohio State University, Columbus, Ohio.