Bony adaptation after expansion with light-to-moderate continuous forces.
BACKGROUND
The purpose of this study was to evaluate the biologic response of dentoalveolar bone to archwire expansion with light-to-moderate continuous forces.


METHODS
With a split-mouth experimental design, the maxillary right second premolars of 7 adult male dogs were expanded for 9 weeks using passive self-ligating brackets (Damon Q; Ormco, Orange, Calif) and 2 sequential archwires (0.016 × 0.022-in copper-nickel-titanium alloy, followed by 0.019 × 0.025-in copper-nickel-titanium alloy). Intraoral and radiographic measurements were made to evaluate tooth movements and tipping associated with expansion; archwire forces were measured using a force gauge. Microcomputed tomography was used to compare buccal bone height, total tooth height, total root height, and buccal bone thickness. Bone formation was evaluated histologically using tetracycline and calcein fluorescent labels and hematoxylin and eosin stains.


RESULTS
Buccal expansion was produced by forces between 73 and 178 g. Compared with the control side, which showed no tooth movement, the experimental second premolars were expanded by 3.5 ± 0.9 mm and tipped by 15.8°. Buccal bone thickness was significantly thinner (about 0.2 mm) in the coronal aspects and significantly thicker (about 0.9 mm) in the apical aspects over the mesial roots. The tipping and expansion significantly (P <0.05) reduced buccal bone height (ie, caused dehiscences) at the mesial (about 2.9 mm) and distal (about 1.2 mm) roots. Bony apposition occurred on the trailing edges of tooth movement and on the leading edges of the second premolar apices. The axial microcomputed tomography slices indicated, and the bone histomorphometry and histology demonstrated, newly laid-down bone on the periosteal side of the buccal cortical surfaces. Ordered osteoblast aggregation was also evident on the periosteal surfaces of buccal bone, just cervical to the apparent center of rotation of the tooth. Tooth and root heights showed no significant differences between the experimental and control second premolars.


CONCLUSIONS
Buccal expansion with light-to-moderate continuous forces produced 3.5 mm of tooth movement, uncontrolled tipping, and bone dehiscence, but no root resorption. Bone formation on the periosteal surfaces of cortical bone indicates that apposition is possible on the leading edge of tooth movements.
Private practice, Dallas, Tex.
Collin D
CD
Kraus
Chairman, Department of Orthodontics, Texas A&M University Baylor College of Dentistry, Dallas, Tex.
Phillip M
PM
Campbell
Associate professor, Department of Biomedical Sciences, Texas A&M University Baylor College of Dentistry, Dallas, Tex.
Robert
R
Spears
Associate professor, Department of Orthodontics, Texas A&M University Baylor College of Dentistry, Dallas, Tex.
Reginald W
RW
Taylor
Professor and director of orthodontic research, Department of Orthodontics, Texas A&M University Baylor College of Dentistry, Dallas, Tex. Electronic address: phbuschang@bcd.tamhsc.edu.
Peter H
PH
Buschang
D000222:Adaptation, Physiological / Q000502:physiology; D000539:Alveolar Process / Q000473:pathology; D000818:Animals; D001641:Bicuspid / Q000473:pathology*; D003300:Copper / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry; D004285:Dogs; D008297:Male; D008437:Maxilla / Q000473:pathology*; D009532:Nickel / Q000737:chemistry; D009967:Orthodontic Appliances; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D010006:Osteoblasts / Q000473:pathology; D010012:Osteogenesis / Q000502:physiology; D012391:Root Resorption / Q000473:pathology; D013193:Stainless Steel / Q000737:chemistry; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry; D019227:Tooth Apex / Q000473:pathology; D014087:Tooth Movement Techniques / Q000295:instrumentation*; D014092:Tooth Root / Q000473:pathology; D055114:X-Ray Microtomography / Q000379:methods
C415948:Copper NiTi; D003722:Dental Alloys; D013193:Stainless Steel; D003300:Copper; D009532:Nickel; D014025:Titanium