Objective:To investigate the role of reducing resistance and distraction in rapid teeth movement and its reliability by establishing the Beagle dogs’ experimental model.
Methods:The left or right sides in mandibles of 20 beagles were randomly operated with different treatments:distraction twice a day through reducing resistance;distraction 6 times a day through reducing resistance;conventional distraction through reducing resistance;and conventional distraction (the control group). Each treatment was carried out in 10 sides. The pulp vitality, tooth mobility and distance of teeth transportation were evaluated at different time points:before the distraction, distraction after 15 days, retaining 30 days after 15 days of distraction. The degree of inclination, root resorption and alveolar bone density of the compressive areas were evaluated by cone-beam computed tomography images.
Results:The distance of teeth transportation was similar in groups distraction twice daily and 6 times a day through reducing resistance (P>0.05), but their speed of transportation was significantly higher than that of conventional distraction through reducing resistance. The conventional distraction group had the lowest speed of transportation. The pulp vitality of distracted teeth was normal, and no root comprehensive resorption and periodontal defect were found. Distracted teeth in the reduced resistance and distraction groups (13.9°±3.5°) tipped more that in the conventional distraction group (6.6°±1.3°) (P<0.05).
Conclusion:Reducing resistance and distraction are inseparable factors to realize fast teeth moving. The rate of orthodontic tooth movement can be accelerated through resistance reduction and periodontal distraction without obvious unfavorable effects but at minimal acceptable teeth inclination.

Objective:To investigate the effects of bone morphogenetic protein 2(BMP-2)expression in the related periodontal tissue on bone remodeling under different distracting force during rapid tooth movement by resistance reduction and distraction. Methods:1 2 Beagle dogs were randomly divided into 4 groups as follows:5 d distraction,1 5 d distraction,1 5 d distraction and 1 0 d retaining and 1 5 d distraction and 90 d retaining.4 4 were distalized.6 teeth in each group were randomly assigned to re-sistance and distracting method,resistance and conventional method and conventional method,and there were 2 teeth in each group.Moving teeth models were prepared regularly.BMP-2 expression was examined by immunohistochemistry.Results:The BMP-2 positive expression of the 3 groups of different distraction schedule showed similar distribution area,and it reached peak at the end of 1 5-day distration,but the group of resistance and distracting method showed the maximum peak(P <0.05)and maximum tooth movement(P <0.01 ).In different stages of distraction,the positive expression in the group of resistance reduc-tion and conventional method was higher than in the group of conventional method but lower than the group of resistance reduction and extraction method(P <0.05).There was no significant difference in BMP-2 positive expression among 3 groups when retai-ning was 90 d(P >0.05).Conclusion:Resistance reduction with sustained strong distracting force can significantly increased the positive expression of BMP-2 and effectively accelerate new bone formation in periodontal tissue.

OBJECTIVETo evaluate the effect of rapid teeth movement through reducing resistance and distraction using cone-beam computed tomography (CBCT).

METHODSThe left or right side of the mandible of 10 beagles (5 males and 5 females) was randomly selected as the control side (for the conventional distraction with a force of about 85 g) and the other side as the experimental side (subjected to reducing resistance and distraction). CBCT images were taken at 5, 10, and 15 days and also after retaining for 10 and 90 days after distraction for 15 days. The distance of teeth transportation, degree of inclination, alveolar bone density of the compressive area and root resorption were evaluated based on the CBCT images and Ez3D2009 visualization software.

RESULTSNo significant difference was found between CBCT-based measurement and direct measurement of teeth transportation distance within the mouths (P>0.05). Teeth inclination on the experimental side was slightly greater than that on the control side (P<0.05). The root resorption on the experimental side was minimal, and the bone density increased gradually along with the teeth migration. The experimental side showed a comparable newly formed alveolar bone density and similar X-ray features of the compressive area with the control side.

CONCLUSIONSCBCT three-dimensional imaging can resolve the problems of overlapping and deformation of the two-dimensional images and is especially useful for measurement of teeth inclination and alveolar bone density in the process of reducing resistance and distraction.

Animals ; Bone Density ; Cone-Beam Computed Tomography ; Dogs ; Female ; Male ; Mandible ; diagnostic imaging ; Tooth ; diagnostic imaging ; Tooth Movement Techniques ; methods