[Related factors and effectiveness of rapid teeth movement through reducing resistance and distraction]

To investigate the role of reducing resistance and distraction in rapid teeth movement and its reliability by establishing the Beagle dogs' experimental model.

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.

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).

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.