Tooth movement limited to periodontal ligament width using interrupted orthodontic force

A new orthodontic appliance with ratchet mechanism (ratchet bracket) was used in experimental animals and clinically, in order to assess tooth movement limited to periodontal ligament (PDL) width, using interrupted orthodontic force.After experimental tooth movement using two beagle dogs’ third incisors, active bone formation was seen at the tension region on fluorescent images, and blood vessels could be seen in the maximal compressed region. No obvious signs of root resorption were seen on the outline of the roots in micro-CT images.The average distal movement of 10 upper canines in six female patients was 1.9 mm (S.D. 0.21) in a month, and 5.5 mm in 102 days, which was the longest period. No patient complained of spontaneous pain during tooth movement or pain on biting. Dental radiography revealed long and thick lamina dura on the tension side of the canines, suggesting bodily tooth movement and a relatively dense bone formation. There was no obvious sign of root resorption in any canines.These results suggested that an interrupted orthodontic force controlled to a distance of 0.26 mm using ratchet mechanism may cause tooth movement without serious damage or pain.