[An experimental study of the effects of root-canal treatment on orthodontic movement in cat cuspids]

To evaluate the effectiveness of orthodontic forces in moving teeth after root canal therapy and the risk of apical resorption which may happen during orthodontic movement in an animal model.

Under general anesthesia, root canal therapy was performed on the mandibular canines on one side of 16 adult cats. Tipping movement of the canines was induced with an orthodontic spring (100 to 120 g). Eight weeks later, tooth movement was assessed from pre- and posttreatment mandibular casts, including measurement of root lengths in both radiographs and histological sections. All the data were analysed with SPSS 11.0 for windows. Student's t test was used for comparisons between paired groups.

The results showed that teeth after root canal therapy and vital teeth moved similar distances when subjected to the same forces (P>0.05). And teeth after root canal therapy had greater loss of cementum after tooth movement than vital teeth (P<0.05), but without significant differences in radiographic root length (P>0.05).

Teeth after root canal therapy can be moved orthodontically as readily as vital teeth when subjected to the same orthodontic forces under the conditions of the study. However, teeth after root canal therapy have more root resorption than vital teeth during orthodontic movement which may not be detected form the radiography.