Abstract: PURPOSE: The clinical suitable range of coronectomy for extraction of impacted wisdom tooth contacting inferior alveolar nerves was comprehensively analyzed by the correlation between the root movement distances and rates of mandibular wisdom tooth, with age, gender, number of roots, impacted angle and the characteristics of new bone formation. METHODS: In 49 patients with root compression of mandibular canal determined by cone-beam CT (CBCT), the root movement distances were measured and the characteristics of root movement rates was proposed; the relationship between rates of root movement and age, gender, root morphology was analyzed, and the appropriate equation of root movement rate was formulated. The application range of coronectomy was determined by the formula of root movement rate combined with clinical operation. RESULTS: The safe distance and the time of residual root extraction could be predicted for the vertically impacted and proximally impacted single wisdom tooth with the fitting equation D=K×（7×10^-8x²-8×10^-5x+0.0239）x·sinθ₁ within 200 days; the second stage of residual root extraction should be controlled in 90 days for the mesioangular impaction, impacted wisdom tooth with multiple-root. The reachable safe distance of the predicted root movement can be used as the main basis for the application of coronectomy to wisdom tooth contacting inferior alveolar nerves. CONCLUSIONS: Estimating the maximum distance of root movement is the main indicator to evaluate the application scope of coronectomy, the formula should be used and pre-judged in accordance with different situations in order to improve the success rate of coronectomy.

Key words: Coronectomy, Crown truncation, Root movement rate, Limited duration, Suitable range