Resorption of Root Apex during Orthodontic Tooth Intrusion Using Light and Heavy Forces

Abstract

Introduction, aim: The aim of this prospective study was to find a relationship between the external apical resorption and magnitude of orthodontic force during tooth intrusion. Relationship between the amount of intrusion and the extent of root resorption was investigated as well. Methods: The sample included 34 premolars in 17 patients. The light force (LF - 50 cN) and heavy intrusion force (HF - 150 cN) were applied on contra-lateral teeth. The measurements were performed at time before treatment (T0) and after six-month intrusion (T1). The measurements were registered also on the extracted premolars at the end of experiment. Two clinical parameters, four Cone Beam CT parameters and two parameters on extracted teeth were evaluated. The differences were statistically processed with two-sample t-test. Results: The extent of intrusion was significantly greater during heavy force activation; it was almost three times higher in comparison with light force (4.64 mm compared to 1.53 mm). The tooth was shortened at vestibular site in both groups (0.31 mm in LF and 0.67 mm in HF). However, the difference between both groups was not statistically significant (p = 0.06). The significantly shortened tooth was at palatal site in both groups (0.49 mm and 0.75 mm) and the difference was also not significant (p = 0.37). In comparison of root lengths, they were significantly shorter at vestibular site (0.49 mm and 0.75 mm), but the difference between groups was not significant (p = 0.18). Conclusion: Heavy forces lead to a more extensive intrusion in comparison with light forces. Significant root length shortening occurs after the intrusion with both 50 cN and 150 cN force. The relationship between the amount of intrusion force or the extent of intrusion and the apical root resorption was not confirmed.

Keywords

• intrusion
• light and heavy intrusion force
• apical root resorption
• premolar