Abstract :
Root resorption is a dangerous side effect in orthodontics, and maxillary incisors are at the highest risk for
root resorption. It is important to understand optimal force considerations for patients with altered root lengths.The
purpose of this study was to investigate the effects of root length on stress distribution on roots by means of threedimensional
finite element method (FEM).
Methods Three dimensional FEM models of maxillary central and lateral incisors were made. Then, root length of the
incisors was changed in the increments of 1 mm from 0-4 mm. Applying 50 g (0.5 N) of force perpendicular to the
tooth crown simulated uncontrolled tipping. Stresses and strains for each model were calculated and Pearson
correlation coefficient was used to analysis the data.
Results There were significant correlations between root length of incisors and maximum stress in PDL. In the centrals
with various root lengths, maximum stress was between 0.010884 and 0.056520 MPa, and in the laterals, it was
between 0.027297 and 0.221040 MPa. By reducing root length of incisors, the maximum stress in buccal apical (r=
0.933,p<0.001 and 0.995, p<0.001 prospectively) and lingual crestal areas (r= 0.974 p=0.005 and 0.992, p=0.001
respectively) were reduced.
Conclusion Although in lateral incisors, stress at the lingual crestal area was more than buccal apical area, in central
incisors with more than 2 mm resorption, the stress distribution of buccal apical was higher. Therefore, in maxillary
central incisors with more root resorption, force control might be even more critical.
