Control of anterior segment using an antero-posterior lingual sliding retraction system: a preliminary cone-beam CT study

Biomechanical model registration for monitoring and simulating large orthodontic tooth movements in the maxilla and mandible

PURPOSE

Superimposition of digital dental-arch models allows quantification of orthodontic tooth movements (OTM). Currently, this procedure requires stable reference surfaces usually only present in the maxilla. This study aimed to investigate the accuracy of a novel superimposition approach based on biomechanical principles of OTM and the equilibrium of forces and moments (EFM)-applicable in both jaws-for monitoring and simulating large OTM.

METHODS

The study included 7 patients who had undergone extraction of the first (PM1-Ex) or second (PM2-Ex) premolar in each quadrant. Digital models taken at start and end of the T‑Loop treatment phase were superimposed by applying 3 EFM variants differing in the number of teeth used for registration. Maxillary OTM results for EFM were validated against those for a conventional surface registration method (SRM). In an additional case study, OTM were simulated for PM1-Ex, PM2-Ex and non-extraction treatment strategies.

RESULTS

The EFM variant that included all teeth of the dental arch achieved the highest accuracy, with median translational and rotational OTM deviations from SRM of only 0.37 mm and 0.56°, respectively. On average, retracted canines and first premolars were distalized by 3.0 mm, accompanied by 6.2° distal crown tipping and 12.2° distorotation. The share of space closure by molar mesialization was 19.4% for PM1-Ex quadrants and 34.5% for PM2-Ex quadrants.

CONCLUSION

EFM allows accurate OTM quantification relative to the maxillary and mandibular bases even in challenging situations involving large OTM. Superimposition of malocclusion and setup models enables realistic simulation of final tooth positions. This may greatly enhance the value of digital setups for decision-making in orthodontic treatment planning.

Comparative study of effect of different lever arm positions and lengths on transverse and vertical bowing in lingual orthodontics - An FEM study

OBJECTIVE

To assess the influence of changing the size and position of lever arm on transverse and vertical bowing effects during retraction in lingual biomechanics.

METHODS

A three dimensional 3D finite element method was used to simulate en masse anterior teeth retraction using lingual appliance with sliding mechanics. Two groups were made, 1st group had lever arm mesial to canine while 2nd group had distal to canine. Each group had 4 subgroups with lever arm height varying from 0mm to 12mm. Displacements of the maxillary anterior teeth were noted in each group.

RESULTS

As the Lever Arm Height (LAH) increased in group I, the vertical bowing effect reduced while the transverse bowing increased with respect to canines. In group II, both vertical and transverse bowing effects increased but transverse bowing was less as compared to group I.

CONCLUSION

Strategic location of the lever arm is required in different clinical situations during en-mass retraction, keeping in mind the location of Centre of Resistance (CRes) as well as the vertical and the transverse bowing effects.