Finite Element Analysis and in Vivo Evaluation of En-Masse Retraction of Maxillary Anterior Teeth Using Palatal TADs and a Clear Appliance

Among various retraction methods for space closure in first premolar extraction, the palatal approach is preferred to labial appliances in cases having high aesthetic demand. A finite element model and clinical randomized prospective trial was undertaken to determine the possibility of en-masse retraction of maxillary anterior teeth using palatal TAD and a clear aligner-like appliance in patients undergoing extraction of maxillary first premolars and to study the effects of the above using three-dimensional scanned models and lateral cephalograms.

A finite element model of maxillary dentition with alveolar bone, an acrylic splint on six anterior teeth, palatal implants, and short e-chain were produced to measure shifting when force was applied from three various levels. Thereafter, the finite element analysis findings were applied to 10 patients requiring fixed orthodontic treatment with first premolar extraction and fulfilling the inclusion criteria. Impressions were made and the rate of retraction was evaluated at 4-week intervals by superimposition of scanned models.

En-masse bodily retraction was seen when both canine hooks and palatal TAD was placed at 10 mm distance from the respective gingival margin. Clinically, subjects showed significant retraction at that level and statistically significant results in some cases. The maximum rate of retraction was seen in the first three months (average: 5.310 mm) with p-value <0.0001.

Translational tooth movement was observed when line of force was at the level of the center of resistance.