Quantification of dental movements in orthodontic follow-up : a novel approach based on registration of 3D models of dental casts

Introduction: The assessment of dental displacement achieved by orthodontic procedures is important as it allows operators to verify their clinical treatment and provide adequate adjustments. Modern 3D image acquisition and elaboration systems may represent a valid method for the three-dimensional assessment of dental movement. A novel protocol for the 3D assessment of success of orthodontic therapy is proposed, based on registration of surfaces. Methodology: Pairs of casts of the upper dental arch, taken at two different time periods during the therapy, were chosen for three patients who underwent an orthodontic treatment. Dental casts were scanned by a 3D laser scanner: for each patient, the two 3D models were then registered according to the least distance at the area including palatal rugae. The chromatic map of changes within the dental arch and the RMS (Root Mean Square) point-to-point distance between the dental profiles from the two models were obtained, and compared with the same data from a control group including five adult individuals who did not undergo orthodontic therapy. Inter- and intra-observer errors were evaluated as well. Results: The novel procedure proved to be repeatable and gave a detailed description of those dental areas most affected by orthodontic therapy: RMS values seem to be related with the weight of dental modifications and are far higher than the same parameters computed in the control group. Conclusion: Further studies are needed in order to explore the possible correlation of RMS value with clinical parameters linked to the improvement of dental function and aesthetics due to orthodontic therapy.