Novel methods for superimposition of digital maxil- lary models and 3D assessment of orthodontic tooth movement
Mohamed, Sameh Mohamed Talaat Taha
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Superimposition of the patient’s 2D cephalograms is traditionally indicated whenever evaluation of orthodontic treatment and/or growth is needed. More recently, superim- posing the 3D digital models or CBCT images makes it possible to assess these changes in a 3D manner. The best fit superimposition method misses the remodeling that happens in the anatomy of the treated patients; therefore it is understood that us- ing stable anatomical landmarks as a reference plane for the superimposition process yields more accurate results. The aim of this dissertation is therefore to identify user friendly, valid and reliable techniques to superimpose digital maxillary models on stable anatomical landmarks and perform subsequent 3D assessment of the orthodontic tooth movement. To this end, data for this retrospective study included the pre- and post- treatment 3D cone beam Computed Tomography and digital maxillary dental models of 20 orthodontic patients treated with maxillary expansion using Hyrax palatal expander. The first study revealed that a newly programed algorithm can superimpose digital maxillary dental models on stable anatomical landmarks in a user friendly manner. This study also revealed a new method for 3D assessment of orthodontic tooth movement along the six degrees of freedom. Based on these results, the second study tested an updated algorithm that further simplifies the amount of work needed by the user to su- perimpose digital maxillary models. Therefore, the innovation task in the third study was framed in the context of full automization of the superimposition process while still us- ing stable anatomical landmarks as a reference plane for the superimposition process. In the fourth study, the full experience was performed on a new platform which is the Microsoft Hololens. The results showed that the new superimposition algorithms yield- ed strong agreements in the measurements taken over the superimposed digital maxil- lary models when to compared to gold standards. Collectively, the data of four studies identified an important message frame: the current digital model softwares available in the orthodontic market depends on the surface based best fit method for superimpos- ing the digital models. This is because of the easiness of the procedure for the end us- ers; yet the systemic errors that may occur are totally neglected. The new software al- gorithms studied in this dissertation were found to offer a valid and reliable landmark based superimposition and still simple to use.