COMPUTERISED ORTHODONTIC TREATMENT SIMULATION BASED ON THIN PLATE SPLINE AND GEOMETRIC TRANSFORMATION

The orthodontic treatment simulation based on thin plate spline and geometric transformation presented in this paper using 4 main methods. Firstly, by applying the radiographic cephalometric analysis on the input data as a soft tissue modeled by registration technique between the radiograph and the photo image. Secondly, by employing the elastic properties for soft tissue deformation by using corresponding statistical facial change based on the orthodontic movement of teeth and jaw. Next, by applying thin plate spline technique to find the grid changes following the soft tissue deformation prediction. Finally, by performing the facial changes of post-treatment using geometric transformation technique. The result has been shown to the orthodontists and patients with satisfaction on a low cost PC platform. Introduction This paper presents a technique for orthodontic treatment simulation based on thin plate spline [4] and geometric transformation [1]. With this simulation, the patients are allowed to see the post-treatment facial structure before the actual orthodontic treatment has been executed. Therefore, the patient who needs braces to correct the teeth’s positions would find the treatment more informative and useful. This simulation has applied the cephalometric radiograph as the data source based on registration technique. The post-operative simulation on the patient can be viewed in twodimensions. Although, there are a number of commercial products for interactive orthodontic simulation such as DentoFacial Planner Plus [9], OnyxCeph [11], QuickCept [12], the prices are expensive and they are proprietary as they do not explain their techniques. The proposed simulation technique explained in this paper may be used as a reference to develop your own software. While the 2D orthographic surgical simulations have become commercial, the researches on interactive 3D simulations for the soft and hard tissues have been developed based on CT [6] and MRI volumetric data [5] as well. However, these systems are costly due to the high cost of the imaging (data acquisition) modalities and high processing requirement for 3D volumetric data, which render the techniques difficult to apply in a typical orthodontists’ office practice. Registration of Cephalometric Tracing from Radiograph to Photo image In order to perform computerized cephalometric analysis, it is necessary to allow line drawing on the lateral surface of a skull to fit the soft surface on the landmarks chosen by the dentists. Angular and distance measurements are computed to detect the extent of the structural abnormalities of the skull and the teeth. Local contrast enhancement technique [2] has been used to enhance the contrast of the soft tissues to enable the dentists to choose accurate landmarks. Tracing is employed on the radiographic images and computed based on the defined landmarks. The computed tracings in the radiology image is applied to the photo image by using registration technique as show in (1) [7] k ) cos( y ) sin( x Y h ) sin( y ) cos( x X s s s s + + = + = θ θ θ θ (1) The rigid registration is applied using 4 user-defined corresponding landmarks in the X-ray as well as the photo images. Using the computed rotation, translation and scaling parameters, from the user defined landmarks in both x-ray and photo, the computerized fitting and the resultant tracing curve is super imposed on the photo image. The registration result between the x-ray and the photo image is as show in Figure 1