Keywords: crowns modelling, dental fabrication, optical tracking, occlusal surface.

Once serious tooth decay cannot be restored with fillings or by alternative treatments, the affected areas can be removed from their existing positions. This may cause some occlusion difficulties and even aesthetic unpleasantness due to the missing teeth. Therefore, dental treatment such as bridges, dental implants, and dentures are given not only for aesthetic reasons but also for functional restoration in mastication and articulation. According to normal occlusion described by Andrews [1], individual dental crowns should conform to the original relationships between the upper and lower teeth when they close together. In this paper, we propose a method to develop a unique occlusion surface of an individual in order to fabricate his/her ideal pontic teeth and dentures.

In this study, we propose a mathematical modelling technique to explore individual occlusal movements and model the associated occlusion surface utilizing coupled points and registration method. An optical tracking device is used to overcome the deficiencies in the conventional mechanical articulator, and will eventually replace its operations. Coordinate registration between the optical system and the dental stone is necessary by adopting a specially designed optical track plate. By tracking the movements of the existing teeth, we can develop personal occlusion surface. The model provides useful information for false teeth manufacture based on the occlusal theorem [2]. Individual jaw movements are recorded and replayed using the collected digital information. Furthermore, it consistently illustrates the complex 3D relationships between the upper and lower jaws for further oral disease diagnosis and therapy. Based on the modelling method, personal occlusion movements can be defined by a few representative coefficients [3]. It would dramatically decrease the capacity demanded in medical historical databanks by storing virtual digital models to replace physical dental casts. Also, in this study, the use of a digital dental model is reconstructed by the scanning images of dental casts, hence, preventing X-ray exposure on the human body.

Based on the outcomes in the individual occlusion surfaces developed, we will move forward to the study on those cases that need the recovery treatment in abutment missing teeth. By incorporating with the miniature numerical control machine, the customized false tooth is directly fabricated for clinical usage. Furthermore, the contact points and the stresses when the upper and lower teeth come together should be taken into account when determining the best implant angle in the drilling safety zones of both upper and lower jaws. Nevertheless, after collecting sufficient cases, we are capable to build up a scientific evaluation method to define the syndrome boundaries between normal, dysfunctional, and para-functional occlusion. Clinical studies in diagnosis and therapy will be improved based on the technique and its associated statistical data.

1

L.F. Andrews, "The six keys of normal occlusion", American Journal of Orthodontics and Orthopedics, 62, 296-309. 1972.

2

S.P. Ramfjord, M.M. Ash, "Occlusion", Philadelphia: WB Saunders Company, 1971.

3

J.J. Fang, T.H. Kuo, "Modeling of mandibular movement", submitted to Journal of Oral Rehabilitation.

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