Image processing techniques for assessment of dental trays

Abstract

Abstract-A tray selected for the dental patient must adapt to the curvature of the teeth and allow the impression material to be in appropriate thickness everywhere.Generally, the impression trays are selected by the practitioner via testing them in the mouth. The present study was conducted to develop an automated technique for the selection of an appropriate tray for the patient. This technique was used for the alignment of six brands of perforated metal trays with 170 lower arch cast models collected from patients having Angle Class 1 type occlusion with minor malocclusions. The cast models and trays were scanned into a computer and critical points of casts and skeleton of the tray bases were collected. After alignment of casts and trays using a distance based alignment routine, the trays which most adopted the curvature of the casts were evaluated using the residual distance of alignment. The alignment was repeated for selected subsets of the points and minimum point set that is necessary for identification of the correct tray was identified. This method can be used in a routine setting eliminating trial and error or to design better trays to fit the needs of a given population. Keywords -Dentistry, tray, cast, distance based alignment I. INTRODUCTIONA dental cast is widely used in dentistry for working on dental prostheses. Due to the problems involved in working within the mouth, the tooth shape and position, which provide fundamental diagnostic information in dentistry, are generally measured in dental casts [1]. An accurate working cast is essential for making a crown or a fixed partial denture fit the abutment precisely [2].Accuracy of the impression is the most important factor for a successful prosthetic appliance. The thickness of the space between the tray and the preparation is one of the important factors related with the dimensional stability of the impression material. In the literature, the sufficient space for the impression material between the tray and the mucosa and teeth is recommended not to be less than two millimeters.The variable thickness of the impression material in each stock tray may result in dimensional changes and inaccuracies in the cast [3][4][5][6][7][8]. It is known that custom trays affect the prognosis of the prosthesis, however it is also known that standard trays are widely used [9]. The time and cost required to construct custom-made impression trays have channelled the manufacturers to provide quick and lessexpensive alternatives. Stock trays are useful for some procedures but their flexibility and construction vary [8]. Even tough the custom perforated trays demonstrate satisfactory results, a wide range of measurements indicate that the use of this type of tray does not guarantee predictable results [10].The ultimate effect of an expansion on the accuracy of the impression depends upon the general contour of the impression tray and the adhesion of material to the tray [11]. There are no scientific data and records about the principles used to produce the dentulous s...