Disocclusion is a common sense in today's prosthetic dentistry. The amount of disocclusion based on quantitative data is not known. Impressions of 25 male subjects with normal dentition and free of TMD were taken using silicone bite material during protrusive and lateral movements. Cutting them through mesio-buccal cusp tip of the lower first molar, distances between them and occlusal surfaces of the opposing teeth, were measured.
The results showed that the average amounts of disocclusion are about 1 mm during protrusive movement and on nonworking side during lateral movement, and about 0.5mm on working side during lateral movement. Standard deviations were 0.3mm-0.6mm.

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Amounts of disocclusion during protrusive movement were measured using leaf gauge, on study models of 25 male subjects with normal dentition and free of TMD, mounnted on a semi-adjustable articulator. The results showed that the average amount of disocclusion for molars is 1.06+0.43mm. The amount of disocclusion of the first molar is larger than those of the first and second premolar portion and the second molar, in average. The amount of disocclusion during protrusive movement of a subject with normal dentition with anterior teeth will never be zero.

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As a basis for analysing the mandibular movement and occlusion utilizing diagrams drawn in actual dimensions or their like figures, seven horizontal reference planes were compared. Anatomical reference points on the skull were plotted in a sagittal plane in actual dimensions taken from the average bony data of the Japanese. Horizontal reference planes were drawn on the figure according to their definitions. Angles between each couple of reference planes were measured on the figure. Among them, a value of 11.8° was obtained for the angle between the Frankfort plane and the Camper's plane defined by Gysi.

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Putting ring-shaped rubber band around a mandibular study model with mounting plate, and using its edge as a reference, mesio-distal positions of mesiobuccal molar cusp tips were meaured in mm using a scale. Comparing the results with the anatomical data reported by Sekikawa et al, good coincidence was obtained.

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Amounts of disocclusion during protrusive movement were measured using leaf gauge, on study models of 25 male subjects with normal dentition and free of TMD, mounted on a semi-adjustable articulator, after removing anterior teeth from the study models. The results showed that the average amount of disocclusion for molars is 0.43±0.43 mm under the condition without anterior teeth, during protrusive movement. That is, the amount of disoclusion without anterior teeth becomes 40% of that with anterior teeth. The difference between the two is up to hinge rotation of the mandible during protrusive movement.

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Conventional dental prostheses have been fabricated with complicated laboratory steps. Even if the prostheses with high accuracy could be made with the development and improvement of dental materials and technologies, the fabrication was still technically sensitive and was influenced by the skill of dental technicians. With the recent development of computer technologies and mechanical engeneerings, the dental CAD/CAM systems have been developed to fabricate the dental prostheses with high quality and less manipulation. In this paper, the dental CAD/CAM systems developed in the world were introduced to understand the basic concept of CAD/CAM process.
Furthermore, the new system developed by us to fabricate a ceramic crown automatically was introduced.

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