A New Method for Measurement of Both Tooth Contact Area in Occlusion and the Occlusal Force

In spite of the well-known facts that trauma from occlusion is one of the most important factor to destroy periodontal tissue, only a few studies regarding the force itself which was added to the tooth surface of individual tooth have been carried out. It seems very important to know the occlusal tooth contact area and the degree of occlusal force.A new method was designed to measure the occlusal contact area on each tooth and the degree of pressure which was added to each contact area on one tooth. Both occlusal areas and the pressure on any one of occlusal contact areas were measured by using occlusal paper, 200μthickness, called “Prescale” by Fuji Photo Film Corporation.Prescale consists of two paper-seats and numerous microcapsules containing a red dye between the paper-seats. When the teeth are brought into occlusion, these microcapsules rapture and discharge the dye staining one of the papers red. The density of the color is in proportion to the degree of pressure added.Tooth contact areas in occlusion recorded on “Prescale” were enlarged by a projector and measured by dental area analyzer.The density of the color was measured with a densitometer after enlarging the colored area under a microscope. This densitometer was improved to measure the density of color limited to an area of diameter less than 1mm. As a sensor of this densitometer, CdS photo cell was used.To study the reproducibility of this method, a study model which teeth are made of metal was used. This study model was fixed on a articulator. Standarized force was added to the articulator ten times.Both occlusal contact area and the pressure added to the same contact area showed almost the same value. From the results obtained, this method basically seems to be a simple and feasible technique for measuring occlusal contact area and the pressure of small contact areas in occlusal surface. Then clinical appliance using few patients was performed. But the reproducibility could not be obtained. It is thought that this result was caused by the thickness of Prescale and that the paper must be improved.