抄録
Effective cusp angle which is defined as “the angle made by the average slope of a cusp with the horizontal reference plane measured buccolingually along the cusp path of the opposing tooth”, was measured on occlusal surfaces of the “cusp fossa design dental model” made by Dr. Peter K. Thomas. The cusp angles were measured on the left and right working and nonworking sides of the model's maxilla and mandible. The cusps of the first and second molars were cut perpendicularly along each cusp path of the opposing tooth, the horizontal reference plane was drawn on each section and the photo of the section was taken and each cusp angle was measured on the section using a graduator. The measurement was done by two dentists and an engineer. The results were analaysed statistically.
The average cusp angles of the first molar on the left and right sides of the model's maxilla and mandible were 15.8° and 22.5° on working and nonworking sides, respectively. The corresponding data measured on the second molar were 15.0° and 22.5°. The standard deviations of each measurement were less than 4.0°.
The above averaged values were compared with the standard values which were determined by means of computerized analysis theoretically and experimentally by Hobo and Takayama. The differences between the both were less than 1° on working side and less than 3° on nonworking side.
The significance of the measurement along the cusp path of the opposing tooth, systematic errors due to the difference of the horizontal reference plane, human errors during measurement, laboratory workmanship errors in the dental model and statistical difference between the effective cusp angles of the model's maxilla and mandible on nonworking side, were discussed.
