総義歯の咬合小面に関する研究 : 経日的変化について

Abstract

The occlusal surface of a complete denture is closely related with stability and masticatory function of the denture, and the surface must be formed in harmony with mandibular movement and is generally adjusted by grinding on an articulator with condylar path regulated on it. However, contact with food and the opposing teeth after insertion of the denture gradually causes abrasion of artificial teeth, and occlusal facets are enlarged and their forms change. Therefore, observation of complete dentures with good prognosis was made, and changes by abrasion in projected area of occlusal plane and in inclination angle of protrusive facet were examined. The results were as follows : 1. The cases of porcelain teeth used at the molar region and those of acrylic resin teeth showed severe abrasion to about the 3rd and 4th months, and the rate of increase decreased thereafter. Abrasion after the 12th month in the cases of porcelain teeth rarely progressed and was stabilized. In contrast, the cases of acrylic resin teeth showed still continuing abrasion at the 12th and 24th months and about twice the abrasion at the 24th month as compared with the porcelain teeth. 2. Protrusive and retrusive facets showed a high change in 5 to 6 months of about 60% of the abrasion resulted by the 24th month. Against this, balancing facet showed abrasion of this extent in 3 to 4 months. The increasing trend in both cases declined thereafter. Thus, balancing facet tended to stabilize earlier than protrusive or retrusive facet. 3. Examination of projected area index for the 24th month of occlusal facets showed no significant statistical difference for the upper and lower jaws, right and left sides, and functional and non-functional cusps. Although no significant statistical difference was found, protrusive facet tended to show higher values than retrusive facet. Protrusive facet showed significantly higher values than balancing facet. No significant difference was found between the premolar and molar regions, but the anterior teeth region showed significantly higher values than the premolar or molar region. 4. Examination by region of inclination angle for the 24th month of protrusive facet showed that the angles became smaller from the anterior teeth region to the molar region. Examination by region between semi-anatomical artificial teeth and functional artificial teeth showed that the angles for semi-anatomical artificial teeth became smaller towards the posterior region from the anterior teeth region to the premolar region, and to the molar region. For functional artificial teeth, the anterior teeth region showed significantly greater angles than the premolar or the molar regions. However, no significant statistical difference was found between the premolar and molar regions. 5. Examination of changes with time in inclination angle of protrusive facet showed a slight increasing trend for the anterior teeth group and a slight decreasing trend for the molar group. However, little change was seen after 24 months. 6. Occlusal facets of complete dentures after 24 months showed considerable abrasion as compared with those at the time of insertion. On the other hand, inclination angle of protrusive facet showed little change. On the basis of the foregoing findings, the inclined plane of occlusal facets is thought to guide functional jaw movement when the occlusal facets are formed properly in harmony with their function.