[A fundamental study on the influence of posterior artificial tooth forms on denture movements during mastication]

The form of posterior artificial tooth is an essential factor related to denture stability during mastication and to masticatory ability. Generally, cusp teeth are selected out of consideration for balance during eccentric occlusion. From another viewpoint, cuspless teeth are selected to ensure stability and to prevent the occurrence of lateral vectors caused by the inclination of the occlusal facet. It has been reported, however, that the counterbalance phenomenon occurring between occlusal facets decreases the lateral vector. Moreover, cusp teeth are useful in increasing the possibility of establishing bilateral balance. Guidelines for selecting posterior artificial teeth in the production of functional dentures are diverse and cannot be said to have been firmly established yet. This model experiment, which employed complete lower dentures, was designed to provide basic information for discussing the influence of occlusal facets of cusp teeth on denture movements during mastication and to arrive at some clinical suggestions for selecting posterior artificial teeth. Artificial teeth with cusp angles of 0 degrees, 10 degrees, 20 degrees, and 30 degrees were made by adjusting setting conditions on a condylar type articulator. Four kinds of experimental dentures were made and used in measuring horizontal movements of lower dentures during the crushing of experimental food. Final phase of chewing stroke was taken into consideration in establishing two types of loading direction. One type was at 70 degrees (DL 70 degrees) to the occlusal plane on the frontal plane and from the outer side (the working side). The other type was 90 degrees (DL 90 degrees) to the occlusal plane. Maximum load was 15kg and the denture displacement was analyzed at 2kg, 4kg, 8kg and 15kg. Experimental foods were smoked cuttlefish (sectile food), raisins (food flattened under pressure), and peanuts (crushable food). Analyses were made of experimental denture movement patterns and denture displacement amounts. Results 1. Experimental denture movement patterns differed according to the nature of the experimental food. The pattern in the case of smoked cuttlefish was mainly of the C type; that is, primarily motion first to the balancing side and then to the working side. The pattern for raisins was mainly of the S type; that is, primarily motion first to the working side, then to the balancing side, and then to the working side again. Several patterns appeared in the case of peanuts.(ABSTRACT TRUNCATED AT 400 WORDS)