Occlusal force distribution in lower complete overdentures.

A space between the denture base and a root cap can effectively control the distribution ratio of occlusal force to abutment teeth and an alveolar ridge. The purpose of this study on abutments was to analyse the effect of variation in space (0 mm (no space), 0.3 mm and 0.6 mm) on the above ratio. Six subjects, 38-65 years of age, each with an edentulous maxilla and several teeth remaining in the mandible, were selected for this experiment. The lower experimental denture had embedded a transducer which could detect a change in the vertical force applied to the experimental tooth. This transducer was capable of changing the vertical space between a denture base and an experimental tooth. Each subject was asked to increase the occlusal force applied to the denture from zero to the maximum loading rate of 5 kgf s-1. The occlusal force and the force exerted on the experimental tooth were recorded in each space 1 month after insertion of new dentures. The following results were obtained: (i) when the occlusal force was applied to the artificial tooth just above the abutment tooth, the mean ratio in the 0 mm space was 60% of the force applied to the denture, the ratio in the 0.3 mm space was 50%, and the ratio in the 0.6 mm space was 30%; (ii) if the occlusal force was applied to the point 10 mm distant from the point just above the experimental tooth, the magnitude of the ratio was decreased by 60-80%.