Selection of retainers in lower overlay denture-in relation to the abutment tooth mobility--(a laboratory study)

This study was done to evaluate the art of retaining the lower sub/complete, overlay denture, in relation to the abutment tooth mobility while the force was applied to the denture. The lower overlay denture was placed on a simulated model which was constructed of methylmethacrylate and silicone rubber. The author developed and used the special devices for measuring the tooth mobility. Results obtained were as follows: 1. When a force is applied directly to the abutment, the tooth mobility, i.e. the lateral excursion of the tooth, is markedly reduced according to the favorable ratio of the clinical crown to the root length. Splinting by the bar is effective to reduce the lateral excursion. 2. When a force is applied to the denture indirectly to the abutment tooth, the lateral excursion changes greatly according to the retainer selected. 3. The clasp retainer shows the greatest change in the lateral excursion against every loading on the denture. 4. All three types of bar attachment show the least value of lateral excursion.