PHYSICAL FACTORS IN DENTURE RETENTION

This investigation was carried out to analyze the physical factors of saliva affecting denture retention. A model of examining denture retention is given by two parallel disks separated by a liquid layer. Metal, polyisobutylene (PIE) and poly (methyl methacrylate) (PMMA) were used instead of a denture and mucous membrane; and glycerol live oil and castor oil instead of saliva. The experiments were performed with three disk conditions: (1) Both upper and lower disks of metal, (2) both upper and lower disks of PMMA, (3) upper disk with PIB lining and lower of PMMA soley. A strain gauge was used in the experimental apparatus in order to obtain a measurement of high accuracy. In the experiments, the retentive forces developed in layers of 50µ thickness were measured and compared with the values calculated from theoretical equations. The results are summarized as follows: (1) Retentive force must be resolved into static adhesive and separating forces, (2) surface tension of liquid may not highly influence the retention, and (3) viscosity of liquid plays an important role when two disks are separated