The development of new soft lining material is attractive because of the reported failures of existing materials and the clinical success of soft lined complete mandibular dentures. Laboratory investigations may indicate suitable materials but these materials must finally be evaluated in clinical use. Sixty persons, most of whom had previous experience of wearing soft lined dentures, had a total of 148 soft lindings placed in their mandibular complete dentures during the three-year period of the study: 71 of the current commerically available silicone rubber material, Molloplast-b, 41 of an experimental powdered elastomer material and 36 of an experimental material with a polymerisable plasticiser. The period of service and the reasons for replacement of the soft linings were recorded. Masticatory effectiveness and maximum biting force were recorded on recall for each person. These were compared with pretreatment measurements and similar measurements on an independent group of persons wearing conventional hard based mandibular dentures. The prevalence of oral yeasts was established and compared with pretreatment isolation and identification. The performance of the experimental materials was disappointing when compared with Mollopolast-b. Although the reasons for failure were predictable, the cause of failure was less certain. However, the soft lined mandibular dentures were associated with a significant improvement in masticatory effectiveness.

Fifty-three persons wearing soft-lined mandibular dentures and heat-cured acrylic-resin maxillary dentures were studied, using imprint cultures, to determine the isolation frequency and density of colonization of denture and mucosal surfaces by yeasts. Yeasts were isolated from 35 (66%) of the persons studied. Nine species of Candida and one each of Trichosporon and Saccharomyces were identified. Candida albicans, occurring either alone or together with another strain, was identified in 66% of the isolates and was associated with a higher mean density/cm 2 than that of other strains. An association between the method of denture cleaning, denture hygiene, and smoking habits and the isolation of yeasts was demonstrated, but a similar association could not be demonstrated with the sex of the person, denture-wearing habits, type and condition of the soft lining, or the clinical appearance of the mandibular denture-bearing mucosa. Although yeasts are more likely to colonize soft-lining materials than the fitting surface of conventional lower dentures, their presence did not significantly affect the soft-lining material. Further, the increased isolation of yeasts on the fitting surface of the soft-lined mandibular denture was not associated with an increased incidence of inflammatory changes in the mandibular denture-bearing mucosa.

There is ample evidence for the clinical success of soft-lining materials, but their use is often discouraged because of reported inadequate physical properties. The desire to correlate properties determined under simulated clinical conditions in the laboratory with success and failure of denture soft-lining materials in clinical use stimulated the present study, the objectives of which were: 1.1. A retrospective study of the clinical success of existing soft-lining materials.2.2. The collection and measurement of data relating to a group of edentulous patients wearing soft-lined mandibular dentures.3.3. A longitudinal study of the clinical success of both existing and new soft-lining materials over a three-year period.

Although soft lining materials are inadequate to their requirements their use is widespread. This paper comprises a summary and the conclusions of a comprehensive investigation of these materials which has been undertaken in an attempt to determine which are the better materials and how they may be evaluated.

Although soft lining materials are inadequate to their requirements, their use is widespread. This paper comprises a preliminary report of a comprehensive study of these materials, which has been undertaken in an attempt to determine which are the better materials, how best to use them and how they may be improved. In addition, some new materials have become available which may have advantages over existing materials. Fifteen materials are under investigation. These have been analysed, their water absorption, water solubility and visco-elastic properties studied and the effect of bonding these soft lining materials to polymethyl methacrylate determined. The study is continuing as there are many aspects of these materials which remain to be investigated.

This paper discusses the development, assessment and application of a method for the investigation of aspects of mandibular posture and movement in edentulous individuals. The validity of the method has been established and it has been shown to be capable of identifying small variations in the position of the mandible (±0·5 mm or better). Only 3 individuals were studied but findings are reported that warrant further investigation. In particular, unexpectedly large variations were found in mandibular posture, which may be a characteristic of the edentulous state. Secondly, the insertion of the recording appliance, small though it was, caused a displacement of the mandible of up to 9 mm, and the period of time for the recovery of this displacement to within the range of mandibular posture was up to 25 seconds.