Norihiro Taguchi

Setting and stress relaxation behavior of resilient denture liners

STATEMENT OF PROBLEM Resilient denture liners are widely used for the patients who are not comfortable with correctly made conventional hard-based dentures because of thin and relatively nonresilient mucosa or severe alveolar resorption. There are several materials used for denture liners and the efficacy in their use is influenced by their viscoelastic properties. PURPOSE This study evaluated the setting behavior and viscoelastic properties of various types of resilient denture liners and the changes in viscoelasticity with the passage of time. MATERIAL AND METHODS Four types of resilient denture liners were used. Setting behavior of 5 autopolymerizing materials was evaluated with an oscillating rheometer. Stress relaxation tests were conducted to evaluate the viscoelastic properties of 9 materials and changes that occurred over time by means of Maxwell model analogies. RESULTS Significant differences were found in the setting behavior of the autopolymerizing materials. The acrylic resin and fluoroethylene materials demonstrated viscoelastic properties and the silicone and polyolephin materials were found to be elastic. The acrylic resin materials exhibited the greatest changes in viscoelastic properties over time when compared with silicone, polyolephin, and fluoroethylene materials. CONCLUSIONS The results suggest that it is important to select denture liner materials according to clinical situations because of the wide ranges of setting behavior, viscoelastic properties, and durability over time.

Effect of viscoelastic properties of resilient denture liners on pressures under dentures

In order to evaluate the influence of viscoelastic properties of resilient denture liners on the pressures under dentures, a series of creep and stress relaxation tests were carried out using a simplified mandibular edentulous model and denture model. Two diaphragm pressure sensors were attached to the edentulous model so that they contacted the residual ridge and the buccal slope. The results may be summarized as follows: (i) The use of resilient denture liners is effective for stress relief under dentures. (ii) The thickness increase of each denture liners causes the effect of stress relaxation. (iii) The material exhibited viscoelastic behaviour after applying the stress and has the ability to distribute stress or stress relaxation. It is important to understand the viscoelastic behaviours of each resilient denture liner and choose the material according to the clinical situation. The information obtained should be useful to clinicians when they select materials for their patients.

Japanese dental trainees’ perceptions of educational environment in postgraduate training

Background: Compulsory postgraduate dental training was introduced in April 2006 to meet social requirements in Japan. Aim: The aim of the present study was to identify the difference in trainees’ perception of the educational environment in two different training settings in the Hiroshima University Hospital postgraduate training program: (1) main hospitals, in Hiroshimas case, the University Hospital: (2) community dental hospitals or offices (cooperating hospitals). Methods: In order to determine how trainees perceive their educational environment, the Postgraduate Hospital Educational Environment Measure (PHEEM) Inventory was administered to 50 vocational dental trainees for two different training settings, both of which all trainees had experienced. Result: The mean total PHEEM score in the main hospital was 102.4, and that in cooperating hospitals was 108.5. The scores for each of the three subscales were as follows: ‘Perception of role autonomy’: 33.9/56 (main hospital), 36.8/56 (cooperating hospitals); ‘Perception of teaching’: 38.1/60 (main hospital), 41,9/60 (cooperating hospitals), and ‘Perception of social support’: 30.4/44 (main hospital), 29.8/44 (cooperating hospitals) respectively. Conclusions: PHEEM provided meaningful diagnostic information on the educational environment, and showed that cooperating hospitals met trainees’ needs more than main hospitals.