Joji Kawano

Leachability of denture-base acrylic resins in artificial saliva☆

We studied the influence of salivary acidity on leachability of denture-base acrylic resins with etiological interest in denture stomatitis because denture surfaces are frequently exposed to acidic conditions in the oral cavities. Auto-, heat-, and microwave-polymerized resins were immersed in artificial saliva with pH ranging from 4.0 to 6.8 at 37 degrees C, and leachables were pursued quantitatively with time. Methyl methacrylate, methacrylic acid, and benzoic acid leached from all resins. Their concentrations in the saliva were markedly high for auto-polymerized resins, while leachability of heat- and microwave-polymerized resins was so low that quantitative analysis of leachables was impossible. Lower pH showed higher concentrations of methyl methacrylate, although no apparent association was confirmed between salivary acidity and its own leachability. The concentrations of methacrylic acid increased remarkably with an increase in pH, which was probably due to hydrolysis of methyl methacrylate. These results suggest that chemotoxic actions of auto-polymerized resins are potentially ascribable to methyl methacrylate under more acidic conditions and to methacrylic acid under less acidic conditions.

In Vitro Comparison of Cone Beam Computed Tomography with Digital Periapical Radiography for Detection of Vertical Root Fracture in Posterior Teeth.

Statement of the Problem: The diagnosis of vertical root fracture (VRF) is a challenging task. Purpose: This in vitro study compared cone beam computed tomography (CBCT) imaging with digital periapical radiography (DPR) made by three different horizontal angels (20°mesial, 0° and 20° distal) for accurate diagnosis of VRF. Materials and Method: Among 120 posterior teeth included in this study, 60 were vertically fractured. Fractured and non-fractured teeth were randomly distributed into three groups defined as group 1 with no filling in the root canal, group 2 with gutta-percha in the canal, and group 3 with the intracanal post. All samples were placed in a dry mandible and imaged with CBCT and DPR techniques. Two blind observers investigated the images. Results: CBCT had higher sensitivity but lower specificity compared with DPR, except for the intracanal post group in which the sensitivity of DPR was higher; though the chi-square test showed the differences to be statistically insignificant. The sensitivity, specificity, and accuracy of CBCT and DPR were reduced in the cases that gutta-percha or post were present in the canal. Inter-observer agreement was higher for CBCT. A set of three DPRs with different horizontal angels were significantly more sensitive for VRF recognition than a single orthogonal DPR. Conclusion: Based on our results, there was no significant difference between CBCT and a set of three DPRs with different angulations for VRF detection in posterior teeth. Therefore, it is suggested to consider DPRs with three different horizontal angels (20°mesial, 0° and 20° distal) for radiographic evaluation before CBCT examination.

Temperature change during polymerization of self-curing resin for rebasing.

Maximum temperatures, time elapsed to reach them and setting times of four kinds of self-curing resins for rebasing were measured during polymerization at 37 degrees C with attention to curing conditions which might lead to the discomfort of patients in direct rebasing. The temperatures were lower and both times were longer than those of ones for making temporary crowns. When varying thickness of the resins, the maximum temperature and the setting time significantly increased depending on an increase in the thickness, although the time elapsed to reach the maximum temperature showed no difference. All values measured were remarkably influenced by pre polymer powder/monomer ratios.

Psychological aspects of dental students in the course of clinical prosthetics

Cornell Medical Index (CMI), Manifest Anxiety Scale (MAS) and Yatabe-Guilford Character test (Y-G test) were carried out on 165 dental students in the course of clinical prosthetics to understand the psychological changes after study in this course. According to the Y-G profile patterns, in male students, the ratio of A, B, C, D, E and F types were 12.6, 6.7, 14.8, 63.0, 2.2 and 0.007%, and in female students, 6.9, 34.5, 17.2, 34.5 and 6.9% respectively. From the results of CMI, most of the students were stable after study in this course. Psychosomatic profile patterns of CMI before study were similar to those after in both sexes. All items of CMI were decreased in males, but some items were not decreased in females. Anxiety measured by MAS was decreased in many students but was increased in some students after study in this course. These results indicate that it is necessary to be concerned with the mental as well as physical well-being in unstable students.

Oral sensation in patients with implant denture. Part 2. Tactile sensibility of implant dentures

The purpose of this study was to compare pressure sensory mechanisms associated with implant dentures with both natural teeth abutments and implant abutments which have no periodontal membrane. With the von Frey feather stimulation technique we measured axial tactile sensibility of fourteen subjects with a total of nineteen implant dentures and compared results with those obtained from thirteen conventional bridges, four splinted mandibular posterior teeth, and all splinted mandibular teeth in ten normal subjects. We also measured the tactile sensibility of other prosthetic appliances in subjects with implant dentures.For the fixed conventional bridge, the minimum tactile sensibility was 9.7 g, maximum was 21.4 g, and the mean was 13.5 g; for the four splinted teeth the minimum tactile sensibility was 7.6 g, maximum was 12.0 g, and the mean was 9.5 g. When all mandibular teeth were splinted the minimum tactile sensibility was 9.7 g, maximum was 12.0 g, and the mean was 10.2 g. Value obtained for the implant denture minimum tactile sensibility were 7.6 g, and the maximum was over 119.9 g. Twelve of the implant dentures of the nineteen tested had the same tactile sensibility as the conventional bridges. In seven of the eight subjects with an implant denture and another prosthetic appliance there was no difference in tactile sensibility between the implant denture and the other appliance.These results suggest that when the tactile sensibility associated with an implant denture is measured, overall sensation created by the prosthesis must be considered in addition to local stimulation caused by the implants.

Restoration of oral function accompanying prosthetic treatment of a patient with cleft lip and palate.

An eighteen year old female patient with cleft lip and palate underwent prosthetic treatment using a partial denture. Examination of electromyography of masticatory muscles, mandibular movement, masticatory efficiency, and articulation test were conducted periodically concerning restoration of oral function after treatment. 1. Examination revealed no occurence of decay in abutment teeth or gingival inflammation, nor any other particular problems even one year after denture placement. 2. Analysis of electromyography revealed a periodic increase to the integral value for maximum clenching the first month but stabilized thereafter. The integral value for chewing varied only slightly. Chewing time decreased slightly and masticatory rhythm stabilized with time. Silent period duration showed little difference before and after treatment. 3. An increase in the speed of rapid opening and closing movement was noted. In the gothic arch, pre-treatment forward movement on the right side was improved and now occurs smoothly. Concerning chewing movement, the distance of sliding contact at closing phase for chewing on the right side decreased, and although a chewing pattern translation from grindertype to chopper-type developed. 4. Masticatory efficiency improved from the second week, but the value itself was considerably smaller than for persons with normal dentition. 5. In the articulation test, these was a significant increase from a pre-treatment 67.2% to a post-treatment 84.8% which after one year rose to 87.3%.