Tetsuo Kawata

Development of in vivo measuring system of the pressure distribution under the denture base of removable partial denture

PURPOSE To develop a system to measure the pressure distribution under the base of a removable partial denture (RPD) and to apply it in vivo. METHODS A tactile sensor sheet with 100 sensing points and a measuring system (I-SCAN, Nitta, Osaka, Japan) were used. The sensor was calibrated before being applied in vivo. A subject with a mandibular RPD (Kennedy class II, division 1) participated in this study, and the RPD was duplicated as the experimental denture. The basal surface at distal extension was accommodated to the sensor in a manner similar to direct relining. Measurements were performed with three patterns of occlusal rest design (mesial and distal rests, mesial rest only, and without a rest) during maximal voluntary clenching (MVC) and gum chewing. RESULTS The calibration measurements showed that the output value from each sensing point and total output of sensing points were positively correlated with the applied load. The pressures recorded in vivo varied depending on the locations of sensing points on the basal surface of the denture. During MVC the pressure distribution changed with the clenching level, and the highest pressure was registered near the residual ridge crest. The pressure distribution also changed according to the number of occlusal rests. The load center shifted about 2mm during MVC and about 4mm during gum chewing. CONCLUSION The measuring system developed here enabled us to measure the pressure distribution under the denture base of RPD. The pressure distribution varied along with the design of the occlusal rest.

Biological-data-based finite-element stress analysis of mandibular bone with implant-supported overdenture

BACKGROUND This study aimed to evaluate the stress distribution in a mandibular bone with an implant-supported overdenture by a biological-data-based finite element analysis (FEA) utilizing personal CT images and in vivo loading data, and to evaluate the influence of the number and alignment of implants and bone conditions on the stress in peri-implant bone. METHODS FEA models of a mandible were constructed for two types of overdentures: 4 implants supported overdenture (4-OD) and 2 implants supported overdenture (2-OD). The geometry of these models was constructed from CT images of a subject, who wore an implant-supported overdenture. The magnitude and direction of the loads on the implants for two types of overdentures during the maximal voluntary clenching were measured with 3D force transducers. FEA using these loads was carried out to observe stress distributions in peri-implant bone. RESULTS Higher stress was observed in cortical bone around the implant neck. Stress in peri-implant bone for 4-OD was reduced in comparison with those for the 2-OD. For the 4-OD, notwithstanding such reduction of the stress, the stress concentrated at the cortical bone around the implant aligned with large deviation from load direction. CONCLUSIONS In this study, biological data from a certain subject was successfully duplicated to the FEA models. The results demonstrate the mechanical prominence of using more implants. Even in 4 implants model, high stress was found around an implant with a large inclination and with thin cortical bone. This suffices to demonstrate the capability and usefulness of the biological-data-based FEA.

In vivo load measurement for evaluating the splinting effects of implant-supported superstructures: a pilot study.

The purpose of this in vivo study was to evaluate the biomechanical effects of splinting of implant-supported superstructures using piezoelectric transducers to measure the three-dimensional forces exerted on implants supporting fixed superstructures. Measuring devices were set into the implant fixtures at the mandibular right second premolar and first molar. During clenching, force magnitudes were allocated more evenly to the two implants if they were splinted compared with the unsplinted control implants. However, this equalization of load distribution was not apparent during wax biting. Splinting of implant-supported fixed superstructures affects the force exerted on implants, especially during clenching.

Oral appliance treatment for obstructive sleep apnoea patients with severe dental condition

This clinical report introduces and evaluates the use of a mandibular advancement oral appliance (OA) attached to a denture base for the treatment of obstructive sleep apnoea syndrome (OSAS) in a patient presenting severe dental problems and multiple missing teeth. It concerned a 58-year-old man with moderate OSAS (apnoea index (AI): 15·9 h(-1) ; apnoea hypopnea index (AHI): 21·7 h(-1) ), presenting ten remaining teeth (maxilla: 5, mandible: 5) and important dental and periodontal problems. A treatment OA comprising both maxillary and mandibular parts was fabricated with an acrylic resin base, simulating the structure of a conventional removable partial denture (RPD). The polysomnography examination performed after the use of the OA showed the treatment induced a significant decrease in OSAS symptoms (AI: 0·7 h(-1) , AHI: 8·2 h(-1) ). All the necessary dental and periodontal treatments were performed to assure the reestablishment of oral health. The treatment OA was modified after each treatment to adapt it to each new oral condition. After 18 months, once the oral health was reestablished with seven remaining teeth (maxilla: 5, mandible: 2), final RPDs and final OA were fabricated. Polysomnography with final OA showed a similar positive result with respect to OSAS symptoms. No side effects related to the OA treatment were detected during the 3-year follow-up. To keep a sound oral condition, periodical dental care was performed by specialists in both periodontal and prosthodontic clinics. This clinical report shows the feasibility of treating OSAS patients with OA even in the presence of severe oral conditions and multiple missing teeth.

Treatment using oral appliance for obstructive sleep apnea syndrome patients with multiple missing teeth

This section is intended to tap into a relatively unique feature of sleep science: images with great educational and conceptual content (e.g., electroencephalograms, electromyograms, polysomnograms, portable devices, actigrams, scans including functional images, pathology specimens, brain slice preparations, fluorescent microscopy and other cutting edge techniques). Please see our web site’s (http://ees.elsevier.com/sleep/) Guide for Authors for instructions. We hope this section will be enriched by the contributions of our colleagues who wish to offer stimulating opportunities for discussion and new insights into the field of sleep.

An in vivo study on load distribution in different implant configurations for supporting fixed partial dentures

PURPOSE The aims of this study were to develop a device for in vivo measurement of three-dimensional (3D) loads on implants and to investigate the effects of implant configuration on the load distribution under a three-unit fixed partial denture (FPD). MATERIALS AND METHODS A 67-year-old female patient with three implants (in the mandibular left second premolar, first molar, and second molar regions) was recruited. Four implant configurations for a three-unit FPD depending on the number and position of the implants were considered in this study. They included a three-implant prosthesis and three types of two-implant prosthesis: a central pontic, posterior cantilever, and anterior cantilever, with the same superstructure (splinted three crowns) for the same occlusal contact. Customized abutments and 3D piezoelectric force transducers were fixed to the implants of the four configurations with the superstructure. The loads on the implants were recorded during maximum voluntary clenching (MVC-test) and when chewing a piece of chewing gum (GUMtest). RESULTS The occlusal forces on the dental arch during MVC-test with the four implant configurations did not exhibit significant differences. In the three-implant prosthesis, there were no significant differences in the mean maximum resultant load on each implant in both tests. In the central pontic, the load on the second premolar was significantly greater than that on the second molar in the MVC-test but there were no significant differences in the GUM-test. High loads were detected on the first molar in both the posterior cantilever and anterior cantilever. The highest load was detected on the first molar in the posterior cantilever during the GUMtest. CONCLUSION The in vivo 3D load-measuring device using the piezoelectric force transducers enabled the measurement of the functional load on implants supporting a FPD. The results suggested, within the limitations of this study, that a three-implant prosthesis and central pontic provide biomechanically beneficial designs compared with the posterior cantilever and anterior cantilever in terms of the equal distribution of loads on supporting implants.

Effect of Configurations of Implants Supporting a Four-Unit Fixed Partial Denture on Loading Distribution

This study aimed to evaluate the effect of the configuration of implants supporting a four-unit fixed partial denture on load distribution. An epoxy resin model missing teeth from the first premolar to the second molar was used. Three-dimensional piezoelectric force transducers were set on implants placed in the missing teeth area with a four-unit experimental superstructure. Three-dimensional loads on the implants were measured with four different implant configurations when a static load of 100 N was applied. The loads on the implants changed significantly depending on the implant number and position and the applied loading points.

Effects of Food Texture on Three-Dimensional Loads on Implants During Mastication Based on In Vivo Measurements.

Introduction:The mechanisms by which the loads exerted on implants that support prostheses are modulated during mastication remain unclear. The purpose of this study was to evaluate the effects of food texture on 3-dimensional loads measured at a single implant using a piezoelectric transducer. Materials and Methods:Two subjects participated in this study. The transducer and the experimental superstructure, which had been adjusted to the subjects occlusal scheme, were attached to the implant with a titanium screw. The foods tested were chewing gum and peanuts. Results:The mean maximum load on the implant in each chewing cycle was significantly higher during peanut chewing than during gum chewing. The direction of maximum load was significantly more widely dispersed during peanut chewing than during gum chewing. The range of changes in load direction during the force-increasing phase of each chewing cycle was significantly wider during peanut chewing than during gum chewing. Conclusions:The load on the implant was affected by food texture in both subjects. This measurement method can be useful to investigate the mechanisms of load modulation on implants during mastication.

Retrospective study on factors that affect removable partial denture usage

The purpose of this retrospective study was to investigate the factors that affected the usage of removable partial dentures (RPDs) and the patients’ satisfaction with their RPDs 5 years after insertion. Sixty-seven patients treated with 90 RPDs that were inserted at the Tohoku University Hospital between 1996 and 2001 participated in this study. The usage rate and 12 factors that might affect usage were examined, and 15 factors regarding satisfaction were evaluated. Statistically significant associations were found between denture usage and patient’s age, location of edentulous area, pain, color of artificial teeth, and arrangement. These findings suggest that the acceptance of RPDs among patients was related to factors such as patient’s age, oral status, and satisfaction.