Sakae Yasui

A multifactorial model of masticatory performance: the Suita study.

Previous studies have identified various factors related to masticatory performance. This study was aimed to investigate variations and impacts of factors related to masticatory performance among different occlusal support areas in general urban population in Japan. A total of 1875 Japanese subjects (mean age: 66·7 years) were included in the Suita study. Periodontal status was evaluated using the Community Periodontal Index (CPI). The number of functional teeth and occlusal support areas (OSA) were recorded, and the latter divided into three categories of perfect, decreased and lost OSA based on the Eichner Index. Masticatory performance was determined by means of test gummy jelly. For denture wearers, masticatory performance was measured with the dentures in place. The multiple linear regression analysis showed that, when controlling for other variables, masticatory performance was significantly associated with sex, number of functional teeth, maximum bite force and periodontal status in perfect OSA. Masticatory performance was significantly associated with number of functional teeth, maximum bite force and periodontal status in decreased OSA. In lost OSA, masticatory performance was significantly associated with maximum bite force. Maximum bite force was a factor significantly influencing masticatory performance that was common to all OSA groups. After controlling for possible confounding factors, the number of functional teeth and periodontal status were common factors in the perfect and decreased OSA groups, and only sex was significant in the perfect OSA group. These findings may help in providing dietary guidance to elderly people with tooth loss or periodontal disease.

Validity and reliability of a visual scoring method for masticatory ability using test gummy jelly

BACKGROUND For quantitative evaluation of masticatory ability of the elderly patients, there should be a simple and reliable method without special techniques and instruments. OBJECTIVE The purpose of this study was to examine the validity and reliability of a visual scoring method for assessing masticatory performance. MATERIALS AND METHODS A 10-stage scale for visually scoring was rated based on the range of the glucose concentration dissolved from comminuted jelly. Photographic images of comminuted jellies were produced as a standard material for each score. Fifty subjects were recruited as raters who graded the visual score for 50 photographic images of comminuted jellies on the screen of a lap-top three times in random order. RESULTS There were strong correlations (rs = 0.911- 0.981, Spearmans rank coefficient) between the actual scores determined from the glucose concentration and the visual scores graded by subjects in all three measurements. The intraclass correlation coefficients (ICCs) of the inter-rater reliability and the ICCs of the intra-rater reliability of the visual scoring ranged from 0.946 to 0.947 and from 0.860 to 0.987 in three measurements, respectively. CONCLUSIONS These results indicated that the visual scoring method was valid and reliable for evaluation of masticatory performance.

A Method of Improving the Evaluation of Masticatory Efficiency in Complete Denture Wearers by Using the Testing Gumi-jelly.

The masticatory efficiency in normal dentate people and complete denture wearers has been evaluated by using testing gumi-jelly. However, some complete denture wearers who cannot chew the testing gumi-jelly (20×20×10mm) within a given chewing stroke are occasionally encountered. In this study, the masticatory efficiency test using testing gumi-jelly (20×10×10mm) cut in half was examined to evaluate the masticatory function of these cases. It was indicated that there was a significant proportional correlation between the surface area of the four kinds of specimens divided into equal parts and the amount of glucose discharged from the surface of the gumi-jelly. The increasing rate of surface area after chewing the half-type was higher than the whole-type in ten complete denture wearers. In particular, the rate of increase after chewing was remarkable in patients whose masticatory efficiency was not shown by using the whole-type. It was suggested that the masticatory efficiency test using testing gumi-jelly cut in half would be an extremely useful method for patients with low masticatory function.

Does the utilization of dental services associate with masticatory performance in a Japanese urban population?: the Suita study

There are numerous reports on the relationship between regular utilization of dental care services and oral health, but most are based on questionnaires and subjective evaluation. Few have objectively evaluated masticatory performance and its relationship to utilization of dental care services. The purpose of this study was to identify the effect of regular utilization of dental services on masticatory performance. The subjects consisted of 1804 general residents of Suita City, Osaka Prefecture (760 men and 1044 women, mean age 66.5 ± 7.9 years). Regular utilization of dental services and oral hygiene habits (frequency of toothbrushing and use of interdental aids) was surveyed, and periodontal status, occlusal support, and masticatory performance were measured. Masticatory performance was evaluated by a chewing test using gummy jelly. The correlation between age, sex, regular dental utilization, oral hygiene habits, periodontal status or occlusal support, and masticatory performance was analyzed using Spearmans correlation test and t‐test. In addition, multiple linear regression analysis was carried out to investigate the relationship of regular dental utilization with masticatory performance after controlling for other factors. Masticatory performance was significantly correlated to age when using Spearmans correlation test, and to regular dental utilization, periodontal status, or occlusal support with t‐test. Multiple linear regression analysis showed that regular utilization of dental services was significantly related to masticatory performance even after adjusting for age, sex, oral hygiene habits, periodontal status, and occlusal support (standardized partial regression coefficient β = 0.055). These findings suggested that the regular utilization of dental care services is an important factor influencing masticatory performance in a Japanese urban population.

Application of Piezography in Complete Denture. Evaluation of Impression Materials.

Piezography used mainly within France and Spain is one of the functional approaches to obtain the proper denture space in complete and partial dentures. The purpose of this study was to find impression materials suitable for Piezography. Five subjects and five operators (mean age: 27.0±1.5 years) were selected for the study. Eleven kinds of commercially available soft impression materials were examined by using Visual Analog Scale (VAS) on six items, irritation to oral soft tissues, operability, aptness to pronounce and to hear words, hardening time, and surface smoothness.As a result, FITT (Kerr Co.) used in the original Piezography was the best impression material. Tissue Conditioner (Shofu Inc.) and Evatouch H-type (Neo Dental Chemical Products Co.) also obtained high evaluation among impression materials tested in this study. In consideration of economic efficiency, it was suggested that Tissue Conditioner was the best impression material for Piezography in Japan.

Effect of Metal Surface Treatment with Gold Dust on Bonding Strength between Metal and Porcelain.

It has been proved in previous studies that the surface treatment of cobalt-chromium alloy with gold dust was effective not only to increase the bonding strength between metal and porcelain, but also to cover metal color and prevent the border coloring.In this study, two kinds of gold alloys for porcelain fusing indifferent compositions (Select 50 and Select 77 H, Ohura Precious Metal Co.) were selected to examine the effect of metal surface treatment with gold dust on the bonding strength. The size of gold dust (Super-Binder OG, Ohura Precious Metal Co.) used in this study was 1.0 μm in a uniform diameter.The results showed that both alloys exhibited stronger bonding strength after treated with gold dust, particularly in the case of Select 50. Most of the gold dust remained on the fractured surface of Select 50 specimens after the shear test, observed by scanning electron microscope. It was also found that gold dust existed on both metal and porcelain surfaces in the case of Select 77 H.The above results suggested that the treatment of a metal surface with gold dust could reinforce the bonding strength between gold alloy and porcelain. Furthermore, the bonding strength would increase greatly if the gold dust was bonded firmly to the metal surface.

New Method of Interocclusal Record using Exchangeable Screw Jack

The determination of the correct vertical and horizontal mandibular position for edentulous patients is one of the most important techniques in complete denture construction.The aim of this study was to develop a new method of interocclusal record using exchangeable screw jack apparatus to determine the vertical dimension utilizing the patients proprioceptive sensation. Furthermore, we expect to develop a method for tracing the Gothic arch and recording the centric jaw relationship which could be easily performed in a one-treatment procedure.The exchangeable screw jack placed on the maxillary occlusal rim makes contact with a plate fixed on the mandibular occlusal rim. The height of each screw is adjusted as follows: from 3mm lower (score 1) than the vertical dimension of the present denture (score 4) to 3mm higher (score 7) at intervals of 1mm. Using the apparatus, the upper and lower borders of the comfortable occlusal zone (COZ) are calculated from the patients perception of mandibular position by the constant method. To understand the reproducibility of the method, each COZ of 5 edentulous patients wearing complete dentures without problem was measured on 3 or 4 different days.There is no significant difference between COZs of different measurement days. On the other hand, the time required for measurement and recording and the patients stress were greatly reduced with the new apparatus.

Electric Resistance Soldering to Fabricate Wrought Wire Clasps-Influence of Heating Duration on Deformation and Mechanical Properties of Clasp Arms and Tensile Strength of Soldered Parts.

In the fabrication of wrought wire clasps, the electric resistance soldering procedure was adopted to conect clasp arms to rests.This procedure surpasses in mechanical properties of clasp arms and strength of soldered parts as compared with other soldering procedures.The purpose of this study was to investigate the influence of heating duration by using this procedure.Two kinds of specimens, circular arm type and straight arm type, were prepared.A clasp arm was soldered to a piece cast with Co-Cr alloy. The heating duration was set to 0, 2, 4, 6, 8 and 10 seconds.Distances between clasp tips, load required for 0.1mm deflection of clasp arms, permanent deformation after 0.5mm deflection thereof and tensile strength of soldered parts were measured.The results were as follows:1.As the heating duration increased, the distance between clasp tips increased.2.Load required for 0.1mm deflection showed almost the same value in every heating duration.3.Permanent deformation showed the lowest value at a duration of 4 seconds (1.73V).4.Tensile strength showed a constant value (63-69kgf) regardless of the heating duration.These results indicated that the heating duration should be within 4 seconds to obtain the best mechanical properties and to avoid deformation of clasp arms.

Questionnaire for Craniomandibular Disorder Patients.

To elucidate the long-term development of symptoms as to craniomandibular disorders, a questionnaire was sent, in May 1992, to 200 patients referred to the clinic of removableprosthodontics of the Hospital attached to Osaka University Faculty of Dentistry, who had beentreated from 1984 to 1991. Ninety-seven (48.5%) patients answered the questionnaire. Theresults from their answers and clinical protocols were as follows:Sixty-one (63.0%) patients developed symptoms 3 to 99 months after the termination oftreatment. Their most common symptoms were TMJ sounds (38.6%), muscle dysfunction (31.1%), trismus (15.9%) and TMJ pain (11.4%), which were 97% of all. Twenty-five (28.3%) patients had recurrence of symptoms: the ratio of recurrence in the patients who had stoppedreceiving regular treatment (46.4%) was significantly higher than that in those who had continuedto the end (18.8%). Few patients had recurrence within a year after treatment, therefore, it issuggested that a clinical recall examination should at least be performed once a year from thetermination of treatment for many years.

Evaluation of Soldering Procedure in Fabrication of Wrought Wire Clasp. Differences in Temporary Attachment and Soldering.

Most wrought wire clasps are attached to the framework of removable partial dentures by soldering. The purpose of this study is to investigate the influence of soldering procedures on deformation and mechanical properties of clasp arms and strength of jointing parts.In this study, circular clasp arms were made from Co-Cr alloy wires and soldered to supporting parts with a silver solder. Two kinds of temporary attachments, investing and spot welding, and two kinds of soldering methods, torch and electric resistance soldering were applied. These temporary attachment and soldering methods were combined, then four different procedures were compared.The results were follows.1. The change of distance between clasp tips during soldering procedure was smaller for temporary attachment by investing than spot welding, and for electric soldering than torch soldering.2. By any soldering procedure, load required for 0.1 mm deflection of clasp arms increased significantly and permanent deformation after 0.5 mm deflection of them decreased considerably.3. In both tensile strength and fatigue profile of jointing part, combination of spot welding and electric soldering was the best of all procedures.These results indicated that without the deformation of clasp arms, combination of spot welding and electric resistance soldering was the most effective procedure in wrought wire clasp construction.