Twelve normal dentate young males with a subjective symptom of clenching during physical exercise were used to investigate the clenching force, the masticatory muscle activity, the elbow flexion strength and the biceps brachial muscle activity at horizontally different mandibular positions. The clenching force was measured by the sensor using the newly developed pressure sensitive conductive silicone rubber sheet. This sensor was a 20-mm square of this rubber sheet placed between the copper foil contact plate the electrode and polyimide resin as electrical insulation.
The results were as follows:
1) There were individual variations in clenching and the subjects were divided into two groups, the hard clenching group (58.9-85.3 kgf) and the soft clenching group (4.9-13.2 kgf).
2) In the hard clenching group, the maximum clenching force was recorded at the tapping point and its standard deviation was minimum.
3) The maximum elbow flexion strength was recorded at the tapping point in both groups.
4) In the hard clenching group, the correlation coefficient between the clenching force and the elbow flexion strength was statistically significant (r= 0.69, p<0.01). On the other hand, it was not statistically significant in the soft clenching group (r=0.04, p>0.05).
In this study, the occlusal function is suggested to be closely related to physical exercise.

View full abstract

The purpose of the present study was to determine whether splinting of healthy teeth affected the mechanical mobility of each tooth. Upper first and second premolars, upper second premolar and first molar, or lower premolar and IMZ implants with titanium element were splinted with the device, without any changes of occlusal tooth contacts, which could be removed by the operator over about 2-month period. Horizontal mechanical mobility of individual teeth and implants were measured periodically.
The results were as follows:
1. The coefficient of variation in the mechanical mobility of splinted teeth for periods of experimental were significantly greater than those in non-splinted control teeth (p<0.01).
2. For a few days after the start of splinting the effect of splinting on mechanical mobility of each tooth splinted was great significant.
3. When a difference between the two initial mobility of teeth was large, the difference tended to become smaller after splinting. And furthermore, there was a greater percentage change in mobility of teeth that initially had smaller mobility than was the case for teeth that initially had greater mobility.
4. The mobility of teeth did not decrease significantly after splinting with implants.

View full abstract

The purpose of this study was to improve the color of castable ceramic crowns. Castable ceramics were used for dowel-cores.
First, whether a difference in dowel-core material would have any effect on the color of castable ceramic crowns was examined.
The color of castable ceramic crown was affected by the color of the dowel-core in some circumstances.
The use of castable ceramics for dowel-cores has the advantage of good color. But the strength of the castable ceramic dowel-cores must be examined. The castable ceramic dowel-cores were not as strong as metal dowel-cores.
Thus prefabricated dowels were made for castable ceramic dowel-cores.

View full abstract

The purpose of this study was to determine the three-dimensional accuracy of a metal base made with the silicone duplicating impression system.
Three kinds of silicone duplicating impression systems were selected: Rema-Sil, Wirosil and Deguform. A partially edentulous maxillary dentition model (Kennedy class III) was used as the master model. Six measuring points were assigned to the abutment teeth and the medial parts of the palatal mucous. Duplicated casts using the duplicating impression systems were prepared. Subsequently based on these duplicated casts the metal base was cast with a cobalt-chrome alloy. The coordinates of each measuring point on the duplicated casts and the metal bases were measured using a three-dimensional measuring system.
The duplicated casts made with Rema-Sil and Deguform had almost the same dimensions as the master model in a horizontal direction to the occlusal plane and were larger than the master model in a vertical direction, while the duplicated cast made with Wirosil was slightly larger overall than the master model. The metal bases made with Rema-Sil and Deguform were slightly smaller horizontally and slightly larger vertically compared with the master model, while the metal base made with Wirosil was almost the same horizontally and slightly larger vertically but nearly the same size as the master model.

View full abstract

The purpose of this study was to investigate EMG profiles of masticatory muscles in orthognathic surgery patients with mandibular prognathism during deliberate unilateral gum chewing.
Vertical jaw movement and EMG activities from bilateral anterior temporal, masseter, and anterior belly of digastric muscles were recorded simultaneously from 12 healthy adults and 12 patients. EMG signal was divided according to the period of the maximum opening position of vertical jaw movement. EMG profiles of the chewing stroke were accomplished by normalizing each period to 100%. Normalization was achieved by setting the mean value of each EMG over the chewing cycle to 100%. The relationship of the EMG profile between normal subjects and patients was evaluated. The degree of similarity and the displacement for each EMG profile in all muscles was investigate by using a cross-correlation technique.
The results were as follows:
1. EMG profiles of patients were different for the “Peak” vale and “Duration” of the activity from those of normal subjects.
2. The similarity was little, and great displacement was found in patients.
3. In patients, the similarity and displacement of EMG profiles had large value on the working side.

View full abstract

This study was performed to determine whether or not malocclusion decreases the interdependent relationship between the chewing path and muscle activity. For experimental premature contact attached to the lower 1st molar on the habitual chewing side, two thicknesses (50 μm and 100μm) of metal foil were used. Chewing movements using a stick of gum were recorded simultaneously as the path and electromyograms. The parameters for the path were the amount of anterior-posterior and right-left movements at 1 mm, 7 mm and lowest point vertically below the intercuspation in the opening-closing path and the maximum amount of mouth opening per stroke, and those for electromyograms were the interval of EMG bursts and the integrated in the central portion of the bilateral masseter muscles and the anterior portion of the bilateral temporal muscles. The presence or absence of premature contact, and changes in the relationship between the chewing path and muscle activity according to the thickness of interference were analyzed in terms of the first canonical correlation coefficient in canonical correlation analysis. Premature contact could be a factor that decreases the first canonical correlation coefficient, but no differences were observed between the two thicknesses.

View full abstract

Dimensional changes of complete dentures, which were constructed by six conventional polymerization methods, were investigated after polymerization and during storage. The discrepancy at median line and alveolar ridge was larger in the dentures constructed in a water bath at 70°C for 40 min and then at 100°C for 30 min, in a hot press and by microwave polymerization than in a water bath at 70°C for 24 hrs, for 8 hrs and by autopolymerization. The discrepancy at the denture border of the dentures constructed by autopolymerization during storage in water for 30 days was 0.174±0.048 mm and in the case of the dentures constructed by other polymerization methods was less than 0.1 mm. Since the dimensional changes of the dentures during storage in water occurred up to 7 days, it seems reasonable that wearing dentures or occlusional adjustment should be carried out after storage in water for more than 7 days. The discrepancy was 3 to 4 times in the dentures stored in air than in water. When the dentures which were stored in air for 30 days was immersed in water for 30 days, the discrepancy at the denture border of the dentures constructed by autopolymerization was restored to 0.214±0.097 mm, but in the case of other polymerization methods, it was restored to about 0.14 mm.

View full abstract

Mandibular movements are coordinated ones caused by TMJ, muscles, dentitions and neuromuscles in stomatognathic system. The pathways in areas of intercuspal position (ICP) during chewing movements which are particularly influenced by dentitions were investigated. An evaluation of these movements will contribute to establising a functional diagnosis method.
An objective assessment fitting the regression line to sample data on pathways in areas of ICP during chewing movements was also reported. In addition to these studies, we developed a system to measurement of mandibular movements during grinding movement utilizing visual feedback system.
In this study, it became possible to establish a new displaying method for tooth grinding curved surfaces and pathways during chewing movements by applying algorithms of perspective transformation, hidden line elimination and coordinate transformation to incisal 3-dimensional data (X, Y, Z) obtained from a Sirognathograph (SGG).
The results were as follows.:
1. Tooth grinding curved surfaces were constructed as the wire frame model.
2. Pathways in areas of ICP during chewing movements were displayed on the tooth grinding curved surfaces.
3. A new method makes possible to display the relation between tooth grinding curved surfaces as anatomical information and pathways in areas of ICP chewing movements as functional information.

View full abstract

In this study the mandibular distortion during mandibular movement was measured. The subjects were three females and one male. Two apatite implants were placed in a unilateral mandibular molar region at an interval of about 10 mm. The measuring apparatus consisted of a magnetic sensor attached to the medial implant and a magnet attached to the distal implant. The position of the distal implant relative to the medial implant during opening and protrusion of the mandible were measured six times every movement.
At the maximum opening the position of the distal implant was deviated lingually in the range of 8 to 25 pm and at the maximum protrusion it was also deviated lingually in the range of 10 to 37 μm.
These findings suggest that the stress concentration on the implant and surrounding bone is caused by mandibular distortion during mandibular movements if several superstructures of implants inserted in the mandibular molar region are connected firmly. In other words, it is important for the mandibular position at the impression and soldering operation procedure for the fabrication of the superstructure to decrease the stress.

View full abstract

A series of studies on the relationship between the condition of the stomatognathic system and the systemic condition has been conducted, it has been found that they both influence the somatic nervous system. In this series, the usefulness of the digital plethysmogram, which is simple, noninvasive, quick, and quantitative among autonomic function tests, was evaluated. Experimental occlusal interference was applied to the lower first molar teeth on the primary mastication side in 5 healthy subjects with natural teeth, and changes in the height of the digital plethysmogram were examined after interference. The following conclusions were drawn concerning the usefulness of the test.
1. The height of the digital plethysmogram was reduced 24 hours after occlusal interference, and its base line was unstable in many subjects. It tended to return to the level before interference one week after discontinuation of interference.
2. These findings suggest that plethysmography is useful for evaluation of the effect of occlusal interference as an abnormality of the stomatognathic system on autonomic activity.

View full abstract

Although the movement of the articular disc and condyle of the temporomandibular joint (TMJ) with reciprocal clicking have been investigated from autopsies of specimens using arthrography and cineradiography, no attempts have been made to analyze the clicking from the standpoint of the relationship of the disc position and morphology to condylar movement. This paper reports the disc's positional alternation to the condylar path deflection by using a magnetic resonance imaging system and a six degrees of freedom jaw tracking device equipped with a joint sound recorder for 18 TMJs with reciprocal clicking in 13 subjects. The interincisal distance was measured to recognize the timing of disc reduction and deflection of the condylar path. The results were as follows:
1. Clicking occurred at a low frequency and with a lesser intensity by decreasing the velocity of the open-close jaw movement.
2. It was found that the velocity of the opening click in the late stage was larger (77%) than those in the intermediate (6%) or early stages (17%).
3. The rate of timing coincidence of disc reduction and deflection of the condylar path was as high as 89% for a closing click, and 33% for opening click.
Since accurate analysis of the disc and condylar movement was possible at closing click, it was possible to find the indication or contraindication of treatments using such devices as repositioning appliances.

View full abstract

The interest for aesthetic improvement by dental treatment has been growing in patients. Recently, Hi Lite^TM (Shofu USA), a new vital teeth bleaching system, has been employed as one of the aesthetic dental treatments in the United States. Nevertheless, the biological effects of vital bleaching to teeth and the surrounding tissues has not been clarified. The purpose of this study was to determine the effect of vital bleaching of human enamel surfaces by using scanning electron microscopy and analytical electron microscopy (SEM-EDS). The medial or distal halves of the axial middle third of teeth crowns were bleached. Untreated medial or distal halves were used as the control group. Enamel surfaces were sequentially bleached several times to determine the repetition effect of the bleaching procedure. The bleaching procedure followed the directions of the manufacturer. Further, enamel surfaces etched by 37% phosphoric acid for 1 min were used as positive controls. The one-time bleached group showed no significant difference in microstructure, when compared with the control group. 3- and 5-time treated groups showed “bubbly” microstructure in enamel surfaces. Furthermore, elemental analysis indicated relatively higher intensities of Ca and P in 3- and 5-time treated groups than the control group. The results of this study suggested that the influences of vital bleaching by Hi Lite^TM on hard tissues comprising enamel would be few.

View full abstract

The purpose of this study was to clarify the relationship between the frequency of Gram-negative anaerobic black-pigmented rods and periodontal disease-inducing occlusal trauma. The occlusal trauma group had a markedly higher level of gingival exudates and higher numbers of bacteria in gingival exudates than the normal control group. The rate of total numbers of bacteria against a definite amount of gingival exudates were found remarkably higher in all subjects with occlusal trauma than normal controls. Facultative anaerobes showed the highest frequency, in which the Gram-positive coccamount isolation rate of bacteria was predominant in all subjects. The frequency of obligate anaerobes increased in the group with occlusal trauma. The frequency of obligate anaerobic Gram-negative rods was observed to have no significant difference between occlusal trauma and normal control groups. All obligate anaerobic Gram-negative black-pigmented rods in the periodontal pockets isolated from patients with occlusal trauma and normal controls were identified with Prevotella intermedia by a biochemical test. Prevalence of obligate anaerobic Gram-negative black-pigmented rods isolated from occlusal trauma maintained a low level throughout the experimental period. These results indicate that alveolar bone loss in occlusal trauma may have no relation to obligate anaerobic Gram-negative black-pigmented rods.

View full abstract

The purpose of this study was to verify the validity of the questionnaire that was reorganized from our previous studies^7-9) and patients' satisfaction for prosthetic treatment with removable dentures. The groups of 123 FD wearers, 134 APD wearers, and 139 PD wearers were analyzed individually.
The results were as follows:
1. The structure of patients' satisfaction consisted of 5 factors for FD and APD, and 4 factors for PD (Table 1).
2. The items most manifesting “performance factor” or “structure factor” from our studies^7-9) provided much information about the factors concerned.
3. The principal components of “dental service factor” were human relations between a patient and a dentist, posttreatment maintenance, and times and duration of treatment.
4. In terms of the relation between content and strength of patients' evaluation, the valid critria for the satisfaction scale were found to be the following 3 grades for each denture group: i.e., “unsatisfied, ”“satisfied, ” and “very satisfied.”
5. It is considered that the structure of patients' satisfaction with denture treatment should be expressed by means of this questionnaire and the analyzing method.

View full abstract

The mandibular movement measuring system has been devised, which can record three-dimensional mandibular movements with high accuracy at high speed. This system consists of two Selspot cameras that measure movements of LED based on the principle of analystic photo survey.
Its characteristic features are as follows:
1. Selspot cameras can be placed anywhere and at any angle, so that it is easy to measure mandibular movements.
2. While measuring, the static error is 0.217 mm maximum ; therefore, the system is accurate enough to record mandibular movements.
3. Mandibular movements, at any point, can be calculated by using this system.

View full abstract

Ti-6 A1-4 V alloy, which has both the excellent biocompatibility and the small specific gravity, can be deformed greatly at the superplastic temperature of 800°C to 900°C. This superplastic forming of Ti-6 Al-4 V is practically applied to the fabrication of the denture base.
In this study, the interface properties on the finishing line between the Ti-6 Al-4 V metal frame and the denture base resin were investigated.
The bonding of the heat-curable resin for denture base containing the adhesion promoting monomer 4-META to the aluminum oxide blasted surfaces of superplastic Ti-6 Al-4 V, the casting of pure titanium and the casting of Co-Cr alloy revealed similar the favorable adhesive strengths, though the surface roughness and the hardness of those metals had slightly different values.
On the finishing line, the cross-sectional shape of the superplastic Ti-6 Al-4 V denture base was roundedge type which was different from the right-angled type called “butt joint” of casting metal frame. In order to prevent separation of the denture base resin from the Ti-6 Al-4 V metal frame, it was effective to obtain the proper bulk for both the metal frame and the denture base resin on the finishing line.

View full abstract

In order to clarify various aspects of bearing stress due to change of buccolingual arrangement at centric occlusion, distribution and mobility of bearing stress applied on the basal seat of the complete upper denture were comparatively studied.
The results were as follows:
1. Bearing stress distribution
1) Bearing stress on bone was low compared with that of mucosa in all of C, B and P arrangements.
2) Bearing stress on the ridge, border and buccal was increased in B compared with C, while it was decreased in P. The stress on the palate and postdam was decreased in B, while it was increased in P.
2. Bearing stress mobility
1) Duration of bearing stress on bone was shorter compared with that of mucosa in all arrangements. It was remarkably shorter on the palate and tuberosity in B as well as on the buccal and tuberosity in P.
2) Duration of bearing stress on the ridge, border and buccal in B was approximately equal to that of C, while it was shorter on the border and buccal in P. The stress on the palate and postdam in B was reduced, while it was extended in P.
3) Load reaching time was approximately equal in all arrangements.
4) Duration of bearing stress was approximately equal to load reaching time in all arrangements. It was shorter on the palate, postdam and tuberosity of bone in B as well as on the border, buccal, postdam and tuberosity of bone in P.

View full abstract

With regard to the relation between articulatory function and the location of the major connector, i.e., a component of the partial denture, variations in function of respective articulatory organs and their autocorrection affected by the location of the major connector are assumed to be important. Therefore, tongue muscular activity prior to articulation was determined for consecutive days in subjects who showed normal occlusion with natural dentition, using three types of experimental partial palatal plates having palatal bars in different locations. The conditions before and after application of these three plates were analyzed, and the following results were obtained.
In accordance with the results of the duration and EMG activity of tongue muscle, different setting positions of the palatal bar were found to be under the influence of the tongue muscle on articulatory function and self-compensation of the articulators. The posterior palatal bar proved to be an attachment of choice when making a partial denture with due consideration for the articulatory function of the tongue muscle.

View full abstract

Fabrication process of fixed or removable prosthesis involves numerous procedures which require well-trained skill of technicians.“DCS Precident”is a computer supported system which enables fabrication of metal copings for porcelain fused metal crowns without waxing up and casting. The system consists of three major parts, a digitizer, a milling machine and a personal computer for controlling the whole system. In this study, the following items were examined.
1) Measuring accuracy of the digitizer
2) Marginal accuracy of milled metal copings As a result, clinically acceptable accuracy in the above-mentioned items was obtained.

View full abstract

This study was conducted to clarify the relationship between extraordinary occlusal contact and temporomandibular disfunction (TMD) symptoms. The subjects were 25 persons with normal occlusion and 100 patients with TMD. These occlusal contacts were recorded at intercuspal, protrusive and lateral positions.
Then the differences of the extraordinary occlusal contact were examined, and comparison was made between the patients with and without orofacial pain as well as the patients with and without the articular disk displacement in TMJ.
The results were as follows:
1. The majority of patients showed occlusal contacts distinctly different from those of the normal subjects.
2. The ratio of the extraordinary occlusal contact was higher for the patients with orofacial pain than those without pain. This tendency was clear especially at intercuspal and protrusive positions.
3. At the ratio of the extraordinary occlusal contact, there was no fixed tendency between the patients with disk displacement and those without disk displacement. But if the patients were divided into three groups (one group without disk displacement, one with disk displacement on one side and one with disk displacement on both sides), at the intercuspal and lateral positions the patients with disk displacement on both sides indicated the highest ratio, and at the protrusive position the patients without disk displacement indicated the highest ratio.

View full abstract

In order to clarify the effect of the location of palatal bar of partial palatal plates on various articulation organs and their self-compensation, three types of experimental partial palatal plates with palatal bars at different locations were applied to subjects showing normal occlusion with natural dentition, and variations over time of the proportion of the duration of preceding consonant on the duration of speech sounds and the duration of pronunciation were evaluated. The above results suggest that the difference in location of palatal bars affects the duration of speech sounds and aspects of self-compensation, special care should be taken for the duration of speech sounds in routine clinical practice, and the mid-palatal bar is the most advantageous for connection of the partial plate denture to the upper mandibule. It is suggested that the rear palatal bar and front palatal bar are slightly inferior.

View full abstract

Soft denture liners are an important treatment option for patients who have chronic soreness associated with their prostheses. Soft denture liners provide a cushion for the denture-bearing mucosa, and this provides comfort for patients.
There are, however, many defects appearing in long-term use in clinics such as a color change, degradation, surface roughness, lack of resiliency, and peeling-off from acrylic resin.
The objective of this study was to analyze the relationship between the physical and mechanical properties and color change of soft lining material. The liner selected for this study was condensation RTV silicone rubber material. Tests were made on samples that were stored in 37°C saline and instant coffee for 1, 2, 3, 4, 12 and 24 weeks before testing.
1. The cause and effect relationship of the degree of color change and physical properties of condensation RTV silicone rubber material was not apparent.
2. It was considered that the physical and mechanical properties for soft liner were influenced by acidity of solutions.
3. It seemed that the relationship between color change and degeneration of soft liners should be analyzed under a bacterial environment in the future.

View full abstract

The purpose of this study was to examine the prevalence of temporomandibular disorders among a sample of complete denture wearers.
Seventy patients were randomly selected to evaluate the relationship between temporomandibular disorders and clinical symptoms. Pseudodynamic MR imaging of the temporomandibular joint were used to evaluate internal derangement of the temporomandibular joint. Of this group, 68.6% had internal derangement of the temporomandibular joint, and 55.7% had osteoarthrosis of the temporomandibular joint. It was also found that internal derangement in complete denture wearers was significantly related to osteoarthrosis.
None of this sample group had any chief complaints regarding TMJ disorders in clinical symptoms.
In addition, there was a prevalence of internal derangement in relation to sex, but not in relation to age. There was a higher frequency of short cycle denture life among the patients suffering from internal derangement in this group of complete denture wearers than those not suffering from internal derangement.
The degree of internal derangement severity in the complete denture wearers was related to abnormality of maxillomandibular relation, quality of the denture, mandibular movement during maximum opening of the mouth at incisal point, and previous clinical manifestations.
It became clear that a functional clinical examination of the temporomandibular joints is an important factor for determining the prognosis of complete denture wearers suffering from internal derangement of the TMJ.

View full abstract

MR imaging is often done to determine whether or not TMJ disorder is present in complete denture wearers. However, if disorders such as internal derangement could be determined through clinical examination, it would be less costly and time-consuming.
The purpose of this study was to establish the diagnostic parameters of internal derangement of TMJ through clinical examinations of complete denture wearers applying discriminant analysis.
Seventy patients were randomly selected from a group of complete denture wearers. Pseudodynamic MR imaging of the temporomandibular joint were used as the standard to evaluate the relationship between internal derangement of the temporomandibular joint and clincal findings.
It was found that five effective diagnostic parameters exist in complete denture wearers suffering from internal derangement of the TMJ. These parameters were age of current denture, maximum lateral deviation of the lower incisal movement when opening the mouth, lateral mandibular deviation degree of menton, right and left differential of CPI, and amount of free space. Incorrect jaw relation in complete denture wearers suffering from internal derangement was a tendency toward horizontal deviation of the mandibular position.
These findings were useful in understanding clinical diagnostic parameters in complete denture wearers suffering from internal derangement of the TMJ. In addition, this type of discriminant analysis and scoring was useful in determining the degree of internal derangement severity.

View full abstract

Many authors attempt to calculate muscle force per unit of cross-section of jaw muscles. However, nothing is known in regard to reduction of the size of jaw muscles in elderly edentulous patients. The purpose of this study was to determine whether or not tooth loss and aging affect the reduction of the jaw muscle cross-section in elderly edentulous patients. Thirty-three selected subjects were 11 young dentate, 11 elderly dentate and 11 elderly edentulous who were the same age as elderly dentate, and magnetic resonance imaging, cephalometric radiography through EMG pattern was used in relation to facial morphology.
There was a significant reduction of the cross-sectional area in the edentulous group, and EMG activity showed a significant reduction in the elderly dentate and especially edentulous groups. The study showed a correlation between cross-sectional area and EMG activity. However, only the edentulous group showed no correlation concerning the posterior temporal muscle.
Tooth loss may affects a reduction in the cross-section of masticatory muscle. Both tooth loss and aging may affect muscle activity in relation to facial morphology.

View full abstract