This review summarizes the presentations of the night session symposium at the 91st Conference of the Japanese Prosthodontic Society, Niigata, in June, 1994. The symposium focused on the role of occlusion for the etiology in temporomandibular disorders (TMD) which has been controversial because of the lack of scientific evidence for causal relationship. To improve the understanding of TMD, the previously reported findings of the etiology, examination methods, diagnostic classification and effectiveness of treatment for TMD were reviewed. In conclusion, morphological and mechanical factors of occlusion, such as the amount of overbite and overjet, anterior open bite, crossbite, Angle malocclusions, the amount of RCP-ICP slides, and unilateral RCP contacts, which the recent reviews handled, were not sufficient to understand the association between the occlusion and TMD. It was proposed that assessment of occlusion in TMD should be based upon more physiological and biomechanical points of view in the masticatory system.

View full abstract

When making a complete denture, not only denture stability but also the restoration of function such as mastication and speech must be considered. The purpose of this study was to compare the pressure distribution in the supporting tissue under simulated upper and lower complete dentures using two different posterior occlusal schemes: fully balanced occlusion and lingualized occlusion.
The results were as follows:
1. In centric occlusion, the occlusal scheme of the artificial posterior teeth did not affect the pressure distribution under complete denture.
2. In case of unilateral biting, the occlusal scheme affected the pressure distribution under complete denture with Livdent FB artificial posterior teeth, remarkably.
3. In case of unilateral biting in eccentric occlusion, the occlusal scheme affected the pressure distribution. The pressure values increased on the nonworking side.
It was concluded that the lingualized occlusion increases the denture stability and distributes the occlusal force to the supporting structures on the nonworking side.

View full abstract

The condition of contact and the distribution of occlusal force is important in the decision of the treatment method and the judgment of the effect of treatment in occlusal examination.
This study was performed to investigate the influence of the insertion area of Prescale on the occlusal contact area, occlusal pressure average, and occlusal force for each tooth in normal persons, and the results were as follows:
1. The occlusal contact area in forward teeth tended to increase when the insertion area of Prescale was moved forward.
2. It was not more prominent than occlusal contact area though occlusal pressure average of forward teeth was increased when the insertion area of Prescale was moved forward.
3. When the insertion area of Prescale was moved forward, the occlusal force of forward teeth tended to increase in the prominence compared with the occlusal contact area and occlusal pressure average.
4. Due to the results, it was suggested that Dental Prescale is a more effective system to analyze occlusal force than occlusal contact area and occlusal pressure average.

View full abstract

Oral movement trajectories in a denture wearer were studied to evaluate masticatory capability by monitoring orofacial movements during mastication of a color-developing chewing gum. The subject was an edentulous patient who had 4 dental implants of the mandible to anchor a mandibular overdenture.
To monitor the orofacial movements, a cordless light-emitting target that was recorded as a shining point with a clear outline when illuminated by a cold spot light was developed. An image processor enabled the recording and autotracking of multiple reference points.
The subject chewed a new color-developing chewing gum that, on mastication, indicates the patient's masticatory capability using the intensity of red.
During 250 strokes of chewing, the subject's face markers were recorded on a video tape by two high-speed TV camaras from two different perspectives, i. e., frontal and lateral. At the end of every 50 strokes, the color of the chewing gum was assessed by a Chroma Meter (CR-300, Minolta Co.), with respect to the degree of redness or a* value. Thus, the same chewing gum was continuously chewed for a total of 250 strokes, with the a* value measured at the end of every 50 strokes in 5 stages.
Then, the video tape recordings of the start of the first stage (1F) and the end of each stage (1L-5L) were reproduced on a high-speed video and fed into an image processor (Image Data, ID-8000). The movements of each marker were automatically tracked by the Image Data, after which the resulting data of the 3-dimensional coordinates were fed into a computer.
The trajectory of each monitored point during the 4 sec of each stage was computed by a 3-D analyzer (Movias 3D) with reference to the following parameters: the total length from start to finish of the trajectory (TL); the distance between the start and finish of the trajectory (SL); the ratio of the TL to the SL (T/S); the volume of the rectangular solid encompassing the entire trajectory (the cubical range); and the mean of the 3-dimensional angles that were created by differences in the direction of the preceding and following trajectories at each measured time (TH).
Our results revealed that the time needed for one chewing cycle reduced gradually from 1F to 5L. Similarly, the TL of the incisal point (IP) and the THs of both the IP and the modiolus (Mo) also gradually reduced. These findings indicated that as mastication proceeds, the range of mouth movement becomes narrower and all the trajectories become smoother.

View full abstract

Recently conical telescopic denture has been used in many clinical treatments, but it has many problems with retentive force of conical double-crown that need to be solved. The purpose of this study was to elucidate the correlation between retentive force and various factors of conical telescopic double-crown. Various factors such as fabricating material, taper angle, height of cone and load were considered as problems in report 1. In this experiment, retentive force related to the diameter of the cone was examined.
The results were as follows:
1. Retentive force was greater as the diameter was decreased compared with retentive forces for two diameters of cone. This effect was greater as the height of the cone and load were increased and the taper angle was decreased.
2. Retentive force decreased as the taper angle of any diameter of cone was increased and this effect was greater as the height of the cone and load were increased. Retentive force depends on the taper angle strongly in any diameter.
3. Retentive force had a tendency to increase slightly as the height of the cone of any diameter of cone was increased and it was greater as the taper angle was decreased and the load was increased. But the increasing rate was less compared with any other factors.
4. Retentive force increased in proportion to the load on any diameter of cone, and this effect was greater as the diameter and taper angle were decreased and the height of the cone was increased.

View full abstract

The purpose of this study was to investigate the relationship between gingival health around abutment teeth and design of proximal minor connector. Twenty-two subjects who have not worn dentures for at least 6 months participated in this study. Four types of proximal minor connector were investigated. Gingival health such as gingival crevicular fluid (GCF) flow, gingival index (GI), plaque index (PlI) and probing depth were examined just before and 12 months after insertion of dentures. The results were as follows:
1. In the conventional design of the proximal minor connector, gingival health had a tendency to worse.
2. In the open design of the proximal minor connector, gingival health had a tendency to improve.
3. On both open and closed sides of the rotational path clasping system, gingival health had a tendency to be unchanged.

View full abstract

This experimental study was performed to investigate bone tissue reaction of apatite-collagen conjugated sponge in the healing process of bone. The research was done on bone formation in relation to microvascular construction using scanning electron microscope.
Octacalcium phosphate (OCP)-collagen conjugated sponge was employed as experimental material, having hydration activity, together with type I collagen gel in a short time under physiological conditions. Japanese monkeys were employed as experimental animals.
Bilateral lower premolars and molars were extracted. After healing of the site, an artificial bone defect was made, and the material was inserted. These animals were sacrificed 2, 3, 4 and 8 weeks after operation. Acryl plastic was injected via the common carotid arteries utilizing the plastic injection method to prepare a microcast around the experimental region. The injected materials were coated with gold in order to use scanning electron microscopy.
In the first two weeks, this OCP-collagen sponge guided a dense capillary network and new bone formation was observed around OCP particles with osteoblasts in the experimental region. And it promoted osseous healing of the sight.
Application of sponge in an alveolar bone defect promotes bone formation in preparation for prosthodontic treatment.

View full abstract

The influence of diabetes on the implant-bone interface of titanium (Ti) implants, inserted transcortically and extending into the medullary canal of rat tibiae, was examined, and the differences in bone reaction were quantitatively assessed using an image processing system. Thirty male Wister King A rats (aged 5 weeks) were used in this experiment, and they were divided into 2 groups, 15 for the control and 15 for the diabetes-induced (DI) group. They were sacrificed 7, 28 and 84 days after implant placement. Toluidine blue-stained undecalcified sections were prepared for histological observation and image analysis. The Ti implants in the bone marrow area had been almost encapsulated in a thick bone layer. The Ti implants in the DI group had been partially surrounded by a thin bone layer, but the thickness of the surrounding bone had decreased. Quantitative evaluation indicated that the control group showed an increase of the percent of bone contact, the thickness of surrounding bone and the area of surrounding bone throughout the experimental period, while the DI group showed a decrease of the thickness of surrounding bone and the area of surrounding bone except for the percent of bone contact.

View full abstract

The growing demand for medical and dental care among people who are in overseas countries has become a major issue. The main objective of this project was to establish a method for analyzing the influence of social and cultural backgrounds of dentists who examine, diagnose, determine necessary treatment, and establish treatment plans for their patients in different countries. Japanese dentists were compared with Canadian dentists using identical patient models in a role playing interview method. Within the limitations of this pilot study, the following statements can be derived:
1. The method used in this study was effective in analyzing differences in decision making among individuals or groups.
2. By using this method, it is possible to establish some guidelines for patients visiting dental offices outside their native countries.

View full abstract

The purpose of this study was to investigate the influence of age, gender, denture-wearing history, and some clinical variables on psychometric traits of the patients who request reconstruction of their removable partial dentures. Fifty-seven patients (22 males and 35 females; mean age 61.0 years) completed the psychometric measurements regarding various aspects of their present partial dentures using visual analogue scales (VAS). Female patients indicated significantly less satisfaction with comfort of dentures than males. Younger patients expressed less satisfaction with esthetics of their dentures than older patients. Period of wearing present denture significantly correlated with psychometric measures of pain, comfort and general satisfaction, suggesting that this clinical variable is an important factor. There was no significant correlation between patient's general satisfaction and retention/stability of denture assessed by the examiner.

View full abstract

In order to clarify the reliability of measurement accuracy of the SDM apparatus, thickness of 9 palatine mucosal regions of 2 normo-dentulous subjects was determined and its correlation with the measured values for the same regions by puncturing was examined. Furthermore, thickness measurement was made of 10 palatine mucosal regions of 25 males and 11 females. The results were as follows:
1. Intra-individual change in the measured value tended to be smaller by SDM method than by puncturing.
2. A high correlation was noted between the measured values of palatine mucosal thickness diameter by puncturing and SDM method.
3. As for the palatine mucosal thickness by SDM method:
1) Palatine median region and retropalatine lateral region showed the smallest and the greatest thicknesses, respectively.
2) Males tended to have greater thickness in all regions that were measured than females.

View full abstract

“Evaluation scale of oral ADL” was designed for the purpose of establishing clinical standards to assess various masticatory conditions in elderly and disabled patients.
Two hundred eight elderly patients with various general condition were examined in order to study the effectiveness of this evaluation method for identifying characteristics of masticatory function and to demonstrate a relationship between masticatory function and general conditions.
The method and results were as follows:
1. The parameter of “Evaluation scale of oral ADL” includes the number of remaining teeth, the condition of denture, types of food which can be chewed and oral maintenance. By evaluating each parameter in a patient with five graded scores, the total scores were expressed as “oral ADL score.”
2. In terms of the teeth score, food score, oral maintenance score, “oral ADL score, ” biting force, grip force and mental score, there was significant difference between the two groups of elderly patients with different backgrounds.
3. It was indicated that there is a relationship between “oral ADL score” and ADL score.
The above indicate that this method is effective for assessment of masticatory function in elderly patients.

View full abstract

This study was on jaw tapping movements made when periodical acoustic signals at various frequencies (0.3-2.8Hz) were applied. The subjects were 10 healthy dentulous young adults with a mean age of 23.9 years. They were told to make jaw tapping movement in time to the signals. Observation was made on the relationship of MKG and acoustic signal. The results were as follows:
1. In control processes, jaw tapping movements with 0.3Hz command signal were different from those with faster periodical signals. The results indicated that the former depended greatly on “an instant performance control”.
2. Signal frequencies had little effect on “the maximum jaw closing velocity” and “the time relation between appearance of the maximum jaw closing velocity and tooth contact with time”.
3. It was concluded that jaw tapping movements with signals of lower frequencies (about 0.3Hz) were more suitable, if early motor control and recognition is observed without taking prediction into consideration.

View full abstract

This study was conducted to investigate the effect of weight change of upper complete denture on masticatory function in case of five maxillary edentulous patients who had adequate retention and stability. Duplicates of dentures were used as experimental dentures. In the denture, the groove was made buccally from right second molar to left second molar for the weight. Denture weight was changed to 20g of Pt-Au alloy and the area was covered with wax (H denture), or the weight removed and the whole area was covered with wax (L denture). Masticatory movements of Gumi chewing, denture vibration of tapping, patients estimate were recorded. These were recorded whether or not the subject recognized the denture weight.
The results were as follows:
1. When the subject did not recognize the denture weight, there was no significantly difference of masticatory movement and no distinction of comfortableness.
2. When the subject recognized the denture weight, there were increased variations among subjects as to the coefficient variation and average variation of masticatory movements. Furthermore, only one patient complained about the H denture.
3. There were no significant differences in duration of denture vibration.
The above results indicated that the weight of upper complete denture does not affect masticatory movements, denture vibrations and patient estimate, if suitable retention and stability of the denture are maintained.

View full abstract

One hundred thirty-four dentures with reinforced polycarbonate resin (PC), utilizing a compression molding method called the Sumipuroi Denture System, were inserted into 82 partially or completely edentulous patients at the clinic of Kyushyu Dental College. Continuous clinical observation of the dentures was conducted from approximately four months to two yesrs after insertion.
The results were as follows:
1. No fractures or stress cracks were found in the denture bases except for one denture base which had been repaired with auto-polymerized acrylic resin at the first insertion.
2. Artificial tooth loss was seen in 6 cases, which were all plastic anterior teeth with high wear resistance. Stain penetration into the interfaces between the plastic teeth and the PC denture base was also seen in some cases.
3. Not a single tooth fell from the denture bases because the PC denture base had excellent adhesion to conventional acrylic resin teeth even without the creation of mechanical retentive shapes and/or the use of any chemical bonding agents on the teeth.
4. No troubles due to shrinkage of denture base and dimensional change of artificial teeth caused by the molding of the PC denture was found during clinical observation.

View full abstract

This study was conducted to investigate the influence of the vertical cuspal interference with the madibular first molar on the appearance of occlusal force during maximum clenching and mandibule tapping.
Occlusal force was measured using a three-dimensional transducer placed on unilateral first molars of mandible. Cuspal interference was applied using stainless foils (10, 30, 50, 70, 100, 200, 500, 1, 000 and 2, 000 m in thickness) to the flat occlusal table. The results were as follows:
1. At the height of cuspal interferences of 10-100μm, the impulse of occlusal force increased by the centralization of force with the increase in height during clenching (10μm: 1.2 times compared to control, 100 m: 5.9 times).
2. At the height of 10-100μm, the impulse of occlusal force increased by the centralization of force with the increase in height, although EMG activity (AOTC, DOTC, APTC·MV) was not changed (10μm: 1.7 times, 100μm: 5.3 times).
3. At the height of 100-200μm, the mandibule became unstable, with marked changes in the impulse of occlusal force, EMG activity and mandibular position. In two of the three subjects, the increase of the occlusal force was inhibited and in the other increased.
4. These findings indicate that cuspal interference is a very serious acute problem for concerned teeth.

View full abstract