When we design a prosthesis we must consider its dynamic movement, in particular, stress-distribution.
Recently, the strain gauge method, the photoelastic method, and the finite element method are applied to measure for prosthesis stress analysis.
By any way, on the assumption that dynamic property of test pieces, especially, Young's modulus and Poisson's ratio are necessary to be known in advance.
We will measure the principal stress-distribution of plate denture finally, we used foil strain gauge and digital strain measuring equipment to measure Young's modulus and Poisson's ratio primarily.
When we measured them, we made the 12 rectangular rectangular test pieces as materials which were the heat curing acrylic resin for denture plate “Acron”(G-C's dental industrial Co., Ltd.) and took compressive test by using Amsler testing machine.
And we measured displacement by foil strain gauge which type was KFR-02-Cl-16 (KYOWA electronic instruments Co., Ltd.).
We searched for maximam compressive unit stress, Young's modulus, and Poisson's ratio, about 12 kinds of test pieces which sizes were 3×3×3mm, 3×3×6 mm, 3×3×9mm, 4×4×4mm, 4×4×8mm, 4×4×12 mm, 5×5×5mm, 5×5×10mm, 5×5×15mm, 6×6×6 mm, 6×6×12mm, and 6×6×18mm.
The strain which was on the point of breaking was caliculated the recurrent expression by method of least squares, from the data.
We did fundamental close examination, we gained the evaluation from the piece which size of 5×5×10 mm, because of stability of data and efficiency of standard-sized test piece, as shown followings.
Maximum compressive unit stress
11.66 S. D.±0.19kg/mm²Young's modulus 190.1 S. D.±6.3kg/mm²Poisson's ratio 0.313 S. D.±0.032kg/mm²

View full abstract

As compared with general prosthodontic treatment, maxillary prosthetics is difficult to make a plan, treatment, and postoperative control, so that it has large defects and denture bearing area decreases, the changing quantity of defective bone is large is the course of time.
This time we experienced the 7 cases of disease (4 upper cases, 3 lower cases) including 5 cases by tumour, 1 case by trauma, and 1 case by cyst.
In case of maxilla, we treated on prosthodontics after radical operation, in case of mandible, we made it after radical operation, recover operations for example implantation for iliac bone dermatoplasty.
As shown under, we know that conclusions we cured defective parts of bomy structured by obturator in case of maxilla chiefly we use the system of bar clasp for remained teeth to make maintenance and stability.
In aim of support, we used flange technique to improve border molding, and used Levin's bladed metal teeth to relieve the mucous charge's quantity by force of bite and keep out of eccentric moments.
Meanwhile, it is difficult for mandible to recover by denture in case of having the missing bomy parts.
Therefore we made prothesis, after implantation of iliac bone, and dermatoplasy, improvement of discrepancy as well as we could in mandible.
The plan of plate in the case like this was carried out, not only in the view of anatomy, but also in the point of dynamics to disperse force of bite well and balance square of implantations with original own jaw's bone.
And in case which we experience so that we could use residual teeth, we use Dolder's bar attachment in order to be lower the point of force and splint of residual teeth for retainer of denture.
The prognosis of all cases were improved on physiologic functions and esthetics.
Especially the 7th cases, though it passed ten years after having denture, the mobility of abutment teeth resorption of transplantationed bone can not be observed and oral hygene condition is good and make various physiologic functions.

View full abstract

In the complete denture prosthodontics, it has been very noticed from old times that the basic occlusal form of artificial posterior teeth have been variously investigated. However, at present, there not always a basis on this point.
In our examinations, Hisamatsu and Kagiya make a comparative studies among the anatomical posterior teeth, the semianatomical posterior teeth and 0° degree posterior teeth. But, they investigate only the biting and masticatory forces on the complete dentures of the various occlusal forms of posterior teeth used, it is necessary for the establishment of the basic condition of occlusal form to be investigated still more. Then, the author analyses electromyographically the masticatory muscle activities on the complete dentures of anatomical and semianatomical posterior teeth arranged.
As the six male subjects in fifties are selected from the complete denture weared between five and ten years, the following conditions are fulfilled.
1. Dental past and present history: Jaw and masticatory movement are not disturbanced clinically.
2. Sagittal and horizontal relation of maxillary ridge to mandibular ridge: Parallel type.
3. Form of maxillary and mandibular ridge: Normal type/Normal type.
4. Compressibility of maxillary and mandibular mucosa: Standard type/Standard type.
5. Dimention of denture base: Medium type/Medium type.
The complete denture are fabricated and adjusted by Hisamatsu's method. The controls are used the Pilkington-Turner vacuum fired 30° posteriors (230M) for the anatomical posterior teeth are fabricated on the Dentatus articulator. Then, the subjects are arranged the Trubyte vacuum fired 20° posteriors (29M) for the semianatomical posterior teeth.
The masticatory and biting forces are measured and recorded by Fukamizu's device and procedure. Then, the muscle activities on the electromyographic analysis during the masticating various foods are studied the same means as Fujimoto.
As the result, the following conclusion are obtained.
1. As for the masticatory forces in various foods (peanut, ham & takuan), the anatomical posterior teeth are a smaller tendency than the semianatomical posterior teeth. But, the antagonistic forces in swallowing period are a counter result.
2. On the masticatory muscle activities in masticating various foods, the anatomical posterior teeth are a smaller tendency. However, in swallowing period, they are a larger tendency.

View full abstract

It has been considered that the occlusal aspects of artificial molar teeth, occlusal types, forms and sizes of denture bases are the significant factors, which have direct effects masticatory function of complete denture wearers. According to the serial studies at our department, it is defined that the difference of occlusal forms and occlusal of complete dentures have influence on the masticatory function of complete denture wearers, especially masticatory force and electromyography (EMG).
As regarding the effect of the difference in border forms and sizes of complete dentures on the masticatory function, it has been analyzed that using the bite force by Moriya and Okane, using the EMG by Nakano, using the masticatory performance ratio and EMG by Sasaki, using the masticatory performance ratio and the activity of masseter by Yanagida and using the masticatory performance ratio by Kapur and so on.
However, there are little studies about the effect of difference in border forms of molar ragion of mandibular complete denture on masticatory function. Then, the author make the following plane to examine about these problems. Two different complete dentures are fabricated. The form and size of the control complete dentures are defined by the functional impression, the subjects are trimed at bilateral buccal shelves, retromylohyoid spaces and retromolar pads. Using these complete dentures, the author examines the masticatory forces and EMG used the semicondoctor element.
The outline of the discussion about these studies as follows;
1. About the masticatory and antagonic force in various foods, such as peanuts, ham and takuan. The measured values of the control complete denture are the same level with the subject complete denture when the patient masticate peanuts, the control is higher when the patient masticate ham and the control is lower when the patient masticate takuan.
2. Concerning the masticatory rhythm and the swallowing pattern in various foods, the duration and a ratio of the duration during electric discharge period on masticatory force for the control complete denture are larger than that of the subject complete denture, and the interval and the cycle for the control are smaller than the subject. On the other hand, the duration, the cycle and a ratio of the duration during electlic discharge period on EMG for the control are smaller than the subject, and the interval for the control are smaller than the subject except ham.
3. The integrated masticatory forces in various foods for the control are larger than that of the subject.
4. The activities of masticatory muscles in masticating various foods for the control, are smaller than that of the subject.
5. The activities of masticatory muscles which are needed for the integrated masticatory force unit and the antagonistic force unit in masticating various foods for the control, are smaller than that of the subject.
6. The masticatory force and integrated masticatory force per unit area of complete denture base in masticating various foods the control, are smaller than that of the subject.

View full abstract

A number of studies on changes in the position of the remaining teeth after a tooth or teeth are lost have been reported. Most consist the gross observation of changes in the position of the remain ing human teeth several years after extraction with plaster models. This may be due to the difficulty concerning the study of changes in the position of the remaining teeth. With close attention to this point, the author devised a method and a device for measuring changes in the position of the remaining teeth. Results were previously reported.
A new study was made, Utilizing these methods and devices, the author examined 11 male students at Nihon University School of Dentistry on the day of and 1, 2 and 3 weeks after preparation in order to investigate with elapsed time the correlation between changes in the position and movement of the abutment and remaining teeth after the preparation of the 5 and 7, 6 was lost.
The Following conclusions were arrived at:
1. In all the subjected sutdents, no significant differences were observed in the distance between measurement point in 1-2 and 1-3 regions during the period of measurement.
2. During the period of measurement, significant differences in distance between measurement points in 1-4, 1-5 and 1-7 areas were observed. In the area of 1-7, all the subjected students demonstrated significant differences. In the area of 1-4, significant differences were observed in ten students except one. In the region of 1-5, significant differences were seen in nine students except two.
3. In comparing the amount of the change in the measurement point to point distant between measurement regions, the largest value existed in the area of 1-7.
The over-all amount of changes in the measurement point to point distant with elapsed time was the hi ghest in 1-4 area, followed by the 1-5 area and then the 1-7 area.
4. The amounts of changes in the measurement point to point distance from the day of to 3 weeks after preparation in all the subjected students were 10-210μ in the region of 1-4, 10-250μ in the region of 1-5 and 10-550μ in the portion of 1-7.
5. A study of the correlation between A, B and C, which were determined for each measurement area of all the subjected students, revealed a significant correlation only between A and C in the region of 1 (r=0.70).
6. In a study of the correlation between A′, B′ and C′, which were determined for each measurement area of all the subjected students, there was a greatly high correlation (r=0.97) between B′ and C′ in the regions of 1-4 and 1-5, and also high correla tions (r=0.66, r=0.69-0.73) between A′ and B′ and between A′ and C′. In the portion of 1-7, high correlations were observed between A′ and B′ and between B′ and C′.

View full abstract

A shape of denture base is uncertain, and has a curved surface. So, some methods were developed and applied for measuring its area. The method of measuring the denture wearing area have been applicating by some methods. In practice, the method of converting the spray film of vinyl chloride into its weight, the method of converting corroded adapted metal film into its illuminating quantity, and the method of measuring adapted film or paper by planimeter, were reported. The usefulness of them are under consideration, they have both merit and demerit. Among other methods, the method of using planimeter are said to use easy, and often applied. But we are anxious about correctness of measurement.
Now we think to improve these defects, so we have developed the method of measuring denture wearing area, which system is made up of micro-computer, X-Y plotter, and digitizer for planimeter. An outline of this system, the figure to measure is made input to the X-Y axis of cordinates as n-polygon, which is calculated by a method of calculation for the area of npolygon, and is made output to computer display and X-Y plotter.
After examinating these soft and hard wear, we have come to a conclusion that was reliable and useful method to measure area. And then, the method to apply micro-computer obtains an effective number of six figures, but the method to apply planimeter obtains an effective number of three figures. And after measured, there is a merit, which the calculated data are printed out by micro-computer. In the correctness of measurement, the method to use micro-computer is superior to using planimeter in 0.21%.
In the near future, we shall develop this program, and make the system to calculate section property, that is, geometrical moment of inertia and section of modulus.

View full abstract