The articulators presently used in dentistry are the results of observations, experiences and researches on human mandibular motion. It would therefore be advantageous to analyze kinematically the motion and the mechanism of existing articulators, for the following reasons:
1. Articulators themselves would contain some truth of mandibular motion.
2. Articulators have the advantage, that they are mechanically clear, easily accessible, adjustable and reproducible.
3. As articulators have the accepted objective in clinical use, the kinematic analysis and the verification of motion of the articulators are important as well as that of the motion of the mandible.
A theorem in kinematics was introduced for the basis of derivation of fundamental expressions of the motion of articulators. It includes Euler's theorem which says that; an arbitrary three dimentional displacement of a rigid body can be. expressed by translation of an arbitrary fixed point on the moving rigid body and a rotation around that point.
The arbitrarily fixed point on the moving rigid body described in the above theorem can be the middle point of the inter-condylar axis in the case of protrusive movement and the opening and closing motion of the mandible, or the kinematic center of the condyle on the working side in the case of the lateral movement of the mandible.
Based upon the theorem, the fundamental expressions for the motion of articulators was derived in a.simple and clear form. In the process of arriving at the result, an approximation had been applied in view of the minute amount of mandibular rotational movement within tooth contact conditions. The approximation became valid, by investigating the secondary degree of minutae.
In addition, a comparison of the accuracies was made between Arcon and Condylar types of articulators. It is pointed out that the problem of handling articulators, for example in the idling movements during lateral movements of Condylar type articulators, is more important than the difference of type in view of accuracy.

View full abstract

Four techniques of manipulation for centric relation, including chin-point technique, three-fingers technique, bilateral technique, and MCL technique, were evaluated.
It was found that three methods of manipulation including three-fingers, bilateral, and MCL techniques were equally effective to obtain the upper-most position of the condyles in centric relation. In addition, these techniques seemed to result in consistant positioning of the condyles. Although latter two techniques need some assisting for other manipulations, a choice among those three techniques might well be up to individual preference.
On the other hand, centric relation obtained by chin-point tecnique was different from that obtained by three techniques mentioned. The condyles would tend to be located in the rearmost position for vast amount of the cases examined. However, in several percent of the cases, it tended to coincide with the upper-most position. When employing this technique, great care has to be made so that no locking of the condyles in the inferior position occurs.
Habitual condylar position was always anterior to those of centric relation.

View full abstract

Dimensional accuracy of multiple pour full-arch stone casts made from non-aqueous elastomeric impression materials, namely Permlastic and President, was studied. A maxillary metal cast, carrying eight reference marks, was employed as the master model. Ten impressions were made of the master model with each impression material under the same conditions. Three consecutively poured full-arch stone casts were fabricated from each impression at pouring times of 5', 40', and 75'. Ten point-to-point distances were determined for each of 60 stone casts; the data obtained from those measurements were compared statistically.
The first pour stone casts from the President impressions were the most accurate. The second and third pour stone casts were only slightly less accurate, a statistically significant difference among pours existing for some of the measured distances but not others. The Permlastic derived stone casts were not as accurate as those from President and showed significant differences in dimensions as the pours progressed. The difference in behavior between the two impression materials studied can be explained, in part, by the greater polymerization and thermal contraction and permanent deformation following strain of the polysulfide.
Although superior dimensional accuracy and stability of the President impression would favor its expanded use rather than the expanded use of Permlastic in the fabrication of fixed restorations, this study did not confirm the definite benefit of the introduction of President impression material for the multiple pour technique.

View full abstract

Patients of over middle age usually have in their mouths variety of diseases such as caries, periodontitis, abrations and etc. Moreover, they usually have inlays, bridges, dentures and other accumulated traits of treatments they have had in the past. In the worst case, they have such oral conditions as that tooth extraction is the only curative means left behind.
When we.reconstruct these mouths based on the concept of Gnathology, we are needed to treat all portions of the mouth. To cope with this kind of situation, we have two curative means. One is that plural specialists undertake their parts, and another is that one operator gives whole treatment comprehensively. Latter is called comprehensive treatment. In this case, the operator is required comprehensive knowledge and technique of high level, and as a result, his burden becomes very heavy.
For patients, however, it will be most comfortable if highleveled inclusive treatment is kindly carried out all along by a single operator. Oral rehabilitation demands to the operators comprehensive and integrated knowledge, but they need such a long time to be thoroughly acquainted with every field.
This time, I presented the case periodontally, endodontically and prosthetically treated by a single operator.

View full abstract

In prosthodontics, we have little chance of finding good ideal occlusions (non-axiversion, non-transversion and non-tornsversion) . We often find malpositions of teeth, abnormalities of arch forms and abnormalities of arch relationships. In this case, we should correct malocclusion by surgical or orthodontic treatment before prosthodontic treatment. If we'll correct malpositions of teeth and abnormalities of arch forms, we'll be able to establish more elastic, more functional and periodontal ideal occlusion.
So, we should have synthetic informations (surgery, orthodontics, endodontics, periodontics and prosthodontics) to occlusal diagnosis.
Now, I present a case of occlusal reconstruction, applying surgical treatment, minor tooth movement and surgical implantation of Bioceram type 5 SIS.

View full abstract