A comparison was made of the effect of different metal surface treatments on the fusion of metal to porcelain.
The following results were obtained.
1. For surface treatment of the metal, usually we followed the following procedures: casting, pickling (HF acid), degassing and then secondary pickling.
Instead of the secondary pickling step, we also tried a sand-blasting technique.
The latter resulted in a greater degree of fusion than the usual procedure.
2. No matter how the surface treatment was done by any method (Table 2), we learned that the degree of fusion was larger when sand blasting, rather than pickling, followed the degassing procedures.
3. The greatest degree of fusion occured with pickling and sand-blasting.
4. In the case where polishing followed sand-blasting (Table 2, # 3) only 1/2 the degree of metal to porcelain fusion was obtained in contrast the other methods.
5. From on data, fusion between porcelain and metal appears to be greatest when the degassing step is included. And this may be due to the formation of an oxidized film. From this information a stronger degree of fusion may be expected by a chemical-bonding system.
6. If a chemical that could remove the residual investment material quickly was used in combination with supersonic cleaning, then it is not necessary to use the HF acid (pickling step).
7. An optical microscopic examination of the porosity condition of the metal surface revealed that the degassing was not able to restrain bubble formation.
8. Two metals used in this experimental alloy were In and Sn. From the results of quantitative analysis, the ratio of these metals which exuded on to the metal alloy surface was 2: 1.

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Post core being used as an abutment tooth for pulpless tooth whose crown tooth substance is considerably damaged is indispensable. Its construction generally depends on indirect methods. There are two constructing techniques: to take wax pattern on an indirect working model using plaster in accordance with the normal method, and to invest wax pattern together with working model prepared by using die-investment (die-investing technique). The former has such demerits as to be difficult in wax pattern taking, the abutment tooth root canal being too narrow and long in shape to see directly, and wax pattern is liable to be deformed and damaged when it is taken out of the root canal. Contrarily the latter requiring no wax manipulation in the root canal, having the merit of improving the demerits of the former, is advantageous in the post core constructing technique.
But in the present die-investing technique, the dimensional accuracy of the cast products is much influenced by the dimensional change in process of constructing working models, as it shows properties quite contrary to those of the conventional cast investment; large in setting expansion and small in thermal expansion. Consequently it is necessary to make out the phases of the dimensional change of working models, in case the die-investing technique is applied to the construction of post cores.
We have hither to performed studies on models for outer cast products, using model investment, but no report has ever been published with regard to post cores, inner cast products, to be adapted in the root canal, and we consider it necessary to examine in order to construct post cores having preferable adaptability.
The author, to find out the post core construting technique, taking advantage of the merit of die-investing technique, choosing upper left incisal, canine and second premolar as experimental objects, examines the effects of the difference in the impression technique and the special liquid concentration on the adaptability of post cores prepared for the respective abutment teeth. The results are as follows:
1. Difference in impression materials
In the case of silicone impression technique, as compared with in the case of agar-alginate combined impression technique, post cores showing a tendency to be large in the upper-lower, bucco-lingual and mesio-distal directions, preferable adaptability can be expected.
2. Difference in special liquid concentration
Post cores show a tendency to be small in the upper-lower, bucco-lingual and mesio-distal directions in case the special liquid concentration is small.
3. Difference in abutment tooth positions Some difference in the adaptability of post cores in the bucco-lingual and mesio-distal directions can be seen in the cases of incisal and canine, but there is little difference of it in both directions in the case of second premolar.
4. Clinically, it is suggested that post cores having preferable adaptability can be obtained: by silicone impession technique with 50% special liquid used in the case of incisal abutment tooth; by agar-alginate combined impression technique with 100% special liquid used in the case of canine abutment tooth ; and by silicone impression technique with 100% and 50% special liquid and by agaralginate combined impression technique with 100% special liquid used in the case of second premolar abutment tooth.

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Many reports have been made by researchers in the past on the study of the mandibular movement, which is a matter of primary concern in prosthodontics. It has been made clear by these reports that the movements of mandibular condyle can be divided into two kinetic elements of translation and rotation. However, almost no report has been made so far concerning in what temporal process these two elements occur at the time of physiologic condyle movement, especially when phonation is made.
Therefore, the author particulary took up the phonation of the [a:] sound, which is least influenced by occlusion and the vertical and horizontal overlap of the anterior. The author then paid attention to the movement of mandibular condyle when the [a:] sound was pronounced. And in order to serve for the diagnosis of dysfunction of the stomatognathic system, the subjects used for the present experiment were limited to those who had no abnormality in their stomatognathic system. By photographic analysis using a multiple stroboscope apparatus, and considering the time element, the author recorded and analyzed the translation and rotation of mandibular condyle, and reached the following conclusion.
1) All the seven subjects tended to show very little difference in the amount of translation and the degree of rotation of their mandibular condyle, as well as in the time required until it came to the position ready to pronounce the [a:] sound.
2) The amount of translation of mandibular condyle from the position of maximal intercuspal occlusion to that when the [a:] sound was ready to be pronounced was between 2.31 mm and 6.15 mm ; the degree of rotation was between 5.03°and 7.73°; and the time required was between 0.115 and 0.174 seconds.
3) The amount of translation from the position of the maximal intercuspal occlusion to that when the mandibular movement stopped with the pronunciation of the [a:]sound was between 3.02 mm and 13.37 mm; the degree of rotation was between 6.42° and 12.81°; and the time required was between 0.194 and 0.326 seconds.
4) When compared before and after the [a:] sound was pronounced, the rotation of mandibular condyle tended to occur earlier than translation.
5) When comparison was made by dividing the entire movement of mandibular condyle into three periods, the speed of change, both in translation and rotation, tended to be quickest in the second period; as for rotation, the degree of rotation tended to be smaller in the third period compared to that in the first.
6) From the result of the present research, it is presu med that the mandibular condyle first moves, featuring rotation, to a comparatively fixed position, and later moves, featuring translation, to the position most appropriate for the pronunciation of the [a:] sound.

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In the clinical practices of the Crown and Bridge Prosthetics, the developments and improvements achieved in the instruments have made the adoption of the indirect method a day-to-day affair and have enabled the making of fixed restorations with adequate accuracy. It has now become possible to easily make a bridge for the portion where 1 or 2 teeth are missing with the one-piece cast technique and this technique is now beginning to be applied also to the making of a bridge for the portion where 3 or more teeth are missing. However, in the cases where there are restrictions due to the abutment tooth contour or where there are many units, the assembly operation is done, even today when the indirect method is already well established, with the soldering method which is employed in parallel with the checking of fitness accuracy. Also, as in the cases where different kinds of metals are joined together or where the prosthetic techniques are employed using attachments or telescope system, there are many instances in which the reliance on the soldering method is either absolutely necessary or its adoption is preferable.
This soldering method not only uses many kinds of materials and requires complex assembling process but also necessitates a high level of technique. Hence, there are many factors that affect the fitness accuracy of the bridge assembled with the soldering method. For this reason, many a study has been made on the soldering method itself but, so far, we can hardly say as yet that a systematic soldering method has been established.
So, the author has taken up, from among the various factors that affect the fitness accuracy of the soldering method, the following two factors, viz., (1) soldering investment and (2) preheating procedure, and, with the purpose of clarifying the effects that these two factors give to the fitness accuracy, measured the three dimen sional distortions of the retainers. Following are the conclusions obtained as a result of the measurements and examinatios done by the author:
1. With respect to the linear distortion and rotational distortion, the effects resulting from the differences in the types of soldering investments and the preheating procedures used were particularly large in terms of the volume of mesiodistal distortion (ΔX).
2. As to the effects given to the fitness accuracy by the soldering investment and the preheating procedure used, the largest effect was given by the soldering inve stment, which was followed in the intensity of effects by the interacation of soldering investment and preheating procedure, and then by the preheating procedure.
3. It was found that, among the various kinds of soldering investments used at the time of the soldering, the Deguvest L (manufactured by the Degussa, Inc.) with the highest thermal expansion ratio produced good fitness accuracy regardless of the type of the preheating proce dures used.
4. It was found that, regardless of the type of the soldering investments used, the preheating at the tem perature of 150°C was a most important factor in obtain ing good fitness accuracy.

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The purpose of this study was to measure the stiffness, defined as the compressive force to a certain displacement, of each pair of masseter muscle during the light, the moderate, and the maximum occluding at centric.
Eight males and ten females (aged from 19 to 29) volunteered as normal subjects.
The result was obtained that the higher the biting strength was, the more the muscle stiffness increased in each subject.

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Zirconia ceramic screw pins, 3 mm in diameter and 16 mm in length, were implanted in the lower first and second molar areas of two monkeys (Macaca fascicularis) two months after tooth extraction. Two months after the implantation, each monkey received a continuous crown with metal crowns set on implant pins the right second premolar and third molar, designated the functional implant side. Zirconia ceramic pins on the non-functional implant side were not covered with metal crowns. The tissue-zirconia ceramic pin interfaces of the functional implant side were histologically compared with those of the non-functional side. Zirconia ceramic pen-implant tissue (periimplantium) was distinguished from the normal tooth periodontium by newly formed tissue elements. At the implant contact epithelium interface, ultrastructural elements were similar to the junctional apparatus of enamel-junctional epithelium interface. This provided direct adhesion between the implant contact epithelium and the implant body. In the subepithelial fibrous tissue, mature and dense collagen fibers with a few inflammatory cells were arranged in parallel or irregular patterns on the implant surface area. Ultrastructurally, the fine granular matrix, collagen fibrils, and the cellular membrane of the fibroblastic process appeared in the interface zone of the subepithelial fibrous tissue. Fibrous capsulation almost never appeared at the interfaces of any functional or non-functional sides of the implant body. Ultrastructurally, the zirconia ceramic implant bodies directly contacted the implant supporting bone or were separated by an electron dense amorphus material layer. These results suggest that zirconia ceramic is a excellent material for endo-ossous dental implants.

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