Dentistry in Japan最新文献

The purpose of this study was to investigate and compare the accuracy of complete dental arch impressions and stone casts made with two kinds of impression materials (addition-type silicone and polysulfide rubber) and trays (custom tray and modified custom tray). In addition, the effect of the quantity of stone was examined. Impressions were made from a metallic model of a simplified maxillary dentition. Impressions and stone casts were measured respectively with a three-dimensional measuring microscope. The results were as follows: 1. Distortions of impressions were so small that the reproducibilities of impressions were superior three-dimensionally. These kinds of impressions and trays did not influence the accuracy of impressions. 2. The setting expansion of the stone in the impression occurred in the outward direction and was affected by the kinds of impressions and trays. 3. The arch widths and lengths of the stone casts tended to increase in number. 4. Stone casts made with addition-type silicone impression material and a custom tray were the most accurate because the combination of the impression material and tray effectively suppressed the setting expansion of stone. 5. The accuracy of stone casts could be improved by controlling the quantity of stone.

In a series of studies to investigate the structural features of biological crystals, using transmission electron microscope, the observations have been made on the shape and arrangement of the cross-sectioned crystal obtained from cross sections through the body of adult human enamel rod, in the surface layer, and in the middle and deep layers. The shapes of the cross sectioned crystals in the surface layer of the enamel are generally different from those in the middle and deep layers. In the surface layer of the enamel, the cross sectioned crystals show a considerable variation in shape and size, and have an irregular shape. The crystals are densely packed. Each crystal is adjacent to the neighboring one, and usually, the arrangement of crystals have an appearance rather like a "stone wall". In contrast, the cross sectioned enamel crystals in the middle and deep layer, are somewhat small than those in the surface layer, and have greater gaps between the crystals. In the middle and deep layers of the enamel, it is rare for the shapes of the crystals to be irregular, therefore, they retain their original shape, most of which are long and hexagonal.

When the ground section of a human tooth is observed through a microscope, the oblique section, or the cross section, the enamel rod is dark and the vertical section it is light. These striae have been called the bands of Schreger. In his book published in 1961, Professor Fujita quoted a paper presented by Preiswerk (1894) as follows: "Schreger found the striae in 1800 (Rosenmüller's und Isenflamm's Beiträge für die Zergliederungskunst, Bd. I, H. 1, Leipzig), but John Hunter from England reported the same findings earlier. For this reason, such striae were called the bands of Hunter-Schreger in Europe and America. In his paper of 1894, Preiswerk reported that Hunter found the striae in 1780; however, in the second edition of his book, The Natural History of the Human Teeth, published in 1778, Hunter showed an illustration that seemed to be the striae and annotated the illustration. The striae may have been reported even in his first edition (1771), but neither edition of the book is available in Japan." Quoting the first edition of Hunter's book, Hoffmann-Axthelm included the illustration of the striae in his book. Through this book, I found that Professor Fujita's conjecture was correct. Moreover, I recently had an opportunity to read the first and the second editions of John Hunter's book. Accordingly, I am reporting this report.

The effects of the masticatory function on age changes of the temporomandibular joint were studied in 163 C3H/He strain male mice, separated into solid and liquid diet groups from 2 weeks of age. The sizes and shapes of the mandibular condyles and glenoid fossae of the two groups were compared up to 60 weeks. The sizes and shapes of the condyles in the solid diet group increased and developed with age, but there was almost no change after 3 weeks of age in the liquid diet group. The sizes and shapes of the fossae increased and developed with age until 20 weeks in both groups, and there was no differences between the two groups. The poor functional stimulus of mastication has distinct effects on the underdevelopment of the condyle. Since the effects on the fossae were less than those on the condyles, not only the amount of mandibular movement, but also its pattern may have affected the liquid diet group.

Studies on the secretory response of rat submandibular tissues to isoproterenol (IPR) and the neurotransmitter receptors show that beta-adrenoceptors are altered with specific changes in mucin secretion by brief treatment of the tissues with IPR. Mucin secretion is stimulated by IPR in a dose dependent manner. Pretreatment with 10 microM of IPR for 10, 15, or 30 min reduces mucin secretion during further incubation with the same amount of IPR and increases the EC50 values of mucin secretion for IPR. A binding experiment of [3H] dihydroalprenolol (DHA) shows that this pretreatment also reduces the Bmax of beta-adrenoceptors from 162 +/- 2 to 140 +/- 1 fmol/mg protein and increases the IC50 values of IPR from 195 +/- 17 to 685 +/- 73 nM. The alteration in beta-adrenoceptors by brief treatment of IPR is paralleled by a change in the cyclic AMP content in the tissues from 143.2 +/- 3.2 to 102.3 +/- 4.6 pmol/mg protein.

Excellent adhesion of adhesives to metals can be realized by simply applying liquid Ga-Sn alloy (Adlloy) on the adherend metal surface. This method is only effective on dental precious metal alloys. Five metals, Au, Pt, Pd, Ag, and Cu, included in dental precious metal alloys were converted by this method to determine the most effective pure metal from bonding strength measurements, water durability at the adhesion interface, and ESCA measurements. All metals converted by Adlloy showed excellent bonding strength and water durability, whereas nonconverted metals showed poor water durability. ESCA measurements showed that metal surfaces converted by Adlloy are covered with a 3-6 nm thick Ga and Sn oxide film and that the diffusibilities of Ga in the metals are in the order Ag greater than Au greater than Pt greater than Cu greater than Pd. From the viewpoint of handling, Ag is the most effective metal.