Kenzo Kawasaki

On the daily incremental lines in human dentine.

Abstract Assuming that the cross-striations on enamel rods represent daily increments, the various incremental lines in dentine between selected pairs of tetracycline markers were identified and correlated with Retzius lines in the enamel, in order to obtain comparative information on the rate of dentine formation. The incremental lines described by Andresen (1898) and von Ebner (1906) are the same and are separated by approx. 20 μm. However, a regular series of lines approx. 4 μm apart were also found and considered to be due to a 24-h rhythm in organic matrix formation. A separate 12-h rhythm influencing mineralization was deduced by comparing the number of calcospherite striae with the 4 μm rhythmic change in fibre orientation of the matrix.

Time-lapse observation of rat periodontal ligament during function and tooth movement, using microcomputed tomography

The aim of this study was to observe the time-lapse changes in the rat periodontal ligament (PDL) during function and tooth movement. Under Nembutal anaesthesia, time-lapse changes in the thickness of the PDL of the first molars were investigated in five 12-week-old adolescent rats with microcomputed tomography. Three-dimensional (3D) images were reconstructed from the data. Histological observation was also performed, using undecalcified frozen sections of the maxillary first molar area. The PDL appeared as a radiolucent furrow on the 3D images. A slight change in the thickness of the PDL was observed 1 hour after initiation of orthodontic force loading, which became significant after 6 hours, with the appearance of pressure-tension zones during the tooth movement. These changes were more significant 3 days after orthodontic loading. Histological observation of the lingual cervical PDL (pressure zone) in nine 12- to 13-week-old rats demonstrated that the periodontal space had become narrow and the cellular elements appeared to be densely packed in the narrowed PDL 6 hours after orthodontic loading. Degeneration of tissues appeared 3 days after loading. Observation of the buccal cervical PDL (tension zone) demonstrated that the PDL was extended 6 hours after orthodontic force loading, and the extension continued for up to 3 days. Alkaline phosphatase activity was distributed in the PDL, except for the degenerating tissues in the pressure zone 3 days after loading. The results suggest that the periodontal reaction was initiated within 6 hours after orthodontic force loading, which was related to the structural changes of the PDL. The changes probably induced an early response in individual cells of the PDL.

Effect of an increase in occlusal vertical dimension on the rate of cyclic actin-myosin interaction in guinea-pig masseter muscle

To study the effects of increased occlusal vertical dimension on these kinetics, the actin-filament sliding velocity on masseter myosins in an in vitro motility assay and the ATPase activity of masseter myosins from normal (control) and bite-opened (5.6 mm increase in the vertical dimension for 1 week) guinea-pigs were measured. In control myosin preparations, the average value (mean +/- SD, n = 5) for the actin-filament sliding velocity at 25 degrees C was 4.0 +/- 0.3 microns/sec. In bite-opened myosin preparations (n = 5), it was 3.4 +/- 0.3 microns/sec, a significant (p < 0.01) decrease. Myosin ATPase activity was also decreased significantly (p < 0.01) from 1.0 +/- 0.1 to 0.7 +/- 0.1 mumol Pi mg per min (mean +/- SD, n = 5) after the bite opening. These results strongly suggest that in guinea-pigs an increase in occlusal vertical dimension for 1 week decreases the turnover rate of actin-myosin interaction in the masseter through changes in the myosin isozyme. These changes may result in a slowing of the rate of detachment of myosin cross-bridges from actin filaments.

Anatomical variations in the tendon sheath of the first compartment

Using Hiranuma’s classification, we carefully examined anatomical variations in the first compartments of 246 human wrist joints from 124 cadavers. Morphological examinations were conducted to determine the number of accessory tendons and the existence of dissepiments for the extensor pollicis brevis (EPB) and abductor pollicis longus (APL) tendons. Anatomical variations of EPBs and APLs were grouped together by type, and appearance ratios were calculated based on Hiranuma’s classification. Of the 246 wrist joints, 156 were categorized as normal type (63.4%), 57 as complete dissepiment type (23.2%), 22 as incomplete dissepiment type (8.9%), and 11 as EPB-lacking type (4.5%). Accessory tendons were identified in both the EPB and the APL tendons of most cadavers, and the incidence of dissepiment in tendon sheaths was approximately 33%. Sixty-six of the 193 wrist joints (34.2%) showed equal numbers of right and left accessory tendons. However, the number of EPB accessory tendons was higher than in previous studies, and in all cases some kind of dissepiment was observed in the APL and EPB. The number of EPB and APL accessory tendons showed no clear differences by gender, age, or right and left specificity.

Histology and tetracycline labeling of a single section of alveolar bone of first molars in the rat

We observed the histology and tetracycline (TC) labeling in a single frontal section of alveolar bone of upper first molars of adolescent rats. A single injection of TC was administered intraperitonealy in adolescent rats. After three weeks, the upper jaws were immersed rapidly in liquid nitrogen and sectioned. Five micrometer unfixed, undecalcified frozen sections were cut and observed by light and fluorescence microscopy. Frontal sections of the upper first molar area revealed that the structural relationships among the roots, the periodontal ligament and the alveolar bone, and also between the cervical enamel and the attachment epithelium were well preserved. The TC labeling lines in the sections were very clear and distinguished new bone from old bone. The brightness of the lines differed among regions. An analysis of the brightness in the same section suggested a difference in the bone forming activity at the time of injection.

Magnetic resonance images and histology of the spheno-occipital synchondrosis in young monkeys (Macaca fuscata)

Magnetic resonance images and the histology of spheno-occipital synchondrosis were examined in young monkeys in order to compare the magnetic resonance images with their histologic observations. In serial magnetics resonance images of posterior cranial base, the spheno-occipital synchondrosis showed a low signal zone with unclear boundaries, running through the posterior cranial base perpendicularly to the clivus. The zone was always interposed between nonsignal zones. These observations were the same as those in young juvenile human beings. The histologic sections also revealed that the low signal zone was really the spheno-occipital synchondrosis, which consisted of hyaline cartilage and that the nonsignal zones were bone tissues. The chondroblasts in the spheno-occipital synchondrosis were arranged bipolarly. Intense alkaline phosphatase activity was located in the areas along the bone. Tetracycline labeling was also noticed in the bone formed in the endochondral ossification. These results suggest that magnetic resonance imaging enables us to observe the spheno-occipital synchondrosis in the posterior cranial base and also to elucidate its influences on the growth of maxilla and mandible in the future.

Soft X-ray microscope with zone plate at UVSOR

Abstract A soft X-ray microscope with zone plates was set up at UVSOR [synchrotron radiation facility (750MeV, 200mA) at Institute for Molecular Science, Okazaki, Japan]. A 50nm line & space pattern could be resolved at λ=3.2nm. With an environmental chamber (wet cell) using SiN windows, wet biological specimens, such as letus protoplasts, rabbit myofibrils, tubulin of COS cell and Deinococcus radiodurans strains, could be observed at λ=2.5nm. In the present microscope, the numerical aperture of the condenser was much smaller than that of the objective. To adjust both the numerical apertures, an ellipsoidal condenser mirror system was tested, and preliminary result (an image of Cu mesh, 12.7μm pitch) was obtained.

Imaging Soft X-Ray Microscopy with Zone Plates in Parallel Use of Optical Microscope for Wet Bio-Specimens in Air at UVSOR

Soft X-ray microscope, a specimen holder of which was placed in air, was constructed at UVSOR, synchrotron radiation facility at Institute for Molecular Science, Japan. This made possible to investigate a specimen without impairing the vacuum of the microscope and to prefocus a specimen with an optical microscope incorporated in the microscope. Dry and wet specimens could be observed at a wavelength of 0.94 nm.

Rat incisor dentin formed under low plasma calcium concentration: Relation of phosphophoryns to the affected dentin

Abstract: When parathyroidectomized (PTX) rats were maintained on a diet containing 0.3% calcium and lacking vitamin D, the forming incisor dentin consisted of two distinct layers that differed in their degree of mineralization. The two layers could be distinguished by hematoxylin staining and by contact microradiography. The layer near the dental pulp was the hypomineralized dentin, different from a predentin, containing a small amount of mineral detected by electron probe and chemical analyses. The mineralization of the outer dentin was almost normal. Biochemical characterization demonstrated that the two dentin layers differed in their phosphophoryn content. The outer dentin contained two phosphophoryns, which is the pattern found in normal dentin. In contrast, the hypomineralized dentin contained only the lower molecular weight and lower phosphorylated phosphophoryn, which may be involved in crystal nucleation. From the distribution of lead, which marked dentin formed at the time of injection, it could be inferred that the mineralized dentin begins as a hypomineralized layer that undergoes secondary mineralization. The secondary mineralization occurs by the active calcium transport of the odontoblasts via odontoblastic processes.

Noncollagenous Proteins of Sea Bream Dentine

The most interesting noncollagenous proteins for mineralization in mammalian dentine are at present thought to be the highly phosphorylated protein, phosphophoryns which may be involved in regulating the ordered deposition of apatite crystals[l]. Lussi et al [2] have shown that phosphophoryn induce mineralization in an ‘in vitro’ system using a phosphophoryn agarose complex. However, Takagi and Sasaki have reported that phosphophoryn is absent in the dentine of dentinogenesis imperfecta type II[3], thus the function of phosphophoryn is still at present obscure.