Osteoclasts are the main cells to resorb calcified tissues. However, it is still uncertain whether cells other than osteoclasts can resorb calcified tissues. In this study, we investigated histologically the process of primary bone marrow cavity formation of humeral bone primordia. To inhibit resorption by osteoclasts, pregnant mice were treated with a daily administration of aminobisphosphonate, 4-amino-1-hydroxybutylidene-1,1-bisphosphonate (AHBuBP: 10 µmol/kg) from 15 to 17 days gestation stage (E15-E17) before the formation of fetal humeral bone marrow cavities. Although the number of primary bone trabecula increased with AHBuBP treatment, both humeral bones of newborn mice with/without AHBuBP treatment developed bone marrow cavities where active hematopoiesis was observed. In the AHBuBP treated group, osteoclasts attached to the surface of trabecula showed no clear zone nor ruffled border. At E16, a primary bone marrow cavity was formed. Ultrastructural study indicated that calcified cartilage became fragmented to form particles that were phagocytosed by macrophages. Furthermore, the density of collagen fibers in calcified cartilage decreased with the process of calcification. These results indicate a new resorption process of calcified tissue, that is the degradation of calcified cartilage and the phagocytosis of calcified cartilage particles by macrophages; in addition, this study suggests that osteoclasts might not be related to the onset of hematopoiesis in the bone marrow cavity.
Many macrophages are recognized in dental pulp. However, their precise functional roles and the origin are not well understood.In this study, we analyzed the characterization and the localization of dental pulp macrophages during tooth development by immunohistochemistry and immunoelectron microscopy. The first mandibular molars at 1 week finished the tooth crown formation and the molars at 6 weeks finished the root formation. In the dental papilla of molars at 1 week, many CD68+ cells were detected. Some of CD68+ cells were invaded into the odontoblastic layer at the tip of cusp. A few MHC class II+cells were localized in the dental papilla. Most of CD68+ cells were CD68+/MHC class II- cells. At 6 weeks, many CD68+ cells in the crown dental pulp were invaded in odontoblastic layer, while no CD68+ cells were detected at the odontoblastic layer in the root pulp.At this stage, most of CD68+ cells were CD68+/MHC class II+cells. These findings indicated the different distribution of dental pulp macrophages in the crown and the root areas, which suggested that the factors for the localization of macrophages might be different in crown and root pulp. Phenotypic changes of macrophages from CD68+/MHC class II- to CD68+/MHC class II+ suggested the functional maturation of dental pulp macrophages within the tooth development.
Recently, glass fiber reinforced plastic (GFRP) posts for root canals have been available clinically. Although the mechanical properties of GFRP posts are important not only for their durability but also for the prevention of root fractures, it is difficult to evaluate the mechanical properties accurately using conventional 3-point bending tests because of the complex shape, small size and flexibility of the materials. Therefore, in this study, we evaluated the bending properties of three types of commercial GFRP posts using a sensitive cantilever test that is able to induce a reliable stress concentration. Typical load-deflection curves of the GFRP posts included a number of sharp decreases of load after the proportional limits and before fractures. We defined the peak load before the first decrease of load as a pop-in load and used it as an index of an important mechanical property. Deboning of the fibers from the matrix and crack initiation after the pop-in load appeared in the electron microscopic images of the GFRP post surfaces. Thus, it may be important to modify the composition and surface texture of posts to eliminate pop-in behavior and to enhance durability. We found that the maximum bending load tended to increase with an increase of post diameter; however, the bending strength decreased with an increase in diameter, most likely due to the small size of the posts. We believe the cantilever test allowed a more accurate assessment of the bending load, in particular the determination of the pop-in load, as compared with conventional methods of determining stress values. Since the elastic moduli of the GFRP posts were compatible with that of dentin, GFRP posts may prevent root fractures, which are typically caused by stress concentrations from a discrepancy of the elastic modulus of the post and dentin.
Objective: Octacalcium phosphate (OCP) is thought to be a precursor of the mineral crystals in biological apatite. Synthetic OCP has been shown to be converted into an apatite structure when implanted in murine calvarial bone, to enhance bone regeneration. This study was designed to investigate whether OCP implantation enhances the formation and resorption of new bone when implanted intramedullary in a mouse bone marrow. Design: Histological and ultrastructural analyses of bone formation and resorption after 2, 4 and 6 weeks implantation was investigated. MicroCT analysis was also applied to detect the amount of newly formed bone mass after implantation. Results: Massive bone formation on OCP was detected at 2 weeks. Then, the amount of bone was decreased gradually until 6weeks. At 4 and 6 weeks, many multinucleated giant cells, including tartrate-resistant acid phosphatase (TRAP)-positive cells, were detected on the newly formed bone and synthetic OCP. Ultrastructural study indicated that the multinucleated giant cells attached either to the bone and OCP surface were osteoclasts forming the clear zones and ruffled borders composed of finger-type and platetype cell processes. However, the ultrastructure of cell processes in ruffled borders showed the irregular shape. No representative cell processes were detected in the cells. Conclusion: These results confirmed the active induction of bone formation and resorption on OCP and also suggested that the structure of ruffled border might be regulated by the target calcified materials.
Although silica is the most popular refractory material, it is known that inhaled silica powder can induce lung or respiratory diseases, potentially leading to cancer. The purpose of this study was to develop experimental paste-type phosphate-bonded investments fabricated with colloidal silica solutions. Paste 1 was prepared by mixing cristobalite powder of 80 g with 30 cc monomagnesium phosphate solution. To investigate the effects of colloidal silica solution within paste 2, three volumes (A: 20 cc, B: 25 cc, C: 30 cc) were prepared with 15 g of MgO each. Basic properties and fit of the casting were compared to commercial phosphate-bonded investment and evaluated. The setting times for A, B and C were statistically different. The quickest setting time was measured from U. The fired strength of U was remarkably greater than those of others. The setting expansion of U was obviously greater than those of the experimental investments. The average value of A was statistically higher than that for B. C expanded minimally while setting. The expansion percentages at 850ºC were no significant differences among experimental investments. In addition, that of U during the entire heating was remarkably low. The degree of the fit differed significantly between U and A because setting expansion of A was insufficient. Although the results are not optimal, the newly developed paste-paste type phosphate-bonded investments produced in this study still offer potential as alternative investment systems due to their excellent fluidity, manipulation and reasonable basic properties.
The aim of the present study was to evaluate whether all-ceramic restorations fabricated by computer-aided design and manufacturing (CAD/CAM) are a panacea for the application to conventional prostheses and implant prostheses or if there exist challenges that must be overcome first. Fracture tests of CAD/CAM milled porcelain single crowns adhered to a master abutment model were performed to evaluate mechanical durability. The fits of CAD/CAM-milled and post-sintered zirconia angled frameworks for bridge restorations (APAPA, A: abutment, P: pontic) were evaluated by measuring the cement space at the margin of the sectioned surface of the framework and abutment. The bonding strengths of porcelain (a machinable glassy ceramic) and zirconia were evaluated by measuring the bending strength of porcelain adhering to zirconia specimens and porcelain fused to zirconia specimens. A CAD/CAM-fabricated porcelain single crown seemed promising, but adhering treatment was mandatory to guarantee its durability. The fits of CAD/CAM-fabricated and post-sintered zirconia frameworks were excellent and satisfied criteria for clinical acceptance of cement-retained superstructures of implants. However, fusing porcelain to a zirconia framework in the conventional manner has several disadvantages. Therefore, we propose a new hybrid all-ceramic restoration system of CAD/CAM porcelain veneering adhering to CAD/CAM zirconia frameworks. In conclusion, CAD/CAM all-ceramic restoration alone is not yet a panacea but already a very useful tool even for implant prostheses.