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Calcium hydroxide is mainly used for dental pulp capping and it is thought that it induces hard tissue formation far better than other materials. Experimentally verifying this fact, Nishikawa et al revealed that bone-like dentin corresponding to tertiary dentin is rapidly formed when calcium hydroxide is applied directly to the pulp. Utilizing the same experimental system, histochemical study of the newly formed hard tissue (reparative dentin) was carried out and the results thereof were reported. Thick and irregular reparative dentin was formed in the pulp cavity and partial narrowing of the root canal was observed in m-CT. Histopathologically, the irregular reparative dentin increased its thickness obliterating the root canal having a diff erent Azan staining of aniline blue compared to primary dentin. Numerous cellular inclusion bodies were also trapped inside the thick dentin. Furthermore, with Schmorl’s thionine picric acid staining,thick reparative dentin was noted around the pulp cavity and dentin. The dentin was densely stained with picric acid with diff erent staining ability from the surrounding dentin. In addition, it was clearly confi rmed that many cells were trapped in reparative dentin. The results of the experiment suggest that the characteristics of the newly formed reparative dentin is comparable to tertiary dentin.

We examined the subcutaneous tissue reactions in rats to bioabsorbable suture thread using histopathological methods. Using Wister rats, Vicryl®, a bioabsorbable suture thread, was embedded into the subcutaneous tissue and histopathological examination was carried out after 4 weeks. Cholesterin crystals were used for the control. Furthermore, immunohistochemistry for CD68 was done. Histopathological examination showed proliferation of granulation tissues inboth experimental and control groups. The majority of cells in the granulation tissues were macrophages and giant cells. Fibroblasts were also observed in the proliferating granulation tissues surrounding the embedded bioabsorbable suturethread. Immunohistochemistry revealed that macrophages and giant cells were positive to CD68. The results suggest that the embedded bioabsorbable suture thread is not only fabricated to undergo absorption but also for phagocytosis bymacrophages and foreign body giant cells.

In this study, cholesterin was implanted in the subcutaneous tissue in mice to induce the formation of cholesterol granuloma. Histological examination was carried out to determine the type and source of cells. The tissue surrounding the embedded cholesterin was examined histologically within the period of 6 months. Cell differentiation in cholesterol granulomas was investigated using ddY mice and GFP bone marrow transplanted mice. Cholesterin was embedded in mice subcutaneously and histopathological examination was carried out in a period of 6 months. Results showed that at 2 weeks, cholesterin was replaced partly by granulation tissues. The majority of cells in the granulation tissues were macrophages and foreign body giant cells and the center consists of small amount of fibroblasts, collagen fibers and capillaries. At 3 months, more granulation tissue was observed compared to 2 weeks. Similar cells were observed, however, there were more fibroblasts, collagen bundles and capillaries present compared to 2 weeks. At 6 months, the cholesterin was mostly substituted by fibrous tissues consisting mainly of fibroblasts and collagen fibers with some macrophages and foreign body giant cells. Specifically, the outer part of the tissue consists of fibroblasts, collagen bundles and capillaries and the inner portion is filled with collagen bundles. Immunohistochemistry revealed that macrophages and foreign body giant cells were positive to GFP and CD68 although the fibroblasts and capillaries in the outer portion of cholesterol granulomas were GFP negative. Some spindle shape fibroblasts were also GFP positive. Immunofluorescent double staining revealed that cells lining the blood vessels were both positive to GFP and CD31 indicating that those were endothelial cells and were actually derived from the transplanted bone marrow cells. The results suggest that macrophages, foreign body giant cells as well as fibroblasts and capillary endothelial cells are bone marrow derived mesenchymal cells.

The mechanism in the formation of periodontal polyp has been established in several histological studies but details on cell differentiation and/or proliferation have not been elucidated. In the present study, we established a convenient and possible experimental system using ddY mice. Briefly, pentobarbital sodium (Somnopentyl) was injected into the abdominal cavity of the mouse followed by access cavity preparation on maxillary first molar using low speed ½ round bur (Merufa Inc), exposing the pulp and then allowed to perforate the floor of the pulp chamber. Observation was done over time until 6 months using micro CT (m_CT) image photography. Results with transmission image using m_CT showed theexpansion in the width of the periodontal ligament in the furcation area. The lesion was excised as one mass and examined histopathologically. The granulation tissue was covered with stratified squamous epithelium. The present experimental technique has been confirmed to be effective in analyzing the formation of periodontal polyp induced by mechanical perforation.

Although studies on the formation of apical periodontitis have somehow been carried out but detailed cellular dynamics remain unclear. We recently established an experiment that could easily be performed using ddY mice. First, under general anesthesia using isoflurane inhalation, the coronal portion of the maxillary first molar was penetrated using a round bur and drill with water irrigation causing pulp exposure until the root apex. Micro computed tomography (R_mCT) was taken over time during observation. Four weeks later, R_mCT confirmed the presence of a radiolucent image at the apex of the tooth, which was then removed for histological examination. The results showed that granulation tissue with fibrosis had gradually formed at the periphery of the abscess. The present method confirmed the effectiveness of the experimental mode to exmine the formation of chronic inflammatory lesions at the root apex.

Perforation of floor of the dental pulp is often encountered during root canal treatment in routine clinical practice of dental caries. If perforation were large, granulation tissue would grow to form periodontal polyp. Granulation tissue consists of proliferating cells however their origin is not clear. It was shown that the cells in granulation tissue are mainly from migration of undifferentiated mesenchymal cells of the bone marrow. Hence, this study utilized GFP bone marrow transplantation mouse model. The floor of the pulp chamber in maxillary first molar was perforated using ½ dental round bur. Morphological assessment was carried out by micro CT and microscopy and GFP cell mechanism was further assessed by immunohistochemistry using double fluorescent staining with GFP-S100A4; GFP-Runx2 and GFP-CD31. Results of micro CT revealed alveolar bone resorption and widening of periodontal ligament. Histopathological examination showed proliferation of fibroblasts with some round cells and blood vessels in the granulation tissue. At 2 weeks, the outermost layer of the granulation tissue was lined by squamous cells with distinct intercellular bridges. At 4 weeks, the granulation tissue became larger than the perforation and the outermost layer was lined by relatively typical stratified squamous epithelium. Double immunofluorescent staining of GFP and Runx2 revealed that both proteins were expressed in spindle-shaped cells. Double immunofluorescent staining of GFP and CD31 revealed that both proteins were expressed in vascular endothelial cells in morphologically distinct vessels. The results suggest that fibroblasts, periodontal ligament fibroblasts and blood vessels in granulation tissue were derived from transplanted-bone marrow cells. Thus, essential growth of granulation tissue in periodontal polyp was caused by the migration of undifferentiated mesenchymal cells derived from bone marrow, which differentiated into fibroblasts and later on differentiated into other cells in response to injury.

PURPOSE A mouthguard can protect stomatognathic systems from traumatic damage. However, severe occlusal wear of teeth and loss of teeth have often been found in players clinically. These problems might originate in strong clenching during sports. Although it is thought that a mouthguard may be effective for these types of clenching, the relation between mouthguards and clenching has not been sufficiently examined. In this study, the effect of a mouthguard (Drufosoft 3mm, EVA) on tooth distortion caused by clenching was measured and examined at three different clenching strengths. METHODS As a test tooth, a lower first molar was selected. A strain gauge applied to the outer surface of the buccal cusp was used to measure the distortion. A muscle balance monitor (GC) was used to regulate clenching strengths (10, 50, and 100%). The maximum-effort clenching without a mouthguard was assumed to be the 100% clenching strength. Measurements were conducted with or without mouthguard. A maximum value during clenching was assumed to be date of distortion by using analytical software AcquKnowledge (BIOPAC System Inc.). Statistical analysis software SPSS (SPSS Japan Inc.) was used for the Mann-Whitney test. RESULTS 1. The tooth distortion by clenching, regardless of the presence of the mouthguard, increased as clenching power strengthened, from 10, 50 to 100%. 2. The tooth distortion, regardless of strength of clenching, was decreased by wearing the mouthguard in all subjects. At 50 and 100% clenching, it was decreased significantly by the mouthguard in all subjects. CONCLUSIONS Mouthguards decreaseed the tooth distortion caused by clenching. Therefore, a mouthguard may prevent not only traumatic injuries in contact sports but also damage to teeth and periodontal tissues and so on, which occur due to frequent strong clenching in many sports.