Immunodetection of osteopontin at sites of resorption in the pulp of rat molars

Evaluation of dentinogenesis inducer biomaterials: an in vivo study

When exposure of the pulp to external environment occurs, reparative dentinogenesis can be induced by direct pulp capping to maintain pulp tissue vitality and function. These clinical situations require the use of materials that induce dentin repair and, subsequently, formation of a mineralized tissue. Objective: This work aims to assess the effect of tricalcium silicate cements and mineral trioxide aggregate cements, including repairing dentin formation and inflammatory reactions over time after pulp exposure in Wistar rats. Methodology: These two biomaterials were compared with positive control groups (open cavity with pulp tissue exposure) and negative control groups (no intervention). The evaluations were performed in three stages; three, seven and twenty-one days, and consisted of an imaging (nuclear medicine) and histological evaluation (H&E staining, immunohistochemistry and Alizarin Red S). Results: The therapeutic effect of these biomaterials was confirmed. Nuclear medicine evaluation demonstrated that the uptake of ^99mTc-Hydroxymethylene diphosphonate (HMDP) showed no significant differences between the different experimental groups and the control, revealing the non-occurrence of differences in the phosphocalcium metabolism. The histological study demonstrated that in mineral trioxide aggregate therapies, the presence of moderate inflammatory infiltration was found after three days, decreasing during follow-ups. The formation of mineralized tissue was only verified at 21 days of follow-up. The tricalcium silicate therapies demonstrated the presence of a slight inflammatory infiltration on the third day, increasing throughout the follow-up. The formation of mineralized tissue was observed in the seventh follow-up day, increasing over time. Conclusions: The mineral trioxide aggregate (WhiteProRoot^®MTA) and tricalcium silicate (Biodentine™) present slight and reversible inflammatory signs in the pulp tissue, with the formation of mineralized tissue. However, the exacerbated induction of mineralized tissue formation with the tricalcium silicate biomaterial may lead to the formation of pulp calcifications

Osteoclasts secrete osteopontin into resorption lacunae during bone resorption

Osteopontin (OPN) is a non-collagenous extracellular sialylated glycoprotein located in bone. It is believed to be one of the key components in osteoclast attachment to bone during resorption. In this study, we characterized OPN and other glycoproteins found in the resorption lacunae to confirm the role of osteoclasts in OPN secretion using electron microscopy and mass spectrometry. Additionally, we examined the glycan epitopes of resorption pits and the effects of different glycan epitopes on the differentiation and function of osteoclasts. Osteoarthritic femoral heads were examined by immunohistochemistry to reveal the presence of OPN in areas of increased bone metabolism in vivo. Our results demonstrate that human osteoclasts secrete OPN into resorption lacunae on native human bone and on carbonated hydroxyapatite devoid of natural OPN. OPN is associated with an elevated bone turnover in osteoarthritic bone under experimental conditions. Our data further confirm that osteoclasts secrete OPN into the resorption pit where it may function as a chemokine for subsequent bone formation. We show that α2,3- and α2,6-linked sialic acids have a role in the process of osteoclast differentiation. OPN is one of the proteins that has both of the above sialic residues, hence we propose that de-sialylation can effect osteoclast differentiation in bone.

The static magnetic field accelerates the osteogenic differentiation and mineralization of dental pulp cells

Dental pulp cells (DPCs) can differentiate into osteoblasts and are deemed a promising cell source for bone regeneration. Static magnetic field (SMF) stimulates osteoblast differentiation but the effect in DPCs remains unknown. The aim of this study was to investigate the effect of SMF exposure on the osteogenic differentiation and mineralization of rat DPCs in vitro. Cells were continuously exposed to SMF at 290 mT in the presence/absence of osteogenic induction [dexamethasone (Dex)/beta-glycerophosphate (beta-GP)]. Results showed that SMF alone did not impair the cell cycle and proliferation. On the other hand, obvious condensation in the metachromatic staining of the extracellular matrix with toluidine blue was observed for SMF-exposed cells as well as the Dex/beta-GP treated cells. SMF in combination with Dex/beta-GP significantly increased the mRNA expression of osteogenic genes, as well as the ALP activity and extracellular calcium concentration at the early stage, followed by obvious calcium deposits later. Besides, SMF exposure increased the activity of extracellular signal-regulated kinase 1/2 (ERK1/2) at 3 h and accelerated the mRNA expression of osteogenic transcription factor, Cbfa1, advancing its activation time from 168 to 72 h under osteogenic induction. In summary, SMF exposure in combination of Dex/beta-GP induction could significantly accelerate the osteogenic differentiation and mineralization of DPCs.

Cellular and extracellular factors in early root resorption repair in the rat

The aim of this study was to investigate the role of extracellular matrix components, such as collagen type I, fibronectin, and osteopontin (OPN) during cementum repair following experimentally induced tooth movement, and to characterize the cells taking part in the regenerative process. The upper right first molars were moved mesially in 21 three-month-old male Wistar rats using a coil spring with a force of 0.5 N. After 9 days, the appliance was removed and the animals were killed in groups of three immediately after withdrawal of the force and 5, 7, 10, 12, 14, and 17 days later. Three rats served as non-experimental control animals. The maxillae were prepared and processed for histological analysis. Together with the disappearance of the multinucleated odontoclasts from the resorption lacunae, signs of repair were visible 5 days after the release of the orthodontic force. The first signs of cementum repair were seen on day 10. The newly produced cementum was of the acellular extrinsic fibre type (AEFC) and reattachment was achieved with the principal periodontal ligament (PDL) fibres orientated almost perpendicular to the root surface. The initial interface formed between the old and new cementum, as well as the new AEFC, was characterized by a strong immunoreaction with OPN and collagen I antibody, but only a weak immunoreaction with the fibronectin antibody. Only a small number of mononuclear cells, which were involved in the repair process, showed a positive immunoreaction with the osteoblastic lineage markers runt-related transcription factor 2 and osteocalcin. These same cells stained sparsely with muscle segment homeobox homologue 2, but not with the E11 antibody. Thus, most of the cells associated with this reparative activity on the surface of the lacunae were differentiated PDL cells of the fibroblastic phenotype. Cells with a defined osteoblastic phenotype seemed to be of minor importance in this repair process.

Root Resorption on Torqued Human Premolars Shown by Tartrate-Resistant Acid Phosphatase Histochemistry and Transmission Electron Microscopy

Objective: To identify clastic cells on the root surfaces of torqued human premolars.

Materials and Methods: A continuous force of 600 cNmm was applied to upper first premolars in patients 13–16 years of age by using a precise biomechanical model with superelastic wires (NiTi-SE). The 28 teeth in 14 patients were divided into five groups (control [nonmoved], and moved for either 1, 2, 3, or 4 weeks) and processed for tartrate-resistant acid phosphatase (TRAP) histochemistry and transmission electron microscopy.

Results: Mononuclear TRAP-positive cells appeared at 2 weeks, wheras large multinucleated TRAP-positive cells were numerous at 3 and 4 weeks. Ultrastructural examination revealed many clastic cells in contact with resorption lacunae. In addition, some cementoblast-like cells appeared secreting new cementum over previously resorbed lacunae.

Conclusions: In general, resorption lacunae and the number of clastic cells, which increased with the duration of the applied force, were found on the cementum surface at the pressure areas. Some signs of cementum repair were also noticed, even with the maintenance of the level of the force.

Histochemical and immunocytochemical study of hard tissue formation in dental pulp during the healing process in rat molars after tooth replantation

Dental pulp is assumed to possess the capacity to elaborate both bone and dentin matrix under the pathological conditions following tooth injury. This study was undertaken to clarify the mechanism inducing bone formation in the dental pulp by investigating the pulpal healing process, after tooth replantation, by micro-computed tomography (mu-CT), immunocytochemistry for heat-shock protein (HSP)-25 and cathepsin K (CK), and histochemistry for both alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP). Under deep anesthesia, the upper right first molar of 4-week-old Wistar rats was extracted and immediately repositioned in the original socket. In control teeth at this age, the periphery of the coronal dental pulp showed intense ALP-positive and HSP-25-positive reactions, whereas there were no TRAP-positive or CK-positive cells. Tooth replantation weakened or terminated ALP-positive and HSP-25-positive reactions in the pulp tissue at the initial stages. At 3-7 days after operation, the ALP-positive region recovered from the root apex to the coronal pulp followed by HSP-25-positive reactions in successful cases showing tertiary dentin formation. In other cases, TRAP-positive and CK-positive cells appeared in the pulp tissue of the replanted tooth at postoperative days 5-10 and remained associated with the bone tissue after 12-60 days. Immunoelectron microscopy clearly demonstrated that CK-positive osteoclast-lineage cells made contact with mesenchymal cells with prominent nucleoli and well-developed cell organelles. These data suggest that the appearance of TRAP-positive and CK-positive cells is involved in the induction of bone tissue formation in dental pulp.

Immunolocalization of receptor activator of nuclear factor-kappaB ligand (RANKL) and osteoprotegerin (OPG) in Meckel's cartilage compared with developing endochondral bones in mice

We examined the immunolocalization of receptor activator of nuclear factor-kappaB ligand (RANKL) and osteoprotegerin (OPG) in areas of resorption caused by osteoclasts/chondroclasts on embryonic days 14-16 (E14-16) in Meckel's cartilage, and compared the results with those in endochondral bones in mice. Intense RANKL and OPG immunoreactivity was detected in the chondrocytes in Meckel's cartilage. On E15, when the incisor teeth were closest to the middle portion of Meckel's cartilage, tartrate-resistant acid phosphatase (TRAP)-positive cells appeared on the lateral side of the cartilage. Furthermore, the dental follicle showed moderate immunoreactivity for RANKL and OPG, whereas osteoblasts derived from perichondral cells were immunonegative for RANKL and OPG in that area. On E16, cartilage resorption by TRAP-positive cells had progressed at the differential position, and intensely immunoreactive products of RANKL were overlapped on and found to exist next to TRAP-positive cells in the resorption area. In developing metatarsal tissue, OPG immunoreactivity was intense in periosteal osteoblasts, whereas RANKL was only faintly seen in some of the periosteal cells. In epiphyseal chondrocytes of the developing femur, RANKL immunoreactivity was moderate, and OPG scarcely detected. These results indicate a peculiarity of RANKL and OPG immunolocalization in resorption of Meckel's cartilage. Growth of the incisor teeth may be involved in the time- and position-specific resorption of Meckel's cartilage through local regulation of the RANKL/OPG system in dental follicular cells and periosteal osteoblasts, whereas RANKL and OPG in chondrocytes seem to contribute to resorption through regulation of the chondroclast function.

Osteopontin Distribution in the Canine Skeleton during Growth and Structural Maturation

The distribution of osteopontin (OPN) was studied immunohistochemically in cells and extracellular matrix in the humerus, scapula, and lumbar vertebrae of growing (age: 6 weeks, 12 weeks, 4.5 months) and adult dogs. OPN was expressed in hypertrophic chondrocytes of epiphyseal cartilage and in chondrocytes of the deep zone of mature articular cartilage, where extracellular matrix was also stained. OPN expression was strongest in 4.5-month-old puppies in cells of the osteoblastic lineage. It also varied with microlocation and was pronounced in areas prone to resorption due to modelling and remodelling activities. Osteoclasts were always strongly labelled with OPN. OPN deposition in extracellular bone matrix was detected particularly as a delineation of cartilage cores within secondary trabeculae and as a lining of the trabecular surfaces in resorption microlocations. The OPN distribution pattern is discussed here for each cell population with regard to its functional implications.

Cementum-like tissue deposition on the resorbed enamel surface of human deciduous teeth prior to shedding

Prior to the shedding of human deciduous teeth, odontoclastic resorption takes place at the pulpal surface of the coronal dentin, and this resorption occasionally extends coronally from the dentinoenamel junction into the enamel. After the end of resorption, however, the resorbed enamel surface is repaired by the deposition of a cementum-like tissue. Using this phenomenon as an observation model, in this study we examined the sequence of cellular and extracellular/matrix events involved in the enamel resorption repair by light and electron microscopy. As the odontoclast terminated its resorption activity, it detached from the resorbed enamel surface; thereafter, numerous mononuclear cells were observed along the resorbed enamel surface. Most of these mononuclear cells made close contact with the resorbed enamel surface, and coated pits or patches were observed on their plasma membrane facing this surface. Furthermore, they frequently contained thin needle- or plate-like enamel crystals in their cytoplasmic vacuoles as well as secondary lysozomes. Following the disappearance of these monononuclear cells, the resorbed enamel surface now displayed a thin coat of organic matrix. Ultrastructurally, this organic layer was composed of a reticular and/or granular organic matrix, but contained no collagen fibrils. Energy-dispersive X-ray microanalysis of this thin organic layer in undecalcified sections revealed small spectral peaks of Ca and P. Cementum-like tissue initially formed along this thin organic layer, increased in width, and appeared to undergo mineralization as time progressed. The results of our observations demonstrate that regardless of type of matrix of dental hard tissues, tooth repair may be coupled to tooth resorption, and suggest that mononuclear cells and an organic thin layer found on the previously resorbed enamel surface may play an important role in the repair process initiated after resorption of the enamel.