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Objectives: Hexavalent chromium (CrVI)-exposure of suckling rats has been shown to delay tooth eruption. However, the effects of CrVI-exposure on bone formation at the base of the alveolus, which provides a motive force for tooth eruption in the early stages of the process, remain unknown. The present work sought to evaluate the effect of CrVI-exposure on bone formation at the base of the alveolus during the intraosseous stage of tooth eruption in suckling rats, using histomorphometric and immunohistochemical studies., Methods: Experimental animals received 12.5 mg/kg-bw/day of potassium dichromate dissolved in saline solution by gavage starting on day 4 of the experiment; controls similarly received an equivalent volume of saline. All the animals were euthanized at the age of 9 days. The base of the developing alveolus at the level of the mesial root of the first lower molar was analyzed histomorphometrically and immunohistochemically. Data were statistically analyzed using student's t-test, with statistical significance set at p < 0.05., Results: CrVI-exposed animals showed lower bone volume and height at the base of the alveolus, a significant preponderance of bone rest on the surface adjacent to the dental follicle, and a significantly lower percentage of positive Runt-related transcription factor-2 (RUNX2+) osteoblasts and a significantly higher number of mesenchymal-like RUNX2+ cells at the latter site., Conclusion: CrVI-exposure during lactation affects bone formation at the base of the developing alveolus, delaying tooth eruption. These findings underscore the importance of controlling drinking water levels of toxic substances since their effects can alter the growth and development of individuals exposed during early childhood., Competing Interests: Conflict of interest The authors declare no potential conflict of interest regarding the research, authorship and publication of this article., (Copyright © 2023 Japanese Association for Oral Biology. Published by Elsevier B.V. All rights reserved.)

The in vivo response of osteocytes to different force magnitudes soon after they are applied remains to be elucidated. The aim of this study was to examine the early effects of applying a very light (LF: 0,16 N) and a very strong (SF: 2,26 N) orthodontic force during one hour on apoptosis and osteopontin (OPN) expression on alveolar bone osteocytes, in rats. Results: LF: compared to the control group, they showed a significant increase in OPN expression, and a significant decrease in the number of TUNELpositive osteocytes. SF: compared to the control group, they showed a significant increase in OPN expression and a significant decrease in the number of TUNELpositive osteocytes. Our results show that osteocytes respond very early to the application of tension and pressure forces of different magnitudes, and application of forces decreases the number of apoptotic osteocytes and increases OPN expression. These results allow concluding that osteocytes activate rapidly when subjected to locally applied forces, whether these forces be pressure or tension, light or strong forces., (Sociedad Argentina de Investigación Odontológica.)

Lack of mechanical stimulation is known to cause disuse osteopenia in bones. However, experimental models for disuse osteopenia on bones other than jawbones are not applicable to jawbones. The little available information in this field has been applied to the study of overeruption of teeth lacking antagonists. However, the absence of an antagonist in the opposite jaw means that there is no stimulation by occlusion. Our hypothesis is that the lack of stimulation due to the absence of teeth causes disuse osteopenia in the interradicular bone of the antagonist teeth. Our aim was to develop a model of disuse osteopenia due to the absence of occlusal forces. We used male Wistar rats with 215-230 g body weight, divided into 2 groups: one absolute control group (C) and one experimental group in which the three right lower molars were extracted (E). The left side of the jaw in the experimental group was used as a paired control (PC). The animals were euthanized 7 days after extraction. The jaws were placed in occlusion, fastened and fixed in 10% formalin. The heads were cut in half and radiographs made of both jaws. The upper jaws were processed histologically. After decalcification, bucco-palatine oriented sections were cut at the level of the mesial root and distal roots of the first upper molars. On the radiographs, the distance from the tip of the cusp on the first upper molar to the antagonist edentulous ridge (DA) was measured. On the microphotographs, the following parameters were measured: passive eruption degree (PED), height of periodontal ligament at the level of the furcation (HPL) and interradicular bone volume (BVI). The data were compared statistically using ANOVA and Bonferroni's post-hoc test, considering p<0.05 as statistically significant. DA in experimental animals was 0.34}0.048 mm. PED in experimental animals was significantly greater than in the control groups, both for the buccal plate and for the palatal plate. HPL showed no significant difference between groups. BVI was significantly lower in the experimental group than in the control group. The results showed that the model used produces a condition of disuse osteopenia, shown by the statistically significant reduction in interradicular bone volume. The use of this model at different experimental times will enable the evaluation of cell responses in periodontal tissues, particularly bone tissue, e.g. to compare them to known responses such as the application of orthodontic forces.

The aim of the present work was to analyze the ultrastructure and mineral composition of the surface of the enamel on a molar with MIH, with and without acid etching. A permanent tooth without clinical MIH lesions (control) and a tooth with clinical diagnosis of mild and moderate MIH, with indication for extraction, were processed with and without acid etching (H3PO4 37%, 20") for observation with scanning electron microscope (SEM) ZEISS (Supra 40) and mineral composition analysis with an EDS detector (Oxford Instruments). The control enamel showed normal prismatic surface and etching pattern. The clinically healthy enamel on the tooth with MIH revealed partial loss of prismatic pattern. The mild lesion was porous with occasional cracks. The moderate lesion was more porous, with larger cracks and many scales. The mineral composition of the affected surfaces had lower Ca and P content and higher O and C. On the tooth with MIH, even on normal looking enamel, the demineralization does not correspond to an etching pattern, and exhibits exposure of crystals with rods with rounded ends and less demineralization in the inter-prismatic spaces. Acid etching increased the presence of cracks and deep pores in the adamantine structure of the enamel with lesion. In moderate lesions, the mineral composition had higher content of Ca, P and Cl. Enamel with MIH, even on clinically intact adamantine surfaces, shows severe alterations in the ultrastructure and changes in ionic composition, which affect the acid etching pattern and may interfere with adhesion.

The occurrence of very early morphological changes in the osteocyte lacuno-canalicular network following application of tensile and/or compressive forces remains unknown to date. Thus, the aim of this study was to perform a morphological and morphometric evaluation of the changes in the three-dimensional structure of the lacuno-canalicular network and the osteocyte network of alveolar bone that take place very early after applying tensile and compressive forces in vivo, conducting static histomorphometry on bright-field microscopy and confocal laser scanning microscopy images. Our results showed that both the tensile and compressive forces induced early changes in osteocytes and their lacunae, which manifested as an increase in lacunar volume and changes in lacunar shape and orientation. An increase in canalicular width and a decrease in the width and an increase in the length of cytoplasmic processes were also observed. The morphological changes in the lacuno-canalicular and osteocyte networks that occur in vivo very early after application of tensile and compressive forces would be an indication of an increase in permeability within the system. Thus, both compressive and tensile forces would cause fluid displacement very soon after being applied; the latter would in turn rapidly activate alveolar bone osteocytes, enhancing transmission of the signals to the entire osteocyte network and the effector cells located at the bone surface., (Copyright © 2013 S. Karger AG, Basel.)

The osteocyte lacuno-canalicular system (OLCS) is a large network intercommunicating the lacunae and canaliculi which contain the osteocytes and their cytoplasmic processes within the mineralized bone matrix. The vitality and functioning of the osteocytes and cytoplasmic processes depend upon this intercommunication. To date, the 3-dimensional features of OLCS in the alveolar bone have not been studied; therefore the aim of this study was to use confocal scanning microscopy to do so. Samples of alveolar bone from male Wistar rats were fixed in buffer formalin and stained with basic fuchsin to visualize the lacuno-canalicular system. In decalcified samples of the same bone, the actin was labeled using fluorescent phallotoxin to visualize the osteocyte network. The samples were observed at the level of the mesial root of the first upper molar in bucco-palatal direction using a confocal laser scanning microscope. The results showed that in the area near the inner aspect (bundle bone) of the buccal plate, the osteocyte lacunae are oval-shaped and relatively uniform in size, aligned parallel to each other and with their major axes parallel to the periodontal bone surface, and the osteocytes are oval-shaped, with their main axes perpendicular to the periodontal bone surface, and the cytoplasmic processes irradiate in all directions. In the area near the inner aspect (bundle bone) of the palatal plate, the osteocyte lacunae are rounded, have different sizes and their orientation does not follow any specific pattern, and the osteocyte bodies have major axes parallel to the periodontal surface, a larger number of cytoplasmic processes, and run in a straighter direction than in the buccal plate. These results will contribute to the understanding of the changes that may occur in OLCS microarchitecture as a result of a pathological process, surgical technique or force applied to the alveolar bone.

The aim of this study was to evaluate, for the first time, the histomorphometry of the cellular and lacunar features of the osteocytes of alveolar bone in acute streptozotocin-induced diabetic insulin-treated or untreated rats. Eighteen male Wistar rats weighing 200 to 260 g were assigned to one of the following groups: I) control group (C), II) diabetic group (DBT), and III) insulin treated diabetic group (DBT+INS). Experimental diabetes was induced by a single intraperitoneal injection of 60 mg/kg of body weight of streptozotocin. Insulin treatment began 24 h after the streptozotocin injection in animals of group DBT+INS in a dose of 4-6 IU of Humulin NPH insulin given as a single daily subcutaneous (s.c.) injection each morning between 07.00 and 10.00 h. The animals were euthanized on the 8th day. The upper maxillae were removed and fixed in buffered formalin, decalcified in EDTA, embedded in paraffin and stained with H-E for histologic and histomorphometric evaluation. Bone activity and lacunar density, osteocyte and empty lacunar densities, lacunar volume and lacunar shape were evaluated. Differences between variables were assessed by one-way ANOVA. Surface bone activity values revealed that bone resorption was significantly greater in the DBT group than in the C group (p < 0.05). Total lacunar density was significantly reduced in the DBT and DBT+INS groups as compared to control (p < 0.05). Concomitantly, a statistically significant reduction in osteocyte density and an increase, albeit not statistically significant, in empty lacunar density was observed in DBT and DBT+INS groups versus control. Lacunar volume did not exhibit statistically significant differences. The osteocyte lacunae in the DBT group lost their rounded shape and acquired intermediate shapes. This study reveals an early response of osteocytes to hyperglycemia, before systemic compensatory mechanisms are turned on. The effects are not always compensated by insulin treatment.

A 350 mg/kg body weight (b.w.) oral dose of uranyl nitrate (UN) caused 100% mortality in mice three days after administration, due to resulting kidney lesions. Mortality decreased 50% after an oral (o) or subcutaneous (sc) dose of bisodic etidronate (EHBP). Given that bone is also a target organ for uranium (U) in acute intoxication, the aim of this work was to study the effect of exposure to a lethal oral dose of UN on endochondral ossification, and the latter's response to EHBP treatment. One hundred male Balb/c mice weighing 25 g were assigned to one of ten groups. Group I served as control. Group II received a lethal 350 mg/kg b.w. oral dose of UN by gavage. Groups III, IV, VII, and VIII received an equal dose of UN immediately followed by a single 500 mg/kg oral dose of EHBP in groups III and VII and a single 50 mg/kg subcutaneous dose of EHBP in groups IV and VIII. Groups V and IX only received a single 500 mg/kg oral dose of EHBP, and groups VI and X received a single 50 mg/kg subcutaneous dose of EHBP. The animals in groups II, III, IV, V, and VI were sacrificed 48 h after the onset of the experiment, whereas those in groups VII, VIII, IX, and X were killed at 14 days. Histologic and histomorphometric studies were performed on the femurs to determine growth cartilage width, bone volume, and metaphyseal bone activity. Our results showed that all growth cartilage and metaphyseal bone histomorphometric parameters were significantly lower in animals exposed to UN at 48 h than in controls. EHPB administration was found to prevent this condition at 48 h reaching similar values to those of controls. Although histomorphometric values did not reach control values at 14 days, they were higher than those of animals exposed to UN at 48 h not treated with EHBP. It is noteworthy that these values also decreased in animals only receiving EHBP at 14 days. Our results show that EHBP effectively ameliorates the adverse effects of a lethal dose of UN on endochondral ossification.

Exposure to uranium is a risk for the workers involved in uranium mining, purification, and manufacture, principally by its ingestion or inhalation. It is also a risk for the population at large in case of intake of contaminated water or food. Uranium induces nephropathy that is characteristic of heavy metals, which can lead to death. The toxic effects of uranium can be prevented by a biphosphonate, ethane-1-hydroxy-1,1-bisphosphonate (bisodic etidronate), administered orally or subcutaneously. Employing bisodic etidronate, our laboratory obtained satisfactory results in terms of survival in adult mice, adult rats, and suckling rats. The aim of the present study was to evaluate the efficacy of bisodic etidronate for preventing renal dysfunction induced by a lethal dose of uranyl nitrate, employing serum levels of urea and creatinine as end-points. Two experiments were performed over different time periods, i.e., Experiment A: 48 h, Experiment B: 14 d. Each experiment was performed with 4 groups of 20 male Balb/c mice each, 25 g average body weight. Three of these groups received 350 mg kg(-1) of body weight of uranyl nitrate by gavage (forced oral administration). Two of the three exposed groups were treated with bisodic etidronate either by gavage in a dose of 500 mg kg(-1) body weight or with a subcutaneous injection of 50 mg kg(-1) body weight. The fourth group served as control. Survivors of the experimental groups were sacrificed at the end of the experiment by overdose of inhalation anesthetic (ether). The kidneys were routinely processed for histological analysis. Blood samples were taken by cardiac puncture to assess urea and creatinine serum levels. Urea and creatinine serum levels were markedly lower at 48 h in exposed animals treated with bisodic etidronate than in untreated exposed animals. On day 14 these values in exposed and treated animals did not differ significantly from control values. The renal function of animals treated with orally or subcutaneous bisodic etidronate that survived uranyl nitrate exposure was markedly improved compared to the controls of untreated exposed animals at 48 h. At 14 days, treatment with bisodic etidronate averted renal damage. At this time, the histologic study of kidneys showed images of tissue recovery. These results suggest that the use of EHBP may be of great value in reducing the renal damage.

Over the last decade, increasing attention has been focused on the role of the osteocyte in bone remodeling, in view of its demonstrated ability to respond to mechanical and electric stimuli applied to bone. A previous "in vivo" study performed at our laboratory demonstrated that the application of orthodontic forces results in osteocytic lacunae enlargement. To our knowledge there are no data on cell and lacunae response to an inflammatory stimulus in the literature. The aim of this work was to determine whether osteocyte response to an inflammatory stimulus is comparable to that observed under mechanical stress and whether the ensuing cellular changes involve changes in the shape of the osteocyte and/or its lacunae. Three groups of ten male Wistar rats each, 200 to 250 g body weight, were used. Group I served as control. A cotton thread cervical ligature was placed around the first upper molars of animals in Group II, and those in Group III were fitted with an orthodontic appliance designed to exert a force toward palatine. All the animals were killed 24 hours after applying the stimuli. The histomorphometric determinations were measured on the interradicular crest between the two distal roots of the first upper molars. Osteocyte and lacunar volumes were measured and lacunar shape was analyzed. Group II exhibited a dense inflammatory infiltrate and slight resorption of the crest. Group III showed slight resorption of the vestibular wall. The lacunar volume increased in both experimental groups as compared to controls. The cell volume to lacunar volume decreased. These results suggest that osteocytes respond to inflammatory as well as to mechanical stimuli of bone resorption, enlarging lacunae without changes in cell volume.