Mechanism Of Resorption Research Articles

Estrogen Receptor 1 (ESR1) and the Wnt/β-Catenin Pathway Mediate the Effect of the Coumarin Derivative Umbelliferon on Bone Mineralization.

Bone physiology is regulated by osteoblast and osteoclast activities, both involved in the bone remodeling process, through deposition and resorption mechanisms, respectively. The imbalance between these two phenomena contributes to the onset of bone diseases. Among these, osteoporosis is the most common metabolic bone disorder. The therapies currently used for its treatment include antiresorptive and anabolic agents associated with side effects. Therefore, alternative therapeutic approaches, including natural molecules such as coumarin and their derivatives, have recently shown positive results. Thus, our proposal was to investigate the effect of the coumarin derivative umbelliferon (UF) using an interesting model of human osteoblasts (hOBs) isolated from osteoporotic patients. UF significantly improved the activity of osteoporotic-patient-derived hOBs via estrogen receptor 1 (ESR1) and the downstream activation of β-catenin pathway. Additionally, hOBs were co-cultured in microgravity with human osteoclasts (hOCs) using a 3D system bioreactor, able to reproduce the bone remodeling unit in bone loss conditions in vitro. Notably, UF exerted its anabolic role by reducing the multinucleated cells. Overall, our study confirms the potential efficacy of UF in bone health, and identified, for the first time, a prospective alternative natural compound useful to prevent/treat bone loss diseases such as osteoporosis.

Tooth transplantation and replantation: Biological insights towards therapeutic improvements

Transplantation and replantation of teeth are effective therapeutic approaches for tooth repositioning and avulsion, respectively. Transplantation involves transplanting an extracted tooth from the original site into another site, regenerating tissue including the periodontal ligament (PDL) and alveolar bone, around the transplanted tooth. Replantation places the avulsed tooth back to its original site, regenerating functional periodontal tissue. In clinical settings, transplantation and replantation result in favorable outcomes with regenerated PDL tissue in many cases. However, they often result in poor outcomes with two major complications: tooth ankylosis and root resorption. In tooth ankylosis, the root surface and alveolar bone are fused, reducing the PDL tissue between them. The root is subjected to remodeling processes and is partially replaced by bone. In severe cases, the resorbed root is completely replaced by bone tissue, which is called as "replacement resorption." Resorption is sometimes accompanied by infection-mediated inflammation. The molecular mechanisms of ankylosis and root resorption remain unclear, although some signaling mechanisms have been proposed. In this mini-review, we summarized the biological basis of repair mechanisms of tissues in transplantation and replantation and the pathogenesis of their healing failure. We also discussed possible therapeutic interventions to improve treatment success rates.

Roles of osteoclasts in alveolar bone remodeling.

Osteoclasts are large multinucleated cells from hematopoietic origin and are responsible for bone resorption. A balance between osteoclastic bone resorption and osteoblastic bone formation is critical to maintain bone homeostasis. The alveolar bone, also called the alveolar process, is the part of the jawbone that holds the teeth and supports oral functions. It differs from other skeletal bones in several aspects: its embryonic cellular origin, the form of ossification, and the presence of teeth and periodontal tissues; hence, understanding the unique characteristic of the alveolar bone remodeling is important to maintain oral homeostasis. Excessive osteoclastic bone resorption is one of the prominent features of bone diseases in the jaw such as periodontitis. Therefore, inhibiting osteoclast formation and bone resorptive process has been the target of therapeutic intervention. Understanding the mechanisms of osteoclastic bone resorption is critical for the effective treatment of bone diseases in the jaw. In this review, we discuss basic principles of alveolar bone remodeling with a specific focus on the osteoclastic bone resorptive process and its unique functions in the alveolar bone. Lastly, we provide perspectives on osteoclast-targeted therapies and regenerative approaches associated with bone diseases in the jaw.

Tooth root resorption: A review.

Tooth root resorption is multifactorial, leading to progressive destruction and eventual loss of tooth root dentin and cement. There are internal and external types of root resorption, each having its variety. The etiology and pathogenesis of tooth root resorption are poorly understood, and the most significant etiological factors are trauma, pulpal infection, tooth bleaching, and orthodontic treatment. Tooth root resorption is primarily asymptomatic; thus, it is revealed accidentally by radiographic examination. Progressive clinical manifestations are pain, tooth discoloration, tooth mobility, and other conditions. Awareness of the causes and risk factors allowing tooth root resorption, and regular radiographic examination, in case of necessity, make it possible to reveal resorption at an early stage and to prevent its further development. Thus, the aim of this study is to present etiopathogenesis, a clinical course, and diagnostic peculiarities of internal and external types of tooth root resorption, enabling practicing dentists to timely diagnose root resorption and take appropriate measures to avoid further complications. Within the limitation of this review, even though the etiopathogenesis of tooth root resorption is yet not fully understood, it is suggested that the etiological factors fall into two groups (endogenic and exogenic) to enhance further understanding of the possible causes and mechanisms of root resorption and allow practitioners to monitor high-risk patients and make timely diagnoses. Moreover, radiographic examination and CBCT are indispensable for the diagnosis of root resorption.

Insights into the Role of Macrophage Polarization in the Pathogenesis of Osteoporosis.

Millions of people worldwide suffer from osteoporosis, which causes bone fragility and increases the risk of fractures. Osteoporosis is closely related to the inhibition of osteogenesis and the enhancement of osteoclastogenesis. In addition, chronic inflammation and macrophage polarization may contribute to osteoporosis as well. Macrophages, crucial to inflammatory responses, display different phenotypes under the control of microenvironment. There are two major phenotypes, classically activated macrophages (M1) and alternatively activated macrophages (M2). Generally, M1 macrophages mainly lead to bone resorption, while M2 macrophages result in osteogenesis. M1/M2 ratio reflects the “fluid” state of macrophage polarization, and the imbalance of M1/M2 ratio may cause disease such as osteoporosis. Additionally, antioxidant drugs, such as melatonin, are applied to change the state of macrophage polarization and to treat osteoporosis. In this review, we introduce the mechanisms of macrophage polarization-mediated bone resorption and bone formation and the contribution to the clinical strategies of osteoporosis treatment.

THE MODEL OF RESEARCH POST-CHOLECYSTECTOMIC PAIN SYNDROME IN EXPERIMENT

The number of surgeries performed by the laparoscopic method is constantly increasing due to the low trauma and fast patients recovery after surgery. However, despite the small surgery traumatism, most patients have the distinct pain syndrome, felt in the post-operative period and directly aff ects the post-operative prognosis. Despite the low trauma, pain after laparoscopic cholecystectomy has two pathways: parietal (somatic) and visceral. Given all the diffi culties in assessing the visceral component of post-operative pain, there is an urgent need to create a research model. The mucosa of the rabbit’s cheek was selected to model the visceral component of post cholecystectomy pain. The pain syndrome in the post-operative period was modeled on rabbits due to the formation of a burn wound on the mucosa of the left and right cheeks. The eff ectiveness of its treatment was studied with the help of combinations of analgesics. The burn wound was created by electrocoagulation EHVCH-300 «ELEPS» on the mucous surfaces of the right and left cheeks, under general anesthesia with propofol at a rate of 7.5 mg/kg. On the experimental (left) side, the studied combinations of analgesics were introduced: 1st group application mixture of 2.0 ml 0.5% bupivacaine with 2.0 ml with 5% dexketoprofen; Group 2 with a mixture of 2.0 ml of 0.5% bupivacaine with 0.5 ml of 1% nalbuphine; Group 3 was injected under the mucosa a mixture of 2.0 ml of 0.5% bupivacaine with 0.5 ml of 1% nalbuphine. The wound on the right cheek was a control, used for comparison. Pain syndrome was assessed by the reaction to fi nger pressure on the outside of the right and left cheeks separately, and refusal to eat (based on the dynamics of the daily diet). Pain control was performed in 6, 12, 24, 48, and 72 hours after surgery. Additionally, there was made an analysis of the dynamics of maintaining the daily diet.The first group there were revealed distinct diff erences in the severity of pain between the controlled (right) and left (experimental) parts for 6 (p˂0.01) and 12 (p˂0.05) hours after surgery, which indicates the clinical signifi cance of local use of a combination of bupivacaine with dexketoprofen. In the 2nd group, there were distinct diff erences in the severity of pain test between the right controlled cheek and left parts for 6 (p˂0.01), 12 (p˂0.01), and 24 (p˂0.05) hours. That is, the inclusion of a narcotic analgesic prolonged the analgesic effect by 100% (from 12 to 24 hours). In the 3rd group, there were distinct diff erences in the severity of pain for 6 (p˂0.01), 12 (p˂0.01), 24 (p˂0.01), and 48 (p˂0.05) hours. On the third day, all animals (20) did not show pain eff ect on the left (experimental) side. However, the resorptive eff ect of the studied combination of bupivacaine with nalbuphine was revealed by submucosal injection.Analysis of the frequency and duration of rabbits’ refusal to eat revealed this criterion in 16 (80%) animals of the fi rst group, and in 17 (85%) animals of the second group. Thus, the application methods of local anesthesia acted locally but had an insu ffi cient analgesic eff ect. In the third group, the refusal to eat was not detected in the majority (60%) of rabbits during this period. This indicates a greater strength and resorptive mechanism of analgesic action in the third group.Therefore, in clinical use, to block the visceral mechanism of suppression of pain impulses in laparoscopic cholecystectomy, it’s prognostically better to use the application method, which provides a certain local analgesic eff ect and clinically insignifi cant resorptive eff ect. This requires an additional and further study of the quantity and quality of analgesics for recommendations on local clinical use.

Traditional Chinese medicine promotes the resorption of herniated intervertebral discs by regulating autophagy and apoptosis

Yiqi Huoxue Decoction (abbreviated as YH in this paper) is a well-accepted traditional Chinese medicine formula used for the treatment of lumbar disc herniation (LDH). The main components of YH, such as tetrandrine, astragaloside IV and ferulic acid, have the effects of regulating inflammation and immunity as well as analgesia. Our lab previously reported that YH could promote the accumulation of reactive oxygen species (ROS) in the nucleus pulposus cells. This study was to determine the effect and mechanism of YH on both ruptured and non-ruptured intervertebral disc (IVD). First, we isolated human primary nucleus pulposus cells, then incubated them with 10 μM H2O2 to imitate the condition of oxidative stress in vivo. We found that YH-containing serum could promote the apoptosis and autophagy of nucleus pulposus cells in vitro. Next, we constructed rat models of both ruptured and unruptured disc herniation. The in vivo results showed that YH significantly could promote the number of autophagosomes, proportion of apoptotic cells, and expression levels of autophagy/apoptosis-related proteins in the nucleus pulposus of ruptured IVD. Also, YH could promote the resorption and degeneration of the ruptured IVD. Further, we investigated the molecular mechanism of YH-enhanced resorption of ruptured IVD. The in vitro data suggested that YH could activate ERK/mTOR in nucleus pulposus cells, leading to excessive autophagy and apoptosis while ERK inhibitor U0126 reversed the effect of YH on the ROS content, proportion of apoptotic cells and expression levels of autophagy. Overall, this study has demonstrated that the traditional Chinese medicine Yiqi Huoxue decoction promotes the resorption of herniated IVD via regulating ERK/mTOR-mediated apoptosis/autophagy in the nucleus pulposus cells, which highlights traditional Chinese medicine has a great potential for clinical conservative treatment for lumbar disc herniation.

Advances in the Study of the Mechanisms of Physiological Root Resorption in Deciduous Teeth.

Physiological root resorption of deciduous teeth is a complex physiological process that is essential for the normal replacement of deciduous teeth and permanent teeth in clinical practice, but its importance is often overlooked due to the presence of permanent teeth. This physiological process includes not only the resorption of hard tissues of deciduous teeth, such as dentin and cementum, but also the elimination of soft tissues, such as pulp and periodontal ligament (PDL). However, the mechanisms of physiological root resorption are not yet clear. In this article, the advances of research on the mechanisms related to physiological root resorption will be reviewed in two main aspects: hard tissues and soft tissues of deciduous teeth, specifically in relation to the effects of inflammatory microenvironment and mechanical stress on the resorption of hard tissues, the repair of hard tissues, and the elimination and the histological events of soft tissues.

Cerebrospinal Fluid Ascitis: Late Complication Of A Ventriculo-Peritoneal Bypass

Cerebrospinal fluid (CSF) ascites is a rare complication of ventriculoperitoneal (PV) shunt. The etiological factors and especially the mechanisms underlying this complication remain difficult to explain. We report the case of a voluminous CSF ascites complicating a PV shunt, 15 years later. This is a 16-year-old patient, valved at the age of one year, admitted for major abdominal distension. The abdominal scanner shows a large free fluid collection in the peritoneal cavity. The puncture of this ascites and above all the conversion of the PV shunt into a ventriculo-atrial bypass allowed the collection to dry up. The various hypotheses mentioned in the literature struggle to explain the occurrence of ascites in this patient. This ascites seems to stem from a progressive failure of the mechanisms of peritoneal resorption over time and this apart from any primary peritoneal pathology

Do leaf nitrogen resorption dynamics align with the slow‐fast continuum? A test at the intraspecific level

Abstract The links between internal nitrogen recycling through the process of resorption from senescing leaves, whole‐plant resource‐use strategies and performance remain elusive. Indeed, tests of such potential linkages are hampered by the classical evaluation of plant nitrogen resorption efficiency (REN) based on ‘snapshots’ of leaf nitrogen concentration from adult and senescent leaves. We significantly increased the resolution for measuring leaf nitrogen resorption by non‐destructively tracking time courses of nitrogen concentration in leaves of 137 natural Arabidopsis thaliana genotypes native to a wide range of climates across Europe, grown in a greenhouse. In addition to the classical measurement of resorption efficiency, we computed the relative maximum resorption rate of nitrogen (RRN), that is, the amount of nitrogen remobilized by a leaf per unit time and per unit nitrogen, together with slow–fast syndrome traits at the leaf and whole‐plant levels. Across genotypes, high rates and efficiencies of nitrogen resorption were associated with low specific leaf area and late flowering. The RRN showed significant heritability, genetic associations and was negatively correlated with the mean annual temperature of the native populations. By contrast, despite the evidence of a correlation with temperature, REN showed lower heritability and no evidence of genetic association, questioning the mechanisms of nitrogen resorption. Overall, our results suggest a much stronger adaptive role for leaf nitrogen resorption than previously uncovered. Read the free Plain Language Summary for this article on the Journal blog.

Aberrant NF-\u03baB activation in odontoblasts orchestrates inflammatory matrix degradation and mineral resorption

Inflammation-associated proteinase functions are key determinants of inflammatory stromal tissues deconstruction. As a specialized inflammatory pathological process, dental internal resorption (IR) includes both soft and hard tissues deconstruction within the dentin-pulp complex, which has been one of the main reasons for inflammatory tooth loss. Mechanisms of inflammatory matrix degradation and tissue resorption in IR are largely unclear. In this study, we used a combination of Cre-loxP reporter, flow cytometry, cell transplantation, and enzyme activities assay to mechanistically investigate the role of regenerative cells, odontoblasts (ODs), in inflammatory mineral resorption and matrices degradation. We report that inflamed ODs have strong capabilities of matrix degradation and tissue resorption. Traditionally, ODs are regarded as hard-tissue regenerative cells; however, our data unexpectedly present ODs as a crucial population that participates in IR-associated tissue deconstruction. Specifically, we uncovered that nuclear factor-kappa b (NF-κB) signaling orchestrated Tumor necrosis factor α (TNF-α)-induced matrix metalloproteinases (Mmps) and Cathepsin K (Ctsk) functions in ODs to enhance matrix degradation and tissue resorption. Furthermore, TNF-α increases Rankl/Opg ratio in ODs via NF-κB signaling by impairing Opg expression but increasing Rankl level, which utterly makes ODs cell line 17IIA11 (A11) become Trap+ and Ctsk+ multinucleated cells to perform resorptive actions. Blocking of NF-κB signaling significantly rescues matrix degradation and resorptive functions of inflamed ODs via repressing vital inflammatory proteinases Mmps and Ctsk. Utterly, via utilizing NF-κB specific small molecule inhibitors we satisfactorily attenuated inflammatory ODs-associated human dental IR in vivo. Our data reveal the underlying mechanisms of inflammatory matrix degradation and resorption via proteinase activities in IR-related pathological conditions.

Calcification and resorption of mouse Meckel's cartilage analyzed by von Kossa and tartrate-resistant acid phosphatase histochemistry and scanning electron microscopy/energy-dispersive X-ray spectrometry.

Meckel's cartilage is essential for the normal development of the mandible. The fate of the intermediate portion of Meckel's cartilage is unique as most of it disappears soon after birth except for the part that forms the sphenomandibular ligament. The mechanism of the disappearance of Meckel's cartilage is unknown; therefore, this study was designed to investigate the process of Meckel's cartilage degradation, focusing on cartilage matrix calcification and the appearance of chondroclasts. Developing mouse mandibles at embryonic days 15, 16, 17, and 18, and postnatal day 2 were processed for whole-mount staining with alcian blue and alizarin red. The mandibles on embryonic days 15, 16, 17, and 18 were fixed and embedded in paraffin. Adjacent sections were processed for von Kossa and tartrate-resistant acid phosphatase (TRAP) histochemistry and scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDS). Calcification and the element concentrations of calcium, phosphorus, and carbon were examined with von Kossa histochemistry and SEM/EDS. The involvement of chondroclasts was investigated using TRAP histochemistry. The results demonstrated that the intermediate portion of Meckel's cartilage is resorbed by chondroclasts after chondrocyte hypertrophy and cartilage matrix calcification and that the mineral concentration of calcified Meckel's cartilage is comparable to that of the surrounding bone. This study contributes to the understanding of the mechanism of Meckel's cartilage resorption and provides useful insights into the development of the mandible.

Morphology and molecular mechanisms of tail resorption during metamorphosis in Rana chensinensis tadpole (Anura: Ranidae)

The tail resorption process was an inevitable and pivotal transformation during amphibian metamorphosis. The present study investigated the mechanisms of tail resorption through histological and transcriptome analysis in Rana chensinensis. The results showed that tail resorption was initiated before the onset of metamorphic climax, and dramatically regressed after metamorphic climax by external-morphology measurement. The drastic disintegration of tail muscle and notochord occurred at Gs42-44, which were consistent with the trend of thyroid follicular cell height. Besides, expression level analysis and functional annotation of DEGs (differentially expressed genes) were conducted through RNA-seq analysis of the tail. Our study also analyzed the expression of genes related to oxidative stress, autophagy, apoptosis and degradation of cellular components in the tail of R. chensinensis. This study enriched the R. chensinensis transcriptome database and laid the foundation of further analysis of tail resorption.

The Beta-Tubulin Isotype TUBB6 Controls Microtubule and Actin Dynamics in Osteoclasts.

Osteoclasts are bone resorbing cells that participate in the maintenance of bone health. Pathological increase in osteoclast activity causes bone loss, eventually resulting in osteoporosis. Actin cytoskeleton of osteoclasts organizes into a belt of podosomes, which sustains the bone resorption apparatus and is maintained by microtubules. Better understanding of the molecular mechanisms regulating osteoclast cytoskeleton is key to understand the mechanisms of bone resorption, in particular to propose new strategies against osteoporosis. We reported recently that β-tubulin isotype TUBB6 is key for cytoskeleton organization in osteoclasts and for bone resorption. Here, using an osteoclast model CRISPR/Cas9 KO for Tubb6, we show that TUBB6 controls both microtubule and actin dynamics in osteoclasts. Osteoclasts KO for Tubb6 have reduced microtubule growth speed with longer growth life time, higher levels of acetylation, and smaller EB1-caps. On the other hand, lack of TUBB6 increases podosome life time while the belt of podosomes is destabilized. Finally, we performed proteomic analyses of osteoclast microtubule-associated protein enriched fractions. This highlighted ARHGAP10 as a new microtubule-associated protein, which binding to microtubules appears to be negatively regulated by TUBB6. ARHGAP10 is a negative regulator of CDC42 activity, which participates in actin organization in osteoclasts. Our results suggest that TUBB6 plays a key role in the control of microtubule and actin cytoskeleton dynamics in osteoclasts. Moreover, by controlling ARHGAP10 association with microtubules, TUBB6 may participate in the local control of CDC42 activity to ensure efficient bone resorption.

Finite Element Analysis on Wall Fluid Shear Stress on Cells under Oscillatory Flow

During mechanical stimulation-induced bone remodeling, interstitial fluid around microcracks may produce a flow field with gradient fluid shear stress (FSS). Osteoclast precursors can sense this gradient FSS and migrate toward the low FSS region. However, the local distribution of wall FSS on bone cells under a flow field with globally gradient FSS remains unknown. In this study, finite element models of a modified plate flow chamber with cells were constructed. The effect of oscillatory flow with different FSS levels and cell spacings or frequencies on the distribution of local wall FSS around cells was simulated by using a fluid–solid coupling method. Results showed that the polarization of wall FSS distribution in a cell decreased with the increase in cell spacing. At a low FSS level, the frequency of oscillatory flow had a minimal effect on the wall FSS distribution. At a high FSS level, the increase in flow frequency enhanced the fluctuation of local wall FSS distribution on cells. These results provide a basis for future research on the flow-induced migration of osteoclast precursors and clarify the mechanism of mechanical stimulation-induced bone resorption.

PSV-4 Peri-estrus ovarian, uterine, and hormonal variables influence the uterine luminal fluid metabolome in beef heifers

Abstract In cattle, uterine luminal fluid (ULF) is the main source of molecules that support embryo development and survival during the peri-implantation period. Overarching hypothesis was that peri-estrus changes in ULF volume through accumulation and resorption mechanisms influence ULF composition during the estrous cycle and early pregnancy. Objectives were (1) to characterize individual temporal and spatial changes in ULF volume, endometrial and luteal vascularity, endometrial and luteal size, and progesterone (P4) concentrations during the peri-estrus period in beef heifers and, (2) associate such changes with the metabolite composition in the ULF, four days after estrus. Fourteen Bos indicus heifers that presented a PGF2α responsive CL received 500 µg PGF2α analog i.m. and were examined daily by rectal B-mode and pulse-wave color-Doppler ultrasonography until the fifth day after estrus (estrus = d 0). Plasma P4 was measured daily. On d 4, the uterine body was sampled using a cytology brush for targeted metabolomic analysis by mass spectrometry. Multivariate analyses clustered heifers according to ovarian, uterine, and hormonal variables in clusters A (n = 5) and B (n = 8 heifers). Individual metabolite concentrations were compared between clusters A and B by univariate analysis using t-test after FDR correction. Concentrations of Pro, Ala, Leu, Gly, Val, Lys, Ile, Phe, Asp, Orn, Tyr, Arg, Trp, Suc, Cit, ADMA, the sum of essential Amino Acids (AA), sum of non-essential AA, sum of aromatic AA, and total AA were greater in cluster A (FDR ≤ 0.05). ULF volume dynamics and associated uterine, ovarian, and hormonal variables during the peri-estrus period presented a concerted variation among heifers, which was associated with the ULF composition four days after estrus. Potential implications for embryo receptivity and reproductive outcomes are the focus of the current investigation.

Effect of simulated occlusal force on periodontal ligament stem cells of the deciduous teeth at different stages of root absorption

Objective: To explore the related mechanisms of biological root resorption in decidual teeth by studying the biological effect of simulated occlusal force on the periodontal ligament stem cells (PDLSC) at different stages of root absorption. Methods: According to the tooth type and root absorption degree, healthy retained deciduous incisors and healthy first premolars that needed to be removed for orthodontic treatment were collected and divided into three groups with six teeth in each group: the deciduous unabsorbed group (UN group), the absorbed group (R group) and the permanent teeth group (P group). PDLSC was isolated from periodontal ligament and cultured. PDLSC of three groups were loaded with dynamic pressure of 0-45, 0-90, 0-135, 0-180, 0-225 and 0-270 kPa, respectively. The proliferation ability was detected by cell counting kit-8 (CCK-8) technique on day 1 to day 7, respectively. The apoptosis levels of PDLSC after loading with dynamic pressure of 0-45, 0-90, 0-135, 0-180 and 0-225 kPa were observed by the flow cytometry. The changes of microfilaments were observed by fibrous actin (F-actin) staining after the cytokeleton was subjected to dynamic pressure of 0-90 kPa. Results: PDLSC of three groups exhibited various proliferation abilities to dynamic pressure. The A values in the UN group and R group were significantly higher than those in the P group and the difference was statistically significant (P<0.05). However, there was no significant difference between the UN group and the R group (P>0.05). The A values of PDLSC in UN group and R group under dynamic pressures of 0-45, 0-90, 0-135 and 0-180 kPa had no statistical significance compared with the control group unloading dynamic pressure (P>0.05). However, under 0-225 and 0-270 kPa dynamic pressures, the A values at the day 3 to day 7 were statistically significant (P<0.05). The A values of PDLSC in P group under 0-45, 0-90, 0-135, 0-180 and 0-225 kPa dynamic pressures for 1 to 7 days were no statistically significant difference compared with the control group (P>0.05). The A value in P group under the 0-270 kPa was statistically significant only on day 3 (1.386±0.131) and day 5 to day 7 (1.728±0.226, 2.029±0.168 and 2.263±0.210, respectively)(P<0.05). The result of apoptosis showed that the A values of PDLSC in UN group, R group and P group were significantly increased under 0-90, 0-135, 0-180 kPa and above dynamic pressures, respectively (P<0.05) compared with the control group unloading dynamic pressure. Under 0-90 kPa dynamic pressure, F-actin fluorescence staining samples in three groups all showed green filaments which were arranged along the long axis of the cells in the R group and the P group, while some fibers in the UN group were closely arranged and promoted stress fiber assembly. Conclusions: The biological characteristics of PDLSC at different root absorption stages were changed when they were stimulated by mechanical stress, and PDLSC of the deciduous teeth at the root unabsorption stage were more sensitive to mechanical stress stimulation.

Controlling Tumor Regression about the Physiological System

It is proposed to study the mechanism of tumor regression from an evolutionary point of view. The proposal is based on the assumption that the evolutionary precursor of this mechanism is the resorption mechanism in sedentary modular invertebrates preparing for diapause in embryos. To understand how the tumor regression mechanism works, it is necessary to investigate the mechanism of resorption of these embryos in these invertebrates.

Bone Resorption in Ameloblastoma and Its Underlying Mechanism

Ameloblastoma, a tumor located in the jaw, grows slowly but locally invasive. Ameloblastoma expands in the jaw based on a mechanism resorbing the surrounding bone. To date, the bone resorption mechanisms of ameloblastoma are associated with the expression of receptor activator of nuclear factor (NF)-κB (RANK) ligand (RANKL), matrix metalloproteinases (MMPs), and tumor necrosis factor (TNF)-α. RANKL plays an important role in generating osteoclastogenesis. MMPs degrade the extracellular matrix. TNF-α can induce the formation of osteoclast and modulate the MMPs. In this review the bone resorption mechanism of ameloblastoma as well its signaling pathway will be disclosed.Keywords: Ameloblastoma, RANKL, MMPs, TNF-α.

External Root Resorption of the Mandibular Second Molar Associated with Completely Impacted Third Molar: A Case Report and Review of the Literature

External root resorption (ERR) of permanent teeth is believed to result from mechanical or inflammatory factors, such as the force pressure of orthodontic appliances, dental trauma, cysts or tumours, chronic apical periodontitis, and poor regeneration of the periodontium in reimplanted or transplanted teeth. Another factor frequently associated with ERR of second molars is an unerupted third molar close to the root of the second molar. This type of root resorption has been observed at the site of contact with the impacted tooth, indicating that the impacted tooth's pressure participates in the resorption process. Though this resorption mechanism is not yet apparent, some investigators deem it similar to the mechanism involved in the resorption of primary teeth. This case report aims to describe a second molar resorption case triggered by an impacted third molar and perform a literature review. Key Words External Root Resorption, Mandibular third molar, Pressure resorption,