Localization of cathepsin D in human odontoclasts. a light and electron microscopical immunocytochemical study

Etiological Mechanisms and Genetic/Biological Modulation Related to PTH1R in Primary Failure of Tooth Eruption

Primary failure of eruption (PFE) is a rare disorder that is characterized by the inability of a molar tooth/teeth to erupt to the occlusal plane or to normally react to orthodontic force. This condition is related to hereditary factors and has been extensively researched over many years. However, the etiological mechanisms of pathogenesis are still not fully understood. Evidence from studies on PFE cases has shown that PFE patients may carry parathyroid hormone 1 receptor (PTH1R) gene mutations, and genetic detection can be used to diagnose PFE at an early stage. PTH1R variants can lead to altered protein structure, impaired protein function, and abnormal biological activities of the cells, which may ultimately impact the behavior of teeth, as observed in PFE. Dental follicle cells play a critical role in tooth eruption and root development and are regulated by parathyroid hormone-related peptide (PTHrP)-PTH1R signaling in their differentiation and other activities. PTHrP-PTH1R signaling also regulates the activity of osteoblasts, osteoclasts and odontoclasts during tooth development and eruption. When interference occurs in the PTHrP-PTH1R signaling pathway, the normal function of dental follicles and bone remodeling are impaired. This review provides an overview of PTH1R variants and their correlation with PFE, and highlights that a disruption of PTHrP-PTH1R signaling impairs the normal process of tooth development and eruption, thus providing insight into the underlying mechanisms related to PTH1R and its role in driving PFE.

Pathophysiological mechanisms of root resorption after dental trauma: a systematic scoping review

Background

The objective of this scoping review was to systematically explore the current knowledge of cellular and molecular processes that drive and control trauma-associated root resorption, to identify research gaps and to provide a basis for improved prevention and therapy.

Methods

Four major bibliographic databases were searched according to the research question up to February 2021 and supplemented manually. Reports on physiologic, histologic, anatomic and clinical aspects of root resorption following dental trauma were included. Duplicates were removed, the collected material was screened by title/abstract and assessed for eligibility based on the full text. Relevant aspects were extracted, organized and summarized.

Results

846 papers were identified as relevant for a qualitative summary. Consideration of pathophysiological mechanisms concerning trauma-related root resorption in the literature is sparse. Whereas some forms of resorption have been explored thoroughly, the etiology of others, particularly invasive cervical resorption, is still under debate, resulting in inadequate diagnostics and heterogeneous clinical recommendations. Effective therapies for progressive replacement resorptions have not been established. Whereas the discovery of the RANKL/RANK/OPG system is essential to our understanding of resorptive processes, many questions regarding the functional regulation of osteo-/odontoclasts remain unanswered.

Conclusions

This scoping review provides an overview of existing evidence, but also identifies knowledge gaps that need to be addressed by continued laboratory and clinical research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01510-6.

Reparative Endodontic Treatment of a Perforating Internal Inflammatory Root Resorption: A Case Report

The aim of this case report was to present a reparative treatment approach of an extensive internal inflammatory resorption with a lateral perforation and apical and lateral inflammatory lesions. Only the necrotic coronal part of the pulp was removed, and the vital pulp tissue within the resorption cavity and the apical part of the root canal was left uninstrumented. Bleeding was induced, and the blood clot was covered with mineral trioxide aggregate. Hard tissue repair and healing of the apical lesion could be observed in the 3-year recall.

Optimizing dentin bond durability: control of collagen degradation by matrix metalloproteinases and cysteine cathepsins

OBJECTIVES

Contemporary adhesives lose their bond strength to dentin regardless of the bonding system used. This loss relates to the hydrolysis of collagen matrix of the hybrid layers. The preservation of the collagen matrix integrity is a key issue in the attempts to improve the dentin bonding durability.

METHODS

Dentin contains collagenolytic enzymes, matrix metalloproteinases (MMPs) and cysteine cathepsins, which are responsible for the hydrolytic degradation of collagen matrix in the bonded interface.

RESULTS

The identities, roles and function of collagenolytic enzymes in mineralized dentin has been gathered only within last 15 years, but they have already been demonstrated to have an important role in dental hard tissue pathologies, including the degradation of the hybrid layer. Identifying responsible enzymes facilitates the development of new, more efficient methods to improve the stability of dentin-adhesive bond and durability of bond strength.

SIGNIFICANCE

Understanding the nature and role of proteolytic degradation of dentin-adhesive interfaces has improved immensely and has practically grown to a scientific field of its own within only 10 years, holding excellent promise that stable resin-dentin bonds will be routinely available in a daily clinical setting already in a near future.

Osteoclasts and odontoclasts: signaling pathways to development and disease

Osteoclasts are cells essential for physiologic remodeling of bone and also play important physiologic and pathologic roles in the dentofacial complex. Osteoclasts and odontoclasts are necessary for tooth eruption yet result in dental compromise when associated with permanent tooth internal or external resorption. The determinants that separate their physiologic and pathologic roles are not well delineated. Clinical cases of primary eruption failure and root resorption are challenging to treat. Mineralized tissue resorbing cells undergo a fairly well characterized series of differentiation stages driven by transcriptional mediators. Signal transduction via cytokines and integrin-mediated events comprise the detailed pathways operative in osteo/odontoclastic cells and may provide insights to their targeted regulation. A better understanding of the unique aspects of osteoclastogenesis and osteo/odontoclast function will facilitate effective development of new therapeutic approaches. This review presents the clinical challenges and delves into the cellular and biochemical aspects of the unique cells responsible for resorption of mineralized tissues of the craniofacial complex.

Investigating autophagy: quantitative morphometric analysis using electron microscopy

Autophagy is a compensatory pathway involving isolation and subsequent degradation of cytosolic material and organelles in eukaryotic cells.(1) The autophagic process can provide a "housekeeping" function by removing damaged proteins and organelles in a selective or nonselective fashion in order to exert a protective effect following stress.(2) Remarkably, after being discovered to be much more of a targeted process than a random one, the role of autophagy became implicated in many normal cellular and disease processes.(3) Several methodologies are routinely employed to monitor the entire autophagic process.(4) Microtubule-associated protein light chain 3, a mammalian homolog of yeast Atg8, has been widely used as a specific marker to monitor autophagy in numerous cell types.(5) While monitoring autophagic flux is extremely important, it is also beneficial to perform a detailed analysis by electron microscopy (EM) to evaluate changes in various autophagic structures, quantify the areas involved, and determine if any particular organelle(s) or area of the cell cytoplasm is being targeted for degradation.(6) The following article describes methods to localize and quantify subcellular areas of autophagy using transmission EM. Also discussed are methods for subcellular localization of specific proteins by employing immunogold EM; this method becomes particularly useful in detecting early changes in cellular homeostasis that may occur before later signs of cellular insult can be observed morphologically.

Alendronate binds to tooth root surfaces and inhibits progression of feline tooth resorption: a pilot proof-of-concept study

Tissue distribution, bioavailability, and efficacy of alendronate in preventing progression of resorption of teeth were evaluated in cats. [Butyl-4-14C-]-alendronate accumulates on subgingival tooth and alveolar bone surfaces adjacent to vascularized tissue resulting in concentration of the drug around tooth roots. Three cats were treated with a 0.03 mg/kg i.v. bolus of [butyl-4-14C-]-alendronate followed by blood, urine, and feces collection and euthanasia 24-hours later. Drug tissue distribution was accessed by autoradiography and sample combustion. To assess bioavailability, 12 cats were administered alendronate orally (3.0 or 9.0 mg/kg in water or 9.0 mg/kg in tuna water) and urine was collected for 24-hours. In these formulations, alendronate oral bioavailability in cats was approximately 3%. In addition, 10 cats with radiographic evidence of pre-existing tooth resorption (14 affected teeth) were treated with vehicle or 3.0 mg/kg alendronate per os once weekly for 22-weeks and, then, 9.0 mg/kg per os twice weekly for 27-weeks in a random, masked study. Radiographic area of resorption was measured and progression scored every 3 to 4-months. In placebo-treated cats, resorption progressed in five of six teeth (+ 97% average increase in area of resorption), whereas progression of resorption was seen in only three of eight affected teeth in alendronate-treated cats with a -22% average change (decrease) in area (P < 0.01 difference in number of teeth showing progression; P < 0.001 difference in area of resorption). Alendronate accumulated preferentially on subgingival tooth surfaces and adjacent alveolar bone and, at a dose of 9 mg/kg twice weekly, effectively slowed or arrested the progression of resorption.

Effect of soluble receptors to interleukin-1 and tumor necrosis factor alpha on experimentally induced root resorption in rats

OBJECTIVE

In this study, the role of the inflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) in the course of mechanically induced root resorption was investigated.

METHODS

Mechanical induction of root resorption was performed on the upper left first molars in 18 male Wistar rats according to the method of Nakane and Kameyama. Starting on day minus 1, six animals received daily intraperitoneal injections of 2 ml of 1 micro g/ml soluble receptors to IL-1 (sIL-1RII) and another six animals were administered the same dose of soluble receptors to TNFalpha (sTNFalpha-RI). Six animals served as a control. On d 7 the left maxillae were prepared for histological and morphometric analysis of the extent of the root resorption that had developed.

RESULTS

The qualitative and quantitative results demonstrated that in both receptor groups the amount of root resorption was significantly reduced. Especially following systemic application of sTNFalpha-RI, root resorption was nearly completely prevented.

CONCLUSIONS

Our results indicate that IL-1 and more particularly TNFalpha are important for the induction and the further process of mechanically induced root resorption in the rat.

Immunohistochemical localization of insulin-like growth factor-II and its binding protein-6 in human epithelial cells of Malassez

So-called epithelial rests of Malassez are derived from the Hertwig's root sheath and are located in the periodontal ligament, with still unknown functions. Different pathological conditions may lead to proliferation of these otherwise non-proliferative cell clusters. The insulin-like growth factor (IGF) system is an important growth factor system controlling proliferation and differentiation. In our study on Malassez cells from extracted human deciduous teeth, we investigated their structure by means of light and electron microscopy. Although they appeared as cellular clusters with a uniform epithelial phenotype, immunohistochemical analyses of components of the IGF system revealed an unique pattern: weak immunoreactivity could be seen for IGF-II while among all IGF binding proteins (IGFBPs) only IGFBP-6 and weakly IGFBP-4 were detectable in epithelial cells of Malassez. Since IGFBP-6 has a very high affinity for IGF-II and can inhibit its functions, we discuss that, in the normal periodontal ligament, autocrine IGFBP-6 may function as an antiproliferative molecule suppressing mitogenic effects of IGFs on Malassez cells.

Immunohistochemical localization of components of the insulin-like growth factor-system in human deciduous teeth

To investigate the occurrence of components of the insulin-like growth factor (IGF) system during the resorption process of shedding human deciduous teeth, we investigated sections of 13 decalcified and paraffin-embedded deciduous teeth immunohistochemically with antibodies against IGF-I and -II, six IGF binding proteins (IGFBPs 1-6) and the IGF receptors IGF1R and IGF2R. The teeth were in different stages of resorption and all showed reparative cementum formation. It was found that acellular extrinsic fiber cementum, reversal lines and reparative cellular intrinsic fiber cementum were immunoreactive for both IGFs and various IGFBPs. Therefore, in human deciduous teeth, all subgroups of cementum, but not dentine, may represent sources of components of the IGF system. Odontoclasts did not carry IGFs or the IGF1R, but IGFBPs and the IGF2R. Therefore, these cells, in contrast to osteoclasts, may not respond to IGFs, but may be involved in the release and sequestration of IGFs from cementum during the resorption process. In contrast to odontoclasts, cementoblasts and periodontal ligament (PDL) fibroblasts carried IGF1R. The influence of the IGF system on the function of these cells with respect to periodontal matrix turnover and cementogenesis is discussed. On the behalf of the IGFBP immunoreactivities found, the PDL extracellular matrix can be considered to be a reservoir for IGF system components, where binding proteins may regulate IGF distribution and activity.