Histology of human teeth: Standard and specific staining methods revisited

Histological Evaluation of Internal Dental Resorption: An Analysis of a Cohort of 50 Cases

Objective

This study aimed to perform a histological evaluation of teeth diagnosed with internal root resorption.

Materials and Methods

A descriptive study involved the examination of 50 human teeth extracted due to an unfavorable prognosis for retention in the oral cavity. Teeth were preserved in 10% buffered formalin and subsequently subjected to the decalcification process. Masson-Goldner staining was applied for comprehensive histological assessment.

Results

In all the 50 teeth examined, resorption gaps within the dentin tissue were identified, accompanied by the presence of reparative cells in the vicinity of these cavities. Marked structural loss and dentin fragmentation were evident, with regions exhibiting fissures and an absence of dentinal tubules.

Conclusions

The histological evaluation of 50 teeth diagnosed with internal dental resorption revealed significant structural alterations, including resorption lacunae, the presence of multinucleated osteoclast-like cells, and reparative connective tissue. These findings highlight the complex and multifaceted nature of internal dental resorption. These histological insights provide a deeper understanding of the pathological processes involved in internal dental resorption and underscore the necessity for early detection and intervention to mitigate tooth loss and preserve dental health.

A comparative in vitro and in vivo analysis of the impact of copper substitution on the cytocompatibility, osteogenic, and angiogenic properties of a borosilicate bioactive glass

The 0106-B1-bioactive glass (BG) composition (in wt %: 37.5 SiO2, 22.6 CaO, 5.9 Na2O, 4.0 P2O5, 12.0 K2O, 5.5 MgO, and 12.5 B2O3) has demonstrated favorable processing properties and promising bone regeneration potential. The present study aimed to evaluate the biological effects of the incorporation of highly pro-angiogenic copper (Cu) in 0106-B1-BG in vitro using human bone marrow-derived mesenchymal stromal cells (BMSCs) as well as its in vivo potential for bone regeneration. CuO was added to 0106-B1-BG in exchange for CaO, resulting in Cu-doped BG compositions containing 1.0, 2.5 and 5.0 wt % CuO (composition in wt %: 37.5 SiO2, 21.6/ 20.1/17.6 CaO, 5.9 Na2O, 4.0 P2O5, 12.0 K2O, 5.5 MgO, 12.5 B2O3, and 1.0/ 2.5/ 5.0 CuO). In vitro, the BGs' impact on the viability, proliferation, and growth patterns of BMSCs was evaluated. Analyses of protein secretion, matrix formation, and gene expression were used for the assessment of the BGs' influence on BMSCs regarding osteogenic differentiation and angiogenic stimulation. The presence of Cu improved cytocompatibility, osteogenic differentiation, and angiogenic response when compared with unmodified 0106-B1-BG in vitro. In vivo, a critical-size femoral defect in rats was filled with scaffolds made from BGs. Bone regeneration was evaluated by micro-computed tomography. Histological analysis was performed to assess bone maturation and angiogenesis. In vivo effects regarding defect closure, presence of osteoclastic cells or vascular structures in the defect were not significantly changed by the addition of Cu compared with undoped 0106-B1-BG scaffolds. Hence, while the in vitro properties of the 0106-B1-BG were significantly improved by the incorporation of Cu, further evaluation of the BG composition is necessary to transfer these effects to an in vivo setting.

Using tissue clearing and light sheet fluorescence microscopy for the three-dimensional analysis of sensory and sympathetic nerve endings that innervate bone and dental tissue of mice

Bone and dental tissues are richly innervated by sensory and sympathetic neurons. However, the characterization of the morphology, molecular phenotype, and distribution of nerves that innervate hard tissue has so far mostly been limited to thin histological sections. This approach does not adequately capture dispersed neuronal projections due to the loss of important structural information during three-dimensional (3D) reconstruction. In this study, we modified the immunolabeling-enabled imaging of solvent-cleared organs (iDISCO/iDISCO+) clearing protocol to image high-resolution neuronal structures in whole femurs and mandibles collected from perfused C57Bl/6 mice. Axons and their nerve terminal endings were immunolabeled with antibodies directed against protein gene product 9.5 (pan-neuronal marker), calcitonin gene-related peptide (peptidergic nociceptor marker), or tyrosine hydroxylase (sympathetic neuron marker). Volume imaging was performed using light sheet fluorescence microscopy. We report high-quality immunolabeling of the axons and nerve terminal endings for both sensory and sympathetic neurons that innervate the mouse femur and mandible. Importantly, we are able to follow their projections through full 3D volumes, highlight how extensive their distribution is, and show regional differences in innervation patterns for different parts of each bone (and surrounding tissues). Mapping the distribution of sensory and sympathetic axons, and their nerve terminal endings, in different bony compartments may be important in further elucidating their roles in health and disease.

Tooth pattern, development, and replacement in the yellow catfish, Pelteobagrus fulvidraco

Studies of teleost teeth are important for understanding the evolution and mechanisms of tooth development, replacement, and regeneration. Here, we used gross specimens, microcomputed tomography, and histological analysis to characterize tooth structure, development, and resorption patterns in adult Pelteobagrus fulvidraco. The oral and pharyngeal teeth are villiform and conical. Multiple rows of dentition are densely distributed and the tooth germ is derived from the epithelium. P. fulvidraco exhibits a discontinuous and non-permanent dental lamina. Epithelial cells surround the teeth and are separated into distinct tooth units by mesenchymal tissue. Tooth development is completed in the form of independent tooth units. P. fulvidraco does not undergo simultaneous tooth replacement. Based on tooth development and resorption status, five forms of teeth are present in adult P. fulvidraco: developing tooth germs, accompanied by relatively immature tooth germs; mature and well-mineralized tooth accompanied by one tooth germ; teeth that have begun resorption, but not completely fractured; fractured teeth with only residual attachment to the underlying bone; and teeth that are completely resorbed and detached. Seven biological stages of a tooth in P. fulvidraco were also described.

GATA4 inhibits odontoblastic differentiation of dental pulp stem cells through targeting IGFBP3

OBJECTIVE

The odontogenic differentiation of human dental pulp stem cells (HDPSCs) is associated with reparative dentinogenesis. Transcription factor GATA binding protein 4 (GATA4) is proved to be essential for osteoblast differentiation and bone remodeling. This study clarified the function of GATA4 in HDPSCs odontoblast differentiation.

METHODS

The change in GATA4 expression during reparative dentin formation was detected by immunohistochemistry staining. The expression of GATA4 during HDPSCs odontoblastic differentiation was detected by western blot and quantitative polymerase chain reaction. The effect of GATA4 on odontoblast differentiation was investigated following overexpression lentivirus transfection. RNA sequencing, dual luciferase assay and chromatin immunoprecipitation (CHIP) were conducted to verify downstream targets of GATA4. GATA4 overexpression lentivirus and small interference RNA targeting IGFBP3 were co-transfected to investigate the regulatory mechanism of GATA4.

RESULTS

Upregulated GATA4 was observed during reparative dentin formation in vivo and the odontoblastic differentiation of HDPSCs in vitro. GATA4 overexpression suppressed the odontoblastic potential of HDPSCs, demonstrated by decreased alkaline phosphatase activity (p < 0.0001), mineralized nodules formation (p < 0.01), and odonto/osteogenic differentiation markers levels (p < 0.05). RNA sequencing revealed IGFBP3 was a potential target of GATA4. CHIP and dual luciferase assays identified GATA4 could activate IGFBP3 transcription. Additionally, IGFBP3 knockdown recovered the odontoblastic differentiation defect caused by GATA4 overexpression (p < 0.05).

CONCLUSIONS

GATA4 inhibited odontoblastic differentiation of HDPSCs via activating the transcriptional activity of IGFBP3, identifying its promising role in regulating HDPSCs odontoblast differentiation and reparative dentinogenesis.

Volumetry of ovine incisors dental pulp for further regenerative therapy

Mesenchymal stem cells (MSCs) are used for regenerative therapy. Dental pulp MSCs make extracted wisdom teeth a useful resource in humans. Preclinical validation of regenerative therapies requires large animal models such as the sheep. Since stem cells can be retrieved from the dental pulp of ovine incisors, the best age to extract a maximal volume of dental pulp needs to be defined. The objective of this ex vivo study was to quantify incisors dental pulp volume, in sheep of various age. Three jaws were dedicated to histology (one per age group); the others were imaged with a computed tomography scanner [3 years-old (n = 9), 4 (n = 3) and 6 (n = 5)]. The incisors dental pulp volume was measured after 3D reconstruction. Multiple linear regression showed that dental pulp volume of ovine incisors decreases with age (β-estimate = -3.3; p < 0.0001) and teeth position from the more central to the more lateral (β-estimate = -4.9; p = 0.0009). Weight was not a relevant variable in the regression model. The dental pulp volume ranged from 36.7 to 19.6 mm3 in 3-year-old sheep, from 23.6 to 11.3 in 4-year-old sheep, and from 19.4 to 11.5 in 6-year-old sheep. The pulp volume of the most central teeth (first intermediate) was significantly higher than the most lateral teeth (corner). Haematoxylin-Eosin-Safran of the whole incisors, and of isolated dental pulps demonstrated a similar morphology to that in humans. The first intermediate incisor of 3-year-old sheep should be selected preferentially in preclinical research to retrieve the highest volume of dental pulp.

Quercetin ameliorates acute lung injury in a rat model of hepatopulmonary syndrome

BACKGROUND

Common bile duct ligation (BDL) is a rat experimental model to induce biliary cirrhosis. Lung fibrosis and pulmonary vascular angiogenesis and congestion are the most common complications of biliary cirrhosis that is known as hepatopulmonary syndrome. The aim of the present work is to investigate the acute lung injury in a BDL model and to investigate the possible protective effect of quercetin on this injury.

METHODS

Twenty-four adult male albino rats of the Wister strain (weighing 150-250 g). Animals were divided into 3 groups, with 8 rats each: Group I: Sham-operated group (control). Group II: Bile duct ligation group (BDL) sacrificed after 28 days from the surgery. Group III: Quercetin-treated bile duct ligation group (Q-BDL) was given orally by gastric gavage in a dose of 50 mg/kg/day, starting from the 4th day of the operation until the 28th day. At the end of the experiment, at day 28, all rats were sacrificed. Lung specimens were processed to measure Endothelin B receptor gene expression by PCR, lung surfactant by ELISA, "eNO" s by immunohistochemistry. Histological assessment was done using; H&E, Masson's trichrome, PAS, toluidine blue-stained semi-thin sections, transmission electron microscope. Histomorphometric and statistical studies were done.

RESULTS

BDL group showed significant increase in lung index together with mononuclear cellular infiltration denoting lung inflammatory state. Also, the significant increase in pulmonary endothelial nitric oxide synthase ("eNO" s) area percent and endothelin B receptor (ET_B) gene expression indicates enhanced angiogenesis. Pulmonary surfactant concentration was significantly decreased together with thickening of interalveolar septa denoting lung injury and fibrosis. Quercetin led to significant decrease in lung index, pulmonary "eNO" s area percent, ET_B gene expression and significant increase in pulmonary surfactant concentration. Quercetin treatment improved histological changes and morphometric measurements, limited mononuclear cellular infiltration and decreased perivascular and perialveolar collagen deposition.

CONCLUSION

Quercetin ameliorates the hepatopulmonary syndrome-induced lung injury through its anti-inflammatory, antioxidative and antifibrotic effects.

Dynamic dentin: A quantitative microscopic assessment of age and spatial changes to matrix architecture, peritubular dentin, and collagens types I and III

To investigate age and site-related changes to human dentin collagen, sound human teeth collected from donors aged 13-29 (young) and 50-74 (aged) years (n = 9/group) were cut to shallow and deep sites. Dentin collagen orientation and fibril bundling was investigated using the Picrosirius Red (PSR) stain observed under cross-polarized light microscopy (Pol), and collagen distribution was investigated using Confocal Laser Scanning Microscopy (CLSM). Collagen types III to I distribution in peritubular dentin (PTD) was revealed using Herovici stain and brightfield microscopy. Image analysis software and linear mixed modelling quantified outcomes. In situ dentin collagen was observed using Xenon Plasma Focussed Ion Beam Scanning Electron Microscopy (Xe PFIB-SEM). The PSR-Pol analysis revealed less coherently aligned and more bundled collagen fibrils in aged dentin (P = 0.005). Deep inner dentin collagen in both groups were less coherently aligned with reduced bundling. Regardless of age, CLSM showed collagen distribution remained stable; and more collagen type III was detectable in PTD located in inner dentin (Young: P = 0.006; Aged: P = 0.008). Observations following Xe PFIB-SEM cross-sectioning showed apatite-like deposits surrounding large intratubular collagen fibers, and evidence of smaller intertubular dentin collagen fibrils in situ. In conclusion, aging changes collagen network architecture, but not distribution or content.

Comparison of collagen features of distinct types of caries-affected dentin

OBJECTIVES

To compare the biodegradability, mechanical behavior, and physicochemical features of the collagen-rich extracellular matrix (ECM) of artificial caries-affected dentin (ACAD), natural caries-affected dentin (NCAD) and sound dentin (SD).

METHODS

Dentin specimens from human molars were prepared and assigned into groups according to the type of dentin: ACAD, NCAD, or SD. ACAD was produced by incubation of demineralized SD with Streptococcus mutans in a chemically defined medium (CDM) with 1% sucrose for 7 days at 37 °C under anaerobic conditions. Specimens were assessed to determine collagen birefringence, biodegradability, mechanical behavior, and chemical composition. Data were individually processed and analyzed by ANOVA and post-hoc tests (α = 0.05).

RESULTS

CDM-based biofilm challenge reduced loss, storage, and complex moduli in ACAD (p < 0.001), while the damping capacity remained unaffected (p = 0.066). Higher red and lower green birefringence were found in ACAD and NCAD when compared with SD (p < 0.001). Differently to ACAD, SD and NCAD presented higher biodegradability to exogenous proteases (p = 0.02). Chemical analysis of the integrated areas of characteristic bands that assess mineral quality (carbonate/phosphate and crystallinity index), mineral to matrix (phosphate/amide I) and post-translational modifications (amide III/CH₂, pentosidine/CH₂, and pentosidine/amide III) (p<0.05) showed that NCAD was significantly different from SD while ACAD exhibited intermediate values.

CONCLUSIONS

CDM-based biofilm challenge produced a dentin ECM with decreased mechanical properties and increased collagen maturity. The compositional and structural conformation of the ACAD suggested that CDM-based biofilm challenge showed potential to produce artificial lesions by revealing a transitional condition towards mimicking critical features of NCAD.

CLINICAL SIGNIFICANCE

This study highlights the importance of developing a tissue that mimics the features of natural caries-affected dentin ECM for in vitro studies. Our findings suggested the potential of a modified biofilm challenge protocol to produce and simulate a relevant substrate, such as caries-affected dentin.

A Compilation of Study Models for Dental Pulp Regeneration

Efforts to heal damaged pulp tissue through tissue engineering have produced positive results in pilot trials. However, the differentiation between real regeneration and mere repair is not possible through clinical measures. Therefore, preclinical study models are still of great importance, both to gain insights into treatment outcomes on tissue and cell levels and to develop further concepts for dental pulp regeneration. This review aims at compiling information about different in vitro and in vivo ectopic, semiorthotopic, and orthotopic models. In this context, the differences between monolayer and three-dimensional cell cultures are discussed, a semiorthotopic transplantation model is introduced as an in vivo model for dental pulp regeneration, and finally, different animal models used for in vivo orthotopic investigations are presented.

Human Amnion Epithelial Cells: A Potential Cell Source for Pulp Regeneration?

The aim of this study was to analyze the suitability of pluripotent stem cells derived from the amnion (hAECs) as a potential cell source for revitalization in vitro. hAECs were isolated from human placentas, and dental pulp stem cells (hDPSCs) and dentin matrix proteins (eDMPs) were obtained from human teeth. Both hAECs and hDPSCs were cultured with 10% FBS, eDMPs and an osteogenic differentiation medium (StemPro). Viability was assessed by MTT and cell adherence to dentin was evaluated by scanning electron microscopy. Furthermore, the expression of mineralization-, odontogenic differentiation- and epithelial–mesenchymal transition-associated genes was analyzed by quantitative real-time PCR, and mineralization was evaluated through Alizarin Red staining. The viability of hAECs was significantly lower compared with hDPSCs in all groups and at all time points. Both hAECs and hDPSCs adhered to dentin and were homogeneously distributed. The regulation of odontoblast differentiation- and mineralization-associated genes showed the lack of transition of hAECs into an odontoblastic phenotype; however, genes associated with epithelial–mesenchymal transition were significantly upregulated in hAECs. hAECs showed small amounts of calcium deposition after osteogenic differentiation with StemPro. Pluripotent hAECs adhere on dentin and possess the capacity to mineralize. However, they presented an unfavorable proliferation behavior and failed to undergo odontoblastic transition.

Experimental study on the biocompatibility and osteogenesis induction ability of PLLA/DDM scaffolds

To investigate the characterization and function of a novel porous osteogenic material (PLLA / DDM) containing polylactic acid and demineralized dentin matrix. The surface morphology and composition of the material were observed by SEM and EDS. The physical characteristics of the material were detected by roughness and water contact angle analyses. The rate of weight loss and change in the pH value of the material were observed by scaffold degradation experiments. Four types of material were investigated: polylactic acid (PLLA) scaffold, demineralized dentin matrix (DDM) particles, PLLA/DDM scaffold and a blank control. The osteogenic effect and osteogenic characteristics of the new materials were explored through in vivo and in vitro osteogenic experiments. SEM analysis showed that DDM powder was uniformly distributed in the polylactic acid scaffold, and the water contact angle revealed that the water absorption of the porous scaffold was improved after the addition of DDM powder. The EDS results showed that the peak values of calcium and phosphorus were obviously increased after the addition of DDM powder, and the porosity test showed that the scaffold had higher porosity after the addition of DDM powder. Scaffold degradation experiments revealed that the scaffold gradually degraded with increasing time, and its pH value slightly increased. The results of cell culture and animal model experiments showed that the porous PLLA/DDM scaffold had good bio-compatibility and promoted cell proliferation and differentiation. In histological and micro-CT evaluations, the material showed good bio-compatibility, biodegradability and bone conductivity with host bone tissue in vivo. PLLA / DDM hybrid showed better performance than PLLA or DDM. The biocompatibility and cell growth promoting properties were stronger than those of single material.

Vibrational Imaging Techniques for the Characterization of Hard Dental Tissues: From Bench-Top to Chair-Side

Currently, various analytical techniques, including scanning electron microscopy, X-Ray diffraction, microcomputed tomography, and energy dispersive X-ray spectroscopy, are available to study the structural or elemental features of hard dental tissues. In contrast to these approaches, Raman Microspectroscopy (RMS) has the great advantage of simultaneously providing, at the same time and on the same sample, a morpho-chemical correlation between the microscopic information from the visual analysis of the sample and its chemical and macromolecular composition. Hence, RMS represents an innovative and non-invasive technique to study both inorganic and organic teeth components in vitro. The aim of this narrative review is to shed new light on the applicative potential of Raman Microspectroscopy in the dental field. Specific Raman markers representative of sound and pathological hard dental tissues will be discussed, and the future diagnostic application of this technique will be outlined. The objective and detailed information provided by this technique in terms of the structure and chemical/macromolecular components of sound and pathological hard dental tissues could be useful for improving knowledge of several dental pathologies. Scientific articles regarding RMS studies of human hard dental tissues were retrieved from the principal databases by following specific inclusion and exclusion criteria.