The Role of Dendritic Cells during Physiological and Pathological Dentinogenesis

The dental pulp is a soft connective tissue of ectomesenchymal origin that harbors distinct cell populations, capable of interacting with each other to maintain the vitality of the tooth. After tooth injuries, a sequence of complex biological events takes place in the pulpal tissue to restore its homeostasis. The pulpal response begins with establishing an inflammatory reaction that leads to the formation of a matrix of reactionary or reparative dentin, according to the nature of the exogenous stimuli. Using several in vivo designs, antigen-presenting cells, including macrophages and dendritic cells (DCs), are identified in the pulpal tissue before tertiary dentin deposition under the afflicted area. However, the precise nature of this phenomenon and its relationship to inherent pulp cells are not yet clarified. This literature review aims to discuss the role of pulpal DCs and their relationship to progenitor/stem cells, odontoblasts or odontoblast-like cells, and other immunocompetent cells during physiological and pathological dentinogenesis. The concept of “dentin-pulp immunology” is proposed for understanding the crosstalk among these cell types after tooth injuries, and the possibility of immune-based therapies is introduced to accelerate pulpal healing after exogenous stimuli.

Biomineralization of Dental Tissues Treated with Silver Diamine Fluoride

Silver diamine fluoride (SDF) is a dental biomaterial used to arrest dental caries. To better understand SDF’s mechanism of action, we examined the localization of silver within the tissues of SDF-treated teeth. Carious primary teeth fixed within 2 min of SDF application (SDF-minutes, n = 3), at 3 wk after SDF application in vivo (SDF-weeks, n = 4), and at 2 y after multiple SDF applications in vivo (SDF-multiple, n = 1) were investigated in this study. Carious primary teeth without SDF application (no-SDF, n = 3) served as controls. Mineral density and structural analyses were performed via micro–X-ray computed tomography and scanning electron microscopy. Elemental analyses were performed through X-ray fluorescence microprobe and energy-dispersive X-ray spectroscopic techniques. SDF-treated teeth revealed higher X-ray–attenuated surface and subsurface regions within carious lesions, and similar regions were not present in no-SDF teeth. Regions of higher mineral density correlated with regions of silver abundance in SDF-treated teeth. The SDF penetration depth was approximated to 0.5 ± 0.02 mm and 0.6 ± 0.05 mm (mean ± SD) for SDF-minutes and SDF-weeks specimens, respectively. A higher percentage of dentin tubular occlusion by silver or calcium phosphate particles was observed in primary teeth treated with SDF-weeks as compared with SDF-minutes. Elemental analysis also revealed zinc abundance in carious lesions and around the pulp chamber. SDF-weeks teeth had significantly increased tertiary dentin than SDF-minutes and no-SDF teeth. These results suggest that SDF treatment on primary teeth affected by caries promotes pathologic biomineralization by altering their physicochemical properties, occluding dentin tubules, and increasing tertiary dentin volume. These seemingly serendipitous effects collectively contribute to the cariostatic activity of SDF.

Evaluating the potential of an amelogenin-derived peptide in tertiary dentin formation

Several novel biomaterials have been developed for dental pulp capping by inducing tertiary dentin formation. The aim of this study was to evaluate the effect of QP5, an amelogenin-based peptide, on the mineralization of dental pulp cells (DPCs) in vitro and in vivo. The cell viability of human DPCs (hDPCs) after treatment with QP5 was determined using the Cell Counting Kit-8 (CCK-8). Migration of hDPCs was assessed using scratch assays, and the pro-mineralization effect was determined using alkaline phosphatase (ALP) staining, alizarin red staining and the expression of mineralization-related genes and proteins. The results showed that QP5 had little effect on the cell viability, and significantly enhanced the migration capability of hDPCs. QP5 promoted the formation of mineralized nodules, and upregulated the activity of ALP, the expression of mRNA and proteins of mineralization-related genes. A pulp capping model in rats was generated to investigate the biological effect of QP5. The results of micro-computed tomography and haematoxylin and eosin staining indicated that the formation of tertiary dentin in QP5-capping groups was more prominent than that in the negative control group. These results indicated the potential of QP5 as a pulp therapy agent.

Tertiary dentin deposition in the proximity of the cervical perforation aperture – A case study

Dead tracts are dentin areas characterized by degenerated odontoblastic processes; may result from injury caused by caries, attrition, erosion, or cavity preparation. Odontoblasts can also form tertiary dentin, as a response to injury, in association with caries, trauma, or restorative procedures. Generally, this dentin is less organized than primary and secondary dentin and mostly localized to the site of injury. The reactive dentin formation that lays under caries, the pulp displays chronic inflammation and tertiary dentinogenesis takes place on the inner walls of the pulp space, in the region of the dentinal tubules associated with the base of the carious lesion. Higher-power photomicrograph of tertiary dentin shown in a primary dentin, first period of tertiary dentin formation, second period of tertiary dentin formation. We initiated a case study regarding depositition of tertiary dentin in the close proximity of the cervical perforation hole on mesial root of the second maxillary molar. The repair material used (Biodentine, Septodont) was found placed under the tertiary dentin layer, rather than at the perforation place, mentioning the fact that the group of residents was not experienced with the management of the endodontic microscope and did not use a proper field. We consider that we have identified dead tracts due to the fact that they were formed consequently carious lesions pathology, thereafter the tertiary dentin at the appearance of the coronal aspect was identified at the end of the dead tracts. The portion of the canal entrances were investigated both with analyzed filters (Crossed Polars) and with compensatory devices (retardation plates). The present study identified tertiary dentine deposits in the coronary portion of the adjacent root canal entered in the perforation. At a thorough analysis of the coronal portions of the mesial root canal with compensating devices and analyzers filters, it was noticed a soft dentin blanket in which the dentinary tubules do not exist or are of very rare deposition.

A microscopic study on the intercanalar isthmuses of the maxillary premolars and associated iatrogenic cracks

The purpose of this microscopic investigation, using stereomicroscopy and light transmited microscopy was to evaluate the configuration of the endodontic treated maxillary premolars, making correlations between the presence of the intercanalar isthmuses and also, to identify possible associated fracture lines. We also evaluated the thickness of the tertiary dentinal layer (irritation dentin layer). The study was based on microscopic investigation on thin sections on fragments or separate preparations resulting from 12 premolars that were clinically compromised. The tertiary dentin is deposited in response to irritations and moderate intensity injuries. As the tendency of crack propagation is directed to the areas corresponding to the root canal towards one of the root surfaces (which is the closest) the crackline – almost without exception, is more or less arched, without detecting an eventual crack in a straight line.

Midkine Promotes Odontoblast-like Differentiation and Tertiary Dentin Formation

Autophagy is an intracellular self-degradation process that is essential for tissue development, cell differentiation, and survival. Nevertheless, the role of autophagy in tooth development has not been definitively identified. The goal of this study was to investigate how autophagy is involved in midkine (MK)–mediated odontoblast-like differentiation, mineralization, and tertiary dentin formation in a mouse tooth pulp exposure model. In vitro studies show that MK and LC3 have similar expression patterns during odontoblast-like cell differentiation. Odontoblast-like cell differentiation is promoted through MK-mediated autophagy, which leads to increased mineralized nodule formation. Subcutaneous transplantation of hydroxyapatite/tricalcium phosphate with rMK-treated human dental pulp cells led to dentin pulp–like tissue formation through MK-mediated autophagy. Furthermore, MK-mediated autophagy induces differentiation of dental pulp cells into odontoblast-like cells that form DSP-positive tertiary dentin in vivo. Our findings may provide 1) novel insight into the role of MK in regulating odontoblast-like differentiation and dentin formation in particular via autophagy and 2) potential application of MK in vital pulp therapy.

Performance of a Biodegradable Composite with Hydroxyapatite as a Scaffold in Pulp Tissue Repair

Vital pulp therapy is an important endodontic treatment. Strategies using growth factors and biological molecules are effective in developing pulp capping materials based on wound healing by the dentin-pulp complex. Our group developed biodegradable viscoelastic polymer materials for tissue-engineered medical devices. The polymer contents help overcome the poor fracture toughness of hydroxyapatite (HAp)-facilitated osteogenic differentiation of pulp cells. However, the composition of this novel polymer remained unclear. This study evaluated a novel polymer composite, P(CL-co-DLLA) and HAp, as a direct pulp capping carrier for biological molecules. The biocompatibility of the novel polymer composite was evaluated by determining the cytotoxicity and proliferation of human dental stem cells in vitro. The novel polymer composite with BMP-2, which reportedly induced tertiary dentin, was tested as a direct pulp capping material in a rat model. Cytotoxicity and proliferation assays revealed that the biocompatibility of the novel polymer composite was similar to that of the control. The novel polymer composite with BMP-2-induced tertiary dentin, similar to hydraulic calcium-silicate cement, in the direct pulp capping model. The BMP-2 composite upregulated wound healing-related gene expression compared to the novel polymer composite alone. Therefore, we suggest that novel polymer composites could be effective carriers for pulp capping.

Estimation of tertiary dentin thickness on pulp capping treatment with digital image processing technology

Dentists usually observe the tertiary dentin formation after pulp capping treatment by comparing periapical radiograph before and after treatment visually. However many dentists find difficulties to observe tertiary dentin and also they can’t measure exactly the thickness of the tertiary dentin. The aims of this study is to assist the dentists to measure the area of tertiary dentin and calculate the dentin formation using b-spline image processing. The dental radiograph of 38 patients of pulp capping in the Dental Hospital Universitas Muhammadiyah Yogyakarta, Indonesia. Each of patient visited dental hospital 3 times. First, the patient got an application of pulp capping material. Second, after one-week treatment and temporary restoration and the third, after more than one month with the composite as the final restoration. Every visited the patient take a radiograph. Dentist placed the dot from the patient's radiograph. The dots were combined and processed with digital image processing. The b-spline method changed the dot to one area. After the calculation, the dentist can see whether there was dentin formation which means it is one of the treatment success indicators. Dentist has the better view to measure the dentin formation by providing area value of its tertiary dentin thickness calculation. We compare the result to the program calculation using the b-spline method and visual observation from the dentist. This study indicated the thickness of tertiary dentin can be measured by this program with an accuracy of 94.2%. Therefore, dentist can make tertiary dentin thickness prediction from patient’s radiograph.