GaAlAs laser-induced pulp mineralization involves dentin matrix protein 1 and osteopontin expression

Establishment of Pulp Damage Repair Models in Miniature Pigs Using Diode Lasers

Objective: To establish a controlled pulp damage repair model in miniature pigs by using a diode laser. Background: Laser is a novel kind of controllable energy, and it is widely used in dentistry. Methods: The premolars of four 24- to 28-month-old miniature pigs were divided into three laser groups, according to the output powers of a diode laser, and the nonirradiated first molars acted as controls. The teeth in laser groups were irradiated under three parameters (output powers 1.5, 2.5, 4 W, continuous wave, frequency 50 Hz for 60 sec). The dental and gingival morphology was observed at 0, 7, 14, and 21 days after laser irradiation. The animals were sacrificed for qualitative and quantitative pulp histopathological analysis. Results: The three laser groups present no seriously irreversible dental and gingival damage. In the 1.5-W group, dental pulp exhibited angiectasis and hyperemia with no inflammation, and did not significantly differ with the control groups at 21 days (p > 0.05). In the 2.5-W group, pulpal inflammation was highest at 7 days and then decreased significantly at 21 days, and the tissue repair appeared at 14 days (p < 0.05). In the 4-W group, pulpal inflammation was significantly highest at 7 days, with an increase in the degree of tissue repair (p < 0.05). Conclusions: The output power of 1.5 W developed a reversible pulpitis model; the output powers of 2.5 and 4 W within 7 days led to the development of irreversible pulpitis models, which proceeded as chronic pulpitis with obvious tissue repair.

Reactions of dental pulp to hydrogen peroxide photolysis-based antimicrobial chemotherapy under ultraviolet-A irradiation in rats

Hydrogen peroxide photolysis-based antimicrobial chemotherapy that utilizes ultraviolet-A irradiation (UVA-H₂O₂ photolysis) has been previously proposed as a method of treatment of cariogenic biofilm. Therefore, in the present study, we aimed to assess time-dependent reactions in the dental pulp of rats after UVA-H₂O₂ photolysis. Maxillary first molars were treated. UVA irradiation (wavelength: 365 nm) with 3 wt% H₂O₂ was performed for 90 s at a radiant emittance of 500-2000 mW/cm² on the rats for 3 consecutive days or only 1 day. The animals were sacrificed at Days 1, 3, 7, and 21 after the treatment for the histological evaluation of inflammatory cells and immunohistochemistry of heat shock protein (HSP)-25, a marker of odontoblasts. Tertiary dentin formation was evaluated at Day 21 by histomorphometry and micro-CT analysis. UVA-H₂O₂ photolysis elicited little infiltration of inflammatory cells, but disturbances in the odontoblast layer and/or presence of localized degenerative tissue were observed on Day 3. This condition was followed by a healing process that was characterized by the reappearance of HSP-25 positive odontoblast-like cells at Day 7 and tertiary dentin formation at Day 21. The amount of tertiary dentin formed was dependent on the intensity of treatment; repeated UVA irradiations of H₂O₂ at 2000 mW/cm² resulted in the largest amount of tertiary dentin formation at the pulp horn regions. Our findings suggest that UVA-H₂O₂ photolysis treatment can be used to treat dental caries clinically because the post-treatment inflammatory reaction was minimal and tertiary dentin formation was substantial, which may prove effective in protecting dental pulp from external irritants. As a cautionary consideration, the radiant emittance of the UVA irradiation should be carefully optimized before clinical application.

Resveratrol rescues TNF‑α‑induced inhibition of osteogenesis in human periodontal ligament stem cells via the ERK1/2 pathway

Periodontitis is a common inflammatory disorder affecting the tissues surrounding the teeth, which can lead to the destruction of periodontal tissue and tooth loss. Resveratrol, a natural phytoalexin, exerts multiple biological effects. For example, its anti-inflammatory activity has been widely studied for the treatment of inflammatory bowel disease for a number of years. However, its effect on bone repair and new bone formation in an inflammatory microenvironment is not well understood. Accordingly, the effect of resveratrol on inflammation-affected human periodontal ligament stem cells (hPDLSCs) requires further investigation. In the present study, the effect of tumor necrosis factor-α (TNF-α), resveratrol, or the combination of both on the osteogenic differentiation of hPDLSCs, as well as the underlying mechanisms involved, were investigated. Cell Counting Kit-8 assay, alkaline phosphatase staining, Alizarin red staining, Oil Red O staining, reverse transcription-quantitative PCR and western blotting were used in the present study. It was demonstrated that resveratrol enhanced hPDLSC osteogenesis and reversed the inhibitory effects of TNF-α on this process. Further mechanistic studies indicated that resveratrol exerted anti-inflammatory activity by activating the ERK1/2 pathway, decreasing the secretion of interleukin (IL)-6 and IL-8 induced by TNF-α, and enhancing hPDLSCs osteogenesis. The present study suggested that resveratrol may be a novel and promising therapeutic choice for periodontitis.

Dentin Matrix Protein 1 Compensates for Lack of Osteopontin in Regulating Odontoblastlike Cell Differentiation after Tooth Injury in Mice

INTRODUCTION

Although dentin matrix protein 1 (DMP1) and osteopontin (OPN) act as substrates and signaling molecules for odontoblastlike cell differentiation after tooth injury, the mutual interaction between these proteins in the mechanism of odontoblastlike cell differentiation remains to be clarified. This study aimed to elucidate the role of DMP1 and OPN in regulating odontoblastlike cell differentiation after tooth injury.

METHODS

A groove-shaped cavity was prepared on the mesial surface of the upper first molars in wild-type and Opn knockout (KO) mice. The demineralized paraffin sections were processed for immunohistochemistry for nestin and DMP1 and in situ hybridization for Dmp1. For the in vitro assay, the experiments of organ culture for evaluating dentin-pulp complex regeneration using small interfering RNA treatment were performed.

RESULTS

Once preexisting odontoblasts died, nestin-positive newly differentiated odontoblastlike cells were arranged along the pulp-dentin border and began to express DMP1/Dmp1. In Opn KO mice, the expression of DMP1/Dmp1 was up-regulated compared with that of wild-type mice. The in vitro assay showed that the gene suppression of Dmp1 by small interfering RNA showed a tendency to decrease the differentiation rate of odontoblastlike cells from 70.1% to 52.2% in wild-type teeth. In addition, the suppression of Dmp1 in Opn KO teeth tended to lead to the inhibition of odontoblastlike cell differentiation.

CONCLUSIONS

These results suggest that the expression of Dmp1 is up-regulated in Opn KO mice both in vivo and in vitro, and DMP1 compensates for the lack of OPN in regulating odontoblastlike cell differentiation after tooth injury.

Characterization of Odontoblast-like Cell Phenotype and Reparative Dentin Formation In Vivo: A Comprehensive Literature Review

INTRODUCTION

The primary aim was to explore the criteria used in characterization of reparative cells and mineralized matrices formed after treatment of pulp exposures, and the sequence of relative events. The secondary aim was to evaluate whether the reparative events depend on the experimental model species, age, and therapeutic intervention.

METHODS

A literature search of databases using different combinations of the key words was undertaken. Data analysis was based only on studies having histological or histochemical assessment of the pulp tissue responses. The search yielded 86 studies, 47 capping material-based and 39 bioactive application-based experiments, which provided data on morphological or functional characterization of the mineralized matrices and the associated cells.

RESULTS

In 64% of capping material-based and 72% of bioactive application-based experiments, a 2-zone mineralized matrix formation (atubular followed by tubular) was detected, whereas characterization of odontoblastic differentiation is provided in only 25.5% and 46.1% of the studies, respectively. In 93.3% of the studies showing odontoblast-like cells, differentiated cells were in association with tubular mineralized matrix formation. Analyses further showed that cell- and matrix-related outcomes do not depend on experimental model species, age, and therapeutic intervention.

CONCLUSIONS

The evidence of the reviewed scientific literature is that dental pulp cells secrete a dentin-like matrix of tubular morphology in relation to primitive forms of atubular or osteotypic mineralized matrix. Furthermore, data analysis showed that dental pulp cells express in vivo the odontoblastic phenotype, and secrete matrix in a predentin-like pattern, regardless of the model species, age, and therapeutic intervention used.

Effect of 1α, 25-dihydroxyvitamin D3 on the osteogenic differentiation of human periodontal ligament stem cells and the underlying regulatory mechanism

1α, 25-dihydroxyvitamin D3 (1,25-D3), an active vitamin D metabolite, is a well-known regulator of osteogenic differentiation. However, how 1,25-D3 regulates osteogenic differentiation in human periodontal ligament stem cells (hPDLSCs) remains to be fully elucidated. The present study aimed to clarify this issue through well-controlled in vitro experiments. After hPDLSCs were treated with 1,25-D3, immunofluorescence and western blotting were used to detect the expression of vitamin D receptor; Cell Counting Kit-8 and western blotting were used to assay the cell proliferation ability. Alkaline phosphatase staining, Alizarin Red staining and western blotting were used to detect the osteogenic differentiation. It was found that treating hPDLSCs with 1,25-D3: i) Inhibited cell proliferation; ii) promoted osteogenic differentiation; iii) upregulated the expression of transcriptional coactivator with PDZ-binding motif (TAZ), an important downstream effector of Hippo signaling that has been demonstrated to be involved in the osteogenic differentiation of stem/progenitor cells; and iv) that co-treatment of TAZ-overexpressing hPDLSCs with 1,25-D3 synergistically stimulated the expression of osteogenic markers. These results suggested that the induction of osteogenic differentiation promoted by 1,25-D3 in hPDLSCs involves, at least in part, the action of TAZ.

Effects of Er:YAG and Diode Laser Irradiation on Dental Pulp Cells and Tissues

Vital pulp therapy (VPT) is to preserve the nerve and maintain healthy dental pulp tissue. Laser irradiation (LI) is beneficial for VPT. Understanding how LI affects dental pulp cells and tissues is necessary to elucidate the mechanism of reparative dentin and dentin regeneration. Here, we show how Er:YAG-LI and diode-LI modulated cell proliferation, apoptosis, gene expression, protease activation, and mineralization induction in dental pulp cells and tissues using cell culture, immunohistochemical, genetic, and protein analysis techniques. Both LIs promoted proliferation in porcine dental pulp-derived cell lines (PPU-7), although the cell growth rate between the LIs was different. In addition to proliferation, both LIs also caused apoptosis; however, the apoptotic index for Er:YAG-LI was higher than that for diode-LI. The mRNA level of odontoblastic gene markers-two dentin sialophosphoprotein splicing variants and matrix metalloprotease (MMP)20 were enhanced by diode-LI, whereas MMP2 was increased by Er:YAG-LI. Both LIs enhanced alkaline phosphatase activity, suggesting that they may help induce PPU-7 differentiation into odontoblast-like cells. In terms of mineralization induction, the LIs were not significantly different, although their cell reactivity was likely different. Both LIs activated four MMPs in porcine dental pulp tissues. We helped elucidate how reparative dentin is formed during laser treatments.

The Crosstalk between HDPSCs and HUCMSCs on Proliferation and Osteogenic Genes Expression in Coculture System

Objectives: The present study established a non-contact coculture system in vitro, aiming to investigate the crosstalk between human dental pulp stem cells (hDPSCs) and human umbilical cord mesenchymal stem cells (hUCMSCs) on proliferation activity and osteogenic genes expression through paracrine. Materials and methods: The stemness of hDPSCs and hUCMSCs were identified by flow cytometric analysis and multipotential differentiation assays. With the help of transwell inserts, the non-contact coculture system in vitro was established between hDPSCs and hUCMSCs. EdU labeling analysis and Western Blot were used to detect the proliferation activity. The mRNA and protein levels of osteogenic genes were evaluated by RT-PCR and Western Blot. The expression of elements in Akt/mTOR signaling pathway were detected by Western Blot. Results: Both hDPSCs and hUCMSCs were positive to MSCs specific surface markers and had multi-differentiation potential. The proportion of EdU-positive cells increased and the expression of CDK6 and CYCLIN A were up-regulated in cocultured hDPSCs. Both prior coculture and persistent coculture improved mRNA and protein levels of osteogenic genes in hDPSCs. While in cocultured hUCMSCs, no statistical differences were observed on proliferation and osteogenesis. The phosphorylation of Akt and mTOR was up-regulated in cocultured hDPSCs. Conclusions: The crosstalk between hDPSCs and hUCMSCs in coculture system increased the proliferation activity and enhanced osteogenic genes expression in hDPSCs. Akt/mTOR signaling pathway might take part in the enhancing effects in both cell proliferation and gene expression.