Dental pulp regeneration: In vitro and in vivo approaches

The impact of 3D-printed LAY-FOMM 40 and LAY-FOMM 60 on L929 cells and human oral fibroblasts

Objectives

LAY-FOMM is a promising material for FDA-approved Fused Deposition Modeling (FDM) applications in drug delivery. Here we investigated the impact on oral cells.

Materials and methods

We evaluated the impact of 3D-printed LAY-FOMM 40, LAY-FOMM 60, and biocompatible polylactic acid (PLA) on the activity of murine L929 cells, gingival fibroblasts (GF), and periodontal ligament fibroblasts (PDLF) using indirect (samples on cells), direct monolayer culture models (cells on samples), and direct spheroid cultures with resazurin-based toxicity assay, confirmed by MTT and Live-dead staining. The surface topography was evaluated with scanning electron microscopy.

Results

The materials LAY-FOMM 40 and LAY-FOMM 60 led to a reduction in resazurin conversion in L929 cells, GF, and PDLF, higher than the impact of PLA in indirect and direct culture models. Fewer vital cells were found in the presence of LAY-FOMM 40 and 60 than PLA, in the staining in both models. In the direct model, LAY-FOMM 40 and PLA showed less impact on viability in the resazurin-based toxicity assay than in the indirect model. Spheroid microtissues showed a reduction of cell activity of GF and PDLF with LAY-FOMM 40 and 60.

Conclusion

Overall, we found that LAY-FOMM 40 and LAY-FOMM 60 can reduce the activity of L292 and oral cells. Based on the results from the PLA samples, the direct model seems more reliable than the indirect model.

Clinical relevance

A material modification is desired in terms of biocompatibility as it can mask the effect of drugs and interfere with the function of the 3D-printed device.

The response of periodontal cells to kaolinite

OBJECTIVES

The impact of kaolinite on human periodontal cells is yet unknown. The aim of the study was to assess the response of human periodontal cells to kaolinite.

METHODS

Human periodontal cells were treated with kaolinite at reducing concentrations from 30 to 0.0015 mg/mL and with conditioned medium, which was depleted of kaolinite. Cell viability was evaluated with a resazurin-based toxicity assay, Live-Dead staining, and MTT assay and staining. The pro-angiogenic factors vascular endothelial growth factor (VEGF) and interleukin (IL)-6 and IL-8 were quantified via ELISA in periodontal fibroblasts. L-929, a standard cell-line used for cytotoxicity studies, served as control cell line. Composition of kaolinite was verified using energy-dispersive X-ray spectroscopy.

RESULTS

Kaolinite in suspension but not in conditioned medium impaired cell viability dose-dependently. VEGF, IL-6, and IL-8 production was not substantially modulated by kaolinite or the conditioned medium in periodontal cells.

CONCLUSION

Overall, kaolinite can decrease cell viability dose-dependently while conditioned medium showed no toxic effect. No pronounced impact of kaolinite on VEGF, IL-6, and IL-8 production was observed. This study provided first insights into the impact of kaolinite on human periodontal cells thereby inferring to the basis for the evaluation of kaolinite as a carrier in regenerative dentistry.

CLINICAL RELEVANCE

Kaolinite, a clay mineral, is successfully used in medicine due to its favorable properties. Also, applications in conservative dentistry are described. However, the response of oral cells to kaolinite is still unclear. Here, we assessed the impact of kaolinite on human periodontal cells.

Contraction dynamics of dental pulp cell rod microtissues

OBJECTIVES

The factors that contribute to the morphological changes of dental pulp cell-derived microtissues are unknown. Here, we investigated the contraction dynamics of rod-shaped microtissues derived from dental pulp cells and examined the underlying cell signaling pathways.

METHODS

Human dental pulp cells were seeded into agarose molds to assemble into rod-shaped microtissues. Resazurin- and tetrazolium-based cytotoxicity assays, Live/Dead staining, and hematoxylin and eosin staining for histological evaluation of rods were performed. Rod contraction was evaluated and measured for a period of 10 days. The role of TGF-β, phosphoinositide 3-kinase (PI3K)/AKT, and mitogen-activated protein kinase (MAPK) signaling pathway was analyzed.

RESULTS

Dental pulp cells readily assembled into rods, maintaining the geometric shape for 48 h. Following this period, they condensed to form stable spheroidal structures that remained vital for 10 days from seeding. Inhibition of phosphoinositide 3-kinase signaling pathway by LY294002 significantly prolonged the diminution in the length of rods formed by dental pulp cells. TGF-β and pharmacological inhibition of TGF-β signaling did not show pronounced effects.

CONCLUSION

Overall, dental pulp cells readily formed rod-shaped patterns of microtissues which, over a period of time, condensed into more stable spheroidal structures. Hence, technologies like bioprinting, using direct fabrication of microtissues need to consider the contraction dynamics.

CLINICAL RELEVANCE

The field of regenerative endodontology will benefit from our findings as it can be applied as a novel platform to test the impact of pharmacological agents, biomaterials, and regenerative approaches including bioprinting.

Evaluation of Resins for Stereolithographic 3D-Printed Surgical Guides: The Response of L929 Cells and Human Gingival Fibroblasts

Additive manufacturing is becoming increasingly important in dentistry for the production of surgical guides. The development of cost-effective desktop stereolithography (SLA) printing systems and the corresponding resins makes this novel technique accessible to dental offices and dental laboratories. The aim of the study was to reveal the response of soft tissue cells to Clear and Dental SG resins used in desktop SLA printing systems at different stages of processing. Cell activity of L929 cells and gingival fibroblasts (GF) in response to the materials was examined in indirect and direct monolayer culture models and a direct spheroid culture model based on MTT, resazurin-based toxicity assays, and live-dead staining. Overall we found that the impact of Clear and Dental SG resins on L929 and GF depends on the processing stage of the materials. Liquid Clear resin induced a stronger reduction of cell activity compared to Dental SG resin. Printing and postcuring reduced the impact on cell activity and viability. As in-house 3D printing for surgical guides is getting integrated in the digital workflow, our data suggest that careful adherence to processing guidelines-especially postcuring-is of clinical relevance.

Formation of spheroids by dental pulp cells in the presence of hypoxia and hypoxia mimetic agents

AIM

To evaluate the impact of hypoxia and hypoxia mimetic agents (HMA) on the formation and activity of spheroids by dental pulp cells (DPC).

METHODOLOGY

DPC on agarose-coated plates were treated with hypoxia and the HMA dimethyloxallyl glycine (DMOG), desferrioxamine (DFO) and L-mimosine (L-MIM). Images of spheroids were taken directly after seeding and at 6 h and 24 h. Spheroid sizes were quantified by area measurement with ImageJ software. Viability was assessed with Live-Dead staining, MTT and resazurin-based toxicity assay. Production of VEGF, IL-8 and SDF-1 was evaluated using immunoassays. Data were analysed using Kruskal-Wallis test and post hoc Mann-Whitney U-test.

RESULTS

DPC formed spheroids in the presence of hypoxia, HMA and combined treatment with hypoxia and HMA. No pronounced difference in spheroid size was found in the groups treated with hypoxia, DMOG, DFO, L-MIM and the combination of hypoxia and the HMA relative to their normoxic controls (P > 0.05). Spheroids appeared vital in Live-Dead and MTT staining and the resazurin-based toxicity assay. Evaluation of protein production with immunoassays revealed significantly enhanced levels of VEGF and IL-8 (P < 0.05), but there was no significant effect on SDF-1 production (P > 0.05). Treatment with a combination of hypoxia and HMA did not further boost VEGF and IL-8 production (P > 0.05).

CONCLUSIONS

Pre-conditioning with hypoxia and HMA increased the pro-angiogenic capacity of spheroids whilst not interfering with their formation. Pre-clinical studies will reveal whether pre-conditioning of spheroids with hypoxia and HMA can effectively improve the efficiency of cell transplantation approaches for regenerative endodontics.