Dental restorative materials have advanced rapidly in recent years, with light-cured composite resins becoming widely used in clinics due to their convenience and aesthetic appeal. However, these materials contain photoinitiators like camphorquinone (CQ) that don't fully participate in the polymerization process during curing. Residual CQ may leach from the material, permeate surrounding tissues, and potentially cause adverse biological reactions - particularly when in direct contact with dental pulp.
This study investigates how CQ affects dental pulp stem cells (DPSCs), focusing on cell viability, cytokine secretion, and odontogenic differentiation capacity to reveal potential mechanisms behind CQ-induced pulp inflammation and dysfunction.
The research employed an in vitro experimental model, treating DPSCs with varying CQ concentrations to assess:
- Cell culture: DPSCs were isolated from human dental pulp tissue, with MC3T3-E1 cells serving as controls for odontoblast differentiation modeling.
- Proliferation and cell cycle analysis: Cell counting and flow cytometry evaluated CQ's impact on DPSC proliferation, while examining expression levels of cell cycle regulators p16(INK4A), p21(WAF1), and p53 - key proteins in cellular senescence and cycle arrest.
- Inflammatory cytokine detection: ELISA measured levels of pro-inflammatory cytokines (IL-6, IL-8) and matrix metalloproteinase-3 (MMP3) in culture supernatants - crucial mediators of inflammatory responses.
- Odontoblast differentiation assessment: Alkaline phosphatase (ALP) activity, alizarin red staining, and gene expression analysis (DSPP, OCN) evaluated CQ's effects on odontogenic differentiation. Alizarin red staining assessed extracellular matrix mineralization, while ALP activity served as an early differentiation marker.
The results demonstrate significant CQ effects on DPSC biological behavior:
- Inhibited proliferation and induced cell cycle arrest: CQ treatment markedly suppressed DPSC proliferation while upregulating p16, p21, and p53 expression - suggesting activation of cellular senescence pathways.
- Increased inflammatory cytokine secretion: CQ-treated DPSCs showed elevated IL-6, IL-8, and MMP3 levels, indicating potential induction of pulp inflammation. MMP3 participates in extracellular matrix degradation during inflammation and tissue remodeling.
- Impaired odontogenic differentiation and mineralization: CQ reduced ALP activity, decreased alizarin red staining, and suppressed DSPP and OCN expression in both DPSCs and MC3T3-E1 cells, suggesting compromised odontoblast differentiation and mineralization capacity.
These findings suggest residual CQ from dental composites may exert toxic effects on pulp tissue by inhibiting DPSC proliferation and differentiation while promoting inflammation.
Cellular toxicity mechanisms: CQ-induced cell cycle arrest and senescence may stem from DNA damage or oxidative stress pathway activation.
Pulp inflammation: CQ-triggered cytokine release could activate immune cells, potentially leading to chronic inflammation, tissue damage, and pulpitis.
Dentin repair implications: As odontoblasts mediate dentin repair, CQ's differentiation-suppressing effects might impair pulp's regenerative capacity, increasing risks of dentin hypersensitivity and pulp disease.
The study highlights the need to minimize CQ residues in dental restorations and develop safer photoinitiators. Future research should further investigate CQ's toxicity mechanisms and develop protective measures for pulp health.
Clinicians should understand composite resin components and potential risks, selecting appropriate materials and following protocols to reduce CQ release. For deep caries cases, special attention should be paid to pulp protection through conservative preparation and biocompatible base materials to minimize direct pulp irritation.
