Bioassays to Evaluate Cellular Response to Dental Resins
with Continuous Gradients in Vinyl Conversion
Nancy J. Lin, LeeAnn O. Bailey, Lori A. Henderson
Biomaterials Group, Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD
In this study, bioassays were applied to examine cells cultured directly on polymeric dental materials. Our objective was to fabricate continuous gradient polymer samples and establish corresponding bioassays to rapidly screen cell response as a function of degree of conversion.
Photoactivated dental resins were prepared using 2,2-bis[p-(2’-hydroxy-3’-methacryloxypropoxy)phenyl]propane (BisGMA) and triethylene glycol dimethacrylate (TEGDMA). Continuous gradients in the degree of conversion were fabricated by curing samples off-centered in a visible-light curing unit. The resulting conversion profiles, determined using near-infrared spectroscopy, depended upon the intensity and duration of light exposure. Samples chosen for cell studies were irradiated for 40 s and had a vinyl conversion ranging from 43.0 % ± 1.7 % to 61.2 % ± 0.7 %.
Resins were sterilized, aged for 7 d in saline solution at 37 °C, and seeded with Raw 264.7 macrophages, a cell type involved in inflammation. Tissue culture polystyrene was also seeded as a control. After 24 h, viability and apoptosis were assessed using fluorescence microscopy. Gene expression of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), two inflammatory cytokines, was evaluated using quantitative, real-time reverse transcription-polymerase chain reaction. As the conversion increased, cell viability increased and apoptosis decreased, while TNF-α gene expression did not change significantly. As the conversion decreased, IL-1β expression decreased slightly but not significantly, with the lowest conversion of 45 % showing no detectable expression. Reduced IL-1β expression at lower conversions may have resulted from the compromised state of the cells and may indicate a reduced ability to respond to environmental challenges.
The continuous variable gradient approach is feasible and efficient for screening biological effects arising from differences in resin conversion levels. The techniques described herein are also adaptable for other dental materials and gradient surfaces.
Name: Nancy J. Lin
Mentor: Francis Wang
Division: Polymers Division (854)
Laboratory: Materials Science and Engineering Laboratory (MSEL)
Location: Room A105, Bldg 224, MS 8543
Phone: (301) 975-4935
Fax: (301) 975-4977
Sigma Xi: Not a member