Photopolymerized multifunctional (meth)acrylates as model polymers for dental applications

Area of Science:

• Polymer Chemistry
• Materials Science
• Biomaterials

Background:

• Dental restorative materials are susceptible to polymerization-induced volume shrinkage.
• This shrinkage can lead to marginal gaps, secondary caries, and restoration failure.
• Understanding factors influencing shrinkage is crucial for developing improved dental polymers.

Purpose of the Study:

• To investigate the volume shrinkage of various polymer networks used in dental applications.
• To determine the influence of monomer structure (e.g., pendant group size, molecular weight, acrylate vs. methacrylate) on volume shrinkage.
• To assess the effect of incident light intensity on polymerization shrinkage and rate.

Main Methods:

• Photopolymerization of several acrylate and methacrylate monomers (e.g., EGDMA, TEGDMA, Photomers) initiated by 2,2-dimethoxy-2-phenyl-acetophenone.
• Dilatometric technique to monitor volume shrinkage during UV polymerization.
• Varied incident light intensities from 1 mW cm⁻² to 20 mW cm⁻².
• Monomer extraction experiments to determine conversion rates.

Main Results:

• Volume shrinkage ranged from 3.5% to 13.5% depending on the monomer.
• Shrinkage decreased with increasing monomer rank and pendant group size.
• Methacrylate monomers exhibited lower volume shrinkage compared to acrylate monomers.
• Higher incident light intensity increased shrinkage rate but not significantly the total volume shrinkage.
• Calculated double bond conversion was low, but monomer unit conversion was significantly higher.

Conclusions:

• Monomer structure is a key determinant of volume shrinkage in dental photopolymers.
• Methacrylate-based systems offer potential advantages in reducing polymerization stress.
• Light intensity primarily affects the rate, not the extent, of shrinkage.
• Discrepancy between double bond and monomer unit conversion suggests network rearrangements or unreacted pendant groups.