Isothermal Monomer Conversion of Model Quaternary-Ammonium-Methacrylate (-Acrylate) Resins

Objectives: To determine monomer conversion of a range of quaternary ammonium-methacrylates (-acrylates) (QAMs) at 25°C. Methods: A range of commercial QAMs were added to co-monomer mixtures of TEGDMA (30 wt%), HEMA (10 wt%), and BisGMA (wt% varied) in water and rendered photocurable by addition of 1% wt TPO: ATA (acrylate) (5, 10, 15 wt%); MCMS (5, 10, 15 wt%), METMAC (5, 10, 15 wt%); MAPTAC 5 wt%, DDAC 5 wt%; a custom non-QAM control (NQC); and a commercial control (Scotchbond Multipurpose Adhesive bottle (SBMP) (3M ESPE). Abbreviations defined in J Dent Res 2011;90:525-540. Thin films of uncured fluid (≈160 microns) were placed on the diamond element of a horizontal attenuated total reflectance unit in a Fourier transform infrared spectrometer and heated to 25°C for 2 min prior to application of 60s light curing (Optillux 401, Kerr). Real-time spectra were obtained at 2cm^-1 resolution (1/s) and total conversion 600s following light application was determined using changes in absorption at 1318 cm^-1 (vinyl in-plane trans (=CH) rock. Five replications per test condition were made. Data were subjected to a 1-way ANOVA. All comparisons were made at a pre-set alpha of 0.05.  Results: ANOVA indicated failure of Shapiro-Wilk normality test, so Kruskal-Wallis 1-Way ANOVA on ranks was performed, with the Tukey post-host test. Table presents ranking of resin systems based on median conversion.

QAM-containing resin median conversions ranged from a low of 78.8% for METMAC 5% to a high of 91.0% for MCMS 15%. Increasing QAM content within a given resin type resulted in increased cure ranking. Median conversion of ATA 10%, DDAC 5%, ATA 15%, and MCMS 15% ranked higher than non-QAM commercial product (SBMP).

Conclusions: Isothermal monomer conversion of some model QAM-containing resins demonstrated significantly greater conversion than a commercial resin adhesive formulation. Increased QAM content resulted in higher median conversion.