Synthesis and properties of liquid crystalline urethane methacrylates for dental composite applications

Abstract

Three novel liquid crystalline methacrylates have been synthesized and characterized to be tested as comonomers in light‐curing dental resin‐based composites. The selected formulations consist of an alkylammonium or cholesteryl urethane methacrylate and 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloyloxypropyl)phenyl]propane (BisGMA) or a BisGMA derivate modified with urethane methacrylate groups, further diluted with triethyleneglycol dimethacrylate (TEGDMA) and reinforced with 70% filler (zirconium silicate nanopowder, silanized filler). This study addresses the relationships between the LC monomer structure, photopolymerization rates (by differential scanning photo calorimetry), and specific properties of the dental resin composites (volumetric shrinkage, water sorption, water solubility, and hydrophobicity). The investigation of LC properties by differential scanning calorimetry and polarizing microscopy indicated that the LC mesophase is stable to room temperature (cationic monomers) or at 40 °C (cholesteryl methacrylate). It was found that the polymerization rate for LC urethane methacrylates used in combination with BisGMA/TEGDMA (0.122–0.136 s−1) is higher than that of the mesogenic monomers alone (0.085–0.107 s−1). The structures of the urethane monomers and, consequently, the viscosity of the comonomer mixture influence both the rate and the degree of conversion (44.8–67.5 %) of the photopolymerization process. Polymerization shrinkage measured by pycnometry showed lower values for LC monomers (3.25–3.43 vol %) comparatively with the monomer mixture (5.19–6.65 vol %). Preliminarily, the effect of ammonium groups from two resin composites incorporating alkylammonium structures (4.5 wt %) was tested on Streptococcus mutans, and distinct zone of inhibition was observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Effect of cinnamate comonomers on the dental formulation properties

“…In spite of numerous advantages reported in the literature, the major deficiencies of such composites are still related to the high‐polymerization shrinkage (PS)7, 8 and incomplete polymerization of the monomers that cause, with time, a deterioration of the physical/mechanical properties in the final materials 9, 10. Further efforts were made to diminish the aforementioned drawbacks through the development of novel monomeric systems such as modified Bis‐GMA,3 liquid crystalline (LC) monomers,11–13 dendritic methacrylates,14 bis‐acrylamides,15 ormocers,16 or more recently, siloranes,17, 18 together with strongly acidic methacrylates that adhere on enamel and dentin 19. Other studies have been evaluated the family of urethane dimethacrylates (UDMAs) for their capability to improve the properties of dental restorative materials,20, 21 owing to the relatively high molecular weight, crosslinking density, and cohesive energy density generated by the urethane structure 22.…”

“…Within this context, several urethane (di)methacrylates have been developed in our group including the reactive acid‐functionalized oligomers24, 25 and nonacid ones,26 LC monomers,13 and Bis‐GMA analogous,13, 27 as well as photopolymerizable polyalkenoates,28 to investigate the influence of chemical structure and composition on the photopolymerization process in some dental formulations. Additionally, the study of the properties of photo‐cured networks resulted from the above monomers was essential to understand their behavior in such resin composites.…”

Recent advances in the development of dental composite resins

“…The larger free volume caused by the partial order within the liquid crystalline phase helps alleviate shrinkage during polymerisation. [38][39][40][41] The thiol-ene reaction has been proposed as an alternative to the more commonly-used radical polymerisation. Thiol-ene polymerisations proceed through a step growth mechanism, meaning that low molecular weight oligomers are produced in the initial stages of the reaction, which significantly delays gelation of the resin and reduces shrinkage.…”

Investigation of Thermal-Induced Changes in Molecular Order on Photopolymerization and Performance Properties of a Nematic Liquid-Crystal Diacrylate

“…The inherent order of monomers in the liquid crystalline phase may significantly alter the mechanisms of polymerization and affect the generated polymer networks. Increased polymerization rate [21][22][23][24][25] and reduced shrinkage [20,[26][27][28][29] have been observed in monomers polymerized in the nematic phase. In addition, tensile modulus is enhanced along the oriented polymer networks [30][31][32] and fracture toughness is improved if highly ordered smectic domains are formed during polymerization [33,34].These advantages of liquid crystal monomers are highly desirable in dental applications.…”