Synthesis and characterization of dimethacrylates containing quaternary ammonium functionalities for dental applications.

OBJECTIVES: The widespread incidence of recurrent caries highlights the need for improved dental restorative materials. The objective of this study was to synthesize low viscosity ionic dimethacrylate monomers (IDMAs) that contain quaternary ammoniums groups (antimicrobial functionalities) and are compatible with existing dental dimethacrylate-based monomers. Such monomers have the potential to copolymerize with other methacrylate monomers and produce antibacterial polymers. METHODS: Two monomers (IDMA-1 and IDMA-2) were synthesized using the Menschutkin reaction and incorporated at 0-30% (by mass) into a 1:1 (by mass) bisphenol A glycerolate dimethacrylate (BisGMA):triethylene glycol dimethacrylate (TEGDMA) resin. Resin viscosity was quantified using rheology, and polymer degree of conversion (DC) and surface charge density were measured using Fourier transform infrared spectroscopy (FTIR) and fluorescein binding, respectively. Effects of IDMA-1 on initial attachment of Streptococcus mutans and on viability and metabolic activity (via reductase enzymes) of RAW 264.7 macrophage-like cells were quantified. RESULTS: IDMA-1 and IDMA-2 were prepared and characterized. IDMA-1 was miscible with BisGMA:TEGDMA and slightly increased the resin viscosity and DC. As expected, polymeric surface charge density increased with increasing IDMA-1. Incorporation of 10% IDMA-1 into BisGMA:TEGDMA reduced bacterial colonization without affecting viability or metabolic activity of mammalian cells. Increasing IDMA-1 up to 30% had no additional effect on bacterial coverage, but ≥20% IDMA-1 significantly reduced macrophage density, viability, and metabolic activity. Leachables from polymers containing IDMA-1 were not cytotoxic. SIGNIFICANCE: The Menschutkin reaction provides a facile, convenient means to synthesize new monomers with quaternary ammonium groups for dental and medical applications.

Effect of ethyl-alpha-hydroxymethylacrylate on selected properties of copolymers and ACP resin composites.

There is an increased interest in the development of bioactive polymeric dental composites and related materials that have potential for mineralized tissue regeneration and preservation. This study explores how the substitution of ethyl alpha-hydroxymethylacryate (EHMA) for 2-hydroxyethyl methacrylate (HEMA) in photo-activated 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenyl]propane (Bis-GMA) and Bis-GMA/tri(ethylene glycol) dimethacrylate (TEGDMA) resins affected selected physicochemical properties of the polymers and their amorphous calcium phosphate (ACP) composites. Rate of polymerization and the degree of conversion (DC) of polymers {EHMA (E), HEMA (H), Bis-GMA/EHMA (BE), Bis-GMA/HEMA (BH), Bis-GMA/TEGDMA/EHMA (BTE) and Bis-GMA/TEGDMA/HEMA (BTH)} were assessed by photo-differential scanning calorimetry and Fourier-Transform Infrared (FTIR) spectroscopy. ACP/BTE and ACP/BTH composites were evaluated for DC, biaxial flexure strength (BFS), water sorption (WS) and mineral ion release. Mid-FTIR and near-IR measurements revealed the following order of decreasing DC: [E, H polymers (97.0%)] > [BE copolymer (89.9%)] > [BH copolymer (86.2%)] > [BTE, BTH copolymers (85.5%)] > [ACP/BTH composite (82.6%)] > [ACP/BTE composite (79.3%)]. Compared to HEMA, EHMA did not adversely affect the BFS of its copolymers and/or ACP composites. Lower WS of BTE copolymers and composites (28% and 14%, respectively, compared to the BTH copolymers and composites) only marginal reduced the ion release from ACP/BTE composites compared to ACP/BTH composites. More hydrophobic ACP composites with acceptable ion-releasing properties were developed by substituting the less hydrophilic EHMA for HEMA.

Chemistry of Silanes: Interfaces in Dental Polymers and Composites.

The performance and service life of glass-or ceramic-filled polymeric composites depend on the nature of their resin, filler and interfacial phases as well as the efficacy of the polymerization process. The synergy that exists between the organic polymer matrix and the usually inorganic reinforcing filler phase is principally mediated by the interfacial/interphasial phase. This latter phase develops as a result of the dual reactivity of a silane coupling agent, (YRSiX3), a bifunctional molecule capable of reacting with the silanol groups of glass or ceramic fillers via its silane functional group (-SiX3) to form Si-O-Si- bonds to filler surfaces, and also with the resin phase by graft copolymerization via its Y functional group, usually a methacrylic vinyl group. In this paper, we explore some of the chemistry of organosilanes, especially that of functional organosilanes (or silane coupling agents as they are commonly known) that are used to mediate interfacial bonding in mineral reinforced polymeric composites. The chemistry of organosilanes can be quite complex involving hydrolytically initiated self-condensation reactions in solvents (including monomers) that can culminate in polymeric silsesquioxane structures, exchange reactions with hydroxylated or carboxylated monomers to form silyl ethers and esters, as well as the formation of silane derived interfaces by adhesive coupling with siliceous mineral surfaces.

Preparation and Comprehensive Characterization of a Calcium Hydroxyapatite Reference Material.

Numerous biological and chemical studies involve the use of calcium hydroxyapatite (HA), Ca10(PO4)6(OH)2. In this study detailed physicochemical characterization of HA, prepared from an aqueous solution, was carried out employing different methods and techniques: chemical and thermal analyses, x-ray diffraction, infrared and Raman spectroscopies, scanning and transmission microscopies, and Brunauer, Emmett, and Teller (BET) surface-area method. The contents of calcium (Ca(2+)), phosphate (PO4 (3-)), hydroxide (OH(-)), hydrogenphosphate (HPO4 (2-)), water (H2O), carbonate (CO3 (2-)), and trace constituents, the Ca/P molar ratio, crystal size and morphology, surface area, unit-cell parameters, crystallinity, and solubility of this HA were determined. This highly pure, homogeneous, and highly crystalline HA is certified as a National Institute of Standards and Technology (NIST) standard reference material, SRM 2910.

Synthesis, Characterization, and Crystal Structure of Dicalcium Glutarylbis(phosphonate) Dihydrate: A Covalently Pillared Layer Structure with the Potential for Epitaxial Growth on Hydroxyapatite.

A new bis(acylphosphonate), glutarylbis(phosphonate) (GlBP), was synthesized. Sodium and calcium salts of the GlBP, disodium dihydrogen glutarylbis(phosphonate), NaHO(3)PC(O)(CH(2))(3)C(O)PO(3)HNa, and dicalcium glutarylbis(phosphonate) dihydrate, Ca(2)[O(3)PC(O)(CH(2))(3)C(O)PO(3)].2H(2)O, were prepared and characterized by chemical analyses, thermogravimetry and Fourier transform infrared spectroscopy (FTIR). The crystal structure of the Ca salt was determined by single-crystal X-ray diffraction. The crystals are orthorhombic with a = 10.970(1) Å, b = 23.694(2) Å, c = 5.580(1) Å, space group Pnma, and Z = 4. This study provides the first example of a structure of a calcium complex involving a nongeminal bis(phosphonate). The structure can be described in terms of a covalently pillared layer-type arrangement of neutral Ca-GlBP-Ca units along the b-axis. Each oxygen atom of the phosphonate group is bonded to a different Ca ion, and each Ca in turn is linked to three phosphonate groups. The Ca octahedra and the phosphonate tetrahedra form a two-dimensional polar sheet perpendicular to the b-axis. The chelate bonds involving the keto groups appear to be important links in the stabilization of the structure and, in turn, to the biological activity of bis(acylphosphonates). A near-perfect lattice match, found between the Ca phosphonate layer and the major crystal faces of hydroxyapatite, indicates that epitaxial growth or incorporation of GlBP can occur on the apatitic surface which may be the mode of action in the inhibition of calcification.