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Polymerization with expansion in volume can be achieved with spiro orthocarbonate monomers through a double ring-opening process wherein two bonds are cleaved for each new bond formed. The resulting expansion can be applied to counter the polymerization shrinkage associated with the conventional methacrylate monomers used in dental composites and thereby provide formulations with drastically reduced degrees of shrinkage. New monomers have been prepared that exhibit enhanced reactivities and ring-opening efficiencies compared with earlier free-radical-polymerizable oxaspiro compounds. In dental composite formulations, the monofunctional oxaspiro monomers provided DTS values equivalent to those of the controls under certain curing conditions; however, only modest reductions in polymerization shrinkage were observed. 2,3-Bis(methylene) spiro orthocarbonate monomers with a conjugated diene structure were also synthesized and evaluated. These novel monomers appear to offer significant potential for future development of free-radical ring-opening polymerization. While visible-light-cured formulations of the bis(methylene) compounds with methacrylate comonomers did not yield acceptable composite materials in this initial attempt, the high reactivity and the ability to form rigid, cross-linked polymers make this type of monomer worthy of continued investigation. These properties may allow the bis(methylene) oxaspiro monomers to be used alone or in concert with other ring-opening monomers for special applications. [ABSTRACT FROM AUTHOR]

A new type of multifunctional oligomer was synthesized, and its potential as a base monomer in dental composite formulations was evaluated. The oligomer of ethoxylated bis-phenol A diacrylate (OEBPA) was prepared in good yield by a formaldehyde insertion/ condensation reaction. Although double bonds along the oligomer backbone are arranged in pairs such that cyclopolymerization is possible, it is not presently known whether this process plays a significant role in the polymerization. Indirect evidence supporting efficient cyclopolymerization involves the reduced polymerization shrinkage observed for polymerized OEBPA relative to polymers of other monomers used as base resins. Photo-cured composites containing either OEBPA, BIS-GMA, or ethoxylated bis-phenol A dimethacrylate (EBPADM) as base resin and TEGDMA as diluent were compared. While the resulting diametral tensile and transverse strengths did not differ significantly, the values for the energy absorbed to failure indicated that the OEBPA- and EBPADM-based formulations yielded composites with somewhat greater toughness than that of the BIS-GMA material. This multifunctional oligomer offers mechanical strength and conversion values that are comparable with those of existing base resin monomers while providing an approximate 30% reduction in polymerization shrinkage. [ABSTRACT FROM AUTHOR]

The simple reaction of conventional monofunctional acrylate monomers with paraformaldehyde has yielded a new class of difunctional monomers. The unique proximity of the double bonds within these compounds allows a facile cyclopolymerization to incorporate a cyclic ether structure into the polymer backbone. The external position of the acrylate esters means that these pendant groups can be varied for alteration of the physical properties of the monomers and the corresponding polymers. A series of the new monomers has been prepared and polymerized under dilute solution and bulk conditions to yield non-crosslinked and crosslinked polymers, respectively. The polymers exhibited high degrees of conversion and significantly reduced polymerization shrinkage, compared with polymers obtained from conventional diacrylate or dimethacrylate monomers. These properties appear to be a direct result of an efficient cyclopolymerization process. The combination of improved conversion to polymer with less contraction makes these monomers ideal candidates for use in dental resin composites. A preliminary evaluation of their potential in this application has shown that with suitable ester functionality, they can be formulated to provide composites with excellent mechanical strength properties. [ABSTRACT FROM AUTHOR]

Vanillate esters such as n-hexyl vanillate (HV) dissolved in a suitable chelating agent -- e.g., o-ethoxybenzoic acid (EBA) -- react with zinc oxide, aluminum oxide, and hydrogenated rosin powder to yield non-eugenol-containing cements that do not inhibit polymerization and are compatible with acrylic monomers. These cements can be modified by adding methyl methacrylate, or the less-volatile, higher-molecular-weight dicyclopentenyloxyethyl, or cyclohexyl methacrylate to the HV-EBA liquid, and silanized glass to the powder. On incorporating a suitable initiator-accelerator system, one can prepare powder-liquid mixes that have good working properties and harden in five to 10 min. The cured materials containing monomethacrylate ingredients have compressive and tensile strength one and one-half to three times that of eugenol-based intermediate restoratives. Cements with even better mechanical properties are obtained using dimethacrylates as monomeric components. Storage stability of the liquids comprising vanillates-EBA and monomethacrylates is excellent. The vanillate-EBA-dimethacrylate liquid containing amine accelerators polymerizes within days when left standing at 45°C. The cement composites adhere strongly to composites, non-precious metals, or porcelains. Rupture of the bond occurs cohesively within the cement. Because of their high strength, low solubility, and excellent adhesion, these cements, subject to their biocompatibility with dental tissues, show great promise as intermediate restorative resins and in the repair of fractured porcelain or porcelain-to-metal crowns and bridges. [ABSTRACT FROM AUTHOR]