Oligomers with pendant isocyanate groups as tissue adhesives: II. Adhesion to bone and other tissues.

The adhesive properties of a series of oligomers prepared from 2-isocyanatoethyl methacrylates (IEM) and/or m-isopropenyl-alpha,alpha-dimethylbenzyl isocyanate (TMI) and various acrylates or methacrylates were studied. The bond strength of bone, dentin, or soft tissue specimens joined with these oligomers respectively to bone, dental composite restorative, or denture base resin were determined by tensile adhesion or shear tests. These oligomers are more effective in forming stronger bonds to bone than are other tissue adhesives. Fracture occurs cohesively, usually within the bone. Thermocycling in water for 1 week between 5 degrees C and 55 degrees C did not decrease adhesion indicating that exposure to water or thermal shock produced no deterioration of the bond. Tensile adhesion of bovine or human dentin joined to composite restorative resin by means of the oligomers is similar to that of the best dental bonding agents such as Gluma (glutaraldehyde and 2-hydroxyethyl methacrylate) or ferric oxalate + N-phenylglycine + dimethylacryloxyethyl-pyromellitate. These oligomers also strongly bond soft tissues and calfskin and to acrylic resins and composites.

Oligomers with pendant isocyanate groups as tissue adhesives. I. Synthesis and characterization.

A series of methacrylate oligomers containing pendant isocyanate groups were synthesized by reacting 2-isocyanatoethyl methacrylate (IEM) and/or m-isopropenyl-alpha, alpha-dimethylbenzyl isocyanate (TMI) in ethoxyethyl acetate with methacrylates ranging from methyl to stearyl methacrylate or allyl-, cyclohexyl-, glycidyl-, i-bornyl-, or dicyclopentenyloxyethyl methacrylate. The oligomers which are stable at room temperature were characterized by IR for NCO, ester, and C = C groups and by their refractive indices. They have a small number of residual double bonds and a molecular weight low enough so that the compounds are liquids at room temperature and dissolve readily in esters and chlorinated hydrocarbons. HPLC showed no residual monomer. GPC and intrinsic viscosity of selected oligomers indicated a molecular weight range from 1400 to 2600. Isocyanate groups were determined titrimetrically and ranged from 15.9% to 5.1%. Concurrent studies have demonstrated that these oligomers bond strongly to hard and soft tissues. Thus, subject to their biocompatibility they could find many applications as tissue adhesives.

Oligomers with pendant isocyanate groups as adhesives for dentin and other tissues.

Oligomers containing pendant isocyanate groups were synthesized from various vinyl monomers, m-isopropenyldimethylbenzyl isocyanate (TMI), and 2-isocyanatoethyl methacrylate (IEM). The liquids were characterized by their refractive indices, infrared spectra, and percentage of isocynate groups in the molecule. Adhesive properties of these compounds were compared with those of oligomers prepared from methacrylate esters, IEM, and/or TMI which had been synthesized previously. Bond strengths of the sodium salt of ethylenediamine-tetraacetic acid (Na2EDTA adjusted to pH 7.4) and glutaraldehyde-treated dentin cemented to composite resin with dilute solutions of the oligomers and then stored in water were determined by the procedure of Kemper and Kilian (1975). These adhesive compositions, especially formulations synthesized from vinyl monomers, adhered at least as well to dentin as did other dentin bonding agents. Oligomers synthesized with methacrylate esters bonded more strongly to bone than did other hard-tissue adhesives. These oligomeric compositions are also excellent soft-tissue adhesives. For example, they provide a strong bond between a collagenous substrate (such as calfskin) and cured denture-base resin. Provided that their biological properties prove satisfactory, these compositions could find many applications as hard- and soft-tissue adhesives in clinical dentistry.

Dependence of curing time, peak temperature, and mechanical properties on the composition of bone cement.

Commercial bone cements usually contain hydroquinone as the polymerization inhibitor and N,N-dimethyl-p-toluidine as the accelerator in the benzoyl peroxide-initiated redox polymerization. The former compounds have certain shortcomings in their biocompatibility profile. Measurements of the setting times, polymerization exotherms, and postpolymerization strengths of the cured monomer-polymer compositions show that the hydroquinone can be replaced by food grade di-tert-butyl-p-cresol (BHT). The more reactive 4-N,N-(dimethylamino)phenethanol can replace 4-N,N-dimethyl-p-toluidine, yielding cements with shorter setting times and increased strengths. Excessive heat liberated on polymerization can be reduced by partial substitution of higher-molecular-weight methacrylates, e.g., dicyclopentenyloxyethyl methacrylate for methyl methacrylate, but there is a decrease in strength of the resulting polymer. More successful has been the addition to the monomer of 1% or 2% of the chain transfer agent pentaerythritol tetra(3-mercaptopropionate), which lowers the peak temperature without changing the physical properties of the cement. Compositions with short curing times, lower exotherms, and mechanical properties that exceed those of a commercial material have been formulated.

Divanillates and polymerizable vanillates as ingredients of dental cements.

Vanillate esters with multifunctional groups the react with metal oxides to give chain-extended molecules have been synthesized. Divanillates were obtained from vanillic acid and the corresponding polymethylenediols. Methacryloylethyl vanillate (MEV) and vanillyl methacrylates were prepared respectively from hydroxyethyl vanillate or vanillyl alcohol and methacryloyl chloride. The properties of cements prepared with liquids incorporating these compounds were determined. Liquids containing divanillates dissolved in the reactive chelating agent o-ethoxybenzoic acid (EBA) when mixed with zinc oxide powders harden within a few minutes. The resulting cements have a tensile strength much higher than the commonly used zinc oxide-eugenol cements, have low solubility, do not inhibit polymerization, and adhere well to metallic substrates. Similarly, liquids with MEV as an ingredient yield cements with excellent strength and good adhesion to stainless steel and composites. Their brittleness can be overcome by addition of an oligomeric methacryloylethyl vanillate to the liquid or silanized glass to the powder ingredient. These cements, subject to their biocompatibility to oral tissues, could be most useful for a number of dental applications.

Intermediate restoratives from n-hexyl vanillate-EBA-ZnO-glass composites.

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 degrees 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.

Cements containing syringic acid esters -- o-ethoxybenzoic acid and zinc oxide.

Fissure caries is reduced when syringic acid is incorporated into a cariogenic diet of rats. It was therefore of interest to synthesize n-hexyl and 2-ethylhexyl syringate and to evaluate the properties of cements with these compounds as ingredients. Liquids containing the esters dissolved in o-ethoxybenzoic acid (EBA) - when mixed with powders made up from zinc oxide, aluminum oxide, and hydrogenated rosin - hardened in from four to nine min. Properties of the cements were determined, when possible, according to ANSI/ADA specification tests. Depending on the powder-liquid ratio employed, we obtained compositions with varying physical properties desirable for different dental applications. The syringate cements, compared with the commonly used ZOE materials, have improved compressive and tensile strength, lower water solubility, do not inhibit polymerization, and are compatible with acrylic monomers. These cements pass, and mostly greatly exceed, the requirements for ZOE-type restorative materials. They also bond significantly to resins, composites, and non-precious metals. The bond strength is somewhat less than that of n-hexyl vanillate-EBA cement, but greatly exceeds the adhesion to various substrates of ZOE luting agents. Cements containing n-hexyl syringate were somewhat brittle. Best results were obtained with liquid compositions containing 5% 2-ethylhexyl syringate, 7% n-hexyl vanillate, and 88% EBA, which yielded non-brittle materials. These cements, because of the syringate ingredient, may possess caries-reducing properties. Thus, perhaps in conjunction with fluoride additives, they would be useful as insulating bases, pulp capping agents, root canal sealers, soft tissue packs, or intermediate restoratives.

Solvent effects on bonding organo-silane to silica surfaces.

Interfacial bonding and stability of gamma-methacryloxypropyltrimethoxysilane with silica surfaces have been studied by means of infrared spectroscopy. The addition of n-propylamine enhances silanization of gamma-methacryloxypropyltrimethoxysilane to silica surfaces in normal aliphatic hydrocarbons, and cyclohexane yields a more water-resistant silica-silane bond, and improves the diametral tensile strength of the composite.

Marginal adaptation of BIS-GMA-based composites containing various diluents.

The aim of this study was to determine how otherwise acceptable diluent monomers affect the marginal adaptation of BIS-GMA-based composites. Based on the results of the investigation, the following conclusions can be drawn: 1. Addition to dimethacrylate diluents containing (CH2) recurring units generally yields composites having better marginal adaptation than do those containing (CH2 CH2 O) groups. Best marginal adaptation for a single diluent is obtained for compositions using 1, 4 and 1, 10-polymethylene glycol dimethacrylate as diluent. 2. Marginal adaptation is improved on lowering the diluent concentration. Optimum adaptation will be obtained for a formulation containing a minimum percentage of diluent with clinically acceptable working properties. 3. Volume changes on temperature cycling resulting from differences in thermal expansion coefficients of composites do not effect the marginal integrity as much as does curing shrinkage.

Isocyanato urethane methacrylates derived from hydroxyethyl methacrylate.

Isocyanato urethane methacrylates were synthesized from five diisocyanates and hydroxyethyl methacrylate. They may be homopolymerized or copolymerized with other methacrylates by the usual free radical methods of initiation and have potential as adhesion-promoting agents for dentin.

New amine accelerators for composite restorative resins.

The overall characteristics of the composites cured with a number of newly synthesized, tertiary aromatic amines compare favorably to those of resins polymerized with commonly used accelerators. Maximum compressive and tensile strength for the composites are obtained only over a narrow concentration range of accelerator used.