R.L. Bowen

Adhesive Bonding of Various Materials to Hard Tooth Tissues: Improvement in Bond Strength to Dentin

Used in sequence, solutions of an acidic mordant, a surface-active comonomer, and a coupling agent having methacrylate and aromatic carboxyl groups were used to prepare dentin surfaces in vitro for strong bonding with a composite resin.

Hardening Shrinkage and Hygroscopic Expansion of Composite Resins

Polymerization shrinkages of various restorative resins were measured. The specimens stored in water expanded, but most did not recover sufficiently to countervail the losses from polymerization.

Dental Composites/Glass Ionomers: the Materials

Most commercial dental composites contain liquid dimethacrylate monomers (including BIS-GMA or variations of it) and silica-containing compositions as inorganic reinforcing filler particles coated with methacrylate-functional silane coupling agents to bond the resin to the filler. They also contain initiators, accelerators, photo-initiators, photosensitizers, polymerization inhibitors, and UV absorbers. Durability is a major problem with posterior composites. The typical life-span of posterior composites is from three to 10 years, with large fillings usually fewer than five years. Polymerization shrinkage and inadequate adhesion to cavity walls are remaining problems. Some pulp irritation can occur if deep restorations are not placed over a protective film. Some have advocated the use of glass-ionomer cement as a lining under resin composite restorations in dentin. The concept of glass-ionomer cements (GICs) was introduced to the dental profession in the early 1970s. Current GICs may contain poly(acrylic acid) or a copolymer. Higher-molecular-weight copolymers may also be used to improve the physical properties of some GICs. Stronger and less-brittle hybrid materials have been produced by the addition of watersoluble compatible polymers to form light-curing GIC formulations. The ion-leachable aluminosilicate glass powder, in an aqueous solution of a polymer or copolymer of acrylic acid, is attacked by the hydrated protons of the acid, causing the release of aluminum and calcium ions. Salt bridges are formed, and a gel matrix surrounds the unreacted glass particles. The matrix is adhesive to mineralized tissues. Provisions must be made for maintenance of the water balance of restorations for the first 24 hours. A varnish to seal newly-placed restorations is provided by most manufacturers. The introduction of metal powder to GICs significantly improved abrasion resistance.

A New Series of X-Ray-Opaque Reinforcing Fillers for Composite Materials

Clear, colorless glasses that absorb roentgen rays were prepared by melting together compounds yielding silica, barium oxide, boric oxide, and alumina. Barium oxide made the glasses radiopaque and gave the desired refractive index. Boric oxide lowered the melt viscosity, and alumina tended to stabilize the glasses. Some of these glasses seem to be suitable for use as the reinforcing fillers for composite dental restorative materials.

Compatibility of Various Materials with Oral Tissues. I: The Components in Composite Restorations:

The basic ingredients in composite restorative materials include: monomers, polymerization stabilizers, color stabilizers, polymerization initiators, polymerization accelerators, inorganic reinforcing fillers, and coupling agents. Typical members of each category are discussed.

Compatibility of Various Materials with Oral Tissues. II: Pulp Responses to Composite Ingredients

Eight ingredients of composite materials were evaluated individually for pulp irritation. None caused significant inflammation as evidenced by its average response. No abscess formations or lesions predominating in leukocytes occurred.

Semiporous Reinforcing Fillers for Composite Resins: I. Preparation of Provisional Glass Formulations

A conceptual means of obtaining improved bonding between filler particles and the polymeric binders of composites is presented. It involves preparing glass particles that separate into two interconnected vitreous phases when heated to an appropriate temperature, and then etching these to produce a porous surface layer. Candidate glass compositions were prepared and subjected to heat treatment in a gradient furnace. Compositions susceptible to phase separations were delineated.

Mechanically-induced generation of radicals in tooth enamel

Mechanical instrumentation of enamel leads to the formation of long-lived free radicals that can be conveniently measured by electron paramagnetic resonance (EPR) spectroscopy. Powdered enamel tissue exhibited EPR signals remarkably similar to the radicals formed by ionizing radiation. The observations described below lead to the conclusion that physical stress will induce a free-radical formation in dental tissues. These observations have significance for other areas of study such as dosimetry and archeological dating.

Amine Accelerators for Methacrylate Resin Systems

Tertiary aromatic amines were synthesized with various nitrogen and ring substituents. They were compared with commercial homologues using composites based on dimethacrylate monomer formulations containing benzoyl peroxide. Equimolar amounts of the different amines were the only variables. Although accelerating ability was a function of both ring and nitrogen substitution, color stability was influenced more by the substituents on the ring than by the substituents on the nitrogen

Effect of Acidic Pretreatment on Adhesion to Dentin Mediated by Gluma

Tensile bond strengths between dentin and a typical restorative resin were measured after the dentin was treated with Gluma. Solutions of phosphoric, pyruvic, nitric, or oxalic acid, also containing various amino acids, were used as pretreatments. Without amino acids in the solutions, the pretreatments conferred bonds of low strength. Use of acidic solutions containing glycine or N-phenylglycine was found to give bonds of high strength to both dentin and enamel.