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Biomedical subjects

R L Bowen

Publications and source records attributed to R L Bowen.

At least 19 recordsLinked to original sources
PubMed1996

New surface-active comonomer for adhesive bonding.

Previous studies have indicated that chemical and physical characteristics of aromatic amines can be influenced by the nature of their substituents. The experimental question examined in the present study relates to the effects of replacing specific hydrogen atoms with methyl groups in a surface-active comonomer utilized in adhesive bonding protocols. N-2-propionic acid-N-3-(2-hydroxy-1-methacryloxy)propyl-3,5-dimethylaniline sodium salt (N35A) was synthesized by an addition reaction of glycidyl methacrylate with the sodium salt of N-reaction of glycidyl methacrylate with the sodium salt of N-(3,5-dimethylphenyl)alanine, which was formed by alkaline hydrolysis of ethyl-N-(3,5-dimethylphenyl)alanate that was prepared by condensation of ethyl-2-bromopropionate with 3,5-dimethylaniline. 1H and 13C NMR spectra and analysis by mass spectroscopy were consistent with N35A after it had been recrystallized from acetone. Color stability and adhesion-promoting capability of N35A were compared with those of N-2-acetic acid-N-3-(2-hydroxy-1-methacryloxy)propyl-4-methylanaline sodium salt (Na-NTG-GMA), the latter being widely used in commercial bonding formulations. Both N35A and Na-NTG-GMA polymerized within a few minutes at 23 degrees C when dissolved in aliquots from a stock solution containing benzene 85 wt%, ethanol 14 wt%, and benzoyl peroxide 1.0 wt%; but with each at 0.018 molal concentration, the N35A suspension was more color-stable than that of the Na-NTG-GMA. In the protocol used, shear bond strengths of a hybrid composite to human dentin with N35A were 30.2 MPa, SD = 7.5 MPa, and with Na-NTG-GMA, 29.7 MPa, SD = 11.8 MPa(n = 7 each; t test, p = 0.93).

Adhesiveness↗
PubMed1994

Physical and chemical properties of resin-reinforced calcium phosphate cements.

OBJECTIVES: The purpose of this study was to improve the handling and physical properties of a self-setting, water-based calcium phosphate cement by combining it with polymerizable resins and to study the setting reactions involved. METHODS: Dual-cured composite cements were prepared from a calcium phosphate cement powder and dental monomers that contain carboxylated hydrophilic resins or resin/water mixtures. The setting reaction of the calcium phosphate cement in the presence of the resins was evaluated by pH measurements, infrared spectroscopy, diametral tensile strength, x-ray diffraction analysis, and scanning electron microscopy. RESULTS: Carboxylated resins were chosen because they can form ionic bonds to the mineral filler, which was confirmed by appearance of an infrared absorbance peak at 1552 cm-1 within 24 h after mixing due to the formation of a carboxylate salt. Hydroxyapatite did not develop in composites prepared from resin and calcium phosphate cement. However, composites from calcium phosphate cement, resin and water showed approximately 40% hydroxyapatite. The resulting composite cements have moderately high DTS of 14-15 MPa and high pH. SIGNIFICANCE: Hydrophilic acidic resins allows mixing with water and/or allow rapid diffusion of water into the resinous cement so that the dissolution and reprecipitation processes required for the conversion of the calcium phosphate components to hydroxyapatite can occur. The characteristics of the resulting composite cements suggest that the materials may be useful in pulp capping and/or cavity lining.

Calcium Phosphates↗
PubMed1993

An esthetic glass-ceramic for use in composite restoration inserts.

The objective of the preliminary work reported here was to prepare an improved formulation of intrinsically colored microcrystalline glass-ceramic. Applications could include "megafillers" for direct composite restorations, precision castings, and CAD-CAM prostheses. The experimental glass-ceramic reported here contained SiO2 56.9, AI2O3 19, LiO2 7, ZnO 6, MgO 5, TiO22, ZrO22, P2O52, and CeO20.1 mole%. The batch materials were melted and stirred at 1,610 degrees C for 2 h, quenched in water and also formed into a block of a clear, slightly yellow glass. To identify the crystalline phases that developed during transformation of the glass to the ceramic, x-ray diffraction was used on ten aliquots taken during 15 h of stepwise heating from 750 to 1050 degrees C. With heating, the yellow color deepened to a very translucent "dark yellow" dental shade, then lightened with gradually increasing opacity during formation of secondary crystalline phases. X-ray opacity was approximately equivalent to that of dental enamel. The refractive index of the glass, nD1.554, increased during nucleation and growth of the crystalline phases to a maximum of 1.586. Intrinsic coloration of these glass-ceramic materials can be controlled by varying the heat treatment and/or composition to match typical dental shades.

Ceramics↗
PubMed1993

Adhesion of composites to dentin and enamel.

Extrapolations based on the history of the development of composites and an adhesion system for bonding dental resins and composites to hard tooth tissues can rightfully be the basis for strong optimism regarding future improvements in esthetic and conservative treatment modalities. Improved understanding of mechanisms of action and the clinical application steps common to current adhesion systems will certainly lead to improved oral healthcare.

Acid Etching, Dental↗
PubMed1992

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 1970's. 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 water-soluble 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Bisphenol A-Glycidyl Methacrylate↗
PubMed1992

Development of an adhesive bonding system.

Building on findings concerning adhesion to enamel, R L Bowen and his colleagues at the Paffenbarger Research Center, National Institute of Standards and Technology began addressing and solving problems associated with (1) silicate cements and unfilled resins, (2) bonding in an aqueous environment, and (3) the development of an adhesion system for both dentin and enamel that could withstand various stresses. This article reviews the development of an adhesion system for bonding dental composites to dentin and enamel.

Benzoates↗
PubMed1991

The effect of catalyst structure on the synthesis of a dental restorative monomer.

The addition product of 2-hydroxyethyl methacrylate (HEMA) and pyromellitic dianhydride (PMDA), known as PMDM, is a mixture of two structural isomers. The para PMDM isomer--currently used in mediating adhesive bonding of restorative materials to hard tooth tissues--is a crystalline solid. The meta isomer is a liquid. In the synthesis of PMDM, the para isomer, which can be purified by crystallization, is usually present to the extent of only 50% of the product mixture. The effect of the amine catalyst structure was studied relative to its role in increasing the yield of the para isomer, either by a reduction in the amount of the meta isomer or by an increase in the extent of overall reaction. The chemical structure of the amine catalyst had an important role in the synthesis of PMDM and influenced the ratio of the isomers. Among aliphatic amines, especially noteworthy as catalysts that gave excellent yields of the para isomer in high purity were N,N-di-isopropyl-ethylamine and hexamethylenetetramine.

Adhesives↗
PubMed1991

Protective coatings for tooth crowns.

Transfer of technology to the dental office could provide thin polymeric coatings over tooth crowns and accessible root surfaces. These coatings can be prepared from relatively inexpensive, commercially available materials in one-step reactions. When the monomer technique becomes available, it will provide caries protection for all of your patients.

Benzoates↗
PubMed1989

Pulpal and micro-organism responses to two experimental dental bonding systems.

Several new bonding systems have been reported that promote strong adhesion. This in vivo study involves treatment with two experimental bonding systems of Class V cavity preparations in the teeth of three Macaca fascicularis primates and reports the pulpal responses and degree of micro-organism invasion associated with each treatment. In each monkey, the teeth in the upper left quadrant were treated with the experimental solution, containing 2.5% aluminum nitrate + 1.5% oxalic acid + 4.9% NPG, followed by application of PMDM and Silux XL composite. The lower right quadrant was treated with the experimental solution, containing 5.7% NPG + 2.4% nitric acid, followed by PMDM and Silux XL composite. The upper right and lower left quadrants were treated with clinical materials to establish positive and negative controls. After four, 25, and 59 days, the teeth were removed and underwent routine histological and bacteriological evaluation. Slight pathological conditions were noted for superficial and deep responses, but all values approached 0.0 by the 59th day. Micro-organisms were seen under only 12% of the restorations. Both experimental systems appear to be safe for human clinical trials.

Animals↗
PubMed1989

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.

Dental Enamel↗
PubMed1989

An in vitro investigation of the effects of glass inserts on the effective composite resin polymerization shrinkage.

We placed an MOD preparation in each of 12 permanent molars, then restored each tooth with a posterior composite resin by means of six different application techniques (I-polymerization as one complete unit; II--polymerization as one complete unit with glass inserts; III--polymerization in gingivo-occlusal increments; IV-polymerization in gingivo-occlusal increments with glass inserts; V--polymerization in bucco-lingual increments; and VI--polymerization in a gingival increment with glass inserts, then bucco-lingual increments). A precision strain gauge was attached to the buccal surface of each tooth and balanced at zero. After each increment was polymerized, the strain appearing on the strain gauge indicator was recorded. Each tooth was restored by use of all techniques; two teeth started with each technique. Results demonstrated the average microstrain units to be 127-I, 102-II, 105-III, 86-IV, 72-V, and 66-VI. A randomized block design was the format used for data evaluation. Scheffé's Test indicated that composite resin placement and polymerization in bucco-lingual increments (V) created significantly less cuspal deflection than polymerization as one complete unit, with or without glass inserts (I and II), p less than 0.001, and gingivo-occlusal increments (III), p less than 0.05. Placement and polymerization in a gingival increment with glass inserts, then bucco-lingual increments (VI), also created significantly less internal deflection than polymerization as one complete unit, with or without glass inserts (I and II), p less than 0.001, and gingivo-occlusal increments (III), p less than 0.005.

Analysis of Variance↗
PubMed1989

Substitutes for N-phenylglycine in adhesive bonding to dentin.

Using bond strength measurements, we investigated a number of related compounds in order to elucidate the role of the surface-active ingredient, N-phenylglycine (NPG), in experimental two-step and three-step bonding protocols resulting in adhesive bonding to dentin. All active compounds identified for the two-step or the three-step protocol were N-aryl-alpha-amino acids, and the results delineate some of the key features of the NPG molecule for bonding. For the three-step protocol, there was a requirement for a secondary or tertiary aromatic amino group, a carboxylic acid group, and a single (secondary or tertiary) methylene unit between those two functional groups of the amino acid. For the two-step protocol, additional substitutions at the para position of the phenyl ring on the amine improved the bond strength. In both protocols, para-methyl- and para-chloro-substituted NPG analogues ranked higher than NPG. A "catalytic" effect of the aromatic tertiary amino group on the polymerization of the adhering resin in both procedures could not be ruled out.

Adhesiveness↗
PubMed1989

Clinical biocompatibility of an experimental dentine-enamel adhesive for composites.

Previous studies have shown that sequential application of an acidified solution of ferric oxalate, N-phenylglycine and PMDM (the reaction product of pyromellitic dianhydride and hydroxyethyl methacrylate) yields strong adhesive bonding of composite resins to both dentine and enamel. The purpose of this study was to evaluate the clinical characteristics and the biocompatibility of this system in human teeth scheduled for extraction in the course of orthodontic treatment. Controls were light-cured Scotch-bond or ZOE in contralateral teeth. Evaluation criteria, which included clinical feasibility, patient acceptability, retention, margin aesthetics and human pulp response, were met. Within the 4-241 day observation periods, there was no postoperative sensitivity, pain, loss of retention, staining or discolouration. All pulp responses (double-blind pulp analysis including all teeth) were acceptable. With mean (+/- SD) remaining dentine thickness (RDT) of 0.67 +/- 0.35 mm, all indicators of pulp inflammation (displacement, superficial response, deep response etc.) averaged between none and slight, under 1 on a 0-4 scale. Both controls gave similar results. Linear regression analysis indicated low responses at all RDTs. The experimental material is safe and effective; further unrestricted clinical evaluations in teeth to be retained are indicated.

Adhesives↗