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Biomedical subjects

I E Ruyter

Publications and source records attributed to I E Ruyter.

At least 19 recordsLinked to original sources
PubMed1992

Chemical, physical, and histologic studies on four commercial apatites used for alveolar ridge augmentation.

The purpose of this study was to evaluate four commercial apatite products. Subperiosteal alveolar ridge augmentation was performed on the maxilla of rats by implantation of granules of two dense products and of two porous products, and the tissue response was compared with the material characteristics obtained by chemical analysis and infrared spectrometry. None of the apatites caused osteoinduction or osteoconduction; fibrous encapsulation with multinuclear giant cells was observed around all four types. One of the apatites was fluorapatite and not hydroxylapatite, as claimed by the manufacturer. The tissue response to this implant material was dominated by multinuclear giant cells.

Alveolar Process↗
PubMed1992

The chemistry of adhesive agents.

The chemical aspects of dental adhesive systems are reviewed and discussed. Adhesive agents must have the ability to wet and then to adhere to hard dental tissues. Several dental bonding systems are available. They are characterized by containing monomers that have hydrophilic and hydrophobic groups. The polymerized adhesive system should provide a stable link between the tooth structure and the bulk of the restoration. Some adhesive systems provide initial acceptable adhesion, but the long-term bonding to dentin is questionable.

Adhesives↗
PubMed1992

Types of resin-based inlay materials and their properties.

The composition of 'chairside' resin-based inlay materials is similar to that of direct resin-based filling materials. The handling and curing procedures vary for the different inlay materials. Some systems involve precuring inside the oral cavity and a final cure at elevated temperature outside the oral cavity. Others are only cured extra-orally. The advantage of the inlay technique is that polymerisation shrinkage of the composite occurs before bonding to tooth structure. After cementation, therefore, the inlay gives good marginal adaptation in occlusal restorations. Some of the curing procedures for inlays give good conversion. The systems with good conversion also show better mechanical properties than the equivalent resin-based material cured according to the direct filling technique.

Chemical Phenomena↗
PubMed1991

Staining of resin-based veneering materials with coffee and tea.

Two light-activated, and three heat-polymerized, resin-based veneering materials were exposed to boiled coffee, filtered coffee, or tea at 50 degrees C and evaluated for color stability. Specimens immersed in distilled water in the dark at 37 degrees C for 4 months were also assessed. One of the light-activated, resin-based veneering materials underwent intrinsic discoloration during the long-term immersion both in distilled water and in the staining solutions. The discoloration of the other materials by tea was mainly due to surface adsorption of the colorants. Discoloration by coffee was due to adsorption, and also to absorption of colorants by two of the materials investigated. This absorption and penetration of colorants into the organic phase of the veneering materials were probably due to compatibility of the polymer phase with the yellow colorants of coffee.

Acrylic Resins↗
PubMed1989

Creep studies of multiphase acrylic systems.

The influence of type and quantity of five different crosslinking agents on tensile creep properties of multiphase acrylic systems has been studied. The polymeric materials, commonly applied in bioengineering, were processed by polymerization of a mixture of liquid methacrylate monomers and poly(methyl methacrylate) powder. The specimens were made with various ratios of methyl methacrylate and crosslinking agents in the monomer liquid. Two different processing conditions were used, i.e., heat-polymerization at 100 degrees C and autopolymerization at 45 degrees C. Creep behavior was determined at 37 +/- 0.2 degrees C and 50 +/- 0.5 degrees C. The investigation showed higher creep values for autopolymerized than for heat-polymerized materials. In heat-polymerized materials the creep curves showed little variation with type and quantity of crosslinking agents at low stress levels. However, at high stress levels the creep values decreased with increasing quantity of crosslinking agents. The autopolymerized materials showed a more inhomogeneous structure, and great variation in creep. Both among the heat-polymerized and autopolymerized materials, the systems with diethyleneglycol dimethacrylate clearly deviated from the others by showing higher creep values.

Biopolymers↗
PubMed1989

An evaluation of the radiopacity of composite restorative materials used in Class I and Class II cavities.

The radiopacity of 28 shades of 18 composite brands, recommended for use in Class I and Class II cavities, and one amalgam were tested in accordance with the instructions in the latest draft standards of ISO for resin-based filling materials. The composition of the inorganic fillers in the materials was analyzed by optical emission spectroscopy. Twelve composites showed radiopacity greater than enamel, for five the radiopacity was lower than that of dentin, and for two materials the radiopacity was between that of enamel and dentin. The optical emission spectroscopy analyses showed a large variety in the composition of the fillers. The elements added to increase radiopacity in the composite materials are barium, strontium, zinc, zirconium, and ytterbium.

Composite Resins↗
PubMed1988

Release of formaldehyde from dental composites.

Polymeric composite materials may contain releasable degradation products or unreacted constituents. Release of formaldehyde from nine different composites was investigated by means of HCHO-hydrazone derivative analyzed with high-performance liquid chromatography. Formation of formaldehyde was found in all the investigated materials. The highest concentrations were observed in specimens polymerized in contact with air. A correlation coefficient, r = 0.83, was found between released formaldehyde and the thickness of the unpolymerized surface inhibition layer. The formaldehyde concentrations were reduced when the inhibition layer was removed prior to testing. A continuous release of formaldehyde was evident during the first ten days. The release decreased with time, but was still detectable after 115 days.

Chromatography, High Pressure Liquid↗
PubMed1987

Composites for use in posterior teeth: composition and conversion.

The purpose of this investigation was to determine the composition, as well as the conversion after polymerization, of some dental composite materials. Eight posterior composites and two anterior composites were investigated. The weight and volume fractions of inorganic fillers were determined by combustion and pycnometric analyses. The monomers were analyzed qualitatively and quantitatively by high performance liquid chromatography, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. Infrared multiple internal reflection spectroscopy was applied for determination of conversion of the methacrylate groups. The conversion in light activated materials was examined at shallow depths, that is, the level of optimal conversion. This investigation demonstrated that the conversion can be correlated with the composition of monomers and oligomers used in the materials.

Acrylic Resins↗
PubMed1987

Carbon/graphite fiber reinforced poly(methyl methacrylate): properties under dry and wet conditions.

The flexural properties of poly(methyl methacrylate) (PMMA) reinforced with carbon/graphite (C/G) fibers with three different surface treatments were investigated by transverse bend testing after dry and wet storage. The fibers used were (1) commercially available fibers, (2) cleaned fibers, and (3) cleaned and sized fibers. The coating agents of commercial unidirectional and braided C/G fibers as well as impurities on C/G fibers for medical uses were characterized by means of high-performance liquid chromatography (HPLC). The agar overlay technique was used to assess the cytotoxicity of leachable elements from different fibers and processed composites. Composites with both unidirectional and braided tubular C/G fibers were investigated after storage in water. Fracture stress and flexural modulus decreased when "commercial" fibers were used as reinforcing material. Composites with cleaned and sized fibers gave only minor differences in flexural properties after dry and wet storage. By means of SEM micrographs the adhesion behavior of unsized C/G fibers, epoxy sized fibers, cleaned fibers, and cleaned and sized fibers were assessed. After water storage a substantial part of the cleaned fibers adhered to the matrix material. The adhesion capacity of the other fibers was reduced since the water absorption caused separation of fiber and matrix.

Biocompatible Materials↗
PubMed1987

Adhesion of resins to Ag-Pd alloys by means of the silicoating technique.

The purpose of the investigation was to study the effect of water storage on the bond strengths between silanized, silicoated Ag-Pd alloys and veneered composites, in comparison with the bond strengths of systems with conventional retention beads. Furthermore, the mechanism of the bonding was examined. The bond strength of silanized, silicoated dry specimens and similar specimens stored in water was measured by four-point bending. Water storage for 90 days at 37 degrees C reduced the bond strength by approximately 30% to about 15-20 MPa. Mechanical retention beads caused bond strengths of approximately 16-18 MPa which were unaffected by water storage. SEM and microprobe investigations showed that sandblasting with AI2O3 prior to silanization caused substantial numbers of cracks and porosities in the surface layer of the alloy, partly filled with Al2O3. Some particles of silicon oxide in these surface defects were produced by the flame-spraying of the so-called silicoating technique. Further painting of the surface with a silane adhesion primer provided chemical bonding to the composite at the densely spaced Si-O-H-containing silica particles. Many cracks were observed in the interfaces between these particles; thus, water is likely to penetrate the interface with time. The bond strength is most likely reduced by reaction between water and the composite/Si-O structure. The silicon oxide particles are probably attached to the alloy substrate by mechanical retention. Without sandblasting, no bonding was obtained by means of the silicoating technique.

Acrylic Resins↗
PubMed1987

Etching patterns of Co-Cr alloys for bonded cast restorations.

Resin-bonded bridges may replace missing teeth and act as splints in periodontal treatment. The objective of this study was to investigate the etch pattern after electrolytic etching of selected Co-Cr alloys in hydrochloric acid and to assess the changes in alloy composition after different etching times. The alloys investigated were Vitallium, Wironit, Wironium, Nobilium Hard, and Niranium NN. Alloy specimens were electrolytically etched in a hydrochloric acid solution for 1, 2, 5, and 10 min. The etched specimens were examined in a light microscope and a scanning electron microscope (SEM). Different etching patterns were revealed in the various alloys. Microprobe analyses after the etching of Vitallium showed generally that Co was released and that Cr content increased at the surface.

Acid Etching, Dental↗
PubMed1987

Surface characteristics of posterior composites after polishing and toothbrushing.

The surface characteristics of eight posterior and two anterior composite resins were studied by SEM and profilometric tracings. The materials included both chemically cured and light-cured resin systems. Two posterior materials were microfilled composites; the others were conventional or hybrid types. The anterior composites were of conventional and hybrid types. At various steps in the procedures the following polishing/brushing treatments were evaluated: 1) dry polishing with Sof-lex discs followed by brushing with toothpaste; and 2) wet polishing with diamond pastes of increasing fineness, followed by brushing with toothpaste. The base line before the polishing/brushing procedures was obtained by wet polishing on silicon-carbide paper (4000 grit). All materials could be polished to a comparable smoothness by the Sof-lex discs, but this polishing procedure was associated with the development of an amorphous surface layer. Polishing with diamond pastes gave various results, with a 20-fold difference in surface roughness values from the smoothest to the roughest material. Toothbrushing after polishing with the Sof-lex system increased the surface roughness for all materials, but to various degrees. The two microfilled and four of the conventional posterior composites showed comparable surface roughness values, whereas two remaining posterior and the two anterior materials showed two to three times higher surface roughness values after toothbrushing.

Composite Resins↗