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Biomedical subjects

B K Moore

Publications and source records attributed to B K Moore.

At least 55 records · Page 3Linked to original sources
PubMed1993

Effect of crosslinking agent content, monomer functionality, and repeat unit chemistry on properties of unfilled resins.

Seven mechanical/physical properties were used to evaluate 10 unfilled resins: eight aromatic dimethacrylates and two urethane dimethacrylates. Physical property tests included compressive strength, Young's modulus in compression, uniaxial tensile strength, intrinsic yield point, toothbrush abrasion, Knoop hardness, and water sorption. Controlled changes were made in the following four material parameters: amount of crosslinking diluent present in the uncured monomer, functionality of the monomer, repeat unit chemistry of the monomer (urethane vs. aromatic structure) and mode of activation (chemical vs. visible light). Polymers containing a high concentration of crosslinking agent (50 wt%) were found to be tougher and to possess lower hardness than materials containing lesser amounts of crosslinking agent. This was attributed to the flexible nature of the triethylene glycol dimethacrylate crosslinking molecule. Exposure to water plasticized the highly crosslinked materials to the degree that the yield point and elastic modulus were effectively lowered. Most of the tested properties were unaffected by differences in functionality except resistance to toothbrush abrasion, which was enhanced for polymers derived from high functionality monomers. The urethane-based polymers sorbed substantially more water than the aromatic-based materials, which presumably resulted in lower values for surface hardness. However, the urethane resins were very tough, and excellent resistance to toothbrush abrasion was observed. Property differences caused by differences in activation mode were small, although the visible light materials did sorb more water.

Absorption↗
PubMed1993

Anodic polarization behavior and microstructure of a gallium-based alloy.

A gallium-based alloy (GA) that was developed as a substitute for dental amalgam was investigated for anodic polarization behavior in deoxygenated Ringers solution, 37 degrees C. The related microstructures were examined and microanalyses were conducted. Four polarization tests were conducted by scanning from -300mV to +1,000 mV (vs. SCE) at 2 mV/s. Polarization of the first sample (GA-1) was stopped after the first anodic dissolution peak (-100 mV, 1.5-2.0 x 10(-3) A/cm2). The fourth sample (GA-4) was interrupted at the secondary peak (+1000 mV, 0.3 A/cm2). It was found that (1) the early stage of the first peak is related to selective dissolution of divalent tin ions, followed by a dissolution of Ga. Transmission electron diffraction (TED) identified the brown corrosion product as Ga2O3; (2) the GA-4 sample was covered with the white corrosion product of mainly Sn+4, identified as SnO2. In addition, the current density of the GA sample when coupled with a high-copper dental amalgam was 0.03 A/cm2 (with +1,000 mV) at the second peak which was about a ten times lower value than for the uncoupled sample; (3) the uncoupled gallium alloy and gallium alloy coupled with a high-copper dental amalgam showed 10(3)-10(4) times higher anodic current density than that of an uncoupled high-copper dental amalgam, suggesting that the gallium alloy is more corrosion prone.

Corrosion↗
PubMed1992

Influence of selected variables on adhesion testing.

Three variables associated with adhesion testing were examined: (1) the test mode, shear and tension; (2) design of the tensile apparatus; and (3) tooth substrate, human and bovine. Findings revealed no significant differences in bond strength by one tensile test and a shear test. However, the shear test produced more true adhesive failures; thus it may be preferable to use a shear test for adhesion testing. Bond strengths with some adhesive systems differed significantly when tested by two different tensile apparatus. Design of the test apparatus appeared to affect values. Bond strength measurements obtained with human and bovine enamel were essentially comparable. Values with dentin varied. There appeared to be a trend for higher bond strength values with bovine than with human dentin.

Adhesiveness↗
PubMed1992

In vitro evaluation of two microleakage detection tests.

Two microleakage detection tests were evaluated to compare their capabilities for revealing the extent of leakage at the interface between amalgam restorations and tooth structure. Class V cavities were prepared in the buccal surfaces of extracted human canine and premolar teeth and were treated in one of the following ways: no liner or varnish, a copal varnish, or an adhesive resin liner. The cavities were restored with a high-copper single composition spherical amalgam alloy and the specimens thermally cycled. Following storage for 6 months, the teeth were exposed to separate solutions of 45Ca and an ultraviolet fluorescing dye. The teeth were hemisected longitudinally and leakage was evaluated by determining the degree of penetration of the two tracers at the occlusal and gingival margins. Statistical analysis revealed a significant difference between the two leakage techniques (P less than 0.05). The radioisotope test generally indicated a greater degree of leakage than did the ultraviolet dye test.

Acid Etching, Dental↗
PubMed1991

Microleakage and shear bond strength of resin and porcelain veneers bonded to cast alloys.

Four resin veneering materials and four methods of retaining the veneer on metal castings were compared with metal ceramic restoration. Variations in microleakage were noted between the four resin materials retained by mechanical retention beads. When mechanical and chemical modes of a resin and porcelain veneer retention were compared, there was no microleakage with one mechanically and two chemically retained resin groups including one metal ceramic group. The resin materials tested understandably produced substantially lower shear bond strengths than the metal ceramic specimens. Higher shear bond strengths were recorded for the retentive beads than for the resins retained by three chemical bonding techniques. There was no direct correlation between microleakage and shear bond strength.

Acrylic Resins↗
PubMed1991

Effect of filler content of light-cured composites on bond strength to bovine dentine.

The bonding of light-cured composites to tooth tissues is known to be disturbed by polymerization shrinkage, and polymerization shrinkage is affected by the filler content of composites. This in vitro research examined the relationship between the filler content and bond strength to dentine of light-cured composites. Experimental light-cured composite systems with filler contents of 45, 55, 65 and 75 per cent by volume were used in both bond strength to dentine and shrinkage tests. The surfaces selected as substrates were a flat surface and a box-shaped cavity prepared in bovine dentine. The lowest bond strength was obtained with the 45 per cent filler content composite in the box-shaped cavity. Bond strength increased with increasing filler content. Volumetric polymerization shrinkage decreased with increasing filler content. The polymerization shrinkage at 120 s after light curing was 5.24 per cent for the 45 per cent filler content system, 4.77 per cent for the 55 per cent, 2.14 per cent for the 65 per cent and 1.68 per cent for the 75 per cent. The correlation between bond strength and shrinkage was greater for the cavity than it was for the flat surface. This implies that bond strength in the box-shaped cavity may have been affected more by polymerization shrinkage than with the flat surface. The findings lend support to the view that filler content is one of the important factors influencing the physical properties of composites.

Acid Etching, Dental↗
PubMed1991

Repairability of type II glass polyalkenoate (ionomer) cements.

Two Type II glass polyalkenoate (ionomer) cements were evaluated for their repairability by measuring tensile bond strength of new material added to previously placed cement. Variables included time of repair (20 min vs. 24 h) and surface condition prior to repair (smooth and unetched, smooth and etched, rough and unetched, rough and etched). Failures were evaluated using light microscopy and categorized as cohesive, adhesive, or mixed. Scanning electron microscopy was employed to view the cement surfaces following each of the four pretreatments. Surface pretreatment was found to significantly affect both materials when repaired at 20 min (P less than 0.05). The highest bond strength was achieved when bonding to the smooth, unetched surface. Surface pretreatment did not significantly affect bond strength when the cements were repaired at 24 h (P greater than 0.05). Tensile bond strengths were greater for repairs made at 20 min than for those made at 24 h, but the differences were not always statistically significant.

Acid Etching, Dental↗
PubMed1991

Incorporation of adhesive liners in amalgam: effect on compressive strength and creep.

This study evaluated the effects of two adhesive resin liners (Panavia EX and Amalgambond) on the compressive strength and creep rate of a single composition high-copper amalgam alloy (Tytin). Cylindrical specimens were prepared by dead-loading or hand-condensing amalgam in a Teflon mold which was unlined, lined with Panavia EX, or lined with Amalgambond. Compressive strength specimens were tested at 1 hour, 24 hours, and 7 days after preparation. Creep specimens were tested at 7 days. The adhesive resin liners did not significantly affect the strength of the Tytin specimens prepared by dead-loading (P greater than 0.05). The Panavia EX significantly reduced the strength of the Tytin specimens prepared by hand-condensing (P less than 0.05). The creep rate was not significantly affected by either resin liner.

Analysis of Variance↗
PubMed1990

Color stability of composite resins.

The color stability of seven visible light-cured and three chemically-cured composite resins was investigated while being subjected to UV light irradiation and storage in an aqueous environment at elevated temperatures. Color shift was evaluated visually and by colorimetric measurements. Significant correlation was found between visual scoring and colorimetric readings. When subjected to UV light, a wide deviation in color change existed from brand to brand in photocured composite resins. The color shift of chemically-cured composite resins was less than but fell within the range of photocured composite resins. When stored in water at elevated temperatures, photocured resins exhibited better color stability than the chemically-cured composite resins.

Chemical Phenomena↗
PubMed1989

In vitro degradation of cements: a comparison of three test methods.

Three in vitro tests were evaluated on the basis of their ability to predict the relative resistance of various types of luting cements to disintegration in the oral cavity. The tests were (1) weight loss, (2) reduction in size of cement films held between glass optical flats, and (3) reduction in transverse strength. Storage media evaluated were H2O and 0.1, 0.01, and 0.001 M HAc. These data were compared with previously obtained measurements on the in vivo disintegration rates of the same cements. The best correlation with in vivo disintegration was obtained by test No. 2 when the specimens were subjected to 0.01 M HAc.

Dental Cements↗
PubMed1989

A comparison of the physical properties of four prosthetic veneering materials.

Four resin materials used to veneer metal castings were compared by evaluating certain physical properties. Three of the materials were microfilled resins and one was an unfilled resin. Although no material proved to be superior in all of the tests, the microfilled materials were generally better than the unfilled materials. The heat- and pressure- polymerized microfilled material was inferior to the two light-polymerized microfilled materials in three of the physical property tests, superior to them in one test, and proved to be equivalent to them in two tests.

Acrylic Resins↗
PubMed1989

A comparative study of the strength of aluminous porcelain and all-ceramic crowns.

This study compared the breaking strengths of all-ceramic crowns constructed with aluminous porcelain, the Cerestore system, and the Dicor system on an anterior tooth preparation. Fifteen crowns from each group were constructed to comparable dimensions on dies from the same master die. Ten crowns from the same group were cemented on the master die and loaded until catastrophic failure. Five crowns from each group were embedded and sectioned to examine internal adaptation. No significant difference was found between the load necessary to produce failure in the aluminous porcelain and Dicor crowns and the load needed to initiate crack formation in the Cerestore crowns. However, seven of the 10 Cerestore crowns showed a two-phase failure pattern; the difference between crack initiation and catastrophic failure was significant. Within the limitation of this study, neither the Cerestore (high alumina core) nor the Dicor (castable glass-ceramic) produced an all-ceramic crown superior to the current aluminous porcelain crown.

Aluminum↗
PubMed1989

Evaluation of color changes of silicone maxillofacial materials after exposure to sunlight.

A number of authors have listed the following qualities as ideal for maxillofacial material: (1) original physical and mechanical properties comparable to the human tissue that they are replacing, (2) the ability to sustain these properties during service, (3) compatibility with human tissues and the adhesives used to adhere the prostheses to tissue, and (4) the quality of being easy to process and an insensitivity to processing variables. Clinical experience has indicated that there is frequent and for the replacement of maxillofacial appliances because of rapid discoloration in the service environment and/or degradation of the physical and dynamic properties of the base elastomer. Color stability in the service environment may be the most important factor in patient acceptance of the prosthesis. The results of this study suggested that aging rather than exposure to sunlight results in most of the color changes observed in the HTV and RTV base polymers studied.

Color↗
PubMed1988

Comparative tensile strengths of brackets bonded to porcelain with orthodontic adhesive and porcelain repair systems.

The acceptance of simplified technical procedures that minimize clinical effort is exemplified by the popularity of direct bonding. This study (1) measured the comparative tensile bond strengths of brackets bonded directly in vitro to both glazed and deglazed porcelains by the use of five adhesive systems, and (2) recorded failure sites. System 1+, Enamelite 500, Isopast/Silanit, and Concise/Scotchprime proved to have strengths that should be acceptable clinically. Ultra-bond produced a bond that was significantly less in strength as compared with the other four systems. There was no significant difference in the bond of glazed and deglazed porcelains. Diamond polishing paste was better at restoring the porcelain surface to original smoothness in comparison with polishing stones. Irreversible damage to the porcelain surface may result from the bonding procedure.

Dental Bonding↗