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Biomedical subjects

B K Moore

Publications and source records attributed to B K Moore.

At least 73 records · Page 4Linked to original sources
PubMed1987

Tensile bond strength between glass ionomer cements and composite resins.

Etching or roughening the surface of glass ionomer cement before use of composite resins and bond agents produces bond strengths comparable to the bond strength between glass ionomers and dentin. Bond failure at such surfaces occurs within the glass ionomer. Adequate washing with water after acid etching the glass ionomer is essential to obtain optimal bond strength. Apparently, some combinations of ionomer cements and resins are more effective than are others in providing a good bond in the "sandwich technique".

Acid Etching, Dental↗
PubMed1987

In vivo disintegration of luting cements.

The in vivo disintegration of luting cements was determined at 6- and 12-month intervals in two test series of 20 participants each. Four cements were inserted in the wells located in the mesial and distal surfaces of cast crowns. Glass ionomer, silicophosphate, polycarboxylate, and zinc phosphate cements prepared with recommended powder/liquid ratios are discussed, and are ranked with respect to disintegration at 6 and 12 months.

Chemical Phenomena↗
PubMed1987

The influence of mixing speed on the setting rate of high-copper amalgams.

This study was undertaken to assess the effect of mixing speed on the setting rate of high-copper dental amalgam. The surface hardness during setting of two representative brands of dental amalgam was related to working and carving times determined by clinicians. From this information, a means of evaluating setting rate of amalgam based on surface hardness was developed.

Chemical Phenomena↗
PubMed1986

The contribution of a pinhole to the retention and resistance form of veneer crowns.

This research quantitatively compared the retention and resistance of various designs of maxillary premolar partial veneer crown preparations. Crowns were evaluated with and without proximal boxes and occlusal pins. In the absence of boxes or grooves, pins markedly enhanced both retention and resistance. In the presence of proximal boxes, pins contributed only to retention and had no significant effect on resistance. If pins are used, the cement should be spiralled into the pin hole. As resistance is usually the more crucial parameter in preparation designs, it seems that wherever efficient axial modifications can be incorporated, the pinhole modification may be of little advantage.

Cementation↗
PubMed1985

A comparison of the physical properties of a room temperature vulcanizing silicone modified and unmodified.

RTV silicone MDX 4-4210 unmodified and modified with the addition of 5%, 10%, and 15% 360 MF 100cs was tested for the following physical properties: tensile strength, ultimate elongation (ASTM D412 die C), tear resistance (ASTM D624, die C), and Shore A Durometer hardness (ASTM D2240). The initial mechanical properties of unmodified RTV silicone were superior to those of RTV silicone modified with 5%, 10%, and 15% 360 MF except for hardness. The value for each property measured was found to decrease linearly with the amount of 360 MF added. If additional softness is desired, it can be achieved with the addition of 360 MF to RTV silicone at the expense of decreased strength, elongation, and tear resistance. Even with the addition of 15% 360 MF the values for tear resistance and elongation were in the standard range. The tensile strength of unmodified RTV silicone fell below the accepted values.

Chemical Phenomena↗
PubMed1985

Polydimethyl siloxane materials in maxillofacial prosthetics: evaluation and comparison of physical properties.

The need for more acceptable materials for use in maxillofacial prosthetics has long been recognized. In this study, the physical properties of several currently available polydimethyl siloxane materials were evaluated and compared with those of two previously tested materials. The properties chosen were tensile strength, elongation, tear strength, and hardness. These properties were chosen as indicators of the strength, flexibility, durability, and lifelike feel of the materials in clinical service. Testing procedures were intended to duplicate as nearly as possible those used by Chalian and Jones and to conform closely to ASTM specifications. In general, the physical properties of the five silicone materials tested in this study were superior to those of MDX-4-4210 and MDX-4-4514, tested previously. This superiority was particularly evident in terms of strength and elongation. Although the materials failed to demonstrate the softness of other materials, they may prove acceptable with the addition of available modifiers. Although no material was consistently superior to the others, potential merit is seen especially in Q7-4635 and SE-4524U. These materials exhibited high strength and softness and are available in one component system. Unlike the two-component addition chemistry systems, these materials have an indefinite pot life and are much more easily manipulated.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗
PubMed1985

Properties of microfilled composite resins as influenced by filler content.

Two series of composite resins were prepared with a light-cured urethane dimethacrylate matrix to which varying amounts of two types of silanated silica particles were added. One series contained volume fractions ranging from 15.8 to 28.8% silica particles of 20 nm in diameter (Type I filler) and the other series volume fractions of from 24 to 49.4% of an agglomerated silica particle of 40 nm in diameter (Type II filler). Tests were conducted to determine the effect of filler level on: depth of cure as determined by hardness measurements; color stability in both UV light and water; water sorption with time; hardness; compressive strength; strain behavior in slow compression; and resistance to toothbrush abrasion and wear by hydroxyapatite. Analysis of the data obtained for these two microfilled series indicate that increased filler levels result in trends for increased depth of cure, color stability, hardness, compressive strength, and stiffness, while water sorption and resistance to both toothbrush abrasion and wear by hydroxyapatite were reduced. These trends were more pronounced for the Type II filler series than for the Type I filler series. However, there was a greater differential in filler levels within the Type II series than within the Type I series.

Acrylates↗
PubMed1985

Effect of filler content and size on properties of composites.

Two series of dental composites, along with the unfilled resin matrix, were examined to determine the effects of filler level and size on selected properties. Both series were prepared by incorporating a silanated barium borosilicate filler into a visible-light-activated polyphenylene polymethacrylate resin matrix. One series had a filler particle size of 2 microns, with filler levels of 20, 40, 45, 50, and 53% (vol). The second series contained a 15-microns filler in amounts of 20, 40, 50, 60, and 65% (vol). Tests conducted included: depth of cure as evaluated by hardness, water sorption, compressive strength, stress-strain behavior under slow compression, toothbrush abrasion, and wear by hydroxyapatite. Analysis of the data indicated that increased filler levels resulted in increased hardness, compressive strength and stiffness, and decreased water sorption. Also, there was a slight trend toward improved depth of cure. Incorporation of the 2-microns filler decreased the abrasion resistance of the resins to toothbrushing as compared with the unfilled resin, while addition of the 15-microns filler improved resistance. All filled resins exhibited a significant improvement in resistance to wear by hydroxyapatite as compared with the unfilled resin. There was a trend for increased wear with increased filler level. The particle size of the filler appeared to have a moderate influence on the properties. When compared with 15-microns filled resins of the same filler levels, the 2-micron filled series appeared to have inferior properties in terms of depth of cure, compressive strength, water sorption, and resistance to toothbrush abrasion. Properties which were less affected by particle size were hardness, stiffness, and wear resistance to hydroxyapatite.

Chemical Phenomena↗
PubMed1984

A comparison of the strength of base metal and gold solder joints.

The purpose of this study was to evaluate the procedures involved in forming high- and low-fusing solder joints between two different base metal alloys and to compare the strength of these joints with the strength of those formed between specimens made from a high-gold content alloy. The conclusions of this investigation can be summarized as follows. All but 11 of the 120 specimens failed through the solder joint, which confirms that the solder joint is usually the weakest part of a fixed partial denture. The high-fusing joints formed between the base metal alloys showed higher relative bending strength values than the high-fusing joints formed between the gold alloy specimens. The low-fusing joints formed between the base metal alloys showed higher relative bending strength values than the low-fusing joints formed between the gold alloy specimens, and the low-fusing base metal joints exhibited the highest strength values in this study. The low-fusing joints formed between gold alloy specimens consistently bent before fracturing. Solder joints fail both adhesively (separation of the solder from the parent metal) and cohesively (fracture through the solder, parent metal, or a combination of both). A correctly formed joint between gold components should show cohesive fracture, whereas adhesive fractures are apparently acceptable with base metal alloys since the low-fusing base metal joints failed in this manner but still exhibited high strength values. Voids of different sizes and locations were observed in most of the solder joints, and within each group tested there was usually less strength exhibited by the joints with larger areas of porosity.

Dental Alloys↗
PubMed1983

The effects of enamel wear on the metal-porcelain interface.

This study evaluated the effects of wear of human tooth enamel on the metal-porcelain interface. Failure in the porcelain half of the specimens occurred only in specimens where the metal angle was 60 degrees. There was failure in one of four of the noble metal alloy specimens. With the base metal alloy specimens, in the first group two specimens showed cracks in the preparation stage while the other two showed no sign of cracks either before or after testing. In a second group of four base metal alloy specimens with a 60-degree angle, all four specimens showed cracks in the porcelain after glazing. These specimens were repaired by grinding out the cracks and filling them with porcelain. After wear-testing, all four specimens developed cracks. The data indicate that the acute angle of metal (60 degrees) at the metal-porcelain interface was more conducive to crack formation than were the other two angles tested. Therefore, in the case of a metal-ceramic restoration, with the occlusion on the metal, an acute angle of metal would not be appropriate. Furthermore, under clinical circumstances cracks that occur after glazing, as arose with the last four base metal alloy specimens (60 degrees), probably should not be ground out and refilled with porcelain. The results of this study indicate that such a practice in a clinical situation could lead to eventual fracture of the porcelain. The porcelain half of the specimens had a deeper and wider wear track than its metal counterpart, which indicated that the porcelain is less resistant than the metal to wear by enamel.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Alloys↗
PubMed1982

Dissolution of amalgam in saline solution.

This experiment was designed to investigate the in vitro corrosion of several modern dental amalgams in saline solution over a six-month period by measuring changes in the soluble corrosion products. Based on the change of the electrical conductivity of the solution, the dissolution rate seemed to decrease gradually for the first three to four months. Then a rapid increase was observed, indicating a reactivated corrosion process. Larger dissolutions of copper and mercury were observed, especially for the high copper alloys, in these later stages. Zinc and indium, if present, were preferentially released at the earlier stages. Silver and tin could not be detected. Evidence exists that the corrosion of tin results in insoluble deposits of corrosion products.

Copper↗
PubMed1982

A comparative study of the strength of aluminous porcelain jacket crowns constructed with the conventional and twin foil technique.

The purpose of this study was to evaluate and compare the strength of aluminous porcelain jacket crowns made in the following manners: (1) the conventional technique, (2) the conventional technique with a pure alumina insert, (3) the twin foil technique, and (4) the twin foil technique with a pure alumina insert. The conclusions of this investigation can be summarized as follows: 1. Porosity was observed in all the restorations made by each of the techniques. 2. The porosity was greater at the porcelain-platinum foil interface than anywhere else throughout the restoration with both the conventional and twin foil techniques. 3. The porosity seemed to be evenly distributed along the interface, with no concentration in any area. 4. Regardless of the technique, crowns that were more porous fractured at lower values. 5. Crowns built by the twin foil technique were significantly more porous at the interface of the tin-plated platinum and the porcelain core than those built by the conventional technique. 6. Crowns constructed with the conventional technique were significantly stronger than those constructed with the twin foil technique. 7. There was no bond between the core porcelain and the platinum foil matrix in crowns constructed by the conventional technique. 8. There seemed to be a strong bond between the core porcelain and the tin-plated platinum matrix in crowns built by the twin foil technique. 9. The presence or absence of the alumina insert on crowns constructed with the conventional and twin foil technique did not affect the strength of the crowns when tested at the incisal edge.

Aluminum↗