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Biomedical subjects

E E Parry

Publications and source records attributed to E E Parry.

16 recordsLinked to original sources
PubMed1999

Three-body wear of a hand-consolidated silver alternative to amalgam.

Recent studies have investigated a mercury-free silver alternative to amalgam, but the silver powders required a relatively high compaction pressure to consolidate. The aim of the present study was to consolidate a precipitated silver powder into a cohesive solid using an air-driven pneumatic condenser fitted with an amalgam plugger at a clinically realistic load, and to study the mechanisms and rates of three-body wear of the consolidated silver in comparison with that of an amalgam. The silver powder was annealed, rinsed with a dilute acid, and consolidated either in a prepared tooth cavity or in a specimen mold at a load of 15 N. A four-station wear machine was used where each specimen was immersed in a slurry containing polymethyl methacrylate beads, then a steel pin was loaded and rotated against the specimen at a maximum load of 76 N. The flexural strength in MPa (mean +/- SD; n = 10) was 86 +/- 20 for amalgam, 181 +/- 45 for silver with a polished surface, and 202 +/- 21 for silver with a burnished surface. After 4 x 10(5) wear cycles, the wear scar depth in microm was 134 +/- 54 for amalgam, 143 +/- 8 for polished silver, and 131 +/- 9 for burnished silver, which were not significantly different (Tukey's multiple comparison test; family confidence coefficient = 0.95). SEM examination revealed cracks and fracture pits in the worn surface of amalgam, in contrast to a smooth surface in silver. Wear and material removal in amalgam occurred by microfracture and dislodgement of cracked segments, while wear in the silver occurred by ductile deformation and flow of materials. To conclude, the consolidated silver possesses a three-body wear resistance similar to that of amalgam, and a higher resistance to wear-induced damage and cracking than amalgam. The mechanism of wear in amalgam is microfracture and material dislodgement, while that in consolidated silver is ductile deformation and flow of material.

Compressive Strength↗
PubMed1996

Castability, opaque masking, and porcelain bonding of 17 porcelain-fused-to-metal alloys.

Seventeen porcelain-fused-to-metal alloys, which represented a cross section of the various alloy types available, were evaluated for castability, opaque masking, and porcelain bond strength. The base metal alloys generally cast more completely than the noble alloys, with the presence of beryllium as an important factor for greater castability among the base metal alloys. Statistically significant differences were observed in the ability of an opaque porcelain to mask the different alloy substrates but no systematic effect of alloy type was observed. Porcelain bond testing revealed that nickel-chromium-beryllium alloys produced significantly better porcelain-metal bonds than nickel-chromium alloys without beryllium. In addition, it was found that palladium-copper alloys produced significantly better bonds with porcelain than palladium-cobalt alloys.

Analysis of Variance↗
PubMed1990

Oxide adherence and porcelain bonding to titanium and Ti-6Al-4V alloy.

The bonding of an experimental low-fusing porcelain to titanium and Ti-6Al-4V was evaluated by an x-ray spectrometric technique that measures the area that remains covered with porcelain following a controlled deformation of the metallic substrate. Oxide adherence strength values for titanium and Ti-6Al-4V oxidized at 750 degrees and 1000 degrees C were measured in tension with use of high-strength adhesives. The effect of further oxidation that would occur during porcelain firing was evaluated via simulated porcelain firings without actual porcelain application. Interface cross-sections of the titanium-porcelain and Ti-6Al-4V-porcelain bonds were examined in a scanning electron microscope (SEM). The porcelain was found to delaminate completely from the metal substrate, leaving less than 1% of the surface covered with porcelain. The oxide adherence of the specimens oxidized at 750 degrees C was good, but those oxidized at 1000 degrees C exhibited significantly lower oxide adherence (p = 0.001). The simulated porcelain-firing oxidation treatments also produced a significant decrease in oxide adherence (p = 0.004). The 750 degrees C oxidation treatments produced oxide films too thin to be visualized in the SEM, whereas the 1000 degrees C oxidation treatments produced oxide films approximately 1 micron thick. The lower oxide adherence of the 1-micron-thick oxide films is consistent with reports in the titanium literature of oxide delamination when the oxide film reaches 1 micron in thickness.

Alloys↗
PubMed1988

The relationship between oxide adherence and porcelain-metal bonding.

The lack of a reliable bond test has hindered the elucidation of the mechanism for porcelain-metal bonding in dental systems, because a test capable of detecting differences among porcelain-metal bonds of various qualities is required before the reasons for these differences may be ascertained. A method was developed in the present study whereby specimens of alloys with differing physical properties may be deformed to a constant strain to yield a fracture surface suitable for measurement of the area fraction of retained porcelain by an x-ray spectrometric technique described previously. The method proved sufficiently discriminating that significant differences could be found in 48 of the possible 66 comparisons among alloys and treatments. Linear regression analysis revealed a strong correlation (r2 = 0.947) between the area fractions of retained porcelain measured in the present study and the oxide adherence strength values measured previously. This strong correlation, when considered in light of the literature evidence for the presence of an oxide layer at the porcelain-metal interface, provides compelling support for the oxide layer theory of porcelain-metal bonding in dental alloy systems.

Dental Bonding↗
PubMed1985

A technique for characterizing casting behavior of dental alloys.

A technique for characterizing casting behavior of dental alloys has been developed and tested. The method employs easily reproducible specimen patterns and uses equipment and procedures generally available in dental prosthetic laboratories. A castability value is arrived at by counting complete segments of a cast alloy grid. Test results indicate that the castability evaluation procedure described can be a valuable aid in the laboratory for both selecting and using dental materials for producing cast restorations. The test method would also appear useful for the evaluation of products and techniques during research and development. An absolute minimum for the castability value determined relative to clinical and laboratory efficacy has yet to be established.

Chemical Phenomena↗
PubMed1984

Measurement of oxide adherence to PFM alloys.

A method has been reported for evaluating adherence of an oxide to its substrate metal to a maximum value of about 40 MPa. Oxidized alloy plates were cemented between two aluminum cylinders with a high-strength cyanoacrylate cement and loaded in tension until failure occurred either at the oxide/metal interface, within the oxide layer, or in the cement itself. Significant differences were found among the oxide adherence values obtained from different PFM alloys. The oxides formed on five of the alloys exhibited adherence strengths in excess of the published value for cohesive strength of dental opaque porcelain, indicating that they possess sufficient adherence to act as the transition zone between the porcelain and the alloy. In addition, a correspondence was found between the quality of porcelain bond for a given alloy and its oxide adherence strength. These results remove the principal objection to the oxide-layer theory of porcelain bonding in dental alloy systems and emphasize the importance of oxide adherence in the establishment of a bond. It is therefore suggested that future work devoted to porcelain-metal bonding should seek to elucidate the mechanism of oxide adherence to PFM alloys and explore the development of new alloys which form adherent oxides.

Adhesiveness↗
PubMed1983

A general practice study of timolol/hydrochlorothiazide/amiloride ('Moducren'), a new therapy for hypertension, and the doctor's influence on management.

An open study was carried out in general practice to assess the efficacy and tolerance of a timolol (10 mg)/hydrochlorothiazide (25 mg)/amiloride (2.5 mg) preparation in 558 hypertensive patients previously receiving multi-dose antihypertensive therapy, and to determine whether the results were influenced by the manner in which the doctor conducted this change in therapy. Patients received 1 or, if necessary, 2 tablets once daily over a period of 12 weeks and were randomly allocated on entry to one of two groups. One group was given a full explanation for the change in therapy, the other group was simply told that treatment was to be changed. The results showed that the change in treatment led to a significant reduction in blood pressure in both groups, at a dosage of 1 tablet daily in over half the patients, and the majority (88%) preferred the new form of treatment. Patient acceptance was good and the number of reports of adverse symptoms decreased during the study period. There was no significant difference in any of the results between the two groups.

Adult↗
PubMed1982

Comparison of timolol/hydrochlorothiazide/amiloride ('Moducren') with cyclopenthiazide/potassium in mild to moderate hypertension.

An open study was carried out in 641 patients with mild to moderate hypertension seen in general practice to assess the effectiveness of treatment with a timolol/hydrochlorothiazide/amiloride preparation compared with cyclopenthiazide/potassium. The timolol/hydrochlorothiazide/amiloride preparation produced better control of blood pressure in a larger percentage of patients after 2 and 6 weeks of treatment than did the diuretic/potassium preparation, and more patients were maintained on 1 tablet per day. Both treatments reduced the number of symptoms complained of by the patients at the initial visit.

Adult↗
PubMed1981

An amine accelerator for colorfree curing of cold-curing methyl methacrylate denture systems.

These tests showed that DMBA, a recently commercialized amine accelerator, is more suitable from the standpoint of color for use in denture base, reline, and repair resins than is the commercially used amine, DMPT. As the curing times of all specimens were approximately the same, the mechanical properties are expected to be similar for the following reasons. Previous experiments have shown that in the same composite formulation, equimolar concentration of DMPT and DMBA produce identical hardening times. A more recent investigation with composite systems indicates that amines yielding comparable polymerization rates produce materials with approximately the same mechanical strength; the same is expected to prevail with unreinforced methacrylate polymers. All specimen disks provided similar resistance to bending by hand.

Chemical Phenomena↗
PubMedDate not supplied

Remineralization effect of a low-concentration fluoride rinse in an intraoral model.

A previous study showed that a sodium hexafluorosilicate-calcium chloride-based two-solution fluoride (F) rinse containing 6 mmol/l of F was more effective than a 12 mmol/l F sodium fluoride rinse in depositing F on tooth surfaces and increasing oral F levels. The present study compared the remineralization effects of these two rinses in an intraoral de- and remineralization model. The results showed that the 6 mmol/l F two-solution rinse produced greater remineralization in increasing lesion mineral contents and reducing lesion depths. The results demonstrated that the effectiveness of an F regimen depends less on the F dose and more on the ability of the treatment to utilize F efficiently for remineralization.

Analysis of Variance↗
PubMedDate not supplied

Edge-bevel fracture resistance of three direct-filling materials.

Edge strength is defined in this study as the resistance to fracture of the beveled extension normally located at the cavosurface margin of a dental restoration. The edge strength of direct-filling alloy restorations plays an important role in maintaining the integrity of margins at tooth-alloy interfaces during functional loading. The purpose of this study was to determine the relative strength of an experimental consolidated silver material in comparison to other direct filling materials. The method used was designed as a simulation for relative edge-strength clinical properties. Stainless steel dies were formed from disks 5 mm thick, each with a centered hole tapered (1/48) toward the bottom side of the disk. A 41 degrees bevel, 0.5 mm wide as viewed from above, was placed on the top-side of the disk. Dispersalloy (D) or Unison (U) amalgam, Z-100 composite (C), hand-consolidated silver powder (HAg), or pneumatically consolidated silver powder (PAg) was used to fill the die opening. Excess was polished from both sides of the disk with 600-grit abrasive paper. The sample was loaded from the beveled side with a 3 mm-in-diameter flat-ended plunger at a rate of 1.0 mm/minute until failure. Failure load and total energy to failure were recorded and compared. Tukey's multiple comparison test (p < 0.05) ranked the materials (U) > (HAg) > (D) > (PAg) > (C) for fracture strength and (HAg) > (D) > (U) > (PAg) > (C) for fracture energy.

Analysis of Variance↗
PubMedDate not supplied

Amalgam buildups: shear strength and dentin sealing properties.

The retentive strength and sealing properties of amalgam buildups were compared in vitro in three groups of specimens. All teeth were prepared with flat, nonretentive surfaces. In the first group, the amalgam buildups were retained by four self-threading Minim pins. In the second group, retention was provided by a circumferential slot prepared in the dentin just inside the DEJ. The third group utilized an adhesive resin for retention. Dentin permeability was measured as a hydraulic conductance before and after placement of the amalgam buildups and before and after thermocycling. All methods of retention sealed dentin very well even in the absence of cavity varnish. The 90 degree retentive strength was: pins, 10.3 +/- 0.9 MPa; slots, 4.1 +/- 0.5 MPa; resin, 3.1 +/- 0.8 MPa (mean +/- SEM).

Adolescent↗
PubMedDate not supplied

Tapered cross-pin attachments for fixed bridges.

The design and fabrication of multi-unit fixed prostheses where abutment teeth are misaligned have been difficult technical challenges for dentists and dental technicians. There have been a number of methods developed to attain a common path of insertion, including modified preparation designs, telescopic copings placed on abutments to correct alignment, adhesively retained bridge frameworks, and mechanical precision attachments between sections of a segmented prosthesis. This paper describes a method of fabricating a precision attachment on a segmented prosthesis that can be rigidly fixed after cementation. The technique involves the use of a cast tapered pin to permanently attach the prosthesis segments together. All parts can be fabricated by conventional lost-wax techniques with a minimum of instrumentation. The technique has the added advantage of being reversible should the prosthesis ever need to be separated for repair or recementation.

Dental Casting Technique↗
PubMedDate not supplied

Consolidation conditions for a cold-welded mercury-free alloy.

Alloys being investigated as possible direct-filling materials rely upon a cold-welded, deformable silver matrix phase for cohesion and strength. The silver matrix is formed by direct consolidation of comminuted silver under an oxide-removing acid. The object of this study was to determine the effect of conditions such as load, increment thickness, and concentration of oxide-removing acid on the properties of the silver matrix. Results indicate that the addition of higher impact loads significantly improved yield strength and specimens built up by using thinner increments were significantly stronger and denser.

Cold Temperature↗