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Biomedical subjects

M M Russell

Publications and source records attributed to M M Russell.

12 recordsLinked to original sources
PubMed1998

Precision of fit: the Procera AllCeram crown.

STATEMENT OF PROBLEM: Strength, color stability, and precision of fit are requirements for all-ceramic restorations. The Procera AllCeram crown system, composed of a densely sintered high-purity alumina core combined with a low fusing surface porcelain, appears to satisfy most of these requirements. However, evaluation of marginal fit has not been reported. PURPOSE: This study measured the precision of fit of the Procera AllCeram crown fabricated with Procera CAD/CAM technology for the premolar and molar teeth fit to a die. MATERIAL AND METHODS: Five ivorine maxillary first premolars and first molars were prepared for full-coverage crowns. Preparations were standardized with a convergence angle of 10 degrees, chamfer margins of 1.3 to 1.5 mm circumferentially, and occlusal reduction of 2.0 mm. AllCeram crowns were fabricated for the dies, and the fit of the crown to the die was determined by using a standardized procedure with a silicone impression material that served a dual role: (1) as a retrievable luting agent, and (2) to replicate the internal aspects of the crown. Laser videography was used to measure the gap dimension between the crowns and the dies at the marginal opening, the axial wall, the cusp tip, and the occlusal adaptation measurement locations. Mean gap dimensions and standard deviations (SDs) were calculated for marginal opening, internal adaptation, and precision of fit. RESULTS: Mean gap dimensions and standard deviations at the marginal opening for the premolar and molar crowns were 56.0 microns SD +/- 21 and 63.0 microns SD +/- 13 microns, respectively. The mean gap dimensions and SDs of the internal adaptation were 69.0 microns SD +/- 17 microns for axial wall, 48.0 microns SD +/- 12 microns for cusp tip, and 36.0 microns SD +/- 7 microns for occlusal adaptation for the premolar crowns; and 49.0 microns SD +/- 3 microns axial wall, 67.0 microns SD +/- 21 microns cusp tip, and 74.0 microns SD +/- 29 microns occlusal adaptation for molar crowns. Precision of fit and SDs for premolar and molar crowns were 52.0 microns SD +/- 19 microns and 63.0 microns SD +/- 20 microns, respectively. Mean marginal openings and precision of fit gap dimensions for the crown groups were not significantly different at the .05 level. However, gap dimensions that defined the internal adaptation at the measurement locations were different (P < or = .05). CONCLUSION: Mean gap dimensions for marginal openings, internal adaptation, and precision of fit for the crown groups were below 70 microns. These findings show that the crowns studied can be prescribed with confidence knowing that the precision of fit will consistently be less than 70 microns.

Aluminum Oxide↗
PubMed1997

The labor-adjusted cesarean section rate--a more informative method than the cesarean section "rate" for assessing a practitioner's labor and delivery skills.

OBJECTIVE: Our purpose was to determine the benefits of an acuity-adjusted labor management tool. STUDY DESIGN: A retrospective review was performed of all deliveries at Good Samaritan Regional Medical Center in Phoenix, Arizona, for a 1-year period from Jan. 1 to Dec. 31, 1994. All physicians with > or = 20 deliveries were included in the analysis. Patients with indications for which most practitioners would perform a cesarean delivery were removed from consideration. Physicians were then compared with respect to labor management in the remaining patients without relative contraindications to vaginal delivery. RESULTS: The total number of deliveries (n = 6062) was performed by 47 attending obstetricians, 9 perinatologists, an obstetrics-gynecology clinic, and a family practice clinic. The "raw" cesarean section rate was 20.1%. Those at high risk for cesarean delivery (n = 534) were excluded, leaving 684 cesarean sections performed in 5528 patients (12.4%) who were appropriate to labor. Differences were observed between the nulliparous cesarean section rate (16%) compared with that for parous patients (10.1%) (p < 0.0001 by Fisher's exact test (two-tailed) but not between attending obstetrician-gynecologists (12.4%) and perinatologists (13.8%) (not significant). CONCLUSION: A labor-adjusted cesarean section rate is more appropriate than just "raw" data. Medical, obstetric, and fetal factors affect a "raw" rate that is out of the control of the obstetrician. This method of assessing the labor and delivery skills of each practitioner and hospital would allow meaningful comparison with others.

Arizona↗
PubMed1997

The precision of fit at the implant prosthodontic interface.

STATEMENT OF PROBLEM: Percussion, visual observation, and conventional periapical radiographs are the methods most frequently used clinically to evaluate the accuracy of implant component assemblies, whereas methods to measure the precision of fit are limited. PURPOSE: In this study the Periotest instrument was used to evaluate the stability of the interfaces between the implant and the abutment, along with the abutment and the gold cylinder under a series of assembly conditions. The hypothesis tested is that a more negative Periotest value (PTV) would indicate an accurate fit and a more positive value PTV would correlate with an inaccurate fit. MATERIAL AND METHODS: To investigate this hypothesis in vitro, two bovine ribs were used as patient simulation models. Each model contained three self-tapping Brånemark implants placed approximately 7 to 10 mm apart and arranged in a reasonable curvature. A series of component assembly conditions were created as accurate and inaccurate with thickness gauges of 25.4 microns, 50.8 microns, and 101.6 microns. RESULTS: The mean Periotest values and SDs for accurately assembled abutments and gold cylinders were -6.0 +/- 0.32 and -3.4 +/- 0.68, respectively. Periotest value data of the assembly conditions were statistically analyzed with multiple regression analysis. The misfit in the implant to abutment interface resulted in a more negative Periotest value trend (r = 0.54) with increases in gauge thickness. However, the same magnitudes of misfit at the abutment to gold cylinder interface produced a more positive Periotest value trend (r = 0.72). CONCLUSION: The PTV trends were consistent with increased stability at the abutment to implant interface from the increasing magnitude of misfit created with the thickness gauges. In contrast, the measurement trends observed for the abutment to gold cylinder interface were consistent with decreased stability with each increase in gauge thickness inserted at the interface.

Acceleration↗
PubMed1995

Clinical, serological and virological characteristics of an outbreak of paresis and neonatal foal disease due to equine herpesvirus-1 on a stud farm.

An outbreak of equine herpesvirus-1 (EHV-1) occurred on a large stud farm with 133 mares, 54 foals and four stallions, and at least 85 mares, 22 foals and three stallions were infected. Clinical disease was observed in 16 mares, two stallions and 13 foals and the predominant clinical signs were scrotal oedema, ataxia and loss of libido in the stallions, ataxia and recumbency in the mares and uveitis and nasal discharge in the foals, although pneumonia and colic with intussusception were also recorded at autopsy. Neurological disease was more common in the mares nursing foals (12 of 38 infected) than in barren mares (one of 46 infected). Three mares died during the outbreak and no mares that had been recumbent bred again. Control procedures were based on virological and serological testing and stringent management practices to limit the spread of infection between groups of mares and foals and away from the stud farm. There were marked antibody responses in the adult horses, but they were generally poor in the foals; three of the nine viraemic foals did not develop significant increases in the levels of circulating antibody. Recommendations are made for the management of future outbreaks.

Animals↗
PubMed1995

A new computer-assisted method for fabrication of crowns and fixed partial dentures.

The availability of high-technology systems that use computer-aided design and computer-aided machining is on the increase. One such system is the Procera system, which is currently providing cost-effective, high-quality dental restorative services to dental laboratories and to dentists. A reduction in cost to the dentist, and ultimately to the patient, is a major advantage of the Procera system. Cost benefits combined with its continued success in producing crowns and fixed partial dentures that meet professional standards of care should enhance the acceptance of this new technology.

Computer-Aided Design↗
PubMed1994

A comparison of the color stability of conventional and titanium dental porcelain.

Simulation of naturally appearing enamel in fixed prosthodontics is best achieved with porcelain. This study investigated the color stability of two different dental porcelains, Ceramco and Procera, after they were exposed to 900 hours of accelerated aging. Twenty titanium plates provided the substrate to which the Procera porcelain samples in shades A3, A3.5, C3, and D3 were fired, five in each shade. An equal number of metal-ceramic alloy (Olympia) plates were cast to the same dimensions to form the 20 substrates to which Ceramco porcelain was fired. The four shades of porcelain were again added to each of the samples. Commission International de l'Eclairage L a b readings were recorded with a Minolta Chroma Meter II before and after exposure to 900 hours of accelerated aging simulation. After the aging process the color differences between the pretest and posttest condition were calculated. Although statistical comparisons demonstrated a difference in color change (p < or = 0.05) between Ceramco and Procera porcelain in three of the shades tested, critical remarks of color refer to both types having "slight" color change. In terms of color stability, neither porcelain had "noticeable" changes after 900 hours of accelerated aging.

Color↗
PubMed1993

The shear strength of polymethyl methacrylate bonded to titanium partial denture framework material.

Premachined titanium frameworks are used in implant-supported fixed complete-arch prostheses. Traditionally, retentive mechanisms are incorporated in the wax patterns to provide retention between polymethyl methacrylate and the cast framework. Nontraditional forms of retention are needed with machined frameworks. This study determined whether three different surface characteristics of titanium improve the bond shear strength of polymethyl methacrylate. Thirty rod shaped specimens of titanium were divided into three equal groups: group 1 received no pretreatment; group 2 was pretreated with 110 microns alumina air abrasive; and group 3 was pretreated with 110 microns alumina air abrasive plus silane (clear). Denture resin was processed around each specimen. A Shell-Nielsen shear test was then performed at a crosshead speed of 0.5 mm/minute to determine the bond shear strength in kilograms per square centimeter. The bond shear strength of group 3 was 63% greater than group 1 (significant, p < 0.01; ANOVA-Scheffé interval 63 kg/cm2). The results of this study indicated that surface pretreatment of titanium with 110 microns alumina air abrasive plus silane coating significantly enhances the bond shear strength of polymethyl methacrylate.

Aluminum Oxide↗
PubMed1989

Comparison of two office tests for determining blood theophylline levels.

The blood theophylline level determination is an important therapeutic tool, but reference laboratories can take from 1 to 3 days before giving results. Several quicker in-office methods for testing blood theophylline levels are currently available. Two methods were compared for reliability and accuracy. Both proved to be accurate, but the Acculevel method was more reliable than the Seralyzer method. The Acculevel appears to be a preferable method for in-office testing of serum theophylline levels.

Humans↗
PubMed1984

The interaction of nivazol with the glucocorticoid receptor from rat and rhesus monkey target tissues.

Steroid hormone receptor competition techniques were used to evaluate the glucocorticoid receptor binding properties of nivazol and its 11 beta-hydroxy derivative, Win 44577 in rat and monkey target tissues. These agents competitively inhibited the binding of 3H-dexamethasone to the glucocorticoid receptor from the liver and anterior pituitary from both rat and monkey with relative binding affinities of Win 44577 greater than dexamethasone greater than nivazol greater than cortisol in all cases. However, nivazol and Win 44577 had approximately twice the affinity for the anterior pituitary glucocorticoid receptor from both species. Neither compound demonstrated any significant binding to rat estrogen, progestin or androgen receptors. These results are consistent with a glucocorticoid receptor mediated mechanism of action for nivazol and Win 44577; however, the difference in the endocrine profile of nivazol in the rhesus monkey versus the rat does not appear to be due to a species selectivity in the affinity of nivazol for the glucocorticoid receptor from central or peripheral target tissue.

Animals↗
PubMedDate not supplied

Polishing sequence for titanium using dental armamentarium: a pilot study.

With the increasing use of titanium in dentistry, the methods for maintenance, particularly the polishing sequence, have become especially important. Thirty test samples of commercially pure grade 2 titanium were sandblasted with 110 microns aluminum oxide at 60 psi to establish a baseline surface roughness. Two samples were exposed to each of 15 different polishing sequences. Scanning electron photomicrographs of the polished samples were taken at x100 and randomly assigned identification numbers. The photomicrographs were evaluated and ranked by six dentists for surface smoothness. The best surface polish was obtained with the following sequence: aluminum oxide stone, green Flexie rubber abrasive wheel, white Flexie rubber abrasive wheel, flour of pumice on a wet rag wheel, buffing bar compound on a felt wheel, rouge on a felt wheel, and rouge on a chamois wheel.

Dental Polishing↗