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Biomedical subjects

C T Smith

Publications and source records attributed to C T Smith.

At least 19 recordsLinked to original sources
PubMed2001

Comparative in vitro evaluation of two provisional restorative materials.

STATEMENT OF PROBLEM: Provisional crowns traditionally have been associated with problems such as poor occlusion, contour, fit, and finish. Fabrication procedures should be uncomplicated and predictable within a realistic time frame. PURPOSE: The purpose of this study was to compare the quality of provisional restorations fabricated by dental students from 2 different materials (bis-acryl composite resin and PMMA) and identify the advantages and disadvantages associated with each material. MATERIAL AND METHODS: This study evaluated the occlusion, contour, marginal adaptation, and finish of 222 provisional crowns fabricated by 2 groups (A and B) of dental students. One bis-acryl composite resin material (Integrity) and 2 PMMA resins (C&B Resin and Snap) were evaluated. RESULTS: For group A, Integrity was statistically superior (P<.05) to C&B Resin in all 4 categories for anterior provisional crowns. For posterior provisional crowns, Integrity proved superior in the categories of contour and marginal adaptation, but no significant differences were established for occlusion and finish. For group B, Integrity was statistically superior to Snap in the categories of occlusion, contour, and marginal adaptation, whereas there was no statistical difference in finish. When all 4 categories were analyzed, Integrity was found to be statistically superior. CONCLUSION: Bis-acryl composite resin (Integrity) was significantly superior to PMMA (C&B Resin and Snap) as a provisional restorative material.

Composite Resins↗
PubMed2000

Platelet noradrenaline and adrenaline efflux in hypercholesterolaemia: studies in platelet-rich plasma.

Collagen-induced (5-80 microg/ml) efflux of free noradrenaline (NA) and adrenaline (Ad) from platelets in platelet-rich plasma was compared in normal human subjects and heterozygous familial hypercholesterolaemic (FH) patients. Stimulated release of NA and Ad to the plasma (platelet-poor; PPP) increased in a dose-dependent fashion in both normal and FH groups. Under resting conditions (0 microg/ml collagen) PPP NA concentrations were increased in hypercholesterolaemics by 38% (non-significant). The absolute amounts of NA released on stimulation with 5 microg/ml and 10 microg/ml collagen (i.e. the differences between resting and stimulated release) were reduced in hypercholesterolaemics by 45% (p<0.01) and 38% (p<0.02), respectively. Collagen EC50 values for NA and Ad release were increased in hypercholesterolaemics by 118% (p<0.001) and 141% (p<0.05). Combining the data for the normal and FH groups revealed that the collagen EC50 values for NA release correlated positively with plasma total cholesterol (p<0.02) and low-density lipoprotein (p<0.02). These data provide additional evidence for catecholaminergic abnormalities in hypercholesterolaemia.

Adult↗
PubMed1999

Effective taper criterion for the full veneer crown preparation in preclinical prosthodontics.

PURPOSE: Effective taper criteria must define a realistic, measurable goal that the student can visualize and achieve. Six degrees is widely accepted as the taper criterion for the full veneer crown preparation. However, studies show the actual taper of most preparations to be greater than 12 degrees. The purpose of this study was to determine whether 12 degrees is an effective taper criterion for the full veneer crown preparation in preclinical prosthodontics instruction. MATERIALS AND METHODS: A group of 191 full veneer crown preparations with 6 degrees as the taper criterion, and a group of 130 full veneer crown preparations with 12 degrees as the taper criterion were evaluated. All preparations were accomplished by preclinical dental students working on typodonts under examination conditions. RESULTS: The overall mean taper for each group exceeded the targeted criterion. The overall mean taper for the 6 degrees group was 14,490. When 12 degrees was the criterion, the overall mean taper was 15,580. The t test results indicate significant differences (p < .0001) between the targeted criterion and the actual preparation mean taper in all samples except one: the faciolingual measurements in the 12 degrees group. The faciolingual measurement of 12,920 was not statistically significantly different (.0542) from the targeted criterion of 12 degrees. CONCLUSION: The use of a 12 degrees taper criterion did not result in preclinical students achieving the goal of a 12 degrees taper. However, a 12 degrees criterion is more realistic than a 6 degrees criterion for full veneer crown preparations.

Crowns↗
PubMed1998

Brief paradoxical sleep deprivation impairs reference, but not working, memory in the radial arm maze task.

Selective deprivation of paradoxical sleep after learning results in memory deficits in a variety of tasks. The present experiment was designed to examine the effects of paradoxical sleep deprivation (PSD) upon spatial working and reference memory. Adult male Sprague-Dawley rats were trained for 10 days in an eight-arm radial maze. Food rewards were available in four of the arms, while the other four arms were never baited. After each daily training session, different groups of rats were given 4 h of PSD, beginning either immediately, 4 h, or 8 h after the training experience. An additional group received PSD during the period 13-24 h following daily training. The group that received PSD for 4 h immediately following daily training showed significant impairment compared to the other groups, but the deficit was limited to the reference component of the task. This result suggests that PSD causes deficits only in long-term forms of spatial memory.

Animals↗
PubMed1998

Pigments and their application in maxillofacial elastomers: a literature review.

PURPOSE: This literature review provides information about pigments used for facial and somatoprostheses. MATERIAL: This information includes common pigment and index names and numbers, lightfastness categories, chemical type and class, and the chemical formulas of the common pigments used in maxillofacial prosthetics. CONCLUSION: It can be deduced from this review that the pigments used with silicone elastomers do exhibit a color change, and that a color change is to be expected.

Humans↗
PubMed1998

Prefabricated post-and-core systems: an overview.

Restorative dentists should have a working knowledge of more than one post-and-core system. This review is designed to encourage them to consider systems they might not have considered otherwise. Many restorative dentists learn to use one prefabricated post-and core system, and they have only one system on hand. When the system on hand is the solution, there is no need for an alternative. However, no single prefabricated post-and-core system can fit all endodontic restorative requirements. The best way to pick an optimum system design is to compare alternatives. The vast assortment of available system components, many supported solely by experimental data without direct clinical corroboration, makes comparison and selection a challenging process.

Dental Cements↗
PubMed1998

Biomechanical criteria for evaluating prefabricated post-and-core systems: a guide for the restorative dentist.

Selecting the optimum prefabricated post-and-core system can be a complex and imprecise exercise for the restorative dentist. First, no single prefabricated post-and-core system fits all situations. Second, the vast number of post-and-core components currently on the market complicates the selection process. Finally, useful biomechanical criteria for evaluating prefabricated post-and-core components are difficult to quantify. The prefabricated post-and-core system consists of three components: the post, a core material, and a luting cement. Each combination of component types is a potential system alternative. This article presents useful biomechanical criteria, based on current restorative guidelines, for evaluating the basic components of any prefabricated post-and-core system.

Biomechanical Phenomena↗
PubMed1997

Bactericidal and inhibitory activity of quinupristin/dalfopristin against vancomycin- and gentamicin-resistant Enterococcus faecium.

There is a need for new agents, or combinations of agents, for the treatment of infections caused by vancomycin- and gentamicin-resistant Enterococcus faecium (VGREF) that may be resistant to all available antimicrobial agents. The early in-vitro activity of quinupristin/dalfopristin (30:70)--an injectable streptogramin--encouraged us to test this agent against VGREF. By broth dilution, the MICs of quinupristin/dalfopristin against 38 isolates of VGREF ranged from 0.06 mg/L to 2.0 mg/L (mode 0.12 mg/L). The addition of 0.5 mg/L of ciprofloxacin significantly reduced the modal MIC of quinupristin/dalfopristin to 0.015 mg/L (P = 5.75 x 10(-8)). Although the addition of 8.0 mg/L of teicoplanin or 4 mg/L of tetracycline did not significantly reduce the modal MIC, the lowest concentration of the MIC range was reduced from 0.06 to 0.015 mg/L. In broth, quinupristin/dalfopristin had slow bactericidal activity against the four strains tested over 48 h, with a 1-2 log10 cfu/mL reduction after 24 h in > 1 mg/L of quinupristin/dalfopristin for two strains and > 8 mg/L for the two other strains. A mixture of quinupristin/dalfopristin in a 70:30 ratio was more bactericidal: against one of the four strains 4-32 mg/L of the combination produced a further 0.5-1.0 log10 reduction in cfu/mL after 24 h and there was a reduction of 6.0 log10 cfu/mL after 48 h for another. By ultracentrifugation, the binding of 32 mg/L quinupristin/dalfopristin to human plasma protein was 90%, and in plasma broth, 32 mg/L of quinupristin/dalfopristin maintained bacteriostatic but not bactericidal activity. There is some useful synergy with ciprofloxacin and tetracycline, and the activity of quinupristin/dalfopristin may be enhanced against some strains by reversing the concentrations of its two components, quinupristin and dalfopristin, as that may occur in vivo.

Anti-Bacterial Agents↗
PubMed1997

Restoration of endodontically treated teeth: a guide for the restorative dentist.

This article provides a decision flow chart that can serve as a guide to selecting the optimum restorations for endodontically treated teeth. The process begins with an assessment of the endodontically treated tooth to determine its restorability. The restorable tooth is then evaluated for the amount of remaining coronal tooth structure. Anterior teeth with minimal or moderate coronal damage do not require complete coverage or a post and core. However, anterior teeth with significant coronal damage will require complete coverage plus a post and core. Posterior teeth with minimal coronal damage may be treated conservatively with partial-coverage restorations. For posterior teeth with moderate damage and those with curved roots, amalgam or resin composite foundations are used to support complete-coverage restorations. Posterior teeth with significant coronal damage require a post and core and a complete-coverage restoration.

Decision Trees↗
PubMed1996

Use of PSA nadir to predict subsequent biochemical outcome following external beam radiation therapy for T1-2 adenocarcinoma of the prostate.

PURPOSE: This study assessed the ability of nadir prostate-specific antigen (PSA) to act as an early surrogate for subsequent freedom from biochemical failure following radiation therapy for T1-2 prostatic adenocarcinoma. METHODS AND MATERIALS: A retrospective analysis was performed on the biochemical outcome of 314 consecutive men with T1-2 disease treated by conventional external beam radiation at the Massachusetts General Hospital. Minimum follow up was 2 years, and failure was defined as three successive rises in serum PSA of greater than 10%. Kaplan-Meier actuarial analysis of outcome was employed. RESULTS: The overall 5-year freedom from biochemical progression was 63%. For those who achieved a PSA nadir of < or = 0.5 ng/ml (n = 123) it was 90%, for 0.6-1.0 ng/ml (n = 103) it was 55%, and for > 1.0 ng/ml (n = 88) it was 34%. Multivariate analysis showed an undetectable PSA nadir to be independent of Gleason grade and initial PSA in predicting subsequent outcome (P < 0.05). The likelihood of achieving an undetectable PSA nadir correlated strongly with the pretreatment value: 74% if this was below 4 ng/ml; 42% for those between 4.1 and 10 ng/ml; and 32% for those above 10 ng/ml. CONCLUSION: A PSA nadir of < or = 0.5 ng/ml represents an early endpoint strongly predictive of a favorable outcome following radiation therapy which may be used for the rapid assessment of new radiation strategies.

Actuarial Analysis↗
PubMed1994

Addition of functional human telomeres to YACs.

Linear mammalian artificial chromosomes (MACs) will require functional telomeres, a centromere and the ability to replicate autonomously. We are investigating the possibility of developing MACs from yeast artificial chromosomes (YACs). Retrofitting vectors have been constructed to replace YAC telomeres with cloned human telomeric DNA. A modified YAC was introduced into mammalian cells by spheroplast fusion and the frequency with which the retrofitted human telomeric DNA seeded the formation of a new telomere was determined by Bal31 digestion and cytogenetic analysis. The telomere adjacent to the selectable marker gene was functional in 5/46 clones (11%) while the telomere 200 kb away at the other end of the YAC was functional in 1/46 clones (2%). These results indicate that despite the in vivo modification of the end of the telomere by the addition of yeast sequences, human telomeres will function at a high enough frequency to allow the construction of MACs by this route.

Chromosome Mapping↗
PubMed1992

Two largest national alliances fine-tune strategies as health care environment changes. Interview by Howard J. Anderson.

The nation's two largest alliances of not-for-profit hospitals and systems are refining their roles for the 1990s. American Health Care Systems (AmHS) and Voluntary Hospitals of America (VHA) are moving away from strategies designed for competition in the marketplace of the 1980s, and toward helping their members change the way they deliver health care in their communities. While AmHS is promoting its health care reform proposal, VHA sees its existing 29 regional organizations of hospitals as a potential infrastructure for the development of community-based, integrated networks of care as envisioned in the AHA's reform plan. Experts add that the alliances clearly have to go beyond group purchasing to serve the changing needs of their members.

Community-Institutional Relations↗
PubMed1992

Hibernation alters the frog's immune system.

The lymphomyeloid organs and blood leukocyte populations of the leopard frog, Rana pipiens, undergo conspicuous changes during hibernation at 4 degrees C. Within the blood, spleen, thymus, jugular bodies, and bone marrow there was a progressive loss of hemopoietic populations resulting in a marked lymphocyte depletion. Termination of the 135-day hibernation period resulted in the restoration of all hemopoietic elements in the blood and lymphomyeloid organs within 30 days. Frogs subjected to experimental hibernation and immunized showed weakened immune responses when brought from the hibernaculum. Plaque-forming cells (PFC) were lower in spleen, jugular bodies, and bone marrow, and serum antibody titers were also lower. Although the kinetics of the primary responses were essentially the same, the secondary responses differed suggesting major rearrangements with respect to the numbers of cells and their function in secreting antibody. The apparent lymphocyte aplasia may contribute to the absence of immunological responsiveness during periods of hibernation.

Animals↗