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Biomedical subjects

R M Shelton

Publications and source records attributed to R M Shelton.

At least 19 recordsLinked to original sources
PubMed2001

The influence of mixing ratio on the toughening mechanisms of a hand-mixed zinc phosphate dental cement.

OBJECTIVE: A range of mixing ratios occur for zinc phosphate cements in clinical usage and trials. The compressive strength of these cements is dependent on mixing ratio and at a critical ratio, a sudden rise in compressive strength is known to occur. This study investigated the mechanisms behind the cement curve behavior in an attempt to explain the strength increase with mixing ratio. METHODS: Crack propagation from indentations produced in cements were examined to identify if any variation in toughening mechanism existed over the range of mixing ratios investigated (1.7-3.2g/ml). Pore distribution within the cylindrical specimens was determined using an image analysis technique. RESULTS: Increasing the powder content from 2.3 to 2.4g/ml increased the number of powder agglomerates formed in the cement mix over individual particles. The likelihood of introducing pores in excess of 42 microm diameter was enhanced when the ratio exceeded 2.6g/ml. SIGNIFICANCE: It is proposed that crack deflection by agglomerates in the cement reduces the energy of the crack fronts emanating from indentations more than would occur with individual powder particles. This decreases the cracks ability to progress and is likely to result in the marked strength increase from 2.3 to 2.4g/ml identified previously. It is suggested that cement pores in excess of 42 microm diameter were probably generated on filling the sample molds with more viscous cements. These results emphasise that the properties of cements manipulated under optimum conditions provide little information on the cement characteristics present in clinical practice.

Compressive Strength↗
PubMed2000

In vitro evaluation of the effect of freshly mixed amalgam and gallium-based alloy on the viability of primary periosteal and osteoblast cell cultures.

The effect of freshly mixed specimens of a gallium-based alloy Galloy and a high copper spherical amalgam Tytin on the viability of primary periosteal and osteoblast cells was investigated. The cells were grown from the parietal bones of 2-3 day old Albino Wistar rats and were seeded in multi-well plates and exposed to the test materials for 1 or 6 days. The number of viable cells in each test group was determined using the Trypan blue dye exclusion test and compared with the controls. The area of cell death around the test specimens was also measured. Statistical analysis (ANOVA, Tukey's pairwise comparisons) showed a significant effect of the test materials on cell viability (P < 0.01). The viability of cultures containing Tytin was significantly lower than cultures with Galloy and the controls (P < 0.05). The viability of cultures containing Galloy was significantly lower (P < 0.05) than controls except for periosteal cells after 1 day. The culture media was analysed using atomic absorption spectrophotometry (AAS) for metal ion content. The results suggested that mercury (Hg) was the main element released from the dental amalgam followed by copper (Cu) and silver (Ag) whilst gallium (Ga) was the main element released from the gallium-based alloy followed by indium (In), Ag and Cu.

Alloys↗
PubMed1999

The influence of clinically induced variability on the bi-axial fracture strength of cemented aluminous core porcelain discs.

OBJECTIVES: Zinc phosphate cements are supplied in powder/liquid form so that a range of mixing ratios are naturally generated in clinical practice. However, these cements are known to have a deleterious effect on dental ceramics and the impact of variations in cement mixing on the strength of dental porcelain was investigated in the present study. METHODS: Vitadur-N core porcelain was fabricated into discs (15 mm diameter and 2 mm thickness), zinc phosphate cements of different mixing ratios were applied to the discs to produce a luting cement thickness and the samples were stored for 24 h prior to testing in a water-bath at 37 +/- 1 degrees C. The mean fracture strength, standard deviation and associated Weibull moduli (m) of the coated porcelain discs were determined as a function of mixing ratio using bi-axial flexure (ball-on-ring) by fracturing sets of 30 specimens coated with cements manipulated at different mixing ratios. RESULTS: The strength data for the coated porcelain discs showed little variation in magnitude and consistency ranging from 108 +/- 8.3 MPa (m = 14.0 +/- 2.6) at 1.7 g/ml to 112 +/- 8.5 MPa (m = 14.6 +/- 2.7) at 2.6 g/ml and 108 +/- 8.1 MPa (m = 14.4 +/- 2.6) at 3.2 g/ml. However, the plots of survival probability against strength for coated specimens prepared using mixing ratios below that recommended by the manufacturers' for luting purposes (2.6 g/ml), appeared to develop an asymmetry at the lower values of strength. SIGNIFICANCE: It was proposed that the increased corrosive acidic environment for cements prepared at mixing ratios below 2.6 g/ml may have extended pre-existing flaws in the porcelain discs thereby possibly producing the asymmetry in the survival distributions.

Aluminum Oxide↗
PubMed1999

Encapsulated verses hand-mixed zinc phosphate dental cement.

Zinc phosphate cements are commonly supplied as two components, powder and liquid, and the proportions of the constituents are determined by operator experience. A capsulated system which is mechanically mixed has been marketed and this study investigated the performance of the encapsulated cement system. The mean fracture strength, standard deviation and associated Weibull Moduli (m) of encapsulated cements were determined by compressive fracturing 20 cement specimens filled directly from the mixing syringe or from narrower cement tubes. Pore distribution within the cylindrical specimens was determined using image analysis to assess the influence of the method of mould filling with the cement. The strength data showed variation in magnitude and consistency ranging from 44.6+/-13.7 MPa (m = 3.18+/-0.71) for cements filled directly from the syringe to 61.0+/-7.8 MPa (m = 8.35+/-1.87) for cements filled from cement tubes. Larger pores were found in specimens consolidated directly from the cement syringe. Mechanical mixing of the encapsulated cement resulted in air entrapment in the cement mix which manifested itself as large pores (over 200 microm diameter) within the cylindrical specimens. The smaller orifice of the cement tube compared with the syringe was considered to be responsible for eliminating the majority of the air entrapped in the cement mass during mixing. Whilst mechanical mixing of encapsulated cements is quicker and more convenient, the encapsulated specimens consolidated according to the manufacturers instructions from the syringe offered no significant advantage in terms of reliability or strength over hand-mixed cements in this investigation.

Biocompatible Materials↗
PubMed1999

The influence of clinically induced variability on the bi-axial fracture strength of aluminous core porcelain discs.

OBJECTIVE: The proportions of the constituents required to produce a porcelain slurry used in crown construction are assessed by experience so that variability is inevitable. The present study investigated the strength dependence of porcelain specimens on slurry consistency. METHODS: Vitadur-N core porcelain was formed into discs and the mean fracture strength, standard deviation and associated Weibull Moduli (m) determined as a function of slurry consistency using bi-axial flexure (ball-on-ring) by fracturing sets of 30 specimens prepared to different powder contents for a constant 0.4 ml of liquid. RESULTS: The strength data for the porcelain discs showed variation in magnitude and consistency ranging from 145 +/- 16.5 MPa (m = 9.7 +/- 1.8) at 1.2 g to 155 +/- 13.8 MPa (m = 12.3 +/- 2.2) at 1.4 g and 142 +/- 13.7 MPa (m = 11.7 +/- 2.1) at 1.6 g of powder. Increasing or decreasing the powder content of the slurry (related to specimens condensed using 1.4 g of powder) resulted in an increase in the apparent porosity and a decrease in the apparent solid density. CONCLUSIONS: There was no significant decrease in the mean bi-axial flexure strengths for the slurry consistencies investigated. However, the reliability of the fracture strength data did vary significantly. The results suggested that an optimum consistency exists (wherein consistent reproducibility of test results was achieved) and appears to have implications for laboratory testing of materials since a comparison between materials can only be achieved if specimen preparation occurs consistently between test centres for all the materials under investigation.

Aluminum Oxide↗
PubMed1998

An in vitro approach for the study of dentinogenesis by organ culture of the dentine-pulp complex from rat incisor teeth.

Culture of the developing dental tissues has contributed to understanding of developmental processes during early odontogenesis. However, to understand fully the mechanisms involved during dentinogenesis and tissue repair there is a need to develop culture models for the dentine-pulp complex from more mature dental tissues. This study describes the development of a system for the organ culture of mature rodent teeth. Slices of incisors from 28-day-old rats were embedded in a semisolid, agar-based medium and cultured on floating Millipore filters at the liquid-gas interface for up to 14 days. Preservation of cell and tissue morphology was observed throughout the entire dentine-pulp complex after each culture period and autoradiographic studies showed that the odontoblasts were actively synthesizing and secreting extracellular matrix during culture. Transmission electron microscopy confirmed that the phenotypic morphology of the odontoblasts had been maintained during culture. These results demonstrate that the dentine-pulp complex from mature rodent tissues can be cultured successfully for substantial periods of time and will provide a useful model for the study of dentinogenesis and tissue repair.

Animals↗
PubMed1998

The use of a curved ophthalmic blade to facilitate incising Mohs micrographic sections with the desired bevel despite anatomic obstructions.

BACKGROUND: Mohs micrographic surgery involves incising the specimen with a bevel, which allows for inversion so that the entire surgical margin may rest in the same plane. Anatomic obstructions occasionally preclude this angle of incision. OBJECTIVE: The purpose of this study is to find a curved blade that can be used for harvesting Mohs specimens when the handle of the blade can not be passed tangentially around the tumor because of anatomic obstructions. METHODS: A Beaver Eye Blade and arthroscopic blade, both of which are curved and have two cutting edges, were used to incise Mohs specimens. RESULTS: The ophthalmic blade was easier to use and has a better angle than the arthroscopic blade. Where the straight blade would only allow for a perpendicular or obtuse angle of incision, the Eye Blade facilitated an acute or a 90-degree angle, respectively. CONCLUSIONS: The Beaver Eye Blade is a welcomed addition to the armamentarium of the Mohs surgeon for difficult-to-harvest sections, especially in the helix or internal nose.

Arthroscopes↗
PubMed1996

Pathologic fracture secondary to subungual melanoma.

Subungual melanoma is uncommon, and delays in diagnosis and misdiagnosis occur frequently. We describe a 61-year-old black male who presented with a non-healing area in his left thumb nailbed with many of the features of subungual melanoma. However, the patient also had a pathologic fracture of the distal phalanx, leading to some initial confusion about the diagnosis. Despite aggressive multimodality therapy, the disease rapidly progressed, resulting in the patient's death. Pathologic fracture due to subungual melanoma may indicate a particularly poor prognosis.

Bone Neoplasms↗
PubMed1994

Sterilization of the handengine. Is it a necessity?

BACKGROUND: The risk of interpatient infection through a dermabrasion handpiece is not known, nor is there a published standard of handpiece maintenance. OBJECTIVE: To investigate the possibility of transferring material through the handpiece and evaluate the methods used by dermatologists to disinfect and/or sterilize dermabrasion equipment. METHODS: Handengines run while immersed in fluorescein-dyed alcohol were observed for fluorescence. After dermabrasion of a fluorescein-basted pig's foot the instrument was inspected. A survey of handpiece disinfection/sterilization procedures was sent to 114 members of the American Society for Dermatologic Surgery. RESULTS: Although material can be transmitted to the motor/handpiece through the chuck and vice versa, contamination of the instrument did not occur in a dermabrasion simulation. 58.7% of respondents sterilize the chuck and only 38.1% sterilize the motor/handpiece. CONCLUSIONS: No absolute requirement to sterilize the handengine is warranted. It is prudent however to sterilize the chuck in a steam autoclave and gas sterilize the motor/handpiece to eliminate the rare possibility of cross-contamination.

1-Propanol↗
PubMed1993

Behavior of primary bone cells on characterized polystyrene surfaces.

Primary bone cells, isolated from the periosteally stripped calvariae of neonate rats, were cultured on 60Co gamma-irradiation-sterilized bacteriologic-grade polystyrene that had been either surface treated with concentrated sulfuric acid or received further gamma-irradiation treatments facilitated cell colonization of the polystyrene compared to those surfaces not treated in the laboratory. x-Ray photoelectron spectroscopy (XPS) showed that the two treatments introduced different chemical groups onto the polymer surface and that cell adhesion was related to gamma-irradiation in a dose-dependent manner. These results show that simple biologic assays, such as cell colonization, are not able to distinguish between differences in surface chemistry demonstrated by such a routinely employed surface analysis technique. Thus, there is a need to develop more sensitive biologic assays that provide functional information of a precision that can be correlated with subtle changes in substratum surface chemistry. Further, we argue that because cells isolated by tissue digestion using proteolytic enzymes respond more readily to changes in the surface chemistry of the substratum they colonize, compared to explanted cells; biologic assays designed for biomaterials testing must take into account changes effected in cell adhesion behavior by isolation procedures.

Animals↗
PubMed1993

510-nm pigmented lesion dye laser. Its characteristics and clinical uses.

BACKGROUND: Benign pigmented lesions are of a cosmetic concern to many individuals. Numerous treatments exist, including several types of lasers. The Candela 510 nm pigmented lesion dye laser has recently been added to this armamentarium. It is designed specifically for the treatment of superficial pigmented lesions while significantly decreasing the risk of scarring and prolonged hypopigmentation. OBJECTIVES: To describe the characteristics of the Candela pigmented lesion dye laser and report on the therapeutic outcome of patients treated for actinic lentigines, café-au-lait macules, melasma and red tattoos by one of the authors (RCG). METHODS: The Candela 510 nm pigmented lesion dye laser was used to treat solar lentigines, café-au-lait macules, melasma and red tattoo. RESULTS: Excellent outcomes resulted on facial and hand lentigines (89% and 88% of patients had greater than 75% clearing, respectively), but often required more than one treatment. Lentigines located on the upper extremities and trunk improved less dramatically. Immediate greying occurred universally. Bruising was often noted. Treatment failures have been observed especially in treating lentigines located on the lower extremities. Café-au-lait macules responded inconsistently, with facial lesions giving the best results. Melasma responded poorly, often with hyperpigmentation. Three red tattoos cleared. Treatment failure may be related to inaccurate clinical assessment of pigment depth or regrowth of the lesion. Several cases are presented to demonstrate clinical and histologic effects of the laser. CONCLUSION: The Candela 510-nm pigmented lesion dye laser is an effective treatment for superficial pigmented lesions. Its associated morbidity is minimal.

Adult↗
PubMed1992

A novel microcarrier bead model to investigate bone cell responses to mechanical compression in vitro.

Periosteal cells grown in macroporous microcarrier bead columns were cyclically loaded with compressive force using a newly developed model. In response to 1/2 h of cyclic compression, RNA synthesis increased significantly by twofold, from 113.4 +/- 19.6 to 260.7 +/- 363 (p < 0.01) after 16 h, whereas DNA synthesis did not increase significantly after 24 h. The microcarrier bead model was calibrated using a linear volume displacement transducer with a range of strain magnitudes applied across the column of 1000-6000 microstrain.

Animals↗
PubMed1990

Reflex sympathetic dystrophy: a review.

Reflex sympathetic dystrophy is a unique traumatic disorder with unusual cutaneous signs. The case of a patient with an uncommon, poorly understood, sharply marginated geometric zone of erythema is reported. Pseudo-Kaposi's sarcoma developed in the same patient in the foot affected by reflex sympathetic dystrophy, an association not previously reported. For effective treatment this disorder must be diagnosed as early as possible. The clinical stages of evolution through which reflex sympathetic dystrophy progresses are described.

Adult↗
PubMed1989

Hospital use and mortality among Medicare beneficiaries in Boston and New Haven.

We compared rates of hospital use and mortality in fiscal year 1985 among Medicare enrollees in Boston and New Haven, Connecticut. Adjusted rates of discharge, readmission, length of stay, and reimbursement were 47, 29, 15, and 79 percent higher, respectively, in Boston; 40 percent of Boston's deaths occurred in hospitals as compared with 32 percent of New Haven's. High-variation medical conditions (those for which there is little consensus about the need for hospitalization) accounted for most of these differences. By contrast, discharge rates for low-variation medical conditions (which tend to reflect the incidence of disease) were similar. Inpatient case-fatality rates were lower in Boston than in New Haven (RR = 0.85; 95 percent confidence interval, 0.78 to 0.92), but when all deaths (regardless of place of death) were measured, the mortality rates in Boston and New Haven were nearly identical (RR = 0.99; 95 percent confidence interval, 0.93 to 1.05). We conclude that the lower rate of hospital use by Medicare enrollees in New Haven was not associated with a higher overall mortality rate. Population-based as well as hospital-based statistics are needed to evaluate differences in hospital mortality rates for high-variation medical conditions.

Aged↗