PubMed Health⌕ Search

Biomedical subjects

D T Turner

Publications and source records attributed to D T Turner.

At least 19 recordsLinked to original sources
PubMed1997

Bond strength of orthodontic composite cement to treated porcelain.

A porcelain-fused-to-metal ceramic was prepared for bonding by five treatments: sandblasting, sandblasting and silanating, hydrofluoric acid etching, hydrofluoric acid etching and silanating, and 600-grit polishing and silanating. Two commercial, all-purpose bonding agents were used to bond a composite cement to the porcelain samples. In vitro tensile bond strengths were compared with samples for which no bonding agent was used. Highest bond strengths (22 to 41 MPa) were obtained, with one exception, when the porcelain surface was silanated; however, the use of silane increased the occurrence of porcelain fracture on debonding. Composite cement bonded without bonding agent to nonsilanated porcelain prepared by sandblasting or etching with hydrofluoric acid had bond strengths of 6.5 MPa and 18 MPa, respectively, with all bond failures at the bracket/composite interface. The use of all-purpose bonding agents and silanating agents may not be necessary for adequate orthodontic direct bonding.

Dental Bonding↗
PubMed1995

Ground transport of an infant on high-frequency jet ventilation: a case presentation.

High-frequency jet ventilation (HFJV) was developed to meet the need for adequate ventilation while avoiding the adverse consequences of conventional mechanical ventilation (CMV). HFJV can be beneficial to infants who have failed CMV. Some infants may need the additional support of extracorporeal membrane oxygenation (ECMO). To be optimally transported to a center that offers this treatment, the infant may need to be ventilated using HFJV. For the transport team, delivery of the infant to the receiving hospital in optimal condition is the goal. The challenges of overcoming the environmental hindrances inherent in transport combine with the challenge of caring for an acutely and critically ill infant. When the infant is transported on HFJV, these challenges are magnified. This article briefly discusses HFJV and examines the preparations and equipment required for transport, as well as special considerations for managing the infant on HFJV during transport.

Female↗
PubMed1989

Water sorption of plasticized denture acrylic lining materials.

The objective was to characterize water sorption of plasticized denture acrylic lining materials, with determination both of uptake and diffusion coefficient (D). Feasibility was investigated first for simple binary mixtures of poly(methyl methacrylate), PMMA, and various phthalate plasticizers prepared by radiation polymerization of methyl methacrylate/plasticizer solutions. These were shown to be tractable when samples were saturated with water and then characterized in desorption measurements. Plasticizers were found to decrease the uptake of water. This decrease was attributed to the hydrophobic nature of the plasticizers and also to their ability to fill microvoids in PMMA which, in their absence, would be available to water. Values of D increased monotonically with increasing volume fractions of plasticizer. It appeared that values of D increased more rapidly in cases where large proportions of plasticizer resulted in samples which were above their glass transition temperature, Tg, at the temperature of testing water sorption. Desorption measurements were extended satisfactorily to a model system made from poly(ethyl methacrylate) powder, methyl methacrylate, and dibutyl phthalate, which was polymerized with a conventional redox initiator. Water desorption results were compared with various proprietary materials which were also characterized with respect to Tg and, cursorily, to composition.

Acrylic Resins↗
PubMed1987

Water sorption of polymethacrylate networks: bis-GMA/TEGDM copolymers.

Polymethacrylate networks were made by copolymerization of a range of compositions of bis-GMA and triethylene glycol dimethacrylate (TEGDM). Polymerization was initiated both by heating with benzoyl peroxide or by photopolymerization (lambda greater than 400 nm) using camphoroquinone as sensitizer. The uptake of water increased from 3 to 6% as the proportion of TEGDM increased from 0 to 1.0. Intermediate compositions took up less water than would be predicted from the law of mixtures. Volumetric changes were determined and clinical significance discussed. A copolymer prepared by photopolymerization took up more water as the temperature was increased from 24-60 degrees C. In this range, values of the diffusion coefficient (D) conformed to the Arrhenius equation, D = Do exp (-E/RT), giving E = 42-46 kJ/mol and Do = 0.13 cm2 s-1.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1987

Characterization of polydimethacrylates and their composites by dynamic mechanical analysis.

The objective was to characterize, by dynamic mechanical analysis (DMA), the polymeric materials used to restore teeth and, in particular, to assign a glass transition temperature, Tg. Generally, in DMA work, Tg is taken as the temperature at which the internal damping, i.e., tan delta, has a maximum value. However, in the present work it was shown that the classical method of assigning Tg corresponds more closely to an assignment based on changes in elastic modulus. On this basis, a bis-GMA copolymer and a proprietary dental composite, both polymerized by exposure to light, were assigned Tg values of -25 degrees C and +10 degrees C, respectively. The composite had an even lower value, Tg = -10 degrees C, after saturation with water. The value of Tg can be increased considerably by treatments which are known to increase the degree of polymerization, i.e., by heating or by gamma-irradiation. The present findings imply that composites made by photopolymerization may undergo marked changes in mechanical state (becoming glassy, leathery, and rubbery) in the oral cavity, due to changes in temperature from about 0 degree C to 50 degrees C. It is not known which of these states would give best service properties, such as wear resistance, but in any case variation of properties in service would appear to be undesirable.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1987

A standardized method of propagating the marine fish parasite, Amyloodinium ocellatum.

The peridinian dinoflagellate Amyloodinium ocellatum was propagated by serial passage in clownfish (Amphiprion ocellaris) and hybrid striped bass (Morone chrysops X Morone saxatilis). Each 25-50-mm fish was exposed to 4,000-6,000 dinospores in 400 ml of artificial seawater for 30 min. Two days after exposure, trophonts were harvested by immersing the fishes in fresh water. After encystment, tomonts were axenized by multiple washes with sterile distilled water and sterile artificial seawater containing penicillin and streptomycin, and then incubated in the antibiotic solution. High yields of both tomonts and dinospores of the same sizes and ages were obtained, and host mortalities were eliminated. Microbial growth in incubating cultures was inhibited until after dinospores had emerged from tomonts, and dinospores remained infective for at least 4 days at 26 C.

Animals↗
PubMed1984

Metronidazole v ampicillin: differing effects on the postoperative recovery.

One hundred and eight adult patients undergoing appendicectomy (37 advanced appendicitis and 71 early appendicitis or normal appendices) were randomised into a trial comparing the effects of ampicillin (anti-aerobic) and metronidazole (anti-anaerobic) based regimes. Although there were less wound infections amongst those patients receiving metronidazole (14%) as compared to ampicillin (27%) this difference failed to reach statistical significance. However, ampicillin appears to be superior in shortening the length of postoperative fever, 3.0 compared to 3.5 d for those patients receiving metronidazole. There is some suggestion that this advantage is reversed amongst those patients with wound infections. Further study is required to clarify this point. Our study suggests further evidence of differing clinical action of these drugs in appendicectomy.

Adolescent↗
PubMed1983

Microscopic observations of the wear of a tooth restorative composite in vivo.

The wear of a composite restorative material in the oral cavity was followed by examining impressions by scanning electron microscopy. It was demonstrated that filler particles protrude from the polymeric matrix and, eventually, are lost leaving holes in the surface. A measure of the rate of wear was obtained by following the recession of the matrix on the faces of a large prominent particle. For a restoration that had been in place for 7 years, the average rate of wear over a further period of several months was estimated to be about 0.1 microns/day. For comparison, the gross wear of 2 mm over the entire 7-year period gives a greater average rate of wear of 0.8 microns/day.

Acrylic Resins↗
PubMed1983

Strong composites of dimethylacrylates with 4-methacryloxyethyl trimellitic anhydride.

Particles of a lithium aluminum silicate, which had been treated with a silane coupling agent, were centrifuged either in an adduct of bisphenol-A/glycidyl methacrylate (Bis-GMA) or in a mixture of Bis--GMA and methyl methacrylate. Polymerization was effected by heating with 2,5-dimethyl-hexane-2,5-dihydroperoxide. Flexural strength passed through an optimum value with increasing loading of the silicate. Inclusion of 4-methacryloxyethyl trimellitic anhydride, 4-META (5 wt % on monomer), increased the optimum flexural strength by about 20% (to 240 MPa). Evidence that 4-META increased the adhesion of filler particles to the polymeric matrix was obtained by examination of fracture surfaces.

Acrylates↗
PubMed1982

A new coupling agent for composite materials: 4-methacryloxyethyl trimellitic anhydride.

Composite materials were made by sedimention of ceramic powders in methyl methacrylate which was then polymerized by gamma-irradiation. Inclusion of 4-methacryloxyethyl trimellitic anhydride (4-META) generally was found to result in an increase in Knoop hardness number, Young's modulus, and transverse strength. Most emphasis was placed on transverse strength which was found to be increased by ca. 30% by inclusion of 4-META (5 wt %) in composites made with silanated LiAlSiO4. However an abrupt decrease in strength was found for composites with greater than ca. 83 wt % silanated LiAlSiO4. This was shown by fractography to be due to increased porosity and dewetting at the higher filler contents. Fractography also indicated that inclusion of 4-META results in a more coherent polymeric matrix. Further evidence for greater coherence was obtained by showing that 4-META confers resistance to disintegration by chloroform.

Acrylates↗
PubMed1978

Treatment of early breast cancer.

The early follow-up of patients treated by simple mastectomy alone or simple mastectomy combined with radical radiotherapy is presented. Both groups were well matched for age, menopausal status, duration of symptoms, size of tumour, and lymph-node involvement. There was no significant difference in survival of patients in the two groups at three years, but local recurrence was significantly more frequent (28%) in the mastectomy-alone patients. Early survival was not adversely affected by radiotherapy.

Age Factors↗