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Biomedical subjects

T E Carrick

Publications and source records attributed to T E Carrick.

10 recordsLinked to original sources
PubMed2006

Recording surface detail on moist surfaces with elastomeric impression materials.

The objective was to assess the ability to accurately record detail on moist surfaces for three elastomeric impression materials derived from different polymers. One polyvinylsiloxane, one polyether and one hybrid material containing a copolymer of siloxane and polyether polymers were used. Impressions were recorded of moist gypsum casts having both a shallow (approximately 20 microm) and deep (approximately 180 microm) groove reproduced on their surface. The grooves in the casts and in the impressions were profiled using a non-contacting laser profilometer Comparisons were made between the groove depths in the casts and impressions (paired t-test). The results indicated that all of the tested materials accurately recorded dimensions in the x-y plane. However, there was evidence that the polyether and hybrid materials were more accurate than the polyvinylsiloxane in recording the true depths of the deep grooves (z plane) under moist conditions. It was concluded that the more hydrophilic nature of the polyether and hybrid materials enabled them to record more accurate impressions of moist surfaces, particularly in areas of difficult access as modelled by the deep grooves.

Calcium Sulfate↗
PubMed2001

Suitability of a shear punch test for dental restorative materials.

OBJECTIVE: The aim of the study was to evaluate the suitability of a shear punch test for determining the mechanical properties of dental restorative materials. The method was evaluated by measuring and comparing the shear punch strength of seven different restorative materials, that is amalgam, composite resin, compomer, composite containing pre-reacted glass ionomer filler, resin modified glass ionomer, glass ionomer and polycarboxylate cement. METHOD: The effects of specimen restraining conditions, specimen thickness and test speed on the shear punch strength were evaluated using polycarboxylate cement and two different equipment set-ups. Using the preferred testing regime as determined in the preliminary experiments, the shear punch strength of seven different materials were measured and compared. Twenty disc specimens, 0.5mm thick and 10mm diameter, were prepared for each material, restrained within the test equipment and tested at a speed of 1.0mm/min. RESULTS: The shear punch strength increased as the torque used for restraining a specimen was increased. There was no difference in shear punch strength for specimens of different thickness. The greatest shear punch strength was obtained at the test speed of 1.0mm/min. The shear punch strength values decreased in the order composite>composite containing pre-reacted glass ionomer filler>amalgam>compomer>resin-modified glass ionomer>glass ionomer>polycarboxylate. A difference in the shear punch strength for seven different kinds of restorative materials clearly emerged. Specimen fracture occurred by circumferential cracking for the shear-punch test. However, for some glass ionomer and amalgam specimens radial cracking was also observed. SIGNIFICANCE: This study suggests that the simple test described is suitable for standardization purposes.

Analysis of Variance↗
PubMed1993

Displacement Rheometer: a method of measuring working time and setting time of elastic impression materials.

A new method of measuring both working time and setting time of elastomeric impression materials has been developed. A Displacement Rheometer was used to monitor the development of elasticity in setting elastomers. The results obtained with the Displacement Rheometer were compared to the results of the ISO test as well as those of the Controlled Stress Rheometer. Working time using the ISO method was calculated according to the standard method described in the specification, while for both the Controlled Stress Rheometer and the Displacement Rheometer working times were the times when initial elastic recovery was observed at 23 degrees C. With the Displacement Rheometer the setting time is the time when the mixed material reaches optimal elastic recovery at 37 degrees C. Statistical analysis with ANOVA showed that for five of the test materials there were no differences between the three methods. For three of the materials the working time determined by the ISO method was significantly longer than that determined by the other two methods. The advantages and disadvantages of each method are discussed and the Displacement Rheometer is recommended as a supplement to the standard specification method.

Alginates↗
PubMed1990

Plastic dental local anaesthetic cartridges: a laboratory investigation.

The pressures applied to the bungs of glass and plastic dental local anaesthetic cartridges which were necessary to cause failure of the system were measured. Plastic cartridges did not fracture, but they failed due to leakage of solution around the bung at pressures less than those needed to break glass cartridges. At the peak injection pressures which may be obtained during intraligamentary injections, it was established that the theoretical incidence of failure was 1.4% for glass and 75.1% for plastic cartridges.

Anesthesia, Dental↗
PubMed1990

Alternative approaches to evaluating the fatigue characteristics of materials.

Two models of fatigue failure (designated type 1 and type 2) have been investigated by use of a total of seven materials. For type 1 behavior, there is a clear relationship between fatigue life and fatigue stress, whereas for type 2 behavior no such relationship exists. For materials exhibiting type 2 behavior, failure occurs at a level of stress below the ultimate strength of the material, but the values of fatigue life appear to be distributed randomly when several specimens of the same material are tested. A value of fatigue limit can be calculated for these materials which is independent of fatigue life. It is likely that, for these materials, resistance to fatigue is primarily dependent upon the presence or absence of flaws such as porosities. For the dental materials investigated in this study, it appears that brittle materials such as dental plaster and heavily filled composites are likely to exhibit type 2 behavior, whereas less brittle materials, such as more likely filled composites, are more likely to exhibit type 1 behavior.

Calcium Sulfate↗
PubMed1990

Onset of elasticity in setting elastomers.

A controlled stress-rheometer used in creep/recovery mode was used for detection of the onset of elasticity in setting elastomers. The time for the materials to develop 5-20% elastic recovery corresponded with the time to reach a phase angle of 60 degrees in an oscillatory test.

Dental Impression Materials↗
PubMed1989

Rheological properties of elastomers during setting.

A controlled stress rheometer has been used to monitor the changes in rheological properties occurring in five elastomeric impression materials during setting. The rheometer differs from conventional rotary viscometers in that the torque is the controlled variable, and the resulting deformation is measured. The use of such an instrument in oscillatory mode enables a range of rheological parameters--including viscosity, rigidity, and elasticity--to be monitored during setting. The polyvinylsiloxane impression materials develop elasticity at a rate that would not be apparent from measurements of viscosity or rigidity alone. This highlights the potential danger of basing the evaluation of clinically important properties, such as working time, on simple measurements of viscosity or rigidity.

Dental Impression Materials↗
PubMed1989

Output from visible-light activation units and depth of cure of light-activated composites.

A simple and reproducible method for monitoring the intensity of radiation from composite light-activation units has been developed. The method depends upon the use of a cadmium sulfide photo-conductive cell, the electrical resistance of which varies with the amount of light falling upon its surface. Filters were used for selection of the wavelength of light that is thought to be most effective in activating polymerization. The use of broad-band wavelength filters failed to give results for light intensity that correlated with depth of cure. Narrow-band interference filters, having a band width of only 10 nm and being selective within the wavelength range of from 460 to 480 nm, produced results for light intensity that correlated with depth of cure. The depths of cure for various types of composite material were measured with use of a penetrometer that enabled the thickness of unpolymerized material at the base of the test mould to be determined. The depth of cure was inversely proportional to the attenuation of light caused by the composite resin at 470 nm. The relationship between depth of cure and light intensity at 470 nm was not a simple linear one over all intensity values. Above a certain critical value of intensity (about 550 lux for a 3.5-mm aperture in these experiments), the depth of cure appeared to be almost independent of intensity. Below this critical value, depth of cure fell markedly with decreasing intensity.

Composite Resins↗
PubMed1987

Dynamic creep of dental amalgam as a function of stress and number of applied stress cycles.

Dynamic creep tests on specimens of dental amalgam gave a relationship between creep (epsilon), applied dynamic stress (sigma), and number of applied stress cycles (N) as epsilon = AN (m sigma + c) where A, m, and c are constants. This equation can be used to predict creep of amalgam at low levels of stress and extended times. The pattern of results produced for different types of amalgam indicates that the creep process is multifactorial in nature.

Chemical Phenomena↗