Structural conformation of in vitro and in vivo aged orthodontic elastomeric modules.
The objectives of this study were to investigate the structural characteristics of open and closed elastomeric modules in the as-received condition, and following (a) 24-hour in vitro loading determined as a 50 per cent extension relative to their original length; (b) 24-hour intra-oral exposure; (c) 3-week intra-oral exposure. Ten specimens of each type (open and closed) of the three brands of elastic chains were included in the study (total of 60). All specimens were subjected to (a) optical transmission microscopy utilizing phase contrast and polarized light modes, (b) micro MIR FT-IR spectroscopy, and (c) scanning electron microscopy and electron probe X-ray microanalysis. Stretched elastomers demonstrated a honeycomb pattern of filament detachment corresponding to strained areas. The chains possessing a well-differentiated inter-modular link presented higher strain concentration gradients located in the link. Phase contrast imaging revealed that the stress adsorption mechanism of these materials involved macromolecular chain orientation and elongation co-axially to the applied load. The specimens retrieved after 24 hours had acquired a proteinaceous film rich in alcohol groups with minimal evidence of phosphate mineralization, while the 3-week retrieved specimens presented precipitation of Ca- and P-forming calcium phosphates. The high protein content of the biofilm organized on the surface of these materials, as well as the calcification pattern found, were similar to a non-specific mechanism of film adsorption of biomaterials exposed to body fluids. The results have clinical implications for aspects of retraction control through sliding mechanics with the use of elastomeric ligatures, and the potential detrimental effects on dental and periodontal tissues such as decalcification and gingival inflammation, respectively. In addition, the experimental protocols adopted for the in vitro study of the force decay of elastomerics should be modified to include parameters pertinent to adsorption phenomena and calcification processes documented to occur in vivo. (+info)
Adsorption and pharmacokinetics of cyclosporin A in relation to mode of infusion in bone marrow transplant patients.
Two main factors that affect the pharmacokinetics of cyclosporin A (CsA) during 24-h durable intravenous (DIV) administration have been reported, namely physiological changes after bone marrow transplantation, and blood sampling through indwelling lines. In addition, it has been found that infusion sets made of polyvinyl chloride (PVC) markedly adsorb CsA. We conducted in vitro adsorption studies of CsA on infusion sets, and the administration routes that are used in the treatment of patients with bone marrow transplantation. We also examined the effects of administration route on CsA pharmacokinetics in clinical practice. The in vitro adsorption study using 30-mm segments of lumen from commercially available infusion sets showed that the degree of CsA adsorption per area of lumen made of PVC was significantly higher than that in those made of polyethylene (PE) or polybutadiene (PB), which showed no adsorption of CsA. Due to its adsorption, use of infusion sets made of PVC resulted in about a 40-50% loss of CsA dose, which affected the pharmacokinetic parameters during 24-h DIV, while those made of PE and PB did not. The use of non-PVC infusion sets should allow for accurate monitoring of CsA results, and provide cost benefit in the treatment of bone marrow transplantation. (+info)
Fabrication of elastomer arterial models with specified compliance.
A simple way of making elastic tubes using a mechanical lathe for precise control of the wall thickness is proposed in this study. These tubes are particularly useful for modeling properties of large arteries. Tubes with different geometric parameters and hence different elastic behavior have been made with a silicon elastomer (Rhodorsil RTV 1556). They have been created to be used for compliance measurements in hemodynamics research. Within a limited range of pressures, depending on the wall thickness, such tubes can be used to study models in which the compliance value is assumed to be constant. (+info)
A prospective controlled clinical trial was undertaken to evaluate the effectiveness of stannous fluoride-releasing elastomeric modules (Fluor-I-Ties) and chain (Fluor-I-Chain) in the prevention of enamel decalcification during fixed appliance therapy. Forty-nine patients (782 teeth) were included in the experimental group, where the fluoride-releasing elastomerics were used. Forty-five patients (740 teeth) who received non fluoride-releasing elastomerics formed the control group. All patients had their elastomerics replaced at each visit. Enamel decalcification incidence and distribution were recorded using an index by direct clinical observation. In the control group enamel decalcification occurred in 73 per cent of patients and in 26 per cent of all teeth. In the experimental group the corresponding incidence was 63 and 16 per cent, respectively. The overall reduction in score per tooth produced by the fluoride-releasing elastomerics was 49 per cent, a highly significant difference (P < 0.001). A significant difference was seen in all but the occlusal enamel zones. The majority (over 50 per cent) of lesions occurred gingivally. The teeth most severely affected were the maxillary lateral incisors and mandibular second premolars. There was no difference in treatment duration between groups. (+info)
A novel method of assessing the effectiveness of protective gloves--results from a pilot study.
We have devised a novel method for evaluating the effectiveness of protective gloves and have undertaken a small study to assess this approach. Three types of glove were tested in a standardised simulation test with a permethrin-based pesticide. Prewashed cotton gloves were used to collect the samples. One was worn over the protective glove on one hand to measure the potential deposition of pesticide on the hands had the gloves not been worn. A second was placed under the protective glove on the opposite hand to measure the actual deposition of permethrin on the hands when the gloves were worn. This regime was reversed half way through each test in an attempt to prevent bias. Measurable inner glove contamination occurred on 25 out of 30 occasions. Geometric mean protection factors were calculated from the ratio of outer and inner sampling glove contamination, with average protection factors of 470, 200 and 96 being obtained for the two nitrile and PVC gloves, respectively. The PVC gloves were the least effective in preventing inner glove contamination, probably because the glove was thick and fairly inflexible, causing more pesticide to enter the glove around the cuff. Although the tasks were standardised, variability occurred due to worker behaviour and equipment failure. The spray pump failed on five occasions, resulting in higher levels of inner glove contamination and a geometric mean protection factor of 32. On the occasions when the pump worked correctly, the level of protection provided by the gloves rose dramatically with mean protection factors of 220 and 450 being obtained for workers categorised as "messy" and "tidy", respectively. (+info)
Slip resistance of industrial floor surfaces: development of an elastomer suited to in-situ measurement.
Slips contribute to 12% of occupational accidents. A slip resistant floor is a mean to prevent slipping accidents occurring in workshops. Floor slip resistance is often evaluated by measuring a friction index, proportional to the force opposing slipping of a reference elastomer on the floor surface under test. When implementing a portable appliance, slip resistance measurements carried out on lubricated floors were not stabilized. The authors advanced the hypothesis of oil impregnating the elastomer. A new elastomer suited to in-situ measurement has been developed to achieve stable measuring conditions. This study highlights the fact that the nature and characteristics of a reference elastomer must be specified when slip resistance measurements are carried out. (+info)
Bacterial colonization associated with fixed orthodontic appliances. A scanning electron microscopy study.
This investigation was undertaken to assess bacterial plaque accumulation adjacent to orthodontic brackets. Experiments were carried out on 11 subjects who were scheduled for orthodontic treatment including extraction of two or four premolars. Metal brackets were bonded to the premolars to be extracted using macro-filled bonding composite. A conventional elastomeric ring was placed around one bracket and a steel ligature wire around the bracket on the contralateral tooth. The subjects were told to continue their normal oral hygiene regimen. Teeth were extracted at 1, 2, or 3 weeks after bracket bonding. Scanning electron microscopic (SEM) examination of brackets, excess composite, and buccal enamel revealed that mature plaque was present on excess composite at 2 and 3 weeks after bonding, whereas plaque on the gingival enamel surface was still at an early stage of development. The results demonstrate that excess composite around the bracket base is the critical site for plaque accumulation due to its rough surface and the presence of a distinct gap at the composite-enamel interface. The method of ligation does not appear to influence the bacterial morphotypes on both composite and enamel surfaces. (+info)
Strength decay of orthodontic elastomeric ligatures.
AIM: To evaluate, over a 12-week period, the tensile strength (TS) and extension to TS of elastomeric ligatures (both clear and coloured) obtained from two companies. SETTING: Ex vivo study. METHOD: Seven replicates of five ligatures from two orthodontic companies were tested using an ex vivo assembly which simulated a clinical situation. RESULTS: The ligatures tested had a similar TS decay pattern, with the TS gradually decreasing over the duration of the study. The Unitek ligatures exhibited a greater TS than their respective Ormco ligatures. Generally, all of the ligatures tested experienced an increase in the extension to TS over time. The pre-stretching procedure used in this study did not produce any long-term detrimental effects on the TS and extension to TS of the ligatures tested. CONCLUSIONS: The results of this study confirm there are differences in TS, and extension to TS between clear and coloured elastomeric ligatures, and that some significant differences also exist between different brands of elastomeric ligatures. (+info)