Trends in elastomeric impression materials

In the past three years more addition silicones have been supplied as hydrophilic materials and heavier viscosities have been provided in automatic mixing cartridges. Also, a polyether is now supplied in an automatic mixing system. There has been an increase in the number of products available as monophase or single viscosity systems. Both addition silicones and polyethers are available as bite registration materials.     

Determination of activation parameters using impression creep data

Impression creep technique is a modified indentation creep test wherein the conical or ball indenter is replaced by a cylindrical, flat bottomed punch. In this study, the impression creep behavior of a few Al-U-Zr alloys was studied in the temperature range 693–783K at different stresses. Impression creep curves generated for Al-22U-2Zr and Al-46U-3Zr (composition in wt %) show a wavy pattern. The reason for the unusual creep curve is found to be in the fact that microstructure is not stable at the creep testing temperature. The velocity of the punch at different stresses and temperatures were evaluated for each of the alloy covered in this study. The stress exponents and thermal activation parameters of the above alloys were determined.     

Setting properties of alginate impression materials in dynamic viscoelasticity

The viscoelastic properties of three alginate impression materials were investigated. A landmark of working time was calculated using a raw phase-time curve. A landmark of setting time was calculated from an inflection point of the divided difference of the first order in the share modulus-time curve. As a result, the working time was common at the point of delta = 45 degrees in variable frequencies. The mean value was obtained with less deviation. The setting times obtained were similar for variable frequencies. The mean values showed a distinct difference for each impression material.     

Dystrophic calcification of silicone scleral buckling implant materials

The local antibody response to the outer membrane protein, P6, of nontypable H. influenzae was measured in middle ear fluids of 30 children during 46 episodes of otitis media, and in nasopharyngeal secretions from 7 children evaluated on 18 occasions. Immunoglobulin G antibody to P6 was detected in 92% of middle ear fluid compared to 70% for IgM, 78% for IgA, and 45% for secretory IgA. Antibody levels ranged from a high of 249 ng/ml for IgG to a low of 11 ng/ml for IgM. Concentrations of P6 specific IgG in the middle ear fluid was directly related to the concentration in the serum, r = 0.89, p < 0.001, and inversely related to the number of bacteria present, r = -0.62, p < 0.05. In contrast, IgA and secretory IgA antibodies to P6 were common (96% and 95%, respectively) and in relatively high concentrations (33 ng/ml and 29 ng/ml, respectively) in nasopharyngeal secretions. There was no relationship between nasopharyngeal and serum levels of antibodies. These data suggest that antibody to P6 nontypable H. influenzae is common, diffuses into the middle ear spaces passively from the serum during otitis media, and is manufactured locally in the nasopharynx in response to colonization.     

Rheological properties of elastomeric impression materials before and during setting

In this study, we examined the rheological properties of elastomeric impression materials, both before and during setting, to assess the clinical significance of certain key characteristics such as viscosity, pseudoplasticity, and the rate of development of elasticity. The hypothesis to be tested was that monitoring the change in tan delta is the most appropriate means of monitoring the setting characteristics of elastomers. The loss tangent (tan delta) and the dynamic viscosity (eta') for five impression materials (both unmixed pastes and mixed/setting materials) were measured by means of a controlled-stress rheometer in a cone/plate configuration. For unmixed pastes, tests were performed at various frequencies (0.1 to 10 Hz) and torques (from 1 to 50 x 10(-4) Nm), while testing on setting materials was performed at constant frequency (1 Hz) and torque (3 x 10(-3) Nm). Most base and catalyst pastes were pseudoplastic before being mixed. Immediately after being mixed, the polyether (tan delta = 9.85) and polysulfide (tan delta = 9.54) elastomers showed tan delta markedly higher than those of other mixed materials (tan delta = 4.96 to 3.01). The polyvinylsiloxane elastomers showed lower initial tan delta, which rapidly reduced even further with time. This suggests that these materials should be used as soon as possible after being mixed. The polyether elastomer had a comparatively long induction period during which the tan delta remained at a high value. These characteristics are thought to be key factors in controlling clinical efficacy and therefore support the hypothesis that monitoring tan delta is an appropriate method for evaluating the setting characteristics of elastomers. One limitation was that the controlled-stress rheometer was unable to monitor rheological properties through to completion of setting.     

Absorption of fluoride following inhalation and ingestion of alginate impression materials

The fluoride (F) contents of ten alginate impression materials in powder form, were found to range from 0.44% to 2.42%. Plasma F concentrations showed no appreciable changes in five dental personnel exposed to aerosols of these powders during routine clinical work. Elevated plasma F levels (120-158 ng/ml) were recorded after ingesting 2 g (approximately 10 mg F) of Zelgan normal-set alginate. The bioavailability of F from the alginate was about 55% of the total F in the administered dose. It is concluded that routine clinical exposure to alginate does not cause any important change in plasma F levels, whereas accidental swallowing of alginate raises the plasma F level significantly.     

Clinical and scintigraphic comparison of silicone and polyvinylpyrrolidone coated silicone perforated plugs

BACKGROUND/AIM: Isolated stenosis of the lacrimal punctum is a frequent cause of epiphora. Treatment relies on surgical opening or dilatation with bi- or monocanalicular prosthesis. Recently, silicone perforated punctum plugs (PPP) were proposed. The drawback with these silicone PPP was that secretions accumulate in the central orifice blocking the spontaneous flow of tears. A modification of the surface of the PPP using polyvinylpyrrolidone (PVP) was thus proposed. The aim was to compare silicone PPP with new PVP surface treated PPP. METHODS: A prospective study was conducted of 20 patients with dilatable stenosis of the lacrimal puncta who developed epiphora. Epiphora, tolerance, implantation of the PPP, and lacrimal drainage were evaluated using scintigraphy of the lacrimal ducts. RESULTS: The raw data and statistical analysis showed evidence of a superior performance of PVP surface treated PPP. CONCLUSION: Long term evaluation of the advantages or risks of PVP plugs and comparison with microsurgical punctoplasty are warranted.     

The non-specific binding of immunoglobulins to silicone implant materials: the lack of a detectable silicone specific antibody

Recent studies have suggested that anti-silicone antibodies develop in patients implanted with silicone materials. The majority of these studies have utilized enzyme-linked immunosorbent assay (ELISA) methodology with a silicone material substrate as a means to detect the presence of the anti-silicone antibody. The current studies were undertaken to determine whether the binding of IgG to a silicone substrate was consistent with an antigen-specific antibody interaction or the result of non-specific hydrophobic interactions. While significant differences were detected in serum from silicone antibody "positive" and "negative" patients when the ELISA was conducted using a phosphate buffered saline (PBS)-0.05% Tween 20 (Tween) blocking system, the difference in the responses was attenuated when protein blocking systems were used or when incubation times were decreased. Furthermore, ELISA studies, using purified mouse and human IgG, demonstrated a concentration-dependent binding of IgG to silicone elastomer substrate which was also attenuated when a protein blocking system was used in lieu of Tween. In controlled animals studies in which female B6C3F1 mice were implanted with silicone gel or silicone elastomer for 180 days, no difference was observed between the implanted animals and the PBS control animals with respect to binding of IgG to the silicone substrate. Similar studies in female Fischer 344 rats implanted with silicone gel for 84 days also failed to demonstrate the presence of anti-silicone antibody. Collectively, the results suggest that the binding of IgG to silicone implant materials is non-specific in nature, consistent with the well-recognized interactions between hydrophobic molecules (IgGs) and hydrophobic surfaces (silicones) in an aqueous-based system.     

Copper electroplating of non-aqueous elastomeric impression materials: a subjective appraisal of their platability

Adolescent students of a rural block were studied to find out variation in blood pressure in relation to sex, caste and socioeconomic status. Females had significantly higher mean values of blood pressure; both systolic and diastolic. There was significant variation in systolic blood pressure amongst adolescents of various socio- economic classes. Prevalence of systolic hypertension (95 percentile) was higher in adolescents of upper middle social class and diastolic hypertension in Prestige castes. It is suggested that screening for hypertension should be done at school leaving age and high risk adolescents should be advised about periodic check-up, proper diet, salt restrictions and exercise so that frank hypertension could be prevented in adulthood.     

Containment of a silicone fluid free surface in reduced gravity

In support of the Surface Tension Driven Convection Experiment planned for flight aboard the space shuttle, tests were conducted under reduced gravity in the 2.2-second drop tower and the 5.0-second Zero-G facility at the Lewis Research Center. The dynamics of controlling the test fluid, a 10-centi Stoke viscosity silicone fluid, in a low gravity environment were investigated using different container designs and barrier coatings. Three container edge designs were tested without a barrier coating: a square edge, a sharp edge with a 45-deg slope, and a saw-tooth edge. All three edge designs were successful in containing the fluid below the edge. G-jitter experiments were made in scaled-down containers subjected to horizontal accelerations. The data showed that a barrier coating is effective in containing silicone fluid under g-levels up to 10^•1 g₀. This paper is based on a presentation made in the symposium “Experimental Methods for Microgravity Materials Science Research” presented at the 1988 TMS-AIME Annual Meeting in Phoenix, Arizona, January 25-29, 1988, under the auspices of the ASM/MSD Thermodynamic Data Committee and the Material Processing Committee.     

Rheological studies of the polymerization of elastomeric impression materials. II. viscosity measurements

As part of a detailed study of the curing of a range of dental elastomeric impression materials, a cone and plate rheometer was used to measure the variation in viscosity due to chain growth. The dependence of this behavior on the catalyst/base ratio, retarding and accelerating agents, and alternative initiators was studied and rationalized in terms of the polymerization chemistry investigated previously. Limited success was achieved with the quantitative interpretation of this data in terms of the polymerization kinetics. Of clinical relevance, only the viscosity behavior of the imine-terminated polyether and one of the thiol-terminated polysulfides approached that of an ideal impression material.     

Clinical significance.

This article initiates the special section on clinical significance. Within a brief précis and overview, the 4 methodological articles and the integrative commentary of the special section are introduced. A call for the inclusion of the assessment of clinical significance in treatment evaluations is extended. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Clinical significance of snoring

Habitual snoring, nocturnal apnea, and excessive daytime sleepiness are leading symptoms of the obstructive sleep apnea syndrome. However, simple snoring without apnea is a more common and normal phenomenon. In certain habitual snorers increased upper airway resistance during sleep may lead to sleep fragmentation and hypersomnolence even in the absence of frank apnea; this condition is termed upper airway resistance syndrome. There is no convincing evidence that snoring in the absence of sleep apnea is an independent risk factor for cardiovascular disease. The evaluation of symptomatic snorers includes a specific history and physical exam, followed by a sleep study if treatment is considered necessary. The choice of treatment modality for snoring is guided by the individual needs and symptoms of the patient. Weight loss, nocturnal application of continuous positive airway pressure, or intraoral appliances which hold the mandible in protrusion during sleep are non-surgical treatment options. According to the patients' subjective assessment conventional or laser-assisted uvulo-palato-pharyngoplasty (UPPP) has a high cure rate for snoring. However, objective documentation of the effect of these interventions on measured snoring noise is scant.     

Simulating the surface roughness of sintered materials

Translated from Poroshkovaya Metallurgiya, No. 6(330), pp. 83–88, June, 1990.     

Parkerizing steel with preliminary surface activation

Attention focuses on how certain activators affect the parkerizing process and the properties of the phosphate films obtained. Comparative corrosion-endurance tests of the films obtained are conducted. The effectiveness of such activators in production conditions is established.     

Clinical significance of insulin resistance

Insulin resistance has emerged in the last 20 years as a concept familiar to clinicians in many specialties. No easily performed laboratory test is available to assess insulin action in routine clinical practice. Several rare syndromes of severe insulin resistance are recognized but most clinicians will encounter insulin resistance as a manifestation of common diseases. Physiological and treatment induced changes in insulin sensitivity influence insulin doses required in insulin-dependent diabetes mellitus. In non-insulin-dependent diabetes mellitus insulin resistance is fundamental to pathogenesis but it is also influenced by standard dietary and pharmacological treatment, and probably mediated by changes in prevailing glycaemia. Antihypertensive agents appear to have diverse effects on the insulin resistance of essential hypertension though the long term significance of these remains unclear. The importance of insulin as a risk factor for coronary heart disease and the concept of an insulin resistance syndrome as a common precursor of conditions with increased vascular risk remains controversial.