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At least 703 records · Page 39Linked to original sources
PubMed1993

The acrylic-wire option in cervical spine fixation. A retrospective study.

This retrospective study was undertaken to assess the stability of the cervical spine after fixation with acrylic wire implants. Of the 44 patients with various pathological conditions of the cervical spine selected for this treatment in the course of 20 years, 36 were considered suitable for long-term follow-up evaluation. In 30 cases (83%) the stability of the spine was rated good. It is concluded that the acrylic-wire combination is a valuable surgical option in certain conditions i.e. old age, short life expectancy, poor general health, mental disease, in which long confinement in bed or in orthopaedic appliances is poorly tolerated.

Acrylic Resins↗
PubMed2004

Gel time of calcium acrylate grouting material.

Calcium acrylate is a polymerized grout, and can polymerize in an aqueous solution. The polymerization reaction utilizes ammonium persulfate as a catalyst and sodium thiosulfate as the activator. Based on the theory of reaction kinetics, this study on the relation between gel time and concentration of activator and catalyst showed that gel time of calcium acrylate is inversely proportional to activator and catalyst concentration. A formula of gel time is proposed, and an example is provided to verify the proposed formula.

Acrylates↗
PubMed2005

Drug release from the enzyme-degradable and pH-sensitive hydrogel composed of glycidyl methacrylate dextran and poly(acrylic acid).

Hydrogels composed of glycidyl methacrylate dextran (GMD) and poly(acrylic acid, PAA) were prepared by UV irradiation method for colon-specific drug delivery. GMD was synthesized by coupling of glycidyl methacrylate to dextran in the presence of 4-(N,N-dimethylamino)pyridine. GMD was photo-polymerized by ammonium peroxydisulfate as initiating system in phosphate-buffered solution (0.1 M, pH 7.4). And then, acrylic acid monomer was added and subsequently heat-polymerized by 2,2'-azobisisobutyronitrile as an initiator. The hydrogels exhibited high swelling ratio (about 20) at 37 degrees C, and showed a pH-dependent swelling behavior. In addition, the swelling ratio of the hydrogel was remarkably enhanced to about 45 times in the presence of dextranase at pH 7.4. The swelling-deswelling behavior proceeded reversibly for the GMD/PAA hydrogels between pH 2 and pH 7.4. Release of 5-aminosalicylic acid from the GMD/PAA hydrogels was evaluated in simulated gastrointestinal pH fluids in the absence or presence of dextranase. We concluded that the hydrogels prepared could be used as a dual-sensitive drug carrier for sequential release in gastrointestinal tract.

Acrylic Resins↗
PubMed2001

Chemo-enzymatically induced copolymerization of phenolics with acrylate compounds.

Initiation of copolymerization of lignin-like phenolic and acrylic compounds by the phenoloxidase laccase (EC 1.10.3.2) and a peroxide species (t-butylhydroperoxide, t-BHP) was compared to a Fenton-like system (ferrous ion, t-BHP). Initially, the relative activity of laccase towards different phenolic compounds and the optimum pH of some characteristic phenolics were determined. The polymer yield and the average molecular weight (Mw) of chemo-enzymatically produced polymers were dependent both on the type of each phenolic tested and on the phenol/monomer ratio. Furthermore, the success of copolymerization of the phenolics was dependent both on their redox potential and on the type of acrylic monomer applied. The extent of phenol incorporation into the polymer chain was enhanced by the presence of laccase in the reaction mixture and was significantly higher than in polymerization initiated by a Fenton-like reaction.

Acrylamide↗
PubMed2006

[Quantitative evaluation of acrylic and silicone intraocular lenses with a sharp optic edge design].

BACKGROUND: At the Department of Ophthalmology, Heidelberg, Germany, posterior capsule opacification (PCO) of a silicone and an acrylic intraocular lens (IOL) with a sharp optic edge design was evaluated. PATIENTS AND METHODS: In a prospective study either the AMO ClariFlex silicone IOL or the Sensar AR40e hydrophobic acrylic IOL were implanted in 47 patients following uneventful phacoemulsification. Mean patient age was 76.2+/-7.8 (ClariFlex) and 73.4+/-12.9 years (AR40e), respectively. The mean follow-up time was 19.7+/-5.34 in the ClariFlex and 21.9+/-1.89 months in the AR40e group. PCO development was evaluated postoperatively using the EPCO 2000 analysis software (scale 0-4). Areas of interest were the total IOL optic, the central 3-mm zone as well as the capsulorhexis. RESULTS: In both groups, all patients achieved a BCVA of 20/32 (AR40e) and 20/25 (ClariFlex), respectively. There was a very low incidence of PCO development with a mean EPCO score of 0.07+/-0.2 (ClariFlex and 0.15+/-0.2 (AR40e). Within the 3-mm zone and the capsulorhexis, there was a tendency for even lower EPCO scores in both groups. We calculated a statistically significant difference for the two lens materials for all investigated IOL areas (Wilcoxon's test, p<0.05). CONCLUSION: Both IOLs with a sharp edge design showed good functional results, a stable position in the capsular bag as well as a low incidence of PCO development. However, the silicone IOL showed statistically significantly lower PCO scores.

Acrylic Resins↗
PubMed2004

Prediction of lower critical solution temperature of N-isopropylacrylamide-acrylic acid copolymer by an artificial neural network model.

In this paper, we have investigated the lower critical solution temperature (LCST) of N-isopropylacrylamide-acrylic acid (NIPAAm-AAc) copolymer as a function of chain-transfer agent/initiator mole ratio, acrylic acid content of copolymer, concentration, pH and ionic strength of aqueous copolymer solution. Aqueous solutions with the desired properties were prepared from previously purified polymers, synthesized at 65 degrees C by solution polymerization using ethanol. The effects of each parameter on the LCST were examined experimentally. In addition, an artificial neural network model that is able to predict the lower critical solution temperature was developed. The predictions from this model compare well against both training and test data sets with an average error less than 2.53%.

Acrylamides↗
PubMed2005

DFT studies on isomerization reactions in the copolymerization of ethylene and methyl acrylate catalyzed by Ni-diimine and Pd-diimine complexes.

Gradient corrected density functional theory (DFT) has been used to investigate the isomerization reactions in the process of the ethylene/methyl acrylate copolymerization catalyzed by Pd-dimine and Ni-dimine complexes, modeled by a generic system NwedgeN-M-(CH3)+; NwedgeN=-N(H)-C(H)-C(H)-N(H)-. The influence of the polar group and of the metal on the isomerization mechanism was studied. The results show that for the Pd-catalyst the isomerization follows the standard mechanism observed in homopolymerization processes, with the beta-hydrogen-transfer to the metal and formation of a pi-olefin-hydride complex. Electron withdrawing character of the polar group results in an increase of the hydride energy and the isomerization barrier. For the Ni-catalyst the overall isomerization picture is modified by the formation of a sigma-olefin-hydride complex, in which the olefin is coordinated to the metal by the oxygen atom of the polar group. Such a sigma-olefin-hydride is lower in energy for the Ni catalyst than the pi-olefin-hydride complex by 9.6 kcal mol(-1) . The latter is preferred by 2.6 kcal mol(-1) for the Pd-based system. The calculated isomerization barriers are 20.9 and 24.0 kcal mol(-1) (with respect to the initial 4-member chelate) for the Pd-catalyst and Ni-catalyst, respectively. This can result in a larger fraction of ester group directly connected to the copolymer backbone observed experimentally for the Ni-catalyst. [Figure: see text]. Structure of the four-membered and five-membered chelates formed after 2,1-insertion of methyl acrylate into the metal-alkyl bond of the catalyst.

Acrylates↗
PubMed1978

Fabrication of interim acrylic resin removable partial dentures with clasps.

An orderly sequence of steps for construction of an interim acrylic resin partial denture has been presented. The technique allows the dentist to fabricate an effective restoration that has a definite path of insertion and removal that can be placed in the patient's mouth with little time spent on adjustment and correction. This technique may be used with heat- or cold-curing acrylic resin.

Acrylic Resins↗
PubMed1980

Bond strength of bimaterial acrylic resin combinations.

While further research is necessary on the subject of the strength and nature of the bond between different types of acrylic resins, our study shows that specimens fabricated from heat-accelerated BPM showed considerably higher transverse strength values when compared with the various bimaterial combinations. From this, and from the fact that all bimaterial combinations broke at the joining interface, it can be inferred that none of the acrylic resin bimaterial combinations developed a true "chemical bond."

Acrylic Resins↗
PubMed1983

Fabricating acrylic resin baseplates for complete dentures.

A technique for fabricating acrylic resin baseplates for complete dentures has been described. With this technique multiple sets of baseplates can be made at a time for a set of master casts. As with all polymethyl methacrylate resins, polymerization shrinkage is present. However, by using denture repair acrylic resin, shrinkage is minimized. Furthermore, when necessary, conventional procedures can be applied to stabilize the baseplates.

Acrylic Resins↗
PubMed1985

Dimensional change of acrylic resin tray materials.

Twelve commonly used acrylic resin tray materials were compared for linear curing shrinkage. Three of the 12 were found to expand slightly during the first few hours, which had the effect of reducing the net shrinkage. All trays, however, exhibited shrinkage during the 24-hour test period. Therefore, autopolymerizing acrylic resin tray materials should not be used for an impression the same day that they are made unless the tray is boiled as suggested by Pagniano et al. This agrees with research already completed even though the magnitude of shrinkage was considerably less than that reported in previous studies.

Acrylic Resins↗
PubMed1988

Bond strength of 4-META acrylic resin denture base to cobalt chromium alloy.

This study was designed to compare the bond strength of a conventional poly(methyl methacrylate) acrylic resin denture base (Lucitone 199) with a recently developed acrylic resin base containing 4-META (Meta-Dent) to CoCr metal alloy by using various designs representative of clinical situations. The mechanical bond strength of Lucitone 199 resin was compared with the chemical and combination chemical and mechanical bond strength of Meta-Dent resin. The following conclusions may be extrapolated from the results. 1. The highest bond strength was observed between Meta-Dent resin and the plain flat metal plate. 2. The second highest bond strength was observed between Meta-Dent resin and the flat metal plate with two posts. 3. The lowest bond strengths were observed between Meta-Dent resin and the samples containing mesh retentive mechanisms. 4. The mean bond strength of Lucitone 199 resin was highest for the flat metal plate with two posts, followed by the large mesh. Bond strength with the small-mesh samples was lowest. These differences were not statistically significant. 5. The mean bond strengths of Meta-Dent resin to flat metal plates with or without posts was significantly higher than any of the Lucitone 199 resin metal bond strengths, to the 99% confidence level. Additional studies will be necessary to confirm the validity of these conclusions with respect to clinical removable partial dentures. Longitudinal investigations will be required to reveal clinical performance of these resin systems.

Acrylic Resins↗
PubMed1990

Polymerization shrinkage of index and pattern acrylic resins.

Inadequate dimensional stability caused by polymerization shrinkage has been reported concerning the various applications of acrylic resins. The objective of the study was to evaluate dimensional changes of two self-curing acrylic resins marketed as pattern and index material. Early volumetric changes were measured with a dilatometer and late linear changes were recorded with an inductive transducer. After 24 hours the volumetric shrinkage was 7.9% for Duralay resin and 6.5% for Palavit G resin; 80% of the change appears before 17 minutes at room temperature. Shrinkage was significantly increased when the proportion of powder in the mix was diminished. Results suggest that these resins should be used with some method to compensate for the shrinkage, when used as index material. However, the dimensional change might provide significant advantages for intracoronal castings.

Acrylic Resins↗
PubMed1992

A shade guide for acrylic resin facial prostheses.

The value and success of a well-fitting and anatomically correct prosthesis are compromised if the color does not match the adjoining tissue. Color and color science are reviewed to help develop a simplified acrylic resin shade guide to aid in fabricating acrylic resin facial prostheses. This guide will help the clinician obtain a good intrinsic shade and minimize extrinsic coloration.

Acrylic Resins↗
PubMed1993

Clear acrylic resin T-bar used in denture identification.

A preformed, T-shaped, clear acrylic resin bar can be utilized as a vehicle for identification of an existing removable dental prosthesis. A printed label attached to the T-bar makes a convenient vehicle for embedding the label in the prosthesis with light-cured acrylic resin. The resultant finished surface of the T-bar assembly provides a protective cover and an exceptionally clear window for viewing the label. The procedure is time-effective and relatively easy.

Acrylic Resins↗
PubMed1994

Assessing shade differences in acrylic resin denture and natural teeth.

Four experiments in this study assess shade differences in acrylic resin denture and natural teeth. The first two examine the perceptual errors made by experienced dentists in their use of a manufacturer-provided shade guide for acrylic resin denture teeth. In the first of four experiments, dentists examine whether the numbering of a selected shade guide corresponds to the arrangement of the tabs from light to dark. In the second experiment, a visual discrimination task determines whether dentists can distinguish shade guide tabs from one another. The results from these two experiments revealed that the numbered progression of the shade tabs does not correspond to a light-to-dark order, that dentists have difficulty discriminating between several shade tabs, and that the shade tabs can be rearranged on an empirical basis. The third experiment demonstrated how the shade of natural teeth varies by age, gender, and complexion. The Biotone shade guide, rearranged in the manner suggested by the second experiment, was used to make these assessments. The fourth experiment examined whether the shades used for complete dentures were similar to shades found in natural teeth. The results from the last two experiments showed that shade selection can be facilitated by use of a rearranged set of shade guide tabs. The results also reveal that natural teeth significantly and clinically darken with age; however, selections made for denture teeth tend to be relatively constant in color, despite the age of the patient. Differences for gender and complexion do not appear to be clinically significant.

Acrylic Resins↗
PubMed1992

Formaldehyde, glyoxal, urethane, methyl carbamate, 2,3-butanedione, 2,3-hexanedione, ethyl acrylate, dibromoacetonitrile and 2-hydroxypropionitrile induce chromosome loss in Saccharomyces cerevisiae.

Induction of mitotic chromosome loss could be demonstrated for the dialdehyde glyoxal, the diketones 2,3-butanedione and 2,3-hexanedione, ethyl and methyl carbamate, ethyl acrylate, dibromoacetonitrile, 2-hydroxypropionitrile and formaldehyde, but only when they were combined with subacute concentrations of propionitrile, which is a strong inducer of chromosomal malsegregation. The same chemicals did not induce mitotic chromosome loss when applied in pure form. However, glyoxal, ethyl acrylate, dibromoacetonitrile and formaldehyde when applied in pure form also induced mitotic recombination. Respiratory deficiency was induced, in the absence of propionitrile, by these recombinogenic agents and also by 2,3-hexanedione and 2-hydroxypropionitrile which are not recombinogenic.

Acetonitriles↗