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Biomedical subjects

W Lacefield

Publications and source records attributed to W Lacefield.

8 recordsLinked to original sources
PubMed2001

Orthodontic in vivo bond strength: comparison with in vitro results.

The purpose of the present study was to test a new in vivo debonding device and compare in vivo bond strengths recorded by this device with in vitro bond strengths recorded by a universal testing machine such as the Instron. For the in vitro part of the study, 60 extracted premolar teeth were divided into 2 groups of 30 each. Both groups of 30 teeth had 3M Unitek Victory Twin brackets, precoated with Transbond XT composite resin, bonded to them. Shear bond strength tests were carried out in vitro using the universal testing machine on one group of 30 teeth while the debonding device was used on the other group of 30 teeth. The mean shear bond strength of the group debonded using the universal machine was 11.02 MPa and that of the group debonded with the debonding device was 12.82 MPa. For the in vivo part of the study, 8 patients randomly assigned to the research clinician from patients in The University of Alabama School of Dentistry, Department of Orthodontics, had a total of 60 premolar teeth bonded with 3M Unitek Victory Twin brackets. Following comprehensive orthodontic treatment (average time of 23 months), shear bond strength tests were carried out using the debonding device, which can measure debonding forces in vivo. The mean shear bond strength recorded in vivo was 5.47 MPa. Statistically significant differences were found between all 3 groups tested. The results appear to indicate that mean bond strengths recorded in vivo following comprehensive orthodontic treatment are significantly lower than bond strengths recorded in vitro.

Analysis of Variance↗
PubMed2000

Bond strength of prosthodontic luting materials to titanium after localized cyclic loading.

PURPOSE: To establish an in vitro analysis system to evaluate the effect of cyclic loading on the bond strengths and durability of luting materials bonded to titanium. MATERIALS AND METHODS: Machine-milled titanium disks were finished with 600 grit silicon-carbide paper and pairs of disks were bonded together using the five different luting materials. A stainless steel stylus was vertically loaded at a center position (Model 1) or at the border (Model 2) of the specimens with a force of 75.6 N at 7500 cycles/hr. When the stylus contacted the specimen surface through the water slurry of poly(methyl methacrylate) beads, it rotated clockwise up to 15 degrees and counter-rotated. Shear bond strengths were determined 1 hr after bonding, after storage in water at room temperature for 24 hr, and after the loading for 100,000 cycles. RESULTS: The bond strengths of the unfilled adhesive resin and resin-based composite cement (RBC) were significantly higher than those of the glass-ionomer cements. Zinc phosphate cement demonstrated no bonding ability to titanium. After 100,000 cycles, peripheral loading in Model 2 significantly reduced the bond strength of the RBC and glass-ionomer cements, while Model 1 loading did not. The highest and the most durable bonds were obtained with the unfilled adhesive resin in both models.

Adhesiveness↗
PubMed1999

An in vitro evaluation of a metal reinforced orthodontic ceramic bracket.

The objectives of the present study were to measure and compare the bond strength and failure sites of a currently available ceramic bracket (Transcend 3M-Unitek) with the new metal reinforced ceramic bracket (Clarity 3M-Unitek) and to evaluate the amount of composite left on the tooth using the Adhesive Remnant Index in the teeth that were debonded with pliers recommended for this purpose. In addition, the presence or absence of enamel damage after debonding was also assessed. One hundred and twenty extracted premolar teeth were divided into 4 groups of 30 each. Two groups of 30 teeth had Transcend 6000 brackets bonded, and the other 2 groups had Clarity brackets bonded. Shear bond strength was carried out on 30 Transcend 6000 brackets and 30 Clarity brackets, whereas the other 2 groups of 30 teeth bonded with Transcend 6000 and Clarity brackets were debonded with debonding pliers recommended by the manufacturer of both ceramic brackets. The mean shear bond strength of the Clarity brackets was 13.27 MPa, whereas that of the Transcend 6000 was 21.19 MPa. Both brackets failed mostly at the bracket-adhesive interface (75%), indicating a possible reduction of the chances of enamel damage. Six of the premolars, bonded with Transcend 6000 brackets and debonded with the plier, showed an increase in the number or length of enamel cracks as evaluated by an optical microscope (Micro-Vu); one premolar, bonded with Clarity brackets and debonded with the pliers, showed an increased enamel crack length. Gross enamel damage, assessed by enamel dislodgment, was not evident in any specimen. Results of this study suggest that the new metal reinforced ceramic bracket (Clarity) may be recommended for clinical use because of its acceptable shear bond strength and possible reduced chances of enamel damage during bracket removal.

Bicuspid↗
PubMed1990

LY277359 maleate: a potent and selective 5-HT3 receptor antagonist without gastroprokinetic activity.

Several 5-hydroxytryptamine (5-HT3) receptor antagonists have been described. In addition to 5-HT3 receptor antagonist activity, many of these agents also possess gastroprokinetic activity. In the present report, we identify compound LY277359 maleate as a potent, p.o. active, highly selective 5-HT3 receptor antagonist lacking gastroprokinetic effects. LY277359 maleate was a potent and selective antagonist of 2-methyl 5-HT-induced contraction in the guinea pig ileum (KB = 1.6 nM), a response mediated by activation of 5-HT3 receptors. Given both i.v. (0.0003, 0.001 and 0.003 mg/kg) and p.o. (0.01 and 0.03 mg/kg), LY277359 maleate inhibited the bradycardic response to i.v. administered 5-HT in urethane-anesthetized rats. The duration of antagonism of 5-HT-induced bradycardia persisted beyond 6 hr after p.o. administration of LY277359 maleate (0.03 mg/kg p.o.). In contrast to its potent 5-HT3 receptor antagonist activity, LY277359 maleate, in doses up to 1 mg/kg p.o., did not affect gastric emptying in rats, suggesting minimal, if any, gastroprokinetic activity of LY277359 maleate. This is in contrast to another 5-HT3 receptor antagonist, zacopride, which did produce a marked increase in gastric emptying in rats at doses of 0.1 mg/kg p.o. and higher. LY277359 maleate (0.03 and 0.1 mg/kg i.v. and 0.07, 0.1, 0.3 and 1.0 mg/kg p.o.) did have effects consistent with other 5-HT3 antagonists, to inhibit cisplatin-evoked emesis in dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Comparison of the 5-HT3 receptor antagonist properties of ICS 205-930, GR38032F and zacopride.

The well-documented 5-HT3 receptor antagonists, ICS 205-930 and GR38032F, have been compared with regard to their inhibitory activity at 5-HT3 receptors to another gastrokinetic agent, zacopride. Zacopride and ICS 205-930 showed similar affinity (-log kB approximately 8.0), whereas GR38032F showed lower affinity (-log ka approximately 7.0) at 5-HT3 receptors in the guinea pig ileum. After i.v. administration to anesthetized rats, zacopride was approximately 10-fold more potent than either ICS 205-930 or GR38032F, which were equipotent as inhibitors of serotonin-induced bradycardia (5-HT3-mediated activation of the von Bezold Jarisch reflex). After oral administration to anesthetized rats, zacopride remained approximately 10-fold more potent than ICS 205-903, which was approximately 2-fold more potent than GR38032F as an inhibitor of serotonin-induced bradycardia. Furthermore, the inhibitory effectiveness of GR38032F persisted for less than 3 hr after oral administration and for less than 15 min after intravenous administration. ICS 205-930 produced maximal inhibition of serotonin-induced bradycardia for over 3 hr with heart rate returning to control values 6 hr after oral administration. Zacopride possessed the longest duration of inhibitory effectiveness in urethane-anesthetized rats with maximal inhibition still apparent 6 hr after oral administration. All three agents inhibited cisplatin-induced emesis after i.v. administration in dogs with zacopride being 10-fold more potent than ICS 205-930 or GR38032F, which were equipotent. These comparative data with three 5-HT3 receptor antagonists indicate that in animals, zacopride was more potent and longer acting than either ICS 205-930 or GR38032F. Furthermore, after oral administration to rats, GR38032F was slightly less potent than ICS 205-930 and possessed the shortest duration of action.

Animals↗
PubMedDate not supplied

[Effect of heat treatment on the structure of a Cu-Zn-Al-Ni system dental alloy].

This article characterizes the structural phases present in the copper-based metallic alloy system "Cu-Zn-Al-Ni" developed for dental use, and relates those phases to other properties. The characterization was obtained after casting (using the lost wax process), and after heat treatment. In order to obtain better corrosion resistance by changing the microstructure, the castings were submitted to 30, 45 and 60 minutes of heat treatment at the following temperatures: 750 degrees C, 800 degrees C, and 850 degrees C. The various phases were analyzed using X-ray diffraction and scanning electron microscopy (SEM). The results after heat treatment showed a phase (probably Cu3Al), that could be responsible for the improvement in the alloy's resistance to corrosion as compared to the as-cast structure.

Aluminum↗