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Biomedical subjects

J D Allen

Publications and source records attributed to J D Allen.

At least 73 records · Page 4Linked to original sources
PubMed1992

Effect of warm air on the shear bond strength of composite resins.

This investigation evaluated the operating characteristics of a recently introduced tooth dryer and its effect on the bond strength of three composite resins to etched enamel. The effect of varying air pressure, distance from the tip of the tooth dryer, and distance laterally from mid-air stream on temperature were measured using a rapid-response thermocouple. Specimens were subjected to shear forces either immediately after bonding or after 5 days of water storage. The air stream required from 32 to 41 seconds to reach maximal temperature; however, more than 90% of the maximal temperature was obtained in 20 seconds. There was an increase in temperature with increased air pressure and a decrease in temperature with increasing distance from the tip. The temperature dropped rapidly laterally from the center of the air stream. The shear bond strength measurements were significantly higher for the specimens prepared using the tooth dryer for one composite resin tested immediately after bonding; there was no statistically significant difference for the other resins. The effect of warm air on the shear bond strength of composite resins to etched enamel may be dependent on the resin used and the time between bonding and testing.

Air↗
PubMed1992

CD4 immunoadhesins in anti-HIV therapy: new developments.

CD4, the cell-surface receptor for the human immunodeficiency virus (HIV), is a member of the immunoglobulin (Ig) gene superfamily. It contains 4 extracellular sequences homologous to Ig variable domains, the first of which (V1) is sufficient for binding to HIV. To develop CD4 as an anti-HIV therapeutic, we engineered a CD4 immunoadhesin (CD4-IgG)--a fusion protein containing the V1 and V2 domains of CD4 with the hinge and Fc regions of human Ig heavy chain. A chimeric protein of this type has several advantages compared to the soluble receptor, including a greatly extended in vivo half-life and greater avidity for HIV; moreover, like an antibody, it performs effector functions via its Fc domains, such as complement activation and antibody-dependent cell-mediated cytotoxicity. In vivo experiments show that CD4-IgG protects against HIV-I IIIB infection of chimpanzees when administered prior to viral challenge. In addition, CD4-IgG is transferred efficiently across the placenta from mother to fetus in rhesus monkeys. To evaluate its safety in humans, we conducted a phase-I clinical trial in adult patients with AIDS and AIDS-related complex. We found that, in a total of 16 patients, administration of CD4-IgG was well tolerated at doses up to 1000 micrograms/kg of body weight, with no important clinical or immunological toxicities noted. Given its unique properties, particularly the ability of CD4-IgG to cross the placenta, we plan to focus future clinical efforts on preventing infection of newborns via maternal-fetal transfer of HIV.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Overdentures and the periodontium.

Several periodontal factors are critical to the prognosis of overdenture abutment teeth. This literature review outlines these factors and discusses the documented effects of long-term overdenture use on periodontal health. The efficacy of a professional periodontal maintenance program, which is coordinated with a home oral hygiene program, is related to the success of overdenture therapy.

Dental Abutments↗
PubMed1992

Time-dependence of inducible ventricular tachycardia in a chronic canine model.

The natural history of inducible ventricular tachycardia in post-infarction dogs was followed with serial programmed electrical stimulation (PES: 1-3 extrastimuli, 4 msec duration, 2 x diastolic threshold). Arrhythmia inducibility was defined as a minimum of four unstimulated ventricular ectopic beats. Of 119 dogs prepared for chronic electrophysiological study, 87 (73.1%) were ambulant 24 hours after surgery. Mean infarct size was 11.1 +/- 1.5% of left ventricular (LV) mass for animals dying in the first week, before stimulation. 92.4% of 66 animals were inducible when stimulated at one week, 66.7% at two weeks and 64.3% and 55.6% at the third and fourth weeks respectively (p less than 0.01, Chi-square analysis). Infarct sizes fell from 7.0 +/- 0.5% LV mass at first stimulation to 4.6 +/- 0.8% at third stimulation and could not be visualized thereafter (p less than 0.01,ANOVA). There was no statistical difference between infarct sizes for inducible and non-inducible animals, but in both cases infarcts were smaller (p less than 0.01) than for those animals which died suddenly during the first week. This time-dependent decrease in arrhythmia inducibility, which may be related to infarct size, should be considered when similar models are employed for chronic electrophysiological studies.

Animals↗
PubMed1991

Film thickness of die coating agents.

Die coating agents are often used during the fabrication of porcelain margins for crowns and fixed partial dentures. These agents seal microscopic irregularities within the stone die and resist abrasion. This investigation measured the film thickness of several die coating agents. A specific reference point was used during the measurement process. The results indicate that there is no significant difference between the die coating agents examined under the conditions of the study. The film thickness measurements ranged between 0.367 microns for Duro Super Glue Material and 2.3 microns for Zap CA material.

Acrylic Resins↗
PubMed1991

Novel murine homeo box gene on chromosome 1 expressed in specific hematopoietic lineages and during embryogenesis.

We describe here a new murine homeo box gene, denoted Hlx, which is expressed within specific hematopoietic lineages. The cDNA sequence indicates that Hlx differs markedly from known vertebrate homeo box genes, and linkage analysis of an interspecific murine backcross showed that it resides at a novel homeo box locus on the distal portion of mouse chromosome 1. The Hlx homeo domain is most similar to that of the Drosophila H2.0 gene, but outside this region the two polypeptides are related only within a few short segments, the most notable being a motif (denoted Hep) also partially conserved in the engrailed and invected homeo proteins and possibly related to an octapeptide in certain paired box proteins. The presence of an intron within the Hlx homeo box at the same position as in several divergent Drosophila genes (H2.0, labial, Distal-less, proboscipedia, Abdominal-B, NK-1) suggests an ancient evolutionary relationship between these genes. RNA analysis of 67 murine hematopoietic cell lines and normal hematopoietic cells revealed Hlx expression throughout the myeloid/macrophage lineage and at early stages of B lymphocyte development but not in T lymphocytes, erythroid cells, or mast cells. Hence, Hlx is a candidate regulator of hematopoietic lineage commitment and maturation. It probably also functions outside the hematopoietic system, however, because Hlx mRNA could be detected in diverse adult tissues and in embryos from as early as day 8 of development.

Amino Acid Sequence↗
PubMed1990

Custom-made condylar inserts for repositioning casts in articulators.

This technique permits temporary repositioning of the condylar elements of a dental articulator for the construction of orthotic prostheses and treatment planning in orthognathic surgery. The procedure is simple and adaptable to various types of articulators in current use. A single set of cast may be mounted in multiple relationships with custom-made inserts that may be retained as a record of the treatment relationship of the casts.

Acrylic Resins↗
PubMed1990

Predictability of repeated challenge: effects on cardiovascular activity in the type A (coronary prone) behavior pattern.

Fifty-two healthy young adults classified either as Type A (coronary prone) or Type B were randomly assigned to a vigilance task during which observing responses produced targets according to either a predictable (i.e., fixed-interval 90-sec) or a nonpredictable (i.e., random-interval 90-sec) reinforcement schedule. During the task, blood volume pulse, interbeat interval, masseter (EMG) activity, and blood pressure were monitored. Transient peripheral vasomotor constriction and heart rate increases were initiated within an 8- to 12-sec period following target detection with the predictable schedule, with subjects evincing greater responsivity than their nonpredictable schedule counterparts. Type A subjects assigned to the random-schedule evinced significantly shorter heart rate and blood volume pulse response durations than did Type B subjects. Longer postevent EMG elevations were evidenced by subjects assigned to the predictable schedule. No significant blood pressure differences were found among the groups. The impact of challenge-contingent behavior on cardiovascular responsivity and the relevance of attentional processes to this relationship and to cardiovascular risk are discussed.

Adult↗
PubMed1990

The effect of interplay interval on adjunctive behavior in humans in a game-playing situation.

Thirty-seven undergraduate students played two consecutive games of backgammon where manipulated interplay intervals were either 10, 22.5, 45, or 90 sec in length. When visual access to the opponent's play was blocked by a curtain during the second game, rates of movement, drinking, and eating increased over baseline rates prevailing in the first game. Grooming rate was not affected. Functions relating behavior rate to interplay interval were not bitonic for any of the behaviors; however, response distributions for drinking demonstrated postplay peaks at each interplay interval. Problems of classifying human behaviors into adjunctive versus faculatative categories were discussed.

Adolescent↗
PubMed1990

Occurrence of temporomandibular disorder symptoms in healthy young adults with and without evidence of bruxism.

Few studies have specifically examined the association between bruxism and symptoms of temporomandibular disorders in adults. In this study 569 freshmen dental students entering the Medical College of Georgia over a 10-year period completed an 18-item "yes/no" questionnaire relating to awareness of tooth clamping/clenching/grinding and signs and symptoms of oral, facial, and craniomandibular discomfort, pain, and disorders. A higher proportion of females than males reported that they were aware of clamping and clenching their teeth, as well as symptoms of stiff jaw, sore jaw or teeth, cracking or locking jaw joint, and headaches in the morning. Reported awareness of tooth clamping and clenching and of someone having heard tooth grinding was significantly associated with reported pain, discomfort, or other sensations in, in front of, or behind the ear in the overall subject group.

Adult↗
PubMed1990

Fourier analysis of ventricular fibrillation of varied aetiology.

Fast Fourier Transform analysis was used to study ventricular fibrillation induced by several different methods in 43 greyhounds anaesthetized with sodium pentobarbitone. The dominant frequency at the body surface of ventricular fibrillation induced electrically in non-ischaemic hearts was initially 9.9 +/- 0.7 Hz, remained above 9 Hz for 70 s and then rapidly fell to 5 Hz. The dominant frequency of ventricular fibrillation induced by acute occlusion (initially 12.3 +/- 0.2 Hz), or by reperfusion (12.2 +/- 0.4 Hz) of the anterior descending branch of the left coronary artery, showed a similar time-course. However, ventricular fibrillation induced by administration of potassium (4.8 +/- 0.8 Hz) or ouabain (7.1 +/- 1.1 Hz) was significantly slower. Fibrillation recorded from the endocardium of the heart initially showed a similar dominant frequency to that recorded at the body surface, but there was no significant fall in frequency over 3.3 mins. There was little difference in the time-course of fibrillation in the non-ischaemic heart recorded directly from the epicardium or from a surface lead. These findings may be of relevance to the poor response to DC countershock after prolonged ventricular fibrillation, hyperkalaemia or cardiac glycosides.

Animals↗
PubMed1990

UK-52,046 (a novel alpha 1-adrenoceptor antagonist) and the role of alpha-adrenoceptor stimulation and blockade on atrioventricular conduction.

The effects of increasing intravenous (i.v.) doses of prazosin, phenylephrine, flecainide, and UK-52,046 on blood pressure (BP), heart rate (HR) and the specialized conduction system (AH and HV intervals) were investigated in anaesthetized dogs. Results indicated that UK-52,046 (1-8 micrograms/kg) had no effect on BP or HR, but reduced (p less than 0.05) BP at doses of 16 and 32 micrograms/kg; no change occurred in HR. During sinus rhythm (SR) the AH or HV intervals did not change as compared with placebo; on pacing (PA) UK-52,046 (4-16 micrograms/kg) decreased the AH interval. After prazosin BP decreased (p less than 0.05) after 20-40 micrograms/kg; HR increased after all doses (5-40 micrograms/kg). The HV interval was unaltered, but the AH interval decreased after 40 micrograms/kg during SR and PA. After phenylephrine (continuous infusion, 50 micrograms/ml/min) BP increased at 33 min and HR was decreased at 23 and 33 min. The AH interval lengthened during PA (p less than 0.05), but there was no effect on the HV interval. Administration of flecainide (0.5-2.0 mg/kg) had no effect on BP or HR but increased the HV interval during SR and PA (1 and 2 mg/kg, p less than 0.05). The results indicate that the alpha 1-adrenoceptor agonist phenylephrine and the alpha 1-adrenoceptor antagonist prazosin, on PA altered the AH (but not the HV) intervals in opposite directions in association with changes in HR and BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1990

Pharmacological analysis of established ventricular fibrillation.

1. The effects of anti-arrhythmic drugs on the power spectrum of established ventricular fibrillation induced by endocardial electrical stimulation, have been studied in greyhounds anaesthetized with sodium pentobarbitone (35 mg kg-1, i.v.). 2. In dogs receiving no drug, initial recording of ventricular fibrillation showed a dominant frequency of 9.9 +/- 0.7 Hz (lead II) and 10.0 +/- 0.6 Hz (endocardium). After 3.3 min the frequency had fallen to 4.0 +/- 0.4 Hz in lead II, but remained high in the endocardium (10.7 +/- 0.5 Hz). 3. Lignocaine significantly reduced the dominant frequency for fibrillation recorded from lead II at (0-80 s), and for endocardial fibrillation at (0-200 s). 4. Pretreatment with propranolol or bretylium had little effect on the time course of the dominant frequency of fibrillation in lead II or the endocardium. 5. Verapamil prevented the fall in frequency seen in lead II after 80 s in the no drug group. A significantly higher frequency was maintained in both lead II (14.7 +/- 0.9 Hz) and the endocardium (14.8 +/- 0.9 Hz) for 3.3 min, compared with the no drug group (P less than 0.01). 6. Activation of fast sodium channels may determine the rapid frequency of the initial stages of ventricular fibrillation. The rapid fall in dominant frequency in lead II after fibrillation for 80 s can be prevented by calcium channel blockade and may be due to intracellular accumulation of calcium.

Animals↗
PubMed1989

Splenectomy. The treatment of choice for human immunodeficiency virus-related immune thrombocytopenia?

Immune thrombocytopenia is a well-recognized part of the clinical spectrum of infection with the human immunodeficiency virus. From November 1985 to February 1988, 15 patients who were human immunodeficiency virus-positive underwent splenectomy for refractory immune thrombocytopenia. Eight patients had thrombocytopenia only, and 7 others were pancytopenic prior to splenectomy. Three of the 15 patients fulfilled criteria for acquired immunodeficiency syndrome before splenectomy, and acquired immunodeficiency syndrome developed in 5 patients during the follow-up period. The median duration of thrombocytopenia prior to surgical therapy was 6 months. A bone marrow biopsy specimen showed hypercellularity with increased megakaryocytes. All patients had a therapeutic response to splenectomy. Long-term remission from thrombocytopenia/pancytopenia was achieved in 14 of the 15 patients during a follow-up period of 2 to 21 months. Splenectomy can be accomplished with an acceptable morbidity. Pneumonia developed postoperatively in 2 patients, but they did not manifest the characteristic picture of overwhelming postsplenectomy sepsis. They had received vaccinations against encapsulated organisms preoperatively. We conclude that splenectomy provides a durable and lasting response for HIV-related thrombocytopenia. Vaccination for Streptococcus pneumonia and Haemophilus influenzae should be given prior to splenectomy although its efficacy is not clear in this group.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Transthoracic defibrillation threshold of sine and trapezoidal waveforms in defibrillation.

The transthoracic defibrillation threshold of trapezoidal (2.5-, 5-, 10-, 15-, 20-, 40-, and 55-msec duration) and damped sine waveforms were established in groups of anesthetized greyhounds. Of the seven trapezoidal waveforms, the threshold current was lowest for the 20-msec pulse but was not significantly different for the 5-20-msec pulses (p greater than 0.05). The threshold delivered energy was not significantly different for the 2.5-20-msec waveforms. The 40- and 55-msec pulses had significantly greater delivered energies than the shorter pulses (p less than 0.01). The transthoracic defibrillation threshold of two trapezoidal (5- and 20-msec) and three damped sine waves (Lown, Edmark, and Belfast) showed that the threshold transthoracic current and energy were not significantly different for the 5-msec trapezoid and three sine waves (p greater than 0.05). The threshold transthoracic energy for the 20-msec trapezoid was significantly greater than that of the four other waveforms. The threshold current for the 20-msec trapezoid was significantly less than that of the Belfast and Edmark waveforms only. Thus, none of the three damped sine waveforms was superior, with the 5-msec trapezoid producing similar results. Although the 20-msec trapezoid had the lowest threshold current, it had the highest delivery energy.

Animals↗
PubMed1989

Time-response effects of pimozide on operant behavior and schedule-induced polydipsia.

Previous research has indicated that the administration of specific doses of pimozide results in the suppression of the acquisition of schedule-induced polydipsia in rats while not affecting operant behavior. The purpose of this study was to determine if these results were due to a specific action of pimozide on schedule-induced polydipsia or if they were due to an insufficient presession time of drug administration. Pimozide at 1.0 mg/kg was administered to three groups of rats at either 30, 60 or 120 minutes presession with control subjects receiving administration of the drug vehicle also at these times. The results of the study were that both operant behavior and the acquisition of schedule-induced polydipsia were affected in a nondifferential and time-dependent manner by pimozide. It was also found that pimozide caused an alteration in the temporal pattern of both schedule-induced polydipsia and operant responding. This latter result appears to have been caused by a disruption in sensorimotor integration due to the dopamine blocking properties of pimozide.

Animals↗