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Biomedical subjects

G Holan

Publications and source records attributed to G Holan.

At least 37 records · Page 2Linked to original sources
PubMed1992

Effect of root canal infection and treatment of traumatized primary incisors on their permanent successors.

The purpose of the present retrospective study was to evaluate the effect of trauma, root canal infection and treatment of non-vital primary incisors on their permanent successors. A total of 117 permanent central incisors were examined clinically and radiographically for the presence of discolorations, hypoplasia, or disturbances in root development. Of these, 29 were succedaneous to traumatized, endodontically involved and treated primary incisors (Group A). Another 29 had their traumatized, endodontically involved, primary predecessors extracted or left untreated (Group B). The remaining 59 incisors were intact and had no history of trauma (Group C). Severe hypoplasia could not be observed in any of the teeth, and no disturbances in root development could be disclosed radiographically. The incidence of defects in Groups B and C was similar, whereas in Group A it was 2 or 3 times higher than in each of the other two groups. Despite this fact, root canal treatment of traumatized non-vital primary incisors should be considered a treatment option, as premature extraction of a primary incisor may lead to speech problems, premature eruption and/or malalignment of the permanent successor, or affect the child's self image.

Chi-Square Distribution↗
PubMed1991

Gamma-aminobutyric acid-modulated benzodiazepine binding sites in bacteria.

Benzodiazepine binding sites, which were once considered to exist only in higher vertebrates, are here demonstrated in the bacteria E.coli. The bacterial [3H]diazepam binding sites are modulated by GABA; the modulation is dose dependent and is reduced at high concentrations. The most potent competitors of E.Coli [3H]diazepam binding are those that are active in displacing [3H]benzodiazepines from vertebrate peripheral benzodiazepine binding sites. These vertebrate sites are not modulated by GABA, in contrast to vertebrate neuronal benzodiazepine binding sites. The E.coli benzodiazepine binding sites therefore differ from both classes of vertebrate benzodiazepine binding sites; however the ligand spectrum and GABA-modulatory properties of the E.coli sites are similar to those found in insects. This intermediate type of receptor in lower species suggests a precursor for at least one class of vertebrate benzodiazepine binding sites may have existed.

Animals↗
PubMed1991

Evaluation of students' performance in obtaining local anaesthesia in children.

This study was designed to determine the success of various local anaesthesia techniques as assessed by the presence or absence of pain during restorative procedures performed by senior undergraduate dental students in a pedodontic clinic. Data gathered from the treatment of 151 patients by 43 students recorded the frequency of pain complaints during procedures for which local anaesthesia had been employed. It was found that 73% of the administrations were successful. The proportion of children who complained of pain during the operative procedure was significantly higher in those with a previous history of a painful dental experience.

Adolescent↗
PubMed1991

Alveolar bone loss in two children with short-bowel syndrome receiving total parenteral nutrition.

Two preschool children who were receiving total parenteral nutrition (TPN) for short-bowel syndrome (SBS) were noted to have radiographic evidence of alveolar bone loss in their primary dentition. Tooth mobility, gingival recession, and premature tooth loss were clinical findings in these children. Both had a 2-year history of recurrent infections and fluctuating serum electrolytes prior to identification of their dental problems.

Alveolar Bone Loss↗
PubMed1991

Dental caries experience of 5-year-old children related to their parents' education levels: a study in an Arab community in Israel.

The purpose of this study was to examine the influence that parents' education may have on the prevalence of dental caries in young children. The study was conducted on 210 kindergarten children aged 5 years in an Arab village. The presence of caries was determined according to the WHO criteria, with an explorer and a dental mirror under natural light. The education of the parents was assessed on a scale of 1-6 according to information obtained from a questionnaire to the parents. The results of this study showed that children of highly educated parents had relatively low dental caries experience. The influence of the mothers was apparent at a lower educational level than that of the fathers. In this population only 0.6% of the dental treatment needs were met. Of the kindergarten children 99.5% had experienced caries. The caries experience was extremely high: the mean dmfs was 17.7 (+/- 12.15), and the means dmft 8.04 (+/- 8.37).

Analysis of Variance↗
PubMed1989

Design of potential anti-HIV agents. 1. Mannosidase inhibitors.

A molecular orbital and molecular graphics study of 12 substrates, inhibitors, reaction intermediates, and substrate analogues of alpha-mannosidase was undertaken. The results indicated that potent inhibitors must be good topographical analogues of the mannopyranosyl cation, an intermediate in the reaction catalyzed by the enzyme. Enzyme recognition and strong binding by the inhibitors requires that they contain, as part of their structure, electronegative atoms which are the topographical equivalent of the mannosyl cation C2 and C3 hydroxyl groups and ring heteroatom. The absence of a topographical analogue of the C4 hydroxyl group of the cation appeared to have little effect on the binding and activity of inhibitors. These results have been utilized in the design of potential anti-HIV drugs whose synthesis is now under consideration.

Alkaloids↗
PubMed1989

Clinical, radiographic, SEM evaluation and assessment of microleakage of Class II composite restorations.

The influence of incremental or bulk filling techniques, and reapplication of unfilled resin (impregnation) to the margins with an enamel bonding agent, on marginal adaptation was evaluated in Class II composite restorations by clinical, radiographic, scanning electron microscope (SEM) and dye penetration techniques. Cavities were prepared in 80 extracted permanent posterior teeth. All cavity walls were treated with polyacrylic acid for 10 seconds. The enamel was etched for 1 minute, rinsed, dried, and lined with Scotchbond. Forty cavities were filled by increments of P30 and 40 cavities in bulk. The margins of the restorations of 20 teeth in each group were re-etched for 30 seconds and Concise Enamel Bond reapplied. The clinical scores were excellent for all restorations. Radiographic examination showed twice as many bubbles in the incrementally filled restoration than in the group filled in bulk. In 53 teeth, a radiolucent area between the dentin and the restorative material was found. After sectioning, this area was found to correspond to a hard material. The SEM revealed excellent margins in the groups of teeth that were impregnated with an unfilled resin, whereas 13 teeth without impregnation showed defective margins. The dye penetration, as a test for marginal leakage, was minimal at the occlusal surface of all teeth. At the cervical surface, 10.5% of the impregnated teeth showed severe dye penetration compared to 18% of the nonimpregnated teeth. No correlation was found between dye penetration at the cervical surface and the thickness of the residual enamel in this area.(ABSTRACT TRUNCATED AT 250 WORDS)

Composite Resins↗
PubMed1988

QSAR studies of hydrazone uncouplers of oxidative phosphorylation.

Semiempirical molecular orbital calculations have been performed on a series of hydrazone uncouplers of mitochondrial oxidative phosphorylation which show insecticidal activity. Regression analysis yielded significant correlations between uncoupling activity, insecticidal potency and such physicochemical or theoretically-derived parameters as lipophilicity, pKa and atom charges.

Adenosine Diphosphate↗
PubMed1987

Electrophysiological comparison of insecticide and alkaloid agonists of Na channels.

Macroscopic currents in Na channels were recorded from adult frog skeletal muscle under voltage clamp as various toxins were added to the bathing medium. Veratridine, cevadine, and 3-(4-ethoxybenzoyl)-veracevine modified the Na channels in a use-dependent manner during depolarizations and held them open for 3, 2.4, and 1.2 s, respectively, at -90 mV. The three alkaloids modified channels in the same way. Activation gating was shifted about -100 mV by the modification, and reversible closing of the channels by strong hyperpolarizations slowed reversal of the modification. The synthetic insecticides deltamethrin, EDO, GH739, and GH414 also modified channels during depolarizations that opened channels. The modification lasted 3 s with deltamethrin, but only 3-5 ms with the others. Hyperpolarization speeded the shutting off of current in insecticide-modified channels, but no reversible activation gating could be demonstrated. The ionic selectivity, PNa/PNH4, of channels was decreased by all of the toxins. This ratio was 0.11 in normal channels, 0.26 in insecticide-modified channels, and 0.7-1.6 in veratrum-alkaloid-modified channels. During use-dependent modification, the veratrum alkaloids reduced the total Na current markedly, while deltamethrin did not. Thus, alkaloid and insecticide modifications share many features but differ in how much the conducting properties of the pore are changed and whether the channel can close reversibly while the toxin remains bound.

Animals↗
PubMed1987

gamma-Aminobutyric acid receptor ionophore complexes: differential effects of deltamethrin, dichlorodiphenyltrichloroethane, and some novel insecticides in a rat brain membrane preparation.

The binding of [35S]t-butylbicyclophosphorothionate ([35S]TBPS), a gamma-aminobutyric acid (GABA)-activated chloride ionophore ligand; [3H]diazepam, a benzodiazepine agonist; and [3H]muscimol, a GABA receptor probe, were used to assess the effects at 100 microM of deltamethrin, dichlorodiphenyltrichloroethane (DDT), and three experimental insecticides--a DDT-pyrethroid hybrid, GH414 (cycloprothrin), and two DDT-analogues, GH266 and GH149 (EDO), on GABA receptor ionophore complexes in a rat brain membrane preparation. GH266 and GH149 were found to inhibit a greater percentage of [35S]TBPS binding than the same concentration of deltamethrin or DDT, although GH414 had little effect. GH266 and GH149 enhanced [3H]diazepam binding by nearly 200%, in contrast to the inhibitory effects of deltamethrin, DDT, and GH414. GH266 and GH149 also caused a dramatic enhancement of [3H]muscimol binding, 367 and 236% of control, respectively, whereas DDT and deltamethrin caused only a moderate enhancement. The effects of the insecticides on binding affinity and density were examined for each of the ligands. The results show a differential interaction of the insecticides on the various ligand binding sites.

Animals↗
PubMed1971

Rational design of insecticides.

A steric model of diaryl insecticides, which includes the structure of DDT and its analogues, was used for the synthesis of new highly active insecticides. The new compounds show low toxicity to mammals and their insecticidal activity can be potentiated by microsomal oxidase inhibitors. There is evidence that they readily undergo biological degradation. However, a spontaneous controlled chemical degradation was also established for the diaryl oxetanes, which form one group of a new series of insecticides. The theoretical model was further investigated using X-ray crystallography to establish one accurate structure. Biologically, the model is supported by studies of the correlation between insect mortalities and temperature and by measurements of nerve impulses at fly chemoreceptors after treatment with selected compounds.

Animals↗