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Biomedical subjects

H Letzel

Publications and source records attributed to H Letzel.

At least 37 records · Page 2Linked to original sources
PubMed1987

Measuring problems in estimating the exposure to passive smoking using the excretion of cotinine.

Quality control studies on cotinine measurements following low level environmental tobacco smoke (ETS) exposure are rare. The exposure to ETS was controlled and systematically changed in a series of experiments in a climatic chamber. Healthy nonsmoking volunteers were exposed to ETS simultaneously. The duration and level of exposure varied using high (8, 17 and 25 ppm CO), and low (2 and 5 ppm CO) exposure levels. The variation between radioimmunoassay (RIA) and gas chromatography (GC) was high as was the variation between the results of RIA laboratories. There was also a high within-laboratory-variation. A 1:10 dilution seems to be preferable over a 1:3 dilution. Freezing the urine samples immediately after collection led to the detection of higher cotinine values than freezing the samples 24 h after collection. Highly reliable data for cotinine were obtained when the urine samples were kept frozen immediately after collection and fractionated sampling over 48-72 h was used. Our data show that estimating low-level ETS exposure by measuring urinary cotinine is highly susceptible to uncontrolled variation and errors. Sufficiently reliable estimates of low-level ETS exposure can be made only when fractionated sampling over 48-72 h is used and when the urine samples are kept frozen just after collection.

Chromatography, Gas↗
PubMed1987

The influence of the condensation instrument on the clinical behaviour of amalgam restorations.

The influence of the condensation instrument on the behaviour of amalgam restorations was investigated in a clinical study for which in a group of forty-nine patients, 125 Class I or II amalgam restorations were made by each of two operators. The restorations were made in series of five per patient. For each restoration within a series, the amalgam was condensed with a different instrument (hand condensation, Amalgam Condensaire, Speedomatic, Bergendal Vibrator and Electro-mallet). For a period of 2.5 years the restorations were checked at half-year intervals for failures. The marginal integrity of the restorations was assessed half-yearly with a six-point photo rating scale. The discolouration, roughness formation and the marginal integrity of the restorations were assessed clinically with four-point rating scales. The number of failures and the assessments were analysed for the effect of the condensation instrument, the patient and the operator. After 2.5 years, 12% of the restorations had failed, which is too few for the tracing of a condensation instrument and a patient effect. The operator, however, had an influence on the failure percentage. The condensation instrument had no influence on the clinical behaviour of the restorations, however the patient had. The operator only had an influence on the marginal integrity. This suggests that clinically the condensation results depend more on the operator rather than the instrument.

Dental Amalgam↗
PubMed1986

Creep versus marginal fracture of amalgam restorations.

In the literature there is controversy over the existence of a correlation between creep and marginal deterioration of amalgam restorations. It was the aim of this study to re-investigate this correlation. In five clinical trials, 2068 amalgam restorations were made of six conventional alloys and ten high copper systems. The results show a correlation between creep and marginal fracture in the conventional, low copper amalgams. No correlation could be found for the group of high copper, non-gamma-2, amalgams. It is emphasized that dental practitioners should not buy their amalgam alloy on the basis of creep data, because wrong decisions might be taken. Evidence from a controlled clinical study is a more reliable criterion.

Chemical Phenomena↗
PubMed1986

Composite versus amalgam restorations. A three-year clinical evaluation.

In a clinical study the behaviour of posterior composite restorations was evaluated. For the study, 232 Class I or II restorations in premolars and molars were made by three operators in a group of forty-nine adult patients. Each patient underwent one or two series of four restorations. The materials within a series were a strontium glass filled composite (Profile), a microfilled composite (Estic MF), a macrofilled composite (Adaptic Radiopaque) and a high copper amalgam (Dispersalloy). The last two materials served as a negative and positive controls respectively. For a period of 3 years the clinical behaviour was evaluated yearly with the USPHS criteria (anatomic form, marginal adaptation, colour match, marginal staining and caries). Differences in the ratings of the criteria between materials, tooth type and evaluation year were tested statistically for significance. The number of restorations replaced after 3 years in clinical service was eight (= 3.6%). The results showed that the material, tooth type and evaluation year all have an influence on the anatomic form and the colour match of the restoration. The behaviour of the three composites with respect to colour match, marginal adaptation and marginal staining was acceptable. For anatomic form, however, only the behaviour of the microfilled composite Estic MF was still acceptable after 3 years.

Adult↗
PubMed1985

[Serum concentration of glyceryl trinitrate (GTN) in transdermal application of GTN dressings of various origins].

Serum levels of glyceryl trinitrate have been determined in eight healthy subjects following transdermal application of four different glyceryl trinitrate plasters using a randomised crossover design. The plasters investigated were Deponit 10, Nitradisc 10, Nitroderm TTS 10 and Nitro-Pflaster-ratiopharm 10. The medians of serum concentrations arranged in decreasing order were 0.17-0.23 ng/ml for Nitroderm TTS 10, 0.13-0.21 ng/ml for Nitradisc 10, 0.08-0.13 ng/ml for Deponit 10, and 0.04-0.09 ng/ml for Nitro-Pflaster-ratiopharm 10. Corresponding areas under the concentration-time curves (AUC 0-24) were 23.15 nmol . h/l (Nitroderm TTS), 20.32 nmol . h/l (Nitradisc), 10.39 nmol . h/l (Deponit), and 5.7 nmol . h/l (Nitro-Pflaster-ratiopharm).

Administration, Topical↗
PubMed1985

Passive smoking under controlled conditions.

Ten healthy subjects were exposed to passive smoking at a high level corresponding to 25-30 ppm CO in the ambient air for 3 h. All subjects were exposed at the same time in a climatic chamber especially designed for exposure experiments. Despite an identical exposure rate considerable interindividual variability of subsequent nicotine and cotinine levels in saliva, plasma and 24-h urine were observed. This variability was more prominent in nicotine than in cotinine levels. The kinetic pattern as reflected by saliva levels for up to 24 h was consistent with previous data found in active smokers. Nicotine levels found in saliva were markedly influenced by repeated sampling. This was not the case for cotinine levels. With regard to laboratory techniques RIA seems to be more sensitive than gas chromatography (GC). The results of this study suggest that measuring cotinine levels in 24-h urine with RIA is presently the most sensitive and reliable criterion for estimating exposure to passive smoking and for validating questionnaires or interviews about short-term exposure to passive smoking.

Adolescent↗
PubMed1985

A method to determine the loss of substance of dental restorations.

A method is described for quantitative in vivo wear measurements on Class I and II composite restorations. Class I gold inlays were made in an acrylic premolar and molar. Over the occlusal parts of the teeth cast silver caps were made after releasing the surface of the inlay with tinfoil. Wear on the restorations was simulated by grinding away some gold from the inlay. Silicon impressions of the teeth were made with the caps both before and after this simulation. The volume and the average thickness of the removed gold was measured from the weight of the enclosed impression material in the cap before and after the wear simulations, the density of the tinfoil and the impression material as well as thickness and the weight of the tinfoil-release. Values expected for the volume and the average thickness of the removed gold were calculated from the weight of the restored acrylic teeth before and after the wear simulation, the weight, the density and the thickness of the tinfoil and the density of the gold used for the inlays. Measured and expected values are linearly correlated (r = 0.97). An average wear thickness of the occlusal surface of a particular tooth of at least 30 micron can be detected. Because of its simplicity, inexpensiveness and accuracy the wear measurement method is highly productive and suitable for large scale and long-term clinical research on the wear behaviour of posterior composites.

Acrylic Resins↗
PubMed1985

Methodological aspects in clinical evaluation of cast restorations with colour slides.

In a methodological investigation colour slides were used for the clinical evaluation of crowns. Four criteria, described in a criteria list or recorded by means of reference slides, were used. In assessing the clinical characteristics of crowns to a certain extent colour slides turned out to be a useful instrument. Shortcomings of the method are discussed and improvements are suggested.

Audiovisual Aids↗
PubMed1985

Cost benefit analysis of direct posterior restorations.

A clinical study was conducted in which three operators made 232 Class I and Class II composite and amalgam restorations in a group of 49 adult patients. The time for different parts of the operative process was measured. The time periods were analysed as to the influence of the factors operator, tooth type and number of surfaces, by an analysis of variance (ANOVA). Results show that the various factors have a significant influence on the total treatment time. The treatment time for amalgam restorations is equal to the treatment time of composite restorations. The productivity of making restorations from the 'best' available amalgams, i.e. the amalgam with an extrapolated half-life time of more than 20 yr, turns out to be more than 3-4 times better than that of the 'worst' amalgams (half-life time 4 1/2-8 yr) and more than two times better than that of making restorations of the best composite material, used in this study (extrapolated half-life time of Estic MF is 10 yr).

Adult↗
PubMed1984

The influence of polishing on the marginal integrity of amalgam restorations.

The influence of the polishing procedure on the marginal integrity of amalgam restorations was investigated in a clinical study. In this study two operators each made 150 class I or II restorations in a group of forty-eight adult patients. The restorations were made in a series of six per patient. Within each series, two restorations were made of three different high copper amalgam alloys. Only one restoration of each pair was polished. From each restoration a black and white photograph was taken after finishing and after 0.5, 1.0 and 1.5 years. The marginal integrity of each restoration at the four time periods was quantified with a 6-point photo rating scale. The quantifications were analysed as to their variance for the factors alloy, polishing procedure, operator and patient. After finishing, all four factors had a significant influence on the marginal integrity. From 0.5 to 1.5 years, the influence of the factors alloy, polishing procedure and patient were very significant. The influence of the patient on marginal integrity was more or less equal to that of the alloy. The size of the polish influence was relatively small. Therefore, it was concluded that the contribution of the polishing procedure to the prevention of marginal deterioration was questionable.

Adult↗
PubMed1984

Long-term influences on marginal fracture of amalgam restorations.

A clinical study was conducted in which two operators made 180 class I or II amalgam restorations in a group of fifty-seven adult patients. The restorations were made in a series of six per patient. Each restoration was made of a different alloy (five conventional composition alloys and one high copper alloy). During a period of 5 years the marginal fracture formation of all restorations was yearly quantified with a 6-point photo rating scale. The quantifications were analysed as to their variance for the factors alloy, patient and operator. The relative importance of significant factors was calculated. The results show that for a period of 5 years the alloy, patient and operator all had a significant influence on the marginal fracture formation. The operator influence was stable in time. This factor was relatively small because the operator sample was highly selected. After 1 year the influence of the patient on marginal fracture was equal to that of the alloy. The patient influence in time was stable. However, the alloy influence increased considerably. The longer the service time of the amalgam restoration the more important becomes the influence of the alloy on the marginal fracture formation.

Adult↗