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Biomedical subjects

A Wenzel

Publications and source records attributed to A Wenzel.

At least 163 records · Page 9Linked to original sources
PubMed1991

Sources of noise in digital subtraction radiography.

In 17 patients, three identical radiographic examinations were performed for the lower premolar-molar region, by two examiners at one visit and by one examiner again approximately 3 months later. Recordings were performed with a newly developed device. The radiographs were converted to digital images in the following way: (1) video camera recording of the radiograph obtained at first visit by the first examiner (A), (2) copying of the numeric image of this radiograph (B), (3) repeated video recording of this radiograph (C), (4) video recording of the radiograph obtained at first visit by the second examiner (D), and (5) video recording of the radiograph obtained after 3 months (E). Subtractions were performed between the images: B - A, C - A, D - A, and E - A. The standard deviation of the histogram for the distribution of gray shades in the subtraction images was used to evaluate noise in the image. The standard deviation was 1.3 between B - A, 2.8 between C - A, 4.0 between D - A, and 4.1 between E - A. Physical noise originating from the video camera and the analog-to-digital conversion process thus constituted the major part of noise seen in subtraction images performed between radiographs recorded with a time interval. This indicates that reproducible recordings could be performed with the present device, which, in combination with a subtraction program able to correct for some geometry and density differences, may aid the use of subtraction radiography in clinical trials.

Adolescent↗
PubMed1991

Radiographic detection of occlusal caries in noncavitated teeth. A comparison of conventional film radiographs, digitized film radiographs, and RadioVisioGraphy.

The aim of this study was to compare the accuracy of conventional film radiographs, digitized radiographs, and RadioVisioGraphy (RVG) for the detection of dentinal caries in occlusal surfaces of noncavitated extracted teeth. Eighty-one fully erupted extracted third molars were assessed by four observers using five radiographic methods: conventional film radiographs, digitized radiographs with contrast enhancement and with a filtering procedure, and RVG with contrast enhancement and with x function. Scoring criteria were dichotomous. Histologic sections (500 to 600 microns thick) served as the validation criterion. The two digital methods with contrast enhancement tended to perform more accurately than, although not significantly different from, the other three methods (p greater than 0.05). Average likelihood ratios (true positive/false positive) were 4.3 (conventional film radiographs), 4.4 (RVG with contrast enhancement), 3.6 (RVG with x function), 4.9 (digitized radiographs with contrast enhancement), and 3.7 (digitized radiographs with filtering procedure). Observers 1 and 2 (oral radiologists) performed better than observers 3 and 4 with all five methods (p less than 0.005).

Adolescent↗
PubMed1991

Predictive QSAR models for estimating ecotoxic hazard of plant-protecting agents: target and non-target toxicity.

Quantitative structure-activity relationships (QSARs) are evaluated for predicting pesticides' effects on non-target and target organisms: aquatic biota, mammals, soil micro-organisms, and plants. Satisfactory estimates of pesticides' fish toxicity are obtained from log POW-dependent QSARs derived using chemicals of similar polarity and reactivity. Algal toxicity of herbicidal compounds reflects interactions with the electron transport chain in photosystem II and can be modelled by QSARs describing the Hill reaction inhibition. The ranking in effects on soil micro-organisms is evaluated from models derived using in-vitro bacteria systems. Mammalian toxicity can be estimated by QSARs using the partition coefficient log POW and electronic terms derived by MNDO quantum mechanical calculations. In general, the targets are more susceptible than the non-target species towards phenylurea herbicides. Plants and algae constitute the most sensitive populations, corresponding to the same mode of action. Differences in mode of action towards bacteria, rats, and fish, which are similarly sensitive organisms, are revealed by QSAR analyses.

Animals↗
PubMed1991

Alterations of hyoid bone position and pharyngeal depth and their relationship after surgical correction of mandibular prognathism.

The present investigation studied changes of hyoid bone position and pharyngeal depth at the levels of the second and fourth cervical vertebrae and their relationships in mandibular prognathism patients who received combined orthodontic-surgical treatment. The material consisted of presurgical and 1-year postsurgical profile cephalograms of 52 adult orthognathic surgery patients (40 females and 12 males) who initially had mandibular prognathism and had undergone bilateral vertical ramus osteotomy through an extraoral incision in the retroangular area. Hyoid bone position and pharyngeal depth were assessed on the profile radiographs with 10 cephalometric variables. Paired t tests were used to evaluate the operative changes in all cephalometric parameters. The relationships between pairs of variables describing hyoid bone position and pharyngeal depth were assessed by means of Pearson's product-moment correlation analysis. Significant differences (p less than 0.01) were observed for the distances of the hyoid bone to the maxilla and the mandible. The distances of the hyoid bone with the anterior cranial base, the vertebral column, and the anterior pharyngeal wall, and the measurements representing pharyngeal depth exhibited no significant changes (p greater than 0.05). Moderate correlations were seen between (1) the depth of the pharynx at the fourth cervical vertebra and the hyosymphyseal distance (r = 0.34) and the distance between the point of the projection of the hyoid bone to the mandibular line with its posterior border (r = -0.34), and (2) the depth of the pharynx at the second cervical vertebra and the distance of the hyoid bone with the anterior pharyngeal wall at the level of the fourth cervical vertebra (r = -0.33).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Approximal caries diagnosis using fiber-optic transillumination: a mathematical adjustment to improve validity.

Several studies were conducted recently to evaluate the use of Fiber-Optic Trans-Illumination (FOTI) in the diagnosis of approximal carious lesions. All these studies utilized radiographic readings to validate the FOTI diagnoses. Other investigations studied the value of radiographic readings using more solid validating techniques, which made it possible to judge the true state of decay, such as histology, cavity preparation and microradiography. In this study, data from both types of studies were used to estimate the validity of FOTI diagnosis of approximal caries relative to the true status of decay through correction for radiographic misclassification. The results indicate that particularly the sensitivity of FOTI diagnosis has yet to be determined.

Dental Caries↗
PubMed1991

Performance for obtaining maximal gain from a program for digital subtraction radiography.

The aim of this study was to evaluate the effect on subtraction image quality of number of a) gray shades sampled during camera recording, and b) reference points positioned in the two images to be subtracted. Intraoral radiographs were obtained in each of 12 patients, one at 0 degrees and one at 15 degrees horizontal angulation in a standardized recording procedure. The radiographs were videorecorded twice sampling 1) 160-180 and 2) 200-220 shades of gray. The 0 degrees radiographic image was digitally copied. Subtractions were performed between the identical (0 degrees/0 degrees) and the non-identical (0 degrees/15 degrees) radiographs from both gray shade samples after positioning 5, 10, 15, and 20 reference points, respectively, in each of the images to be subtracted. The standard deviation in the subtraction image histogram was used as the test parameter for image quality. No differences existed between image quality obtained from the radiographs sampled using 160-180 and 200-220 shades of gray (P greater than 0.05). The standard deviation fell continuously, the more reference points were positioned in the images. For the 0 degrees/0 degrees images the difference was statistically significant between the 5 and 10 point images (P = 0.045) while for the 0 degrees/15 degrees images differences existed between 5 and 10 point images (P = 0.077) and the 10 and 15 point images (P = 0.048). The precision of reference point positioning as evaluated in the two identical images was satisfactory, the divergence being on average 1.4 pixels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Detection of occlusal caries without cavitation by visual inspection, film radiographs, xeroradiographs, and digitized radiographs.

The study compared visual inspection, conventional film radiographs, xeroradiographs, and digitized radiographs for the detection of caries in occlusal surfaces without cavitation. 166 extracted premolars and permanent molars without macroscopic cavitation were included. Eight observers assessed five grades of occlusal caries by visual inspection and by the three imaging techniques. Histologic sections (700-1,000 microns) served as validating criterion for the presence and depth of carious lesions, 82 teeth being found carious (27 with deep dentinal involvement) and 84 being scored as sound. Approximately 20% of the dentinal carious lesions were detected by visual inspection and 40% by conventional film radiography (both with a minimal number of false-positive observations). By xero- and digital radiography, an increasing number of false-positive scorings was seen. By digital radiography the true-positive detection rate was similarly increased to 60%. The predictive values of a positive test were, on average, 0.85 for visual inspection, 0.89 for film, 0.78 for xero-, and 0.82 for digital radiography and for a negative test 0.56, 0.61, 0.61, and 0.69, respectively. However, digital radiography was able to detect over 70% of deep dentinal lesions in contrast to 45% by the other two imaging methods, without an increase in false-positive diagnoses of truly caries free teeth, compared with the other techniques.

Bicuspid↗
PubMed1991

The MYCN protein of human neuroblastoma cells is phosphorylated by casein kinase II in the central region and at serine 367.

The MYCN gene has been implicated in certain neuronal tumours, such as neuroblastomas and retinoblastomas. These tumours express high levels of mRNA and protein of MYCN as a result of amplification. MYCN encodes a short-lived nuclear phosphoprotein whose function has not yet been elucidated. This study was undertaken to determine the pattern of MYCN protein (pMYCN) phosphorylation in human neuroblastoma cells. We report that pMYCN is phosphorylated in vitro by purified casein kinase II (CK-II). Two-dimensional phosphopeptide maps showed that most of the phosphopeptides of pMYCN phosphorylated in vitro by CK-II correspond to those phosphorylated in vivo. Fine mapping of the phosphorylation sites was performed using two synthetic MYCN peptides corresponding to pMYCN CK-II consensus sequences. Both peptides were found to be phosphorylated by CK-II and competitively inhibited CK-II phosphorylation of pMYCN in vitro. Thus, we have localized two major CK-II phosphorylation sites in pMYCN, one to the highly acidic central region and the second to serine 367 proximal to the C-terminus. Our data demonstrate that pMYCN is a physiological substrate for CK-II and, since CK-II activity is stimulated in response to mitogens, CK-II phosphorylation of pMYCN may, therefore, represent one signal transduction pathway used by neuroblastoma cells.

Amino Acid Sequence↗
PubMed1990

Augmented MYCN expression advances the malignant phenotype of human neuroblastoma cells: evidence for induction of autocrine growth factor activity.

Amplification and enhanced expression of the MYCN oncogene are thought to contribute to the development and progression of human neuroblastomas. Here, we have transfected human neuroblastoma cells that harbor a single MYCN gene copy with the human MYCN gene driven by a viral enhancer/promoter, and we have compared the properties of the parental and the transfected cells. The transfected cells show an enhanced expression of the exogenous MYCN gene. Unlike the parental cells, they have acquired an increased proliferative potential, induce tumors in nude mice, grow in soft agar, and require low amounts of exogenous growth factors in order to proliferate. The MYCN-transfected, but not the parental, cells can synthesize and utilize autocrine growth factor activity. These results demonstrate that enhanced MYCN expression contributes to malignant progression of human neuroblastoma cells, conceivably by stimulating the expression of autocrine growth factor activity.

Animals↗
PubMed1990

Diagnostic value of clinical examination for the identification of children in need of orthodontic treatment compared with clinical examination and screening pantomography.

Ninety children in the 5th school grade (means age = 11.9 years) participated in this investigation. As part of the orthodontic screening examination, pantomograms of all children had been performed as a routine procedure. Prior to assessment of the pantomograms each child was assigned to one of the following treatment categories based on clinical examination: -T (no indication for orthodontic treatment), O (observation of dentition development) and +T (indication for orthodontic treatment). Children, in whom clinical symptoms gave rise to a radiographic examination, were selected and their pantomograms assessed. Finally, the pantomograms of all children were interpreted, and the clinically established treatment categories re-evaluated on basis of the findings on the pantomograms. Fifteen children were selected for pantomography, but only one changed treatment category (from O to +T) due to observation of developmentally missing premolars. Three of the children not selected for pantomography changed categories from -T; two to O and one to +T. Clinical examination with selective pantomography was thus able to correctly identify 97 per cent of children in need of immediate orthodontic treatment, while it was able to correctly exclude 94 per cent of the healthy children. On the basis of these results, routine screening pantomography may be omitted.

Anodontia↗
PubMed1990

Longitudinal study of accuracy of clinical examination for detection of permanent tooth aplasia.

It was the aim of the present investigation to evaluate the accuracy of clinical examination for the detection of permanent tooth aplasia in the 3rd/4th grade and again 1 yr later and to record the number of children initiating orthodontic treatment in the interval between the two examinations. The validating criterion for tooth aplasia was a panoramic radiograph taken in a routine procedure. 628 children participated in the study. The clinical examinations were performed without knowledge of the radiographic evidence. During the examination children exhibiting symptoms of permanent tooth aplasia were selected for radiography. At both occasions clinical examination was very sensitive for the detection of children with aplasia of permanent incisors (nosological sensitivity = 1.00). It was, however, less sensitive for the detection of children with premolar aplasia (nosological sensitivity = 0.22 at both examinations). The nosological specificity for identification of children without aplasia of incisors and premolars was more than 0.90 at both examinations. Twenty-two children had started orthodontic treatment in the timespan between the two clinical examinations, but only three on the basis of observations on their radiographs alone (aplasia of permanent teeth). The present clinical method would have selected two of these children, thus in only one child postponing panorama screening might have affected treatment prognosis. Between the two examinations all permanent teeth mesial to the permanent second molars had erupted in 181 children who might therefore totally avoid screening radiography.

Adolescent↗
PubMed1990

Oral radiographic screening in Danish children.

The aim of the present study was to ascertain frequency and type of radiographic screening in the Danish Dental Service for children. A 5-item questionnaire was sent to each department of public dentistry in the 275 communities of Denmark. A total of 269 questionnaires were returned, four unanswered. Radiographic screening examinations were done on 162 respondents. Of these, 25% had bitewing screening and 25% panoramic screening. Two types of routine radiographic examinations were performed on more than one third of the respondents. The most frequent combination for screening radiography was bitewing and panorama. Even though the risks included in the use of ionizing radiation for dental screening purposes may be considered negligible, it is still ethically correct to avoid unnecessary exposure by a careful selection of patients prior to radiography. As economic support for dental health care had been cut, the radiographic screening procedure must prove itself to be cost/effective to be kept unchanged.

Child↗
PubMed1990

Depth of occlusal caries assessed clinically, by conventional film radiographs, and by digitized, processed radiographs.

Occlusal caries depth was assessed in 47 extracted premolars and permanent molars by 4 observers on a rank scale by eye inspection, by film radiographs, and by 2 of the observers also by digitized radiographs after filtering and contrast enhancement of the image. Quantitative estimates of caries depth were obtained from the digitized radiographs. Accuracy of scorings was determined with the histologic section as validating criterion. Occlusal caries was present in a spectrum from incipient fissure decalcification to large cavity formation. Clinical as well as radiographic scorings most frequently under-estimated lesion depth. Accuracy of radiographic assessments increased substantially by digital processing of the radiographic image. Quantitative measures of caries depth on digitized radiographs were strongly correlated to the histologic measures (r = 0.91). Interobserver agreement was fair to moderate according to kappa coefficients for the clinical and the radiographic scorings. The agreement was highest for the scorings of the digitally enhanced images. The study suggests that digital processing of radiographic images constitutes a diagnostic aid that may give a more accurate estimate of occlusal caries depth.

Analog-Digital Conversion↗
PubMed1989

Antigenic differences between metastatic and nonmetastatic BSp73 rat tumor variants characterized by monoclonal antibodies.

Variants AS and ASML of the BSp73 rat tumor differ markedly with respect to morphology and to the capacity for spontaneous metastasis via the lymphatics. Monoclonal antibodies (MAbs) were raised in order to identify surface molecules associated with both phenotypes. Mice were immunized with either whole cells or isolated membranes and hybridoma supernatants were screened according to the criteria of selective binding to cultured cells of the variant used for immunization. Of two MAbs reacting with the nonmetastasizing AS variant, one showed immunostaining of AS tissue. From 11 MAbs binding to the metastatic ASML variant, 6 showed specific staining of ASML tissue, while the remaining 5 MAbs showed cross-reaction with normal rat tissues. According to Western blot data, the 6 MAbs selectively binding to ASML tissue identified at least 2 different antigens, one of them showing up as a complex of 12 bands.

Animals↗