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Biomedical subjects

A Wenzel

Publications and source records attributed to A Wenzel.

At least 145 records · Page 8Linked to original sources
PubMed1994

A quantitative analysis of subtraction images based on bite-wing radiographs for simulated victim identification in forensic dentistry.

The comparison between ante- and post-mortem radiographs constitutes an important basis for victim identification in forensic dentistry. Due to the decline in dental caries among children that has occurred in Western countries over the last 20 years, the number of restorations in future populations will be limited. It is likely that this will impede successful victim identification in the future. It was the aim of this study to evaluate a new radiographic technique, subtraction radiography based on bitewing radiographs and determine whether it could provide an objective quantitative measure for victim identification. Bite-wings randomly sampled from a large population of adolescents (13-19 yrs) were video-camera-recorded and digitized. Subtraction images were performed of pairs of bite-wings originating from the same individual (identical images) and from different individuals (non-identical images). The images were separated into two groups, one without fillings (12 identical and 48 non-identical) and one with simple amalgam fillings (15 identical and 60 non-identical). The distribution of grey shades in the subtraction image was used as the parameter for evaluation of homogeneity in the images. Subtraction images derived from identical radiographs were significantly more homogeneous than those derived from non-identical radiographs (p < 0.001) in both group with and without fillings. Although the difference was statistically highly significant, the distribution of grey shades in the two groups overlapped. Thus, the grey shades in the subtraction image cannot per se unequivocally establish the identity of a victim, but may add to the subjective comparison of two radiographs in victim identification.

Adolescent↗
PubMed1993

Performance of electrical resistance measurements adjunct to visual inspection in the early diagnosis of occlusal caries.

The detection of small carious lesions at occlusal surfaces is a difficult task, particularly in low caries prevalence populations and individuals. The aim of this study was to evaluate the performance of electrical resistance measurements (ERM) in diagnosing small dentinal lesions at one site per occlusal surface in low caries prevalence populations when used adjunct to visual inspection, and to compare the performance of ERM to that of radiographic examination. The occlusal surfaces of 81 third permanent molar teeth extracted from young adolescents were diagnosed by four examiners, who measured the electrical resistance of enamel on a one measurement per surface basis, and furthermore assessed the occlusal surfaces visually and radiographically. The teeth were sectioned for validation by histological examination. The ERM had the highest sensitivity (0.67), and visual inspection had the highest specificity (0.89). ROC analysis showed no statistically significant differences between the performance of the observers when using visual inspection and ERM (z-score test; P > 0.05). One examiner performed statistically significantly better by measuring the electrical resistance of enamel than by radiographic examination (P < 0.05). The average sensitivity and specificity of the three diagnostic systems were used to express the positive and negative predictive values as a function of caries prevalence. At a caries prevalence of 0.2 the negative predictive values for visual inspection, ERM and radiographic examination were 0.88, 0.91 and 0.89, and the positive predictive values were 0.53, 0.48 and 0.42 respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Developments in radiographic caries diagnosis.

The developments that have been taking place in radiographic caries diagnosis, within the context of the changes occurring in both the disease process and the available technology, are reviewed. The decline in caries prevalence seen in many western countries has been accompanied by changes in the pattern and behaviour of lesions. More lesions are now seen on occlusal surfaces, more are concealed (and thus imperceptible to conventional diagnostic techniques), while the average progression rates for approximal lesions have also slowed. Systems employed for caries diagnosis must take account of these changes and the varying needs of users employing different diagnostic thresholds. This paper reviews and discusses developments in: conventional film radiography; xeroradiography; indirect digital imaging (with computer image analysis and subtraction radiography), and direct digital imaging. It is concluded that: for the detection in high caries prevalence groups of both approximal caries (especially small lesions in enamel) and dentinal occlusal lesions in teeth with little or no surface breakdown, radiography is still a significant and reasonably accurate diagnostic method; and that, in spite of the more limited resolution, digital imaging methods seem to perform as well or better than conventional film radiography. Digital systems possess a number of advantages, primarily the possibility for image enhancement and significant dose reduction. It may be predicted that digital imaging techniques will enter the clinical routine in the near future.

Dental Caries↗
PubMed1993

Reliability of landmark recording on film and digital lateral cephalograms.

The aims of this study were: (a) to evaluate reliability of landmark location in digital processed images of film cephalograms of varying quality with that obtained in the films, and (b) to evaluate the pattern of error in landmark location with the two techniques. The sample consisted of 20 original cephalograms (OQ), 10 'high' quality images (Q1), and 10 'average' quality images (Q2). Measurements on films were performed using a digitizer connected to a PC and controlled by a cephalometric program, while measurements on digital images were obtained using a mouse and a cephalometric program for landmark sampling. To assess the digital images (DQ), the films were video recorded (B/W video camera), digitized (matrix = 512 x 512 x 8), stored in a PC, and displayed on a quality monitor. Fifteen cephalometric landmarks were recorded by three observers twice on each of the 20 images by the two methods. Mean x- and y-values were calculated for each landmark to obtain the best estimate of each landmark position. Comparisons between the OQ and DQ group, and between the subgroups of different film quality were performed (Wilcoxon's rank sum test). In general, measurements from the OQ images were more reliable than from the DQ images (P < 0.02). The pattern of recording error also differed between the two techniques, OQ images being more reliable along the x-axis (P < 0.01), while along the y-axis, reliability was not significantly different between the two groups. Q1 and Q2 images did not differ significantly in either group (P > 0.05). A difference was, however, observed between OQ2 and DQ2 images (P < 0.02), while this was not the case for OQ1 and DQ1 images. The generally lower reliability for measurements on the digital images could be ascribed to the much larger error, especially in the y-axis, for the Q2 images.

Cephalometry↗
PubMed1993

Assessment of diagnostic accuracy in caries detection: an analysis of two methods.

The quality of a diagnostic tool for caries detection is usually evaluated by quantification of observer performance using sensitivity and specificity values calculated from data obtained from ordinal caries depth rating scales. The application of Receiver Operating Characteristic (ROC) analysis has been restricted to the use of confidence rating scales. The aim of this investigation was to study the appropriateness of ROC analysis using caries depth ratings by comparing sensitivity and specificity values to parameters of diagnostic performance obtained by ROC analysis. In two recent reports, sensitivity and specificity values were utilized to express diagnostic accuracy of observer performance from specified caries diagnostic systems. The raw data from these investigations were subjected to ROC analysis in the current study. The results illustrated that ROC analysis, producing estimates of sensitivities for all specificities, yielded more comprehensive measures of diagnostic performance than single values for sensitivity and specificity. In particular, the area under the ROC curve constituted a clearly interpretable parameter representing the quality of diagnostic performance.

Analysis of Variance↗
PubMed1993

Applicability of Receiver Operating Characteristic (ROC) analysis on discrete caries depth ratings.

Accuracy of diagnostic tests for caries detection is frequently evaluated by sensitivity and specificity values obtained from data acquired on an ordinal rating scale which classifies lesions according to the depth in enamel and dentin. The interpretation of these parameters may, however, be difficult. Receiver Operating Characteristic (ROC) analysis, on the other hand, yields an expression for overall diagnostic accuracy in a single parameter, facilitating a comparison of performance of several diagnostic tests. The basis for applying ROC analysis has been that data were collected on a confidence (likelihood) scale. The aim of this preliminary study was to investigate whether the application of ROC analysis would yield as valid parameters for diagnostic accuracy in assessment of approximal caries on a depth rating scale as on a likelihood rating scale. The results demonstrated that the accuracy of observer performance was not influenced by the type of rating scale employed, justifying the application of ROC analysis on discrete caries depth ratings.

Chi-Square Distribution↗
PubMed1993

Perception of image quality in direct digital radiography after application of various image treatment filters for detectability of dental disease.

This study evaluated dentists' perception of the quality of digitally captured radiographs. Thirty radiographs were taken with the Visualix digital video radiographic system, 10 periapicals for tooth and bone anatomy, 10 periapicals for bone disease and 10 bitewings for dental caries. Three numeric copies were made of each image and treated with three different filters: 'optimize', 'enhance' and 'enhance + smooth', respectively. Four images of the same case were displayed simultaneously in a random sequence on the monitor. Twenty dentists ranked each set of four images on a scale from 1 to 4. In general, most dentists preferred a treated image to the original. The optimized and enhanced images were selected most frequently as first or second choice from the tooth and bone anatomy and bone disease groups. The original image was ranked lowest in more than half (55%) of the series. For the bitewings, the smoothed images were ranked significantly higher. In conclusion, image treatment possibilities should be offered in digital radiography as the majority of dentists preferred a treated image to the original version. The image treatment chosen seemed to be task dependent; less treatment was required to delineate the more subtle tissue differences.

Dental Caries↗
PubMed1993

Computer-aided image manipulation of intraoral radiographs to enhance diagnosis in dental practice: a review.

In conventional film radiography, image quality is determined once the film has left the processing solutions. Conversely, in digital imaging, image quality may be interactively manipulated after image acquisition. Each of the parameters which define image quality: contrast, blur and noise, may be altered digitally. Filtering of the digital image may result in a reduction of blur of structure boundaries. Studies have shown that digital contrast enhancement and filtering increased diagnostic accuracy for the detection of caries lesions and for the estimation of lesion depth. Digital subtraction reduces anatomic image noise and has been demonstrated to aid the detection of differences in two images taken with a time interval. The technique has been demonstrated as being particularly useful for the detection of small tissue changes in marginal alveolar bone. The era of digital imaging in dentistry has certainly commenced and current intraoral digital systems have been shown to provide definite diagnostic advantages. Further, the direct digital systems rationalise the radiographic routine due to avoiding film and wet processing and conserve the environment. The major advantages may, however, be the significant dose reductions and the ability for image quality manipulation.

Humans↗
PubMed1993

Activation of gene transcription by the amino terminus of the N-Myc protein does not require association with the protein encoded by the retinoblastoma suppressor gene RB1.

N-Myc encodes a nuclear phosphoprotein that contains a basic region (BR), a helix-loop-helix (HLH) and a leucine zipper (Zip). These motifs are hallmarks of certain transcription factors. In pursuit of the question if N-Myc can activate transcription, we have employed an experimental model involving the yeast transcription factor Gal4. We have first generated fusion proteins containing the Gal4 DNA-binding domain joined to portions of N-Myc. Subsequently we have analysed if chimeric proteins can transactivate the transcription of a reporter under the control of Gal4 binding sites. Here we show that the amino terminal portion of N-Myc activates transcription. Activation maps to a domain highly conserved among Myc-proteins and to other non-conserved sequences, suggesting functional redundancy. Previous studies had documented in vitro association of the RB1 protein with N-Myc (Rustig et al., 1991). We here confirm this observation and identify the region encompassing the transactivation domain as responsible for RB1 binding. Analyses of N-Myc transactivation in retinoblastoma cell line WERI lacking a function RB1 protein gave results similar to those with cell lines having an intact RB1 protein, showing that RB1 protein is not required for transactivation by N-Myc. The present findings leave open the question if deregulated expression of N-Myc contributes to tumorigenesis by transcriptional activation of as yet unidentified target genes or by functionally inactivating the protein encoded by the tumor suppressor gene RB1, or by a combination of both.

DNA-Binding Proteins↗
PubMed1992

Digital subtraction radiography after stannous fluoride treatment for occlusal caries diagnosis.

The material in this study consisted of 38 fully erupted, extracted third molars without clinical cavitation in the occlusal surface. A radiograph was made of each tooth before and after 5, 10, and 20 minutes of stannous fluoride treatment. The radiographs were digitized and subtraction performed between the images obtained after stannous fluoride treatment and the pretreatment image. Two observers assessed the stannous fluoride treated radiographic and the subtraction images on a monitor: 0 = no change, 1 = intensity increase (white area interpreted as a carious lesion) in dentinoenamel area. Caries was assessed on conventional film radiographs made before treatment: 0 = no caries in dentin, 1 = caries in dentin. The presence of caries in dentin was validated histologically. Sensitivity for intensity increase as a sign of caries was overall higher for the subtraction images based on 20-minute treatment than for the radiographic images (0.025 > p > 0.01) but not significantly higher than for the conventional radiographs. However, neither observer gave false-positive scorings in the subtraction images, whereas observer 1 had five false-positive scorings on the conventional films. Observer 2 had none. The subtraction method did not provide a higher sensitivity for dentinal occlusal caries than conventional film radiography, but the intensity increase could be trusted more than the traditional radiolucency as a sign of a dentinal lesion.

Adolescent↗
PubMed1992

Digital subtraction radiography in assessing bone changes in periodontal defects following guided tissue regeneration.

19 patients with a total of 23 periodontal lesions were selected for the study. Following flap-elevation, an occlusive membrane (Gore Tex) adjusted to the size and shape of the lesion was applied. The membrane was removed 4-6 weeks later by a 2nd operation. Clinical attachment levels were measured and intraoral radiographs taken prior to surgery, and 6 and 12 months postoperatively. The root length and marginal bone level were measured on paper drawings of the teeth magnified (15x) from the conventional radiographs. The radiographs were digitized for analysis of the subtraction images between the preoperative and the 6- and 12-month postoperative images. Clinical attachment gain was seen in 78% of the teeth after 6 months and 70% after 12 months. Bone gain was recorded in 56% and 22% after 6 months and in 44% and 66% after 12 months by conventional and digital subtraction radiography, respectively. The bone level measurements on conventional radiographs differed significantly (p = 0.001) between the preoperative and 6-month postoperative, but not between the 6- and 12-month, (p = 0.29) conventional radiographs. There was no significant relationship between the clinical measurements and the assessments of bone changes on conventional radiographs (r = 0.28, p = 0.25), while a stronger relationship was observed between assessment of clinical attachment gain and assessment of bone changes on the subtraction images (r = 0.58, p = 0.01).

Alveolar Bone Loss↗
PubMed1992

Digital subtraction radiography for assessment of simulated root resorption cavities. Performance of conventional and reverse contrast modes.

A previous study of the sensitivity and accuracy of a standardized radiographic technique for the disclosure of root cavities in a cadaver material indicated that it was not possible to perceive small artificial "resorption" cavities. Using the same material, the aim of the present study was to evaluate whether the use of subtraction radiography would improve the detection of root cavities. In an autopsy material of five mandibular blocks each containing two premolars, small, medium, and large cavities were drilled in the cervical, middle, and apical thirds of the proximal and oral root surfaces. Each jaw block was radiographed before (B) and after (A) cavity preparation with three different exposure times resulting in light, medium, and dark film densities. The radiographs were digitized. Digital subtraction was performed between the A- and B images of varying densities by a computer program developed for dental subtraction radiography. Conventional and reverse contrast modes of the subtraction image were assessed independently by four observers. The results showed small inter- and intraobserver differences in diagnostic accuracy for assessment of total number of root cavities. Original film density did not influence the diagnostic performance in the resulting subtraction image. Contrast mode in the subtraction image influenced diagnostic performance as the majority of observers did best with the reverse contrast mode (p < 0.05). Some of the small root cavities were disclosed by the subtraction technique, but overall accuracy was not increased compared to conventional radiography.

Humans↗
PubMed1992

Validity of diagnosis of questionable caries lesions in occlusal surfaces of extracted third molars.

This study was to evaluate the accuracy of visual inspection, conventional radiography, and digital radiographic methods for the detection of occlusal carious lesions in third molars from a present-day adolescent population. Seventy-eight third molars, considered clinically to be without occlusal cavities, were extracted from young soldiers. Before extraction, an intra-oral radiograph was obtained. After extraction, the teeth were examined visually as per the criteria: 0 = no caries, 1 = chalky/stained fissure indicative of enamel caries, 2 = chalky and dark-stained fissure considered indicative of a dentinal lesion, and 3 = as per criterion 2, but with small surface defects (microcavities). The radiographs were digitised, and image enhancement with contrast stretch and a filtering procedure was performed, respectively. The three types of radiographic image were assessed as per the criteria: 1 = no caries/caries confined to enamel, 2 = caries involving the outermost dentine, and 3 = deep dentinal caries extending half-way or more to the pulp. Ground sections (500-600 microns in thickness) served as validation for lesion depth. The digital radiographic method with contrast stretch performed overall best of the four methods (greater than 70% detection rate) while visual inspection (53% detection rate) performed better than conventional radiography (48% detection rate). When results from visual inspection and conventional radiography were combined, an increase in the detection rate of 11% was obtained with a 7% increase in false-positive scorings. When digitally contrast-manipulated radiographs were combined with visual inspection, a gain of 33% was obtained with an 11% increase in false positives.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Accuracy of visual inspection, fiber-optic transillumination, and various radiographic image modalities for the detection of occlusal caries in extracted non-cavitated teeth.

Occlusal caries lesions may progress into the dentin without this resulting in a macroscopic breakdown of the enamel surface. Imaging methods may therefore be needed to aid in the visual detection of occlusal caries. It was the aim of this study to evaluate diagnostic accuracy in a laboratory set-up of visual inspection (VI), fiber-optic-transillumination (FOTI), conventional radiography (CR), and two digital radiographic image modalities (DRm and DRr) for detection of occlusal caries in clinically non-cavitated teeth. Eighty-one extracted third molars from 18-20-year-old males were assessed by four observers on a five-rank confidence scale by the five methods. Ground sections (500-600 microns) served as validation for true state of disease: 1 = no caries in dentin, 2 = caries just beyond dentino-enamel junction, or 3 = deep dentinal caries, halfway or more to the pulp. ROC analysis was performed on the basis of the confidence rank scale data on two diagnostic thresholds, T1 = caries in dentin (disease state 2+3) and T2 = caries deep in dentin (state 3). On the T1 level, use of the FOTI method gave on average the most accurate diagnosis, closely followed by VI, both performing better than use of radiography. On the T2 level, all five diagnostic methods performed equally well.

Adolescent↗
PubMed1991

A new variant of glycoprotein CD44 confers metastatic potential to rat carcinoma cells.

Using a monoclonal antibody (MAb1.1ASML) raised against a surface glycoprotein of the metastasizing rat pancreatic carcinoma cell line BSp73ASML, cDNA clones have been isolated that encode glycoproteins with partial homology to CD44, a presumed adhesion molecule. In one of the clones, pMeta-1, the epitope marks an additional extracellular domain of 162 amino acids inserted into the rat CD44 protein between amino acid positions 223 and 247 (by analogy to human and murine CD44). The new variants are expressed only in the metastasizing cell lines of two rat tumors, the pancreatic carcinoma BSp73 and the mammary adenocarcinoma 13762NF; they are not expressed in the non-metastasizing tumor cell lines nor in most normal rat tissues. Overexpression of pMeta-1 in the nonmetastasizing BSp73AS cells suffices to establish full metastatic behavior.

Amino Acid Sequence↗
PubMed1991

The N-Myc oncoprotein is associated in vivo with the phosphoprotein Max(p20/22) in human neuroblastoma cells.

Proteins encoded by the proto-oncogenes c-myc, L-myc, and N-myc contain at their carboxy-terminus a tripartite segment comprising a basic DNA binding region (BR), a helix-loop-helix (HLH) and a leucine zipper motif (Zip), that are believed to be involved in DNA binding and protein-protein interaction. The N-Myc oncoprotein is overexpressed in certain human tumors that share neuroectodermal features due to amplification of the N-myc gene. Using a monoclonal antibody directed against an N-terminal epitope of the N-Myc protein in immunoprecipitations performed with extracts of neuroblastoma cells, two nuclear phosphoprotein, p20/22, forming a hetero-oligomeric complex with N-Myc are identified. Both proteins are phosphorylated by casein kinase II in vitro. By partial proteolytic maps we show that p20 and p22 are structurally related to each other and that p20 is identical with Max, a recently described in vitro binding partner of myc proteins. Time course experiments show the presence of the complex in cellular extracts immunoprecipitated within a 5 min interval after the preparation of the cell extract. While the expression of N-myc is restricted, expression of both Max(p20/22) and the murine homolog Myn(p20/22) was observed in cells of diverse human and murine embryonal lineages as detected by heterologous complex formation. By introduction of expression vectors containing the wild type N-myc gene or N-myc genes with in frame deletions or point mutations into recipient cells and subsequent immunoprecipitation of the resulting N-Myc proteins we show that the HLH-Zip region is essential to the formation of the N-Myc-p20/22 complex.

Animals↗