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Biomedical subjects

K Horner

Publications and source records attributed to K Horner.

At least 55 records · Page 3Linked to original sources
PubMed1996

The imaging performance of a storage phosphor system for dental radiography.

Direct digital imaging systems are becoming increasingly common in dental radiography. The majority of these systems are based on charge coupled device (CCD) technology. A relatively new system, based on photo-stimulable phosphor luminescence (PSPL), is now commercially available. This system appears to overcome some of the restrictions of CCD systems including those associated with the bulky detector, connecting wire, limited image size and limited exposure latitude. A physical evaluation of the PSPL system was conducted including measurements of sensitometric response, modulation transfer function (MTF), noise power spectrum (NPS), noise equivalent quanta (NEQ) and detective quantum efficiency (DQE). These measurements were compared with results obtained previously for Kodak Ektaspeed (E-speed) film. The results of the evaluation indicate that the PSPL system may be capable of operating at exposures up to 80% lower than for film with comparable image quality.

Humans↗
PubMed1996

Mandibular bone mineral density as a predictor of skeletal osteoporosis.

A considerable amount of work has been performed on methods of detecting individuals with low bone mass at an early stage. Some researchers have considered if dental radiographs could have a role in the detection of individuals with osteoporosis. A basic requirement for this would be that bone mass in the jaw relates significantly to that of other skeletal sites in which osteoporosis is a significant problem. The first aim of this study was to investigate the relationship between mandibular bone mineral density (BMD) and that of other skeletal sites commonly used for bone densitometry in the detection of osteoporosis. The second aim was to assess the validity of mandibular BMD as a predictor of BMD in these other sites. 40 edentulous females underwent dual energy X-ray absorptiometry (DXA) of the lumbar spine (L2-L4), DXA of the right femoral neck, single photon absorptiometry (SPA) of the proximal and distal forearm and DXA of the mandible. Significant correlations were observed between BMD in the mandibular body, ramus and symphysis and all other skeletal sites (p < 0.02). Five patients (12.5%) had age matched Z-scores of -1.0 or lower in all three non-mandibular sites (lumbar spine, femoral neck and forearm). Using these patients as the proportion of the population with a positive finding of "low bone mass", the sensitivity and specificity of mandibular BMD in predicting low bone mass for these patients was determined. Where a diagnostic threshold for low mandibular BMD was set at one standard deviation below the mean, the mandibular body BMD measurement gave high sensitivity (0.8) and specificity (0.97), the symphysis BMD low sensitivity (0.4) but a high specificity (0.77), while the ramus BMD had a moderate level of sensitivity (0.6) and high specificity (0.91). It is concluded that mandibular BMD assessed by DXA correlates significantly with BMD measurements of other important skeletal sites. The higher correlation coefficients and the greater sensitivity and specificity for the body of mandible suggest that this site should be used for any potential clinical application of dental radiographs in detection of osteoporosis.

Absorptiometry, Photon↗
PubMed1995

The impact of quality control on radiography in general dental practice.

The aim of this study was to assess the impact of two quality control measures upon the quality of periapical radiographs in general dental practices. Five general dental practitioners took part in the study. Periapical radiographic quality was assessed before and after the introduction of film holders and quality control measures for processing. Prior to the introduction of the quality control measures, 49% of radiographs were assessed as being 'unacceptable', 49% exhibited faults but were 'acceptable' for diagnostic purposes, while only 2% of radiographs were 'excellent' being entirely free of faults. After the introduction of film holders and processing quality control procedures 39% were 'unacceptable' (P < 0.05), 56% were 'acceptable' and 5% of radiographs were classified as 'excellent'. It is concluded that current recommendations to dentists to use film holders and to carry out processing quality control are justified in terms of an improvement in the diagnostic quality of radiographs. However, improvements in undergraduate and continuing education for all members of the dental team, with emphasis on practical 'hands-on' instruction, may improve the effectiveness of these recommendations.

Chi-Square Distribution↗
PubMed1995

Some factors affecting the standards of radiography in general dental practice.

This study had three aims. The first was to examine the influence of legislative and educational factors on facilities and equipment in dental practices, the second to find out if these and practice size affected standards and the third to assess the degree to which technique and other faults not connected with processing accounted for inadequate diagnostic quality in intra-oral radiography. Dentists from 62 practices returned questionnaires about the sizes of their practices, facilities and equipment for radiography and relevant updating, training and education of their staff. The quality of 305 radiographs taken in a sample of 11 practices was assessed. Ten examples of good radiographic practice were used to evaluate standards in the general practices. The 'good practice score' ranged from 2 (two practices) to 10 (one practice) with a mean of 6.2. Practices whose principals had engaged in the recommended educational activities scored more highly than those that had not (P < 0.05), and the mean scores in practices of two or more dentists were higher than in single-handed (P < 0.05). Of the 305 radiographs, the dentists, without the use of criteria to assess them, rejected 13.8%; with criteria they rejected 39.3% (P < 0.05). The researcher rejected 63.9% (P < 0.05). All films were processed under controlled conditions and it is likely that reject rates would have been higher under normal processing conditions. It is concluded that the use of criteria to assess radiographs and acceptance of postgraduate opportunities, particularly by single-handed practitioners, would improve the conduct of radiography. Further improvements might be gained by orienting updating courses and materials towards behavioural change.

Education, Dental, Continuing↗
PubMed1995

A laboratory evaluation of Ektaspeed Plus dental X-ray film.

OBJECTIVES: The aim of this study was to make a laboratory evaluation of the image quality of a new dental X-ray film, Ektaspeed Plus, compared with Ektaspeed and Ultraspeed films. METHODS: Films of each emulsion type underwent a range of exposures at both 50 kVp and 70 kVp, and characteristic curves were constructed to give a comparison of fog, speed and contrast. Line pair and contrast detail test objects were used to assess the resolution of radiographs and the ability of the two film types to reproduce minor differences in subject contrast. The sensitivity of the emulsions to safelighting for a range of times was also tested. RESULTS: Ektaspeed Plus had the same speed, a slightly higher base plus fog density but a higher contrast (50 and 70 kVp) than Ektaspeed. The speed of Ektaspeed Plus was higher and the contrast similar to that of Ultraspeed film. Limiting resolutions of the three films were the same. There was a slightly better imaging of one contrast detail phantom with Ektaspeed Plus compared to Ektaspeed at 70 kVp only. All three emulsions were insensitive to recommended safelighting conditions. CONCLUSION: The improved image contrast of Ektaspeed Plus may be more acceptable to dentists than Ektaspeed and lead to a greater acceptance of E-speed film, contributing to dose reduction.

Emulsions↗
PubMed1995

An in vitro comparison of 10 radiographic methods for working length estimation.

The aim of this in vitro study was to assess the efficacy of 10 currently available methods of producing radiographic images, two conventional and eight rapid, in working length estimation. Thirty extracted teeth comprising 42 root canals were mounted in blocks of poly(methylmethacrylate) and access cavities prepared. A size 15 Hedstrom file was inserted into each root canal and sealed into position. Each tooth was imaged by 10 methods: combinations of conventional (D- and E- speed) film processed with conventional manual chemistry of two proprietary brands of rapid processing chemistry (Westone Rapid Dental and Kodak 'Rapid Access'), Super X30 packet processed film, Hanshin Hi-Fi and Nix NF45-100 films processed using their respective manufacturers' monobath solutions, and the Sens-A-Ray digital X-ray system. Comparisons of length of file visible were made between the D-speed films (conventionally processed using Kodak chemistry) and the nine other radiographic methods. No significant differences in percentage length of file seen were found between D-speed film processed with conventional chemistry and E-speed film processed with the same chemistry or between D-speed film processed with with conventional chemistry and six of the rapid imaging systems studied. The percentage length of the file visible was significantly less for Sens-A-Ray (P=0.02) and for Nix NF45-100 film (P<0.005) when compared with D-speed film processed with conventional chemistry. This difference in file length is probably not of clinical importance for the Sens-A-Ray images but may be so for the Nix images.

Dental Pulp Cavity↗
PubMed1995

The dental phenotype in familial adenomatous polyposis: diagnostic application of a weighted scoring system for changes on dental panoramic radiographs.

A weighted scoring system (Dental Panoramic Radiograph Score) taking into consideration the nature, extent, and site of osseous and dental changes on dental panoramic radiographs in familial adenomatous polyposis is described. The weighting takes into consideration the incidence of the anomaly in the general population. The reliability of the system was tested by application to 85 people known to be affected by clinical or mutation analysis, 30 people lacking mutation in the adenomatous polyposis gene, and 19 people shown to be at low risk (< 1%) by linkage analysis. Using the highest thresholds, a specificity of 100% and sensitivity of approximately 68% was obtained. If all positive findings were considered as significant, sensitivity was increased to approximately 82% but the specificity was reduced to approximately 88%. Significant DPRS findings were observed at a significantly higher frequency in patients aged over 20 compared to the patients aged 20 and under. Overall, approximately 68% of the affected subjects had significant changes, and approximately 18% had normal appearance on DPR, with the remainder having changes classified as minimal or equivocal.

Adenomatous Polyposis Coli↗
PubMed1995

Severe Gardner syndrome in families with mutations restricted to a specific region of the APC gene.

Familial adenomatous polyposis (FAP) is associated with a number of extraintestinal manifestations, which include osteomas, epidermoid cysts, and desmoid tumors, often referred to as "Gardner syndrome." Recent studies have suggested that some of the phenotypic features of FAP are dependent on the position of the mutation within the APC gene. In particular, the correlation between congenital hypertrophy of the retinal pigment epithelium (CHRPE) and APC genotype indicates that affected families may be divided into distinct groups. We have investigated the association between the dentoosseous features of GS on dental panoramic radiographs (DPRs) and APC genotype in a regional cohort of FAP families. DPRs were performed on 84 affected individuals from 36 families, and the dento-osseous features of FAP were quantified by a weighted scoring system. Significant DPR abnormalities were present in 69% of affected individuals. The APC gene mutation was identified in 27 of these families, and for statistical analysis these were subdivided into three groups. Group 1 comprised 18 affected individuals from seven families with mutations 5' of exon 9; these families (except one) did not express CHRPE. Groups 2 comprised 38 individuals from 16 families with mutations between exon 9 and codon 1444, all of whom expressed CHRPE. Group 3 comprised 11 individuals from four families with mutations 3' of codon 1444, none of whom expressed CHRPE. Families with mutations 3' of codon 1444 had significantly more lesions on DPRs (P < .001) and appeared to have a higher incidence of desmoid tumors. These results suggest that the severity of some of the features of Gardner syndrome may correlate with genotype in FAP.

DNA↗
PubMed1994

The acceptability of five periapical radiographic techniques to dentists and patients.

Dentists are now advised to use film holders as an aid to intra-oral radiography. The aim of this investigation was to compare a range of commercially available film holders for periapical radiography with the traditional bisecting angle technique using the patient's finger as support for the film, in terms of the ease of use for the dentist and patient comfort. Twelve general dental practitioners (GDPs) were asked to perform 50 periapical examinations using their conventional (bisecting angle) technique (BA) followed by 50 using, in turn, four film holders: the Stabe (S), the Eggen (E), the Rinn (R) and the 'Superbite' devices (SB). There was no difference between BA, S and SB techniques in terms of difficulty experienced by the GDPs. However, both E and R film holders led to an increase in examinations reported as 'difficult' to perform. There was no difference in patient discomfort between the BA and SB techniques, but the use of the E and R film holders and, to a lesser degree, the S film holder was associated with increased discomfort. There was no consistent association between dentists' assessments of examinations as 'difficult to perform' and patients' opinions on discomfort. It is concluded that SB film holders provide a simple means of intraoral radiographic positioning with no increase in patient discomfort.

Adult↗
PubMed1994

Alterations of auditory nerve responses by hypoxia in normal and hydropic ears of awake guinea pigs.

Total interruption of blood or oxygen supply to the inner ear produces very rapid and drastic effects, whereas moderate decreases can be well tolerated by normal ears. In experimental endolymphatic hydrops some moderate alterations of cochlear vasculature have been described which might affect cochlear adaptation to moderate blood or oxygen deficiencies. In order to test this hypothesis an hypoxia at 5% oxygen was imposed for 30 min in normal and hydropic ears of awake guinea pigs and cochlear function was monitored with an electrode at the round window. Electrophysiological recordings used measures of compound action potential (CAP) amplitudes evoked by high-intensity tones, and of CAP thresholds. In normal ears hypoxia induced threshold elevations at all frequencies and decreases of CAP amplitude only for high frequencies. Hydropic ears presented similar or smaller threshold elevations but showed CAP amplitude decreases extending to lower frequencies and showed a much slower recovery both for CAP thresholds and amplitudes. The data indicate that hypoxia had different effects on auditory nerve responses evoked by high versus low intensity tones. The deleterious effects of hypoxia were increased in hydropic ears. Hypoxia-induced alterations were measured twice at one week intervals during which an anti-ischemic drug was administered to the animals; some beneficial effects of the drug treatment were observed on normal but not on hydropic ears.

Acoustic Stimulation↗
PubMed1994

A laboratory evaluation of four quality control devices for radiographic processing.

Quality assurance programmes for radiographic processing traditionally employ expensive sensitometric and densitometric techniques. However cheap and simple devices for monitoring radiographic processing are available. The aim of this study was to make a comparison of four such devices in terms of their ability to detect variations in radiographic density of clinical significance. Three of the devices are commercially available while the fourth is easily manufactured from waste materials. Ideal bitewing exposure times were selected for four different kilovoltage/film speed combinations. Phantom bitewing radiographs, exposed using these exposure times, were processed using a variety of times and developer temperatures to simulate variations in radiographic quality due to inadequate processing conditions. Test films, produced using the four monitoring devices, were exposed and processed under identical conditions. The phantom bitewings were judged to have 'acceptable' quality when the optical density of that part of the film not showing calcified structures was within +/- 0.5 of that of the film processed under optimal conditions. The efficacy of the monitoring devices in indicating the adequacy of processing was assessed by a comparison of their readings with those made from the phantom bitewings. None of the monitoring devices was ideal for all the kilovoltage/film speed combinations tested, but the homemade device proved to be the most generally effective. We conclude that guidelines to dentists on radiographic quality assurance should include reference to and details of this simple device.

Densitometry↗
PubMed1994

Review article: radiation protection in dental radiology.

Dental radiology represents the most frequent diagnostic radiological investigation in the industrialized world, with over 16 million examinations performed annually in England and Wales alone. Although individual doses and risks are low in dental radiography, the collective dose is not inconsiderable and many examinations are performed in younger age groups. Radiation protection of patients in dental radiology is achieved in three ways: by appropriate selection criteria for patients and equipment, methods of dose limitation and quality assurance procedures. There is a lack of agreed radiographic selection criteria to guide British dentists and this may lead to overuse of certain techniques, principally panoramic radiography. In intraoral radiography the use of fast (E-speed) film and rectangular collimation offer dose reductions of approximately 50% and 60%, respectively. Constant potential X-ray units and rare-earth filtration permit further reductions. In panoramic and cephalometric radiography, improved collimation offers a simple means of dose limitation, while doses can be reduced by up to one-eighth by combining the use of constant potential X-ray units, rare-earth intensifying screens and rare-earth filtration. Lead protection of the abdomen has little relevance to radiation protection; however, thyroid shielding has some value. Concern has been expressed about the poor diagnostic quality of radiographs taken in the general dental services. Consequently a quality assurance programme plays an essential part in dental radiation protection by improving diagnostic yield and limiting repeat examinations.

Filtration↗
PubMed1994

A comparative study of radiographic quality with five periapical techniques in general dental practice.

The use of film holders for intraoral radiography is advocated in current guidelines to British dentists. No assessment of the use of film holders has been carried out in a general dental practice environment. The aim of this study was to compare the performance of a range of film holders for periapical radiography in general dental practices in terms of the diagnostic quality of the radiographs. Twelve general dental practitioners (GDPs) were recruited to participate in the study. Each GDP was asked to perform 50 periapical radiographs using their conventional (bisecting angle) technique (BAT) followed by 50 using, in turn, four film holders: the Stabe (S), the Eggen (E), the Rinn (R) and the 'Superbite' devices (SB). Each radiograph was examined simultaneously by two assessors, scored for film faults and diagnostic acceptability. With BAT, 44.5% of radiographs were diagnostically unacceptable, while using film holders 32.8% (S), 33.7% (E), 38.2% (R) and 35.8% (SB) were unacceptable. These reductions in unacceptable films were highly significant (P < 0.01) for S and E techniques, significant (P < 0.05) for SB, while with R the reduction was not statistically significant. These results give support for the use of film holders for periapical radiography. However, their effectiveness may be improved by better manufacturers' instructions and practical training of GDPs.

Adult↗
PubMed1994

Condylar hyperplasia: correlation of histological and scintigraphic features.

Scintigaphy using 99mTc-MDP is widely advocated as a method of diagnosis and presurgical assessment of patients with condylar hyperplasia. A previous study has demonstrated that hyperplasia of the mandibular condyle is characterized histologically by the presence of an uninterrupted layer of undiffentiated germinative mesenchyme cells, a layer of hypertrophic cartilage and the presence of islands of chondrocytes in the subchondral trabecular bone. This study was undertaken to determine whether there was any association between the degree of 99mTc-MDP uptake and the histological features of condylar hyperplasia. The parameters examined were trabecular bone volume, depth of cartilage islands and the presence of forming and resorbing surfaces. The images were analyzed by three experienced observers, who ranked the images according to degree of asymmetry between sides and the degree of uptake on the affected side. There was a significant correlation between the proportions of resorbing and osteoid covered bone surfaces and scintigraphic appearances. The rank correlations were rs = 0.55 (P = 0.3) between the resorptive surfaces and degree of symmetry and rs = 0.53 (P = 0.04) between the osteoid surfaces and absolute uptake. The correlation was higher for both methods (rs = 0.64 in each case) when the osteoid surface and resorptive surface measurements were combined. The results indicate that visual examination of radioisotope bone scans by experienced observers is a valid form of assessment of bone activity in condylar hyperplasia.

Adolescent↗
PubMed1994

[Effect of hypoxia at 5% oxygen on global electrophysiological responses from normal awake guinea pigs].

All experiments were conducted on awake guinea pigs warranting a normal physiological function of the circulatory system. Global electrophysiological responses from the round window of cochlea were monitored: cochlear microphonic (CM), summating potential (SP) and auditory compound action potential (AP). The results showed that hypoxia induced a threshold elevation at all frequencies thus affecting the whole cochlea, and also very large diminutions of AP at high intensity level exclusively in response to a high frequency, and very large increases of SP at 2 kHz and 8 kHz. After hypoxia, which lasted thirty minutes, a considerable recovery occurred, and at the end of the session recovery reached around eighty percent. Alterations of cochlea action potential in response to high intensity stimuli were dissociated from threshold changes. We speculate that threshold elevation could be associated with over-all energetic (ATP) decrease leading to diminution of endolymphatic resting potential. Action potential changes at high intensity and at cochlear base could reflect neurotransmission (afferent, efferent or sympathetic) disturbance.

Action Potentials↗
PubMed1993

Familial occurrence of periapical cemental dysplasia.

A family with periapical cemental dysplasia is reported. The affected individuals displayed classical features of periapical cemental dysplasia on radiographic examination. The lesions consisted chiefly of radiolucent areas; however, some had central areas of radiodensity. Histopathological examination of one of the lesions revealed fibrous elements containing fused dense sclerotic cemental masses. Familial incidence of florid cemento-osseous dysplasia with an autosomal mode of inheritance has been reported previously. The condition described in this report appears to be different. However, the two conditions may be part of a spectrum occurring in a single genetic entity with the diversity possibly resulting from variable expressivity of a single gene.

Cementoma↗
PubMed1993

The radiological features of calcifying odontogenic cyst.

Calcifying odontogenic cyst is a rare benign lesion of the jaws, with no particular specificity for age, sex or site. Three new cases are presented together with a review of the radiological literature. There appear to be no pathognomonic radiological features, although a superficial location on the affected bone and the presence of internal calcification may be useful signs. The role of radiology appears to be limited to determining lesion extent prior to surgery.

Adult↗