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Biomedical subjects

S C White

Publications and source records attributed to S C White.

At least 55 records · Page 3Linked to original sources
PubMed1994

Detection of mineral loss in approximal enamel by subtraction radiography.

The purpose of the present study was to determine whether digital subtraction radiography will improve detectability of small, mechanically prepared defects within dental enamel. Lesions with an extent of 1 mm in vertical direction and representing 5% to 10% mineral loss in the direction of the x-ray beam were prepared in eight extracted molars. Radiographs of teeth with defects were subtracted from radiographs taken before the lesions were prepared. Seven observers evaluated the images using a five-point confidence rating scale (receiver operating characteristic technique). Examination of the original radiographs showed increasing accuracy of radiographic interpretation with increasing mineral loss as judged from the areas beneath the receiver operating characteristic curves. The same observation was made using subtraction images with and without contrast enhancement. There was no indication that subtracted images provided better diagnostic validity than the original radiographs. In conclusion, subtraction images do not seem to improve the diagnosis of well-defined lesions within dental enamel.

Dental Enamel↗
PubMed1993

Uncoupling the correlates of locomotor costs: a factorial approach.

Although the metabolic cost of running has been found to vary systematically with running speed and body mass in animals, no mechanistic model of cost determination has been widely accepted. Because two suggested cost determinants--mechanical power output and the rate of force application--covary with running speed when gait (stride frequency) is unconstrained, examining the influence of each factor on cost has been problematic. We experimentally uncoupled the usual relationships between three readily manipulated cost correlates--speed, stride frequency, and mass distribution--to study the determinants of the cost of running in humans along a section of the cost response surface. Two levels of each cost correlate were used in a factorial design in which subjects ran at all eight combinations of factor levels while rate of oxygen consumption (VO2), mechanical power, and contact time were measured as response variables. Contact time and mechanical power were measured from high-speed cinefilm. Mechanical power accounted for 88%, and contact time (rate of force application) 57%, of speed-related VO2 variation. Variation in cost produced by changes in stride frequency and mass distribution were largely explained by mechanical power. Contact time was not significantly correlated with overall variation in VO2, while mechanical power output explained 80% of that variation. For the range of conditions tested, we conclude that the mechanical power derived from muscular contractions is an important determinant of the cost of running. While we have shown that the rate at which muscles shorten is not the sole determinant of the cost of running, the extent to which this factor influences cost remains unclear.

Analysis of Variance↗
PubMed1993

Radiographic secondary caries prevalence in teeth with clinically defective restorations.

Decisions to replace existing restorations are often based on clinical findings of margin discrepancies and other restoration defects. Previous studies have suggested that such findings do not correlate well with the actual presence of secondary caries, and that treatment should be deferred until caries is clinically or radiographically evident. The purpose of this study was to assess the frequency with which clinically defective restorations are associated with radiographic secondary caries. As part of a study to assess the efficacy of guidelines for the ordering of dental radiographs, 6285 restored teeth in 490 subjects were examined clinically and radiographically by three calibrated investigators. Specific criteria were used to determine whether restorations were intact or defective. Of the total, 822 teeth (13%) were judged to have clinically defective restorations. Of these, 113 teeth (14%) had radiographic secondary caries. Of the 5463 teeth with intact restorations, 5% had radiographic secondary caries. We found that the likelihood of radiographic secondary caries was nearly three-fold higher for defective restorations than for intact restorations. The large percentage (86%) of defective restorations with no radiographic secondary caries suggests, however, that replacement of all defective restorations due to risk of secondary caries may constitute overtreatment. The use of defective restoration status and presence of radiographic secondary caries as a combined criterion for replacement may potentially reduce such overtreatment. The prevalence of secondary caries under defective restorations should be determined clinically so that the usefulness of combining the criteria of defective restoration with those of radiographic secondary caries can be evaluated.

Analysis of Variance↗
PubMed1992

An algorithm for ordering pretreatment orthodontic radiographs.

A study was conducted to identify selection criteria for ordering pretreatment orthodontic radiographs. Thirty-nine orthodontists evaluated six test cases. They provided information on the rationale for ordering each specific radiograph and the impact of the radiograph on the diagnosis and treatment plan. Skeletal relationship of the jaws was the most common indication for a radiograph request, followed by root formation/length and molar position or development. Of the radiographs, 16% produced a change in diagnosis, and 20% produced a change in treatment plans. The criteria specified for the radiographs, their impact, and relevant information in the literature were used to develop an algorithm or set of decision rules that, when tested on the six test cases, resulted in a 36% reduction in the total number of radiographs.

Airway Obstruction↗
PubMed1992

1992 assessment of radiation risk from dental radiography.

Recent studies suggest that the lifetime cancer risks from exposure to low levels of ionizing radiation may be greater than previously estimated. This review first summarizes the findings of these studies as they pertain to dental radiology, then uses their concepts in combination with dosimetry from the dental literature to estimate the radiation risk from dental radiology. Estimation of risk from groups of exposed individuals requires use of mathematical models that fit the epidemiological data. The ICRP estimates that a single brief whole-body exposure of 1 Gy to 10,000 people results in about 500 additional cancer deaths over the lifetime of the exposed individuals, assuming a dose rate effectiveness factor of 2 for cancers other than leukaemia. Leukaemias are seen as a wave from 5 to 30 years following exposure. Cancers other than leukaemia typically start to appear about 10 years following exposure and remain in excess for as long as most exposed populations are followed, presumably for the lifetime of the exposed individuals. The gonadal dose is so small from dental radiography that the risk of heritable defects is negligible in comparison with the somatic risk. The dental literature contains several studies reporting sufficient dosimetric data for radiosensitive sites in the head and neck to allow estimation of the risk of fatal cancers from intra-oral and panoramic radiography. The highest estimated risks (using the ICRP data) are for leukaemia (bone marrow), thyroid and bone surface cancer. The total risk is estimated to be 2.5 fatal malignancies per 10(6) full-mouth examinations made with D-speed film and round collimation.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormalities, Radiation-Induced↗
PubMed1992

Comparative means of dose reduction in dental radiography.

This review on dose reduction in dental radiography focuses on criteria for selecting the frequency and type of radiographs to be performed on patients. By making radiographs only when there is a reasonable probability of a finding that will influence patient care, patient exposure and other radiographic costs may be substantially reduced. Patient dose may also be reduced by half by changing from D-speed film to E-speed film for intraoral radiography and by more than half by changing from calcium tungstate intensifying screens to rare-earth intensifying screens for panoramic and cephalometric radiography. Using rectangular collimation for intraoral radiography will also further reduce patient exposure by about fourfold. Finally, the use of time-temperature processing will prevent overexposure of the patient and underprocessing of the radiographs; optimal radiographs will be provided.

Humans↗
PubMed1991

Evaluation of Niobi-X filtration in intraoral radiology.

This investigation studied the effect of adding niobium filtration to the dental x-ray beam assessing reduction in patient x-ray exposure and changes in image quality. Clinical radiographs were made with the use of D- or E-speed film with either aluminum or aluminum plus 25 microns or 30 microns of added niobium filtration. Similar exposures were made on a head phantom, measuring the absorbed dose to radiosensitive sites in the head and neck. Results indicated that the addition of 25 microns or 30 microns of niobium filtration does not significantly degrade the subjective image quality of diagnostic radiographs when D-speed film is used. With E-speed film, however, the addition of niobium filtration significantly degrades the diagnostic image quality. The addition of niobium filtration results in a 20% to 30% reduction in patient dose. We conclude that the use of niobium filtration with D-speed dental film is a positive contribution to patient care.

Aluminum↗
PubMed1991

Contribution of pretreatment radiographs to orthodontists' decision making.

A study was conducted to determine the amount of diagnostic and treatment planning information gained by orthodontists when pretreatment radiographs are added to a set of orthodontic records. Thirty-nine orthodontists evaluated six test cases and formulated a diagnosis and treatment plan. Information was collected about the participants' certainty with their diagnoses and treatment plans, the impact of the radiographs, the number and type of radiographs that were selected, and the difficulty of each case. Results showed that orthodontists were approximately 75% confident of their diagnosis before reviewing any radiograph. There were 741 radiographs ordered, of which 192 produced changes to the diagnostic process. The lateral cephalometric radiograph was the most productive. Panoramic and full-mouth series were productive but provided largely duplicative information.

Adolescent↗
PubMed1991

Ixodes scapularis (Acari: Ixodidae) in Kansas: a new distribution record.

The blacklegged tick, Ixodes scapularis Say, previously known to occur only in the extreme southeastern corner of Kansas, has been collected in Douglas and Jefferson counties in the northeast. The new collections extend the northern range of this species in Kansas by approximately 240 km. The role of I. scapularis as a vector of the Lyme borreliosis spirochete, Borrelia burgdorferi, makes this a noteworthy extension of its known range. The proximity of these new collection sites to large centers of human population is of special significance to health-care providers in that region.

Animals↗
PubMed1991

Analysis of upper extremity movement in four sitting positions: a comparison of persons with and without cerebral palsy.

The purposes of this study were to compare the arm movements of persons with and without cerebral palsy and to determine if the alteration of the seat angle of a chair affected the quality of those movements. Twelve subjects--3 men and 3 women with spastic cerebral palsy and 3 men and 3 women without any known anomalies that could affect arm movements--were studied. The number of movement elements constituting a reach was used to measure the quality of movements. The findings demonstrated significant differences in the number of movement elements used by the subjects with and without cerebral palsy regardless of position. No significant differences could be attributed to the seating positions. Implications are discussed in relation to the method used in the analysis of movements and the effect of the findings for research and treatment.

Adult↗
PubMed1990

Visualization of stannous fluoride treatment of carious lesions by subtraction radiography.

To determine whether treatment with SnF2 results in changes in radiographic density, eight extracted teeth with lesions confined to the enamel and five with lesions extending into the dentin were radiographed before and after treatment with a 10% SnF2 solution. Although visual comparison of pretreatment and post-treatment radiographs showed increased density in some areas where the pretreatment radiographs had shown demineralization and unchanged conditions in other instances, subtraction images of these radiographs revealed density increase in all the demineralized areas. Even in cases with white spot lesion not visible on radiographs, the subtraction images disclosed an increase in radiographic density.

Dental Caries↗
PubMed1990

Prediction of efficacy of bitewing radiographs for caries detection.

Although bitewing (BW) radiographs play an indispensable role in the detection of interproximal caries, it is not always clear when they should be made. The present study was designed to test the hypothesis that a person's caries and restorative history may be predictive of his or her caries future. Full-mouth radiographic examinations (FMX) and subsequent BW radiographs from 349 adults (age 20 or more) selected at random were examined. Possible risk factors for caries recorded for each patient included the number and type of carious lesions and the restorative experience of the patient. Linear logistic regression models were evaluated to estimate the efficacy of the possible risk factors as predictors of the presence of caries on the BW radiographs. Of the 349 adults examined, 91 (26%) had one or more new carious lesions at the time of their BW examination. The probability of caries in this population at the time of the BW examination increases both with lengthening interval between the FMX and the BW radiographs and with the number of restorations at the time of FMX. A regression model was adopted that estimates the probability of caries being detected on BW radiographs. We found that to provide the most good for the most patients (minimize cost), the threshold level for ordering follow-up radiographs should be when the probability of detecting caries is 5%. It may be seen that even when a person has no caries or restorations at the time of the FMX there will be a 5% chance that BW radiographs will reveal the presence of caries 1.5 years later. The 5% threshold is reached sooner in the presence of caries or restorations.

Adult↗
PubMed1990

Brain and salivary gland tumors related to prior dental radiography: implications for current practice.

Five epidemiological studies of brain, cranial meninge, and salivary gland tumor sites reviewed implicate prior dental radiography with increased risk of subtentorial intracranial meningiomas and tumors of the parotid gland. Diagnostic radiography (medical and dental) was the most important risk factor identified for parotid gland cancers; among Los Angeles County residents, about 85% of the cumulative parotid dose from diagnostic radiography came from dental examinations. Irradiation of patients during dental radiography declined substantially from 1920 to 1988; it is uncertain whether current low doses increase risk. Recommendations for exposure reduction are made.

Adolescent↗
PubMed1989

A three-dimensional musculoskeletal model for gait analysis. Anatomical variability estimates.

Three-dimensional coordinates defining the origin and insertion of 40 muscle units, and bony landmarks for osteometric scaling were identified on dry bone specimens. Interspecimen coordinate differences along the anterior-posterior axis of the pelvis and the long bone axes of the pelvis, femur and leg were reduced by scaling but landmark differences along the other axes were not. The coordinates were mapped to living subjects using close-range photogrammetry to locate superficial reference markers. The error of predicting the positions of internal coordinates was assessed by comparing joint centre locations calculated from local axes defining the orientation of segments superior and inferior to a joint. A difference was attributed to: anatomical variability not accounted for by scaling; errors in identifying and placing reference landmarks; the accuracy of locating markers using photogrammetry and error introduced by marker oscillation during movement. Anatomical differences between specimens are one source of error in defining a musculoskeletal model but larger errors are introduced when such models are mapped to living subjects.

Anthropometry↗