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Biomedical subjects

L Lorton

Publications and source records attributed to L Lorton.

At least 19 recordsLinked to original sources
PubMed1992

Comparison of the shear bond strength of a light-cured glass ionomer and a chemically cured glass ionomer for use as an orthodontic bonding agent.

Light-cured glass ionomers with an initial set of 20 seconds may produce higher initial bond strengths, as well as decreased sensitivity to moisture contamination and desiccation, than chemically cured glass ionomers making them attractive for use as orthodontic bonding agents. The purpose of this study was to determine and compare the shear bond strength of stainless steel orthodontic attachments to enamel with a light-cured glass ionomer (Zionomer) tested at 60 minutes and 24 hours, and a rapidly setting chemically cured glass ionomer (Ketac-Bond) tested at 60 minutes and 24 hours. Fifty-two recently extracted human premolars were randomly divided into four groups--1-hour and 24-hour light-cured glass ionomer groups and 1-hour and 24-hour chemically cured glass ionomer groups. Stainless steel lingual buttons were bonded to prepared enamel surfaces, and the samples were placed in a water bath at 37 degrees C until ready for testing. The shear bond strength of each sample was determined with a universal testing instrument. Results from the study conclude: (1) The mean shear bond strength of the light-cured glass ionomer is greater than that of the chemically cured glass ionomer at 1 and 24 hours. (2) The mean shear bond strength of both glass ionomers increases from 1 to 24 hours. (3) The mean shear bond strength of the light-cured glass ionomer is not significantly different from 1 to 24 hours, but the shear bond strength of the chemically cured glass ionomer cement is different.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid Etching, Dental↗
PubMed1990

Ceramic bracket bonding: a comparison of bond strength with polyacrylic acid and phosphoric acid enamel conditioning.

The purpose of this study was to compare in vitro shear bond strength with three different enamel surface preparations: (1) 37% phosphoric acid etch, (2) sulfated polyacrylic acid etch with removal of crystals by vigorous rinsing and (3) polyacrylic acid etch with crystal growth. Forty extracted human premolar teeth were divided into four groups of ten. Ceramic brackets were bonded to teeth in each of three groups. The fourth group used was bonded with metal brackets and a phosphoric acid enamel preparation. The same lightly filled resin cement was used for all groups. A shearing force was applied to the teeth. The results demonstrated that the shear force needed to debond with ceramic brackets was 21% greater than the shear force with metal brackets. The polyacrylic acid crystal growth group had shear bond strength values approximately one half as great as the phosphoric acid etch group when ceramic brackets were used. Bond failures in the phosphoric acid etch group were at the bracket/resin interface with the bulk of the resin remaining on the tooth compared with the polyacrylic acid crystal growth group in which the bond failure was at the enamel resin interface. Enamel fractures were not found when healthy nonrestored teeth were subjected to the shearing force. In a preliminary test using phosphoric acid etch and teeth with compromised enamel (large restorations involving three or more surfaces), half of the teeth fractured during debonding. The study demonstrated that a polyacrylic acid conditioning of the enamel surface produces different retentive surfaces, depending on the presence or absence of crystal growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid Etching, Dental↗
PubMed1990

Statistics: curse of the writing class.

Research projects and reports may fail because of investigators' misunderstandings about the principles underlying basic data analysis. Such errors may taint otherwise valid conclusions; related mistakes may serve to falsely support incorrect results. This article explains some of the principles underlying the use of statistical analysis for normally distributed interval data and explores the potential ramifications of misusing summary statistical tests on non-normal distributions. A discussion of the meaning of the statement of probability concerning hypothesis testing and a suggested attitude for researchers toward significance testing is also included.

Data Interpretation, Statistical↗
PubMed1990

The effect of hydrogen ion concentration on the force-degradation rate of orthodontic polyurethane chain elastics.

The effect of pH on the force-degradation rates of seven commercial orthodontic polyurethane chain elastics was evaluated in an in vitro study. The pH values of 4.95 and 7.26 were selected for testing because they represent values close to the reported extremes of plaque and saliva pH. Seven test elastic products were extended to (1) equal distances and (2) equal initial force levels, and the force-degradation rates were recorded over 4 weeks. All the test products yielded a significantly greater force-decay rate in the basic (pH 7.26) solution than in the acidic (pH 4.95) solution over 4 weeks. A hypothesis is presented that the decay rate of orthodontic polyurethane chain elastics is inversely proportional to the oral pH, with a corollary that basic pH levels are most hostile to polyurethane chain elastics.

Analysis of Variance↗
PubMed1989

The effect of patient movement on resolution.

The effect of long exposure time on patient movement and resulting radiographic resolution was simulated and then measured by visual-light photographic techniques for four radiographic projections. A mathematic relation was then derived to transform these measurements to the maximum resolutions that could have been obtained with radiographs under similar conditions. The results indicate that radiographs of rigid structures such as bones and teeth can be taken with reasonable resolution at exposure times much longer than normally used in clinical practice. It was also found that radiographs taken with the film rigidly fixed to the object being studied will exhibit remarkably less blurring from patient motion than radiographs taken when the patient and the film are not coupled. In addition it was found that motion artifacts are reduced to a minimum when the plane of the film is perpendicular to the radiation beam.

Adult↗
PubMed1989

Dental characteristics of a large military population useful for identification.

The number and complexity of dental restorations has decreased for younger Americans. Since the presence and extent of restorations are important data for forensic science identification purposes, the Computer-Assisted Postmortem Identification (CAPMI) system was used to assess the practical effect of the decreased selectivity expected as a result of improved dental health. Dental examination data from 7030 soldiers were recorded on optical mark read forms and entered into a database. The data were reorganized and analyzed to generate summary statistics about the incidence of each type of restoration (divided into 16 categories) for both anterior, posterior, upper, lower, and combined segments. Patients' ages ranged from 17 to 49 with a mean of 24 years 5 months. Sixty percent were from 18 to 25 years old. A characteristic is defined as any situation other than a virgin tooth; for example, extracted, missing, unerupted, or restored. The average subject had 7 dental characteristics with approximately 75% having 4 or more. Within the entire population, 9% had 32 unrestored teeth. 3.6% had only one characteristic. To test the selectivity and uniqueness of various combinations of dental characteristics, 363 simulations using the CAPMI system were made against the entire 7030 subject database. Sample records (33 per group) with 2, 3, 4, 5, 6, 7, 8, 9-11, 12-14, 15-18, and 19+ characteristics were chosen at random from the database and searches were made.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

A new algorithm for use in computer identification.

On 9 May 1987, a Soviet-made IL-62M Polish airliner, LOT Flight 5055, crashed, exploded, and burned, killing the crew and 183 passengers. A forensic science team from the Armed Forces Institute of Pathology, comprised of 6 dental officers, 3 forensic pathologists, and 3 medical photographers, worked in concert with the Polish forensic science team. The small number of antemortem records and the extreme fragmentation of the remains presented a new scenario for computer use. Typically, the Computer-Assisted Postmortem Identification (CAPMI) software is used to compare remains against an antemortem database. Results are listed by the number of tooth-to-tooth matches based on restorative or other characteristics or both. The Polish disaster confounded this approach to some degree, however, and suggested a reconsideration of the theory on which the sort is made, that is, that the cases with maximum number of matches to preexisting dental records would be the most likely identification (ID) match. A hypothesis was constructed that, if searches were accomplished for fragments with a minimum number of mismatches, the correct matches would appear higher in the rank order. Six antemortem records (that had all dental information) were sorted against one hundred and twelve postmortem fragmented records. The resulting report was reordered so that records were listed by minimum number of mismatches. There was significant improvement in rank placement for all of the records. Thus it was accepted that in the situation of highly fragmented remains a different sorting based on the number of mismatches is indicated. Programming changes to make this option available have been implemented in the new version of CAPMI.

Accidents, Aviation↗
PubMed1989

The Computer-Assisted Postmortem Identification (CAPMI) system: sorting algorithm improvements.

Refinements to the original Computer-Assisted Postmortem Identification (CAPMI) software algorithms and general data handling were suggested as a result of observations made following the Gander plane crash of 1985. The presence of highly fragmented and scattered remains following most plane crashes suggested that changes to procedure might improve CAPMI performance for use in these types of disasters. A total of 162 ante- and postmortem dental records which had been used successfully to identify victims of the Gander disaster were coded for anonymity and used for this investigation. Changes in data construction and management were made to CAPMI, according to concepts which were thought might improve system performance, and tested. Although most tested techniques improved CAPMI performance, the data suggested that replacement of "virgin" chartings with "data unknown" results in improved performance of CAPMI largely independent of other factors. Of 162 possible record matches, the original algorithm successfully listed the true record match in the top 20 possibilities 74% of the time; the tested variations on the original algorithm yielded results across a range of 38 to 83% successes, with most techniques performing better than the original algorithm. Results of this investigation have been incorporated into improved CAPMI procedures and software.

Accidents, Aviation↗
PubMed1988

The Computer-Assisted Postmortem Identification (CAPMI) System: a computer-based identification program.

The Computer-Assisted Postmortem Identification (CAPMI) system was developed at the U.S. Army Institute of Dental Research to facilitate rapid identification of human remains. The increasing requirement for dental based identification of high-energy fatalities and decomposed remains has dovetailed with the development of computer capabilities permitting automation of most of the highly repetitive chart-by-chart screenings characteristic of traditional identification taskings. This report summarizes the concepts upon which CAPMI is based, describes how it works, and reviews suggested applications and limitations. CAPMI software is available to governmental, civic, or humanitarian organizations at no cost.

Dental Records↗
PubMed1987

Order of magnitude dose reduction in intraoral radiography.

This comparative clinical investigation concerns the radiation dose from intraoral radiography using E-speed film and rectangular and circular beam collimation. Dose to organs not of diagnostic importance (brain, lens of the eye, thyroid, and breast) is reduced by approximately an order of magnitude when rectangular collimation and E-speed film are used in periapical radiography. And dose to the thyroid and breast is further reduced by a third with the use of a full leaded apron and thyroid shield.

Breast↗
PubMed1986

Exposure reduction of 96% in intraoral radiography.

This study compared the diagnostic quality of E-speed film, xeroradiographic cassettes, and a screen-film imaging system used in medical radiology. The surfaces of defects simulating caries were scored for the presence and depth of the defects under ideal viewing conditions by independent observers. Receiver Operator Characteristics analysis of the data showed no significant differences regarding diagnostic potential among the three systems. The true-positive fraction was 1.00 for all systems and all operators, and the false-positive fraction was .011, .011, and .007, respectively. An exposure of 5.5 mR was used to produce images with the screen-film combination, and 150 mR was used for standard dental systems. This study showed that an exposure reduction of 96% is possible while maintaining high-quality radiographs for the diagnosis of caries.

Dental Caries↗
PubMed1986

Design and use of a computer-assisted postmortem identification system.

The organization and rationale for the design of a computer-assisted postmortem identification system are discussed along with results of the use of this system in extensive simulation trials on a database of 578 records. The selectivity of dental characteristics is so great that any individual with 4 or more characteristics (either fillings or missing teeth), can be separated from a group of 578 people for final verification of the identity match. The effects of errors in the database are discussed and the actual effects of different error rates on identification are shown. Error rates of up to 30% have only small effects on the ability of the system to pick out correct identity matches. The system is presently implemented on a portable microcomputer, a representative desktop computer, and a large minicomputer. The present efforts include statistical analysis of an enlarged database and testing of a data acquisition system to allow the building of a large identification database (25 000 records) in a quick and economical manner.

Computers↗
PubMed1985

The incidence of unerupted permanent teeth and related clinical cases.

The impacted or mal-erupted tooth and its associated pathosis provide great diagnostic challenges to the dentist. The frequency of occurrence of impaction was found to be over 10,000 in 5,000 Army recruits. The type and position of impaction are summarized in tables. The incidence of impactions was higher than previously reported and may reflect some sampling bias. The incidence of impacted second and fourth molars is higher than expected. Impactions or mal-eruptions were seen to involve every permanent tooth except the mandibular incisors and first molars. Impactions can occur because of malpositioning of the tooth bud or obstruction in the path of eruption. However, the exact mechanism is still unknown. Six unusual cases of impacted permanent teeth are described to illustrate the importance of panoramic radiographs in the discovery of some anomalously located impactions.

Adolescent↗
PubMed1985

Gemination and twinning in the permanent dentition.

Gemination and twinning are uncommon developmental anomalies of the hard dental tissue. These aberrations are manifested either as anomalous teeth or as supernumerary teeth. Six cases of gemination and twinning are presented in this article. A simplified classification of these anomalies has been suggested.

Adolescent↗