Force decay and deformation of orthodontic elastomeric ligatures.

This study evaluated commercially available molded gray elastomeric ligatures from seven companies for force decay, dimensional change, and the relationship between ligature dimension and force. The initial wall thickness, inside diameter, outside diameter, and force levels of each ligature were measured. Three of four test groups of ligatures were stretched over stainless steel dowels with a circumference approximating that of a large orthodontic twin bracket. Test group 1 was kept at room temperature and humidity for 28 days and test group 2 in a synthetic saliva bath at 37 degrees C, pH 6.84 for 28 days. The residual forces and dimensional changes were measured. The third test group was placed in a synthetic saliva bath at 37 degrees C, pH 6.84, and force levels recorded at initial, 24 hours, 7 days, 14 days, and 28 days. The fourth test group of unstretched samples was placed in a synthetic saliva bath at 37 degrees C, pH 6.84 for 28 days to evaluate dimensional changes due solely to moisture sorption. The results for stretched samples in a simulated oral environment revealed the following: (1) Moisture and heat had a pronounced effect on force decay and permanent deformation, (2) a positive correlation existed between the wall thickness and force, (3) a negative correlation existed between the inside diameter and force, (4) a weak correlation existed between outside diameter and force, (5) the greatest force loss occurred in the first 24 hours and the decay pattern was similar for all ligatures tested, and (6) unstretched ligatures absorbed moisture in the range of 0.060% to 3.15%. The ligatures tested appear to be suitable for use during initial aligning and leveling. However, the rapid force loss and permanent deformation of these products may preclude their use for rotational and torque corrections.

Frequency of Bolton tooth-size discrepancies among orthodontic patients.

The purpose of this study was to determine the percentage of orthodontic patients who present with an interarch tooth-size discrepancy likely to affect treatment planning or results. The Bolton tooth-size discrepancies of 157 patients accepted for treatment in an orthodontic residency program were evaluated for the frequency and the magnitude of deviation from Bolton's mean. Discrepancies outside of 2 SD were considered as potentially significant with regard to treatment planning and treatment results. Although the mean of the sample was nearly identical to that of Bolton's, the range and standard deviation varied considerably with a large percentage of the orthodontic patients having discrepancies outside of Bolton's 2 SD. With such a high frequency of significant discrepancies it would seem prudent to routinely perform a tooth-size analysis and incorporate the findings into orthodontic treatment planning.

Adult pulpal diagnosis. I. Evaluation of the positive and negative responses to cold and electrical pulp tests.

This study investigated the positive and negative responses of 1488 teeth in 60 patients to two electric pulp testers and a cold thermal pulp test. Three subgroups of known pulpless or pulpally diseased teeth (teeth receiving root canal therapy, teeth with root canal fillings, or teeth with confirmed associated apical radiolucencies) were identified and their responses evaluated separately. Testing was performed on two tooth surfaces, the facio-occlusal and faciocervical, and on all restorations. The gingival tissue of each patient also was tested using both electrical tests. The primary findings were: (a) teeth not responding to cold and either not responding or responding at readings greater than the tissue response to electrical had a high probability of being in the known pulpless or pulpally diseased subgroups; (b) the only false positive responses to cold in the three subgroups were in multirooted teeth with probable vital tissue remaining in at least one canal; and (c) in the three subgroups, if the false positive responses to electrical that responded at levels higher than the patient's tissue response were considered to be negative responses, the difference in false positives between cold and electrical became not statistically significant (p = 0.07).

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)

Sequencing platinum foil matrix removal in postceramic soldering of the collarless veneered retainer.

Postceramic soldering of collarless veneered retainers in which the porcelain margins were formed with a platinum foil matrix technique was investigated. The purpose of the study was to determine if removing the platinum foil matrix before or after indexing and soldering procedures would affect the porcelain margin integrity in fixed partial dentures. Prostheses were fabricated on a nickel-chromium laboratory model using both sequences. Six test cycles were performed. Each cycle included one soldering with matrix support and one without the matrix, for a total of 12 solderings. The fixed partial dentures were compared for degree of marginal seating with a measuring microscope and for configuration changes at the porcelain margins with scanning electron micrographs. In the microscopic analysis of marginal closure, soldering without foil matrix was statistically equal to soldering with foil in place. Removal of the platinum foil matrices prior to indexing provided for no further seating of the metal ceramic retainers. Evaluation by scanning electron microscopy demonstrated distinct configuration changes in the porcelain margins for the specimens soldered without matrix support.

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.

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)

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.

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)

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.

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.

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.

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.

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.