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Biomedical subjects

A Boghosian

Publications and source records attributed to A Boghosian.

8 recordsLinked to original sources
PubMed1996

An accurate and simple method for the measurement of dental composite wear.

This study describes a relatively simple mechanical technique for measuring occlusal wear at the margin of dental restorations. The device was essentially a custom profilometer which consisted of a linear variable differential transformer with its core supported by double cantilever springs, a specially shaped stylus, a motor driven microscopic stage, custom computer software utilizing a colour coding to separate differences in slope, and a cross-hair-shaped mouse cursor to differentiate the boundary of wear. Two sets of visual standard stone casts were evaluated. The first set consisted of 17 stone replicas of machined steel dies and the second set consisted of five clinical casts, which have been used to measure the wear of composite restorations by direct vision. The reproducibility found when measuring the stone replicas of the machined steel dies was 2 microns, while, for the clinical standards, it was 16 microns.

Calcium Sulfate↗
PubMed1996

Visual versus mechanical wear measurement of dental composite resin.

This study compares a visual method for measuring composite wear with a relatively inexpensive mechanical technique. The visual measurements used a set of 17 graduated stone standards as the reference. Two sets of 10 unknown casts were evaluated. The first was a set of 10 stone replicas selected from the reference set in the range of 25-250 microns. The second set was composed of 10 casts of clinical restorations. The mechanical test employed a computer-controlled custom profilometer. Depth was recorded at 50 equidistant positions around the margin. A significant correlation was found (r > 0.98) between the visual and mechanical means for both measurement techniques. Mean values were equivalent for the standard casts. However, visual estimation of the clinical casts were significantly lower (61% of mechanical values) and thus not accurate for clinical use.

Analysis of Variance↗
PubMed1996

Clinical evaluation of a filled adhesive system in Class 5 restorations.

The restoration of the Class 5 lesion has proved to be an excellent model to measure the clinical efficacy of dentin adhesive materials. This is the result of numerous factors, such as the nonretentive nature of the lesion, large areas of exposed dentin with limited enamel margins, and the high degree of flexure from occlusion that is transmitted to the restoration. The role of the adhesive agent has been critical to the successful restoration of the lesion. Numerous improvements have been introduced to correct deficiencies of earlier-generation bonding systems. The addition of filler particles to the resin adhesive has provided significant benefits, especially in marginal adaptation. The clinical performance of OptiBond, a filled dentin adhesive system, was investigated through the restoration of 80 Class 5 abrasion lesions in 35 patients in accordance with the Guidelines for Dentin and Enamel Adhesive Materials of the American Dental Association. At 2 years, all clinical evaluation parameters were rated 94% to 100% alpha. OptiBond has demonstrated therapeutic effectiveness in eliminating the dentin hypersensitivity that often occurs in Class 5 abrasion lesions.

Adult↗
PubMed1993

Radiometric and spectroradiometric comparison of power outputs of five visible light-curing units.

The spectral distributions of the radiation emitted by five visible range curing lights were measured spectroradiometrically. The light intensities in specific wavelength bands were evaluated by graphical integration. The results were then compared with the instantaneous readings of power density of all of the units as measured with a commercial curing radiometer. The data obtained by both techniques correlated well at narrower specific wavelengths (450-500 nm), which are assumed to be more effective for photopolymerization. This finding indicates that curing radiometer is sensitive to the desired wavelengths and may be an effective tool to quickly characterize the curing efficiency of dental photocuring sources in a clinical setting.

Absorption↗
PubMed1977

SP-10 bacteriophage-specific nucleic acid and enzyme synthesis in Bacillus subtilis W23.

Bacillus subtilis W23 was infected with a clear-plaque variant of SP-10 phage, namely, SP-10c. Exogenous thymidine was not incorporated into phage DNA (even in the presence of deoxyadenosine), nor was there any transfer of thymidine nucleotides from bacterial to viral DNA. The lytic program was unaffected by concentrations of 5-fluorodeoxyuridine sufficient to reduce bacterial DNA synthesis by greater than 95%. Although these data are consistent with the interpretation that thymidine nucleotides are excluded from phage DNA, formic acid digests of SP-10c DNA contained what appeared to be the four conventional bases; however, adenine and thymine were not recovered in equimolar yields. DNA-RNA hybridization and hybridization competition experiments were done. Synthesis of host RNA started to wane moments postinfection and stopped completely by 36 min. SP-10c coded for discrete classes of early and late RNA. The possibility of discrete subclasses of early RNA exists. Replication of the bacterial genome appeared to terminate 12 min postinfection. Degradation of the host DNA to acid-soluble material started at 36 min and, by the end of the latent period, greater than 90% of the host chromosome was hydrolyzed. Four apparent phage-coded enzymes have been identified. A di- and triphosphatase degraded dUTP, dUDP, dTTP, and dTDP (and, to a lesser extent, dCDP and d CTP) to the corresponding monophosphates; the enzyme had no apparent activity on dATP and dGTP. SP10c also coded for a DNA-dependent DNA polymerase, lysozyme, and a nuclease that degrades native bacterial DNA. Judging from the dependence of enzyme synthesis on the time of addition of rifampin (an inhibitor of the initiation of RNA synthesis), messengers for the di- and triphosphatase, as well as the nuclease, are transcribed from promoters that start to function 6 min postinfection. Promoters for polymerase and lysozyme did not become functional until 8 and 16 min postinfection, respectively.

Aminoglycosides↗