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Biomedical subjects

S D Campbell

Publications and source records attributed to S D Campbell.

At least 19 recordsLinked to original sources
PubMed1992

Thermal cycling distortion of metal ceramics: Part I--Metal collar width.

The complex three-dimensional geometry of conventional full crown restorations severely complicates the study of thermal cycling distortion in metal ceramic castings. A simplified experimental geometry was developed to (1) maximize the measuring sensitivity, (2) eliminate the casting variables, (3) allow the direct measurement of casting distortion, and (4) evaluate the thermal cycling distortion of a wide range of metal collar widths. It was found that all of the one-walled castings distorted during the initial thermal cycling (oxidation) of the alloy. There was no significant distortion associated with porcelain application or glazing. The castings with an 0.8 mm metal collar had significantly less distortion than those with 0.1 and 0.4 mm collars at 2 of the 10 sites measured (inferior or facial margins).

Analysis of Variance↗
PubMed1992

Thermal cycling distortion of metal ceramics: Part II--Etiology.

The three-dimensional geometry of conventional fixed prostheses complicates the study of the thermal cycling distortion in metal ceramic alloys. Any explanation of the etiology of thermal cycling distortion in metal ceramic restorations must account for the observed magnitude, timing, and direction of the deformation. The simplified experimental geometry developed in Part I was applied to elucidate the etiologic factors involved in metal ceramic deformation. Techniques to minimize the thermal cycling distortion were also studied. It was found that all of the significant distortion occurred during the first thermal cycling of the alloy (oxidation) and that no distortion resulted from the application of body porcelain. The specimens that were cold worked and then oxidized had significantly more distortion than any other group. A significant reduction in distortion was observed when the initial thermal cycling was completed before the specimens were cold worked. It was determined that the release of casting- and cold working-induced stresses had a synergistic effect.

Aluminum Oxide↗
PubMed1991

Comparison of condylar control settings using three methods: a bench study.

Articulators that program eccentric condylar pathways minimize occlusal adjustments of dental prostheses. This bench study compared three groups of methods for recording the immediate Bennett shift and the protrusive condylar path of the mandible. The experimental design restricted the variable associated with these methods. The various methods for recording protrusive excursions from best to worst were: (1) electronic pantography (Denar); (2) mechanical pantography (Denar); and (3) simplified mandibular motion analyzers (Whip-Mix and Denar). The methods of recording immediate side shift from best to worst were: (1) electronic pantograph; (2) polyether interocclusal records; (3) mechanical pantography (Denar) and simplified mandibular motion analyzer (Panadent); (4) simplified mandibular motion analyzer (Whip-Mix and Denar); and (5) zinc oxide interocclusal records.

Analysis of Variance↗
PubMed1991

Cloning and characterization of the scalloped region of Drosophila melanogaster.

Viable mutants of the scalloped gene (sd) of Drosophila melanogaster exhibit defects that can include gapping of the wing margin and ectopic bristle formation on the wing. Lethal sd alleles characterized in the present study now implicate this gene in a genetic function essential for normal development. In order to further characterize the developmental role of this gene, we have undertaken to clone and characterize the region where sd maps. A P[ry+] transposon insertion at 13F associated with sd[ry+2216] served as the starting point for a 42-kb chromosomal walk. Molecular lesions associated with viable and lethal sd alleles were characterized by genomic hybridization analysis as a means of defining the extent of the gene. DNA rearrangements associated with 11 viable sd alleles map to a 2-kb interval which appears to be a "hot spot" for P element activity. Four of five recessive lethal sd mutations were mapped by denaturing gradient gel electrophoresis to a region 12-14 kb away from the region of viable lesions. In a sd+ genotype, at least two structurally related and developmentally regulated transcripts hybridize to the genomic region where several sd lethal alleles have been localized. A viable mutation, sd58, used for comparison in the transcript analysis, makes at least two slightly smaller transcripts that also hybridize to this region. Preliminary analysis of cDNA clones has identified three structurally related transcripts that hybridize to this genomic region. The 5' end of these transcripts extends into the 2-kb genomic region wherein DNA rearrangements were seen in the P element rearrangements. We favor the view that the transcripts represented by these cDNA clones are products of the sd gene. If this is true, the sd gene would include genomic sequences extending over at least 14 kb of the described chromosomal walk, and would appear to be subject to alternative splicing.

Alleles↗
PubMed1990

Evaluation of the relationship between anterior and posterior functionally disclusive angles. Part II: Study of a population.

The lateral and protrusive anterior and posterior disclusive angles were recorded and measured by using a newly developed method (part I) on a population of 50 subjects (mean age 27.2 years). All of the subjects had natural anterior teeth, 45 had a clinically acceptable anterior guidance, and the remaining five had a partial (unilateral) or total lack of anterior guidance. A statistically significant correlation between the anterior and posterior disclusive angles was not found either in the entire population (n = 50) or in the stratum of the population that consisted of subjects with a clinically acceptable anterior guidance (n = 45). The Angle class of occlusion or anterior deep bite malocclusion were not identified as possible confounders or effect modifiers. This study suggested that the intra-articular tissues of the temporomandibular joint played a significant role in the relationship of their osseous components. Practical guidelines to determine anterior guidance could be established by using population means.

Adult↗
PubMed1990

Comparison of conventional paint-on die spacers and those used with the all-ceramic restorations.

The study compared the thickness of conventional (Tru-Fit and Belle de St. Claire) and all-ceramic (Dicor and Cerestore) die spacers. Three coats of Tru-Fit, two coats of Belle de St. Claire, and two coats of Cerestore die spacers provided a 25 microns thickness. A single coat of the Dicor spacer resulted in a 37 microns layer. A significantly thinner layer occurred at the convex occlusal line angles for all of the materials tested. This could impede the flow of the luting agent at the time of cementation.

Aluminum Oxide↗
PubMed1990

Evaluation of the relationship between anterior and posterior functionally disclusive angles. Part I: Literature review, instrumentation, and reproducibility.

Authors are not in agreement concerning the existence of an anatomofunctional interrelationship between condylar and anterior guidances of the mandible in humans. Current literature consists either of speculative statements or studies omitting the role of the meniscus. This article (part I) describes a unique method to correlate the condylar functional anatomy to the lingual inclines of the maxillary anterior teeth (anterior guidance) and acknowledges all components of the temporomandibular joint. The measurements obtained by means of this method were reproduced five different times on five different subjects, making possible a valid statistical analysis of the correlation between condylar and anterior guidances of the mandible (part II).

Analysis of Variance↗
PubMed1990

The hinged-clasp assembly removable partial denture.

Severe undercuts and malpositioning of teeth can create problems with the path of insertion of removable partial dentures. Prostheses that have conventional clasp designs are not well-suited for these situations because a common path of placement must exist for all clasps. A technique that incorporates a hinged-clasp assembly to overcome this problem is described.

Dental Abutments↗
PubMed1989

Fracture-surface analysis of dental ceramics.

This study demonstrated that quantitative fractography can be used to study failed aluminous and glass-ceramic central porcelains. Fracture surfaces of DICOR and Vitadur-N core porcelain modulous-of-rupture bars were studied to identify fracture mirror features useful in (1) locating the source of fracture and (2) calculating the stress at fracture in clinically failed restorations. The morphology of fracture surfaces results from events related to the initiation and propagation of the crack front during failure. Modulus-of-rupture testing was performed in four-point bending. Fracture surfaces were studied by scanning electron microscopy. The mean fracture stress for the Vitadur-N porcelain was 94.7 +/- 12.4 MPa (13,730 psi); for DICOR the fracture stress was 55.4 +/- 10.6 MPa (8,030 psi). The standard quantitative fractography relationship between in mirror radius and ln fracture stress was followed for both materials. This quantitative fractography relationship was used to calculate the in vivo stress at failure in a clinically fractured DICOR molar crown. Five clinically failed DICOR crowns were seen to fail from the internal surface.

Aluminum↗
PubMed1989

Nondestructive, three-dimensional internal fit mapping of fixed prostheses.

Crown fit may be three-dimensionally mapped by using a nondestructive optical technique. Reflected light transmission through thicknesses of a colored impression material was shown to follow the Beer-Lambert relationship over a range of approximately 10 to 300 microns, a useful range of interest for study of cement layer thickness. Control thicknesses of impression material were first formed between the measuring platens of a micrometer, and light transmission values (relative reflections) were measured through these control thicknesses of impression material held against air-abraded, noncast gold alloy. Relative reflection values were similarly measured from impression material formed inside cast gold crowns seated on their respective dies and these values were plotted against direct thickness measurements by using the Beer-Lambert relationship. It was established that the micrometer-produced control specimens yielded a valid standard curve for use with the cast gold crowns. Precementation space measurements determined photometrically were found to correlate significantly (r = 0.72, p less than 0.001) with zinc phosphate cement thickness measured on subsequently cemented and cross-sectioned crowns. A three-dimensional representation of the precementation space inside one crown was developed after mapping of 45 points in less than 5 minutes.

Cementation↗
PubMed1989

A comparative strength study of metal ceramic and all-ceramic esthetic materials: modulus of rupture.

The modulus of rupture for three metal ceramics and five all-ceramic substructures with and without veneer porcelain was compared. Support of the veneer porcelain was directly related to the modulus of elasticity and not to the strength of the substructure material. The higher the modulus of elasticity, the greater was the strength of the veneered restoration. For each 1 x 10(6) increase in the modulus there was a corresponding 1040 psi increase in strength. The veneered all-ceramics had 45% to 70% of the strength of the metal ceramic restorations. The veneered nonprecious and gold-palladium metal ceramic test bars were significantly stronger than any veneered all-ceramic material.

Aluminum Oxide↗
PubMed1989

Evaluation of surface roughness and polishing techniques for new ceramic materials.

The surface roughness of crown and bridge materials should be minimized to obtain optimal biocompatability. This study used scanning electron microscopy to evaluate the effect of polishing procedures on two all-ceramic crown materials (Dicor and Cerestore). The "as formed," unpolished specimens of both Dicor and Cerestore materials presented a rough surface. It was found that any attempt to polish the Cerestore coping material resulted in an extremely rough surface. Finishing of the Dicor ceramic resulted in a smoother but pitted surface. Polishing of both ceramic materials resulted in a surface that was rougher than the glazed metal ceramic controls. The smoothest finish was obtained when the glazed veneer (Cerestore) and shading porcelain (Dicor) were applied to the all-ceramic materials.

Aluminum↗
PubMed1989

Use of an elastomeric material to improve the occlusal seat and marginal seal of cast restorations.

A method to improve the fit of castings by the use of a light-bodied condensation silicone impression material was tested. Eighteen-full coverage castings were made on individual resin dies and divided into two groups. The experimental group was adjusted internally to a uniform precementation space by using the silicone impression material as a disclosing agent for binding of the castings on the axial or occlusal walls. Measurements of marginal fit were made with a light microscope using a filar eyepiece both externally and internally by sectioning after cementation with a zinc phosphate cement. Results demonstrated a significant improvement in marginal seal and occlusal seating in the experimental group compared with the control group. The condensation silicone material proved to be an appropriate research tool for nondestructive, three-dimensional evaluation of the postcementation space and offers a new method of evaluation of cement thickness because seating was found to be not significantly different from that with zinc phosphate cement.

Cementation↗
PubMed1989

Null mutation of copper/zinc superoxide dismutase in Drosophila confers hypersensitivity to paraquat and reduced longevity.

The role of copper/zinc-containing superoxide dismutase (cSOD; superoxide:superoxide oxidoreductase, EC 1.15.1.1) in metabolic defense against O2 toxicity in Drosophila is examined through the properties of a mutant strain carrying a cSOD-null mutation, cSODn108. Homozygotes are viable as larvae, which indicates that cSOD is not essential for cell viability per se. cSODn108 confers recessive sensitivity to the superoxide anion (O2-)-generator paraquat and to the transition metal compound CuSO4, which indicates that the cSOD-null condition in fact leads to impaired O2- metabolism. The primary biological consequences of the reduced O2- dismutation capacity of cSODn108 Drosophila are realized in the adult as infertility and reduction in life-span. We conclude that the infertility and reduced life-span of cSODn108 adults arise as a consequence of the reduced capacity of embryos, larvae, and pupae to adequately protect developing preimaginal cells from O2- -initiated cytotoxic damage.

Animals↗
PubMed1988

Evaluation of the fit and strength of an all-ceramic fixed partial denture.

A laboratory investigation of the fit and strength of three-unit all-ceramic FPDs was performed with a metal-ceramic FPD control. The conclusions were: 1. No difference was found between the marginal seal of the metal-ceramic and all-ceramic FPDs. 2. The all-ceramic FPDs had a more uniform cement space and their occlusal seat was significantly (99.9%) better than the metal-ceramic restorations. 3. The metal-ceramic FPDs were significantly stronger than the all-ceramic FPDs. 4. Load calculations suggest that short-span all-ceramic FPDs may be strong enough to resist normal masticatory forces for selected patients. However, generalized usage will probably result in an unacceptable failure rate.

Aluminum Oxide↗
PubMed1986

Effects of butylated hydroxytoluene on membrane lipid fluidity and freeze-thaw survival in mammalian cells.

Butylated hydroxytoluene (BHT) increases the fluidity of membrane lipids in the hydrocarbon but not the polar regions, as measured by electron spin resonance spin label probes. BHT also sensitizes nucleated mammalian cells to freeze-thaw damage as measured by colony formation survival assays. Furthermore, the membranes of BHT-exposed cells are more susceptible to physical stress, as reflected by the BHT-induced sensitization to hypotonic stress. Since others have shown that BHT induces hexagonal phase lipids in lipid bilayers, this phenomenon may also influence the above survival results.

Animals↗