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Biomedical subjects

S E Eckert

Publications and source records attributed to S E Eckert.

At least 19 recordsLinked to original sources
PubMed2001

Sexual diploids of Aspergillus nidulans do not form by random fusion of nuclei in the heterokaryon.

The sexual stage of Aspergillus (Emericella) nidulans consists of cleistothecia containing asci, each with eight ascospores. The fungus completes the sexual cycle in a homokaryotic or a heterokaryotic mycelium, respectively. The common assumption for the last 50 years was that different nuclear types are not distinguishable when sexual development is initiated. When cultured on a medium limited for glucose supplemented with 2% sorbitol, sexual development of A. nidulans is slowed and intact tetrads can be isolated. Through tetrad analysis we found that unlike haploid nuclei fuse preferentially to the prezygotic diploid nucleus. When heterokaryons are formed between nuclei of different genetic backgrounds, then recombinant asci derived from opposite nuclei are formed exclusively. Strains in the same heterokaryon compatibility group with moderate differences in their genetic backgrounds can discriminate between the nuclei of a heterokaryon and preferentially form a hybrid diploid nucleus, resulting in 85% recombinant tetrads. A. nidulans strains that differ at only a single genetic marker fuse the haploid nuclei at random for formation of diploid nuclei during meiosis. These results argue for a genetically determined "relative heterothallism" of nuclear recognition within a heterokaryon and a specific recruitment of different nuclei for karyogamy when available.

Aspergillus nidulans↗
PubMed2000

Developmental and metabolic regulation of the phosphoglucomutase-encoding gene, pgmB, of Aspergillus nidulans.

We have isolated the pgmB gene from Aspergillus nidulans, which encodes a phosphoglucomutase, one of the key enzymes in carbohydrate metabolism. The pgmB gene is located on chromosome VII and its ORF encodes 557 amino acids. Mutant phenotypes were analysed by expression of high levels of pgmB antisense RNA, which lead to a loss of detectable levels of sense RNA. Under conditions of antisense RNA expression, a 30% reduction in the growth rate was observed in comparison to wild-type. On the enzyme level, expression of pgmB antisense RNA resulted in a 35% reduction in total phosphoglucomutase activity. Two pgmB mRNAs were observed under all conditions tested and differ with respect to the location of the poly(A) site. Expression of pgmB driven by the GAL1 promoter in Saccharomyces cerevisiae complemented the growth phenotype of a pgm2delta mutant strain and suppressed the sensitivity of a gcn4delta mutant strain to amino acid starvation in the presence of galactose. Cultivation of A. nidulans in the presence of glucose or galactose as carbon source did not affect transcription of pgmB. However, amino acid starvation conditions resulted in a six-fold reduction in the level of pgmB mRNA, while genes for amino acid biosynthesis showed increased transcription. Transcription of pgmB was low during hyphal growth and in the sexual phase of development, but was significantly increased during the asexual stage of the A. nidulans life cycle.

Amino Acid Sequence↗
PubMed2000

The tryptophan synthase-encoding trpB gene of Aspergillus nidulans is regulated by the cross-pathway control system.

The tryptophan synthase-encoding gene, trpB, of Aspergillus nidulans was cloned and characterized. It was mapped to chromosome I, between the gene medA, which is required for sexual and asexual development, and an ORF encoding a protein with significant similarity to subunit B of vacuolar ATP synthases. The 5' untranslated region was found to be at least 142 nucleotides (nt) long, the poly(A) addition site was localized at position + 216 relative to the stop codon by sequencing of several independent cDNA clones. The trpB gene contains two exons separated by an intron of 105 nt, which is located close to the 5' end of the ORF. Directly upstream of the transcriptional start site, one well conserved potential binding site for the cross-pathway control transcriptional activator CPCA was found. The level of trpB transcript was shown to be regulated by cross-pathway control. A knockout mutant for trpB displays tryptophan auxotrophy, no trpB transcript is detectable, and development is perturbed to an extent that is dependent on the amount of tryptophan added to the medium. The trpB gene encodes a protein of 723 amino acids, with a calculated molecular weight of 77.6 kDa. The deduced amino acid sequence shows 72.6% similarity to the tryptophan synthase of Neurospora crassa. Most amino acid residues essential for catalytic activity in the tryptophan synthase of Salmonella typhimurium are conserved. The linker region joining the two domains of the enzyme is 13 residues longer than the longest connector found so far in tryptophan synthases from fungi.

Amino Acid Sequence↗
PubMed2000

How to evaluate a diagnostic test.

Tests are used in dentistry to establish, confirm, or reject the clinical impression of a diagnosis. Not all tests are equal in their ability to establish a diagnosis, with some tests demonstrating positive results when no disease is present (false positive) or negative results when disease is present (false negative). Using simple mathematical computations, it is possible to determine the extent to which a test can reliably establish the presence or absence of disease. This article describes the concepts of sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratios through the evaluation of a clinically relevant paper on vital staining for oral carcinoma. This article also describes methods for literature evaluation to determine whether a test conveys meaningful diagnostic information.

Carcinoma↗
PubMed1999

Sexual development of Aspergillus nidulans in tryptophan auxotrophic strains.

The interplay between sexual development and amino acid biosynthesis in the ascomycete Aspergillus nidulans was studied. The growth and differentiation of four tryptophan auxotrophic strains that are unable to regulate their tryptophan biosynthesis, were examined. These strains are sterile on medium containing low tryptophan concentrations. Fruitbody formation was restored by supplementation with high concentrations of tryptophan and was promoted by supplementation with indole or auxin. Tryptophan supplementation resulted in auxin production of A. nidulans. Fertility of ascospores of the tryptophan auxotrophic strains could only be partially re-established. trpC transcript levels and enzyme activities remained stable in cleistothecia and conidiophore extracts as compared to those of mycelium, while levels of gene transcripts involved in glycolysis were lower in fruitbodies and conidiospores. Auxotrophic strains unable to form fruitbodies at intermediate amino acid supplementation levels turned on the cross-pathway regulatory system that is induced by amino acid starvation. We conclude that there is a connection between the genetic network of cross-pathway control and sexual development in A. nidulans.

Aspergillus nidulans↗
PubMed1998

Retrospective review of 1170 endosseous implants placed in partially edentulous jaws.

STATEMENT OF PROBLEM: Implant-supported restorations in the partially edentulous jaw have been performed at the Mayo Clinic for more than 10 years. Clinical performance of the implants and the prostheses should be reported to ensure effectiveness of this procedure. PURPOSE: This retrospective study described results for implant survival, implant fracture rate, prosthetic complications, and design changes that may impact these results. MATERIAL AND METHODS: A retrospective chart review was conducted of all registered implant patients in a large multispecialty medical center. Patients with a partially edentulous jaw who had received endosseous implants to support and retain dental prostheses were included in this review. Implant survival and fracture, prosthetic complications, and demographic data were recorded and analyzed through Kaplan-Meier methods. RESULTS: A total of 1170 implants were placed in four anatomic locations: anterior maxilla, posterior maxilla, anterior mandible, or posterior mandible. Location of implants was shown to have no effect on implant survival (p = 0.7398), implant fracture rates (p = 0.2385), screw loosening (p = 0.8253), or screw fracture (p = 0.2737). Development of new restorative components has resulted in significantly better rates of implant survival without fracture (p = 0.0054), screw function without loosening (p < 0.0001) and screw function without fracture (p = 0.0013). Implant survival seems to have been improved with the new components (p = 0.0513). CONCLUSIONS: Implant survival in this study was independent of anatomic location of implants. Virtually all clinical performance factors were improved by design changes in implant restorative components that were brought to market in early 1991.

Adolescent↗
PubMed1997

Implant reconstruction in the posterior mandible: a long-term retrospective study.

STATEMENT OF PROBLEM: Because there is a lack of long-term data, it is unclear whether the determinants of implant and prosthesis survival include the location, angle, design, or number of implants and use of prosthesis cantilevers. PURPOSE: This retrospective study evaluated the long-term outcome, determinants of outcome, and the type and prevalence of prosthetic complications in a series of patients treated consecutively with Brånemark implants in the partially edentulous posterior mandible. MATERIAL AND METHODS: A total of 392 consecutively placed Brånemark implants were inserted in 152 partially edentulous patients and restored with 56 single-tooth and 168 fixed partial dentures restorations. RESULTS: The cumulative success rates of implants and prostheses were 89.0% +/- 0.03% and 81.9% +/- 0.03%, respectively, at 6 years, with no further decrease in success noted during the remainder of the 10-year study. Significantly fewer major complications were found in prostheses supported by one or more implants, located exclusively in premolar sites, versus prostheses supported by either molar implant(s) or both premolar and molar implants. In single-tooth restorations, fewer major complications were seen in the cemented restorations, compared with the screw retained. CONCLUSION: The results were strongly influenced by the phase of experience.

Adolescent↗
PubMed1997

Validation of dental implant systems through a review of literature supplied by system manufacturers.

STATEMENT OF PROBLEM: The use of endosseous implants to support and retain dental prostheses has become a routine treatment option in many dental practices. Although physical, mechanical, and chemical differences exist among implant systems, survival claims are similar. PURPOSE OF STUDY: This review solicited literature from six implant manufacturers that was thought, by their standards, to be pertinent to the validation of their implant system. METHODS: The literature was reviewed and categorized. CONCLUSION: On the basis of the literature supplied by the manufacturers, only one implant system demonstrated scientifically valid long-term success.

American Dental Association↗
PubMed1996

Endosseous implants in an irradiated tissue bed.

Endosseous implants have been placed at the Mayo Clinic Department of Dental Specialties for over 12 years. On the basis of the clinical success of the osseointegration program, the use of implants has been expanded to include placement into tissue beds that have been exposed to therapeutic radiation. This article details preliminary data regarding implant survival in the previously radiated tissue beds. Presurgical evaluation and surgical technique are described and postprosthetic reconstruction complications are also related. Consideration is given to the relatively small number of patients in this review. It is suggested that the results should be shared among multiple institutions to create a meaningful data bank.

Dental Implantation, Endosseous↗
PubMed1995

Food and Drug Administration requirements for dental implants.

The Food and Drug Administration (FDA) is a section of the Department of Health and Human Services of the United States Government, and its primary responsibility is to control the distribution of food, drugs, and medical devices within the country while ensuring public safety. The sale and distribution of dental implants is under the regulatory control of the FDA. Device classification, procedures for approval, and the current status of the approval process for endosseous implants are described in this article. The premarket approval procedure of the FDA is compared with the American Dental Association certification process. Issues related to the safety and effectiveness of dental implants are discussed.

American Dental Association↗
PubMed1994

Maxillofacial prosthetics: a preliminary analysis of Resource Based Relative Value Scale.

A study done by the American Academy of Maxillofacial Prosthetics to evaluate the Medicare Resource Based Relative Value Scale (RBRVS) as it relates to maxillofacial prosthetics. The method of RBRVS formulation is described. The degree of difficulty and treatment time were determined for nine Physicians' Current Procedural Terminology-edition 4 (CPT-4) codified maxillofacial procedures. A preliminary survey indicates that practice expense and malpractice expense ratios were 66% and 1%, respectively. Correlation of maxillofacial procedures to other medical procedures was not performed because an additional study with a greater sample size is needed.

Ear↗
PubMed1994

Maxillary antral and nasal one-stage inlay composite bone graft: preliminary report on 30 recipient sites.

A one-stage antral and nasal inlay composite bone grafting procedure is described. Preliminary statistical data (1 to 6 years experience with the procedure) is presented for 30 recipient sites in 20 patients. A complete bone-supported fixed prosthesis was used and has provided continuous function in all patients to date. Implant survival has approached that of implants placed in uncompromised maxillary or mandibular bone.

Bone Transplantation↗
PubMed1989

Patient evaluation and prosthodontic treatment planning for osseointegrated implants.

This article describes the pertinent medical and dental indications and contraindications for implant-supported prostheses. The importance of a thorough clinical investigation as well as the evaluation of appropriate radiographs and diagnostic casts prior to surgical intervention is emphasized. The cooperation of the surgeon and prosthodontist is essential for implant success; their appropriate roles are discussed. The various prosthetic options are evaluated with emphasis on the advantages and disadvantages of each. Those factors that create the ideal implant candidate are reviewed along with corrective measures that would be required to improve the condition of those patients who are not ideal candidates for implants.

Bone Transplantation↗
PubMedDate not supplied

Analysis of surgical referral patterns for endosseous dental implants.

Endosseous implants have traditionally been surgically placed by oral and maxillofacial surgeons, periodontists, and general practitioners. The purpose of this study was to examine surgical referral patterns for patients receiving implants in the treatment of partial edentulism. The records of 542 patients who received 1,313 implants between 1993 and 1997 were analyzed. Data relative to anatomic area, patient demographics, type of implant system, and any complication encountered were collected. Surgical cohorts were compared using Wilcoxon's rank-sum or chi-square tests, and complication rates were estimated using survival analysis methods. Results indicate no significant difference (P > .05) between cohorts with regard to placement of implants in the anatomic locations of the anterior mandible, anterior maxilla, posterior mandible, and posterior maxilla. Patient demographic information was not statistically different, with the exception of mean patient age, where oral and maxillofacial surgeons have been younger patients (P < .0001). Relatively few complications were seen, with no significant difference in complications rates between cohorts (P > .05). The type of implant system used showed no significant difference with respect to anatomic location or complication occurrence (P > .05). This study indicates that implant surgical referral patterns were similar in this setting between periodontal and oral and maxillofacial surgeons, with the only difference being a tendency to refer younger patients to the oral surgeons.

Adolescent↗
PubMedDate not supplied

Maxillary antral-nasal inlay autogenous bone graft reconstruction of compromised maxilla: a 12-year retrospective study.

During a 12-year period (1984-1996), 118 maxillary inlay autogenous bone grafts and 248 commercially pure titanium threaded root-form endosseous implants were placed in 54 consecutively treated patients with compromised maxillary bone. In this retrospective clinical study, 3 groups of patients were reviewed, group selection being based on anatomic location and surgical access to the recipient site. Group 1 included patients with bone grafts placed in the antrum floor via an intraoral antrostomy exposure, group 2 included patients with bone grafts placed in the nasal floor via an anterior intraoral nasotomy exposure, and group 3 included patients with bone grafts placed in the antral and nasal floor via an intraoral Le Fort I osteotomy downfracture exposure. Each patient received an implant-supported dental prosthesis. For the combined 3 groups, survival rates were 87% for endosseous implants and 100% for autogenous bone grafts. The success rate for the dental prostheses in the 3 groups was 95%. Sixty-nine dental prostheses functioned a mean of 57.1 months, whereas 3 prostheses required remaking because of implant loss. Of the medical and mechanical risk factors tabulated in this study, current use of nicotine, history of sinusitis, molar site implant placement, and shorter implant lengths had the most influence on implant failure.

Adolescent↗
PubMedDate not supplied

Retrospective review of grafting techniques utilized in conjunction with endosseous implant placement.

Bone resorptive patterns may prevent the ideal placement of endosseous implants. Numerous techniques have been described to create a more favorable surgical site for implant placement. This retrospective review was conducted to determine the frequency of need for implant site preparation in an outpatient clinical setting. In addition, different techniques of surgical site preparation were evaluated to determine their frequency of use and surgical outcome. A history review was conducted of all consecutively treated partially edentulous patients between January 1993 and December 1997. This review evaluated the number of implants placed, the age and gender of patient, the type of graft used, and the status of the implant. In all, 542 patients were seen in this time interval, with a total of 1,313 implants placed. Implant site preparation was needed in 4.4% of the patients, with the requirement for grafts occurring more frequently in the maxilla. Implant site preparation is a relatively infrequent requirement in the general population. Grafts are required more frequently in the maxilla than in the mandible. Complications following grafting were relatively infrequent and were not severe.

Age Factors↗
PubMedDate not supplied

Analysis of incidence and associated factors with fractured implants: a retrospective study.

Osseointegrated threaded titanium screw-type implants rarely lose integration after the first year of clinical function. Implant failure can occur for other reasons, with implant fracture being one of the major reasons for late failure. The purpose of the present study was to determine the incidence of implant fracture in completely edentulous and partially edentulous arches and to determine what factors may predispose an implant to a higher fracture risk. A retrospective evaluation of 4,937 implants was performed to determine the incidence of and factors common to fractured implants from a sample of implants placed and restored in one institutional setting. Based on the results of this study, the following observations were made: implants fracture at similar rates in the maxilla as in the mandible (0.6%), implant fractures occur more frequently in partially edentulous restorations (1.5%) than in restorations of completely edentulous arches (0.2%), all observed fractures occurred with commercially pure 3.75-mm-diameter threaded implants, and prosthetic or abutment screw loosening preceded implant fracture for the majority of the implants. More studies would be helpful to further explore the relationship and progression of factors associated with implant fracture.

Dental Implantation, Endosseous↗