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Biomedical subjects

G R Hoffman

Publications and source records attributed to G R Hoffman.

29 records · Page 2Linked to original sources
PubMed1995

The stability of facial osteotomies. 3. Chin advancement.

Surgical repositioning of the chin can be used to improve function and aesthetics. The most commonly employed technique involves a sectioning of the lower border of the anterior mandible, thus allowing a sliding movement of the chin. It is generally accepted that the maintenance of a soft tissue attachment provides a clinically stable skeletal and predictable soft tissue change with minimal postoperative osseous resorption. Part 3 of this series of papers addresses the issues of treatment planning, surgical technique and clinical indications for undertaking advancement genioplasty. These, combined with the surgeon's artistic sense of facial harmony, are pre-conditions necessary for successful chin surgery.

Adolescent↗
PubMed1995

The stability of facial osteotomies. 4. Maxillary and mandibular (with or without chin) advancement with rigid internal fixation.

The short-term (6 weeks postoperative) and long-term (12 months postoperative) horizontal skeletal stability of combined maxillary and mandibular advancement was evaluated by cephalometric analysis of 15 patients. The mean horizontal advancement of the maxilla was 5.84 mm. Six weeks later a mean horizontal relapse of 0.03 mm (0.05%) was identified. The mean horizontal relapse at long-term follow-up was 0.59 mm (10.1%). The mean horizontal advancement of the mandible was 12.35 mm at menton and 12.65 mm at pogonion. At 6 weeks, mean horizontal relapse, respectively at the above landmarks, was 0.11 mm and 0.21 mm (1.3%). The mean horizontal relapse at long-term follow-up was 2.19 mm and 1.98 mm (16.6%) respectively for the same landmarks. Subjectively and objectively, improvements were seen in facial aesthetics and dental occlusion. The results indicate that rigid fixation of osteotomies undertaken to correct 'horizontal facial deficiency' is a surgically predictable and relatively stable procedure when reviewed up to 12 months after surgery.

Adolescent↗
PubMed1995

The stability of facial osteotomies. 1. The evolution of maxillary, mandibular and chin osteotomies.

Surgical repositioning of the dento-skeletal components of the face, combined with appropriate orthodontic treatment, can be used to improve function and aesthetics. An extensive number of osteotomies are performed within the maxillofacial region. The most common of these are the Le Fort I osteotomy of the maxilla, the bilateral sagittal split osteotomy of the mandibular ramus, and the horizontal osteotomy of the anterior mandible. The attainment of three dimensional stability following corrective jaw surgery continues to be a major problem in the post-surgical period, in spite of the widespread adoption of rigid internal osteosynthesis. The evolution of these osteotomies to advance dento-skeletal components is traced from their inception to the present day and the concept of stability is explained (Part I). This serves as a prelude to an investigation into the stability of these procedures, undertaken in isolation or combination, to advance selected segments of the mid- and lower face (Parts 2, 3, 4, 5).

Chin↗
PubMed1994

The stability of facial advancement surgery (in the management of combined mid and lower dento-facial deficiency).

The short-term (6 weeks postoperative) and long-term (12 months postoperative) skeletal stability of combined maxillary and mandibular advancement was evaluated by cephalometric analysis in 15 patients. The mean horizontal advancement of the maxilla was 5.84 mm. 6 weeks later a mean relapse of 0.03 mm (0.5%) was identified. The mean relapse at long-term follow-up was 0.59 mm (10.1%). The mean horizontal advancement of the mandible was 12.35 mm at menton and 12.65 mm at pogonion. At 6 weeks, mean horizontal relapse, respectively at the above landmarks, was 0.11 mm and 0.21 mm (1.3%). The mean relapse at long-term follow-up was respectively 2.19 mm and 1.98 mm (16.9%). Subjectively and objectively improvements were seen in facial aesthetics and dental occlusion. The results indicated that rigid fixation of osteotomies undertaken to correct 'horizontal facial deficiency' is a surgically predictable and relatively stable procedure when reviewed up to 12 months after surgery.

Adolescent↗
PubMed1994

Cephalometric alterations following facial advancement surgery. 2. Clinical and computerised evaluation.

Part 1 of this investigation identified an established patient cohort whose treatment is best suited to combined surgical-orthodontic correction of dento-facial deformity. This is as opposed to the attempted correction of the problem by an orthodontics-only or a surgery-only approach. Experienced surgeons will subjectively assess facial aesthetics and devise surgical treatment objectives in terms of the beneficial soft tissue improvements derived from dento-skeletal manipulation. None the less, traditional and soft tissue cephalometric parameters remain a guideline in the diagnostic phase of treatment. Part 2 of this investigation compared pre and postoperative clinical and computerised evaluations of patients diagnosed as having combined mid and lower dento-facial deficiency with Class 1 dento-skeletal parameters.

Cephalometry↗
PubMed1994

Cephalometric alterations following facial advancement surgery: 1. Statistical evaluation. A review of aesthetic evaluation of the face and an attempt to assess treatment validity.

Simultaneous maxillary and mandibular advancement surgery, with or without chin advancement, was performed to correct combined mid and lower dento-facial deficiency, the diagnosis of the deformity in this study being based purely on a clinical analysis. The purpose of this investigation was to test the validity of the diagnosis, surgical treatment objective, and subsequent surgical result, by comparing pre- and postoperative cephalometric data with 'Class I dento-skeletal parameters', derived from three different analyses. Lateral cephalometric radiographs were obtained from patients who had undergone 'facial advancement surgery'. The radiographs were subjected to cephalometric analysis in an attempt both to quantify and qualify the skeletal and dental changes that had taken place, following surgical correction of 'horizontal facial deficiency'. A statistical analysis was then used to assess postoperative change to normal, and how the proportion of patients so defined varied by method. All patients had optimal improvements in aesthetics, and in dental occlusion. Dento-skeletal changes remained stable at 12 months post surgery. In spite of these successes, the results of this investigation showed that no greater than 50% of preoperative abnormal measurements per patient were normalised by surgery.

Adolescent↗
PubMed1983

Genetic instability associated with the aroC321 allele in Salmonella typhimurium involves genetic duplication.

Strains of Salmonella typhimurium that contain the aroC321 allele require phenylalanine, tyrosine, and tryptophan for growth but revert to tryptophan-prototrophy at high frequencies (about 10(-4) per cell plated). The Trp+ derivatives remain auxotrophic for phenylalanine and tyrosine and are genetically unstable, in that they readily give rise to cells that require all three aromatic amino acids. On the basis of growth characteristics and genetic instability, it has been proposed that reversion to tryptophan-prototrophy in aroC321 strains occurs by genetic duplication. This paper provides genetic evidence in support of that hypothesis. The data indicate, moreover, that the tryptophan prototrophs contain a duplication that extends at least from glpT to xyl, a region of greater than 30% of the Salmonella chromosome. The aroC locus is found within the duplicated region, and aroC321/aroC321 merodiploids apparently grow as tryptophan prototrophs because of a gene-dosage effect.

Chromosome Mapping↗
PubMedDate not supplied

Genetic duplications in bacteria and their relevance for genetic toxicology.

Tandem genetic duplications of various lengths occur at high frequency and at many chromosomal locations in bacteria. Most duplications are formed and lost by recombinational mechanisms. Since they readily give rise to haploid segregants, duplications are characteristically unstable. Various selection procedures permit measurements of duplication frequencies, and several mutagens have been shown to induce the formation of duplications in haploid bacteria and the loss of duplications from merodiploid bacteria. Although the data base is not extensive, it includes agents that interact with DNA by a variety of molecular mechanisms. Grounds on which the induction of genetic duplications in bacteria can be relevant for genetic toxicology are discussed.

Bacteria↗
PubMedDate not supplied

The super PET 3000-E: a PET scanner designed for high count rate cardiac applications.

OBJECTIVE: Mathematical models for the delineation of regional myocardial perfusion and metabolism with PET require faithful reconstruction of arterial and myocardial time-activity curves following administration of radiotracers. High temporal resolution is often required in such measurements. Many commercially available tomographs exhibit long dead times that limit their count rate capabilities. To overcome these limitations, we developed and tested a whole-body tomographic device (Super PET 3000-E) with high count rate capabilities. The use of cesium fluoride scintillation detectors coupled with a one-to-one detector photomultiplier configuration reduces the system resolving and dead times. MATERIALS AND METHODS: The Super PET 3000-E was subjected to a series of tests with phantoms to determine its resolution, sensitivity, linearity, count rate capabilities, dead time, and random coincidence contribution. RESULTS: The system sensitivity is 136 kcounts/s/microCi/ml and its transverse and longitudinal resolutions are 8.5 and 10.5 mm full width at half-maximum, respectively. The system can easily record a total event rate of 2.0 Mcounts/s with minimal dead time loss and excellent linearity. CONCLUSION: The system fulfills its design goals and allows the very high count rate performance needed for the application of the physiological models used in our cardiac studies.

Algorithms↗