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Biomedical subjects

G Wall

Publications and source records attributed to G Wall.

At least 19 recordsLinked to original sources
PubMed2001

Radiographic stereophotogrammetric evaluation of intersegmental stability after mandibular sagittal split osteotomy and rigid fixation.

PURPOSE: The purpose of this study was to determine if rigid fixation with bicortical screws and/or miniplates with monocortical screws prevent mobility at the osteotomy site after bilateral mandibular sagittal split osteotomy. PATIENTS AND METHODS: Three metal bone markers were inserted in the proximal and the distal segments of the mandible during the sagittal split operation in 10 patients. These served as measurement points in postoperative follow-up by radiographic stereophotogrammetry. The patients were examined at intervals during the first postoperative year. At each examination, 2 sets of radiographic stereograms were obtained: 1 in rest position and 1 with stress applied to the osteotomy sites. The difference in the position of the proximal segment in relation to the distal segment between the 2 sets of stereograms was recorded. Findings greater than 0.4 degrees and 0.2 mm change indicated true displacement of the bone segments. RESULTS: Immediately after surgery, mobility at of the osteotomy site(s) was found in 8 of 10 patients, and after 1 year it was still present in 4 patients. CONCLUSIONS: Fixation with bicortical screws or miniplates and monocortical screws does not prevent mobility at the osteotomy site after sagittal split osteotomies. This mobility may remain as long as 1 year after surgery. The term "rigid fixation" is thus not a proper term for this kind of fixation.

Adolescent↗
PubMed2001

Postoperative migration at the individual osteotomy site following sagittal split ramus osteotomy: a stereometric radiographic study.

The aim of the present study was to evaluate whether migration occurs at individual osteotomy sites following sagittal split osteotomy of the mandible stabilized with rigid internal fixation, and if it occurs, how long it lasts. In 10 consecutive patients operated with bilateral sagittal split osteotomies, postoperative migration, defined as displacement of the proximal segments in relation to the distal over time, was studied 3-dimensionally by means of stereometric radiography. Follow-up was performed with stereometric radiographs obtained at intervals from 2 days until 1 year after surgery. During the 1-year observation period, migration at one or both of the osteotomy sites was found at some stage in all of the patients and in as many as 4 patients during the final 6 months. It is concluded that rigid internal fixation, as performed in the present study, does not prevent postoperative migration at the osteotomy. Furthermore, stable bone union at the osteotomy site appears to be a slower process than previously expected, thus emphasizing the importance of follow-up procedures to prevent relapse.

Adolescent↗
PubMed1998

Postoperative migration of the osteotomy segment stabilized by titanium miniplate osteosynthesis following Le Fort I osteotomy: an x-ray stereometric study.

The aim of the present study was to evaluate whether titanium miniplate fixation prevents postoperative migration of the osteotomy segment following Le Fort I osteotomy and, if not, to evaluate whether postoperative migration varies with the direction and amount of surgical repositioning. In 10 consecutive patients who received Le Fort I osteotomies, postoperative migration of the osteotomy segment was studied in a three-dimensional system by means of x-ray stereometry. Surgical repositioning was recorded by cephalometry in lateral head films obtained before surgery and at 2 days postoperatively. X-ray stereograms were obtained at intervals from 2 days to 1 year after surgery. During the 1-year observation period, significant postoperative migration of the osteotomy segment was found at some stage in nine patients. No correlation between the amount of surgical repositioning and postoperative migration was found. However, a tendency toward superiorly directed postoperative migration of the osteotomy segment, independent of the direction of surgical repositioning, was observed. It is thus concluded that titanium miniplates do not prevent postoperative migration of the osteotomy segment. The weak correlation between the amount of surgical repositioning and postoperative migration of the osteotomy segment indicates that predictions of individual outcomes of surgical corrections are uncertain.

Adolescent↗
PubMed1997

FORUM: Is Ecotourism Sustainable?

/ It is legitimate to ask whether and in what form tourism might contribute to sustainable development. This is not the same as sustainable tourism which, as a single-sector approach to development, may overlook important linkages with other sectors. If tourism is to contribute to sustainable development, then it must be economically viable, ecologically sensitive and culturally appropriate. Ecotourism is often advocated as being a sustainable form of tourism but imprecision in terminology clouds basic issues and there are strong economic, ecological, and cultural reasons for believing that, even in its purest forms, ecotourism is likely to present substantial challenges to destination areas, particularly if it competes for scarce resources and displaces existing uses and users. Sustainable tourism and ecotourism are not synonyms, many forms of ecotourism may not be sustainable, and if ecotourism is to contribute to sustainable development, then careful planning and management will be required.KEY WORDS: Ecotourism; Sustainable development; Development; Tourism

Journal Article↗
PubMed1996

Accuracy of cephalometry in measurements of postoperative migration of the maxilla after Le Fort I osteotomy.

The aim of the study was to evaluate the accuracy of cephalometry when point A is used to assess the migration of the maxilla following Le Fort I osteotomy. In 10 consecutive patients, postoperative migration of the maxilla was studied by means of cephalometry and x-ray stereometry. Because the precision and accuracy of the x-ray stereometric method are known to be high, this method was used as a norm against which the results obtained by cephalometry were compared. The values of postoperative migration obtained by cephalometric analysis exceeded the corresponding values obtained by x-ray stereometry in all but four recordings. In 16 of 40 recordings, migration in opposite directions was found. The differences were statistically significant. Cephalometric analysis may be an inaccurate tool for postoperative follow-up of minor segment migration such as that usually found after osteotomies.

Cephalometry↗
PubMed1995

Dual regulation of the Drosophila hsp26 promoter in vitro.

Efficient heat shock induction of Drosophila hsp26 gene transcription in vivo requires binding sites for heat shock factor (HSF) and GAGA factor (GAF) close to the TATA box (proximal elements) as well as 350 bp upstream of the start site of transcription (distal elements). We have evaluated the contribution of hsp26 promoter sequences to transcriptional activity in extracts from either heat shocked or unstressed fly embryos. Efficient transcription in either extract was governed by distinct regulatory principles. Transcription in extracts from unstressed embryos relied solely on GAGA elements which efficiently counteracted repression by abundant non-specific DNA-binding proteins. Transcription in extracts from heat shocked embryos depended only a little on GAGA elements, relying mainly on functional HSEs. Constitutively active recombinant HSF or native factor in an extract from heat shocked embryos was able to truly activate transcription essentially via proximal HSEs, but not when bound to distal sites. These two modes of regulation in vitro may correspond to the two functional states of the promoter before and after heat shock in vivo.

Animals↗
PubMed1995

Chromatin remodeling by GAGA factor and heat shock factor at the hypersensitive Drosophila hsp26 promoter in vitro.

The chromatin structure at the Drosophila hsp26 promoter in vivo is characterized by two DNase I-hypersensitive (DH) sites harboring regulatory elements. Proximal and distal DH sites are separated by a positioned nucleosome. To study the contribution of transcription factors to the establishment of this specific chromatin configuration we assembled nucleosomes on the hsp26 promoter using a cell-free reconstitution system derived from fly embryos. Both DH sites were readily reconstituted from extract components. They were separated by a nucleosome which was less strictly positioned than its in vivo counterpart. The interactions of GAGA factor and heat shock factor with their binding sites in chromatin occurred in two modes. Their interaction with binding sites in the nucleosome-free regions did not require ATP. In the presence of ATP both factors interacted also with nucleosomal binding sites, causing nucleosome rearrangements and a refinement of nucleosome positions. While chromatin remodeling upon transcription factor interaction has previously been interpreted to involve nucleosome disruption, the data suggest energy-dependent nucleosome sliding as main principle of chromatin reorganization.

Animals↗
PubMed1995

Mobility of the osteotomy site following Le Fort I osteotomy stabilized by titanium plate osteosynthesis.

PURPOSE: This study analyzed whether titanium plate osteosynthesis prevents mobility after Le Fort I osteotomy and, if not, how long the osteotomized segment is mobile. PATIENTS AND METHODS: In 10 patients aged 17 to 49 years, three metal bone markers were inserted below and three above the osteotomy during the Le Fort I procedure, each set forming a triangle. The patients were examined at intervals until 1 year postoperatively. At each examination two sets of x-ray stereograms were obtained; one in rest and one with pressure applied to the anterior part of the maxilla. The difference in position of the maxillary segment in relation to the reference segment between the two sets of stereograms, ie, the mobility, could thus be recorded. Findings of 0.4 degrees and 0.2 mm are considered significant. RESULTS: Immediately after surgery mobility in the osteotomy site was found in 7 of the 10 patients. One year postoperatively mobility in the osteotomy site was still found in four patients. CONCLUSION: Titanium plate osteosynthesis does not prevent mobility between the osteotomy segments after Le Fort I osteotomies. The osteotomized segment may remain mobile at least until 12 months after surgery. During this period the impact of the functional matrix may cause migration of the segment.

Adolescent↗
PubMed1990

[Special ceramic hard substances as separating agents in cast-on procedures for the construction of precision attachments].

A new direct cast-on technology for the construction of telescopic crowns and precision attachments using non-precious alloys is described. Special ceramic hard substances, such as silicides and borides, are used as separating agents for the casting of the secondary structure. The application of the ceramic layers to the primary crown is accomplished with a chemical vapor deposition method. The layer thickness can be controlled and may range between some hundred nanometres and up to a few micrometres. The attainable gaps between primary and secondary casting range between 1 and 8 microns after separating and finishing.

Crowns↗
PubMed1986

Occlusal wear in miners.

The degree of occlusal wear was studied in two groups of miners, one with an employment time of 5-7 years and one who had been working in the mines for more than ten years. They were compared with two matched groups of white collar workers. In the two groups of miners a statistically significant higher degree of occlusal wear was found when comparisons were made with the control groups. The older miners had a poorer dental health and a higher degree of clinical signs of mandibular dysfunction than their control group, but no differences were found in these respects between the two younger groups. Because of this, it is concluded that the most possible reason for the differences found in occlusal wear between miners and white collar workers is differences in working environment, probably abrasive components in the air. In line with this, severe occlusal wear in miners ought to be classified as a damage caused by their work if no other factor can be traced as having a significant influence on the occlusal wear.

Adult↗
PubMed1975

Dilute performic acid--a versatile and easily to handle oxidant in general histology and histochemistry of structure bound sulphur compounds.

Performic acid normally leads to frequent and nearly inevitable detaching of commonly attached tissue sections, thus rendering such methods unrecommendable for histological and histochemical routine work. By the use of alcohol dilute solutions instead of the crude reagent, this problem can be managed easily. Special attention is drawn to the ambiguity of methods for tissue sulphur, based on the demonstration of oxidation induced strong basophilia.

Brain↗