Biomedical subjects

U Stratmann

Publications and source records attributed to U Stratmann.

At least 37 records · Page 2Linked to original sources

PubMed1998

Sutural mineralization of rat calvaria characterized by atomic-force microscopy and transmission electron microscopy.

The application of transmission electron microscopy (TEM) and atomic-force microscopy (AFM) aid the acquisition of detailed structural information on the process of hard tissue formation. The sutural mineralization of rat calvaria is taken as a model for a collagen-related mineralization system. After cryofixation or chemical fixation an anhydrous tissue preparation technique with no staining procedures is used. The atomic-force microscope and the transmission electron microscope are used for structural analysis of the mineralizing region of the sutural tissue. With the application of AFM the collagen macroperiod is shown to be well represented in the unmineralized sutural tissue. At the mineralization front the collagen fibrils are found to be thickened and to change to a characteristic stacked platelet structure. Using TEM the macroperiod is faintly visible before mineral crystallites have formed and is more prominent after the apatite crystallization has started in the fibrils. In this step a needle-like structure of the newly formed apatitic crystals is visible.

Animals↗

PubMed1998

[Low-dose computerized tomography of the jaw bone in pre-implantation diagnosis. Limits of dose reduction and accuracy of distance measurements].

Absorbed radiation doses delivered by computed tomography and panoramic radiography were measured in 16 anatomic sites using a head and neck phantom and thermoluminescent dosimetry. The recommended kilovoltage and scan time for dental scanning was reduced step by step, rating the quality of the low-dose scans. A reduction of up to 76% could be achieved without loss of diagnostic accuracy. Measured absorbed radiation dose ranges from 0.30 mGy (thyroid) to 29 mGy (skin) at 187.5 mAs and 1.0 mm-slices (25 mm scanning distance for maxilla, 30 mm for mandible). After reduction to 45 mAs, 0.07 mGy (thyroid) to 6.9 mGy (skin) was measured. Distance measurements on human jaw specimens were compared with corresponding CT image measurements. Average deviation was 0.1-0.3 mm. A dose reduction of 75% had no effect on the results. However, the doses of CT-scans reduced by 76% exceed by an average factor of 10 the doses of conventional panoramic radiography. Therefore, CT should be reserved for the planning of complex implant treatment in the direct vicinity of the maxillar sinus and nerves and for multiple implant insertion.

Body Burden↗

PubMed1998

General principle of ordered apatitic crystal formation in enamel and collagen rich hard tissues.

The biomineralization processes in different hard tissues like enamel, circumpulpal dentine, epiphyseal growth plates were analyzed morphologically and ultrastructurally by an energy filtering transmission electron microscope. In the primary stage of crystal formation Ca- and phosphate-ions accumulate at charged sites, "active sites", along the fiber matrix-molecules of the extracellular matrix. After exceeding the critical radius for nucleation, crystal nuclei appear that develop to "chains" of stable nanometer-sized paracrystalline particles. In the latest studies of small area electron diffraction it was found that in the earliest stage of crystal formation these mineral chains show a parallel orientation in the direction of the c-axis of apatite. This was supported by a texture of the 002 reflection in the corresponding diffraction patterns. Since apatite is bipolar in this direction crystal growth would be in like manner in both directions. Thus the center-to-center distances between nucleating sites along the matrix macromolecules show with the chains of nanometer islands the same process of biomineralization in the different mineralizing hard tissue systems. This way of crystal formation might be a general principle of apatitic biomineralization.

Animals↗

PubMed1997

The mineralization of mantle dentine and of circumpulpal dentine in the rat: an ultrastructural and element-analytical study.

The purpose of this study was to compare the biomineralization of circumpulpal dentine with that of mantle dentine by ultrastructural and element-analytical techniques. Forty upper second molar germs of 10-day-old albino rats were cryofixed in liquid nitrogen-cooled propane and embedded in resin after freeze drying. Semithin dry sections were cut for analyzing the calcium and phosphorous concentration in initial mantle dentine, at the mineralization front of circumpulpal dentine, in the middle region of circumpulpal dentine and in mantle dentine peripheral to circumpulpal dentine. For the morphological evaluation of mineral deposits we compared ultrathin and unstained sections of cryofixed molars with chemically fixed molars. For both dentine types it was found that they develop via identical steps of mineral formation at collagen fibrils and non-collagenous matrix molecules. In circumpulpal dentine no globular mineral protrusions along the mineralization front (i.e. calcospherites) and no indications of interglobular dentine at the transition from circumpulpal dentine to mantle dentine were present. Two von Korff fibres were not only visible in mantle dentine but also in circumpulpal dentine. Matrix vesicles were present only during the formation of an initial coherent layer of mantle dentine and could not be observed during successive formation of mantle dentine and circumpulpal dentine. The element-analytical data did not demonstrate any difference in the mineral content between the two dentine types. Therefore, we conclude that mantle dentine and circumpulpal dentine in the rat molar possess a high degree of structural and chemical similarity and that only the extent of terminal branching of the odontoblast processes gives an approximate estimation of the thickness of mantle dentine.

Animals↗

PubMed1997

Analysis of a general principle of crystal nucleation, formation in the different hard tissues.

We have found, at high EM magnification, on ultrathin sections of shock-frozen, freeze-dried, embedded pieces of the developing hard tissues, that the primary crystallites consist of strands composed of nanometer-sized apatitic islands, which rapidly coalesce to needles and afterward to platelets. By small-area electron diffraction, with energy-filtered electrons, it was clarified that these strands are already crystallographically oriented along the bipolar c-axis so that the center-to-center distances between the islands would reflect the distances between crystal-nucleating sites along the matrix. The EM analysis of the cross-cut stained unmineralized and of the unstained mineralized collagen fibers of turkey tibia tendon shows that the staining "nuclei" and the early crystallites, appearing as dark dots, surround "light" round structures, which we interpret as the collagen microfibrils, surrounded by the apatitic crystallites.

Animals↗

PubMed1997

Magnesium in newly formed dentin mineral of rat incisor.

Small amounts of magnesium are always detectable in addition to calcium and phosphorus in mineralized tissues such as dentin or bone. Magnesium has been considered to influence the mineralization process, especially crystal growth. The present study reports on the location and enrichment of magnesium in the newly mineralized dentin by using the high lateral resolution of energy dispersive X-ray microanalysis combined with scanning transmission electron microscopy. To this end, we have used the continuously growing rat incisor as a model for a collagenous mineralizing system. Dental tissue was dissected free and cryofixed in liquid nitrogen-cooled propane. The distribution of elements was measured in freeze-dried ultrathin cryosections. The magnesium distribution of the newly formed dentin area near the predentin area was found to be inhomogeneous. In certain small dentin areas, characteristical magnesium enrichments were observed. Further, high magnesium-to-phosphate molar ratios were found in these areas, and these were correlated with low calcium-to-phosphate molar ratios. Our results support the theory that magnesium is involved in the process of biological apatite crystal formation.

Animals↗

PubMed1997

[Pyogenic periproctitis infections in childhood].

A total of 128 pediatric pyogenic perianal infections were recorded prospectively in 1984-1995; over 70% arose in children below the age of 2 years. A quarter of all perianal abscesses developed a recurrence between 3 weeks and 3 years after the initial operation, while five children had an anal fistula after deroofing of anal abscesses. The early age of onset and frequent anomaly of anal crypts (12%) suggests a partly congenital etiology due to impaired fusion of the proctodaeal membrane or rudimentary anorectal duplications for both conditions.

Abscess↗

PubMed1996

Mineralization during matrix-vesicle-mediated mantle dentine formation in molars of albino rats: a microanalytical and ultrastructural study.

The purpose of this study was to elucidate the mineralization process of mantle dentine by ultrastructural and element-analytical investigation of matrix vesicles and successive stages. Upper second molars of albino rats were cryofixed and embedded in resin after freeze drying. Semithin dry sections were prepared for analyzing the calcium and phosphorus concentrations in the mineralized matrix vesicles or noduli, larger mineralized islands, and the mantle dentine. For ultrastructural studies, it was necessary to reduce section contact with hydrous fluids to a minimum in order to avoid preparation artifacts. The first mineral deposits were recognized as dot-like formations both in the interior of matrix vesicles and in association with the inner vesicle membrane. This indicated the existence of mineral nucleating sites located both at the inner membrane and at calcium-phosphate-binding macromolecules in the interior of the matrix vesicles. A significantly higher mineral content was found in mineralized matrix vesicles than in the mineralized extravesicular regions of the mineralized islands, suggesting the existence of a rapidly and densely mineralized matrix in the matrix vesicles. A significant increase in mineral content per volume proceeding from the mineralized islands to mantle dentine suggested a further increase in the density of mineral.

Animals↗

PubMed1996

Early mineralization of matrix vesicles in the epiphyseal growth plate.

Matrix vesicles (MVs) induce the primary mineralization in collagen-rich hard tissues such as bone, mineralizing cartilage and dentine. Calcium and phosphate ions accumulate at the inner MV membrane. This accumulation takes place in association with phospholipids alone and/or in association with Annexin V, which displays Ca ion channel activity when inserted in membranes; consequently, Annexin V may be involved in Ca uptake by matrix vesicles. The first crystal nuclei are formed at these macromolecules of the MV inner membrane. They grow to stable nanometre-sized particles, dots, which coalesce to form chains of dots along the macromolecules of the MV inner membrane. At the same time, or shortly afterwards, chains of these Ca phosphate dots also develop inside the MVs. The measured centre-to-centre distances between these dots represent approximately the distances between the nucleating sites, called active sites, along the MV matrix molecules. The mineralization does not stop at the MV membrane but expands continuously into the extravesicular region in radial directions to form nodules. These radiating Ca phosphate chains, which coalesce to form needles, are composed of such primary dots, which have developed at the nucleating sites of the corresponding macromolecules.

Animals↗

PubMed1996

The extent of enamel surface fractures. A quantitative comparison of thermally debonded ceramic and mechanically debonded metal brackets by energy dispersive micro- and image-analysis.

This clinical study investigated the practical value of two methods for debonding brackets attached by the adhesive Concise to acid-etched enamel surfaces. Forty-two Ultratrimm Standard metal brackets and 42 Fascination ceramic brackets were collected from juvenile patients undergoing orthodontic treatment. All metal brackets were mechanically debonded by a conventional bracket removal plier, whereas the ceramic brackets were thermally debonded by a commercial Dentaurum ceramic debonding unit. All brackets were evaluated by scanning electron microscopy for the morphology of their adhesive fracture surfaces and for the occurrence of mineral-like particles attached to the adhesive fracture surfaces. These particles were analysed by an energy dispersive X-ray microprobe for their Ca/P ratios and by image analysis of scanning electron micrographs for measurement of their areas. The scanning electron micrographs showed 4 types of debonding fractures. The most frequent fracture was type 1 (between adhesive and bracket base) and type 2 (between adhesive and enamel surface). In the group of mechanically debonded metal brackets type 1 (38 per cent) and type 2 (45 per cent) showed a similar frequency, whereas thermally debonded ceramic brackets predominantly showed fracture type 1 (79 per cent) and only a minor percentage of type 2 (11 per cent). A statistical evaluation was applied to estimate the range of reproducibility of fracture types with a 95 per cent confidence interval (level of significance alpha = 5 per cent). In both groups the microprobe analysis of fracture surfaces lying completely or partly between adhesive and enamel surface identified the mineral-like particles as enamel mineral. They occurred partly as single particles (range of thickness: 5-25 microns, mean area: 3500 microns2) and partly as a coherent covering with a total area of 1.9-5.8 mm2. It is concluded that the thermodebonding technique is superior to conventional mechanical debonding, because the frequent occurrence of fracture type 1 after thermodebonding affords a protection for the enamel surface, whereas mechanical debonding entails a comparatively high risk of enamel fractures.

Acid Etching, Dental↗

PubMed1996

Morphometric investigation of condylar cartilage and disc thickness in the human temporomandibular joint: significance for the definition of ostearthrotic changes.

106 human TMJ specimens from 53 individuals (age: 65-85 years) were examined macro- and microscopically and measured for discal and condylar cartilage thickness at five points defined on a mediolateral axis along the middle dense part of the disc. 27% of the discs showed lateral and laterocentral perforations. In 8% the lateral portion was thinned down to a translucent layer. 62% showed no gross destruction or deviation in shape and thickness. The remaining 3% displayed extensive destruction and their condyles were osteoarthritic. All discs showed a significant decrease in thickness from their medial towards their lateral portions. The condyles displayed either a smooth articular surface (16%) or an irregular and progressively remodelled surface (81%) with histologically normal fibrocartilage. The condylar cartilage did not show a significant gradient of thickness in amediolateral direction. The results support our previously developed working hypothesis, that the joint is seemingly loaded along its entire articular surface and that a lateral disc perforation in older individuals can be due to a physiological process of wearing rather than to a pathological sequel of functional disorders.

Aged↗

PubMed1996

Laparoscopic and thoracoscopic surgery in infancy and childhood, the Münster/Gent experience.

Laparoscopic and thoracoscopic surgery have had a tremendous impact on adult surgery, but are still rarely used in children. In the past 3 years 168 children have been treated endoscopically in the three cooperating institutions. The course of all patients was documented prospectively in order to determine the value and prove the safety of endoscopic surgery in children. The operations performed endoscopically comprised appendectomy (n = 39), diagnostic procedures (24), adhesiolysis (n = 22), cholecystectomy (n = 13), bowel resection (n = 8), pyloromyotomy (n = 6), ovarial resection (n = 6), hiatus hernia repair (n = 22), splenectomy (n = 6), first stage of Fowler-Stephens operation for kryptorchidism (n = 3) and interruption of persistent botallic ducts (n = 6) in preterm infants. Apart from four wound infections (2.4%) following perforated appendicitis, one of which required laparotomy for perityphlitic abscess there were no serious complications. No patient died, and overall morbidity related to the procedure was 1.8% (i.e. incidence of uneventful minor intraoperative complications). Furthermore endoscopic surgery provides a better diagnostic survey of the abdomen or thorax so that missing of secondary pathology is unlikely. Pain and reflectory impairment of bowel-function or respiration were diminished, the aesthetic results were excellent and hospitalization could be reduced to a minimum. It is concluded that laparoscopic and thoracoscopic surgery are safe and reliable procedures for children and yield very encouraging results.

Adolescent↗

PubMed1996

[Assessment of the resectability of Wilms' tumors in childhood].

Over the last ten years 62 children were operated for renal tumours. The therapeutic aim in Wilms' tumours is complete macroscopic resection of the primary tumour, assessing resectability as accurately as possible. Overestimating surgical possibilities may lead to intraoperative rupture of the tumour (three cases), while overestimating local tumour extent may result in too much preoperative chemotherapy, which resulted in the life-threatening complication of venous occlusive disease of the hepatic veins (VOD) in three infants. The assessment of resectability may become particularly problematic in bilateral (six cases) or multifocal Wilms' tumours (two cases), and in nephroblastomatosis (two cases), i.e. the persistence of embronal renal tissue, a facultatively precancerous lesion, which requires quarterly sonographic controls and which induced a second metachronous contralateral Wilms' tumour in one child.

Adolescent↗

PubMed1995

Tracheoesophageal anastomosis, continent gastrostomy and oesophagostomy--a new experimental model in minipiglets.

Tracheoesophageal fistulae endanger newborn children by aspiration pneumonia. An animal model of this dangerous malformation was thought to be impossible until now. By tracheoesophageal anastomosis, occlusion of the oesophagogastral junction, proximal cervical oesophagostomy and continent gastrostomy in 25 minipiglets a reliable model of tracheoesophageal fistula has been developed. After establishing the model in a pilot study the mortality following the establishment of this procedure was 5.6% and the minipiglets survived in excellent condition for 2-10 week periods under complete alimentary restriction and gastrostomy feeding. Therefore the method seems to be suitable for long-term investigations on major oesophagotracheal surgery.

Anastomosis, Surgical↗

PubMed1995

The interaction of laser energy with ureter tissues in a long-term investigation.

This study investigates tissue responses after laser irradiation of the rabbit ureter, which serves as an experimental model for rectourogenital fistulae of children. Twenty-five rabbit ureters were irradiated intraluminally by a Nd:YAG laser 1320 nm (2 Watt, 20 seconds and 3 Watt, 8 seconds) via an applicator with radialsymmetrical light distribution. Immediately, 2 weeks, 4 weeks, 8 weeks, and 16 weeks after irradiation, the ureters were X-rayed with contrast solution and prepared for light and transmission electron microscopy. For the parameters employed, no apparent morphological differences could be observed. Immediately, the central laser zone showed a transmural thermonecrosis prevailed by cellular destruction, condensed ground substance and occlusion of most vascular lumina. Peripheral laser zones displayed urothelial vacuolations. Between 2 and 16 weeks, urothelial regeneration and ingrowth of granulation tissue caused a luminal stenosis or occlusion followed by transformation into scar tissue. In some peripheral laser zones, a hydroureter with marked luminal dilatation developed. We conclude that the ureter is occluded if the expanding force of the growing scar tissue exceeds the hydrostatic pressure of the obstructed urine. A laser occlusion of rectourogenital fistulae will be easier to achieve since fistula occlusion does not entail an obstruction of the urine flow.

Animals↗

PubMed1995

The morphological tissue response of the piglet oesophagus to experimental irradiation by 1320 nm Nd:YAG laser.

The oesophagus of 18 minipiglets was exposed to endoscopic intraluminal irradiation with a 1320 nm Nd:YAG laser (10 W, 20 s) via a radial applicator with strictly radially symmetric light distribution. Immediately and at 2, 3, 4 and 8 wk after irradiation, the oesophagus was perfusion-fixed and filled with contrast solution. Radiographs were taken for evaluation by microradiometry. The specimens were subsequently prepared for light and transmission electron microscopy. The immediate reaction to irradiation was a morphological gradient of damage extending from the centre of the laser exposure where there was cellular thermonecrosis in all layers of the wall and condensation of the extracellular matrix, to a peripheral zone (at a distance of up to 8 mm from the region where the laser was centred) which showed only minor tissue damage manifested by intracellular vacuolation. In this zone dilatation of most vascular lumina was prominent. In the period between 2 and 8 wk after irradiation all phases of wound healing were observed and resulted in occlusion of the lumen of the oesophagus by early scar tissue after an interval of more than 3 wk at the former centre of laser exposure. Peripherally, epithelial regeneration resulted in a new luminal lining. Both the process of epithelial regeneration and that of fibrous repair indicated a good reparative capacity of laser-irradiated oesophageal wall tissues resembling the phases of normal wound healing. The immediate laser interaction with tissue indicated that the noncellular matrix components of tissues are more resistant to the photothermal effect than the cellular components.

Animals↗

PubMed1995

The effect of ArF-excimer laser irradiation of the human enamel surface on the bond strength of orthodontic appliances.

This study investigated enamel laser conditioning as an alternative to acid etching in bracket therapy. In preliminary experiments optimal laser parameters for achieving a bond strength of 6-10 N/mm2 were defined. Enamel surface morphology was assessed and the ablation depth was measured on serial enamel sections. Thirty human molars were exposed to 193 nm ArF-excimer laser radiation (energy density: 260 mJ/cm2) by single pulse application of 23 nanoseconds. Thirty molars were etched with phosphoric acid (37%) for 60 seconds. The brackets from the treated molars and 30 untreated molars were debonded vertically for tensile bond strength measurement. Roughened enamel surfaces were attained by 450 and 900 laser pulses with a mean ablation depth of 10.13 +/- 4.84 microns. After 1-10 laser pulses, the enamel surface appeared intact. The tensile bond strength was 6.63 +/- 2.18 N/mm2 in the laser-treated group (1 pulse), 8.75 +/- 3.61 N/mm2 in the acid-etched group, and 4.61 +/- 3.15 N/mm2 in the untreated group. We conclude a laser-selective ablation of the membranous enamel pellicle. Since the irradiated area can be adapted to bracket base and the enamel surface remains morphologically intact, pulsed ArF-excimer laser treatment seems to be superior to the acid etching technique.

Acid Etching, Dental↗

PubMed1993

[The cell response of rat esophagus after intraluminal irradiation with Nd-YAG-laser (1064 nm) after various postoperative times: a light and electron microscopic study].

The esophagi of Wistar rats were irradiated by a Nd-YAG-laser and studied by light and transmission electron microscopy immediately, 2 days and 14 days after the operation. In the immediate group the lasercentre showed a destruction of the stratified epithelium. On the contrary the cells and fibres of the underlying connective tissue were hardly affected. In the lasercentre we have found occlusion of microvascular lumina. Both the layer of smooth muscular tissue and the layer of skeletal muscular tissue showed defects in their myofilaments and altered nuclei. The damage of the skeletal muscle fibres extended up to 4 mm distant from the lasercentre. After 2 days a migrating epithelial sheet was present below the necrotic epithelium and an inflammatory reaction was found in the connective tissue. After 14 days a new regenerated epithelium and an underlying granulation tissue had caused a stenosis of the esophageal lumen. The smooth and striated muscle fibres also showed signs of regeneration. We assume a high regenerative capacity of all involved tissues.

Animals↗