Biomedical subjects

U Joos

Publications and source records attributed to U Joos.

At least 37 records · Page 2Linked to original sources

PubMed2003

Evaluation of accuracy of insertion of dental implants and prosthetic treatment by computer-aided navigation in minipigs.

The survival of loaded implants is critically dependent on their biomechanical stability. We have used a computer-guided navigation technique to evaluate the accuracy of computer-assisted insertion for immediately-loaded implants in minipigs. On the basis of computed tomographical data, the Robodent system was used for preoperative planning and guidance of inserting the implant. An optical tracking system allowed positioning of the implant and immediate prosthetic rehabilitation by inserting it in a plaster model and during the operation. Postoperative computed tomograms (CT) showed that the implants were placed precisely in the preoperatively planned position. The accuracy achieved corresponded well with the spatial resolution of the CT used. Immediate placement of the prefabricated crowns resulted in favourable occlusal positioning. Histological cross-sections showed that the implants were biomechanically stable. The accuracy of insertion of oral implants illustrated here suggests that insertion and prosthetic modelling of implants may benefit from computer-assisted navigation.

Animals↗

PubMed2003

Aneurysmal bone cyst of the mandible: a case report.

The case of a 6-year-old boy with a rapid growing mass in the right angle of the mandible that clinically and radiographically resembled a malignant lesion is presented. The biopsy specimen showed an aneurysmal bone cyst. The patient was treated surgically via extraoral approach including immediate mandibular reconstruction with with iliac crest bone. The literature is briefly reviewed.

Bone Cysts, Aneurysmal↗

PubMed2003

Are collimated low-dose digital radiographs valid for performing Delaire's architectural analysis?

Computed radiography (CR) provides the dynamic exposure range to reveal objects in film areas exposed by very low X-ray exposure. Conventional cephalometric radiographs are normally beam limited to the facial skeleton. The cranial vault and cervical vertebra are collimated and only exposed by extra-focal radiation and scatter. We hypothesize that, on conventional cephalometric radiographs obtained with CR, image data of collimated film areas can be enhanced for reliable performance of Delaire's cephalometric analysis of the entire skull. Therefore the aim of the present study was to compare the reproducibility of landmark placement on normal and underexposed film areas of CR images. Intra- and inter-observer reproducibility of landmark identification was evaluated on 200 randomly selected radiographs by calculating the error radius of repeated landmark placements. A paired-samples t-test revealed differences (P< 0.001) between intra- and inter-observer reproducibility. Intra-observer accuracy was influenced (P< 0.001) by variability of suture obliteration (bregma). Identification of landmarks in areas of extra-focal radiation showed no difference (P> 0.05) from that of landmarks inside the normally exposed area. CR offers the opportunity to perform of a full cranial analysis on a cephalometric radiograph collimated to the facial region.

Cephalometry↗

PubMed2002

[Experimental study on the biomechanical stability of different internal fixators for use in the mandible].

BACKGROUND: Comparative studies of different forms of osteosynthesis require that biomechanical and biological criteria be observed. The conditions in experimental studies should be as close as possible to the in vivo situation. The aim of our study was to develop a fracture model that would allow determination of the micromovements in the gap tissue following different forms of internal fixation in fractured human mandibles. METHODS: Micromovements in the gap tissue of five human mandibles treated with different osteosynthetic systems (DCP, EDCP, Miniplates, 3-D systems) following osteotomy or fracture in the region of the corpus and median region were investigated by means of strain gauges. By fitting the human mandibles in plaster according to a method of our own it was possible to create fractures at predictable and comparable localizations. RESULTS: Our investigations show that the micromovements in the gap tissue of osteotomied and fractured mandibles are different and not dependent on the form of osteosynthesis applied. Physiological micromovements in the gap tissue were found under strain for all osteosynthetic systems used in fractured and congruently reset mandibles. DISCUSSION: Our fracture and osteosynthesis model allows the quantitative determination of micromovements in the gap tissue and shows the importance of ideal realignment, which has a decisive influence on micromovements in the gap tissue.

Biomechanical Phenomena↗

PubMed2002

[Possibilities and limitations in evaluating treatment concepts in lip-jaw-palate clefts].

BACKGROUND: Recently, government and medical practitioners have shown considerable interest in the discipline of evidence-based medicine. LITERATURE RESEARCH AND RESULTS: In this study, we investigated the literature concerning treatment concepts in cleft surgery according to criteria of evidence-based medicine. Over the last decade 996 articles on cleft patients were published, 181 of which were studies evaluating the clinical outcome of distinct treatment options. Only 57 studies proved to be classifiable due to a well-described study protocol. One treatment study of cleft patients reached the strength of evidence grade I and strength of recommendation grade A, whereas all other studies had a lower evidence rating. DISCUSSION: The reasons behind these findings seem to be due to problems faced by the specialty of this disease.

Child, Preschool↗

PubMed2002

[Evaluating angiogenesis and osteogenesis modified by vascular endothelial growth factor (VEGF)].

PURPOSE: This intention of this study was to investigate the influence of controlled release of vascular endothelial growth factor (VEGF) on angiogenesis and osteogenesis in a mandibular defect model. METHODS: A total of 56 rabbits were operated and bicortical holes were placed in the mandible. The defects were filled with collagen type I implants, collagen implants complexed with 0.8-microgram VEGF165, or left without any filling. After 3, 7, 14, and 28 days specimens were taken and histologic, histomorphometric, and immunohistologic analyses were carried out concerning density of vessels, total surface of vessels, bone surface, and bone density. RESULTS: The number of vessels was increased in all groups up to 14 days, followed by physiologic regression in the control groups, whereas the study group showed persistently high numbers. The density of regenerated bone was significantly higher in the study group. CONCLUSION: The activation of angiogenesis using VEGF165 leads to more intensive angiogenesis and bone regeneration.

Animals↗

PubMed2002

First experience with a public domain computer-aided surgical system.

The outcome of complex craniofacial operations is critically dependent on careful and accurate preoperative planning. Recent advances in computer technology enable the surgeon to do surgical simulations directly on to a computer terminal. We describe the clinical application of a public domain-based computer-aided system in craniofacial surgery. Operation planning was based on clinical investigations and radiological images, with particular use of a virtual three-dimensional surgical simulation. Three patients with complex craniofacial malformations were admitted for orbital correction. Surgical simulation defined numerically the extent of bone movements and the extent of resection areas. Operations were guided by the virtual planning. The outcome was compared with the planning to assess the accuracy of the operative correction. Our first experience confirms that computer-assisted simulation is a reliable and useful tool that improves surgical planning and helps to evaluate the surgical outcome.

Adult↗

PubMed2001

Electrical stimulation influences mineral formation of osteoblast-like cells in vitro.

The aim of the present study was to assess the structure of newly formed mineral crystals after electrical stimulation of osteoblast-like cells in vitro. Pulsed electrical stimulation was coupled capacitively or semi-capacitively to primary osteoblast-like cells derived from bovine metacarpals. Computer calculations revealed that the chosen input signal (saw-tooth, 100 V, 63 ms width, 16 Hz repetition rate) generated a short pulsed voltage drop of 100 microV (capacitive coupled mode) and of 350 microV (semi-capacitive coupled mode) across the cell-matrix layer. Stimulated cultures showed an enhanced mineral formation compared to the non stimulated controls. In cultures exposed to capacitively coupled electric fields and in control cultures nodules and mineralized globules were found. Nodules with a diameter of less than 200 nm covered the cell surface, whereas mineral globules with a diameter of up to 700 nm formed characteristic mineral deposits in the vicinity of the cells similar to biomineral formations occurring in mineralizing tissues. In contrast, large rod-shaped crystals were found in cultures stimulated by semi-capacitive coupled electric fields, indicating a non-physiological precipitation process. In conclusion, osteoblasts in culture are sensitive to electrical stimulation resulting in an enhancement of the biomineralization process.

Animals↗

PubMed2001

Increase of RM3/1-positive macrophages in radiation-induced oral mucositis.

The purpose of this study was to describe the distribution patterns of various leukocyte subpopulations in the oral mucosa during the course of radiotherapy and to determine whether there are dose-dependent alterations, or any correlation between the clinical stages and the population density of specific leukocytes. The distribution and density of various leukocytes in oral mucosa in 13 head and neck cancer patients were immunohistochemically analysed before radiotherapy at 30 and 60 Gy and compared with the clinical degree of oral mucositis. Antibodies were used which characterized different subtypes of macrophages (27E10, 25F9, RM3/1) and recognized epitopes of granulocytes (CD15) and T cells (CD3, CD4, CD8). The study showed that whereas macrophages reactive with RM3/1 increased significantly at 30 Gy (p<0.01) and showed a further increase at 60 Gy (p<0.01), no significant alterations could be detected in the density of macrophages which stained positively for 27E10 or 25F9. Moreover, the percentage of macrophages reactive with RM3/1 showed a non-linear correlation with the clinical mucositis score (p<0.05). No significant alterations were detected in the percentage of T cells and granulocytes, compared with the values before radiotherapy. In conclusion, radiation-induced mucositis is characterized by features of an intermediate stage of an inflammatory response, suggesting active involvement of down-regulatory macrophages in its pathogenesis.

Aged↗

PubMed2001

[Surgical procedures in mouth, jaw and facial surgery in Thiel embalmed body donors].

METHODS: This study investigates whether human cadavers embalmed according to Thiel can be used for research and education in oral-maxillo-facial surgery. Different surgical approaches were tested on such cadavers. The usability of the specimen was judged jointly by anatomists and surgeons. Color, structure, and consistency of the different tissues were comparable to vital conditions. Thiel's embalming technique applied to human cadavers provides an optimal basis for research and for basic and postgraduate medical education.

Curriculum↗

PubMed2001

[Forensic evaluation of injuries to nerves and jaw bone after wisdom tooth extraction from the viewpoint of current jurisprudence].

The removal of lower wisdom teeth is one of the most frequent operations in oral surgery. Iatrogenic lesions of the lingual and inferior alveolar nerve and fractures of the lower jaw are rare, but can lead to actions for damage and compensation for personal suffering. The aim of our investigation was to elaborate recommendations for the oral surgeon from the legal point of view. Therefore we investigated in two data banks all court decisions concerning wisdom teeth and analysed them in regard to the obligation to provide information, documentation and the minimum requirements of the surgical treatment. In 57% of all court decisions the obligation to provide information was omitted by the surgeon. Surprisingly, regarding injuries of the lingual nerve we found different opinions from various law courts. In some former decisions only the fact of the damage was equivalent to a lack of care, while recently other courts had the opinion that an injury of the lingual nerve could also be caused in spite of careful treatment. With regard to lower jaw fracture all courts emphasized that the patient must be informed about the risk by the surgeon. Moreover, minimum requirements for the removal of wisdom teeth were given. In conclusion, the recent court decisions restrict the liability for complications but demand the observance of minimum requirements for the surgical treatment. Additionally, all courts stress that informed consent about the risk of nerve damage of jaw fracture must be obtained before the removal of wisdom teeth.

Germany↗

PubMed2001

[New aspects in managing mandibular fractures].

BACKGROUND: The aim of osteosynthetic mandibular fracture treatment is a bony bridging of the fracture gap. The gap distance and the fragment movement determine the micromovement in the gap tissue. They are known to be the main factors associated with the clinical outcome of fracture treatment. LITERATURE: The term fracture stability and the underlying mechanically modulated tissue reactions are not well described in the literature. MODEL: In this article we describe experimental results of strain related bone regenerate reactions in vivo. Additionally, in an in vitro model of osteosynthetic fracture treatment micromovements in the sense of bone strains were determined in the gap area. Implications for the osteosynthetic treatment of mandibular fractures are discussed on the basis of our biological and biomechanical results.

Animals↗

PubMed2001

[Treatment of frontobasal trauma and polytrauma].

BACKGROUND: This paper describes the historical development as well as current concepts of frontobasal fracture treatment by maxillofacial surgeons. TREATMENT CONCEPT: Based on the experience of many years a diagnostic and therapeutic treatment concept was developed, which proved to be adequate in 320 patients with 90 frontobasal fractures in the last five years.

Facial Bones↗

PubMed2001

[Mechanical stimulation of osteoblasts in cell culture].

BACKGROUND: Mechanical loading of bone is known to play a crucial role in bone remodeling and regeneration. Whereas the clinical effects of mechanically modulated bone healing have been extensively studied, less is known about the underlying mechanisms on a cellular level. This study was aimed at investigating the effects of uniaxial strains on osteoblast-like cells in culture. Mechanical loading was applied in physiological and hyperphysiological magnitudes. Nonstimulated cultures served as controls. RESULTS: Cultured primary bovine periosteal cells exhibited phenotypic features of osteoblast-like cells. Application of physiological strains (2,000 mu strain) led to a bone-specific expression of extracellular matrix proteins (osteonectin, osteocalcin, collagen type I). Hyperphysiological loads (10,000 mu strain) were associated with an increased synthesis of proteoglycans. Proliferation of cells was higher than the controls at 10,000 mu strain and showed no difference from physiologically loaded osteoblasts. DISCUSSION: Our study demonstrates that physiological loading of osteoblast-like cells enhances the regenerative capacity of bone, whereas hyperphysiological loads may impair bone regeneration.

Animals↗

PubMed2001

Late effects of radiotherapy on oral mucosa in humans.

In order to gain further understanding of the late effects of radiotherapy on oral mucosa, we analysed the histomorphological alterations, the cell populations in the subepithelial tissue, and the endothelial expression pattern of different adhesion molecules. Biopsies were taken from patients before irradiation, directly after 60 Gy, and 6-12 months after radiotherapy. Besides the histomorphological evaluation of the vessels, the endothelial expression of ICAM-1, VCAM-1 and E-selectin was determined as well as the distribution of LFA-1-, Mac-1-, VLA-4-, RM3/1-, 27E10- and 25F9-bearing cells in the subepithelial tissue. The expression of ICAM-1 was downregulated after radiotherapy, whereas the percentage of LFA-1- and VLA-4-bearing cells increased. VCAM-1 remained at low levels. The subepithelial infiltration was still dominated by RM3/1-positive macrophages. The number of vessels decreased, while the lumen of the remaining vessels increased. In conclusion, the late effects of radiotherapy are characterized by a decreased number of blood vessels and by significantly different expression patterns of the adhesion molecules studied, and of integrins and macrophage subpopulations, compared to the conditions before irradiation and directly after irradiation with 60 Gy.

Aged↗

PubMed2001

Comprehensive management of cleft lip and palate deformities.

PURPOSE: The controversy regarding the timing of repair of the deformities associated with cleft lip and palate still exists. The goal of this article is to present a versatile, universal philosophy of management of these deformities involving early repair. PATIENTS AND METHODS: Over 20 years, 2,698 new patients with cleft lip and palate deformities were treated. These included 1,298 unilateral and 320 bilateral cleft lip and palate patients. The remaining patients (1,018) had isolated palatal clefts. All patients were operated according to the same protocol and the same surgical procedure. The treatment philosophy was based on early, wide myoperiosteal-periosteo-sutural reconstruction by a modified Delaire functional cheilorhinoplasty and alveolar gingivoperiosteoplasty at 3 months, followed by soft and hard functional palatoplasty at 9 months. RESULTS: All patients were followed longitudinally and retrospectively. The parameters investigated were facial symmetry, presence or absence of growth retardation, and oropharyngeal and nasal function. The parameters studied indicated that when this treatment schedule was followed and the procedures were performed on time and according to the protocol, there was minimal growth retardation of the maxilla. When early gingivoperiosteoplasty was performed in 25% of the patients there was a sufficient amount of alveolar bone for eruption of the primary and permanent dentition. This negated the need for secondary alveolar bone grafting. The development of the upper lip was harmonious, and usually no further corrective procedures were necessary. The nose was usually well developed and functionally normal. CONCLUSION: Optimal rehabilitation of the patients was achieved by following the principles and treatment strategies described. If the treatment principles are not incorporated in the functional repair (ie, joining of the primary and the secondary growth centers during corrective procedures), compromised results are to be expected.

Child↗

PubMed2001

Influence of distraction rates on the temporomandibular joint position and cartilage morphology in a rabbit model of mandibular lengthening.

PURPOSE: Although various aspects of bone formation during distraction osteogenesis have been studied extensively, there are only limited experimental data concerning the influence of mandibular distraction rates on structural alterations in the temporomandibular joint (TMJ). In this study, a rabbit model of unilateral mandibular distraction was used to test the effects of various strain schedules on the position and morphology of the TMJ. MATERIAL AND METHODS: Fifty-two immature white female rabbits were used. The distraction procedure was performed using physiologic (2,000 microstrains, 1 per day) and elevated strain magnitudes (20,000 microstrains, 1 per day), as well as high strain magnitudes (200,000 and 300,000 microstrains, 1 per day). The investigation of the TMJ included clinical, radiologic, and histologic aspects. RESULTS: Clinical and radiologic examinations at the end of the distraction period showed no evidence of joint luxation even at maximal distraction rates. Histologic and ultrastructural analyses revealed a positive correlation between the degree of mechanical loading and the development of degenerative alterations in the cartilage. In samples distracted at hyperphysiologic strain magnitudes, all cartilaginous layers were reduced in the regions of the TMJ that had been exposed to the higher pressure forces. The fibrous layer became nearly completely destroyed. CONCLUSIONS: These experimental data show that distraction schedules with single but hyperphysiologic loads may lead to degenerative or even early arthrotic changes in the condyle. These data support the principle that distraction protocols should be performed without extensive mechanical loading on the TMJ.

Animals↗

PubMed2001

Tissue differentiation and cytokine synthesis during strain-related bone formation in distraction osteogenesis.

To investigate the contributions of various cytokines that are involved in mechanically related bone formation, we applied defined uniaxial strains in a rabbit model of mandibular elongation and examined the regenerating bone during early stages of dist raction osteogenesis by histomorphometry. We also measured serum concentrations of various cytokines during the distraction. Cell proliferation and differentiation indices correlated significantly (P<0.001) with the extent of load application. Serum concentrations of insulin-like growth factor-1 (IGF-1) decreased after osteotomy whereas transforming growth factor beta1 (TGFbeta1) showed a postoperative increase. Prostaglandin E2 (PGE2) concentrations were constant throughout the experimental period. Collagen degradation decreased slightly postoperatively and increased in samples exposed to higher magnitudes of strain. Our data show that it is the magnitude of mechanical strain that decides tissue response by a characteristic cell proliferation and differentiation. The operative trauma leads to inverse changes in serum concentrations of TGFbeta1 and IGF-1, thereby promoting the recruitment of osteoblastic precursor cells as well as collagen matrix synthesis.

Animals↗