Finite element analysis of a tandem screw configuration in sagittal split osteotomy using biodegradable osteosynthesis screws

The goal of the present study was to determine the mechanical stability of selected osteosynthesis screws in a paired linear configuration in cases of bilateral sagittal split osteotomy of the mandible. A mandible model was created that consisted of 22,846 elements and 4,879 nodes. The following screws were tested in the tandem screw configuration: the poly-L-lactic acid (PLLA) in accordance with Harada and Enomoto, the Isosorb screw (Aesculap, Germany), the BioSorbFX screw (Bionix Implants, Finland), and the Lactosorb screw (WL. Lorenz, USA). The mechanical parameters of the materials studied were adopted from the literature or were based on manufacturer information. With the precondition that the materials each be stressed to the ultimate tensile strength, the following chewing forces could be neutralized: 100 N by 2.0-mm titanium mini-screws, 117.5 N by PLLA screws in accordance with Harada and Enomoto, 90.0 N by Isosorb screws, 89.0 N by BioSorbFX screws, and 35.0 N by Lactosorb screws. Here the peri-implant bone was stressed within limiting values with the titanium miniscrew, and the PLLA screw according to Harada and Enomoto, but not the osteosynthesis material itself. The finite element method (FEM) appears suitable for simulating complex mechanical stress situations in the maxillofacial area. As a result, significant time and materials (animal tests) can be saved when developing new or modified materials

[The FAMI screw for temporary intermaxillary fixation. Report of experiences for extending indications]

The aim of this study was to demonstrate the suitability of the FAMI screw (fixation and adaptation in mandibular injuries) for maxillomandibular fixation in the maxillofacial area in orthognathic and trauma surgery. This FAMI screw was used in 28 patients for maxillomandibular fixation with wiring or elastics. The screw is inserted into the labial or buccal surfaces of the alveolar process without predrilling. Adequate intermaxillary fixation with balanced occlusion was created intraoperatively in all patients. In comparison with conventional splinting methods, this technique was far less time-consuming. The use of the FAMI screw has the advantage of being quick and simple, particularly if only a brief period of maxillomandibular immobilization is planned. Furthermore, the risk to the surgeon of sustaining a puncture injury from wire ligatures is distinctly reduced. Screws can be removed without local anesthesia. The above-mentioned method is minimally traumatic, effective, timesaving, and hence inexpensive. It can be used for maxillomandibular immobilization in dentate as well as in edentulous patients.

Study by finite element method of the mechanical stress of selected biodegradable osteosynthesis screws in sagittal ramus osteotomy

We tested the stability of the bilateral sagittal split osteotomy using four resorbable osteosynthesis screws (the PLLA screw introduced by Harada and Enomoto, the Isosorb screw, the BioSorbFX screw and the Lactosorb screw) which are all currently in clinical use. The distribution of stress in both the bicortically inserted screws and the adjacent bone of a computer-generated mandible was recorded by the three-dimensional finite element method. The stress of the materials under investigation was postulated to have reached threshold values for stability, and maximum chewing forces of 132 N (Harada and Enomoto), 117 N (Isosorb), 115 N (BioSorbFX) and 46.4 N (Lactosorb) were determined. As far as the postoperative chewing forces were concerned, all four screws were sufficiently stable at the osteotomy gap. Finite element modelling seems to be an appropriate method of investigating these clinical issues when the mechanical stress both in implants and in the adjacent bone is taken into account.

[Patient satisfaction with the outcome of surgical orthodontic intervention and effect of esthetic and functional criteria]

BACKGROUND

The aim of the study was to analyze the influence of possible temporary or permanent disorders of sensation on the degree of the patient's satisfaction following an orthognathic operation.

PATIENTS AND METHODS

After an average of 47 months (range: 9-141), a follow-up examination was performed in 78 women (64.5%) and 43 men (35.5%) with an average age of 24.3 years (range: 19-40) at the time of operation. In 67 cases there had been a sagittal division of the mandible, in 11 cases a Le Fort I osteotomy, in 26 cases a bimaxillary osteotomy, in 4 cases an isolated genioplasty, and in 13 cases a segmental osteotomy in the upper or the lower jaw. In the peripheral area supplied by the nerves V2 and V3 sensation was examined by the two-point discrimination test and the result related to the patients' satisfaction using the chi-square test.

RESULTS AND DISCUSSION

The following qualities of sensation were recorded: anesthetic (2.7%), hypesthetic (16.6%), paresthetic (8.3%), and normesthetic (72.4%). The patients' satisfaction was rated as very satisfied in 51.3%, as satisfactory in 44.8%, and in 3.9% the patients' expectations had not been fulfilled; 75% regarded their outward appearance as markedly improved and a good 50% of the patients noted improved mastication. Therefore, three-fourths of all the patients would even be willing to be operated on again. Two-dimensional analysis, however, demonstrated only a weakly significant positive relationship between patient satisfaction and the preserved, or restored, sensation in the trigeminal region.

[Complications in surgical treatment of malocclusions. Report of 50 years experience]

BACKGROUND

During the past few decades, orthognathic surgery has become routine in oral and maxillofacial surgery. As these surgical interventions are elective, the goal is a low complication rate. The aim of this study was to analyze the intraoperative and postoperative complications after orthognathic surgery without considering orthodontic relapse.

PATIENTS AND METHODS

The medical files of 507 patients were reviewed who had been treated in the department of oral maxillofacial surgery at the Martin-Luther-Universität in Halle-Wittenberg during a period of 51 years. The indication for orthognathic surgery was mandibular hyperplasia in 314 cases (61.9%), mandibular hypoplasia in 69 cases (13.6%), mandibular hyperplasia with a frontal open bite in 53 cases (10.5%), maxillary hyperplasia with a cleft in 30 cases (5.9%), maxillary hyperplasia in 22 cases (4.3%), severe laterognathia in 10 cases (2.1%), and isolated frontal open bite in 9 cases (1.5%). The surgical procedures were as follows: bilateral sagittal split osteotomy (n = 336, 66%), Le Fort I osteotomy (n = 29, 5.9%), bimaxillary osteotomy (n = 35, 6.3%), and segment osteotomy (n = 107, 21.1%). Rigid fixation was used in 147 patients.

RESULTS

In 55% of the patients a postoperative neurosensory deficit of the inferior alveolar nerve was observed, which was only found in 28% after 1 year. Inflammatory wound healing was found in 5.3% of the patients.

CONCLUSION

Due to antibiotic perioperative prophylaxis and modern rigid osteosynthesis devices, orthognathic surgery has become a routine method in maxillofacial surgery with predictable surgical results.

[Finite element assisted study of the mechanical stability of 2 selected osteosynthesis systems for mandibular osteotomy]

The aim of this study was to use the finite element method (FEM) to compare the stability of 2.0 mm titanium screws in a triangular configuration with that of a 2.0 mm titanium miniplate as osteosynthesis material following bilateral sagittal split osteotomy. To this end, a model of the mandible was produced, consisting of 19,854 elements and 4285 nodes. The mechanical parameters of the materials investigated were taken from the literature or notified by the manufacturer. On condition that the materials were subjected only to their respective ultimate tensile stress, it was possible to neutralise the following masticatory force: 124.6 N with the miniplate and 167.5 N with the bicortical triangular screw configuration. The limitation of stress ensued from the peri-implant bone and not from the osteosynthesis material per se. The finite element method (FEM) appears to be suitable for simulating complex mechanical stress situations in the maxillofacial area, as also demonstrated by the fact that our data agree with those in the literature and with clinical experience. It will enable considerable savings to be made in terms of time and materials (animal experiments) in the future development of osteosynthesis materials and techniques.

Structural characterization of human recombinant and bone-derived bone sialoprotein. Functional implications for cell attachment and hydroxyapatite binding

Human bone sialoprotein (BSP) comprises 15% of the total noncollagenous proteins in bone and is thought to be involved in bone mineralization and remodeling. Recent data suggest a role for BSP in breast cancer and the development of bone metastases. We have produced full-length recombinant BSP in a human cell line and purified the protein from human bone retaining the native structure with proper folding and post-translational modifications. Mass spectrometry of bone-derived BSP revealed an average mass of 49 kDa and for recombinant BSP 57 kDa. The post-translational modifications contribute 30-40%. Carbohydrate analysis revealed 10 different complex-type N-glycans on both proteins and eight different O-glycans on recombinant BSP, four of those were found on bone-derived BSP. We could identify eight threonines modified by O-glycans, leaving the C terminus of the protein free of glycans. The recombinant protein showed similar secondary structures as bone-derived BSP. BSP was visualized in electron microscopy as a globule linked to a thread-like structure. The affinity for hydroxyapatite was higher for bone-derived BSP than for recombinant BSP. Cell adhesion assays showed that the binding of BSP to cells can be reversibly diminished by denaturation.

Cartilage oligomeric matrix protein (COMP) and collagen IX are sensitive markers for the differentiation state of articular primary chondrocytes

Primary chondrocytes dedifferentiate in serial monolayer with respect to their morphological and biosynthetic phenotype. They change from a round to a flattened fibroblast-like shape, and collagen I is secreted instead of the cartilage-specific collagen II. We analysed in detail the time course of dedifferentiation of mature bovine articular chondrocytes in monolayer for up to 32 weeks. Assessment of RNA expression by reverse transcription-PCR led to the identification of two novel phenotypical markers, the cartilage oligomeric matrix protein (COMP) and collagen IX, which are down-regulated faster than the widely accepted marker, collagen II. The different kinetics of COMP and collagen expression suggest differential regulation at the level of transcription. Immunostaining and metabolic labelling experiments confirmed the switch in the collagen expression pattern and the rapid down-regulation of de novo synthesis of COMP and collagen IX. Culture of chondrocytes in a three-dimensional matrix is known to stabilize the chondrocytic phenotype. We maintained cells for up to 28 weeks in an alginate bead system, which prevented dedifferentiation and led to a stabilization of collagen and COMP expression. Immunohistochemical analysis of the alginate beads revealed a similar distribution of matrix proteins to that found in vivo. Chondrocytes were transferred after a variable length of monolayer culture into the alginate matrix and the potential for redifferentiation was investigated. The re-expression of COMP and collagen IX was differentially regulated. The expression of COMP was re-induced within days after transfer into the three-dimensional matrix, while the expression of collagen IX was irreversibly down-regulated. In summary, these results demonstrate that the potential for redifferentiation decreases with increasing length of monolayer culture and show that the alginate bead system represents an attractive in vitro model to study the chondrocyte de- and re-differentiation processes, as well as extracellular matrix assembly.

Comparison of long-term transgene expression after non-viral and adenoviral gene transfer into primary articular chondrocytes

Different gene transfer approaches to achieve long-term transgene expression in cultured primary bovine chondrocytes were compared using enhanced green fluorescent protein (EGFP) as a reporter. Transduction with a high-capacity adenoviral vector was 82% efficient when analysed by fluorescence microscopy, while up to 42% of plasmid-transfected cells were EGFP positive with FuGene as a transfection reagent. Rapid dominant marker selection of plasmid-transfected cells was achieved in monolayer culture. With either method of gene transfer, a high proportion of the chondrocytes remained transgene positive during prolonged alginate culture. Transgene transcription in single cells was quantified with a confocal laser scanning microscope. Detection of EGFP expression was more sensitive with this method, identifying more transgene-expressing cells than conventional fluorescence microscopy. Long-term EGFP expression was higher in adenovirally transduced chondrocytes embedded in alginate as compared to plasmid-transfected cells cultured in monolayer or in alginate. Both the adenoviral and the plasmid-based approach appear suited for studies of the molecular and cellular mechanisms by which mutations in cartilage matrix proteins cause disease.

[Early rehabilitation in Baden-Wurttemberg--a study of all Baden-Wurrtemberg early rehabilitation centers]

Over a period of 12 months, all persons among the 10.4 million inhabitants of the state of Baden-Württemberg were included in the study who had suffered severe brain damage and were treated in special early rehab units, comprising 147 beds for adults and 43 for children. With 830 patients admitted, the incidence of severe brain damage was 7.98/100.000 in adults and 1.11/100.000 in children. 50 to 70 year old patients were over-represented, those older than 70 years were underrepresented due to geriatric rehab facilities for the latter. Male patients dominated, while female were somewhat younger. 54% of the patients were admitted from the hospital which had performed primary care, with an average stay of 67 days. Average early rehab duration was 53 days (arithmetic average; median 40 days, some patients required up to one year). 32.8% of the patients had suffered traumatic brain damage (ICD 851, 852, 854) and 40.9% non-traumatic brain affection (ICD 430, 431, 433-438, 310, 348), including 12.2% CVA (ICD 433-438), 8.5% subarachnoid and 12.3% intracerebral hemorrhage. Severity as indexed by the early rehab Barthel index improved from an initial average of -119 to -34 at discharge. 80% of the patients showed an overall improvement (71% of them by up to 200 points and 46% by up to 100 points).

Brain potentials in human patients with extremely severe diffuse brain damage

To test higher cortical functions of neurological patients, oddball tasks are often used in which a frequent and a rare stimulus are randomly presented and a P3 brain wave is recorded to the rare stimulus. We examined 33 patients with extremely severe brain injury. Three oddball conditions were used: with two sine tones (ST), with two complex tones (CT) and with vowels 'o' and 'i'. Across all patients, CT elicited P3 more often than ST, and the occurrence of the P3 after vowels was intermediate. However, among patients who showed a distinct P3 wave, its amplitude in the subgroup with traumatic brain injury was larger to vowels than to CT. In patients with non-traumatic etiology, CT and vowels elicited a P3 of a nearly equal amplitude. Stimuli of sufficient complexity should be used when the P3 technique is applied for assessment of cortical functions in severely impaired patients.

Mutations in cartilage oligomeric matrix protein causing pseudoachondroplasia and multiple epiphyseal dysplasia affect binding of calcium and collagen I, II, and IX

Mutations in type 3 repeats of cartilage oligomeric matrix protein (COMP) cause two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED). We expressed recombinant wild-type COMP that showed structural and functional properties identical to COMP isolated from cartilage. A fragment encompassing the eight type 3 repeats binds 14 calcium ions with moderate affinity and high cooperativity and presumably forms one large disulfide-bonded folding unit. A recombinant PSACH mutant COMP in which Asp-469 was deleted (D469 Delta) and a MED mutant COMP in which Asp-361 was substituted by Tyr (D361Y) were both secreted into the cell culture medium of human cells. Circular dichroism spectroscopy revealed only small changes in the secondary structures of D469 Delta and D361Y, demonstrating that the mutations do not dramatically affect the folding and stability of COMP. However, the local conformations of the type 3 repeats were disturbed, and the number of bound calcium ions was reduced to 10 and 8, respectively. In addition to collagen I and II, collagen IX also binds to COMP with high affinity. The PSACH and MED mutations reduce the binding to collagens I, II, and IX and result in an altered zinc dependence. These interactions may contribute to the development of the patient phenotypes and may explain why MED can also be caused by mutations in collagen IX genes.

The nuclear export receptor Xpo1p forms distinct complexes with NES transport substrates and the yeast Ran binding protein 1 (Yrb1p)

Xpo1p (Crm1p) is the nuclear export receptor for proteins containing a leucine-rich nuclear export signal (NES). Xpo1p, the NES-containing protein, and GTP-bound Ran form a complex in the nucleus that translocates across the nuclear pore. We have identified Yrb1p as the major Xpo1p-binding protein in Saccharomyces cerevisiae extracts in the presence of GTP-bound Gsp1p (yeast Ran). Yrb1p is cytoplasmic at steady-state but shuttles continuously between the cytoplasm and the nucleus. Nuclear import of Yrb1p is mediated by two separate nuclear targeting signals. Export from the nucleus requires Xpo1p, but Yrb1p does not contain a leucine-rich NES. Instead, the interaction of Yrb1p with Xpo1p is mediated by Gsp1p-GTP. This novel type of export complex requires the acidic C-terminus of Gsp1p, which is dispensable for the binding to importin beta-like transport receptors. A similar complex with Xpo1p and Gsp1p-GTP can be formed by Yrb2p, a relative of Yrb1p predominantly located in the nucleus. Yrb1p also functions as a disassembly factor for NES/Xpo1p/Gsp1p-GTP complexes by displacing the NES protein from Xpo1p/Gsp1p. This Yrb1p/Xpo1p/Gsp1p complex is then completely dissociated after GTP hydrolysis catalyzed by the cytoplasmic GTPase activating protein Rna1p.

Proteoglycans in the nervous system--the quest for functional roles in vivo

Large numbers of different proteoglycans are expressed in tightly regulated spatio-temporal patterns by both the nerve cells (neurons) and the supporting glial cells of the nervous system. Several of these proteoglycans have been shown by studies in vitro to affect the migration of neural precursor cells, the elongation and pathfinding of neurites and the formation and stabilization of synapses. Such processes are important for the accurate wiring of the nervous system, and so it has been postulated that proteoglycans play an essential role during neural development. However, with few exceptions, the phenotypes of null mutations in mice and some human genetic diseases have provided little support for this view. Here we will review recent data from both in vitro and in vivo studies analyzing the function of proteoglycans in the nervous system in order to provide possible explanations for their apparent lack of function.

Thrombospondin-4 binds specifically to both collagenous and non-collagenous extracellular matrix proteins via its C-terminal domains

Full-length and truncated forms of rat thrombospondin-4 (TSP-4) were expressed recombinantly in a mammalian cell line and purified to homogeneity. Biochemical analysis revealed a limited proteolytic processing, which detaches the N-terminal heparin-binding domain from the rest of the molecule and confirmed the importance of the heptad-repeat domain for pentamerization. In electron microscopy the uncleaved TSP-4 was seen as a large central particle to which five smaller globules are attached by elongated linker regions. Binding of TSP-4 to collagens and to non-collagenous proteins could be detected in enzyme-linked immunosorbent assay-style ligand binding assays, by surface plasmon resonance spectroscopy, and in rotary shadowing electron microscopy. Although the binding of TSP-4 to solid-phase collagens was enhanced by Zn(2+), that to non-collagenous proteins was not. The interactions of TSP-4 with both classes of proteins are mediated by C-terminal domains of the TSP-4 subunits but do not require an oligomeric structure. Major binding sites for TSP-4 are located in or close to the N- and C-terminal telopeptides in collagen I, but additional sites are detected in more central regions of the molecule.

Nup2p, a yeast nucleoporin, functions in bidirectional transport of importin alpha

Import of proteins containing a classical nuclear localization signal (NLS) into the nucleus is mediated by importin alpha and importin beta. Srp1p, the Saccharomyces cerevisiae homologue of importin alpha, returns from the nucleus in a complex with its export factor Cse1p and with Gsp1p (yeast Ran) in its GTP-bound state. We studied the role of the nucleoporin Nup2p in the transport cycle of Srp1p. Cells lacking NUP2 show a specific defect in both NLS import and Srp1p export, indicating that Nup2p is required for efficient bidirectional transport of Srp1p across the nuclear pore complex (NPC). Nup2p is located at the nuclear side of the central gated channel of the NPC and provides a binding site for Srp1p via its amino-terminal domain. We show that Nup2p effectively releases the NLS protein from importin alpha-importin and beta and strongly binds to the importin heterodimer via Srp1p. Kap95p (importin beta) is released from this complex by a direct interaction with Gsp1p-GTP. These data suggest that besides Gsp1p, which disassembles the NLS-importin alpha-importin beta complex upon binding to Kap95p in the nucleus, Nup2p can also dissociate the import complex by binding to Srp1p. We also show data indicating that Nup1p, a relative of Nup2p, plays a similar role in termination of NLS import. Cse1p and Gsp1p-GTP release Srp1p from Nup2p, which suggests that the Srp1p export complex can be formed directly at the NPC. The changed distribution of Cse1p at the NPC in nup2 mutants also supports a role for Nup2p in Srp1p export from the nucleus.

Peroxynitrite does not decompose to singlet oxygen ((1)Delta (g)O(2)) andnitroxyl (NO(-))

According to Khan et al. [Khan, A. U., Kovacic, D., Kolbanovskiy, A., Desai, M., Frenkel, K. & Geacintov, N. E. (2000) Proc. Natl. Acad. Sci. USA 97, 2984-2989], peroxynitrite (ONOO(-)) decomposes after protonation to singlet oxygen ((1)Delta(g)O(2)) and singlet oxonitrate (nitroxyl, (1)NO(-)) in high yield. They claimed to have observed nitrosyl hemoglobin from the reaction of NO(-) with methemoglobin; however, contamination with hydrogen peroxide gave rise to ferryl hemoglobin, the spectrum of which was mistakenly assigned to nitrosyl hemoglobin. We have carried out UV-visible and EPR experiments with methemoglobin and hydrogen peroxide-free peroxynitrite and find that no NO(-) is formed. With this peroxynitrite preparation, no light emission from singlet oxygen at 1270 nm is observed, nor is singlet oxygen chemically trapped; however, singlet oxygen was trapped when hydrogen peroxide was also present, as previously described [Di Mascio, P., Bechara, E. J. H., Medeiros, M. H. G., Briviba, K. & Sies, H. (1994) FEBS Lett. 355, 287-289]. Quantum mechanical and thermodynamic calculations show that formation of the postulated intermediate, a cyclic form of peroxynitrous acid (trioxazetidine), and the products (1)NO(-) and (1)Delta(g)O(2) requires Gibbs energies of ca. +415 kJ .mol(-1) and ca. +180 kJ.mol(-1), respectively. Our results show that the results of Khan et al. are best explained by interference from contaminating hydrogen peroxide left from the synthesis of peroxynitrite.

Calcium affinity, cooperativity, and domain interactions of extracellular EF-hands present in BM-40

The structure and function of cytosolic Ca(2+)-binding proteins containing EF-hands are well understood. Recently, the presence of EF-hands in an extracellular protein was for the first time proven by the structure determination of the EC domain of BM-40 (SPARC (for secreted protein acidic and rich in cysteine)/osteonectin) (Hohenester, E., Maurer, P., Hohenadl, C., Timpl, R., Jansonius, J. N., and Engel, J. (1996) Nat. Struct. Biol. 3, 67-73). The structure revealed a pair of EF-hands with two bound Ca(2+) ions. Two unusual features were noted that distinguish the extracellular EF-hands of BM-40 from their cytosolic counterparts. An insertion of one amino acid into the loop of the first EF-hand causes a variant Ca(2+) coordination, and a disulfide bond connects the helices of the second EF-hand. Here we show that the extracellular EF-hands in the BM-40 EC domain bind Ca(2+) cooperatively and with high affinity. The EC domain is thus in the Ca(2+)-saturated form in the extracellular matrix, and the EF-hands play a structural rather than a regulatory role. Deletion mutants demonstrate a strong interaction between the EC domain and the neighboring FS domain, which contributes about 10 kJ/mol to the free energy of binding and influences cooperativity. This interaction is mainly between the FS domain and the variant EF-hand 1. Certain mutations of Ca(2+)-coordinating residues changed affinity and cooperativity, but others inhibited folding and secretion of the EC domain in a mammalian cell line. This points to a function of EF-hands in extracellular proteins during biosynthesis and processing in the endoplasmic reticulum or Golgi apparatus.