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Biomedical subjects

W Bähr

Publications and source records attributed to W Bähr.

At least 19 recordsLinked to original sources
PubMed2001

[Cortical thickness of the mandible with special reference to miniplate osteosynthesis. Morphometric analysis of autopsy material].

Thirty-two human mandibles were marked with three typical fracture lines: a low condylar fracture, a fracture of the mandibular angle, and one through the mental foramen on each side. The mandibles were sectioned at the fixation sites of the miniplate screws. The thickness of the cortical layer was measured with a scaled magnifying glass at the points of anthropological interest and at the marked screw holes. The inferior cortical layer turned out to be thickest in the anterior area. In contrast, it was very thin at the mandibular angle, which might explain the higher complication rate in treating fractures in this region. The thickness of the lingual cortex increased up to the symphysis, whereas the buccal cortical layer showed a decline in size from the mandibular angle up to the chin. The cortical bone at the alveolar ridge was porous. The cortical supply for miniplate osteosynthesis at the condylus ranged from 1.1 mm up to 1.74 mm, which seems to be limited, but due to the small diameter of the condylus most common screws obtain additional anchorage in the inner cortex. The thickness of the cortical layer at the mandibular angle increased from 1.47 mm at the ramus up to 1.97 mm at the beginning of the corpus, reaching 2.14-2.38 mm for the lower plate at the mental foramen. The results for the upper plate were slightly lower.

Bone Plates↗
PubMed1999

Biodegradable osteosynthesis material for stabilization of midface fractures: experimental investigation in sheep.

The most frequently tested biodegradable osteosynthesis materials have up to now largely consisted of poly-L-lactide (PLLA). The PLLA polymers appear to have sufficient mechanical strength for fracture treatment in the midface, but their degradation does not seem to be uniform enough to allow their clinical use. During the degradation process the disintegration products elicit a foreign body reaction due to non-uniform degradation rates. The foreign body reaction is sometimes combined with a fluctuant swelling at the implantation site. Implants injection-moulded from 90:10 PLLA/PGA (polyglycolic acid) have a more uniform degradation rate and seem to lead to a milder foreign body reaction. We bridged Le Fort I osteotomies in sheep using a system of injection-moulded PLLA/PGA 90:10 plates and screws and compared it with 2 mm AO miniplates and mini-screws made from titanium. Light microscopy evaluation showed that the PLLA/PGA copolymer system experienced its highest mechanical stress at the transition from screw head to screw shaft. Nevertheless, the fragments fixed with the copolymers were on the whole only slightly less stable than those fixed with the titanium system. The foreign body reaction solely due to co-polymer degradation was not severe, considering the fibrous tissue response that was found associated with the titanium components. The study does show that the copolymer investigated is adequate for clinical use as a biodegradable osteosynthesis material, at least in low stress bearing areas.

Absorbable Implants↗
PubMed1998

Vascular anastomosis using a biodegradable device with a heat-shrinking sleeve: a preliminary report.

PURPOSE: The objective of this study is to present a simple mechanical anastomosis system capable of uniting vessels of differing diameters and to evaluate its applicability. MATERIALS AND METHODS: A new mechanical system for anastomosis of small vessels was used in 30 rabbits to join 100 sectioned carotid arteries and jugular veins. The system is resorbable and consists of a cuff and a shrinkable sleeve. To carry out the anastomosis, one vessel end is pulled through the cuff and everted over it. The second vessel end is then slipped over the everted vessel end and the cuff. A heat-shrinking sleeve is positioned over the site and shrunk to produce permanent fixation. RESULTS: The overall patency rate of the anastomoses was 96.6% in the arteries and 93.3% in veins. Microscopically, the intima-to-intima contact sites were bridged by an endothelial layer in the first postoperative weeks. CONCLUSION: Advantages of the system include a short insertion time, simple instrumentation, a high patency rate, and resorbability. However, the method requires additional vessel length for eversion, and it cannot be used for end-to-side anastomoses.

Absorbable Implants↗
PubMed1998

Use of the "double barrel" free vascularized fibula in mandibular reconstruction.

PURPOSE: Microvascularized fibula transplants have become established in reconstruction of the mandible. However, because of the limited diameter of the fibula compared with the height of the mandible, the vertical distance between the reconstructed segment and the occlusal plane can be substantially large. This is a particular problem in nonatrophic or dentate mandibles, especially when rehabilitation with dental implants or an implant-borne denture is contemplated. The large leverage forces resulting from the high vertical dimension of the prosthetic construction can lead to overloading of the osseointegrated implants and endanger the longevity of the prosthetic restoration. This article describes experience with a new method of circumventing this problem. PATIENTS AND METHODS: This procedure was used in eight patients. A fibula graft corresponding to at least twice the length of the mandibular defect was harvested, halved perpendicular to its length, and the resulting struts folded on top of each other to form a "double barrel." The struts are then fixed to each other with screws and plates and stabilized in the defect using a reconstruction plate. RESULTS: Compared with the conventional one-strut fibula transplant, the "double-barrel" graft achieved more bone height and appreciably reduced the vertical distance to the occlusal plane. CONCLUSIONS: This technique creates better conditions for prosthetic rehabilitation. In comparison with the iliac graft, the fibula is easier to harvest, more reliable regarding anastomosis, and is associated with less postoperative morbidity.

Adult↗
PubMed1998

Blood supply of small fibula segments: an experimental study on human cadavers.

When vascularized fibula grafts are used in mandibular reconstruction, it is often necessary to divide the graft into segments so as to follow the mandibular curvature. The periosteal blood supply to the segments is usually sufficient. It is unclear, however, how short the segments can be without compromising the blood supply. The present study sought to clarify this issue by injecting Indian ink into the afferent vessels in human cadavers. The evaluation of 300 specimens showed the ink perfusion to be significantly higher in segments longer than 1 cm than in shorter segments. Furthermore, the perfusion in the cortical outer third of the shaft was markedly higher than in the cortical inner two-thirds. The staining was significantly more intense in the younger (32-55 years) than in the older (56-73 years) age group. With correct dissection and successful anastomosis, however, fibula segments 1 cm or longer are probably sufficiently perfused, independent of the patient's age. The perfusion in shorter segments is uncertain. Clinically this means that segments shorter than 1 cm ought to be used only in a surgically non-compromised recipient site, where they could also take as non-vascularized grafts.

Adult↗
PubMed1996

Limits of the mandibular symphysis as a donor site for bone grafts in early secondary cleft palate osteoplasty.

With the assistance of computed tomography, the bone volume in the symphysis was assessed on 28 historic mandibles with mixed dentition, before the eruption of the canines. The quantification gave an average bone volume of 1.0 cm3, and the values fitted a normal distribution curve. Assuming that there were no appreciable differences in size between the historic and recent mandibles, the mandibular symphysis can theoretically be used as a donor site in early secondary osteoplasty in about 92% of cleft patients to augment a cleft volume of 0.5 cm3, in 50% for a cleft volume of 1.0 cm3, and in 18% for a cleft volume of 1.5 cm3. With cleft volumes larger than 1.5 cm3, the symphysis can hardly be considered. If, however, a safety margin of 5 mm from the apices of the front teeth is maintained, the chance that the mandibular symphysis will suffice decreases for a 0.5 cm3 volume to 64%, for a 1.0 cm3 cleft to 3.5%, and for a 1.5 cm3 cleft to 0%.

Bone Transplantation↗
PubMed1993

A comparative animal experimental study of differently dimensioned osteosynthesis screws used in the mid-face.

The soft tissue covering most of the midfacial skeleton is relatively thin. On account of this plates and screws of the 2 mm systems used in the osteosynthesis of this region can bulge and/or be palpable through the thin integument. This shortcoming has prompted the need to develop smaller systems. The present study was designed to investigate whether these more delicate systems are capable of withstanding the midfacial forces that come to bear during functional mastication. For the study a Le Fort I osteotomy was carried out in 10 sheep. The mobile maxilla was fixed with osteosynthesis plates and screws. This paper reports on 40 plates and 170 screws of two AO titanium systems. It compares the strength of 1.5 mm and 2.0 mm AO screws. The anchorage of the screws was assessed by evaluating the nature of contact between the screw and interfacial bone. The loaded screws showed no discernible differences in postoperative bone remodelling that could be correlated to the osteosynthesis systems. Although the experimental situation may not be directly comparable to the trauma or osteotomy case, this study lends credibility to the assumption that the 1.5 mm screw system could be used instead of the 2.0 mm system, even in mid-face areas associated with high masticatory loads.

Analysis of Variance↗
PubMed1993

[Osteosynthesis of the middle third of the face. A comparative analysis of screws inserted with or without preliminary tapping].

Results of osteosynthesis of middle third of face were compared after insertion, with or without pre-tapping, of more than 400 miniscrews (AO, 2 mm diameter). The parameters measured were the torque, the screw/bone interface and the morphology of the implant bed. The screw/bone area of contact was large and the torque superior in the absence of pre-tapping. Greater screw retention values were also be gained by applying the miniscrews without pre-tapping in cases where bone thickness does not exceed 5 mm. Pre-tapping would appear to be indicated when the bone is thicker, to make screw insertion easier and to prevent its fracture during insertion.

Bone Screws↗
PubMed1992

Comparison of torque measurements between cortical screws and emergency replacement screws in the cadaver mandible.

The so-called emergency screws are designed for use in a drill hole where the conventional screw has failed following a stripped bone thread. It is not known, however, if these screws are as well anchored in bone as cortical screws, nor is it known how well they secure contact to the previously damaged screw bed. On the basis of torque measurements in mandibles of fresh cadavers, emergency screws were compared with cortical screws. Further, the contact between emergency screw and bone was investigated on interfacial sections after embedding in methyl methacrylate resin. The maximum torque reached during insertion of the AO emergency screws was about 70% of the value measured with 2.7-mm conventional cortical screws and 67% of this value when the 3.2-mm emergency screws were used. While the emergency screws had good contact to the bone in the thread crest area, no bone contact was evident at the bottom of thread groove. This experimental situation can not be entirely extrapolated to the clinical situation. However, the study seems to suggest that emergency screws do not fully meet the demands of rigid internal fixation.

Adolescent↗
PubMed1992

The response of midfacial bone in sheep to loaded osteosynthesis screws in pretapped and nontapped implant sites.

This study compared the functional retention of pretapped and self-tapping 2-mm AO miniscrews (Stratec Medical, Waldenburg, Switzerland) in an animal experimental model. Histologic evaluation of the bone surrounding the loaded screws showed significantly more remodeling when pretapped screws were used than when self-tapping screws were used. Although the experimental situation may not be directly comparable with the clinical situation, this study does lend credibility to the assumption that pretapping is not advisable in the thin bone of the midface.

Animals↗
PubMed1992

Nasal intubation in the presence of frontobasal fractures: a retrospective study.

In most cases, surgical management of craniofacial fractures involves correction of occlusion. This requires nasal intubation. In the case of frontobasal fractures with simultaneous cerebrospinal fluid (CSF) fistula, nasal intubation is thought to increase the risk of meningitis. An analysis of the records of 160 patients with frontobasal fractures and CSF fistulae showed that the route of intubation had no influence on the postoperative complication rate. Nasal intubation is therefore not contraindicated in frontobasal fractures with CSF fistulae.

Anti-Bacterial Agents↗
PubMed1992

Intraoperative histological evaluation of tumor resection borders without prolonging surgery.

Frozen sections permit an intraoperative check for margin clearance during tumor surgery. However, much time is usually lost while waiting for the evaluation of the specimens, especially if they are many. In 24 patients with oral cancer, biopsies were taken from the regions of the intended resection borders before beginning with the lymphadenectomy. While histological evaluation was being performed by the pathologist, the surgical team proceeded to remove the regional lymphatic drainage. This procedure offers the advantage of being able to evaluate a large number of frozen sections without substantially prolonging the operation.

Adipose Tissue↗
PubMed1992

The loadability of the 0.8-mm micro-system in thin midfacial regions--an animal experimental study.

The so-called 2-mm systems are well established in the osteosynthesis of the mid-face. Due to the relatively thin soft tissue covering of most of the mid-face, however, the plates and screws of these systems often appear large, and disturb the patient because they are palpable and/or bulge through the skin. To avoid this disadvantage, more delicate systems have been designed. The question arises here, however, whether the more delicate systems could also be applied in thin mid-face regions that experience high functional loads. This study compares the functional loadability of 0.8-mm Luhr and 2.0-mm AO screws in an animal experimental model. Histological evaluation of the implant beds of the loaded screws showed significant differences in postoperative bone remodelling which could be correlated to the systems. Extrapolation of the results to the clinical situation suggests that care should be exercised when using Micro-Systems in highly loaded regions of the mid-face.

Animals↗
PubMed1992

Comparison of transcutaneous incisions used for exposure of the infraorbital rim and orbital floor: a retrospective study.

One hundred and five patients were investigated for functional and aesthetic impairments following treatment of orbital trauma through subciliary, mid-lower eyelid, or infraorbital incisions. The progress of impairments with time was assessed, and the merits and shortcomings of each of the three approaches were established. The results showed that impairments persisting up to 6 months postoperatively have virtually not receded even after 6 years. The infraorbital incision showed the highest frequency of impairments, followed by the subciliary incision. The mid-lower eyelid incision showed the best results, with an impairment frequency well below those of the other two approaches. This approach seems to combine the advantages of the infraorbital incision with the unnoticeable scar formation associated with the subciliary incision.

Adolescent↗
PubMed1992

[Nasal intubation for frontobasal fractures?].

In most cases the surgical management of craniofacial fractures involves a correction of the occlusion. This requires nasal intubation. In a frontobasal fracture with simultaneous CSF fistula, nasal intubation is thought to increase the risk of meningitis. An analysis of the records of 160 patients with frontobasal fractures and CSF fistulae revealed that the route of intubation had no influence on the post-operative complication rate. Nasal intubation is therefore not contraindicated in frontobasal fractures with CSF fistulae.

Cerebrospinal Fluid Rhinorrhea↗
PubMed1991

Pre-tapped and self-tapping screws in children's mandibles. A scanning electron microscopic examination of the implant beds.

One hundred 2 mm AO miniscrews were inserted into the mandibles of eight fresh cadavers aged 8 to 12 years. Scanning electron microscopic examination of the implant beds showed cracks and accumulated bone material, as well as signs of crushing and shearing stress, regardless of whether the screws were pre-tapped or not. When, during screw insertion, the axis of the screw deviated by at least 10 degrees from the axis of the tap, two intersecting threads resulted. It is concluded that during osteosynthesis in child mandibles pre-tapping is not recommended.

Bone Screws↗