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Biomedical subjects

M Wehmöller

Publications and source records attributed to M Wehmöller.

At least 19 recordsLinked to original sources
PubMed2002

[Reconstruction of the frontal bone with individual titanium implants after surgical therapy of osteomyelitis of the frontal bone].

Individually prefabricated titanium implants enable the reconstruction of the frontal bone after surgical therapy of osteomyelitis without compromising mechanical stability or aesthetic results. Primarily the infected bone tissue is removed. Helical computed tomographic systems are used for the aquisition of patient data. After being transmitted to a computer aided design system (CAD-system) this data is used for construction of the implant geometry using freeform-surfaces. The outer surface contour is derived from the contours of the bone defect. The completed computer-based implant design is finally transformed into control data to run the milling machine which produces the implant from a block of titanium. Modern industrial CAD/CAM-technology allows standardized prefabrication using data from CT-scans. The precision of all implants was predictable and duration of the reconstructive procedure could be reduced. During postoperative follow-up (5-24 months) no loss of implant or recurrence of the osteomyelitis could be observed.

Adolescent↗
PubMed2002

[Osseous processes of the skull--analysis of requirements for robot-assisted surgery].

To design a roboter-assisted trepanation setting of the cranium, an evaluation was done to classify patients with osseous lesions according to pathologies, dimensions and localisations. Emphasis was laid on dimensions and localisation of the pathology to gain information on future configurations of work spaces for robotics in the neurosurgical operation room. All patients with surgery of osseous lesions of the cranium in the years 1993-2001 were evaluated retrospectively. Localisations, dimensions of trepanation and histologic results were evaluated.

Adult↗
PubMed2002

[Cadaver study: robot-assisted cranial resection and implantation of titanium plates].

A processing chain for the prefabrication of individual titanium implants for cranioplasty was developed at the Ruhr-University Bochum. In patients with tumours a simultaneous resection of cranial bone and insertion of the individual implant is desirable. At first resection templates were used for this. New developments aim at a preoperative definition of resection trajectories for surgical robots corresponding to both the planning of the resection and the implant. This study used ovine cadaver skulls for robot resection experiments. The results demonstrate possible applications, limitations and necessary prerequisites in robot assisted cranial surgery.

Animals↗
PubMed2002

[A graded composite material for use in the area of the cranial and facial skull].

For the reconstruction of complex skull defects with individual prefabricated CAD/CAM-implants titanium is well established as bone substitution material. The aim of our studies was to optimize a composite material from polyesters and calcium phosphate. Therefore two different operating procedures (hot pressing and gas-flushing) were combined. As a result the graded composition and porosity of the implants allow a spatial guided degradation progress and cell ingrowth. First biocompatibility tests in vitro with primary human osteoblasts showed a much better pH-characteristic and a better biocompatibility of the composites in comparison with the pure polymers. Degradation experiments in vitro confirmed the different expected degradation rates of the composite materials. As a next step in vivo experiments in ovine skulls are in progress.

Animals↗
PubMed2002

[SOP-surgical operation planning].

Our active research project DFG Eu-49/1-2 strives to the reconstruction of bone defects basing on the individual craniofacial implants prefabricated within the TICC-processing-chain. In cases of disease of the bone the defect is to plan and the bone has to be resected. The planning of the defect is done on CT- and CAD-data. The common visualisation of this different data-types (CT-data as pixel- or voxel-data on the one hand and CAD-data as geometry-data on the other hand) was not possible in the used application. The development of "Surgical Operation Planning" (SOP) results in an application between CT-visualisation and CAD-application and allows the common visualisation and planning for defect reconstructions.

Brain Neoplasms↗
PubMed2001

[Management of craniofacial bone defects with individually prefabricated titanium implants. Follow-up and evaluation of 78 patients with 78 titanium implants 1994-1998].

STUDY: From 1994 to 1998, 78 prefabricated titanium implants were used for the reconstruction of large and complex cranial and craniofacial defects in 76 patients at 19 European centres. After a mean follow-up of 8 months, a clinical and radiological examination was used to determine the results of the reconstruction and the patients' satisfaction. Using a standardized questionnaire patients were also able to comment, subjectively, on improvements or alterations after the insertion of the implant. RESULTS: Two implants were removed after an early infectious complication and in a another two cases the implants were removed in order to obtain a tissue sample for histological examination. All other patients showed constant good to excellent clinical and radiological findings with high patient satisfaction. DISCUSSION: The use of titanium fulfils the highest demands of biocompatibility while at the same time allowing the possibility of an oncological examination using suitable turbo-spinecho-sequences in MRI.

Adolescent↗
PubMed2001

[Alternative bone replacement substances for preoperative design of individual CAD/CAM skull implants].

BACKGROUND: The preoperative manufacturing of individual skull implants using computer aided design (CAD) and computer aided manufacturing (CAM) is based on the use of titanium, although the use of other materials is also potentially possible. THE USE OF OTHER MATERIALS: The use of poly-(D,L-lactide) (PDLLA) as an implant material was investigated using an adult, formalin fixed sheep's head with a complex frontolateral defect. A standard individual titanium implant as well as a resection template made of aluminium were milled in order to allow bone resection and reconstruction within one operation. A mould was made of Teflon for the fabrication of the PDLLA implant using carbon dioxide at high pressure. This procedure allowed a critical comparison to be made of both implant materials and showed that the production of a biodegradable PDLLA implant is possible. At present the titanium implant is superior to the PDLLA implant, as PDLLA settled with slightly larger dimensions than the mould, although the structure itself was exact. DISCUSSION: The goal of the present research is the fabrication of a functionally graded material made of polylactide, polyglycolide, calcium phosphate and osteoinductive proteins using existing technology, which will meet all of the requirements for stability, resorption kinetics, biocompatibility, radiotranslucence and osteogenic potency of an ideal implant material.

Bone Substitutes↗
PubMed2000

[Pure titanium as bone substitute. Geometric and substance-specific aspects of computer-assisted fabrication and follow-up imaging].

Computer-assisted prefabricated skull implants of pure titanium as a bone replacement material have been used in 22 departments since 1994. Our experience with 104 implants includes clinical aspects (indication; tissue quality; surgical technique; patient guidance), but also geometric and material-specific parameters (acquisition, transfer, and evaluation of CT data; construction; manufacturing; cleaning; postoperative use of radiologic techniques). While the clinical aspects are responsibly defined by the respective surgeon, the geometric and material-specific parameters of individual implants have to comply with the laws on medical products. Therefore, the prospective documentation for each implant includes: helical CT acquisition parameters; geometric data of the computer-based skull model and implant; the cleaning procedure; and the individual marking. Medically specified pure titanium is processed by milling only so that neither purity nor structure is impaired. A specially developed milling technique guarantees the fabrication of all constructed elements down to fine details of 50 microns. Considering the necessary radiologic follow-up of defects after tumor surgery, all patients in our hospital undergo postoperative MRI examination, partly with preoperative documentation as an intraindividual control. Such comprehensive documentation and quality assurance is essential for techniques of prefabricated bone substitution. Hand in hand with scientific research and clinical application, these formal criteria have to be elaborated and fulfilled for the respective techniques. The successful determination of specifically adapted MRI sequences goes even one step further: spin-echo sequences minimize inhomogeneities of the magnetic field induced by the titanium implants and enable accurate postoperative documentation and diagnostics especially in the follow-up after tumor surgery.

Bone Substitutes↗
PubMed2000

Synthesis of CAD/CAM, robotics and biomaterial implant fabrication: single-step reconstruction in computer-aided frontotemporal bone resection.

The preoperative manufacturing of individual skull implants, developed by an interdisciplinary research group at Ruhr-University Bochum, is based on the use of titanium as the most common material for implants at present. Using the existing technology for materials that can be milled or moulded, customized implants may be manufactured as well. The goal of the study was to examine biodegradable materials and to evaluate the practicability of intraoperative instrument navigation and robotics. Data acquisition of an adult sheep's head was performed with helical computer tomography (CT). The data were transferred onto a computer aided design/computer aided manufacturing system (CAD/CAM system), and two complex defects in the frontotemporal skull were designed. Standard individual titanium implants were milled for both of the defects. Additionally, for one of the defects a resection template, as well as a mould for the biodegradable poly(D,L-lactide) (PDLLA) implant, were fabricated by the CAD/CAM system. A surgeon carried out the first bone resection (#1) for the prefabricated titanium implant using the resection template and an oscillating saw. The robot system Stäubli RX90CR, modified for clinical use, carried out the other resection (#2). Both titanium implants and the PDLLA implant were inserted in their respective defects to compare the precision of their fit. A critical comparison of both implant materials and both resection types shows that fabrication of a PDLLA implant and robot resection are already possible. At present, the titanium implant and resection using a template are more convincing due to the higher precision and practicability.

Absorbable Implants↗
PubMed1999

One-step resection and reconstruction of the mandible using computer-aided techniques--experimental and clinical results.

In patients with advanced oral cancer, a resection of the mandible continuity is often indicated. This new method presented here uses computer-aided design and manufacturing (CAD/CAM) for preoperative fabrication of individual mandibular prostheses and their corresponding resection templates in a direct fashion without the need for additional physical models. In this experimental application, a segment of a dried mandible was resected and replaced by a titanium prosthesis prefabricated by CAD/CAM. It was the aim of this investigation to verify the processing chain and its precision, i.e., the fit of an individual implant, such as this. Although this new technique offers fascinating opportunities, possible clinical drawbacks have to be taken into account.

Bone Screws↗
PubMed1999

Experimental computer-assisted alloplastic sandwich augmentation of the atrophic mandible.

PURPOSE: This study evaluated the effectiveness of a technique that combined computer-aided surgery with alloplastic augmentation and implant-borne prosthodontic rehabilitation of the atrophic mandible. MATERIALS AND METHODS: Computed tomographic (CT) data from an atrophic cadaver mandible were transferred to a computer-aided design (CAD) system that prepared an anterior sandwich osteotomy. The cranial segment was moved upward and backward to provide an ideal alveolar relationship, and the geometry of the intermediate space was used to design a titanium implant. Furthermore, a surgical template was derived for the osteotomies, and insertion of dental implants was planned to stabilize both the transposed bone and the intermediate implant on the bony base. An identical implant for augmentation was also fabricated from poly-D,L-lactide in a mold as a possible resorbable carrier for osteoinductive proteins. RESULTS: The experimental surgery was successfully performed with maximum precision on the dried mandible. The fabrication of an implant made out of poly-D,L-lactide for the same purpose was also possible. CONCLUSIONS: This preliminary experiment showed that it is possible to use CAD/computer-aided manufacturing (CAM) technology to prepare a prefabricated template and a corresponding titanium implant for mandibular augmentation with a high degree of exactness. Dental implants could be planned and integrated in this procedure as well. The fabrication of a mold using this method also provided the opportunity to give a complex shape to possible carriers of osteoinductive substances.

Alveolar Bone Loss↗
PubMed1999

Reconstruction of an extreme frontal and frontobasal defect by microvascular tissue transfer and a prefabricated titanium implant.

A 30-year-old man was referred to us with an extreme frontal and frontobasal defect from a motorbike accident 12 years before. Multiple attempts at frontal and frontobasal revision and reconstruction had been performed over the years, with several episodes of meningitis. Reconstruction was planned in two steps. First, a revision of the anterior skull base with mobilization of meningeal adhesions and duraplasty, removal of infected masses of polymethylmethacrylate out of the upper ethmoid sinuses, and coverage with a deepithelialized latissimus dorsi free flap were performed. In the second step 3 months later, aesthetic forehead reconstruction was achieved with a pre-fabricated individual titanium implant. The predictable result of this two-step reconstruction was very pleasing. Safe separation of the cranial cavity from the upper airways was essential, requiring free tissue transfer in this case, and is a prerequisite for any alloplastic forehead reconstruction. Timing of the two-step procedure, including the CT data acquisition; handling of soft tissues, bone, and foreign material; and construction details of the implant demonstrate the necessary complex management of this, the most difficult case of the 88 applications of the new computer aided design and manufacturing technique thus far. Even the most elaborate computer aided preparation cannot be successful without consideration of established surgical principles.

Adult↗
PubMed1998

Single-step fronto-orbital resection and reconstruction with individual resection template and corresponding titanium implant: a new method of computer-aided surgery.

In the cranio-maxillofacial field, computer-aided surgery based on computed tomography (CT) data is becoming more and more important. Navigation systems, which allow the precise intraoperative orientation of surgical instruments, can be used for greater accuracy in determining resection margins of tumours. These techniques support ablative procedures very well, but defect reconstruction still remains a problem. In contrast, computer-aided design (CAD) and computer-aided manufacturing (CAM) systems allow the construction and fabrication of individual templates for bone resection based on coherent numerical 3-D models. The template determines the exact pathway of an oscillating saw so that the planned extent of the resection and, if necessary, also the orientation of the cutting plane are verified. An individual titanium implant is prefabricated with a geometry fitting to that of the template. This implant closes the bone defect so that the contour is reconstructed precisely and individually. This new method was used for the first time for a single-step resection of a meningioma and defect-reconstruction. The tumour which had infiltrated the frontal bone resulting in a protrusion. Fronto-orbital resection and insertion of the titanium implant worked precisely as planned, so that this method offers promising new applications in the field of computer-aided surgery.

Adult↗
PubMed1998

Individual prefabricated titanium implants in reconstructive craniofacial surgery: clinical and technical aspects of the first 22 cases.

The reconstruction of craniofacial bone defects by intraoperative modeling of implants restricts the choice of material and its biocompatibility and also reduces the predictability of the aesthetic result. These shortcomings go hand in hand with a prolonged surgical procedure time and increased stress on the patient. In contrast, modern industrial computer-aided design and computer-aided manufacturing systems allow the prefabrication of titanium implants, i.e., individual computer-based three-dimensional models of the bone defect are generated after acquisition, transfer, and evaluation of helical computed tomographic data. Based on these data, the individual shape of the implant is designed using freeform-surfaces geometries and is fabricated by a numerically controlled milling machine in a direct fashion. The conical margins of this implant are designed with a precision of 0.25 mm to the borders of the defect, and the surface contours are generated harmonically to the nonaffected neighboring contours with a constant thickness of 1.5 mm. Individual constructions for fixation with the dimensions of microplates are integrated in this process if screw holes cannot be drilled in thin overlapping implant margins. The reconstruction of 22 posttraumatic, postoperative, or primary cranial and craniofacial defects measuring up to 18 cm was performed using this new method. Wound healing was uneventful in all but one case, although some of the patients had been operated on several times before. The result was always predictable and constant using this highly precise technique, and duration of surgery was reduced dramatically.

Adolescent↗
PubMed1997

Individual prostheses and resection templates for mandibular resection and reconstruction.

This new technique uses helical computed tomography data and computer-aided design and manufacturing for preoperative fabrication of individual mandibular prostheses together with corresponding resection templates. Coherent 3D geometries for computer-based models are the basis for the construction of prostheses and provide data for a computerized numerical control fabrication. Fixation plates are fabricated with the titanium prostheses. The identical data of these plates are used for the computer-aided design and manufacturing of resection templates, which guide an oscillating saw in a precisely determined resection plane. This plane again is identical with the prostheses' margins for mandibular body replacement. The use of this technique in four patients is reported on: after temporary insertion of the templates for resection and after resection, the prostheses were stabilized with the same screws in the same screw-holes where the templates had been. Resection and reconstruction were thus highly precise, safe and fast and primarily led to excellent aesthetic and functional results. Wound-healing depends on a safe soft-tissue reconstruction over these large prostheses. Coverage with flaps seems obligatory. In spite of the superior technical aspects, the clinical long-term results of this new technique were poor.

Adult↗