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Beat Hammer

Publications and source records attributed to Beat Hammer.

13 recordsLinked to original sources
PubMed2005

Possible problems of moulding the regenerate in mandibular distraction osteogenesis -- experimental aspects in a canine model.

INTRODUCTION: Moulding of the regenerate created by distraction osteogenesis has been shown clinically to be efficient and good enough so that for complex three-dimensional deformities, final adjustments by moulding the regenerate may be part of the treatment plan. This study assessed possible drawbacks of moulding a regenerate, taking into consideration compressive and tensile forces acting simultaneously on the fresh callus. METHOD: Distraction osteogenesis in 15 Beagle mandibles was performed using custom made devices which allowed for lengthening as well as for angulation. After linear distraction of 10 mm, a defined 20 degrees angulation was performed in one step. The position of the fulcrum of the device allowed simultaneously compression and stretching of the regenerated bone. Effects on bone healing were assessed after 6 and 13 weeks of consolidation respectively and compared with a control group where only linear distraction was performed. RESULTS: Radiological and histological investigations demonstrated that no significant differences between the biological behaviour of the compressed and the stretched zones of the regenerate could be found. However, there were signs showing the more critical character of the stretched area. After 6 weeks of consolidation some specimens revealed delayed ossification of the stretched zone. Under stable conditions, this delay was compensated for after 13 weeks of consolidation and complete osseous healing occurred. CONCLUSION: Under stable conditions, a fresh regenerate can be moulded to a considerable extent without permanently endangering osseous healing. Nevertheless tensile forces acting on the regenerate should be minimized to prevent damage to the new bone. This can be achieved by overdistraction prior to callus moulding or by gradually changing the vector of distraction during the lengthening process.

Animals↗
PubMed2005

Callus mineralization following distraction osteogenesis of the mandible monitored by scanning acoustic microscopy (SAM).

BACKGROUND: Scanning acoustic microscopy uses ultrasound to analyse histomorphology of tissues with microscopic resolution and delivers data about physical properties of the specimen. MATERIAL AND METHODS: Bony consolidation was monitored by scanning acoustic microscopy in 12 embedded specimens of dog mandibles after distraction osteogenesis. Increasing mineralization was detected by measurements of acoustic impedance (Z). RESULTS: There was a strong correlation between acoustic impedance and time of consolidation. Measurements of the speed of sound (v) provided specific information about non-mineralized zones of the distracted area. Distribution of density in the distracted area could be reconstructed by using the measurements of acoustic impedance and speed of sound. CONCLUSION: The method seems suitable for studying bone remodelling qualitatively and quantitatively.

Acoustics↗
PubMed2005

Distraction osteogenesis of the canine mandible: the impact of acute callus manipulation on vascularization and early bone formation.

PURPOSE: Manipulations of the newly created regenerate, using adjustable multiplanar devices during distraction osteogenesis or as a 1-step molding procedure at the end of the distraction process, may be necessary to correct the position of the mandible. Treatment of complex deformities may require preplanned major angulation provided by adjustable devices. We sought to assess the effects of molding the fresh regenerate on vascularization and early bone formation within clinically relevant dimensions. MATERIALS AND METHODS: Evaluation of the nature of the problem in mechanical terms was based on a geometrical model, its dimensions chosen with clinical relevance. Custom-made devices, allowing the simultaneous compression and stretching of a regenerate 10 mm long, were fixed bilaterally in the angular region of beagle mandibles (n = 14). Angulation of 20 degrees (n = 7) or 30 degrees (n = 7) was performed immediately after ending the lengthening period, and the animals were killed after a 7-day consolidation period. The vascular system was stained via intravital Procion red infusion and post mortem carbon ink (Deperussol P130; Degussa AG, Frankfurt, Germany) perfusion to assess possible damages. Qualitative and quantitative evaluations of the mineralized tissue were performed with contact radiography, quantified computed tomography, and histologic assessment. RESULTS: The only finding indicating mechanical forces acting on the regenerate was related to orientation of the collagenous fibers. Vascular damage was not observed. Mineralization patterns were identical in both the compressed and the stretched zone. The degree of angulation had no visible impact on early bone formation, even if compression and stretching of the regenerate at a range of 33% to 54% exceeds most clinical requirements. However, the amount of callus formation differed independent of the shaping angle, revealing parameters other than the degree of angulation to be important. CONCLUSIONS: Although the newly forming bone is highly sensitive to nonphysiologic strain during the lengthening process, a completed fresh regenerate, created by distraction osteogenesis, can be manipulated to a considerable extent without endangering early callus formation. Manipulation of the regenerates would provide a precise final result, minimizing the need for secondary corrections and diminishing treatment duration and costs.

Animals↗
PubMed2004

Reconstruction of maxillary and mandibular defects using prefabricated microvascular fibular grafts and osseointegrated dental implants -- a prospective study.

The fibular flap can be used for a variety of indications. Recently, the treatment of four patients with severely atrophied upper jaws using a method to prefabricate the vascularized fibular graft has been published. This technique consists of a two-stage operation procedure that allows simultaneous prosthodontic rehabilitation and immediate placement of dental implants. In this paper eight patients with 29 ITI implants (Straumann AG, Waldenburg, Switzerland) who had reconstruction of either the upper or lower jaw are presented. The aim of the study was (i) to evaluate the behavior of the newly formed soft tissue around implants inserted in the fibula by applying periodontal parameters, (ii) to monitor prospectively the integration of the implants in the fibular graft, and (iii) to assess the osseous integration of the fibular graft used for reconstruction of the upper or lower jaw. Two implants failed during the observation time because of avascular bone at the distal end of the fibular graft. Stabilization of the graft, however, was never compromised. Due to the prefabrication firmly attached gingiva-like soft tissue could be provided preventing periimplant soft tissue inflammation and facilitating oral hygiene. After 1 year of observation the mean attachment level was similar to implants placed in original bone whereas vertical bone loss measured radiographically was lower in the present study. This may indicate that the remodeling of a bicortical bone requires a longer period of time compared with the bone of the alveolar crest. The prospective 1-year results are promising but long-term evaluation of periodontal and radiological parameters are required.

Adult↗
PubMed2003

A faster method for 3D/2D medical image registration--a simulation study.

3D/2D patient-to-computed-tomography (CT) registration is a method to determine a transformation that maps two coordinate systems by comparing a projection image rendered from CT to a real projection image. Iterative variation of the CT's position between rendering steps finally leads to exact registration. Applications include exact patient positioning in radiation therapy, calibration of surgical robots, and pose estimation in computer-aided surgery. One of the problems associated with 3D/2D registration is the fact that finding a registration includes solving a minimization problem in six degrees of freedom (dof) in motion. This results in considerable time requirements since for each iteration step at least one volume rendering has to be computed. We show that by choosing an appropriate world coordinate system and by applying a 2D/2D registration method in each iteration step, the number of iterations can be grossly reduced from n6 to n5. Here, n is the number of discrete variations around a given coordinate. Depending on the configuration of the optimization algorithm, this reduces the total number of iterations necessary to at least 1/3 of it's original value. The method was implemented and extensively tested on simulated x-ray images of a tibia, a pelvis and a skull base. When using one projective image and a discrete full parameter space search for solving the optimization problem, average accuracy was found to be 1.0 +/- 0.6(degrees) and 4.1 +/- 1.9 (mm) for a registration in six parameters, and 1.0 +/- 0.7(degrees) and 4.2 +/- 1.6 (mm) when using the 5 + 1 dof method described in this paper. Time requirements were reduced by a factor 3.1. We conclude that this hardware-independent optimization of 3D/2D registration is a step towards increasing the acceptance of this promising method for a wide number of clinical applications.

Algorithms↗
PubMed2003

In vivo efficacy of bone-marrow-coated polycaprolactone scaffolds for the reconstruction of orbital defects in the pig.

Alloplastic materials offer a number of advantages over bone autografts in the reconstruction of craniofacial defects. These include: lack of donor site morbidity, unlimited quantities of available material, and the possibility to conform exactly to the defect. An ideal bioresorbable material would degrade slowly, and have osteoconductive properties to allow replacement and remodeling by osseous tissue. This is seldom observed, the materials instead being replaced by fibrous tissue. Polycaprolactone (PCL), an FDA-approved bioresorbable polymer, has several properties that might make it suitable for reconstruction of craniofacial defects. The technique of fused deposition modeling (FDM) allows for the fabrication of highly reproducible bioresorbable 3D scaffolds. The nature of the fully interconnected pore network might enhance vascular ingrowth and osteoconductive properties. It was hypothesized that coating the scaffolds in bone marrow might enhance bone formation due to the osteoinductive nature of the bone-marrow mesenchymal cells. This study aimed to test these hypotheses in the pig model. Defects measuring 2 x 2 cm were surgically created in each orbit of eight Yorkshire pigs. The orbits were divided into three groups: Group 1 (n=4), no reconstruction (control); Group 2 (n=6), reconstruction with no coated PCL scaffolds; and Group 3 (n=6) reconstruction with bone-marrow-coated PCL scaffolds. The results were evaluated at 3 months by histological and histomorphometric analyses. The defects in Group 1 were covered with fibrous scar tissue. The shape of the reconstructed area was insufficient. The defects in Groups 2 and 3 were reconstructed correctly. In Group 2 the noncoated scaffolds showed 4.5% of new bone formation compared with 14.1% in Group 3, which is statistically significant (p<0.05). The entirely interconnected 3D polycaprolactone scaffold seems to be a promising material. It induces the bone ingrowth required for reconstructing craniofacial and orbital defects. Further long-term evaluations of these PCL scaffolds must be made in order to confirm these conclusions.

Absorbable Implants↗
PubMed2003

Theoretical considerations for the surgical correction of mandibular deformity in hemifacial microsomia patients using multifocal distraction osteogenesis.

PURPOSE: This theoretical pilot study investigated the geometric changes necessary to normalize the mandibular shape in hemifacial microsomia. Using the mandibular deformity of a 13-year-old patient affected by hemifacial microsomia as an example, we addressed 2 main issues. First, the number of segments needed for adequate reshaping of the deformed mandible is evaluated. Second, the geometry of the intersegmental gaps resulting from reposition of the segments is correlated with established parameters of distraction osteogenesis to theoretically predict the practicability of correction using multifocal distraction osteogenesis. MATERIALS AND METHODS: Virtual surgery was performed on a solid mandible model created from computed tomography (CT) data from a patient with hemifacial microsomia type IIB. In the first step, ideal mandibular reshaping was achieved according to anthropometric standard measurements using 7 osteotomies. By scanning and superimposition of the virtual models and variation of distraction sites and numbers, we assessed the minimal number of osteotomies necessary for optimal correction of the deformity. Geometrical evaluation of the regeneration and assessment of the possibilities of continuous curved distraction were also performed. RESULTS: Three osteotomies were shown to be sufficient for complete mandibular reshaping. Using accepted parameters for distraction osteogenesis, the geometry of the regenerate allows for continuous curved distraction. However, simultaneous movements at several distraction sites result in interfering vector forces, making coordination of multifocal distraction difficult. CONCLUSION: Theoretical assessment of a severe mandibular hypoplasia in hemifacial microsomia revealed the 3-dimensional (3D) complexity of the deformity for corrective procedures, especially distraction osteogenesis. Despite precise planning and transfer of the plan to the patient, multifocal 3D distraction may result in deviations from the planned result. Manipulation of the fresh regeneration may be necessary to correct inaccuracies.

Adolescent↗
PubMed2003

Maxillofacial reconstruction with prefabricated osseous free flaps: a 3-year experience with 24 patients.

Between January of 1998 and May of 2002, 25 prefabricated osseous free flaps (23 fibula and two iliac crest flaps) were transferred in 24 patients to repair maxillary (six flaps) or mandibular (eight flaps) defects after tumor resection, severe maxillary (four flaps) or mandibular (one flap) atrophy (Cawood VI), maxillary (one flap) or mandibular (three flaps) defects after gunshot injury, and maxillary (two flaps) defects after traffic accidents. Prefabrication included insertion of dental implants, positioned with a drilling template in a preplanned position, and split-thickness grafting. Drilling template construction was based on the prosthetic planning. The template determined the position of the implants and the site and angulation of osteotomies, if necessary. The mean delay between prefabrication and flap transfer was 6 weeks (range, 4 to 8 weeks). While the flap was harvested, a bar construction with overdentures was mounted onto the implants. The overdentures were used as an occlusal key for exact three-dimensional positioning of the graft within the defect. The bar construction also helped to stabilize the horseshoe shape of the graft. The follow-up period ranged from 2 months to 4 years (mean, 21 months), during which time two total and three partial flap losses occurred. One total loss was due to thrombosis of the flap veins during the delay period, whereas the other total loss was caused by spasm of the peroneal artery. Two partial losses were due to oversegmentation of the flaps with necrosis of the distal fragment, whereas one partial loss was caused by disruption of the vessel from the distal part. Of the 90 implants that were inserted into the prefabricated flaps during the study period, 10 were lost in conjunction with flap failure; of the remaining 80 implants, four were lost during the observation period, for a success rate of 95 percent. Flap prefabrication based on prosthetic planning offers a powerful tool for various reconstructive problems in the maxillofacial area. Although it involves a two-stage procedure, the time for complete rehabilitation is shorter than with conventional procedures.

Accidents, Traffic↗
PubMed2002

Treatment of severe atrophy of the maxilla with the prefabricated free vascularized fibula flap.

Treatment of severe maxillary atrophy despite complex major surgery often ends up with an unsatisfactory result. This paper presents the augmentation of the maxilla with a prefabricated free vascularized fibula flap in combination with ITI implants (Straumann AG, Waldenburg, Switzerland) in 4 patients. The technique of prefabrication for the reconstruction of maxillofacial defects is described based on the experience with 17 patients. The key points of this treatment are i) preoperative planning and fabrication of the drilling template; ii) prefabrication of the fibula with ITI implants and performing of a 'vestibuloplasty" using a skin graft; iii) technical construction and fabrication of the suprastructure and the denture; iv) reconstruction of the maxilla using the prefabricated fibula as free vascularized flap. The reconstructions with the fibula flaps were successful and the 18 ITI implants that have been inserted showed good osseointegration without loss of attachment in all 4 patients after a mean observation period of 12 months.

Algorithms↗
PubMed2002

The sphenozygomatic suture as a key site for osteosynthesis of the orbitozygomatic complex in panfacial fractures: a biomechanical study in human cadavers based on clinical practice.

The aims of this study were to determine the forces required for fracturing the intact orbitozygomatic complex and to evaluate the strength of the orbitozygomatic complex-fixation, especially with regard to the sphenozygomatic suture as a fixation point. In severe midfacial and panfacial fractures, the sphenozygomatic suture is routinely used in the authors' practice as a key site for fixation of the orbitozygomatic complex, thus establishing a stable outer frame as a basis for subsequent reconstruction. However, this has never been formally described, nor has it been biomechanically tested. Eight human cadaver heads were subjected to forces applied in a standard fashion to the orbitozygomatic complex on both sides (n = 16) using a servohydraulic testing machine. The force required to break the intact orbitozygomatic complex was measured on both sides. Subsequently, fracture patterns were noted and each orbitozygomatic complex (n = 16) was assigned to one of four groups: four-point fixation (zygomatic arch, frontozygomatic suture, infraorbital rim, zygomaticomaxillary buttress) using a 1.3/2.0-mm titanium system (group 1) and a 2.0-mm bioresorbable system (group 3); or three-point fixation (zygomatic arch, frontozygomatic suture, sphenozygomatic suture) using 1.3/2.0-mm titanium system (group 2) and a 2.0-mm bioresorbable system (group 4). Forces for failure of the constructs were measured. The force for failure of the intact orbitozygomatic complex was 1826 +/- 852 N. The mean force required for failure of the reconstructed orbitozygomatic complex was 504 +/- 178 N for group 1, 620 +/- 304 N for group 2, 93 +/- 22 N for group 3, and 133 +/- 31 N for group 4. The titanium constructs provided 27.7 percent (four-point fixation) and 31.7 percent (three-point fixation) of the intact breaking strength of the orbitozygomatic complex, which was significantly higher (p < 0.05) compared with 5.4 percent (four-point fixation) and 7.7 percent (four-point fixation) for the bioresorbable system. Plate bending (91 percent) was the primary cause for failure in the titanium plating system, whereas plate and screw breakage (57 percent) was responsible for failure of the resorbable system. The fixation of the sphenozygomatic suture was a key site in the fixation of the orbitozygomatic complex, which could be demonstrated with superior results in the three-point fixation group compared with the four-point fixation group. The bioresorbable system showed the lowest values in this cadaver study. Further experimental and clinical studies might determine whether the bioresorbable materials are sufficient for the treatment of complex fractures of the orbitozygomatic complex.

Absorbable Implants↗
PubMed2002

Computer-assisted secondary reconstruction of unilateral posttraumatic orbital deformity.

Until now, computer-assisted surgery has not been practiced as part of the surgical routine of posttraumatic orbital reconstruction. The purpose of this study was to investigate the use of a navigation system for computer-assisted preoperative planning with virtual reconstruction to obtain symmetry of the orbits and intraoperative control of virtual contours in comparison with the clinically achieved surgical results. A further objective of the computer-assisted orbital analysis was to use an ideal measurement for the two-dimensional and three-dimensional changes following orbital reconstruction and to check the equality of the postoperative values for the affected orbits in comparison with those of the unaffected sides. Patients with unilateral posttraumatic orbital defects (n = 18) underwent computer-assisted surgery and preoperative planning using a spiral computed tomography database. Surgical procedures were preplanned with virtual correction by mirroring an individually defined three-dimensional segment from the unaffected side onto the deformed side, creating an ideal unilateral reconstruction. These computer-models were intraoperatively used as virtual templates to navigate the preplanned contours and the globe projection using the Stryker-Leibinger navigation system. Individual noninvasive registration with an overall inaccuracy of approximately 1 mm was achieved by using a maxillary occlusal splint with four markers. The mirroring of the unaffected side allowed an ideal virtual reconstruction. A mean decrease in enlarged orbital volume of 4.0 (SD +/- 1.9) cm was achieved, as was a mean increase in the sagittal globe projection of 5.88 (SD +/- 2.98) mm. With a paired Student test, the decrease between the preoperative and postoperative differences of the affected and unaffected sides was proved significant for orbital volume, globe projection, and computed tomography-based Hertel scale changes (p < 0.01). In 15 of 18 cases, simultaneous malar bone advancement resulted primarily in an additional increase in orbital volume before intraorbital augmentation with calvarial split-bone grafts could be performed. Intraorbital bony augmentation included one (n = 1), two (n = 7), three (n = 8), and all four (n = 2) orbital walls. Computer-assisted preoperative planning enables the surgeon to predict reconstructive surgical steps before the operation. Highly vulnerable structures such as the optic nerve can be detected and avoided intraoperatively, and virtually preplanned bone graft positions and/or orbital frame contours can be checked. Computer-assisted preoperative planning and surgery thus advance the difficult surgical field of orbital reconstruction, particularly through a greater exploitation of radiologic information without additional radiation to the patient.

Adolescent↗