Christoph Zizelmann

Semiautomatic procedure for individual preforming of titanium meshes for orbital fractures.

Background: Three-dimensional reconstruction of the orbital floor is a key procedure in primary or secondary orbital deformity. A new procedure for individually bending and preforming implants preoperatively for the reconstruction of orbital fractures is presented. Methods: By using diagnostic computed tomographic scan data, the topography of the orbital floor and wall structures can be recalculated. After mirroring the unaffected side onto the affected side, the defect can be reconstructed virtually. Data of the individual virtual model of the orbital cavity are sent to a template machine that reproduces the surface of the orbital floor and medial walls automatically. A titanium mesh can then be adjusted preoperatively for exact three-dimensional reconstruction. Twelve patients with orbital fractures were treated using individually preformed titanium implants. Results: All patients treated with this procedure showed normal eye mobility and function after primary reconstruction. The accuracy of the preformed implants lies in the range of 1 mm. Conclusions: This procedure offers an individual anatomical reconstruction of the orbital cavity true to original, especially when the deep orbital cone is affected. Navigation-aided procedures guarantee intraoperatively an exact placement of the preformed mesh even for precise reconstruction of extensive orbital defects.

Bone regeneration in sinus lifts: comparing tissue-engineered bone and iliac bone.

Lifting of the sinus floor is a standard procedure for bony augmentation that enables dental implantation. Although cultivated skin and mucosal grafts are often used in plastic and maxillofacial surgery, tissue-engineered bone has not achieved the same success. We present the clinical results of dental implants placed after the insertion of periosteum-derived, tissue-engineered bone grafts in sinus lifts. Periosteal cells were isolated from biopsy specimens of periosteum, resuspended and cultured. The cell suspension was soaked in polymer fleeces. The cell-polymer constructs were transplanted by sinus lift 8 weeks after harvesting. The patients (n=35) had either one or both sides operated on. Seventeen had a one-stage sinus lift with simultaneous implantation (54 implants). In 18 patients the implants were inserted 3 months after augmentation (64 implants). Selected cases were biopsied. A control group (41 patients: one stage=48 implants, two stage=135 implants) had augmentation with autologous bone only. They were followed up clinically and radiologically for at least 24 months. Both implants and augmentation were significantly more successful in the control group. Failure of augmentation of the tissue-engineered bone was more common after large areas had been augmented. Eleven implants were lost in the study group and only one in the control group. Lifting the sinus floor with autologous bone is more reliable than with tissue-engineered transplants. Although lamellar bone can be found in periosteum-derived, tissue-engineered transplants, the range of indications must be limited.

An Evaluation of Face-Bow Transfer for the Planning of Orthognathic Surgery

PURPOSE The purpose of this study was to evaluate the error magnitude in the clinical application of face-bow devices. Technical and methodologic inaccuracies, as well as deviations from reference planes, were determined. MATERIALS AND METHODS The presented method is part of a 3-dimensional virtual planning procedure for orthognathic surgery and included 15 patients with dentoskeletal deformities. Cone beam computed tomography datasets obtained from patients with a referenced face-bow plane and a centric registration splint were matched with cone beam computed tomography datasets of the registered plaster model of the maxilla mounted in an articulator. To assess potential sources of methodologic errors, angulations were measured between the virtual face-bow plane and the horizontal cross bar of the virtual articulator. To evaluate the reproducibility of the anatomic reference plane, angulations between the Frankfort plane and the horizontal cross bar of the articulator were measured. Statistical significance was set at P < .05 and tested by univariate analysis of variance. RESULTS Technical and methodologic errors showed a mean deviation of 3.5°, with a median of 3.6° and SD of 2.7°. The values did not reach statistical significance (P = .1). However, there was a significant error (P < .05) in determining the position of the anatomic reference plane by face-bow transfer. The mean deviation was 7.7° (values ranged between 1.2° and 18.9°), with a median of 6.7° and SD of 5.3°. CONCLUSIONS In this study the traditional use of face-bow devices showed inaccuracies in model mounting as well as in assignment of anatomic reference planes. Three-dimensional virtual computer-assisted planning seems to be more accurate than conventional methods.

A comprehensive approach to objective quantification of orbital dimensions.

rbital cial rophliniertel for culsymsoft echto ients an disan chand rtips ith e a ugh e, s in exunil mild p ger. B grap antif oni rim r ment ns d os a ist: l the b phy a and n lu CT, R t ent o ntent. A was u use o segm erio app al c ct bital s imp at t tant f ere i bital v t al r cm c uk e ich e ng i askin e ma b late e to s postry, he position of the globe relative to the lateral o im is subject to considerable individual and ra ariations. Although several methods have been p osed to evaluate globe position, the Hertel exo halmometer remains the most frequently used c al tool in the evaluation of proptosis. The H xophthalmometry, however, has been criticized ts low accuracy and low reproducibility. The diffi ies of this method are well known, including a etry of the lateral orbital rims, compression of issues, parallax errors, and lack of uniform t ique. Subtle degrees of proptosis are difficult etect and even more difficult to measure. In pat ith orbital injury, periorbital edema may lead to nderestimation of protrusion, while a posterior lacement of the lateral orbital rim may cause verestimation of protrusion. Other clinical te iques such as viewing the position of the globes ids from above the brows or insertion of finge etween the inferior orbital rims and globes w imultaneous palpation of corneal apices can giv ough clinical orientation, but are not precise eno or measurement and documentation. Furthermor he clinician must be aware of several condition hich proptosis is more apparent than real, for mple, in unilateral lid retraction, in which the

Virtual restoration of anatomic jaw relationship to obtain a precise 3D model for total joint prosthesis construction for treatment of TMJ ankylosis with open bite

Temporomandibular joint (TMJ) reconstruction with a TMJ Concepts total joint prosthesis (TMJ Concepts, Ventura, USA) requires a precise 3D model of the jaws in centric occlusion. The authors present a virtual procedure for repositioning the lower jaw in centric occlusion to obtain a precise stereolithographic model for TMJ reconstruction using a custom-made total joint prosthesis in a case of TMJ ankylosis and anterior open bite.

In Vitro Biomechanical Comparison of the Effect of Pattern, Inclination, and Size of Positional Screws on Load Resistance for Bilateral Sagittal Split Osteotomy

PURPOSE The purpose of this in vitro investigation was to determine whether the pattern, angle of placement, or size of positional screws affected their ability to resist vertical loads resembling mastication in the bilateral sagittal split osteotomy system. MATERIALS AND METHODS Standardized bone substitutes were secured with three 12- to 16 mm-long, 1.85-, 2.0-, 2.1-, and 2.4-mm outer diameter, self-tapping titanium screws (Synthes, Solothurn, Switzerland) in various patterns using a positional screw technique. These patterns included transbuccal triangular, intraoral triangular, and transbuccal linear patterns. The models were secured in a jig and subjected to vertical loads by a mechanical testing unit (1475 UPM; Zwick, Ulm, Germany) until failure. Loading test data analysis was based on peak load values resulting in mechanical deformation of the system (1-, 3-, and 5-mm displacement), maximal force, and stiffness (load/displacement slope curve) for each group. Means and standard deviations were derived and compared for statistical significance using univariate analysis of variance with a confidence level of 95% (P values < .05). RESULTS The designed study demonstrated that 1.85- and 2.0-mm-diameter positional screws provided similar stability in all 3 setups. Three screws placed in an inverted L pattern at 90° (simulating a transbuccal approach) showed significantly higher resistance to vertical forces for advancement movements at 1-, 3-, and 5-mm displacement when compared with the inverted L group of screws placed at an angle (intraoral approach) or 3 screws in a linear pattern placed at 90° (transbuccal approach) (P < .01). CONCLUSIONS Under the conditions tested in this in vitro study, differences in the load resistance of positional screws placed in a transbuccal or intraoral approach could be demonstrated depending on the fixation technique. The transbuccal group of 3 screws in an inverted L pattern showed significantly greater stability than the intraoral group of 3 screws placed in an inverted L pattern and the transbuccal group of 3 screws in a linear pattern. Resistance to vertical loads with 1.85-mm screws was similar to that with the standard 2.0-mm screws in all 3 setups. The results of this study suggest that the angle of screw placement (surgical approach) and pattern have a greater influence on the stability of the bilateral sagittal split osteotomy system than the screw size.

Transient myopia as a complication after complex orbital reconstructions with computer-assisted navigation surgery.

Surgical reconstruction of orbital deformities can be technically demanding.1,2 The average complication rate is around 10 to 15 percent.3 The complications that have previously been reported were related to the surgical incision,4–9 graft donor site,10 and graft material.11 Ophthalmologic complications were rarely reported, and most of them were related to optic nerve injury12–17 and entrapment of extraocular muscles.3,18 There have been reports of blindness,12–17 but refractive disorders have never been documented to be a complication of orbital reconstruction. Since 1997, we routinely reconstruct orbital deformities with the assistance of computer imaging planning and navigation systems. Patients undergo spiral computed tomography (1-mm collimation/slice thickness) of the whole head before surgery. Surgical plans are made using the mirrored three-dimensional images from the bony orbit of the normal side. Bicoronal and transconjuctival incisions are usually used for the surgical approach. Zygomatic osteotomy with advancement is often necessary in complicated cases. Reconstruction of orbital walls is accomplished by incorporating titanium mesh and autologus calvarial bone grafts. The adequacy of reconstruction is determined by the computer navigation system with a noninvasive reference19 using frameless stereotaxy. A probe connected to the navigation system can show real-time computed tomographic images on the system and is used to determine the position of reconstructed sites intraoperatively. Technical details related to the computer-aided navigation system have previously been published.20 Between January of 1999 and July of 2004, a total of 26 cases were successfully reconstructed using this surgical technique. Transient myopia was noted in three patients after the operation.