Joachim A. Obwegeser

Comparison of different registration methods for surgical navigation in cranio-maxillofacial surgery

BACKGROUND Surgical navigation requires registration of the pre-operative image dataset with the patient in the operation theatre. Various marker and marker-free registration techniques are available, each bearing an individual level of precision and clinical practicability. In this study the precision of four different registration methods in a maxillofacial surgical setting is analyzed. MATERIALS AND METHODS A synthetic full size human skull model was registered with its computer tomography-dataset using (a) a dentally mounted occlusal splint, (b) the laser surface scanning, (c) five facial bone implants and (d) a combination of dental splint and two orbital bone implants. The target registration error was computed for 170 landmarks spread over the entire viscero- and neurocranium in 10 repeats using the VectorVision2 (BrainLAB AG, Heimstetten, Germany) navigation system. Statistical and graphical analyses were performed by anatomical region. RESULTS An average precision of 1mm was found for the periorbital region irrespective of registration method (range 0.6-1.1mm). Beyond the mid-face, precision linearly decreases with the distance from the reference markers. The combination of splint with two orbital bone markers significantly improved precision from 1.3 to 0.8mm (p<0.001) on the viscerocranium and 2.3-1.2mm (p<0.001) on the neurocranium. CONCLUSIONS An occlusal splint alone yields poor precision for navigation beyond the mid-face. The precision can be increased by combining an occlusal splint with just two bone implants inserted percutaneously on the lateral orbital rim of each side.

Factors influencing survival of free-flap in reconstruction for cancer of the head and neck: a literature review.

Microvascular free tissue transfer is a reliable technique for head and neck reconstruction with success rates of 90–99%. Currently, there is no consensus concerning antithrombotic agents, antibiotics, or monitoring techniques. Therefore, the aim of this study was to review current literature dealing with microvascular free‐tissue transfer and factors influencing the outcome. In addition to excellent microsurgical techniques, coupling devices are a promising new technique, but are not useful in all arteries. Antibiotics should be given in three doses, as a more lengthy dosage time seems to have no advantage. The risk for elderly patients can be best assessed by the American Society of Anesthesiologists (ASA) score, but early mobilization, including intense chest physiotherapy, is important. Anticoagulation can be considered in cases of small vessels, significant size mismatch, vein graft, or vessels of poor quality. Monitoring should be done hourly during the first 24 hours and then every 4 hours for the next 2 postoperative days.

Osteopathology induced by bisphosphonates and dental implants: clinical observations

ObjectivesAlthough there are many reports about risk factors for the development of BP-associated osteonecrosis of the jaws, the role of dental implants as a local risk factor is still discussed, especially in patients with oral BP treatment. Until now, a few case reports and surveys display a possible minor risk in patients with oral BP therapy, whereas the avoidance of implant placement is generally accepted in patients with intravenous BP therapy.Patient and methodsIn this study, the cases of 14 patients with osteonecrosis of the jaws in association with BP therapy and dental implant placement were analyzed carefully with a detailed literature review.ResultsOf 14 patients, nine had underlying malignant disease and five patients had osteoporosis. In ten patients, implants were placed either in the posterior mandible or maxilla; the mean interval between implant insertion and disease onset was 20.9 months. Pain (n12) and signs of infection (n10) were the most common symptoms. Histologically, signs of infection were found in nine of 11 analyzed patients with presence of Actinomyces in six patients. Two patients turned out to have infiltration of underlying malignant disease.ConclusionsPosteriorly placed implants seem to be of higher risk of development of osteonecrosis of the jaws. Not only the implant placement but also the inserted implant itself seems to be a continuous risk factor.Clinical relevanceThe herein elaborated risk factors help dentists plan dental rehabilitation with implants in this high-risk group of patients and indicate careful and regular dental recall.

Surgical Navigation in Craniomaxillofacial Surgery: Expensive Toy or Useful Tool? A Classification of Different Indications

The complex 3-dimensional (3D) anatomy and geometry of the human skull and face combined with the need for precise symmetry poses challenges for reconstructive surgery of the region. Therefore, and with the technical improvements during the past 10 years or so, surgical navigation has become an established technique in craniomaxillofacial surgery. 1-4 Many technical problems have been solved, and the accuracy of multiple strategies of imaging and registration has been proved. 5 However, the procedure of preparing a patient for navigation is still linked to extra effort for the patient and surgeon. Even noninvasive registration procedures, such as a splint fixed to the upper jaw, as described by Schramm et al, 6 require dental impressions and additional imaging with the splint in situ. Insecurity surrounds surgical navigation of the lower jaw with different techniques available, such as mounting a dynamic reference frame to the mandible 7-9 or retaining the mandible in a defined position against the maxilla. 7,10-15 Thus, the state of surgical navigation of the mandible has been deemed unsatisfactory to date. 16 The aim of the present study was to evaluate the feasibility and limitations of surgical navigation. In addition, we determined the time and effort of the surgical team in relation to the benefit.

Point-to-point registration with mandibulo-maxillary splint in open and closed jaw position. Evaluation of registration accuracy for computer-aided surgery of the mandible

INTRODUCTION Computer navigation plays an increasingly important role in craniomaxillofacial surgery. The difficulties in computer navigation at the craniomaxillofacial site lie in the accurate transmission of the dataset to the operating room. This study investigates the accuracy of the dental-splint registration method for the skull, midface, and mandible. MATERIAL AND METHODS A synthetic human skull model was prepared with landmarks and scanned with cone beam computer tomography (CBCT). Two registration splints fixed the mandible against the viscerocranium in two different positions (closed vs. open). The target registration error was computed in all 278 landmarks spread over the entire skull and mandible in 10 repeated measurements using the VectorVision(2) (BrainLAB Inc., Feldkirchen, Germany) navigation system. RESULTS If registered in the closed position an average precision of 2.07 mm with a standard deviation (SD) of 0.78 mm was computed for all landmarks distributed over the whole skull. Registration in the open position resulted in an average precision of 1.53 mm (SD=0.55 mm). For single landmarks the precision decreases linearly with distance from the reference markers. The longer the three-dimensional distance between the registration points, the more precise the computer navigation is, mainly in the most posterior area of the cranium. CONCLUSION Our findings in the cranium are comparable with those of other studies. Artificial fixation of the lower jaw via splint seems to introduce no additional error. The registration points should be as far apart from each other as possible during navigation with the splint.

Bioconvertible screws made of allogenic cortical bone for osteosynthesis following sagittal split ramus osteotomy without postoperative immobilisation

Since 1990, 12 patients have been operated on by sagittal split ramus osteotomy with subsequent osteosynthesis using screws made of allogenic cortical bone without any postoperative immobilisation. These cases have been followed-up and were clinically and cephalometrically analysed. In all patients no complications were recorded. Preliminary data suggests that the stability of the segments is in good accordance with procedures using metallic devices for osteotomy fixation. The advantage of the screws presented can be seen by the fact that the material used is bioconvertible and therefore no removal operation is needed. Thermal treatment of these screws prevents problems of infection.

3-Dimensional Imaging for Lower Third Molars: Is There an Implication for Surgical Removal?

PURPOSE Surgical removal of impacted third molars may be the most frequent procedure in oral surgery. Damage to the inferior alveolar nerve (IAN) is a typical complication of the procedure, with incidence rates reported at 1% to 22%. The aim of this study was to identify factors that lead to a higher risk of IAN impairment after surgery. MATERIALS AND METHODS In total 515 surgical third molar removals with 3-dimensional (3D) imaging before surgical removal were retrospectively evaluated for IAN impairment, in addition to 3D imaging signs that were supposed predictors for postoperative IAN disturbance. Influence of each predictor was evaluated in univariate and multivariate analyses and reported as odds ratio (OR) and 95% confidence interval (CI). RESULTS The overall IAN impairment rate in this study was 9.4%. Univariate analysis showed narrowing of the IAN canal (OR, 4.95; P < .0001), direct contact between the IAN and the root (OR, 5.05; P = .0008), fully formed roots (OR, 4.36; P = .045), an IAN lingual course with (OR, 6.64; P = .0013) and without (OR, 2.72; P = .007) perforation of the cortical plate, and an intraroot (OR, 9.96; P = .003) position of the IAN as predictors of postoperative IAN impairment. Multivariate analysis showed narrowing of the IAN canal (adjusted OR, 3.69; 95% CI, 1.88 to 7.22; P = .0001) and direct contact (adjusted OR, 3.10; 95% CI, 1.15 to 8.33; P = .025) to be the strongest independent predictors. CONCLUSION Three-dimensional imaging is useful for predicting the risk of postoperative IAN impairment before surgical removal of impacted lower third molars. The low IAN impairment rate seen in this study-compared with similar selected study groups in the literature of the era before 3D imaging-indicates that the availability of 3D information is actually decreasing the risk for IAN impairment after lower third molar removal.

Cephalometric and three-dimensional assessment of the posterior airway space and imaging software reliability analysis before and after orthognathic surgery.

PURPOSE This study aimed to compare the reliability of three different imaging software programs for measuring the PAS and concurrently to investigate the morphological changes in oropharyngeal structures in mandibular prognathic patients before and after orthognathic surgery by using 2D and 3D analyzing technique. MATERIAL AND METHODS The study consists of 11 randomly chosen patients (8 females and 3 males) who underwent maxillomandibular treatment for correction of Class III anteroposterior mandibular prognathism at the University Hospital in Zurich. A set of standardized LCR and CBCT-scans were obtained from each subject preoperatively (T0), 3 months after surgery (T1) and 3 months to 2 years postoperatively (T2). Morphological changes in the posterior airway space (PAS) were evaluated longitudinally by two different observers with three different imaging software programs (OsiriX(®) 64-bit, Switzerland; Mimics(®), Belgium; BrainLab(®), Germany) and manually by analyzing cephalometric X-rays. RESULTS A significant increase in the upper airway dimensions before and after surgery occurred in all measured cases. All other cephalometric distances showed no statistically significant alterations. Measuring the volume of the PAS showed no significant changes in all cases. All three software programs showed similar outputs in both cephalometric analysis and 3D measuring technique. CONCLUSION A 3D design of the posterior airway seems to be far more reliable and precise phrasing of a statement of postoperative gradients than conventional radiography and is additionally higher compared to the corresponding manual method. In case of Class III mandibular prognathism treatment with bilateral split osteotomy of the mandible and simultaneous maxillary advancement, the negative effects of PAS volume decrease may be reduced and might prevent a developing OSAS.

Anatomy of impacted lower third molars evaluated by computerized tomography: is there an indication for 3-dimensional imaging?

OBJECTIVE Surgical removal of impacted third molar is one of the most frequent procedures in oral surgery. Today 3-dimensional (3D) imaging is occasionally used. The aim of this study was to describe and estimate the frequencies of anatomic variations of lower third molars in patients with panoramic findings at high risk for inferior alveolar nerve (IAN) injury. STUDY DESIGN The investigators designed and implemented a retrospective cases series study with a study population composed of patients presenting with an impacted lower third molar with projection of the tooth over the full width of the IAN in panoramic radiograph and, therefore, 3D imaging before a planned surgical removal. Spatial relationship to the IAN, type of angulation, root configuration and maturation were primary study variables. Descriptive statistics were computed for all variables. RESULTS A total of 707 wisdom teeth in 472 patients (54% female, 46% male) were evaluated. A close relationship to the IAN was seen in 69.7%, and in 45.1% the diameter of the mandibular canal was reduced. In 52.8% the IAN was vestibular and in 37.3% lingual to the roots; there were 9.9% with an inter- or intraroot course. Most teeth had 1 or 2 roots (86.7%), but 13.3% had ≥3 roots. Mesial angulation was the main type (40.2%), followed by vertical (29%), horizontal (13.9%), distal (10.2%), and transverse (6.8%) positions. CONCLUSION Based on the range of variations in the course of the nerve and the number of roots the authors recommend 3D imaging before surgical removal of a lower third molar that shows signs of a close relationship to the IAN.

Evaluation of the pectoralis major flap for reconstructive head and neck surgery

PurposeThe pectoralis major myocutaneous flap (PMMF) is a commonly used flap in reconstructive head and neck surgery, but in literature, the flap is also associated with a high incidence of complications in addition to its large bulk. The purpose of the study is the evaluation of the reliability and indication of this flap in reconstructive head and neck surgery.Patients and methodsThe records of all patients treated with a PMMF between 1998 and 2009 were systematically reviewed. Data of recipient localization, main indication, and postoperative complications were analyzed.ResultsThe male to female ratio was 17:3, with a mean age of 60 years (45-85). Indications in 7 patients were recurrence of a squamous cell carcinoma, in one case an osteoradionecrosis and in 12 cases an untreated squamous cell carcinoma. In 6 male patients (30%), a complication appeared leading to another surgery.ConclusionThe PMMF is a flap for huge defects in head and neck reconstructive surgery, in particular when a bulky flap is needed in order to cover the carotid artery or reconstructive surgery, but the complication rate should not be underestimated in particular after radiotherapy.