J. Abeloos

A cone-beam CT based technique to augment the 3D virtual skull model with a detailed dental surface

Cone-beam computed tomography (CBCT) is used for maxillofacial imaging. 3D virtual planning of orthognathic and facial orthomorphic surgery requires detailed visualisation of the interocclusal relationship. This study aimed to introduce and evaluate the use of a double CBCT scan procedure with a modified wax bite wafer to augment the 3D virtual skull model with a detailed dental surface. The impressions of the dental arches and the wax bite wafer were scanned for ten patient separately using a high resolution standardized CBCT scanning protocol. Surface-based rigid registration using ICP (iterative closest points) was used to fit the virtual models on the wax bite wafer. Automatic rigid point-based registration of the wax bite wafer on the patient scan was performed to implement the digital virtual dental arches into the patients skull model. Probability error histograms showed errors of < or =0.22 mm (25% percentile), < or =0.44 mm (50% percentile) and < or =1.09 mm (90% percentile) for ICP surface matching. The mean registration error for automatic point-based rigid registration was 0.18+/-0.10 mm (range 0.13-0.26 mm). The results show the potential for a double CBCT scan procedure with a modified wax bite wafer to set-up a 3D virtual augmented model of the skull with detailed dental surface.

The use of a wax bite wafer and a double computed tomography scan procedure to obtain a three-dimensional augmented virtual skull model.

A detailed visualization of the interocclusal relationship is essential in a three-dimensional virtual planning setup for orthognathic and facial orthomorphic surgery. The purpose of this study was to introduce and evaluate the use of a wax bite wafer in combination with a double computed tomography (CT) scan procedure to augment the three-dimensional virtual model of the skull with a detailed dental surface. A total of 10 orthognathic patients were scanned after a standardized multislice CT scanning protocol with dose reduction with their wax bite wafer in place. Afterward, the impressions of the upper and lower arches and the wax bite wafer were scanned for each patient separately using a high-resolution standardized multislice CT scanning protocol. Accurate fitting of the virtual impressions on the wax bite wafer was done with surface matching using iterative closest points. Consecutively, automatic rigid point-based registration of the wax bite wafer on the patient scan was performed to implement the digital virtual dental arches into the patients skull model (Maxilim, version 2.0; Medicim NV, St-Niklaas, Belgium). Probability error histograms showed errors of ≤0.16 mm (25% percentile), ≤0.31 mm (50% percentile), and ≤0.92 (90% percentile) for iterative closest point surface matching. The mean registration error for automatic point-based registration was 0.17 ± 0.07 mm (range, 0.12-0.22 mm). The combination of the wax bite wafer with the double CT scan procedure allowed for the setup of an accurate three-dimensional virtual augmented model of the skull with detailed dental surface. However, from a clinical workload, data handling, and computational point of view, this method is too time-consuming to be introduced in the clinical routine.

Reconstruction of the severely resorbed maxilla with a combination of sinus augmentation, onlay bone grafting, and implants

PURPOSE A new method of reconstruction of the atrophic maxilla by combining a bilateral sinus floor elevation and cancellous bone graft with buccal and labial onlay graft using L-shaped corticocancellous blocks from the posterior iliac crest is presented. PATIENTS AND METHODS Seventeen patients were treated with this procedure. One hundred one IMZ implants were placed in 14 patients, and 22 Brånemark implants were placed in three patients. Patients were observed for 6 months after prosthetic rehabilitation. RESULTS All patients were fully rehabilitated with fixed bridges except one, who preferred an overdenture. Only two implants were lost at the time of the abutment connection. Some bone resorption was seen around six implants. The success rate with this procedure was 92.7% 6 months after prosthetic rehabilitation if implants with bone resorption were considered failures. CONCLUSIONS These preliminary results indicate that this surgical procedure is suitable for reconstruction of most atrophic maxillas.

Nasal profile changes after maxillary impaction and advancement surgery

PURPOSE The profile changes in the nasal tip and columello-labial region that occur after maxillary advancement and impaction surgery were measured to test the hypothesis that a subspinal osteotomy would induce less nasal tip change and would result in a more acute columello-labial angle than a conventional Le Fort I-type osteotomy. PATIENTS AND METHODS The lateral cephalograms of 2 matched groups of 23 advancement/impaction cases with and without subspinal osteotomy were analyzed electronically. RESULTS There was no difference in nasal tip elevation and change in nasal tip projection between the 2 groups. The columello-labial angle was, on average, unchanged by the surgery. A linear correlation with a weak clinical relevance could be demonstrated between nasal tip projection and maxillary advancement in the group that was treated without subspinal osteotomy. Such a correlation was not detected for nasal tip elevation in either of the groups. Palatal plane rotation had a significant influence on nasal tip projection but not on tip elevation in both groups. The correlation was strongest in the group treated conventionally. The multiple regression equation with maxillary advancement and rotation as predictors had a r2 of .6071 (nasal tip projection = 0.9 + 0.19 maxillary advancement + 0.18 palatal plane inclination) in this group. CONCLUSION The results indicate that the advancing piriform aperture pushing on the alae, and not the nasal spine, is responsible for the increase in nasal tip projection. The subspinal osteotomy is not superior to the conventional Le Fort I-type osteotomy in regard to minimizing nasal tip changes and obtaining control over the columello-labial angle.

The 'sandwich' zygomatic osteotomy: technique, indications and clinical results.

The classical approach to lateral midface hypoplasia is reconstruction with onlays. Dislocation and asymmetry, early and late infection, and extrusion are possible complications with alloplastic implant materials. Unpredictable resorption, irregular contours and asymmetry are problems that can arise with autogenous, homogenous and hetergenous onlay grafts. We describe a technique by which the zygomatic body is luxated laterally and ventrally after a combined oblique-horizontal and vertical osteotomy. The resultant greenstick fracture at the temporo-zygomatic suture together with minimal lateral degloving causes the malar body to return to its former position. An interpositional porous hydroxyapatite block acts as a space maintainer until the osteotomy sites are ossified. The restoration of contour is performed by the zygomatic body itself, not by the implants. The indications are discussed and the results of three year follow-up are illustrated.

Prediction of mandibular autorotation

PURPOSE The purpose of this investigation was to test the hypothesis that the mandible rotates around the same point during maxillary impaction surgery as during initial jaw opening. This point, called the center of mandibular autorotation (CAR), could then be used to predict mandibular position and to decide whether only maxillary impaction would be needed to correct the occlusion and the facial profile. PATIENTS AND METHODS Preoperatively, two lateral cephalograms were obtained from a consecutive series of 20 patients who underwent maxillary impaction without concomitant mandibular ramus osteotomy. One cephalogram was taken with the mandible in centric relation using a wax bite wafer and another with a jaw opening of 10 mm using a fabricated acrylic bite block with the mandible manipulated to its most retruded position. The CAR was calculated before and after jaw opening using the Rouleaux method on the lower incisor and gonion point. A third lateral cephalogram was taken within 2 days postoperatively. The postoperative lower incisal point was then transferred to the first cephalogram using cranial base superimposition. RESULTS When the preoperative and postoperative distances between CAR and incisal point were compared, there was no significant difference between these distances, proving the hypothesis. CONCLUSIONS The method used is a practical and precise way to determine the center of mandibular autorotation on an individual basis. The center of rotation during initial jaw opening is the same as during impaction surgery.

Presentation of a cone-beam CT scanning protocol for preprosthetic cranial bone grafting of the atrophic maxilla

The use of autologous calvarian split thickness bone grafts is a well accepted preprosthetic surgical procedure for reconstruction of the severely atrophied maxilla. Although generally accepted as being a superior bone graft regarding long-term stability, the reported risks in the literature may dissuade the surgeon. A modified cone-beam computed tomography (CBCT) scanning protocol (extended field of view starting from 1cm below the occlusal plane up to the limit of the cranial vault, 0.4 voxel) is proposed that allows assessment of both the cranial donor site as the maxillary receptor site and the sinus conditions with a single scan. Issues regarding quality of the data, radiation dose and clinical practicability are discussed.

Long-term quality of life outcomes of maxillomandibular advancement osteotomy in patients with obstructive sleep apnoea syndrome

This study was performed to evaluate the long-term impact of maxillomandibular advancement (MMA) surgery on the apnoea-hypopnoea index (AHI) and quality of life (QoL) in patients with obstructive sleep apnoea syndrome (OSAS). The medical files of 12 OSAS patients who underwent MMA by one surgeon between 1995 and 1999 were reviewed retrospectively. Patients received a clinical assessment, polysomnography, and QoL questionnaires as part of routine care preoperatively (n=12), within 2 years postoperative (n=12), and again in 2016 (n=9). A successful surgical outcome was defined as an AHI decrease of >50% with <20 events/h. Of the 66.7% (8/12) of patients who were initially cured, 66.7% (4/6) remained stable at a median follow-up of 19 years. Only the two patients with the highest AHI showed abnormal Epworth Sleepiness Scale scores. After convalescence, most patients reported stable symptomatic improvement. Aesthetic changes were found acceptable and all but one patient stated that they would undergo the surgery again. It is concluded that MMA is a safe and effective procedure. Ageing and weight gain might counterbalance the positive effects of surgery in the long term. It is therefore suggested that re-evaluation every 5 years should be scheduled, since a spontaneous AHI increase over time does not seem to be reflected by symptomatic changes.

Three-dimensional volumetric changes in the upper airway after maxillomandibular advancement in obstructive sleep apnoea patients and the impact on quality of life

Obstructive sleep apnoea (OSA) is a sleep-related breathing disorder, characterized by repetitive airway obstructions, causing disruptive snoring and daytime sleepiness. Maxillomandibular advancement (MMA), which enlarges the upper airway, is a therapeutic surgical approach. However, no study has performed an upper airway sub-region analysis using validated three-dimensional (3D) anatomical and technical limits on cone beam computed tomography (CBCT). Hence, this prospective, observational trial was performed to evaluate 3D volumetric changes in the upper airway according to validated 3D cephalometric landmarks, before and after MMA, for all patients with a polysomnography diagnosis of OSA (apnoea-hypopnoea index (AHI) ≥5). The secondary objective was to evaluate the impact of MMA on the AHI and in a subjective manner with the Epworth Sleepiness Scale (ESS) and OSA questionnaire. Eleven consecutive OSA patients were included. A significant volume increase in the oropharynx (P=0.002) and hypopharynx (P=0.02) was observed, in contrast to a non-significant volume reduction in the nasopharynx (P >0.05). The median AHI (P=0.03) and ESS score (P=0.004) decreased significantly as a result of surgery. In conclusion, MMA significantly enlarges the airway volume of the oropharynx and hypopharynx and is associated with improved quality of life.