Virtual occlusion in planning orthognathic surgical procedures.

Accurate preoperative planning is mandatory for orthognathic surgery. One of the most important aims of this planning process is obtaining good postoperative dental occlusion. Recently, 3D image-based planning systems have been introduced that enable a surgeon to define different osteotomy planes preoperatively and to assess the result of moving different bone fragments in a 3D virtual environment, even for soft tissue simulation of the face. Although the use of these systems is becoming more accepted in orthognathic surgery, few solutions have been proposed for determining optimal occlusion in the 3D planning process. In this study, a 3D virtual occlusion tool is presented that calculates a realistic interaction between upper and lower dentitions. It enables the surgeon to obtain an optimal and physically possible occlusion easily. A validation study, including 11 patient data sets, demonstrates that the differences between manually and virtually defined occlusions are small, therefore the presented system can be used in clinical practice.

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 patient's 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.

Evaluation of reproducibility and reliability of 3D soft tissue analysis using 3D stereophotogrammetry.

In 3D photographs the bony structures are neither available nor palpable, therefore, the bone-related landmarks, such as the soft tissue gonion, need to be redefined. The purpose of this study was to determine the reproducibility and reliability of 49 soft tissue landmarks, including newly defined 3D bone-related soft tissue landmarks with the use of 3D stereophotogrammetric images. Two observers carried out soft-tissue analysis on 3D photographs twice for 20 patients. A reference frame and 49 landmarks were identified on each 3D photograph. Paired Student's t-test was used to test the reproducibility and Pearson's correlation coefficient to determine the reliability of the landmark identification. Intra- and interobserver reproducibility of the landmarks were high. The study showed a high reliability coefficient for intraobserver (0.97 (0.90 - 0.99)) and interobserver reliability (0.94 (0.69 - 0.99)). Identification of the landmarks in the midline was more precise than identification of the paired landmarks. In conclusion, the redefinition of bone-related soft tissue 3D landmarks in combination with the 3D photograph reference system resulted in an accurate and reliable 3D photograph based soft tissue analysis. This shows that hard tissue data are not needed to perform accurate soft tissue analysis.

The accuracy of matching three-dimensional photographs with skin surfaces derived from cone-beam computed tomography.

The state-of-the-art diagnostic tools in oral and maxillofacial surgery and preoperative orthodontic treatment are mainly two-dimensional, and consequently reveal limitations in describing the three-dimensional (3D) structures of a patient's face. New 3D imaging techniques, such as 3D stereophotogrammetry (3D photograph) and cone-beam computed tomography (CBCT), have been introduced. Image fusion, i.e. registration of a 3D photograph upon a CBCT, results in an accurate and photorealistic digital 3D data set of a patient's face. The purpose of this study was to determine the accuracy of three different matching procedures. For 15 individuals the textured skin surface (3D photograph) and untextured skin surface (CBCT) were matched by two observers using three different methods to determine the accuracy of registration. The registration error was computed as the difference (mm) between all points of both surfaces. The registration errors were relatively large at the lateral neck, mouth and around the eyes. After exclusion of artefact regions from the matching process, 90% of the error was within+/-1.5 mm. The remaining error was probably caused by differences in head positioning, different facial expressions and artefacts during image acquisition. In conclusion, the 3D data set provides an accurate and photorealistic digital 3D representation of a patient's face.

Accuracy of implant placement based on pre-surgical planning of three-dimensional cone-beam images: a pilot study.

AIM: To evaluate the precision of transfer of a computer-based three-dimensional (3D) planning, using re-formatted cone-beam images, for oral implant placement in partially edentulous jaws. MATERIAL AND METHODS: Four formalin-fixed cadaver jaws were imaged in a 3D Accuitomo FPD cone-beam computed tomography (CT). Data were used to produce an accurate implant planning with a transfer to surgery by means of stereolithographic drill guides. Pre-operative cone-beam CT images were subsequently matched with post-operative ones to calculate the deviation between planned and installed implants. RESULTS: Placed implants (length: 10-15 mm) showed an average angular deviation of 2 degrees (SD: 0.8, range: 0.7-4.0 degrees ) as compared with the planning, while the mean linear deviation was 1.1 mm (SD: 0.7 mm, range 0.3-2.3 mm) at the hex and 2.0 mm (SD: 0.7 mm, range 0.7-2.4 mm) at the tip. CONCLUSIONS: Cone-beam images could be used for implant planning, taking into account a maximal 4 degrees angular and 2.4 mm linear deviation at the apical tip.

Predicting soft tissue deformations for a maxillofacial surgery planning system: from computational strategies to a complete clinical validation.

In the field of maxillofacial surgery, there is a huge demand from surgeons to be able to pre-operatively predict the new facial outlook after surgery. Besides the big interest for the surgeon during the planning, it is also an essential tool to improve the communication between the surgeon and his patient. In this work, we compare the usage of four different computational strategies to predict this new facial outlook. These four strategies are: a linear Finite Element Model (FEM), a non-linear Finite Element Model (NFEM), a Mass Spring Model (MSM) and a novel Mass Tensor Model (MTM). For true validation of these four models we acquired a data set of 10 patients who underwent maxillofacial surgery, including pre-operative and post-operative CT data. For all patient data we compared in a quantitative validation the predicted facial outlook, obtained with one of the four computational models, with post-operative image data. During this quantitative validation distance measurements between corresponding points of the predicted and the actual post-operative facial skin surface, are quantified and visualised in 3D. Our results show that the MTM and linear FEM predictions achieve the highest accuracy. For these models the average median distance measures only 0.60 mm and even the average 90% percentile stays below 1.5 mm. Furthermore, the MTM turned out to be the fastest model, with an average simulation time of only 10 s. Besides this quantitative validation, a qualitative validation study was carried out by eight maxillofacial surgeons, who scored the visualised predicted facial appearance by means of pre-defined statements. This study confirmed the positive results of the quantitative study, so we can conclude that fast and accurate predictions of the post-operative facial outcome are possible. Therefore, the usage of a maxillofacial soft tissue prediction system is relevant and suitable for daily clinical practice.

The use of a new 3D splint and double CT scan procedure to obtain an accurate anatomic virtual augmented model of the skull.

Three-dimensional (3D) virtual planning of orthognathic surgery requires detailed visualization of the interocclusal relationship. The purpose of this study was to introduce the modification of the double computed tomography (CT) scan procedure using a newly designed 3D splint in order to obtain a detailed anatomic 3D virtual augmented model of the skull. A total of 10 dry adult human cadaver skulls were used to evaluate the accuracy of the automatic rigid registration method for fusion of both CT datasets (Maxilim, version 1.3.0). The overall mean registration error was 0.1355+/-0.0323 mm (range 0.0760-0.1782 mm). Analysis of variance showed a registration method error of 0.0564 mm (P < 0.001; 95% confidence interval = 0.0491-0.0622). The combination of the newly designed 3D splint with the double CT scan procedure allowed accurate registration and the set-up of an accurate anatomic 3D virtual augmented model of the skull with detailed dental surface.

Trans-sinusoidal maxillary distraction in three cleft patients.

The trans-sinusoidal maxillary distractor (TS-MD) was used to achieve maxillary advancement in three patients with repaired cleft lip and palate. After preoperative computer-aided planning of the distraction vectors, each TS-MD was bent on a stereolithographic model of the maxilla of the patient. The devices were intraoperatively positioned using a methyl-methacrylate template. After standard Le Fort I osteotomy the devices were intraorally activated. After distraction the devices remained in situ for 3 months as rigid internal fixation of the maxilla. All patients were successfully distracted according to protocol. Maxillary advancement was 12, 8 and 11 mm. In two patients, additional maxillary widening of 6 and 8 mm was achieved by choosing divergent distraction vectors. After distraction a clockwise rotation of the maxilla was observed in two patients. There was no relapse during the 3 months of consolidation and 12-month follow-up. The TS-MD allows not only distraction but also rigid internal fixation after distraction. It was easy to apply but difficult to remove. Owing to preoperative 3D planning of the distraction vectors, the results were predictable, but clockwise rotation of the maxilla during distraction should be considered in planning. The distractor did not interfere with function or social activities during distraction and retention periods. After removal it left no extraoral scars.

Trans-sinusal maxillary distraction for correction of midfacial hypoplasia: long-term clinical results.

Maxillary distraction osteogenesis is indicated in severe angle class III malocclusions, and severe maxillary hypoplasia among some cleft patients and other craniofacial deformities. Twenty patients, aged 8-48 years (mean 17.8+/-10.5 SD) with maxillary and midfacial hypoplasia were treated. The follow-up period was 13-65 months (mean 35+/-16.3 SD). A trans-sinusal maxillary distractor was placed intraorally at each side of the maxilla. The distraction vector was predicted using specialist software, and was transferred to the patients using stereolithographic models and individual templates. A (high) Le Fort I type osteotomy was performed. The amount of activation varied from 8 to 17.5 mm (mean 13.1+/-2.9 SD). Soft and hard tissue formation resulted in complete healing across the distraction gaps. The distractors are almost completely submerged, and can be left in place as long as necessary to avoid relapse. Wit's appraisal was used to measure the stability of the long-term distraction results. Results up to 5 years after distraction showed considerable maxillary advancement with long-term stability. Ongoing growth of the facial skeleton must be considered when distraction osteogenesis is chosen in growing patients.

Effect of platelet-rich-plasma on cranial distraction osteogenesis in sheep: preliminary clinical and radiographic results.

The purpose of this study was to investigate the effect of platelet-rich-plasma (PRP) on cranial distraction osteogenesis. Standardized calvaria critical size defects (6 cm x 5 cm) were created in 16 adult female sheep. Bifocal cranial transport distraction osteogenesis with autogenous free calvaria bone grafts (2 cm x 4 cm) was performed at a rate of 1mm once daily to a total of 30 mm. The 16 sheep involved in the experiment were randomly divided into four groups, four animals in each: Group 1 (no PRP, latency 5 days); Group 2 (no PRP, latency 0 day), Group 3 (PRP, latency 5 days) and Group 4 (PRP, latency 0 day). After a consolidation phase of 6 weeks, the animals were sacrificed and specimens harvested for conventional radiological and 3D quantitative computer tomographic (3D-QCT) assessment. New bone was generated in the distraction zone in all groups. There were significantly (P < 0.05) higher densities in the proximal region of the distraction regenerate in Group 4 (PRP, latency 0 day) compared to Group 2. However, no significant differences in mean density of the total distraction regenerate were found, neither in volume of the bony regenerate between the experimental groups. This study showed that PRP only had an effect on bone regeneration if active distraction was started immediately after application of PRP in the distraction gap.

Radiation dose vs. image quality for low-dose CT protocols of the head for maxillofacial surgery and oral implant planning.

The goal of this study was to determine the acquisition parameters for a low-dose multi-slice CT protocol and to compare the effective dose and the image quality of this low-dose protocol with the image quality of a clinical multi-slice CT protocol, routinely used for visualisation of the head. The low-dose protocol was derived from a clinical multi-slice CT protocol by lowering mA s and kV and increasing the pitch. The low-dose protocol yielded a dose reduction from 1.5 to 0.18 mSv for a multi-slice CT scan of the whole head, whereas noise in the low-dose CT images was increased. For bone segmentation, noise could be reduced by use of a non-linear edge preserving smoothing filter. Tests on ESP and skull phantom indicated that the accuracy of the measurements on low-dose CT is acceptable for image-based planning of maxillofacial and oral implant surgery, reducing the dose by a factor of 8.

Assessment of the distraction regenerate using three-dimensional quantitative computer tomography.

This study presents a new method for objective assessment of the distraction regenerate using three-dimensional quantitative computer tomography (3D-QCT). The distraction specimens of 16 sheep that underwent bifocal cranial distraction osteogenesis to reconstruct a critical size defect were used to evaluate this method. To analyse the validity of this method the results were compared to conventional quantitative computer tomography (QCT). Squared correlation coefficients (r(2)) according to Sackett showed a high reliability (r(2) > 70% for the total DO regenerate, DO Regions 2-4). Method comparison according to Bland-Altman (< or =6.25% of measurements out of 95% limits of agreement) showed that three-dimensional computer tomography based bone densitometry is valid for future DO research.

The nasopalatine canal revisited using 2D and 3D CT imaging.

OBJECTIVES: To assess the location, morphology and dimensions of the nasopalatine canal on two-dimensional and three-dimensional (2D and 3D) CT images. METHODS: Material included 34 spiral CT scans for pre-operative planning of implant placement in the maxilla. Scanning was performed using a standard exposure and patient positioning protocol. 2D and 3D spiral CT images were carefully examined for the location, morphology and dimensions of the nasopalatine canal by two independent observers. A comparison was made between 2D observations and a 2D/3D combined observation strategy (paired t-tests). RESULTS: The nasopalatine canal typically appeared as a canal with a mean (standard deviation (SD)) length of 8.1 (3.4) mm. Its palatal opening is the incisive foramen with a mean (SD) inner Ø of 4.6 (1.8) mm. At the level of the nasal floor often 2 (Y-canal morphology), but sometimes 3 or 4 openings could be observed. In particular cases, the canal showed up as a cylinder with only one nasal opening. The average (SD) maximum width of the nasopalatine canal structure at the level of the nasal floor was 4.9 (1.2) mm. The buccopalatal width of the jaw, anterior to the canal was 7.4 (2.6) mm. Interpretation of canal morphology was significantly different when comparing 2D image observation with a 2D/3D combined observation strategy. However, dimensional measurements of the canal were not significantly different for a 2D and a combined 2D/3D approach. CONCLUSIONS: The nasopalatine canal may show important anatomical variations, both with regard to morphology and dimensions. To avoid any potential complications during surgical procedures such as implant placement, a careful pre-operative observation is required. Cross-sectional imaging may be advocated to determine canal morphology and dimensions and to assess anterior bone width for potential implant placement buccally to the canal.

[Bone distraction osteogenesis]. / L'ostéogenèse par distraction osseuse.

Bone osteogenesis has been used by many surgeons to compensate dissymmetry due to congenital malformations, diseases or traumas. Bone distraction is the process of generating new bone in a gap between two bone segments in response to the application of graduated tensile stress across the bone gap. Different types of distraction are actually proposed to be an alternative to facial osteotomies or bone grafting techniques. Distraction can be unilateral, bilateral and correct the deficiencies in one, two or three dimensions. The advantages of the distraction osteogenesis are the possibilities to obtain bone lengthening together with simultaneous expansion of the functional soft tissue matrix including skin, muscles, nerves, cartilage, blood vessels and periosteum. Distractors are internal or external devices made of pins or miniplates fixed on the bone and connected by lengthening--screw--systems allowing elongation.

An image-based 3D planning environment for hemicricolaryngectomy and reconstruction by tracheal autotransplantation.

OBJECTIVE: A new conservation method for unilateral glottal cancer with significant subglottal extension consists of a hemicricolaryngectomy and subsequent reconstruction of the laryngeal defect with a transferable patch of revascularized cervical trachea. In order to restore the three crucial functions of the larynx - airway patency, speech, and swallowing--the reconstructed larynx should resemble a situation with one paralyzed and one intact vocal fold at the glottal level. We hypothesize that this result can be achieved when the tracheal patch meets a typical surgical constraint--the so-called paramedian position at the glottal level - and when the patch is rigidly applied. This hypothesis was tested by developing and using an image-based planning system in a number of situations. MATERIALS AND METHODS: An image-based surgery simulator was developed according to the working hypothesis. To validate the transfer from planning towards actual surgery, a cadaver study was set up. Based on a patient case-study, the sufficiency of the hypothesis for obtaining good functional results was evaluated. Finally, post-operative images of patients who were doing well after being operated without pre-operative planning were compared with retrospective planning to check the necessity of the hypothesis in obtaining good functionality of the neolarynx. RESULTS: We were able to design an efficient surgery simulator. The transfer from planning towards actual surgery is accurate, and satisfactory functional results were obtained from the patient case-study. The results from the retrospective planning showed that the hypothesis is not necessary to obtain good functional results, and that the smallest possible resection is preferred from the oncological point of view. CONCLUSION: The working hypothesis is sufficient for good functional results, but is unnecessary and often undesirable from an oncological point of view. Important lessons are drawn concerning our long-term goal of pre-operative determination of the shape and position of a tracheal patch suitable for optimizing the (neo-) laryngeal functions.