3-D COSMOS: a new 3-D model based computerised operation simulation and navigation system

Effectiveness of individualized 3D titanium-printed Orthognathic osteotomy guides and custom plates

BACKGROUND

Computer-aided design/manufacturing (CAD/CAM) technology was developed to improve surgical accuracy and minimize errors in surgical planning and orthognathic surgery. However, its accurate implementation during surgery remains a challenge. Hence, we compared the accuracy and stability of conventional orthognathic surgery and the novel modalities, such as virtual simulation and three-dimensional (3D) titanium-printed customized surgical osteotomy guides and plates.

METHODS

This prospective study included 12 patients who were willing to undergo orthognathic surgery. The study group consisted of patients who underwent orthognathic two-jaw surgery using 3D-printed patient-specific plates processed by selective laser melting and an osteotomy guide; orthognathic surgery was also performed by the surgeon directly bending the ready-made plate in the control group. Based on the preoperative computed tomography images and intraoral 3D scan data, a 3D virtual surgery plan was implemented in the virtual simulation module, and the surgical guide and bone fixation plate were fabricated. The accuracy and stability were evaluated by comparing the results of the preoperative virtual simulation (T0) to those at 7 days (T1) and 6 months (T2) post-surgery.

RESULT

The accuracy (ΔT1‒T0) and stability (ΔT2‒T1) measurements, using 11 anatomical references, both demonstrated more accurate results in the study group. The mean difference of accuracy for the study group (0.485 ± 0.280 mm) was significantly lower than in the control group (1.213 ± 0.716 mm) (P < 0.01). The mean operation time (6.83 ± 0.72 h) in the control group was longer than in the study group (5.76 ± 0.43 h) (P < 0.05).

CONCLUSION

This prospective clinical study demonstrated the accuracy, stability, and effectiveness of using virtual preoperative simulation and patient-customized osteotomy guides and plates for orthognathic surgery.

The accuracy and stability of the maxillary position after orthognathic surgery using a novel computer-aided surgical simulation system

Background

Many reports have been published on orthognathic surgery (OGS) using computer-aided surgical simulation (CASS). The purpose of this study was to evaluate the accuracy of the maxillary repositioning and the stability of the maxilla in patients who underwent OGS using a newly developed CASS program, a customized osteotomy guide, and a customized miniplate.

Methods

Thirteen patients who underwent OGS from 2015 to 2017 were included. All patients underwent a bimaxillary operation. First, a skull-dentition hybrid 3D image was rendered by merging the cone beam computed tomography (CBCT) images with the dentition scan file. After virtual surgery (VS) using the FaceGide® program, patient-customized osteotomy guides and miniplates were then fabricated and used in the actual operation. To compare the VS with the actual surgery and postoperative skeletal changes, each reference point marked on the image was compared before the operation (T0) and three days (T1), four months (T2), and a year (T3) after the operation, and with the VS (Tv). The differences between ΔTv (Tv-T0) and ΔT1 (T1-T0) were statistically compared using tooth-based reference points. The superimposed images of Tv and T1 were also investigated at eight bone-based reference points. The differences between the reference points of the bone surface were examined to evaluate the stability of the miniplate on the maxilla over time.

Results

None of the patients experienced complications. There were no significant differences between the reference points based on the cusp tip between ΔTv and ΔT1 (p > 0.01). Additionally, there were no significant differences between the Tv and T1 values of the bone surface (p > 0.01). The mean difference in the bone surface between Tv and T1 was 1.01 ± 0.3 mm. Regarding the stability of the miniplate, there were no significant differences between the groups. The difference in the bone surface between T1 and T3 was − 0.37 ± 0.29 mm.

Conclusions

VS was performed using the FaceGide® program, and customized materials produced based on the VS were applied in actual OGS. The maxilla was repositioned in almost the same manner as in the VSP plan, and the maxillary position remained stable for a year.

Estimating patient-specific and anatomically correct reference model for craniomaxillofacial deformity via sparse representation

PURPOSE

A significant number of patients suffer from craniomaxillofacial (CMF) deformity and require CMF surgery in the United States. The success of CMF surgery depends on not only the surgical techniques but also an accurate surgical planning. However, surgical planning for CMF surgery is challenging due to the absence of a patient-specific reference model. Currently, the outcome of the surgery is often subjective and highly dependent on surgeon's experience. In this paper, the authors present an automatic method to estimate an anatomically correct reference shape of jaws for orthognathic surgery, a common type of CMF surgery.

METHODS

To estimate a patient-specific jaw reference model, the authors use a data-driven method based on sparse shape composition. Given a dictionary of normal subjects, the authors first use the sparse representation to represent the midface of a patient by the midfaces of the normal subjects in the dictionary. Then, the derived sparse coefficients are used to reconstruct a patient-specific reference jaw shape.

RESULTS

The authors have validated the proposed method on both synthetic and real patient data. Experimental results show that the authors' method can effectively reconstruct the normal shape of jaw for patients.

CONCLUSIONS

The authors have presented a novel method to automatically estimate a patient-specific reference model for the patient suffering from CMF deformity.

Accuracy of a computer-aided surgical simulation protocol for orthognathic surgery: a prospective multicenter study

PURPOSE

The purpose of this prospective multicenter study was to assess the accuracy of a computer-aided surgical simulation (CASS) protocol for orthognathic surgery.

MATERIALS AND METHODS

The accuracy of the CASS protocol was assessed by comparing planned outcomes with postoperative outcomes of 65 consecutive patients enrolled from 3 centers. Computer-generated surgical splints were used for all patients. For the genioplasty, 1 center used computer-generated chin templates to reposition the chin segment only for patients with asymmetry. Standard intraoperative measurements were used without the chin templates for the remaining patients. The primary outcome measurements were the linear and angular differences for the maxilla, mandible, and chin when the planned and postoperative models were registered at the cranium. The secondary outcome measurements were the maxillary dental midline difference between the planned and postoperative positions and the linear and angular differences of the chin segment between the groups with and without the use of the template. The latter were measured when the planned and postoperative models were registered at the mandibular body. Statistical analyses were performed, and the accuracy was reported using root mean square deviation (RMSD) and the Bland-Altman method for assessing measurement agreement.

RESULTS

In the primary outcome measurements, there was no statistically significant difference among the 3 centers for the maxilla and mandible. The largest RMSDs were 1.0 mm and 1.5° for the maxilla and 1.1 mm and 1.8° for the mandible. For the chin, there was a statistically significant difference between the groups with and without the use of the chin template. The chin template group showed excellent accuracy, with the largest positional RMSD of 1.0 mm and the largest orientation RMSD of 2.2°. However, larger variances were observed in the group not using the chin template. This was significant in the anteroposterior and superoinferior directions and the in pitch and yaw orientations. In the secondary outcome measurements, the RMSD of the maxillary dental midline positions was 0.9 mm. When registered at the body of the mandible, the linear and angular differences of the chin segment between the groups with and without the use of the chin template were consistent with the results found in the primary outcome measurements.

CONCLUSIONS

Using this computer-aided surgical simulation protocol, the computerized plan can be transferred accurately and consistently to the patient to position the maxilla and mandible at the time of surgery. The computer-generated chin template provides greater accuracy in repositioning the chin segment than the intraoperative measurements.

A novel design of a computer-generated splint for vertical repositioning of the maxilla after Le Fort I osteotomy

OBJECTIVE

The objective of this study was to evaluate the efficacy of a novel tooth/bony-supported virtual splint design to control the maxillary vertical, rotational, and anteroposterior intraoperative movements.

STUDY DESIGN

A tooth/bone-borne splint was designed to position the osteotomized maxilla intraoperatively. Lateral cephalometric radiographs were obtained 1 week before the operation and 1 week after to compare the planned and actual movements of the maxilla.

RESULTS

The paired t test showed no significant difference between the planned and actual movements in both the vertical and horizontal measurements (P ≤ .05). The difference between the planned and actual horizontal movements in 4 (66.7%) of the 6 patients was 1 mm or less. For the vertical movements, 5 (83.3%) of the 6 patients showed a difference equal to or less than 1 mm.

CONCLUSIONS

The 2-piece surgical stent showed accurate control on the osteotomized maxilla and succeeded its repositioning to the preplanned positions.

Computer-assisted orthognathic surgery: feasibility study using multiple CAD/CAM surgical splints

OBJECTIVE

We present a virtual planning protocol incorporating a patented 3-surgical splint technique for orthognathic surgery. The purpose of this investigation was to demonstrate the feasibility and validity of the method in vivo.

MATERIALS AND METHODS

The protocol consisted of (1) computed tomography (CT) or cone-beam computed tomography (CBCT) maxillofacial imaging, optical scan of articulated dental study models, segmentation, and fusion; (2) diagnosis and virtual treatment planning; (3) computed-assisted design and manufacture (CAD/CAM) of the surgical splints; and (4) intraoperative surgical transfer. Validation of the accuracy of the technique was investigated by applying the protocol to 8 adult class III patients treated with bimaxillary osteotomies. The virtual plan was compared with the postoperative surgical result using image fusion of CT/CBCT dataset by analysis of measurements between hard and soft tissue landmarks relative to reference planes.

RESULTS

The virtual planning approach showed clinically acceptable precision for the position of the maxilla (<0.23 mm) and condyle (<0.19 mm), marginal precision for the mandible (<0.33 mm), and low precision for the soft tissue (<2.52 mm).

CONCLUSIONS

Virtual diagnosis, planning, and use of a patented CAD/CAM surgical splint technique provides a reliable method that may offer an alternate approach to the use of arbitrary splints and 2-dimensional planning.

New Methods to Evaluate Craniofacial Deformity and to Plan Surgical Correction

The success of cranio-maxillofacial (CMF) surgery depends not only on surgical techniques, but also upon an accurate surgical plan. Unfortunately, traditional planning methods are often inadequate for planning complex cranio-maxillofacial deformities. To this end, we developed 3D computer-aided surgical simulation (CASS) technique. Using our CASS method, we are able to treat patients with significant asymmetries in a single operation which in the past was usually completed in two stages. The purpose of this article is to introduce our CASS method in evaluating craniofacial deformities and planning surgical correction. In addition, we discuss the problems associated with the traditional surgical planning methods. Finally, we discuss the strength and pitfalls of using three-dimensional measurements to evaluate craniofacial deformity.

Outcome study of computer-aided surgical simulation in the treatment of patients with craniomaxillofacial deformities

PURPOSE

The purpose of this study was to determine whether the surgical outcomes achieved with computer-aided surgical simulation (CASS) are better than those achieved with traditional methods.

MATERIALS AND METHODS

Twelve consecutive patients with craniomaxillofacial (CMF) deformities were enrolled. According to the CASS clinical protocol, a 3-dimensional computer composite skull model for each patient was generated and reoriented to the neutral head posture. These models underwent 2 virtual surgeries: 1 was based on CASS (experimental group) and the other was based on traditional methods 1 year later (control group). Once the 2 virtual surgeries were completed, 2 experienced oral and maxillofacial surgeons at 2 different settings evaluated the 2 surgical outcomes. They were blinded to the planning method used on the virtual models and each other's evaluation results. The primary outcome was overall CMF skeletal harmony. The secondary outcomes were individual maxillary, mandibular, and chin harmonies. Statistical analyses were performed.

RESULTS

Overall CMF skeletal harmony achieved with CASS was statistically significantly better than that achieved with traditional methods. In addition, the maxillary and mandibular surgical outcomes achieved with CASS were significantly better. Furthermore, although not included in the statistical model, the chin symmetry achieved by CASS tended to be better. A regression model was established between mandibular symmetry and overall CMF skeletal harmony.

CONCLUSION

The surgical outcomes achieved with CASS are significantly better than those achieved with traditional planning methods. In addition, CASS enables the surgeon to better correct maxillary yaw deformity, better place proximal/distal segments, and better restore mandibular symmetry. The critical step in achieving better overall CMF skeletal harmony is to restore mandibular symmetry.

The accuracy of two-dimensional planning for routine orthognathic surgery

Two-dimensional cephalometric planning software should be helpful for prediction of hard tissue outcome after bilateral sagittal split ramus osteotomy (BSSRO) or bimaxillary osteotomy, but transferring two-dimensional data to three-dimensions (including mock operation and surgery) may result in errors. The objective of this retrospective study was to analyze deviations between predicted results and postoperative outcome using cephalometric analyses, and to evaluate this procedure for daily use. Fifty-four subjects (mean (SD) age 26 (8) years) had a BSSRO (n=21) alone or in combination with Le Fort I osteotomy (n=33). Predictions were made for each case by cephalometric planning software and mock operations done with study models. Postoperative cephalograms were obtained after 14 days and compared with predicted cephalograms for sagittal (SNA, SNB, ANB,) and vertical (ArMeGo, ML-NSL, NL-NSL) measurements. Mean (SD) differences for all measurements varied between 1.3 degrees (1.1 degrees) and 2.2 degrees (1.6 degrees) for BSSRO; and between 1.1 degrees (1.3 degrees) and 2.2 degrees (1.6 degrees) for bimaxillary osteotomy. There were no significant differences between measurements or operations, indicating that the predictions were accurate. A difference of up to 8.5 degrees could be measured in a single case. Cephalometric prediction therefore remains an accurate tool for planning, particularly maxillary rearrangement in the vertical and sagittal dimension for routine operations. If greater shifts in the transversal dimension are necessary, exact planning should be adapted with three-dimensional planning devices to avoid significant differences.

A novel method for the 3-dimensional simulation of orthognathic surgery by using a multimodal image-fusion technique

INTRODUCTION

The aim of this study was to establish a novel method for simulating orthognathic surgery in 3-dimensional (3D) space.

METHODS

This system mainly consists of 6 procedures: (1) reconstruction of a virtual skull model (VS) from presurgical computed tomography scans; (2) reconstruction of virtual dentition models from 3D surface scanning of dental casts occluded at presurgical and postsurgical intercuspal positions (VD1 and VD2, respectively); (3) reconstruction of a preliminary fusion model of VS and VD1 by an initial intermodality registration; (4) reconstruction of another preliminary fusion model of VS, VD1, and VD2 by a second intramodality registration; (5) repositioning of bony segments by a third intramodality registration and reconstruction of final fusion models at presurgery and postsurgery; and (6) 3D analysis of the movement of bony segments. To test this system, 2 patients with severe skeletal deformities, who had undergone presurgical orthodontic treatment, were used as models. Registration accuracy was determined by the root mean squared distance between the corresponding fiducial markers in a set of 2 images.

RESULTS AND CONCLUSIONS

The sum of the root mean squared error of the 3 registration processes was less than 0.4 mm in both patients. This simulation system could be used to precisely realize the presurgical and postsurgical occlusal relationships and craniofacial morphology of a patient with severe skeletal deformities, and to quantitatively describe the movement of a given anatomical point of bony segments. It is assumed that there could be significant benefits in sharing visual and quantitative 3D information from this simulation system among orthodontists and surgeons.

A new navigation system based on cephalograms and dental casts for oral and maxillofacial surgery

Intraoperative navigation systems help surgeons to accurately carry out preoperative plans without injuring anatomically important structures. A system is evaluated that uses cephalograms instead of computed tomographic (CT) scans to create images. Three-dimensional (3D) dental casts provide registration between imaging data and the patient. Cephalograms are widely employed in orthognathic and oral and maxillofacial surgery and expose patients to lower doses of radiation than CT. The system uses a dental cast to register the operation field to a pair of frontal and lateral cephalograms. The cast is transformed to 3D data with a laser scanner and a programme that runs on a personal computer. 3D data describing the dental cast, cephalograms and the oral and maxillofacial region of the patient are integrated with specialized software. The optical tracking system for navigation uses charged-coupled-device (CCD) video cameras and light-emitting diodes (LEDs). Two CCD video cameras follow the 3D coordinates of LED assemblies attached to the head, lower jaw and a handpiece. Errors occurring when a dental cast was transformed to 3D data ranged from 0.08 to 0.21 mm. Mean errors were 0.71 mm (0.21-1.09 mm) for the right maxillary central incisor, 0.62 mm (0.04-1.69 mm) for the right maxillary 2nd molar and 1.02 mm (0.23-1.47 mm) for the left maxillary 2nd molar. This surgical navigation system is sufficiently accurate for use in oral and maxillofacial surgery.

Preoperative hepatic 3D models: virtual liver resection using three-dimensional imaging technique

Emerging new techniques for liver resections set new requirements for the preoperative imaging and planning. Open surgery is a three-dimensional procedure and planning of the resection line may be difficult when basing on conventional two-dimensional CTs or MRIs, although all the information is there. With multidetector-row CT (MDCT), thin slices can be obtained with excellent temporal resolution, and precise three-dimensional (3D) models can be created. We regard 3D imaging technique useful in most liver resections. It improves the surgeon's knowledge of liver anatomy and makes even more complicated liver resections safe. Better knowledge of three-dimensional appearances of liver structures may further improve the results of curative liver surgery. However, before becoming a routine clinical procedure, research and development are still needed. Also, careful testing and evaluation of the methods have to be performed. In the future, 3D models will probably play an important role in the preoperative planning of liver resections.

Anterior transmandibular osteodistraction: clinical and model observations

INTRODUCTION

The aim of this paper was to study the effect of transmandibular distraction on the periodontal and dental structures, and the initial movements of the mandibular halves, when using an axial plane non-rigid bone-borne distractor (TMD).

MATERIAL AND METHODS

Fourteen patients undergoing bimaxillary transverse osteodistraction had their six lower anterior teeth assessed for mobility, sensitivity, and pocket depth. Recordings were made pre-operatively, post-distraction, post-consolidation and at 1-year follow-up. Selected landmarks on pre-operative and post-consolidation models were also digitised in three dimensions to study individual tooth movements, and positional changes of the mandibular halves.

RESULTS

Pockets depths around the incisor teeth increased during the consolidation period (probably due to reduced oral hygiene), but returned to normal by the 1-year post-operative consultation. Tooth mobility increased temporarily in the active phase (central incisors, lateral incisors) and in the consolidation phase (lateral incisors, canine teeth). Sensitivity to cold was temporarily lost in the incisor teeth, probably as a result of 'apical contusion'. One central incisor was inadvertently apically osteotomized and needed root canal treatment. The angle between the mandibular halves closed by 9.4 degrees.

CONCLUSION

Periodontal and dental morbidity is transient and limited to the distraction and consolidation period, as long as the tooth apices are avoided when the osteotomy is performed. A step-design osteotomy may be preferable when the central incisor apices are close to each other. The transmandibular distractor (TMD) allows for rotation at the temporomandibular joints.

A new technique for the creation of a computerized composite skull model

PURPOSE

The goals of this study were to develop a technique for creating a computerized composite skull model and to test its accuracy. The computerized composite skull model is the combination of a 3-dimensional (3D) computed tomography (CT) bone model with digital dental models.

MATERIALS AND METHODS

A dry skull with intact dentition was used in development of the technique. The creation of the computerized composite skull model was divided into 3 steps. The first step was to create digital dental models. The second step was to create a 3D CT bone model of the craniomaxillofacial skeleton. The last step was to incorporate the digital dental models into the 3D CT skull model, creating a computerized composite skull model. The accuracy of the computerized composite skull model was assessed. Bone-to-bone, tooth-to-tooth, and bone-to-tooth measurements were made on the computerized composite skull model and the dry skull. Pearson correlation coefficient and linear regression tests were performed.

RESULTS

A technique to create a computerized composite skull model was developed. This computerized model not only represented bony structures from CT data but also reproduced dentition from digital dental models. For the bone-to-bone measurements, the mean difference between the computerized composite skull model and the dry skull was 0.5 +/- 0.6 mm. For the tooth-to-tooth measurements, the mean difference was 0.1 +/- 0.2 mm. For the bone-to-tooth measurements, the mean difference was 0.2 +/- 0.3 mm.

CONCLUSIONS

This study showed the feasibility of creating a computerized composite skull model as well as its accuracy.

Analysis of midface asymmetry in patients with cleft lip, alveolus and palate at the age of 3 months using 3D-COSMOS measuring system

INTRODUCTION

Patients suffering from unilateral cleft lip, alveolus and palate exhibit a varying degree of asymmetry of the midface. Evaluation of this asymmetry can be carried out by means of 3D-CT, or a laser surface scanner.

MATERIAL AND METHODS

In this paper, 3D-CT-scan data of 21 patients with unilateral clefts of lip, alveolus and palate were analysed using three-dimensional models. Evaluations of the 3D-models were carried out with the computer-aided 3D-operation simulator 3D-Cosmos.

RESULTS

Asymmetry was found in the orbital, nasal and maxillary regions. The infraorbital rims were displaced craniocaudally and horizontally as well as laterally of the cleft-sided piriform aperture. This asymmetry corresponded to a dislocation of the maxillary segment on the cleft side. A deficit in volume was not reliably found.