An in vitro study of the accuracy of a new protocol for planning distraction osteogenesis of the mandible

Assessment of knowledge and practices of additive manufacturing in dentistry among university teaching faculty in Saudi Arabia

BACKGROUND

In recent era, digitalization in the dental sciences has been observed in wide ranges. This cross-sectional study aimed to assess knowledge and practice of additive manufacturing (AM) in dentistry among university teaching faculty in Saudi Arabia.

METHODS

A questionnaire was prepared and validated to distribute to the different dental colleges in Saudi Arabia. The questionnaire was divided into three parts: demographic information, knowledge and practices of AM among the dental teaching faculty. After receiving all the responses, descriptive statistics were used for the frequency distribution of all the responses.

RESULTS

A total of 367 responses were received from the different faculty members. Most of the participants were male (67.30%), holding assistant professor (52.50%) positions in the field of prosthodontics (23.40%). In terms of knowledge, even though most of the participants were aware of AM (64.30%); however, do not understand the AM techniques (33.50). Moreover, 71.90% of the participants had no experience working with AM and only 13.60% of participants used AM in their respective dental colleges.

CONCLUSION

AM techniques are not commonly used in the field of dentistry in Saudi Arabia; therefore, more platforms should have created to enhance the knowledge and practice of AM in the current population.

Knowledge on Applications of 3D Design and Printing in Dentistry Among Dental Practitioners in Saudi Arabia: A Questionnaire-Based Survey

Background: This knowledge, attitude, and practices (KAP) survey will provide baseline data and identify gaps that may facilitate understanding and further action to plan, implement, and evaluate practice toward 3D-printing technology among dental practitioners in Saudi Arabia.

Aims and objectives: The present study aims to assess dental practitioners' self-reported knowledge, attitude, and practice of 3D printing in Saudi Arabia.

Methodology: A cross-sectional, closed-ended questionnaire of registered dental practitioners in Saudi Arabia was conducted. A sample size of 156 was considered for analysis. After obtaining approval from the Institutional Review Board, Riyadh Elm University, the research was conducted during the month of April 2022 amongst 154 registered dental practitioners. The research was distributed among dental health specialists either working in dental colleges, dental clinics, or both in government as well as private settings. Dentists who were not actively involved in 3D printing were excluded. SPSS software, version 25.0, (IBM Corp., Armonk, NY) was used to analyze the data.

Results and conclusion: Of all dentists included in the study, 98% were found to be aware that 3D printing in dentistry is used in Saudi Arabia and 2 % were not aware of its usage in Saudi Arabia. In total, 78.60% of the dentists felt that 3D-printed implant guides made the placement of implants the most accurate and least complicated procedure, and 21.40% of the dentists felt it was the least accurate and most complicated procedure.

Conformity of the Virtual Surgical Plan to the Actual Result Comparing Five Craniofacial Procedure Types

BACKGROUND

The "accuracy" of virtual surgical planning across multiple procedure types is not known. The authors aimed to compare the planned outcome from virtual surgical planning to the actual postoperative outcome for five craniofacial procedure types performed by a single surgeon: implant cranioplasty, cranial vault remodeling, orthognathic surgery, mandible reconstruction, and mandibular distraction.

METHODS

Stereolithography formats were obtained from virtual surgical planning and compared to postoperative computed tomographic scans for consecutive patients who underwent one of the five procedure types. Volumetric renderings of the operated bony region of interest were overlaid and compared using a Boolean operation to compute conformity (as a percentage of the region of interest). Conformity across procedure type was analyzed using analysis of variance and post hoc Bonferroni analysis, where appropriate.

RESULTS

One hundred thirty patients were included (51.5 percent male and 49.5 percent female; mean age, 27 years; 59 orthognathic surgery, 32 cranial vault remodeling, 16 mandible reconstruction, 12 mandibular distraction, and 11 implant cranioplasty patients). The highest tier of conformity was obtained for implant cranioplasty (median, 76.8 ± 10.3 percent) and mandible reconstruction (mean, 69.4 ± 11.2 percent), followed by orthognathic surgery (mean, 55.0 ± 7.3 percent) and mandibular distraction (median, 41.9 ± 20.3 percent), followed by cranial vault remodeling (mean, 22.2 ± 12.1 percent) (p < 0.001 between tiers and p > 0.05 among tiers).

CONCLUSIONS

Virtual surgical planning resulting in custom permanent implants and intraoperative guides provides more predictable results compared to virtual surgical planning used for procedures involving higher degrees of skeletal repositioning and postoperative movement (i.e., mandibular distraction and nonrigid cranial vault remodeling). In cases with expectedly lower conformity, excellent outcomes can be achieved with sound intraoperative judgment.

Combined application of virtual surgery and 3D printing technology in postoperative reconstruction of head and neck cancers

Background

The complex anatomy of the head and neck creates a formidable challenge for surgical reconstruction. However, good functional reconstruction plays a vital role in the quality of life of patients undergoing head and neck surgery. Precision medical treatment in the field of head and neck surgery can greatly improve the prognosis of patients with head and neck tumors. In order to achieve better shape and function, a variety of modern techniques have been introduced to improve the restoration and reconstruction of head and neck surgical defects. Digital surgical technology has great potential applications in the clinical treatment of head and neck cancer because of its advantages of personalization and accuracy.

Case presentation

Our department has identified the value of modern digital surgical techniques in the field of head and neck surgery and has explored its utility, including CAD/CAM technology and VR technology. We have achieved good results in the reconstruction of head and neck surgical resection defects.

Conclusion

In this article, we share five typical cases from the department of head and neck surgery where the reconstruction was performed with the assistance of digital surgical technology.

3D printing for preoperative planning and surgical training: a review

Surgeons typically rely on their past training and experiences as well as visual aids from medical imaging techniques such as magnetic resonance imaging (MRI) or computed tomography (CT) for the planning of surgical processes. Often, due to the anatomical complexity of the surgery site, two dimensional or virtual images are not sufficient to successfully convey the structural details. For such scenarios, a 3D printed model of the patient's anatomy enables personalized preoperative planning. This paper reviews critical aspects of 3D printing for preoperative planning and surgical training, starting with an overview of the process-flow and 3D printing techniques, followed by their applications spanning across multiple organ systems in the human body. State of the art in these technologies are described along with a discussion of current limitations and future opportunities.

Dimensional Error in Rapid Prototyping with Open Source Software and Low-cost 3D-printer

Rapid prototyping models (RPMs) had been extensively used in craniofacial and maxillofacial surgery, especially in areas such as orthognathic surgery, posttraumatic or oncological reconstructions, and implantology. Economic limitations are higher in developing countries such as Mexico, where resources dedicated to health care are limited, therefore limiting the use of RPM to few selected centers. This article aims to determine the dimensional error of a low-cost fused deposition modeling 3D printer (Tronxy P802MA, Shenzhen, Tronxy Technology Co), with Open source software. An ordinary dry human mandible was scanned with a computed tomography device. The data were processed with open software to build a rapid prototype with a fused deposition machine. Linear measurements were performed to find the mean absolute and relative difference. The mean absolute and relative difference was 0.65 mm and 1.96%, respectively (P = 0.96). Low-cost FDM machines and Open Source Software are excellent options to manufacture RPM, with the benefit of low cost and a similar relative error than other more expensive technologies.

Three-dimensional brain arteriovenous malformation models for clinical use and resident training

BACKGROUND

To fabricate three-dimensional (3D) models of brain arteriovenous malformation (bAVM) and report our experience with customized 3D printed models of patients with bAVM as an educational and clinical tool for patients, doctors, and surgical residents.

METHODS

Using computerized tomography angiography (CTA) or digital subtraction angiography (DSA) images, the rapid prototyping process was completed with specialized software and "in-house" 3D printing service. Intraoperative validation of model fidelity was performed by comparing to DSA images of the same patient during the endovascular treatment process. 3D bAVM models were used for preoperative patient education and consultation, surgical planning, and resident training.

RESULTS

3D printed bAVM models were successful made. By neurosurgeons' evaluation, the printed models precisely replicated the actual bAVM structure of the same patients (n = 7, 97% concordance, range 95%-99% with average of < 2 mm variation). The use of 3D models was associated shorter time for preoperative patient education and consultation, higher acceptable of the procedure for patients and relatives, shorter time between obtaining intraoperative DSA data and the start of endovascular treatment. Thirty surgical residents from residency programs tested the bAVM models and provided feedback on their resemblance to real bAVM structures and the usefulness of printed solid model as an educational tool.

CONCLUSIONS

Patient-specific 3D printed models of bAVM can be constructed with high fidelity. 3D printed bAVM models were proven to be helpful in preoperative patient consultation, surgical planning, and resident training.

Salt as a new colored solid model for simulation surgery

BACKGROUND

Simulated craniomaxillofacial surgery is critical for planning the procedure, shortening operative time, and practicing the procedure. However, typical models are expensive, given their solid materials, and the surgical sensations do not accurately reflect the procedure performed using human bone. To solve these problems, a new solid salt model has been developed.

METHOD

Stereolithography data was generated using computed tomography data, and a salt model was created using a 3D inkjet printer. By extracting specific data for elements such as the teeth and mandibular canal, these elements were highlighted in the solid model using different colored material. Also, we compared the maximum load and plastic deformation of the salt model, a stereolithographic resin model, and a pig limb.

RESULT

The salt model had similar tenacity to bone, and the risk of damage to the teeth and inferior alveolar nerve was easily confirmed.

CONCLUSION

The material cost of the salt model is extremely low, and the salt model may provide a more accurate sensation of cutting human bone. Thus, this model is useful for both simulated operation and practice for inexperienced surgeons.

Rapid prototyping-assisted maxillofacial reconstruction

Rapid prototyping (RP) technologies have found many uses in dentistry, and especially oral and maxillofacial surgery, due to its ability to promote product development while at the same time reducing cost and depositing a part of any degree of complexity theoretically. This paper provides an overview of RP technologies for maxillofacial reconstruction covering both fundamentals and applications of the technologies. Key fundamentals of RP technologies involving the history, characteristics, and principles are reviewed. A number of RP applications to the main fields of oral and maxillofacial surgery, including restoration of maxillofacial deformities and defects, reduction of functional bone tissues, correction of dento-maxillofacial deformities, and fabrication of maxillofacial prostheses, are discussed. The most remarkable challenges for development of RP-assisted maxillofacial surgery and promising solutions are also elaborated.

A paralleling device and ethylene vinyl acetate baffles for use with mandibular distraction osteogenesis: technical note

A novel method for planning the placement of intra-oral lengthening devices using a paralleling device is described and illustrated with a case report. Simple radiographic measurements and study models are all that is required to construct a simple acrylic splint with guides, which allows accurate positioning of the distractors at surgery. The construction of ethylene vinyl acetate (EVA) baffles to prevent trauma to the labial mucosa from the intra-oral link arms is a technique that enhances patient comfort during distraction of the mandible. The case report demonstrates the application of the surgical planning technique and the use of EVA baffles for a patient with an overjet of 21.5 mm.

Diagnosis and Treatment Planning using Rapid Prototyping Technology in Surgical Endodontics

Medical imaging technologies involve from X-rays to more advanced imaging modalities like computerized tomography (CT) and magnetic resonance imaging (MRI). These new technologies are able to provide detailed three-dimensional (3D) pictures of areas of interest and therefore valuable data for diagnosis and therapeutic management. The construction of a physical model using this data provides numerous advantages like better visualization of complex anatomic areas, pretreatment surgical practice and enhanced communication and patient education. The following paper describes a case report of a large periapical lesion involving upper anterior teeth requiring periapical surgery. The use of rapid prototyping technology aided in the accurate diagnosis and the precise measurements of the size and location of the lesion and its subsequent management.

How to cite this article

Ramachandran A, Khan SIR. Diagnosis and Treatment Planning using Rapid Prototyping Technology in Surgical Endodontics. J Contemp Dent 2013;3(3):147-150.

The role of distraction osteogenesis in the management of craniofacial syndromes

In patients with craniofacial syndromes, the skeletal discrepancy is often severe, and the ability to achieve the desired movement by immediate surgical repositioning is difficult because of restrictions of the soft-tissue envelope. The technique of distraction osteogenesis has provided an additional option for managing congenital and acquired craniofacial deformities. The use of distraction osteogenesis is, however, still within its infancy as a treatment modality. It is unlikely that the procedure will obviate the need for definitive orthognathic surgery at skeletal maturity in most patients with craniofacial anomalies. The role of distraction osteogenesis in craniofacial surgery will continue to evolve rapidly with increasing experience and technological advancement. Because distraction osteogenesis in the facial skeleton is a relatively new approach, analysis of the contemporary literature is imperative, and future long-term studies on the effects and outcome of distraction are essential.

Prototyping for surgical and prosthetic treatment

Techniques of rapid prototyping were introduced in the 1980s in the field of engineering for the fabrication of a solid model based on a computed file. After its introduction in the biomedical field, several applications were raised for the fabrication of models to ease surgical planning and simulation in implantology, neurosurgery, and orthopedics, as well as for the fabrication of maxillofacial prostheses. Hence, the literature has described the evolution of rapid prototyping technique in health care, which allowed easier technique, improved surgical results, and fabrication of maxillofacial prostheses. Accordingly, a literature review on MEDLINE (PubMed) database was conducted using the keywords rapid prototyping, surgical planning, and maxillofacial prostheses and based on articles published from 1981 to 2010. After reading the titles and abstracts of the articles, 50 studies were selected owing to their correlations with the aim of the current study. Several studies show that the prototypes have been used in different dental-medical areas such as maxillofacial and craniofacial surgery; implantology; neurosurgery; orthopedics; scaffolds of ceramic, polymeric, and metallic materials; and fabrication of personalized maxillofacial prostheses. Therefore, prototyping has been an indispensable tool in several studies and helpful for surgical planning and fabrication of prostheses and implants.

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.

Oblique osteotomy and coronoidectomy in extreme prognathism of Apert syndrome

We report a case of oblique osteotomy and coronoidectomy for correction of extreme prognathism in Apert syndrome.A 16-year-old girl presented with a prognathic mandible. A prototype model was formed using computed tomography. After a mock bilateral oblique osteotomy of the mandible, the distal segment did not overlap the proximal segment, and it caused bony impingement between the coronoid process and the subcondyle of the proximal segment. An oblique osteotomy of the mandible was done through a submandibular approach, and bilateral coronoidectomy followed. After surgery, mandibular parameters were reviewed. The mandibular plane-Frankfort horizontal (MP/FH) angle decreased from 44 to 11 degrees; and the mandibular plane-sella nasion (MP/SN) angle, from 52 to 17 degrees. The mandible rotated backward and caudally after the surgery.It is predictable that there will be a bony impingement between the coronoid process and the subcondyle of the proximal segment before surgery, and so an oblique osteotomy and coronoidectomy are planned ahead through an external approach.

Modified animal model and computer-assisted approach for dentoalveolar distraction osteogenesis to reconstruct unilateral maxillectomy defect

PURPOSE

The purpose of this report is to show the establishment of an animal model with a unilateral maxilla defect, application of virtual reality and rapid prototyping in the surgical planning for dentoalveolar distraction osteogenesis (DO).

MATERIALS AND METHODS

Two adult dogs were used to develop an animal model with a unilateral maxillary defect. The 3-dimensional model of the canine craniofacial skeleton was reconstructed with computed tomography data using the software Mimics, version 12.0 (Materialise Group, Leuven, Belgium). A virtual individual distractor was designed and transferred onto the model with the defect, and the osteotomies and distraction processes were simulated. A precise casting technique and numeric control technology were applied to produce the titanium distraction device, which was installed on the physical model with the defect, which was generated using Selective Laser Sintering technology, and the in vitro simulation of osteotomies and DO was done.

RESULTS

The 2 dogs survived the operation and were lively. The osteotomies and distraction process were simulated successfully whether on the virtual or the physical model. The bone transport could be distracted to the desired position both in the virtual environment and on the physical model.

CONCLUSIONS

The novel method to develop an animal model with a unilateral maxillary defect was feasible, and the animal model was suitable to develop the reconstruction method for unilateral maxillary defect cases with dentoalveolar DO. Computer-assisted surgical planning and simulation improved the reliability of the maxillofacial surgery, especially for the complex cases. The novel idea to reconstruct the unilateral maxillary defect with dentoalveolar DO was proved through the model experiment.

Craniofacial distractor applicator

Craniofacial distraction can be planned using cephalograms, computed tomography, medical models, and other forms of anatomic data. However, it is often difficult to translate this plan to the patient. Specifically, it is difficult to obtain true parallel placement of bilateral midface and mandibular distractors. Intraoperative translation of preoperatively determined vectors is also troublesome. One method of application uses computed tomography data with radiofrequency triangulation technology in a specially equipped room. This helps with the issue of placement on the patient but does not establish parallelism. We have developed a simple-to-use craniofacial application stabilization device that allows equal placement of bilateral distractors and measurement of distraction vectors. The applicator measures 20 cm in length in its open configuration. The terminal portion of the device has a coupler that holds the distractor during placement. The device is hinged in 3 points so that it can be easily folded into a compact and autoclavable device (7 x 3 cm). The hinges allow equal placement of bilateral distractors. Each hinge can be calibrated to determine the vector of distraction and confirm equal application. Lastly, the stabilizer can be fixed to nasion with a Steinmann pin for reference, allowing intraoperative translation of distraction vectors. We demonstrated on skull models that the craniofacial distractor applicator can accurately allow parallel intraoperative placement of craniofacial distractors. We demonstrated simultaneous placement of the distractors allowing a more precise determination of end points.

Computer-assisted implantology: historical background and potential outcomes-a review

BACKGROUND

The accurate transfer of preoperatively determined implant positions to the patient mouth is very beneficial to the dental practitioner as well as patients. The objective of this paper was to review the gradual development of computer-assisted implant surgery.

METHODS

All of the major data sources including unpublished data in the internet are considered

RESULTS AND CONCLUSIONS

Computer-assisted/-guided/-aided implantology has been founded to overcome the errors encountered during implant osteotomies and to position the implants more precisely. The protocols followed by this sophisticated technique are based upon the advocated concept of prosthetic-driven implantology and CT-scan analysis recently approved. Although several attempts have been made to improve this approach more and more, little has been done regarding the patient's demands, including cost. The inherent complexity of the techniques and materials utilized necessitates several degrees of training before attempting treatment and must be taken into account.

Virtual Reality Surgical Planning for Maxillofacial Distraction Osteogenesis: The Role of Reverse Engineering Rapid Prototyping and Cooperative Work

PURPOSE

The purpose of this article is the demonstration of virtual reality (VR) and rapid prototyping (RP) in surgical planning in maxillofacial surgery. The authors emphasize the role of reverse engineering (RE) and RP, suggesting a model of cooperative work, with the interaction of maxillofacial surgeons, radiologists, and engineers.

MATERIALS AND METHODS

Data acquisition is performed using computed tomography. The 3D model is the result of RE practices based on image segmentation, and the real model is produced via stereolithography. Virtual simulations are performed on the 3D model obtained from image segmentation. All these stages require the interaction and collaboration of various experts: maxillofacial surgeons, radiologists, and RE and RP experts.

RESULTS

VR and stereolithography models represent a new technology to help the surgeon who has to work in cooperation with engineers and radiologists to improve the results in surgical planning of maxillofacial distraction.

CONCLUSION

When performing the VR simulation, surgeons and engineers operate together in order to optimize the exploitation of the instruments available. Both VR and RP, with different and complementary advantages and limitations, can improve surgical planning activities and this is particularly effective when dealing with complex anatomical structures in maxillofacial surgery.

Clinical Feasibility of Computer-Aided Surgical Simulation (CASS) in the Treatment of Complex Cranio-Maxillofacial Deformities

PURPOSE

The purpose of this study was to establish clinical feasibility of our 3-dimensional computer-aided surgical simulation (CASS) for complex craniomaxillofacial surgery.

MATERIALS AND METHODS

Five consecutive patients with complex craniomaxillofacial deformities, including hemifacial microsomia, defects after tumor ablation, and deformity after TMJ reconstruction, were used. The patients' surgical interventions were planned by using the authors' CASS planning method. Computed tomography (CT) was initially obtained. The first step of the planning process was to create a composite skull model, which reproduces both the bony structures and the dentition with a high degree of accuracy. The second step was to quantify the deformity. The third step was to simulate the entire surgery in the computer. The maxillary osteotomy was usually completed first, followed by mandibular and chin surgeries. The shape and size of the bone graft, if needed, was also simulated. If the simulated outcomes were not satisfactory, the surgical plan could be modified and simulation could be started over. The final step was to create surgical splints. Using the authors' computer-aided designing/manufacturing techniques, the surgical splints and templates were designed in the computer and fabricated by a stereolithographic apparatus. To minimize the potential risks to the patients, the surgeries were also planned following the current planning methods, and acrylic surgical splints were created as a backup plan.

RESULTS

All 5 patients were successfully planned using our CASS planning method. The computer-generated surgical splints were successfully used on all patients at the time of the surgery. The backup acrylic surgical splints and plans were never used. Six-week postoperative CT scans showed the surgical plans were precisely reproduced in the operating room and the deformities were corrected as planned.

CONCLUSION

The results of this study have shown the clinical feasibility of our CASS planning method. Using our CASS method, we were able to treat patients with significant asymmetries in a single operation that in the past was usually completed in 2 stages. We were also able to simulate different surgical procedures to create the appropriate plan. The computerized surgical plan was then transferred to the patient in the operating room using computer-generated surgical splints.

Condyle as the point of rotation for 3-D planning of distraction osteogenesis for hemifacial microsomia

AIM

The purpose of this study is to present an exact simulation method for mandibular rotational movement in distraction osteogenesis for hemifacial microsomia.

METHODS

Three-dimensional (3-D) surgery simulation software programmes (V-Works and V-Surgery; Cybermed, Seoul, Korea) were used, based on 3-D CT data in addition to the conventional data, which included facial photography, panoramic radiograph, cephalogram, and dental models. After measuring the mandibular deficiency (horizontal and vertical) from a 3-D model reconstructed using the software, the angulation of the distraction device to the mandibular border (posterior or inferior) was determined. The rotation axis in the V-Works simulation was defined as the line perpendicular to the plane made by condylion and the distraction vector location on the mandible. The mandible moves along the plane around this rotational axis during distraction. After the 3-D simulation with the software programme, mock surgery on a rapid prototyping model was performed. This planning method was applied to models of two hemifacial microsomia patients.

RESULTS

With this protocol, it was possible to simulate the rotational movement of the mandible on the axis passing through the condylar head of the unaffected side.

CONCLUSION

The sequential planning procedure presented in this paper is considered to be helpful in performing effective preoperative simulation of distraction osteogenesis for hemifacial microsomia.

Accuracy of treatment planning based on stereolithography in computer assisted surgerya)

Three-dimensional stereolithographic models (SL models), made of solid acrylic resin derived from computed-tomography (CT) data, are an established tool for preoperative treatment planning in numerous fields of medicine. An innovative approach, combining stereolithography with computer-assisted point-to-point navigation, can support the precise surgical realization of a plan that has been defined on an SL model preoperatively. The essential prerequisites for the application of such an approach are: (1) The accuracy of the SL models (including accuracy of the CT scan and correspondence of the model with the patient's anatomy) and (2) the registration method used for the transfer of the plan from the SL model to the patient (i.e., whether the applied registration markers can be added to the SL model corresponding to the markers at the patient with an accuracy that keeps the "cumulative error" at the end of the chain of errors, in the order of the accuracy of contemporary navigation systems). In this study, we focus on these two topics: By applying image-matching techniques, we fuse the original CT data of the patient with the corresponding CT data of the scanned SL model, and measure the deviations of defined parameter (e.g., distances between anatomical points). To evaluate the registration method used for the planning transfer, we apply a point-merge algorithm, using four marker points that should be located at exactly corresponding positions at the patient and at connective bars that are added to the surface of the SL model. Again, deviations at defined anatomical structures are measured and analyzed statistically. Our results prove sufficient correspondence of the two data sets and accuracy of the registration method for routine clinical application. The evaluation of the SL model accuracy revealed an arithmetic mean of the relative deviations from 0.8% to 5.4%, with an overall mean deviation of 2.2%. Mean deviations of the investigated anatomical structures ranged from 0.8 mm to 3.2 mm. An overall mean (comprising all structures) of 2.5 mm was found. The fiducial registration error of the point-merge algorithm ranged from 1.0 mm to 1.4 mm. The evaluated chain of errors showed a mean deviation of 2.5 mm. This study verifies that preoperative planning on SL models and intraoperative transfer of this plan with computer assisted navigation is a suitable and sufficiently reliable method for clinical applications.

Medical rapid prototyping technologies: state of the art and current limitations for application in oral and maxillofacial surgery

PURPOSE

We describe state-of-the-art software and hardware requirements for the manufacture of high quality medical models manufactured using medical rapid prototyping. The limitations of medical models, the source of artefacts, and their physical appearance are illustrated along with remedies for their removal.

MATERIALS AND METHODS

Medical models were built using predominantly stereolithography and fused deposition modeling at both institutions over a period of 6 years. A combined total of 350 models have been produced for a range of maxillofacial, neurosurgical, and orthopedic applications. Stereolithography, fused deposition modeling, computerized numerical milling, and other technologies are described along with computer software requirements.

RESULTS

A range of unwanted artefacts that create distortions on medical models have been identified. These include data import, computed tomography gantry distortion, metal, motion, surface roughness due to support structure removal or surface modeling, and image data thresholding. The source of the artefact has been related to the patient, imaging modality performance, or the modeling technology. Discussion as to the significance of the artefacts on clinical use is provided.

CONCLUSIONS

It is recommended that models of human anatomy generated by medical rapid prototyping are subject to rigorous quality assurance at all stages of the manufacturing process. Clinicians should be aware of potential areas for inaccuracies within models and review the source images in cases where model integrity is in doubt.

Comparison of two computerassisted surgery techniques to guide a mandibular distraction osteogenesis procedure Technical note

The accuracy of distracted facial bone displacement depends on the preoperative clinical assessment, surgical planning and technique. The aim of this study was to evaluate two different techniques to guide the mandibular distraction surgical procedure using an intraoral device. This study was performed on a fresh cadavre. 3D reconstructions from a computed tomographic (CT) acquisition were used for the two techniques. The first technique comprised a customised stereolithographic template and the second technique used a computer-assisted surgery (CAS) unit to guide the osteotomy and the positioning and screwing of the distractor device. Both methods were planned and compared with the same 3D software. The authors discuss the feasibility and reliability of the two techniques. The accuracy of the two techniques appears to be comparable for clinical applications, although the rapid prototyping template technique appears to be more satisfactory.

Analysis of skeletal movements in mandibular distraction osteogenesis

PURPOSE

The purpose of this study was to use geometric parameters of movement, calculated from 3-dimensional computed tomography (CT) data, to determine the curvilinear distractor dimensions required to correct mandibular deformities in a series of patients.

MATERIALS AND METHODS

Preoperative CT scans from 15 patients with symmetric (n = 5) and asymmetric (n = 10) deformities were imported into a CT-based software program (Osteoplan; an open-source visualization application developed by Gering et al at the Surgical Planning Laboratory [SPL, Brigham and Womens Hospital, Boston, MA]). The software was used to reconstruct virtual 3-dimensional models from these scans. Two experienced surgeons, working with a computer scientist, then used Osteoplan to create an ideal treatment plan for each patient. In each case, the 3-dimensional curvilinear movement was quantified using 4 "parameters of movement" (POMs). These parameters were then used to prescribe a distraction device capable of executing the planned skeletal correction. Curvilinear distractor dimensions calculated by Osteoplan included the radius of curvature of the prescribed device, and the distractor elongation, pitch, and handedness.

RESULTS

Treatment plans including POMs were developed for each patient. The radii of curvature for the prescribed distractors ranged from 2.3 to 14.1 cm, the distractor elongation dimensions ranged from 0.7 to 3.2 cm, and the pitch (horizontal plane) dimensions ranged from 0.005 to 0.8 cm. Handedness was either a left (n = 12) or right (n = 8) turning helix.

CONCLUSION

The results of this study indicate that, using geometric parameters of movement calculated from 3-dimensional CT scans, curvilinear devices could be prescribed for correction of the range of skeletal deformities in this group of patients.

Reliability of Distraction Vector Transfer in Unilateral Vertical Distraction of the Mandibular Ramus

Mandibular distraction osteogenesis fails in correcting the skeletal deformities if the vector of distraction is incorrect. Lack of vector control is caused mainly by two factors: first, deficient vector planning and transfer, and, second, resistance of the masticatory muscles and the remaining soft tissue envelope toward elongation. To enhance predictable placement of intraoral distraction devices during surgery and thereby the treatment outcome, a method combining planning, simulation, and transfer was developed. The presurgical planning was based on frontal and lateral head films, and the planned position and orientation of the distraction device was applied on the stereolithographic model. This model was cut according to the planned osteotomy, and the distraction was simulated. The transfer procedure copied the planned and simulated position of the distraction device during surgery by use of an individual guiding splint. The guiding splint was fabricated on plaster models, and transferred to the stereolithographic model to reproduce the planned and simulated distraction treatment during surgery. The reliability of the vector-transfer method was evaluated cephalometrically in a homogenous group of 13 patients and their respective stereolithographic models in comparison with the planned, simulated, and transferred distraction vectors.

Three-Dimensional Surgical Planning for Maxillary and Midface Distraction Osteogenesis

Computerized surgical planning protocols for distraction osteogenesis are still in their rudimentary phase. The authors have developed a system to plan distraction osteogenesis in craniofacial and maxillofacial surgery that uses three-dimensional computed tomography scans and computer simulation in a virtual reality environment. This involves the creation of a three-dimensional bone model of the craniofacial skeleton, which incorporates virtual globes. Virtual osteotomies are performed on the bone model and the movements of the bone segments are simulated. The program generates a recipe for the linear and the angular changes necessary to achieve the desired outcome. The purpose of this article is to present this surgical planning process and discuss its use in maxillary and midface distraction.

The temporomandibular joint: clinical and surgical aspects

Advances in imaging techniques have greatly enhanced the ability to visualize the internal anatomy of the temporomandibular joint and have increased understanding of the etiology of many temporomandibular disorders. When used together with careful history and physical examination, this knowledge can contribute to better treatment outcomes.

Vector control in lower jaw distraction osteogenesis using an extra-oral multidirectional device

PURPOSE

This cephalometric study describes structural changes in facial features and occlusion during distraction of the mandible.

PATIENTS

Seven patients aged 7-16 years with severely retrognathic lower jaws were treated by bilateral extra-oral distraction. The direction of the distraction was changed during the distraction period (mean 30 days) using the adjustable hinge in the distractor. Cephalometric follow-up documents were analysed for changes in facial and occlusal structures. The distraction therapy proceeded in two phases. First, horizontal distraction was undertaken to achieve a good incisor relationship. After this, the direction was changed to a more vertical plane with the use of a hinge axis, and the tips of the lower incisors were used as the axis of rotation.

RESULTS

The most remarkable changes were in the more anterior position of the lower jaw, the increase in ramus height and good dental overjet. The mandibular occlusal plane became more horizontal, creating a posterior open bite. By guiding the vector of distraction, no anterior open bite or lateral crossbite appeared.

CONCLUSION

This study points out the advantages of using extra-oral multidimensional distractors. Severe lower jaw deficiency requires not only a long working length of the device but also precise control of the vector during the active phase of distraction.