Reproducibility of three-dimensional CT-assisted model production in the maxillofacial area

Three-Dimensional (3D) Stereolithographic Tooth Replicas Accuracy Evaluation: In Vitro Pilot Study for Dental Auto-Transplant Surgical Procedures

After immediate tooth extraction or after alveolar socket healing, tooth transplants are increasingly used for functional restoration of edentulous maxillary areas. Recent studies have shown the periodontal ligament (PDL) viability and the tooth housing time in the adapted neo-alveolus as key factors for transplantation success. During surgical time, 3D stereolithographic replicas are used for fitting test procedures. In this paper, the accuracy of 3D dental replicas, compared with the corresponding natural teeth, is assessed in surgical transplantation. Lamb skulls were selected and submitted to Cone Beam Computer Tomography (CBCT). Scanning information, converted into Standard Digital Imaging and Communications in Medicine (DICOM) and Standard Triangulation Language (STL), was sent to the Volux X-ray Centre for 3D replica printing. After the tooth extractions, all lambs’ incisors were measured with a digital caliber and compared with the 3D replicas. Volume and dimensional error values were evaluated. All replicas showed macroscopically smaller volume (45.54%). Root replicas showed higher variations compared with the crown areas, with several unreplicated apical root areas. The cement–enamel junction tooth area was replicated quite faithfully, and the base area relative error showed 9.8% mean value. Even further studies with a larger number of replicas are needed. Data obtained confirmed high volumes of macroscopic discrepancies with several unreproduced apical root sites. The achieved accuracy (90.2%) confirmed that the 3D replicas cannot be used to reduce the surgical time during transplantation predictable procedures.

Determining the Accuracy of the Mandibular Canal Region in 3D Biomodels Fabricated from CBCT Scanned Data: A Cadaveric Study

OBJECTIVE

To validate the accuracy of the mandibular canal region in 3D biomodel produced by using data obtained from Cone-Beam Computed Tomography (CBCT) of cadaveric mandibles.

METHODS

Six hemi-mandible samples were scanned using the i-CAT CBCT system. The scanned data was transferred to the OsiriX software for measurement protocol and subsequently into Mimics software to fabricate customized cutting jigs and 3D biomodels based on rapid prototyping technology. The hemi-mandibles were segmented into 5 dentoalveolar blocks using the customized jigs. Digital calliper was used to measure six distances surrounding the mandibular canal on each section. The same distances were measured on the corresponding cross-sectional OsiriX images and the 3D biomodels of each dentoalveolar block.

RESULTS

Statistically no significant difference was found when measurements from OsiriX images and 3D biomodels were compared to the "gold standard" -direct digital calliper measurement of the cadaveric dentoalveolar blocks. Moreover, the mean value difference of the various measurements between the different study components was also minimal.

CONCLUSION

Various distances surrounding the mandibular canal from 3D biomodels produced from the CBCT scanned data was similar to that of direct digital calliper measurements of the cadaveric specimens.

Emergence of Three-Dimensional Printing Technology and Its Utility in Spine Surgery

In the last decade, spine surgery has advanced tremendously. Tissue engineering and three-dimensional (3D) printing/additive manufacturing have provided promising new research avenues in the fields of medicine and orthopedics in recent literature, and their emergent role in spine surgery is encouraging. We reviewed recent articles that highlighted the role of 3D printing in medicine, orthopedics, and spine surgery and summarized the utility of 3D printing. 3D printing has shown promising results in various aspects of spine surgery and can be a useful tool for spine surgeons. The growing research on tissue bioengineering and its application in conjunction with additive manufacturing has revealed great potential for tissue bioengineering in the treatment of spinal ailments.

Three-Dimensional Printing Role in Neurologic Disease

Three-dimensional printing has evolved dramatically in recent years and is now available for clinical use. Technical operations of 2 of the most common rapid prototyping processes (stereolithography and fused deposition modeling) and the steps involved in the creation of a prototype are discussed. Current applications in human neurosurgery including presurgical planning and educational opportunities are reviewed before focusing on the current applications in veterinary neurology.

"Black Bone" MRI: a novel imaging technique for 3D printing

OBJECTIVES

Three-dimensionally printed anatomical models are rapidly becoming an integral part of pre-operative planning of complex surgical cases. We have previously reported the "Black Bone" MRI technique as a non-ionizing alternative to CT. Segmentation of bone becomes possible by minimizing soft tissue contrast to enhance the bone-soft tissue boundary. The objectives of this study were to ascertain the potential of utilizing this technique to produce three-dimensional (3D) printed models.

METHODS

"Black Bone" MRI acquired from adult volunteers and infants with craniosynostosis were 3D rendered and 3D printed. A custom phantom provided a surrogate marker of accuracy permitting comparison between direct measurements and 3D printed models created by segmenting both CT and "Black Bone" MRI data sets using two different software packages.

RESULTS

"Black Bone" MRI was successfully utilized to produce 3D models of the craniofacial skeleton in both adults and an infant. Measurements of the cube phantom and 3D printed models demonstrated submillimetre discrepancy.

CONCLUSIONS

In this novel preliminary study exploring the potential of 3D printing from "Black Bone" MRI data, the feasibility of producing anatomical 3D models has been demonstrated, thus offering a potential non-ionizing alterative to CT for the craniofacial skeleton.

Detection of root perforations using conventional and digital intraoral radiography, multidetector computed tomography and cone beam computed tomography

OBJECTIVES

This study aimed to compare the accuracy of conventional intraoral (CI) radiography, photostimulable phosphor (PSP) radiography, cone beam computed tomography (CBCT) and multidetector computed tomography (MDCT) for detection of strip and root perforations in endodontically treated teeth.

MATERIALS AND METHODS

Mesial and distal roots of 72 recently extracted molar were endodontically prepared. Perforations were created in 0.2, 0.3, or 0.4 mm diameter around the furcation of 48 roots (strip perforation) and at the external surface of 48 roots (root perforation); 48 roots were not perforated (control group). After root obturation, intraoral radiography, CBCT and MDCT were taken. Discontinuity in the root structure was interpreted as perforation. Two observers examined the images. Data were analyzed using Stata software and Chi-square test.

RESULTS

The sensitivity and specificity of CI, PSP, CBCT and MDCT in detection of strip perforations were 81.25% and 93.75%, 85.42% and 91.67%, 97.92% and 85.42%, and 72.92% and 87.50%, respectively. For diagnosis of root perforation, the sensitivity and specificity were 87.50% and 93.75%, 89.58% and 91.67%, 97.92% and 85.42%, and 81.25% and 87.50%, respectively. For detection of strip perforation, the difference between CBCT and all other methods including CI, PSP and MDCT was significant (p < 0.05). For detection of root perforation, only the difference between CBCT and MDCT was significant, and for all the other methods no statistically significant difference was observed.

CONCLUSIONS

If it is not possible to diagnose the root perforations by periapical radiographs, CBCT is the best radiographic technique while MDCT is not recommended.

Accuracy and precision of polyurethane dental arch models fabricated using a three-dimensional subtractive rapid prototyping method with an intraoral scanning technique

OBJECTIVE

This study aimed to evaluate the accuracy and precision of polyurethane (PUT) dental arch models fabricated using a three-dimensional (3D) subtractive rapid prototyping (RP) method with an intraoral scanning technique by comparing linear measurements obtained from PUT models and conventional plaster models.

METHODS

Ten plaster models were duplicated using a selected standard master model and conventional impression, and 10 PUT models were duplicated using the 3D subtractive RP technique with an oral scanner. Six linear measurements were evaluated in terms of x, y, and z-axes using a non-contact white light scanner. Accuracy was assessed using mean differences between two measurements, and precision was examined using four quantitative methods and the Bland-Altman graphical method. Repeatability was evaluated in terms of intra-examiner variability, and reproducibility was assessed in terms of inter-examiner and inter-method variability.

RESULTS

The mean difference between plaster models and PUT models ranged from 0.07 mm to 0.33 mm. Relative measurement errors ranged from 2.2% to 7.6% and intraclass correlation coefficients ranged from 0.93 to 0.96, when comparing plaster models and PUT models. The Bland-Altman plot showed good agreement.

CONCLUSIONS

The accuracy and precision of PUT dental models for evaluating the performance of oral scanner and subtractive RP technology was acceptable. Because of the recent improvements in block material and computerized numeric control milling machines, the subtractive RP method may be a good choice for dental arch models.

Minimizing the extra-oral time in autogeneous tooth transplantation: use of computer-aided rapid prototyping (CARP) as a duplicate model tooth

OBJECTIVES

The maintenance of the healthy periodontal ligament cells of the root surface of donor tooth and intimate surface contact between the donor tooth and the recipient bone are the key factors for successful tooth transplantation. In order to achieve these purposes, a duplicated donor tooth model can be utilized to reduce the extra-oral time using the computer-aided rapid prototyping (CARP) technique.

MATERIALS AND METHODS

Briefly, a three-dimensional digital imaging and communication in medicine (DICOM) image with the real dimensions of the donor tooth was obtained from a computed tomography (CT), and a life-sized resin tooth model was fabricated. Dimensional errors between real tooth, 3D CT image model and CARP model were calculated. And extra-oral time was recorded during the autotransplantation of the teeth.

RESULTS

The average extra-oral time was 7 min 25 sec with the range of immediate to 25 min in cases which extra-oral root canal treatments were not performed while it was 9 min 15 sec when extra-oral root canal treatments were performed. The average radiographic distance between the root surface and the alveolar bone was 1.17 mm and 1.35 mm at mesial cervix and apex; they were 0.98 mm and 1.26 mm at the distal cervix and apex. When the dimensional errors between real tooth, 3D CT image model and CARP model were measured in cadavers, the average of absolute error was 0.291 mm between real teeth and CARP model.

CONCLUSIONS

These data indicate that CARP may be of value in minimizing the extra-oral time and the gap between the donor tooth and the recipient alveolar bone in tooth transplantation.

Application of virtual surgical planning with computer assisted design and manufacturing technology to cranio-maxillofacial surgery

Computer aided design and manufacturing (CAD/CAM) technology today is the standard in manufacturing industry. The application of the CAD/CAM technology, together with the emerging 3D medical images based virtual surgical planning (VSP) technology, to craniomaxillofacial reconstruction has been gaining increasing attention to reconstructive surgeons. This article illustrates the components, system and clinical management of the VSP and CAD/CAM technology including: data acquisition, virtual surgical and treatment planning, individual implant design and fabrication, and outcome assessment. It focuses primarily on the technical aspects of the VSP and CAD/CAM system to improve the predictability of the planning and outcome.

Rapid prototyping in orthopaedic surgery: a user's guide

Rapid prototyping (RP) is applicable to orthopaedic problems involving three dimensions, particularly fractures, deformities, and reconstruction. In the past, RP has been hampered by cost and difficulties accessing the appropriate expertise. Here we outline the history of rapid prototyping and furthermore a process using open-source software to produce a high fidelity physical model from CT data. This greatly mitigates the expense associated with the technique, allowing surgeons to produce precise models for preoperative planning and procedure rehearsal. We describe the method with an illustrative case.

From implant planning to surgical execution: an integrated approach for surgery in oral implantology

BACKGROUND

Using oral implantology software and transferring the preoperative planning into a stereolithographic model, prosthodontists can produce the related surgical guide. This procedure has some disadvantages: bone-supported stent invasiveness, lack of references due to scattering and non-negligible stereolithography cost. An alternative solution is presented that provides an ideal surgical stent (not invasive, precise, and cheap) as a result. This work focuses on the third phase of a fully 3D approach to oral implant planning, that starts by CT scanning a patient who wears a markers-equipped radiological stent, continues exploiting built-on-purpose preoperative planning software, and finishes producing the ideal surgical template.

METHODS

A 5-axes bur-equipped robot has been designed able to reproduce the milling vectors planned by the software. Software-robot interfacing has been achieved properly matching the stent reference frame and the software and robot coordinate systems. Invasiveness has been avoided achieving the surgical stent from the mucosa-supported radiological mask wax-up. Scattering is ignored because of the surgical stent independency from the bone structure radiography. Production cost has been strongly reduced by avoiding the stereolithographic model. Finally, software-robot interfacing precision has been validated comparing digitally a multi-marker base and its planning transfer.

RESULTS

Average position and orientation errors (respectively 0.283 mm ± 0.073 mm and 1.798° ± 0.496°) were significantly better than those achieved using methods based on stereolithography (respectively, 1.45 mm ± 1.42 mm and 7.25° ± 2.67°, with a general best maximum translation discrepancy of about 1.1 mm).

CONCLUSIONS

This paper describes the last step of a fully 3D approach in which implant planning can be done in a 3D environment, and the correct position, orientation and depth of the planned implants are easily computed and transferred to the surgical phase.

Development of a simulation system in mandibular orthognathic surgery based on integrated three-dimensional data

Purpose

Surgical simulation should reflect the 3D movement of dentition and the resultant movement of the osteotomized segments, which can influence surgical outcome. The present study was aimed at developing a new simulation system that enables virtual osteotomy of a given surgical situation and evaluation of the bony interference between the osteotomized segments of the mandible.

Subjects and methods

The data of 3D computer tomography (CT) for maxillomandibular dental casts were integrated into the standard coordinates of a 3D cephalogram. To evaluate the accuracy of the system, measurement errors of the 3D CT virtual model from a dry skull were compared with the computer simulation system and a contact-type 3D digitizer. To examine the clinical accessibility, 15 mandibular prognathism patients with mild to severe asymmetry were evaluated with the simulation program.

Results

The average error of measurement in all directions was 1.31 mm. It was possible to simulate various osteotomy procedures by conversion of the 3D coordinates of the dental cast and CT data into the standard coordinate system of a 3D cephalogram. Using this simulation system, it was possible to prevent condylar torque or segment malpositioning by removing the bony interference visualized by a 3D virtual model.

Conclusion

A new system, which enables the precise visualization of osteotomized segments and calculation of bony interference, was proposed in the present study. This new system provides an acceptable precision of treatment planning of orthognathic surgery, especially for facial asymmetry.

Laser direct writing of micro- and nano-scale medical devices

Laser-based direct writing of materials has undergone significant development in recent years. The ability to modify a variety of materials at small length scales and using short production times provides laser direct writing with unique capabilities for fabrication of medical devices. In many laser-based rapid prototyping methods, microscale and submicroscale structuring of materials is controlled by computer-generated models. Various laser-based direct write methods, including selective laser sintering/melting, laser machining, matrix-assisted pulsed-laser evaporation direct write, stereolithography and two-photon polymerization, are described. Their use in fabrication of microstructured and nanostructured medical devices is discussed. Laser direct writing may be used for processing a wide variety of advanced medical devices, including patient-specific prostheses, drug delivery devices, biosensors, stents and tissue-engineering scaffolds.

Accuracy of MRI vs CT imaging with particular reference to patient specific templates for total knee replacement surgery

BACKGROUND

The present study compares the accuracy of MRI and CT imaging for the manufacture of patient-specific templates for total knee replacement surgery.

METHODS

A total of 10 ovine knees were imaged using MRI and CT scanners. Each set of images was reconstructed in 3D and then used to manufacture physical models of each bone, using rapid prototyping technology. After imaging the soft tissues were removed and specific measurements of the bony anatomy compared with measurements from the MRI and CT models.

RESULTS

Bone models generated from MRI scans were dimensionally less accurate than those generated from CT scans. Furthermore, the bone models generated from MRI scans were visibly inferior to those generated from the CT scans.

CONCLUSIONS

Current MRI scans do not offer a viable alternative to CT. Although adaptation of the template system to accommodate MRI imaging is possible, the changes required are neither practical nor desirable.

Surgical planning for resection of an ameloblastoma and reconstruction of the mandible using a selective laser sintering 3D biomodel

Ameloblastoma is a benign locally aggressive infiltrative odontogenic lesion. It is characterized by slow growth and painless swelling. The treatment for ameloblastoma varies from curettage to en bloc resection, and the reported recurrence rates after treatment are high; the safety margin of resection is important to avoid recurrence. Advances in technology brought about great benefits in dentistry; a new generation of computed tomography scanners and 3-dimensional images enhance the surgical planning and management of maxillofacial tumors. The development of new prototyping systems provides accurate 3D biomodels on which surgery can be simulated, especially in cases of ameloblastoma, in which the safety margin is important for treatment success. A case of mandibular follicular ameloblastoma is reported where a 3D biomodel was used before and during surgery.

[Rapid prototyping in planning reconstructive surgery of the head and neck. Review and evaluation of indications in clinical use]

PURPOSE

The aim was to define the indications for use of rapid prototyping models based on data of patients treated with this technique.

PATIENTS AND METHODS

Since 1987 our department has been developing methods of rapid prototyping in surgery planning. During the study, first the statistical and reproducible anatomical precision of rapid prototyping models was determined on pig skull measurements depending on CT parameters and method of rapid prototyping.

RESULTS

Measurements on stereolithography models and on selective laser sintered models confirmed an accuracy of +/-0.88 mm or 2.7% (maximum deviation: -3.0 mm to +3.2 mm) independently from CT parameters or method of rapid prototyping, respectively. With the same precision of models multilayer helical CT with a higher rate is the preferable method of data acquisition compared to conventional helical CT. From 1990 to 2002 in atotal of 122 patients, 127 rapid prototyping models were manufactured: in 112 patients stereolithography models, in 2 patients an additional stereolithography model, in 2 patients an additional selective laser sinter model, in 1 patient an additional milled model, and in 10 patients just a selective laser sinter model.

CONCLUSION

Reconstructive surgery, distraction osteogenesis including midface distraction, and dental implantology are proven to be the major indications for rapid prototyping as confirmed in a review of the literature. Surgery planning on rapid prototyping models should only be used in individual cases due to radiation dose and high costs. Routine use of this technique only seems to be indicated in skull reconstruction and distraction osteogenesis.

Optimizing presurgical orthodontic planning by means of the transverse coordinate simulation system (TCSS)

INTRODUCTION

When planning bilateral sagittal split osteotomies according to Obwegeser and Dal Pont, inaccuracies in the presurgical prediction of the transverse osteotomy gaps may occur. This is due to limitations of plaster models when simulating surgery on an articulator.

AIM

This paper demonstrates the transverse coordinate simulation system which allows presurgical prediction of the transverse discrepancy between the tooth bearing and the proximal segment after displacement, thus minimizing uncertainty for the surgeon.

METHOD

Diagnostic landmarks (taken from lateral and frontal cephalograms) and clinical data describing mandibular dimensions are transferred to a two-dimensional coordinate diagram. A mandibular model is then constructed using the anterior arch form, the temporomandibular joint distance and the prospective incision pattern.

RESULT

Movements in the horizontal plane and displacement of the three segments (two condylar and one mandibular arch segment) can be simulated and measured.

CONCLUSION

Transverse coordinate simulation system effectively increases the accuracy of presurgical planning without additional CT data or three-dimensional jaw models. This technique may decrease the number of additional surgical manoeuvres resulting from unexpectedly wide transverse discrepancies at the osteotomy site, which often increase surgery time, necessitate additional bone grafting, and entail the risk of healing disturbances and of malrotation or dislocation of the condyle.

Analysis of errors in medical rapid prototyping models

Rapid prototyping (RP) is a relatively new technology that produces physical models by selectively solidifying UV-sensitive liquid resin using a laser beam. The technology has gained a great amount of attention, particularly in oral and maxillofacial surgery. An important issue in RP applications in this field is how to obtain RP models of the required accuracy. We investigated errors generated during the production of medical RP models, and identified the factors that caused dimensional errors in each production phase. The errors were mainly due to the volume-averaging effect, threshold value, and difficulty in the exact replication of landmark locations. We made 16 linear measurements on a dry skull, a replicated three-dimensional (3-D) visual (STL) model, and an RP model. The results showed that the absolute mean deviation between the original dry skull and the RP model over the 16 linear measurements was 0.62 +/- 0.35 mm (0.56 +/- 0.39%), which is smaller than values reported in previous studies. A major emphasis is placed on the dumb-bell effect. Classifying measurements as internal and external measurements, we observed that the effect of an inadequate threshold value differs with the type of measurement.

Groningen temporomandibular joint prosthesis. Development and first clinical application

Patients with a severely degenerated temporomandibular joint (TMJ) may benefit from an alloplastic TMJ replacement. The aim of the study was to develop a safe and properly functioning TMJ prosthesis. The design was based on imitation of anterior condylar translation by an inferiorly located centre of rotation, unrestricted mandibular movements by a double articulation, correct fit to the skull by a self-adjusting skull part consisting of two connected parts, and stable fixation by bone screws that are rigidly connected to the prosthesis parts. The prosthesis consists of a titanium skull part with ceramic inlay, a titanium mandibular part with a ceramic spherical head, and an intervening polyethylene disc. Titanium-alloy bone screws are used for fixation. All parts are available in a number of different shapes. In vitro laboratory and in vivo animal tests showed a low wear rate, the possibility of a close fit to the skull, a stable fixation, sufficient mechanical strength, appropriate choice of materials and proper functioning. Thereafter the step to first patient application was made. First patient application was carried out without adverse events. In conclusion, the presented TMJ prosthesis passed the pre-clinical tests and has progressed to clinical application. The fit to the skull, the expected lifetime of the device and the reliability of the implantation procedure require further evaluation in well-designed clinical trials.

Polyurethane real-size models used in planning complex spinal surgery

STUDY DESIGN

The application of polyurethane real-size models for planning and performing complex spinal surgery is described.

OBJECTIVE

To determine the feasibility of using polyurethane real-size models to plan osteotomies, resections, and designs of custom-made spinal implants in complex spinal surgery.

SUMMARY OF BACKGROUND DATA

In selected patients with complex spinal pathology, exact planning of the surgical procedure is not possible using current imaging methods. In these cases, real-size spinal models would be desirable to enhance pre- and perioperative planning by visual and tactile feedback, and to improve the production of custom-made spinal implants.

METHODS

A real-size spinal model of six patients was produced from hardened polyurethane foam on the basis of data from contiguous computer tomography slices. In two patients, the models were used to plan correction osteotomies and resections, with the assistance of image-guided surgery in one of the patients. In four patients, the models were used to plan tumor resections and to produce custom-made spinal implants.

RESULTS

In all the patients, the surgical procedure could be performed exactly according to the preplanned intervention. The polyurethane real-size models provided essential and additional information by direct visual and tactile feedback. They allowed in vitro testing of custom-made spinal implants with a perfect fit.

CONCLUSIONS

Real-size spinal models made from polyurethane foam can be used to provide excellent understanding of the complex spinal pathology in highly selected patients. These models allow complex spinal surgery with a more predictable outcome.

Changes in the dimensions of milled mandibular models after mandibular sagittal split osteotomies

Three-dimensional models created by milling machines and stereolithography from the three-dimensional computed tomograms (CTs) have become important in the diagnosis and preoperative planning of some craniomaxillofacial irregularities. In this study three-dimensional milled models were used to verify operative results after patients had undergone bilateral sagittal split osteotomies of the mandible. Fifteen models of patients with mandibular prognathism and 31 with retrognathism were created preoperatively and 6 weeks postoperatively to examine the changes of the osseous anatomical structures in three dimensions. There was a forward shift in the mandibular corpus of between 1 and 3 mm in patients with retrognathism and a backward shift to the same extent in the group with prognathism. In the latter group the intercondylar distance increased by a mean of 2.0 (SD 1.2) mm and by 2.9 (SD 1.0) mm in patients who had had a mandibular advancement operation. Furthermore the distance between the coronoid processes increased by 6.6 (SD 1.8) mm in the retrognathic group and decreased by 1.6 (SD 1.4) mm in the prognathic group. The Bonewill angle increased by 1.7 (SD 0.4) degrees in the prognathic group and decreased by 1.6 (SD 0.3) degrees in the retrognathic group. Both increase and decrease of the homolateral gonion angle were accompanied by a contrarotary movement of the contralateral gonion angle. We conclude that remarkable changes in condylar position and anatomy take place after bilateral ramus sagittal split osteotomy.

Integration of three-dimensional cephalometry and 3D-skull models in combined orthodontic/surgical treatment planning

In 15 adult patients with severe dentomaxillofacial deformities we integrated 3-dimensional cephalometry and 3D-model surgery with individually milled or stereolithographically built skull models in our combined orthodontic/surgical diagnosis and treatment planning. After the generation of contiguous axial CT-scans the CT data sets were transferred to a commonly used computing system (IBM-PC) to reconstruct 3D-images from any point of view. After the definition of measurement points, distances and angles at the skin and bone surface a 3-dimensional cephalometric analysis could be performed directly in the 3D-objects on the monitor. This allows a quantitative assessment of skeletal asymmetries. The transfer of CT data to life-size 3D-skull models and replacement of imprecise dental arches by dental casts different orthodontic and surgical treatment concepts could be evaluated. The 3D-model surgery represents a new quality of treatment prediction in the individual dentomaxillofacial morphology. The orthodontic set-up and 3D-model surgery permit a verification of the feasibility of the most suitable mobilization and placement of bone segments. The clinical treatment sequences indicated that the integration of 3-dimensional cephalometry and 3D-model surgery in patients with severe asymmetric dentomaxillofacial deformities allowed a higher precision of diagnosis and treatment planning.

Individual model fabrication in maxillofacial radiology

Oral and maxillofacial surgery has long needed a methodology for accurate definition of the third dimension. The introduction of computer-aided tomography in the 1970s provided surgeons with multiple 2-D maps which they themselves had to conceptualize into a third dimension. The later advent of computerized summation of these data made it possible to display a perspective view of the third dimension on a TV monitor. CT, and more recently MRI, with the further analytical refinement afforded by software processing (interactive data presentation, contour detection and summation, hypothetical 3-D construction and interactive visualization) now provide the basic information that is needed for the fabrication of an individual model. Such models can be milled from a variety of materials. More recently, laser-hardened acrylic resins have been shown to be a useful alternative. Both systems are described and their advantages and disadvantages in the planning and performance of oral and maxillofacial surgical procedures are discussed.

Accuracy of stereolithographic models of human anatomy

A study was undertaken to determine the dimensional accuracy of anatomical replicas derived from X-ray 3D computed tomography (CT) images and produced using the rapid prototyping technique of stereolithography (SLA). A dry bone skull and geometric phantom were scanned, and replicas were produced. Distance measurements were obtained to compare the original objects and the resulting replicas. Repeated measurements between anatomical landmarks were used for comparison of the original skull and replica. Results for the geometric phantom demonstrate a mean difference of +0.47 mm, representing an accuracy of 97.7-99.12%. Measurements of the skull produced a range of absolute differences (maximum +4.62 mm, minimum +0.1 mm, mean +0.85 mm). These results support the use of SLA models of human anatomical structures in such areas as pre-operative planning of complex surgical procedures. For applications where higher accuracy is required, improvements can be expected by utilizing smaller pixel resolution in the CT images. Stereolithographic models can now be confidently employed as accurate, three-dimensional replicas of complex, anatomical structures.