ORIGINAL ARTICLE
Salt as a New Colored Solid Model for Simulation Surgery Takayuki Okumoto, MD, Yoshiaki Sakamoto, MD,y Suguru Kondo, MD, Hisao Ogata, MD,y Kazuo Kishi, MD,y and Yohko Yoshimura, MD 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. Key Words: Solid model, simulation surgery, salt, craniomaxillofacial surgery, distraction osteogenesis, hemifacial microsomia (J Craniofac Surg 2015;26: 680–681)
T
he development of computer-generated 3-dimensional computed tomography imaging (3D CT) was a milestone achievement in the field of preoperative diagnosis and treatment planning.1,2 The availability of 3D-CT images also created a new field of ‘‘simulated surgery,’’ which allowed surgeons to select the optimal surgical technique.3 However, these images force surgeons to superimpose abstract spatial information on their intraoperative field of view, which requires a high level of expertise. Also, these images cannot simulate the sensation of touching and manipulating a tangible 3-dimensional object. Thus, 3D solid models were developed using CT data to facilitate preoperative surgical planning for various procedures, including craniomaxillofacial surgery, neurosurgery, and traumatology.4–8 Furthermore, 3D solid models are also used to provide training for inexperienced surgeons. From the Department of Plastic and Reconstructive Surgery, Fujita Health University School of Medicine, Aichi; and yDepartment of Plastic and Reconstructive Surgery, Keio University School of Medicine, Tokyo, Japan. Received November 14, 2014. Accepted for publication December 23, 2014. Address correspondence and reprint requests to Yoshiaki Sakamoto, MD, Department of Plastic and Reconstructive Surgery, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ward, Tokyo 1608582, Japan; E-mail: [email protected] The authors report no conflicts of interest. Copyright # 2015 by Mutaz B. Habal, MD ISSN: 1049-2275 DOI: 10.1097/SCS.0000000000001539
680
Currently, 3D printers use plaster of Paris, styrofoam, or acrylic resin (for stereolithography) as template materials.4–8 The public availability of 3D inkjet printers and their template materials9 has led to an increased familiarity with this equipment. However, 3D solid models remain expensive and fragile, whereas the surgical sensations provided by these models (eg, during osteotomy or handling) do not accurately reflect those experienced during operating on human bones. Therefore, we have developed a new 3D solid model, constructed using colored salt, which provides surgical sensations similar to those experienced while operating on human bone.
MATERIAL AND METHODS Data Collection for the Solid Model To produce an accurate solid model, we obtained CT data consisting of 0.5-mm-slice images. To facilitate accurate reproduction of the mandible element, separate from the maxilla element, CT scanning was performed with the patient’s mouth slightly open. Volume rendering was performed using the CT value for skeletal bone, and stereolithography (STL) data with skeletal bone information were generated using DICOM manager (Mimics; Materialise., Leuven, Belgium). For simulation of maxillofacial surgery, such as Le Fort I and sagittal spit ramus osteotomy (SSRO), we wished to highlight the teeth and mandibular canal, in contrast to the skeletal bone in the region of interest. By selecting and saving STL data for these elements, a tint color was applied to the each element when the solid model was constructed.
Construction of the Solid Model For the raw material, we used salt granules with a particle size of approximately 30 mm, consisting of sodium chloride (80%), hygroscopic material (15%), and bonding agent (5%). These granules have an extremely smooth particle exterior (Fig. 1), in contrast to the basic cubic crystal structure of standard salt granules. The smooth salt granules were applied and laminated using a 3D inkjet printer (Fig. 2), and only the colored elements were stiffened. During postprocessing, the non-stiffened salt granules were removed, and the model was completed using an atomized impregnant substance to promote solidification (Fig. 3).
Evaluation of the Model Three pig ribs were used as controls and were scanned using a 320-detector row CT scanner (Aquilion ONE; Toshiba Medical Systems, Otawara-shi, Japan). From the CT data, STL data were
FIGURE 1. Electron microscope image of smooth salt granules. Note the extremely smooth particles with a diameter of approximately 30 mm.
The Journal of Craniofacial Surgery
Volume 26, Number 3, May 2015
Copyright © 2015 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
The Journal of Craniofacial Surgery
Volume 26, Number 3, May 2015
FIGURE 2. Creating the solid model using a 3D inkjet color printer.
FIGURE 3. Frontal and lateral views of the finished product.
created, and both salt and stereolithographic resin models of each rib were constructed. Each model was evaluated using a 3-point bending test, where the specimen was placed on 2 supports (22 mm apart), with an actuator applying a constant force at 10 mm/s precisely in the center of the 2 supports. The loads and deflections for each specimen were recorded.
A Solid Model Made of Salt
FIGURE 5. Simulated SSRO surgery. Note the clearly distinguished inferior alveolar nerve.
surgery. With advances in computer technology, we can now stereoscopically visualize the operative area, although computeraided simulation surgery requires expensive software and does not provide a tactile experience. Although expert surgeons may find this technique useful, inexperienced surgeons may not benefit from stereoscopic images alone and should physically practice the basic surgical techniques using physical models. In this regard, the solid salt model is particularly valuable as it allows the learner to visualize the relationship between their osteotomy and the surgical outcome, using the color-coding of the nerves, vessels, and teeth. In conclusion, the colored solid salt model is similar to human skeletal bone and provides an economically efficient model for simulated surgery and training of inexperienced residents.
ACKNOWLEDGMENTS The authors would like to thank Sony EMCS and Tomita Pharmaceutical for their support.
RESULTS The load-deflection curves for both the pig ribs and salt models were similar. Both exhibited properties of a flexible material; with increasing load, the flexible curve was extended prior to breakage. In contrast, the load-deflection curve for the resin model exhibited a sharp increase, indicative of a hard and brittle material (Fig. 4). We were able to accomplish the simulation in case of distraction that was difficult in the conventional models without any cracks by entering the pin of device. Using our coloring method for preoperative simulation of Le Fort I and SSRO, the tooth roots and inferior alveolar nerve are clearly visible (Fig. 5).
DISCUSSION Previous reports have described the usefulness of simulation surgery using solid models, particularly for mandibular distraction in hemifacial microsomia.10,11 However, conventional solid models typically cost more than $2000 to construct,11,12 and the hardness and viscosity of the model do not accurately replicate human skeletal bone. As a result, traditional solid models often break during drilling, plating, or fixation of the distraction devices.12 In contrast, the cost of a salt model is approximately one-fifteenth of a traditional model, and we can control hardness and viscosity of the model to bring it close to the living bone by changing the impregnant. Simulation surgeries are currently divided into 2 categories: computer-aided simulation surgery and solid model simulation
FIGURE 4. The load-deflection curve for each material: (left) pig rib, (center) salt model, (right) resin model. The pig rib and salt model provided similar flexibility curves, in contrast to the sharp increase seen for the resin model.
#
2015 Mutaz B. Habal, MD
REFERENCES 1. Lambrecht JT, Hammer B, Jacob AL, et al. Individual model fabrication in maxillofacial radiology. Dentomaxillofac Radiol 1995;24:147–154 2. Watzinger F, Wanschitz F, Wagner A, et al. Computer-aided navigation in secondary reconstruction of post-traumatic deformities of the zygoma. J Craniomaxillofac Surg 1997;25:198–202 3. Fujino T, Nakajima H, Kaneko T, et al. Concept of simulation surgery. Keio J Med 1993;42:104–114 4. Nakajima T, Yoshimura Y, Nakanishi Y, et al. Integrated life-sized solid model of bone and soft tissue: application for cleft lip and palate infants. Plast Reconstr Surg 1995;96:1020–1025 5. Gateno J1, Allen ME, Teichgraeber JF, et al. An in vitro study of the accuracy of a new protocol for planning distraction osteogenesis of the mandible. J Oral Maxillofac Surg 2000;58:985–990 6. Brown GA, Milner B, Firoozbakhsh K. Application of computergenerated stereolithography and interpositioning template in acetabular fractures: a report of eight cases. J Orthop Trauma 2002;16:347–352 7. Chang PS, Parker TH, Patrick CW Jr et al. The accuracy of stereolithography in planning craniofacial bone replacement. J Craniofac Surg 2003;14:164–170 8. Mutoh T, Ishikawa T, Ono H, et al. A new polyvinyl alcohol hydrogel vascular model (KEZLEX) for microvascular anastomosis training. Surg Neurol Int 2010; 23;1:74 9. Waran V, Narayanan V, Karuppiah R, et al. Utility of multimaterial 3D printers in creating models with pathological entities to enhance the training experience of neurosurgeons. J Neurosurg 2014;120:489– 492 10. Ogata H, Sakamoto Y, Sakamoto T, et al. Maxillomandibular tandem osteotomy with distraction osteogenesis for hemifacial microsomia. J Craniofac Surg 2012;23:1362–1363 11. Sakamoto Y, Ogata H, Nakajima H, et al. Role of solid model simulation surgery for hemifacial microsomia. Cleft Palate Craniofac J 2013;50:623–626 12. Kobayashi M, Fujino T, Nakajima H, et al. Significance of solid modelling of the skull using laser-curable resin in simulation surgery. Eur J Plast Surg 1993;16:47–50
681
Copyright © 2015 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
Salt as a New Colored Solid Model for Simulation Surgery Takayuki Okumoto, MD, Yoshiaki Sakamoto, MD,y Suguru Kondo, MD, Hisao Ogata, MD,y Kazuo Kishi, MD,y and Yohko Yoshimura, MD 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. Key Words: Solid model, simulation surgery, salt, craniomaxillofacial surgery, distraction osteogenesis, hemifacial microsomia (J Craniofac Surg 2015;26: 680–681)
T
he development of computer-generated 3-dimensional computed tomography imaging (3D CT) was a milestone achievement in the field of preoperative diagnosis and treatment planning.1,2 The availability of 3D-CT images also created a new field of ‘‘simulated surgery,’’ which allowed surgeons to select the optimal surgical technique.3 However, these images force surgeons to superimpose abstract spatial information on their intraoperative field of view, which requires a high level of expertise. Also, these images cannot simulate the sensation of touching and manipulating a tangible 3-dimensional object. Thus, 3D solid models were developed using CT data to facilitate preoperative surgical planning for various procedures, including craniomaxillofacial surgery, neurosurgery, and traumatology.4–8 Furthermore, 3D solid models are also used to provide training for inexperienced surgeons. From the Department of Plastic and Reconstructive Surgery, Fujita Health University School of Medicine, Aichi; and yDepartment of Plastic and Reconstructive Surgery, Keio University School of Medicine, Tokyo, Japan. Received November 14, 2014. Accepted for publication December 23, 2014. Address correspondence and reprint requests to Yoshiaki Sakamoto, MD, Department of Plastic and Reconstructive Surgery, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ward, Tokyo 1608582, Japan; E-mail: [email protected] The authors report no conflicts of interest. Copyright # 2015 by Mutaz B. Habal, MD ISSN: 1049-2275 DOI: 10.1097/SCS.0000000000001539
680
Currently, 3D printers use plaster of Paris, styrofoam, or acrylic resin (for stereolithography) as template materials.4–8 The public availability of 3D inkjet printers and their template materials9 has led to an increased familiarity with this equipment. However, 3D solid models remain expensive and fragile, whereas the surgical sensations provided by these models (eg, during osteotomy or handling) do not accurately reflect those experienced during operating on human bones. Therefore, we have developed a new 3D solid model, constructed using colored salt, which provides surgical sensations similar to those experienced while operating on human bone.
MATERIAL AND METHODS Data Collection for the Solid Model To produce an accurate solid model, we obtained CT data consisting of 0.5-mm-slice images. To facilitate accurate reproduction of the mandible element, separate from the maxilla element, CT scanning was performed with the patient’s mouth slightly open. Volume rendering was performed using the CT value for skeletal bone, and stereolithography (STL) data with skeletal bone information were generated using DICOM manager (Mimics; Materialise., Leuven, Belgium). For simulation of maxillofacial surgery, such as Le Fort I and sagittal spit ramus osteotomy (SSRO), we wished to highlight the teeth and mandibular canal, in contrast to the skeletal bone in the region of interest. By selecting and saving STL data for these elements, a tint color was applied to the each element when the solid model was constructed.
Construction of the Solid Model For the raw material, we used salt granules with a particle size of approximately 30 mm, consisting of sodium chloride (80%), hygroscopic material (15%), and bonding agent (5%). These granules have an extremely smooth particle exterior (Fig. 1), in contrast to the basic cubic crystal structure of standard salt granules. The smooth salt granules were applied and laminated using a 3D inkjet printer (Fig. 2), and only the colored elements were stiffened. During postprocessing, the non-stiffened salt granules were removed, and the model was completed using an atomized impregnant substance to promote solidification (Fig. 3).
Evaluation of the Model Three pig ribs were used as controls and were scanned using a 320-detector row CT scanner (Aquilion ONE; Toshiba Medical Systems, Otawara-shi, Japan). From the CT data, STL data were
FIGURE 1. Electron microscope image of smooth salt granules. Note the extremely smooth particles with a diameter of approximately 30 mm.
The Journal of Craniofacial Surgery
Volume 26, Number 3, May 2015
Copyright © 2015 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
The Journal of Craniofacial Surgery
Volume 26, Number 3, May 2015
FIGURE 2. Creating the solid model using a 3D inkjet color printer.
FIGURE 3. Frontal and lateral views of the finished product.
created, and both salt and stereolithographic resin models of each rib were constructed. Each model was evaluated using a 3-point bending test, where the specimen was placed on 2 supports (22 mm apart), with an actuator applying a constant force at 10 mm/s precisely in the center of the 2 supports. The loads and deflections for each specimen were recorded.
A Solid Model Made of Salt
FIGURE 5. Simulated SSRO surgery. Note the clearly distinguished inferior alveolar nerve.
surgery. With advances in computer technology, we can now stereoscopically visualize the operative area, although computeraided simulation surgery requires expensive software and does not provide a tactile experience. Although expert surgeons may find this technique useful, inexperienced surgeons may not benefit from stereoscopic images alone and should physically practice the basic surgical techniques using physical models. In this regard, the solid salt model is particularly valuable as it allows the learner to visualize the relationship between their osteotomy and the surgical outcome, using the color-coding of the nerves, vessels, and teeth. In conclusion, the colored solid salt model is similar to human skeletal bone and provides an economically efficient model for simulated surgery and training of inexperienced residents.
ACKNOWLEDGMENTS The authors would like to thank Sony EMCS and Tomita Pharmaceutical for their support.
RESULTS The load-deflection curves for both the pig ribs and salt models were similar. Both exhibited properties of a flexible material; with increasing load, the flexible curve was extended prior to breakage. In contrast, the load-deflection curve for the resin model exhibited a sharp increase, indicative of a hard and brittle material (Fig. 4). We were able to accomplish the simulation in case of distraction that was difficult in the conventional models without any cracks by entering the pin of device. Using our coloring method for preoperative simulation of Le Fort I and SSRO, the tooth roots and inferior alveolar nerve are clearly visible (Fig. 5).
DISCUSSION Previous reports have described the usefulness of simulation surgery using solid models, particularly for mandibular distraction in hemifacial microsomia.10,11 However, conventional solid models typically cost more than $2000 to construct,11,12 and the hardness and viscosity of the model do not accurately replicate human skeletal bone. As a result, traditional solid models often break during drilling, plating, or fixation of the distraction devices.12 In contrast, the cost of a salt model is approximately one-fifteenth of a traditional model, and we can control hardness and viscosity of the model to bring it close to the living bone by changing the impregnant. Simulation surgeries are currently divided into 2 categories: computer-aided simulation surgery and solid model simulation
FIGURE 4. The load-deflection curve for each material: (left) pig rib, (center) salt model, (right) resin model. The pig rib and salt model provided similar flexibility curves, in contrast to the sharp increase seen for the resin model.
#
2015 Mutaz B. Habal, MD
REFERENCES 1. Lambrecht JT, Hammer B, Jacob AL, et al. Individual model fabrication in maxillofacial radiology. Dentomaxillofac Radiol 1995;24:147–154 2. Watzinger F, Wanschitz F, Wagner A, et al. Computer-aided navigation in secondary reconstruction of post-traumatic deformities of the zygoma. J Craniomaxillofac Surg 1997;25:198–202 3. Fujino T, Nakajima H, Kaneko T, et al. Concept of simulation surgery. Keio J Med 1993;42:104–114 4. Nakajima T, Yoshimura Y, Nakanishi Y, et al. Integrated life-sized solid model of bone and soft tissue: application for cleft lip and palate infants. Plast Reconstr Surg 1995;96:1020–1025 5. Gateno J1, Allen ME, Teichgraeber JF, et al. An in vitro study of the accuracy of a new protocol for planning distraction osteogenesis of the mandible. J Oral Maxillofac Surg 2000;58:985–990 6. Brown GA, Milner B, Firoozbakhsh K. Application of computergenerated stereolithography and interpositioning template in acetabular fractures: a report of eight cases. J Orthop Trauma 2002;16:347–352 7. Chang PS, Parker TH, Patrick CW Jr et al. The accuracy of stereolithography in planning craniofacial bone replacement. J Craniofac Surg 2003;14:164–170 8. Mutoh T, Ishikawa T, Ono H, et al. A new polyvinyl alcohol hydrogel vascular model (KEZLEX) for microvascular anastomosis training. Surg Neurol Int 2010; 23;1:74 9. Waran V, Narayanan V, Karuppiah R, et al. Utility of multimaterial 3D printers in creating models with pathological entities to enhance the training experience of neurosurgeons. J Neurosurg 2014;120:489– 492 10. Ogata H, Sakamoto Y, Sakamoto T, et al. Maxillomandibular tandem osteotomy with distraction osteogenesis for hemifacial microsomia. J Craniofac Surg 2012;23:1362–1363 11. Sakamoto Y, Ogata H, Nakajima H, et al. Role of solid model simulation surgery for hemifacial microsomia. Cleft Palate Craniofac J 2013;50:623–626 12. Kobayashi M, Fujino T, Nakajima H, et al. Significance of solid modelling of the skull using laser-curable resin in simulation surgery. Eur J Plast Surg 1993;16:47–50
681
Copyright © 2015 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
