decompressive craniectomy is a critical treatment modality for the control of highly increased intracranial pressure10,18,21 ) .
nonetheless , it can lead to large cranial defect that requires subsequent cranioplasty for neural tissue protection , successful cosmetic outcome and improvement of cerebral function4,20 ) .
an autogenous bone flap obtained at the time of the craniectomy can be used in subsequent cranioplasty because it is viable and fits well into the cranial defect . however , in many clinical situations , autogenous bone is unavailable because of bone resorption preventing good cosmetic outcome and cerebral protection14 ) . recently , alloplastic materials including polymethyl - methacrylate ( pmma ) , hydroxyapatite , and metallic mesh have been suggested as intra - operative malleable substitutes .
these materials , however , require complex processes , such as intraoperative mixing for the preparation , adaptation , and contouring of the implant for the defect , which result in increased surgical time .
in addition , the molding process may lead to poor cosmetic outcomes in patients with large or complicated defects .
furthermore , the contouring of implant by direct contact to the dura can develop exothermic reactions or the release of toxic monomers intraoperatively .
it results in focal tissue damage , which implicate local and systemic reactions9,19 ) . in order to overcome the shortcomings of intraoperative molding ,
many techniques have been introduced for the prefabrication of customized cranioplastic implants using medical imaing and three - dimensional ( 3d ) biomodeling1,3,5,6,8,11,12,17,19,22 ) .
the prefabrication of alloplastic implants that are tailored to individual patients ' defects not only improves aesthetic outcomes , but also decreases surgical time , blood loss , and the risk of infection16 ) . in this study ,
the authors demonstrate a simple and cost - effective cranioplasty method using individualized mold prefabrication with a 3d printer and pmma casting .
between november 2009 and april 2011 , 16 patients with large skull defects ( > 100 cm ) underwent cranioplasty with individualized prefabricated molds created by the 3d model and pmma casting method at our institution .
the median patient age at the time of cranioplasty was 52.5 years ( range , 16 to 71 years ) .
the cranial defects were caused by head trauma in eight cases ( 50% ) , cerebral infarction in three cases ( 19% ) , and intracerebral hemorrhage in five cases ( 31% ) .
most of the cranial defects were located in the fronto - temporo - parietal region ( 88% ) ( table 1 ) . for unilateral cranial defect ,
digital imaging and communications in medicine ( dicom ) data were acquired with the spiral volumetric technique during preoperative axial 1-mm spiral computed tomography ( ct ) scans ( philips brilliance 64 slice ct , philips healthcare , best , the netherlands ) .
subsequently , the dicom data were processed and converted to 3d images with mimics 13.1 software ( interactive medical image control system ; materialise inc . ,
the image of the implant was generated by a digital subtraction mirror - imaging process whereby the normal side of the cranium was used as a model ( fig .
preoperative spiral ct scan data ( 5- to 10-mm slice thickness ) were obtained before the decompressive craniectomy ( fig .
the stair - like surface of the 3d - implant model was processed with a smoothing technique by the mimics 13.1 software ( materialise inc . )
the pre- and postcraniectomy ct images were merged , and the 3d implant images were then cropped ( fig .
the 3d modeling of the mold was processed with magics 15 software ( rapid prototyping software ; materialise inc . )
prefabrication of the mold was performed by powder depositional modeling with the use of a spectrum z 510 3d printer ( z corporation , burlington , ma , usa ) ( fig .
the prefabrication process took an average of 6 hours , and the mold was then sterilized by autoclave .
after aseptic draping , a skin incision was made along a scar from a previous operation .
the pmma implant was constructed using the prefabricated mold during the dissection procedure . due to the unknown biocompatibility of the prefabricated materials ,
the molds were wrapped with two layers of sterilized plastic . in order to prevent adhesion between the implant and the plastic ,
the volume of pmma was determined from the volume of the implant , which had been calculated preoperatively with the mimics 13.1 software ( materialise inc . ) .
the pmma resin was prepared by mixing polymer powder with a liquid monomer . in the liquid state
, the pmma resin was poured into the prefabricated molds and the molds were compressed to each other .
the implant required minor trimming around the margins in order to achieve an exact fit into the defective region .
the pmma implant was fixed to the defective region with titanium plates and self - tapping screws of 4 mm in length .
plane x - rays of the skull and a ct scan were conducted immediately after surgery .
between november 2009 and april 2011 , 16 patients with large skull defects ( > 100 cm ) underwent cranioplasty with individualized prefabricated molds created by the 3d model and pmma casting method at our institution .
the median patient age at the time of cranioplasty was 52.5 years ( range , 16 to 71 years ) .
the cranial defects were caused by head trauma in eight cases ( 50% ) , cerebral infarction in three cases ( 19% ) , and intracerebral hemorrhage in five cases ( 31% ) .
most of the cranial defects were located in the fronto - temporo - parietal region ( 88% ) ( table 1 ) .
for unilateral cranial defect , digital imaging and communications in medicine ( dicom ) data were acquired with the spiral volumetric technique during preoperative axial 1-mm spiral computed tomography ( ct ) scans ( philips brilliance 64 slice ct , philips healthcare , best , the netherlands ) .
subsequently , the dicom data were processed and converted to 3d images with mimics 13.1 software ( interactive medical image control system ; materialise inc . ,
the image of the implant was generated by a digital subtraction mirror - imaging process whereby the normal side of the cranium was used as a model ( fig .
preoperative spiral ct scan data ( 5- to 10-mm slice thickness ) were obtained before the decompressive craniectomy ( fig .
the stair - like surface of the 3d - implant model was processed with a smoothing technique by the mimics 13.1 software ( materialise inc . )
the pre- and postcraniectomy ct images were merged , and the 3d implant images were then cropped ( fig .
the 3d modeling of the mold was processed with magics 15 software ( rapid prototyping software ; materialise inc . ) following the imaging of the required implant ( fig .
prefabrication of the mold was performed by powder depositional modeling with the use of a spectrum z 510 3d printer ( z corporation , burlington , ma , usa ) ( fig .
the prefabrication process took an average of 6 hours , and the mold was then sterilized by autoclave .
after aseptic draping , a skin incision was made along a scar from a previous operation .
the pmma implant was constructed using the prefabricated mold during the dissection procedure . due to the unknown biocompatibility of the prefabricated materials ,
the molds were wrapped with two layers of sterilized plastic . in order to prevent adhesion between the implant and the plastic ,
the volume of pmma was determined from the volume of the implant , which had been calculated preoperatively with the mimics 13.1 software ( materialise inc . ) .
the pmma resin was prepared by mixing polymer powder with a liquid monomer . in the liquid state ,
the pmma resin was poured into the prefabricated molds and the molds were compressed to each other .
the implant required minor trimming around the margins in order to achieve an exact fit into the defective region .
the pmma implant was fixed to the defective region with titanium plates and self - tapping screws of 4 mm in length .
plane x - rays of the skull and a ct scan were conducted immediately after surgery .
the median operation time was 184.3626.07 minutes ( range , 150 - 380 minutes ) .
the median follow - up period was 23 months ( range , 14 - 28 months ) .
post - operative ct scans showed excellent restoration of the bony symmetry in all cases ( fig .
one patient who had an open wound defect developed a postoperative infection , which resulted in implant removal at 6 weeks .
a representative case of a unilateral cranial defect and a case of bilateral cranial defects are described in this paper .
a 71-year - old woman underwent cranioplasty with individualized pmma casting for the reconstruction of a large right fronto - temporo - parietal cranial defect .
she had undergone a decompressive craniectomy for severe brain swelling that had been caused by a middle and posterior cerebral artery infarction 6 months before .
using the mirror - imaging process , an image of the cranial defect was generated , and the mold was prefabricated with the 3d printer .
intraoperatively , the pmma implant was created with the mold and then fit into the defect .
a 49-year - old man underwent a bilateral decompressive craniectomy due to traumatic brain swelling .
a 71-year - old woman underwent cranioplasty with individualized pmma casting for the reconstruction of a large right fronto - temporo - parietal cranial defect .
she had undergone a decompressive craniectomy for severe brain swelling that had been caused by a middle and posterior cerebral artery infarction 6 months before .
using the mirror - imaging process , an image of the cranial defect was generated , and the mold was prefabricated with the 3d printer .
intraoperatively , the pmma implant was created with the mold and then fit into the defect .
a 49-year - old man underwent a bilateral decompressive craniectomy due to traumatic brain swelling .
an intra - operative molding process is required in traditional cranioplasties using allografts , although it causes poor cosmetic result , increased operation time and tissue injury . in order to overcome these shortcomings ,
however , there are some drawbacks for customized models including manufacturing time , biocompatibility , and cost . in this study
, we developed a computer - generated model , which can be applied a prefabricated mold to the cranial defect . by using the pmma casting method
our model may have beneficial effects on the clinical application for the reconstruction of cranial defects .
craniofacial biomodels can be fabricated by conventional milling techniques , laser stereolithography , and 3d printing technology5,8,11,16,19,23 ) . in 1990 , the construction of biomodels using 4-axis computer numerical control milling techniques was first reported .
these biomodels were then used as templates for implants or as a master tool for making molds for the fabrication of implant15 ) . however , a major disadvantage of the conventional milling technique was that it was not able to accurately represent the complex anatomy or the inner structure of the craniofacial bones5 ) . in the late 1990s ,
modified cranioplasty techniques were introduced to the reconstruction of complex or extensive cranial defects , consisting of 3d stereolithography and template modeling5,7 ) .
laser stereolithography is accurate to less than 1 mm , which is an improvement compared to conventional milling techniques .
in addition , this technique demonstrated excellent results for the replication of complex geometric shapes5 ) .
in customized cranioplasty using stereolithography , the defect - bearing biomodel is utilized to mold a master implant following the creation of an impression mold of the cavity .
subsequently , a carbon - fiber reinforced polymer or acrylic implant is shaped by the mold5,19,23 ) .
however , the master implant must be constructed by hand into the defect in this model .
in addition , the biomodel manufacturing time for stereolithography is about twice as long as that of 3d printing technology .
recently , the development of 3d printing technology has introduced 3d medical models to generate an exact copy of various patients ' skulls and facial bone structures8,16,17 ) .
it allows prefabricated copy models to simulate preoperative or intraoperative procedures3 ) . in the present study , we applied 3d printing technology for the prefabrication of a mold which can create an implant for the reconstruction of the cranial defect .
the image of the implant was generated by a digital subtraction mirror - imaging process whereby the normal side of the cranium was used as a model .
we developed a 3d model by using high - resolution ( 1-mm cuts ) spiral ct scans .
consequently , the prosthesis had a stair - like surface because the 3d model was manufactured using the relatively thick spiral ct data .
therefore , a routine ct image may not be suitable for the creation of a precise model .
it can not develop precise model because there is no normal side of the cranium to use as a model . in order to overcome this problem
, we used a precraniectomy routine ct image and modified it with a 3d model image program .
it can also be useful by minor trimming around the margins as shown in fig .
it may be a first time report to develop customized cranioplasty implant in bilateral cranial defect . by using our 3d model during the cranioplasty , the operation time may be reduced . in this study ,
the median operation time was 184.3626.07 min , whereas , in our previous report , it was 285128 min for cranioplasties using non - customized pmma implants13 ) .
the reason is that the preparation of the implant is performed during the exposure of the cranial defect .
in addition , most of the pmma implants used in this study required only minor trimming before being fit into the cranial defects .
a postoperative infection was found in one case ( 6.2% ) , who had an open wound defect previously .
considering the infection rate , this model is comparable to other procedures2 ) . there were no other complications for 23 months follow - up period .
pmma is one of the most biocompatible alloplastic materials currently available , and its use has long been established for cranioplasty .
. however , pmma induces an exothermic and potentially toxic nature of polymerization when it is conducted in situ .
polymerization can cause damage to sensitive dural and subdural structures and release monomers into the patient 's blood circulation5,9,16 ) .
therefore , a prefabricated implant has the advantage to prevent these potential complications of pmma , as like our model .
individualized prefabrication of the mold and pmma casting is an easier and more cost - effective method than the previously customized cranial prostheses3,5,6,8,11,16,19 ) . in the present study
, we performed the cranioplasty in two steps : the prefabrication of the mold and the casting of the pmma implant .
it takes 1 and 6 hours to generate 3d images for the molding and prefabrication process , respectively .
in addition , the cost of manufacturing a prefabricated mold is $ 450 usd approximately .
there are some considerations for our customized cranioplasty method in case of complex cranial defects . in cases of bilateral cranial defects and asymmetrical skulls ,
although we used precraniotomy routine ct scans ( 5- to 10-mm slices ) to generate 3d images of the implant for the bilateral cranial defects , satisfactory results may sometimes not be obtained as readily as with unilateral cranial defects .
in addition , the degree of skin contracture over large or complex cranial defects can cause a problem with skin closure5 ) .
therefore , one must be careful to assess the degree of skin contracture required over large or complex cranial defects prior to implant design , although we did not have this problem .
in conclusion , cranioplasty using the individualized prefabrication of implants assures satisfactory aesthetic results , reduces surgical time , and decreases the potential complications associated with the use of pmma .
in addition , our customized cranioplasty model may have advantages with respect to cost , manufacturing time , and the simplicity of the procedure .
 objectivethe prefabrication of customized cranioplastic implants has been introduced to overcome the difficulties of intra - operative implant molding . 
 the authors present a new technique , which consists of the prefabrication of implant molds using three - dimensional ( 3d ) printers and polymethyl - methacrylate ( pmma ) casting.methodsa total of 16 patients with large skull defects ( > 100 cm2 ) underwent cranioplasty between november 2009 and april 2011 . for unilateral cranial defects , 3d images of the skull 
 were obtained from preoperative axial 1-mm spiral computed tomography ( ct ) scans . 
 the image of the implant was generated by a digital subtraction mirror - imaging process using the normal side of the cranium as a model . 
 for bilateral cranial defects , precraniectomy routine spiral ct scan data were merged with postcraniectomy 3d ct images following a smoothing process . 
 prefabrication of the mold was performed by the 3d printer . 
 intraoperatively , the pmma implant was created with the prefabricated mold , and fit into the cranial defect.resultsthe median operation time was 184.3626.07 minutes . 
 postoperative ct scans showed excellent restoration of the symmetrical contours and curvature of the cranium in all cases . 
 the median follow - up period was 23 months ( range , 14 - 28 months ) . 
 postoperative infection was developed in one case ( 6.2% ) who had an open wound defect previously.conclusioncustomized cranioplasty pmma implants using 3d printer may be a useful technique for the reconstruction of various cranial defects . 