**5. Conclusion**

Using custom implants are widely accepted in maxillofacial and dental reconstruction surgery [49], in part due to the complexity of the bone and soft tissue reconstructions required. Titanium meshes have been used to create support patches to aid the repair of significant skeletal lesions [50], and splints for mandibular reconstructions [51–54]. Bespoke implants have helped reduce post-operative cosmetic deformities, which are commonly associated with these surgeries [55]. The most common PSI are those created for cranioplasty to restore cranial anatomy either after surgery or repair cranial defects, as opposed to the standard treatment of autologous bone. Implants constructed out of titanium, PEEK and polymethylmethacrylate (PMMA) have all been successfully implemented surgically, and the process is becoming common practice in a number of centres [56–58]. Overall a review of custom cranial implants found the all were found to accurate and reduce operating room time, with the overwhelming majority demonstrated improvement in clinical outcomes, arising from the improved anatomical verisimilitude [41]. Neurosurgery also has the potential to benefit from 3D printing due to complexity of the anatomical considerations, with meticulous planning required due to the associated risks. Therefore a reduction of surgery time would be a considerable benefit in these cases [59]. Xu et al. [60] fabricated a 3D titanium alloy axial vertebral body that was implanted for upper cervical spinal reconstruction following a C2 Ewing sarcoma resection. A bespoke vertebral body has also been successfully implanted for reconstruction after removal of a T9 Primary bone tumour [61].

Beyond reconstructing bone and rigid structures, 3D printing methods have been developed to create bioresorbable structures, which can be used as temporary stents and splints [62, 63]. For example, a bespoke bioresorbable airway splint was successfully implanted into a child

There are numerous applications for 3D printing technology being developed. A promising area for the integration of 3D printing technology is tissue engineering. Tissue engineering is set to provide a solution to the unmet demand for tissues and organs for regenerative medicine. This will be achieved using a combination of stem cell, bio-materials, and engineering technologies. Experts in this field believe radical improvement to tissue engineering could come from 3D printing [8]. One main problems with the synthetic scaffolds currently used is the inability to adequately mimic in vivo microarchitecture. Advances in 3D printing technol-

While 3D printing in healthcare is becoming more prevalent and technological advancements appear promising across a wide spectrum of applications, there are some drawbacks which must be taken into consideration. The technology is evolving and long-term evidence for the benefit of 3D printing for various applications is unknown. The potential risks of basing decisions on or carrying out procedures with poorly executed models (due to errors at any stage of the model production pipeline) is yet unknown. Another challenge is the considerable time it takes to complete the pre-print component of the pipeline. While surgery is the

ogy may allow production of scaffolds, which do not suffer from this problem [8].

with tracheobronchomalacia [8, 64].

**3.5. Tissue engineering**

128 3D Printing

**4. Limitations**

3D printing is permeating nearly every aspect of medicine from education, from before treatment begins in improving education and communication, through to improving surgical planning and reducing surgery times. As the technology becomes ubiquitous, there is increased demand for extracting the relevant anatomy from medical imaging data. This places further emphasis on the tools used to automatically create representative geometry and process them in a form, which is ready to be printed. There is of course, further emphasis on demonstrating the reliability of the technologies themselves, to reduce the time taken to produce the models, and the level of expertise to use them. The review presented here gives an overview of the myriad applications of 3D printing in medicine. The workflow to create the anatomical models along with a worked example would be helpful to medical and surgical students who need access to anatomical models, and also to students from associated fields who wish to gain a hands-on understanding of surgical training and planning.
