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Bolstering Medical And Dental Applications With 3D Printing

Manufacturers have been relying on 3D printing rapid prototyping, helping to de-risk new designs before committing to production tooling which can be costly. By Shaun Lim, strategic business development manager, Renishaw, ASEAN

Metal 3D printing technology provides the opportunity to do more than just make models, but it also the production of additively-manufactured components, from parts of an aerospace engine to healthcare implants.  According to market intelligence agency SmarTech’s latest analysis, the 3D printing applications in dental and medical sectors have been forecast to generate more than US$5 billion in revenues by 2021.

Traditional Implant Versus 3D Printed Parts

Since the early 1900s, surgeons have been using metal implants in healthcare, typically to treat bone diseases including osteoarthritis and inflammatory rheumatoid arthritis, as well as in reconstruction therapy. Though a long-established technology, traditional implants often cause challenges for patients and surgeons.

One of the key challenges that traditional implants present is loosening. This may occur due to wearing over time and is exacerbated by factors that include infection and poor compliance with advised physiotherapy regimes.  Another limitation of traditional metal implants is that they are only manufactured in a discrete number of shapes and sizes. Thus, it is unlikely patients will receive an implant that fits them accurately. This can cause poor physical function and contribute to loosening.

Additive manufacturing technology caters to the rising demands of personalised medical care by providing customised medical implants based on individual needs. “Digital healthcare” makes 3D scan-to-parts by utilising medical scanning and imaging technologies (CT, MRI and ultrasound) offer highly effective solution for the medical and dental industry, 3D printing then utilises a layer-by-layer addition technique to build implants from the three-dimensional digital file that are more accurately fit for the patient and lead to a faster recovery.

This manufacturing method also has fewer geometric constraints than subtractive manufacturing—parts are tailor-made according to patient’s digital scan to encourage better integration, hence reduce failure risk, surgical time as well as overall cost.

Total Accuracy With 3D Laser Printing

Removable partial dentures have been a mainstay of the dental industry, but the dimensional change during the manufacture of removable partial dentures has always been a difficult technical challenge due to the reliance on traditional techniques.  Proslab Dental in Australia relies on additive manufacturing solutions provider Renishaw’s 3D laser printing system to build accurate partial denture that fits perfectly first time and bring smiles on patients’ faces.

Proslab Dental has been manufacturing cobalt chrome frames for many years, but the casting process was always the challenge—there was no accurate technique to finish off the process that the dental clinic has in scan and design, not to mention the long lead time and human error caused.  The aim was to create complex geometries and highly customised dentures was able to be realised by using the Renishaw AM400 metal 3D printing system.

The additive manufacturing system uses metal powder bed fusion technology to build complex, fully dense components direct from 3D CAD files.  Parts are built from a range of fine metal powders that are fully melted in a tightly controlled atmosphere layer by layer in thicknesses ranging from 20 to 100 microns.  The dental clinic also uses metal powders for partial denture production, and the metal powders are CE certified thereby ensuring high quality, for reliable and consistent system parameters.

“We are now in a position to produce the most accurate ‘casting’ for the patient that there is. It allows us to be more confident in our work with none of the dimensional change in the framework that we had become accustomed to from traditional techniques,” said Damian Synefias from Proslab Dental.

Patient-Specific Implants

Surgeons are turning to metal 3D printing technology over standard implants or traditionally manufactured implants to deliver better, and more predictable outcomes in terms of patient safety and satisfaction, and hospital efficiencies and economies.

A 68-year-old female patient presented to Dr Bartolomé Oliver’s department at the Teknon Medical Center in Barcelona, Spain with a benign growth from the left side of her cranium, caused by a meningioma, a tumour that arises from the meninges—the membranes surrounding brain and spinal cord.  She required a craniectomy to remove the growth and a cranioplasty to rebuild her skull.

Dr Oliver planned for the combined craniectomy and cranioplasty operation, allowing the patient to be treated in a single procedure. He chose to partner with PDR, a design consultancy and applied research centre based in the UK, and Renishaw as a 3D metal printing partner, as it had shown repeated evidence of supporting predictable outcomes in complex facial reconstructive surgery. nDr Oliver briefed PDR to design both a patient specific implant (PSI) cranial plate for the cranioplasty and a custom surgical cutting guide for the craniectomy.

The hospital’s computerised axial tomography (CT) scans were transferred from Spain to the UK, imported into a software program, and then converted into a file for modelling by PDR.  The company then created a 3D virtual model of the cranial plate by mirroring the healthy side of the cranium using the Geomagic Freeform Plus software to deliver a suitable aesthetic design. The cutting guide was then modelled which would be placed on the cranium to help mark the perimeter or limit of the craniectomy and act as an aid in freehand work during surgery.

After receiving the files of both the implant and cutting guide, Renishaw 3D printed and dispatched the components to Barcelona within two weeks.  The parts were manufactured on the AM250 metal 3D printing system in titanium with a satin finish. The material used was Ti MG1 tested to ISO 10993 part 1, which was then treated with X-flex technology to ensure high ductility, which is important to prevent the risk of breakages in surgery should the implant need to be adjusted, for example due to unexpected hard tissue changes.

Precise Design With Virtual Modelling

While the virtual modelling enabled precision design, the plate needed to be thin enough to maintain aesthetics, but resilient enough to handle all of the other necessary requirements: additional screw holes to give Dr Oliver flexibility to fix the implant and perforations to allow fluid transfer and tissue to grow through it.

The implant extended 8 mm past the cut margin—giving an 8 mm offset allowed for cutting tool radius and standard screw diameter – and was designed for 1.55 mm diameter screws. This design freedom enabled by the additive manufacturing process meant that the material was thicker around the screw holes but 0.5 mm overall, to fit Dr Oliver’s precise specification.

Dr Oliver had specified that a “pan-handle” be designed into the cutting guide to help position it during the craniectomy, aiding stability and improving the ergonomic performance of the device. An arrow was added onto the guide to indicate the orientation.  The decision was taken to use the cutting guide to mark the perimeter of the craniotomy. Dr Oliver executed a freehand incision following the markings, after the guide was removed. This approach enabled an easier way to handle the complex skull geometry around the temporal area which curved to a tight radius.

The operation was successful and incident-free with the cranial plate being fitted safely and accurately.  The patient was discharged after four days in hospital and examined in follow-up appointments after 15 days and at monthly intervals. She was free from complications and post-operative CT scans showed good implant performance.

Metal 3D printed patient specific implants are proved to improve the predictability, accuracy, safety and speed of operations.  Addictively manufacturing technology is successfully reshaping current supply chains for medical and dental markets, minimising high-costs and long lead-times.

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