Researchers create go-to guide for all things 3D printing in implantology

Commonly used 3D-printing technology in implantology

Without delving too deeply into the many potential applications, such as surgical guides and titanium meshes for regeneration, it is first key to know the fundamentals of 3D printing in implantology. Manufacturers in the field of implant dentistry primarily employ one of four main types of additive manufacturing processes. Most clinicians will recognise the acronyms referring to the sub-technologies of these types, as 3D-printing companies use these to advertise their particular technology.

The four overarching categories of additive manufacturing are vat photopolymerisation (VPP), powder bed fusion (PBF), material extrusion (MEX; also known as fused filament fabrication, FFF) and material jetting. VPP uses light to harden liquid resin layer by layer into the desired 3D shape. PBF uses a heat source like a laser or electron beam to fuse powder materials, such as plastic, metal, ceramic and glass, layer by layer to form the 3D object. MEX, likely the most well-known method, pushes material (commonly plastic) through a heated nozzle that moves around to deposit the material layer by layer according to the 3D design. Material jetting creates objects much like a regular inkjet printer, but instead of ink, it sprays liquid materials that are instantly polymerised by UV light.

VPP encompasses three separate sub-technologies. The first methodology is stereolithography (SLA), which uses a high-intensity UV laser to polymerise the resin, tracing each layer of the object. It is ideal for creating detailed and accurate objects, but can be slower because it has to draw each layer. Digital light processing (DLP) is the second method. Unlike SLA, which polymerises resin bit by bit, DLP projects the light on to the whole layer of the object being printed at once, making the process faster. However, DLP might not provide as much detail as SLA. The third technique is Continuous Liquid Interface Production (CLIP), a faster version of DLP. In CLIP, the object is pulled from the vat of resin while the UV light constantly projects on to the next layer. An oxygen layer stops the resin from polymerising at the bottom of the vat, allowing for continuous printing and fast production.

PBF is commonly used for creating metal parts used in dentistry, for example titanium implants and cobalt–chromium frameworks, fabricated either through selective laser melting (SLM) or selective laser sintering (SLS). SLM fully melts the powder (typically metallic) to form each layer of the object. It is typically used for making strong, dense parts. In contrast, SLS does not completely melt the powder. Instead, it heats it up until it sticks together to form the object, and SLS is usually used with plastic or ceramic powders. The third subtype of PBF production is electron beam melting (EBM), which is similar to SLM but uses an electron beam instead of a laser. It has the advantages of high energy utilisation and high power density, making it suitable for implant production.

Regarding MEX technologies, many clinicians will be familiar with fused deposition modelling (FDM). FDM melts thermoplastic filament and extrudes it on to the build platform, creating the object layer by layer. It is an inexpensive, popular method for hobbyists and prototyping, but does not offer the same level of detail as SLA.

For higher-resolution parts, material jetting, specifically PolyJet technology, is a useful option that does not require a secondary polymerisation process and offers greater precision than is possible with SLA.

Producing surgical guides

Surgical guides have been produced with 3D printing for more than ten years. Being fast and economical, SLA is the most widely used technology for guide fabrication, but PolyJet technology has been proved to produce more accurate guides.

Factors affecting the accuracy of surgical guides:

1. System errors: These errors are generated during CBCT scanning and data conversion and are beyond human control.
2. Manufacturing errors: These are associated with the type of 3D printer used, selection of printing materials, use of supporting structures, and the slicing method and software types.
3. Layer thickness and build angle: Research indicates that printing at 50 µm layer thickness gives better overall guide dimensions than printing at 100 µm. Also, printing at 0° and 45° build angles results in the most accurate surgical guides.
4. Other factors: There are additional considerations that can influence the accuracy of surgical guides, such as guide position, fixation method, type of guide, flap approach, implant system, sterilisation method and support mode (i.e. bone, soft tissue or teeth).

Fabricating implants

Customised implants can be made to closely mimic the natural tooth root, giving a more personalised implant—a root-analogue implant. This customisation allows the implant to better match the extraction socket, improve stability and mimic the natural gingival profile. Data from CT or CBCT scans is used to build a 3D model of the teeth, and then CAD software is used to design the implant, which is then printed. The whole process ensures that the stress conduction and distribution are similar to those of natural teeth. 3D printing can also create patient-matched implants that are not as customised as root-analogue implants, but are still optimised for specific patient needs, such as narrow-diameter implants for patients with insufficient alveolar bone width.

Titanium, titanium alloys and zirconia are the primary materials used for 3D-printed implants. Some researchers have proposed using titanium for the root portion and zirconia for the abutment for ideal osseointegration and soft-tissue attachment.

Further potential optimisation using 3D printing

The authors of the review include additional insight into further uses of 3D printing within implantology, as well as discuss emerging materials, technologies and innovations that clinicians should take note of.

3D printing has multiple applications in the restoration stage of implant therapy and can offer numerous advantages over traditional techniques. The use of 3D-printing technologies not only increases efficiency and precision but also reduces the risk of error and the amount of material waste. However, attention should be paid to the choice of 3D-printing technology, the selection of materials and the printing process to ensure that the resulting products meet the required standards.

The study, titled “Additive manufacturing technologies in the oral implant clinic: A review of current applications and progress”, was published online on 20 January 2023 in Frontiers in Bioengineering and Biotechnology.

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