Based on the trends of the last few years, it can be stated that the digital revolution in dentistry has begun and seems to be irreversible. The question is no longer whether it should be introduced, but when, at what rate and to what extent.
3D printing, and more specifically metal 3D
According to forecasts, the world of dentistry will be profoundly transformed by digital dentistry technologies. Experts agree that in the coming years, changes will be driven and impacted the most by 3D printing (additive manufacturing).
3D printing has made a spectacular entry and given a new impetus to the spreading of digital dentistry. Two areas can be mentioned, where the technology is already widely applied and its impact has been significant: 1) the manufacture of invisible orthodontic aligners and 2) metal restorations. This article gives an overview of the latter, based primarily upon the experience gained in Central-Eastern Europe.
Nowadays, typically CoCr restorations are produced by 3D printing in dentistry. At the same time, titanium restorations gain also ground, the share of which is expected to grow by a significant rate in the coming years. 3D printed titanium restorations – owing to the advantageous features of titanium and 3D printing – offer a competitive alternative to restorations made of CoCr and zirconia, as well as restorations made by casting and milling technologies.
Casting is the longest used and most widely spread technology in dentistry. Both CoCr and titanium products can be fabricated by casting. As casting of titanium requires a higher level of technical competence and is also more expensive, with the exception of special works, the prosthetic restorations are typically made of CoCr.
The advantage of casting is its low investment cost, and in line with this the low price of the final product. However, some of the restorations produced by casting (about 10 to 20%), due to the features of the technology, contains inhomogeneity and inclusions. As these products are faulty, they must (should) be fabricated again.
The alternative to casting has been CNC milling for about two decades. CNC milling opened up the way to using new materials in addition to CoCr and titanium, too. A material frequently used for such prosthodontic restorations is zirconia. Zirconia restorations, for the time being, can only be produced with this technology. Moreover milling of zirconia requires a milling machine of lower capacity than that of CoCr or titanium.
One of the great advantages of the milling technology is that it produces a homogenous structure, reducing the ratio of the structurally faulty products practically to zero. An additional important advantage of the technology is that it results in a smooth surface, which is an indispensable requirement at the parts of the restorations fitting to the implants or implant interfaces (referring to as fitting parts later). A drawback of CNC milling is the high price of the product, which is resulted from the high investment costs and the high quantity of raw material (disk) to be used that finally turns into waste to a great extent.
As a result, CNC milling is used primarily for the production of zirconia, and to a smaller extent of CoCr and titanium restorations.
Metal 3D printing offers a new, viable option over casting and CNC milling. 3D printing is suitable for the production of both CoCr and titanium restorations. This latter, due to the explosive nature of titanium-oxide, requires a printer with a working chamber expressly engineered for this purpose, as well as greater technological competence and discipline. (It might be a reason of the current less extensive use of titanium vis-à-vis CoCr).
The product obtained by 3D printing, similarly to milling, has a homogeneous structure, therefore, the proportion of the faulty products is practically zero, too.
The surface of the product is rougher than that of the product made by milling, at the same time – with the exception of the fitting parts – this roughness is acceptable, since in case of veneering with ceramics it can be compensated, and in case of veneering with composites it is even advantageous.
Thanks to the recently developed processes combining 3D printing and milling (e.g. sint&mill), the fitting parts can also be produced in the required quality. Owing to this process, the smoothness of the fitting parts is equivalent to that obtained by CNC milling (as it is made by CNC milling), at the same time, the overall cost of production will be lower than in case of milling.
While the initial investment cost in case of 3D printing is also high, the significantly smaller amount of raw material (powder) required and the higher productivity result in lower specific fabrication costs and, consequently, a favourable product price when compared to milling.
In case of CoCr, the price of the 3D printed products is already competitive with that of the cast items, whereas their quality is higher. Due to the competitive price, 3D printing increasingly replaces casting and CNC milling in some Central-Eastern European countries. What is more, there are several dental labs in the region which produce restorations exclusively by 3D printing.
3D printing opened up new prospects for the fabrication and application of titanium restorations. The use of technology leads to higher quality compared to casting, a lower price compared to milling and greater conformity of the digital model and product compared to both. The advantage of 3D printing over milling is manifest particularly in the case of the various implants (e.g. circular, symmetric traditional or one-off platforms resting on the cortical bone surface) and traumatic platforms, as printing allows the production of such forms, which are practically impossible to make by milling.
Using titanium improves the sense of comfort, as well as extends the lifecycle of the restoration, with the patient being the ultimate winner. The weight of the restorations made of titanium is lower than those made of zirconia and particularly of CoCr (one half of this latter), and their tensile strength and elasticity features are much closer to those of the natural bone. An additional argument in favour of using titanium is its good osseointegration property, which is an important criterion in case of implants, whereas its biocompatibility is preferred in case of sensitivity to traditional metal restorations.
The increasing reputation of 3D printing generated by the positive experience gained so far, as well as the declining prices of 3D printers and raw materials are suggesting the more and more widespread application of 3D printed metal restorations. This is particularly true for titanium restorations, which can also be applied in cases when the use of CoCr is not recommended or not possible.
Those practitioners, who have not yet done so, should try the application of 3D printed metal restorations. To do so, it is not necessary to invest in an own 3D metal printer since there are several service providers and centre on the market which can print these restorations, and naturally we are also pleased to help in respect to both CoCr and titanium restorations.
I express my thanks to my colleague, Mr. Lajos Bozsányi, for this contribution to this article.
About the Author:
Zsolt is strongly engaged in the application of 3D printing in the healthcare sector. He is the Managing Director of Premet (www.premet.hu), a company focusing on the production of 3D printed products, including those made of CoCr, titanium and PEEK, for the dental and medical sectors. He is the leader of a3D Printing Training Centre that delivers