3D in the dental laboratory: why, and what applications and advantages

The digital revolution, with its introduction of 3D technologies, has profoundly transformed the dental laboratory. The term “3D technologies” refers to all those tools — hardware and software — that are an integral part of the CAD-CAM (Computer Aided Design – Computer Aided Manufacturing) workflow (1–3).

Today, 3D printers, CAD/CAM software and benchtop scanners are everyday tools in many laboratories, offering new operational possibilities, greater accuracy and more efficient management of workflows than ever before (4). Thanks to these and other CAD/CAM technologies, it is now possible to design and produce prosthetic, orthodontic, gnathological, surgical and implant devices (5–7).

However, the use of 3D technologies is not always feasible and practicable and must be evaluated based on the specific clinical application, the materials used and the choice between in-house production and outsourcing, particularly for metalworking (8,9).

The phases of the 3D workflow in a dental laboratory

In the dental laboratory, the use of 3D is divided into different phases of the workflow (10). The first is that of acquisition, which can be done via a digital impression taken directly in the office with intraoral scanners or via a traditional impression or a plaster model that is subsequently digitised using a benchtop scanner.

The generated STL file represents the starting point for modelling the device prescribed by the dentist. Using the CAD software, the digital design of the required product is created, working directly on the acquired STL file. This allows for the design of crowns, bridges, implant structures, surgical guides, bites and orthodontic appliances.

Once the project is completed, the process advances to the production phase, which can be carried out using subtractive CAM technologies – such as milling – or additive ones via 3D printing (11,12).

The advantage is twofold: on the one hand, the times and costs associated with manual phases, such as wax modelling, are reduced; on the other, a standard product is obtained in terms of mechanical-chemical characteristics, with a shape that is perfectly reproducible starting from the STL file of the project (3).

3D Dental Technology Laboratory: In-house or External production centres

For all these operational phases, particularly the CAM phases, the dental laboratory can choose whether to rely on external production centres (industrial manufacturing) or keep the production internal, in-house (13). This choice is particularly relevant in the management of metallic materials (9).

In fact, metals are more difficult to work with digital workflow inside the laboratory, as they require advanced and very expensive technologies such as selective laser melting (SLM or DMLS), as well as controlled environments for post-processing treatment (9,14). Even among subtractive technologies, metal milling presents certain challenges: it is a particularly abrasive process for the cutters, which deteriorate rapidly.

Pros and Cons of In-House Production

Today, “soft” metals (chromium-cobalt) are also available which are easier to mill with standard machinery, but which require subsequent sintering treatment. This involves a dimensional shrinkage of approximately 10%, which must be carefully considered in the design phase (15).

As a result, many laboratories prefer to entrust the production of metal structures to milling centres or specialised industrial services. These centres rely on high-precision machinery, which is often more expensive and complex to maintain for a medium-small company and offer high quality standards within competitive timeframes.

In-house production proves more advantageous for other types of processes, in particular for the printing of 3D models, resin devices (such as temporaries or bite splints) or customised surgical guides (16). Ceramics are also easy to work with in the laboratory. Zirconium, for example, is milled during the pre-sintering phase with a very soft, plaster-like consistency. After sintering, it also undergoes a dimensional contraction (of approximately 20%) and is then characterised by the technician (17,18).

Furthermore, with the spread of high-performance 3D printers and increasingly reliable and certified composite/ceramic hybrid materials, many laboratories are able to obtain clinically valid results even in the direct production of final restorations (19).

Using the 3D printed model

A crucial issue remains the use of the 3D printed model(20): when is it really necessary and when can it be avoided? The answer depends on the type of work and the materials used. Certainly 3D printed models are always useful as medico-legal documentation, verification and adaptation tools, as replicas for the patient or as aids for communication between the practice, laboratory, and patient.

In the orthodontic field, 3D models are the basis for the thermoforming of aligners and for the digital archiving of cases, while in implantology they represent a fundamental aid for the control of the fit of prostheses on implants for complex cases (21). They are also useful for testing the fit of surgical guides in preparation for guided surgery.

In natural-tooth prosthetics, models are especially useful when precise occlusal control and passive fitting are required. They serve as a reference for finishing, for checking contacts and for aesthetic control. 3D printed models can also be used to make masks that are useful for creating direct aesthetic mock-ups (22).

However, in some selected cases it is possible to work in completely model free mode, that is, without going through the printing of the model (23). This is the case, for example, with temporary restorations on teeth, preliminary restorations and permanent restorations on single or multiple implants. In these contexts, the adoption of model-free digital flows enables even faster management with even shorter job delivery times (24).

Advantages and limitations of 3D technologies

In conclusion, 3D technologies have profoundly changed the way the dental laboratory works, bringing significant advantages in terms of precision, speed and reproducibility.

However, to get the most out of these technologies, it is essential to have a good understanding of the intended uses, the limitations of the materials and to effectively balance in-house production with industrial outsourcing.

Only this way will the laboratory be able to offer high-quality prosthetic and orthodontic devices, effectively responding to the clinical needs of the present and the future.

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