How is a titanium mesh made by 3D printing?

From image to part: the digital workflow

It all starts with a cone beam CT, the three-dimensional dental scan. It produces images in DICOM format, the medical imaging standard. These images are greyscale slices: they do not yet contain an “object” that can be manufactured.

A review of 23 studies describes the following steps ^[1]:

• Segmentation: the software isolates bone from other tissues and turns it into a 3D model.
• Conversion to STL: the model is exported to a surface format used by all printing machines.
• Design (CAD): the bone volume to rebuild is drawn around the future implants, then the mesh is shaped over that volume: thickness, perforations, screw positions.
• Manufacturing, quality control and sterilisation, usually by a specialist manufacturer.

Laser powder bed fusion

The international vocabulary standard for additive manufacturing (ISO/ASTM 52900) groups processes into seven families. The one used for meshes is powder bed fusion: thermal energy selectively fuses regions of a powder bed ^[3].

What about machining?

Machining removes material from a block with cutters, like a sculptor. For titanium meshes it is used mainly for finishing: surface correction, drilling, dimensional adjustments ^[4]. Five-axis milling is also used to make other custom scaffolds, in PEEK (a polymer) or bone, from pre-formed blocks ^[1].

The material: which titanium?

Titanium has been the reference metal for dental implants and bone surgery plates for decades. In contact with air or tissue, its surface spontaneously forms a thin, stable oxide layer that makes it very unreactive in the body: this is what is meant by its biocompatibility. It is also light, rigid for its weight and can be produced in very thin sheets, three qualities useful for a mesh that must hold a volume without irritating the gum covering it.

Two families are used. Ti-6Al-4V (titanium alloyed with 6% aluminium and 4% vanadium, known as “grade 5”) is the reference alloy in metal 3D printing. A dedicated standard, ASTM F3001, covers its extra-low-interstitial (ELI) version made by powder bed fusion; it addresses the powder, process parameters, composition, mechanical properties, heat treatment and dimensional inspection ^[5].

Unalloyed titanium (grades 2 or 4) is also used. In the review of 23 studies, grade IV, Ti-6Al-4V and grade V were all found ^[1]; a Japanese series of 14 cases used grade 2 titanium in 0.3 mm sheets ^[6]. Mesh thickness varies between studies, from 0.1 to 2 mm, around 0.5 mm on average; the two studies that report perforation size give about 1 mm ^[1].

After printing: post-processing

A part straight out of the machine cannot be used as it is. The usual steps are:

• Removal of unfused powder and cutting away the supports that held the part during printing.
• Heat treatment to relieve internal stresses caused by rapid melting and cooling cycles; hot isostatic pressing (HIP) can reduce residual porosity ^{[4, 5]}.
• Surface treatment: melting leaves partly fused powder particles on the surface, removed by polishing, blasting or chemical or electrochemical etching ^{[1, 4]}.
• Dimensional inspection, cleaning and packaging.

Sterilisation

The mesh is either supplied sterile by the manufacturer or sterilised at the practice using a validated protocol, for example by autoclave (pressurised steam). The review of 23 studies notes that the sterilisation method is not reported in many publications ^[1]; the Japanese series describes autoclaving at 121 °C ^[6]. At Dr Hazout’s practice in Levallois-Perret, sterilisation follows the usual pathway for medical devices, with traceability.

How accurate is it?

Three levels of accuracy must be distinguished. First, the image, which depends on the cone beam CT ^[2]. Next, manufacturing: one manufacturer states dimensional deviations of about ± 0.1 mm for features of comparable size ^[7]. Finally, placement: on models, the mean deviation between planned and achieved contour was about 0.8 to 1 mm depending on mesh design, with a “self-positioning” design reducing the deviation ^[7]. That study was carried out in vitro: it does not replace measurements in patients.

In other words, the machine is rarely the weak link. Image quality, design and the stability of the mesh during surgery matter more.

Not to be confused with laser metal deposition (DED)

In directed energy deposition (DED), powder or wire is fed into the laser beam and melted as it is deposited ^[3]. It is another family in the ISO/ASTM 52900 standard. It is mainly used to build or repair large industrial parts. Its resolution is not suited to a shell a few tenths of a millimetre thick such as a dental mesh.

What does it mean for the patient?

Additive manufacturing does not change the biology: it is still the graft that becomes bone. What it offers is a part fitted before the operation, with no bending at the chairside, which limits sharp edges and operating time ^[8].

Nor does it remove the complication known to all titanium meshes: exposure, when the gum opens and the metal becomes visible. In the literature it most often affects 20 to 30% of cases, and early exposure, in the first weeks, is associated with more fibrous tissue and less bone formation ^[8]. The smooth edges and precise fit of a printed mesh reduce pressure points on the gum, but tension-free closure of the gum and stopping smoking remain decisive. The clinical figures, how an exposure is managed and the treatment steps are presented on the Custom titanium mesh page.

Frequently asked questions