How is a titanium mesh made by 3D printing?

From image to part: the digital workflow

Everything starts with a cone beam CT, the three-dimensional dental scan. It delivers images in DICOM format, the medical imaging standard: greyscale slices that do not yet contain any “object” that could be manufactured.

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

• Segmentation: the software isolates bone from the other tissues and derives a 3D model from it.
• Conversion to STL: the model is exported to a surface format that every printing machine can read.
• 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, most often entrusted to a specialist manufacturer.

Laser powder bed fusion

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

What about machining?

Machining takes material away from a block with cutters, as a sculptor would. For titanium meshes it serves 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, for decades, the reference metal for dental implants and bone surgery plates. In contact with air or tissue, its surface covers itself with a thin, stable oxide layer that makes it very unreactive in the body: this is its biocompatibility. Light, rigid for its weight, it can be produced in very thin sheets; three qualities invaluable in a mesh that must hold a volume without troubling the gum that covers 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, governs its extra-low-interstitial (ELI) version produced by powder bed fusion; it covers the powder, process parameters, composition, mechanical properties, heat treatment and dimensional inspection ^[5].

Unalloyed titanium (grades 2 or 4) has its place too. The review of 23 studies records grade IV, Ti-6Al-4V and grade V ^[1]; a Japanese series of 14 cases used grade 2 titanium in 0.3 mm sheets ^[6]. Mesh thickness ranges, across 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 fresh out of the machine cannot be used as it is. The usual steps:

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

Sterilisation

The mesh arrives either sterile from the manufacturer or is sterilised at the practice under a validated protocol, for example by autoclave (pressurised steam). The review of 23 studies notes that the sterilisation method often goes unreported in 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 full traceability.

How accurate is it?

Three levels of accuracy stand apart. First, the image, which depends on the cone beam CT ^[2]. Next, manufacturing: one manufacturer quotes 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 ran from about 0.8 to 1 mm depending on the mesh design, a “self-positioning” shape reducing it ^[7]. That study was conducted in vitro: it is no substitute for measurements in patients.

In other words, the machine is rarely the weak link. Image quality, design and the stability of the mesh during surgery weigh 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 the instant it is laid down ^[3]. It is another family in the ISO/ASTM 52900 standard, devoted mainly to building or repairing large industrial parts. Its resolution is unsuited to a shell a few tenths of a millimetre thick such as a dental mesh.

What does it mean for the patient?

Additive manufacturing changes nothing about the biology: it is still the graft that becomes bone. What it brings is a part fitted before the operation, with no bending at the chairside, hence fewer sharp edges and a shorter operation ^[8].

Nor does it erase the complication shared by all titanium meshes: exposure, when the gum opens and lets the metal show. In the literature it most often affects 20 to 30% of cases, and early exposure, in the first weeks, comes with more fibrous tissue and less bone formation ^[8]. The smooth edges and close fit of a printed mesh reduce pressure points on the gum; tension-free closure and stopping smoking remain decisive all the same. The clinical figures, what is done about an exposure and the treatment steps are presented on the Custom titanium mesh page.

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