Scanners, software and printers in facial prosthetics

For most of its history a facial prosthesis began with plaster on a face. Over the past two decades scanners and software have started to replace that first step and, in some places, the wax sculpture and mold that follow. The change is easy to overstate. This page sets out what is being done, what published reviews and trial protocols actually say about it, and where they say the evidence runs out.

Capturing the face without plaster

A 2022 review in Frontiers in Oral Health describes how specialists have looked to digital technologies to replace or assist steps such as molding and sculpting, which it calls an artisanal and time-consuming process. The earliest digital attempts used MRI and CT data. It says colored facial scanning has grown popular over the last 20 years, and that structured light scanners entered facial prosthesis workflows in the past decade. CT is used for surface capture only when implants are being planned, the review adds, because the aim there is to combine bone and surface data.

Not all of it needs expensive equipment. A 2016 paper in the Journal of Otolaryngology, Head and Neck Surgery set out a method of turning photographs from a mobile device into a three-dimensional model of a face, using free software and a capture protocol, as a digital facial impression. The authors suggest in their clinical implication that free software and low-cost equipment could improve access for centers that lack expensive technology. They also describe why impressions are worth replacing: the weight of the materials and the airway tubes used can distort the residual tissues, and a conventional impression records only the defect, not the likely result.

Designing on screen

Once a face is a 3D model, a prosthesis can be designed in software. The 2016 paper lists designing a prosthesis by mirroring the healthy side, capturing structures from a healthy donor, and designing templates or flask models for the silicone as uses of digital impressions. The 2022 review says the virtual model has to be manipulated within a CAD program whatever scanning technology is chosen. Where implants are involved, a 2021 systematic review in the International Journal of Environmental Research and Public Health found digital planning software used for placing implants, making molds, designing retentive attachments and printing silicone prostheses. That review covered nasal prostheses and craniofacial implants only.

Printing molds, and sometimes the prosthesis

The Queensland University of Technology review summarizes the printing approaches: scan the anatomy, model the prosthesis in 3D, then either print the prosthesis directly or print a mold. It says studies comparing 3D printing with traditional methods have highlighted reduced cost and time. The 2022 review lists the methods in use, from subtractive milling of wax, metals and polyether ether ketone to additive methods such as fused filament fabrication, stereolithography and selective laser sintering, and, more recently, silicone 3D printing.

Direct printing of silicone is the hard part. The Queensland review reports that standard silicone formulations lack the yield stress needed for some printing processes, and that one extrusion-based attempt had marginal adaptation that was not as smooth as with traditionally made prostheses because of the layer thickness of 0.4 mm, requiring post-processing. Its authors are optimistic about newer silicone formulations, which they say could enable directly printed prostheses with customizable properties, but that is their expectation rather than a finding. In the meantime, printing a mold and filling it with intrinsically colored silicone is one route the review describes. How the silicone is formulated and colored is on materials and colour matching.

What the evidence shows

The systematic review of digital planning for nasal prostheses included 21 studies covering 23 patients. Planning used CT in nine cases, cone-beam CT in six and laser scans in six; ten surgical templates were designed and printed to place 36 implants. The authors say digital technology has been claimed to reduce clinical and laboratory time, with equipment cost remaining a limitation. These are case reports and small case series, assessed for risk of bias with standard tools for that kind of design. That is useful for showing what is feasible, and thin as proof of benefit.

A 2023 trial protocol in Pilot and Feasibility Studies frames the gap candidly. It says that a wide variety of digital techniques have been applied to different stages of facial prosthesis manufacture, that manufacture has not yet shifted to complete digital fabrication, and that there is currently no single set of standards exclusive to digitally manufactured facial prostheses. The authors call for a well-designed randomized trial comparing the clinical and cost-effectiveness of digital with conventional manufacture and describe a feasibility trial in which participants receive two new prostheses, one made each way, to prepare for one. The Frontiers review, for its part, notes that digital workflows allow teams to reduce the active time of patients and clinicians and improve cost-efficiency, which it presents as an opportunity. Results of that kind of head-to-head test are not yet in the sources opened for this page.

What stays human

The International Journal of Dentistry review says several steps in making maxillofacial prostheses are still artisanal, requiring time and skill, and that modern techniques need improvement, reduced cost and wider availability to deliver a promising future. Coloring is a good example: the Frontiers review mentions work on algorithms that detect the coloring of a prosthesis with a neural network, which is research, not routine practice. The sculptor's judgment about a face that moves, and the clinician's judgment about a person, are not things the sources suggest software has replaced. The conventional chain that digital tools are modifying is described on how a facial prosthesis is made, and the longer arc from plaster casts to printers is on the timeline.

In brief

Scanning, computer design and 3D printing are already used to avoid uncomfortable impressions, plan implants and print molds, and silicone printing is under development. Reviews describe possible savings in time and cost, but the evidence is mostly small case series and a head-to-head trial is still being planned. Whether any digital step is used for a particular prosthesis depends on the center.