**Colour Image Reproduction for 3D Printing Facial Prostheses**

Kaida Xiao, Sophie Wuerger, Faraedon Mostafa, Ali Sohaib and Julian M Yates

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/63339

#### **Abstract**

In this chapter, using colour 3D printing technology, a 3D colour image reproduction system is detailed for the semi-automated and accurate additive manufacturing of facial soft tissue prostheses. A protocol for 3D colour image reproduction was designed based on the six steps of processing. For this specific application, protocols for each sub‐ process required development and details of each technique applied are discussed. The quality of facial prostheses was evaluated through objective measurement and subjec‐ tive assessment. The results demonstrated that the proposed colour reproduction system can be effectively used to produce accurate skin colour with fine textures over a 3D shape, with significant savings in both time and cost when compared to traditional techniques.

**Keywords:** facial prostheses, colour image reproduction, 3D colour printing, 3D im‐ age acquisition, 3D image processing

#### **1. Introduction**

Maxillofacial prosthetics or anaplastology refers to the specialty that designs and manufac‐ tures prostheses used to replace part or all of any stomatognathic and/or craniofacial struc‐ ture. The process provides descriptive evidence of the prosthesis, including location, retention, support, time, materials, and form. It is both an art and a science of cosmetics, anatomy and functional reconstruction, that is achieved by means of artificial substitutes of head and neck structures that are missing or defective. It is the branch of dentistry that rehabilitates intra‐ and extra‐oral deformities [1]. Extensive tissue loss involving facial (or indeed any other body structure), on many occasions, cannot be corrected surgically due to a lack of sufficient or

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adequate donor tissue that may be required for the surgical repair and reconstruction. Further‐ more, the patient's age and general condition may not permit extensive surgical procedures or allow for the morbidity often associated with protracted courses of reconstructive surgery and recovery [2]. Additionally, the final outcome can often be aesthetically and functionally compromised. In such cases, defects may be replaced artificially with the provision of facial prostheses to provide functional rehabilitation and aesthetic improvements. Often there is an associated improvement in social, emotional status and overall quality of life [3].

Traditional methods of prosthesis production are well established and are used even today. These include taking an impression, manufacturing a cast and ultimately hand crafting a prosthesis in a silicone based or similar material. The provision of prostheses in this manner has provided considerable comfort and support to many patients over many years, and allowed them to continue with normal day‐to‐day activities and enhance their social interac‐ tion [4]. Despite the advantages this method can provide, its application has shown some limitations and shortcomings. These are primarily related to the processing strategy, technical expertise required, time, effort, cost and retention problems. Furthermore, there are durability issues due to material degradation and colour fade after a relatively short period of service because of general wear and tear and exposure to ultraviolet radiation. For these reasons, facial prostheses require renewing and periodic replacement, which is a costly and time‐intensive process, which places a burden on both patients and prosthodontists alike [3].

In the last decade, additive manufacturing technology, including three‐dimensional (3D) printing, has advanced dramatically. Colour 3D printing has also evolved to produce full spectrum coloured solid objects utilising a range of materials [5, 6]. With the evolution of various 3D imaging techniques, accurate acquisition and transformation of target object geometric data into 3D digital models can be achieved. By combining the 3D image capture and printing techniques, there is huge potential to achieve 'What You See Is What You Get' processing. More importantly, it has the ability to directly interconnect with advanced manufacturing techniques, allowing customisation with high accuracy, resulting in savings of both time and costs [7]. It has been extensively utilised in rapid prototyping [7], successfully applied in medical sciences [8, 9], and is gaining popularity in multidisciplinary applications [10–12]. For medicine, captured digital 3D models have great accuracy and have been effec‐ tively used for facial disfigurement diagnosis, surgical planning and assessing treatment outcomes for several years [13, 14]. Additionally, there is the potential to develop this auto‐ matic additive manufacture technology for facial prosthetics.

Compared with conventional image capturing technology, image processing between 3D image devices has much more complicated working processes. For 3D printing, the quality of 3D printed objects is not only affected by the printing itself including binder/substrate interaction and printer resolution, but also the printing material and any post‐processing or finishing stages [15]. Therefore, without a specific protocol, 3D objects can often be produced with poor reliability, accuracy and quality. Moreover, in terms of 3D image reproduction, image processing methods to transform 3D images from a 3D camera to a 3D printer are far less well developed than existing processes that use 2D technology. Furthermore, accurate colour reproduction for facial prostheses is highly desired and the quality of skin colour reproduction can affect the overall quality of the facial prostheses significantly. Therefore, accurate colour management processes are not only essential, but also needs to run in con‐ junction with the specific 3D manufacturing processes used.

In recent times, new and innovative methods for manufacturing facial soft tissue prostheses that prioritises accurate 3D colour image reproduction have been developed and a framework and protocol for specific 3D processing designed [16–18]. Additionally, colour management processes have been developed and successfully applied to 3D imaging devices and manu‐ facturing processes.
