Craniofacial Implants: a Comparison Between Traditional and Virtual Design Technologies

Objectives: Currently cranial and maxillofacial implants are constructed by swaging commercially pure titanium (cp-Ti) plate, or mesh between dies duplicated from relatively costly stereolithographic (SLA) resin models produced from Computerised Axial Tomography (CT) data. This study considered the feasibility for constructing customised implants using, either lost wax casting, or conceptual virtual design technology and direct Rapid Prototyping (RP). Methods: CT data for patients with congenital facial asymmetry and trauma were selected and customised implants produced. Method 1 required an SLA resin model, to be produced, on which a mandibular onlay was created in wax prior to casting from cp-Ti. Method 2 adopted a more intuitive virtual approach. A customised implant was created for each patient case from a 3D model acquired from the previous CT data. All virtual design was undertaken using a Haptic design tool (SensAble Technologies). The completed designs were manufactured from resin or cp-Ti using either Selective Laser Sintering (SLS), or Computer Numerical Control (CNC) machining. Results: Although previous results for lost wax castings were successful for customised Ti implants weighing ≤18 grams, where larger volumes are required miscast occurred owing to the maximum casting weight of ~40 grams being insufficient. The second part of the study show that a virtual customised onlay or cranioplasty could be successfully designed by a non-CAD (Computer Aided Design) engineer using Haptic technology and the resultant (STL) file recognised by RP or CNC software. However, difficulties exist when machining more complex surfaces owing to tool flute length, diameter & cutting angle. Conclusions: Both lost wax and virtual implant design and construction can produce acceptable results. However, lost wax casting is restricted by volume and a number of other well recognised problems. The use of Haptic technology can produce large complex shapes and avoid the manufacture and cost associated SLA model construction.