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Comparative Accuracy of Facial Models Fabricated Using Traditional and 3D Imaging Techniques
Ketu P. Lincoln, DMD,1 Albert Y. T. Sun, PHD, Cswa,2 Thomas J. Prihoda, PHD,3 and Alan J. Sutton, DDS, MS, FACP 4
1Department of Graduate Prosthodontics, USAF, Joint Base San Antonio-Lackland, San Antonio, TX
2Department of Mechanical Engineering, National Taipei University of Technology, Taipei, Taiwan
3Department of Pathology, University of Texas Health Science Center, San Antonio, TX
4Department of Restorative Dentistry, University of Colorado School of Dental Medicine, Aurora, CO
Abstract
Purpose: The purpose of this investigation was to compare the accuracy of facial models fabricated using facial moulage impression methods to the three-dimensional printed (3DP) fabrication methods using soft tissue images obtained from cone beam computed tomography (CBCT) and 3D stereophotogrammetry (3D-SPG) scans.
Materials and Methods: A reference phantom model was fabricated using a 3D-SPG image of a human control form with ten fiducial markers placed on common anthropometric landmarks. This image was converted into the investigation control phantom model (CPM) using 3DP methods. The CPM was attached to a camera tripod for ease of image capture. Three CBCT and three 3D-SPG images of the CPM were captured. The DICOM and STL files from the three 3dMD and three CBCT were imported to the 3DP, and six testing models were made. Reversible hydrocolloid and dental stone were used to make three facial moulages of the CPM, and the impressions/casts were poured in type IV gypsum dental stone. A coordinate measuring machine (CMM) was used to measure the distances between each of the ten fiducial markers. Each measurement was made using one point as a static reference to the other nine points. The same measuring procedures were accomplished on all specimens. All measurements were compared between specimens and the control. The data were analyzed using ANOVA and Tukey pairwise comparison of the raters, methods, and fiducial markers.
Results: The ANOVA multiple comparisons showed significant difference among the three methods (p < 0.05). Further, the interaction of methods versus fiducial markers also showed significant difference (p < 0.05). The CBCT and facial moulage method showed the greatest accuracy.
Conclusions: 3DP models fabricated using 3D-SPG showed statistical difference in comparison to the models fabricated using the traditional method of facial moulage and 3DP models fabricated from CBCT imaging. 3DP models fabricated using 3D-SPG were less accurate than the CPM and models fabricated using facial moulage and CBCT imaging techniques.
Craniofacial dysmorphology (CD) is the study of structural defects caused by trauma, treatment of neoplasms, or congenital anomalies characterized by complex irregularities in the shape and configuration of facial soft tissue structures.1 Patients with CD may undergo extensive surgical procedures, including the fabrication of facial prostheses to restore an extraoral maxillofacial defect.2 The facial prostheses are not functional, but provide the patient with an esthetic result for psychological and social acceptance.3–6
Anthropometry is a way to assess changes in facial soft tissue over time through line measurements between two landmarks.7 The challenge has been to identify landmarks and plot them accurately in the three planes of space, in order to describe the dimensions of the face.8 Traditionally, direct anthropometry was done using calipers. This assessment was a reliable and inexpensive method for data collection of surface measurements.4 However, there were several limitations, including technician training, direct patient contact requiring extensive time to make multiple measurements, patient compliance to sit in one position, inability to archive information, difficulty attaining several measurements as tissue undergoes changes with time, and finally comparing tissue changes with accurate landmark location.9
Making a facial moulage impression was, and still is, another means for 3D facial structure capture, analysis, and documentation. This method has been used successfully for almost 100 years, dating back to World War I.10 Currently, various impression materials like alginate, poly(vinyl siloxane), and reversible hydrocolloid are used to create a facial moulage. The facial moulage method can be time consuming, and soft tissue deformation is a significant problem. Furthermore, it is difficult to obtain accurate impressions of certain defects involving the orbit where the periorbital tissue displaces easily.11 The casts made from the impressions are fragile and require large physical storage space, and it is extremely difficult to communicate physical data to other providers in distant locations.12 Also, archival preoperative casts may not be available for many patient treatments due to storage limitation.
Several types of 3D imaging systems have been created in the past thr...
