Comparison of trueness and repeatability of facial prosthesis design using a 3D morphable model approach, traditional computer-aided design methods, and conventional manual sculpting techniques.

STATEMENT OF PROBLEM: Manually sculpting a wax pattern of a facial prosthesis is a time-, skill-, and resource-intensive process. Computer-aided design (CAD) methods have been proposed as a substitute for manual sculpting, but these techniques can still require high technical or artistic abilities. Three-dimensional morphable models (3DMMs) could semi-automate facial prosthesis CAD. Systematic comparisons of different design approaches are needed. PURPOSE: The purpose of this study was to compare the trueness and repeatability of replacing facial features with 3 methods of facial prosthesis design involving 3DMM, traditional CAD, and conventional manual sculpting techniques. MATERIAL AND METHODS: Fifteen participants without facial defects were scanned with a structured light scanner. The facial meshes were manipulated to generate artificial orbital, nasal, or combined defects. Three methods of facial prosthesis design were compared for the 15 participants and repeated to produce 5 of each design for 2 participants. For the 3DMM approach, the Leeds face model informed the designs in a statistically meaningful way. For the traditional CAD methods, designs were created by using mirroring techniques or from a nose model database. For the conventional manual sculpting techniques, wax patterns were manually created on 3D printed full face baseplates. For analysis, the unedited facial feature was the standard. The unsigned distance was calculated from each of the several thousand vertices on the unedited facial feature to the closest point on the external surface of the prosthesis prototype. The mean absolute error was calculated, and a Friedman test was performed (α=.05). RESULTS: The median mean absolute error was 1.13 mm for the 3DMM group, 1.54 mm for the traditional CAD group, and 1.49 mm for the manual sculpting group, with no statistically significant differences among groups (P=.549). Boxplots showed substantial differences in the distribution of mean absolute error among groups, with the 3DMM group showing the greatest consistency. The 3DMM approach produced repeat designs with the lowest coefficient of variation. CONCLUSIONS: The 3DMM approach shows potential as a semi-automated method of CAD. Further clinical research is planned to explore the 3DMM approach in a feasibility trial.

IMproving facial PRosthesis construction with contactlESs Scanning and Digital workflow (IMPRESSeD): study protocol for a feasibility crossover randomised controlled trial of digital versus conventional manufacture of facial prostheses in patients with orbital or nasal facial defects.

BACKGROUND: Facial prostheses can have a profound impact on patients' appearance, function and quality of life. There has been increasing interest in the digital manufacturing of facial prostheses which may offer many benefits to patients and healthcare services compared with conventional manufacturing processes. Most facial prosthesis research has adopted observational study designs with very few randomised controlled trials (RCTs) documented. There is a clear need for a well-designed RCT to compare the clinical and cost-effectiveness of digitally manufactured facial prostheses versus conventionally manufactured facial prostheses. This study protocol describes the planned conduct of a feasibility RCT which aims to address this knowledge gap and determine whether it is feasible to conduct a future definitive RCT. METHODS: The IMPRESSeD study is a multi-centre, 2-arm, crossover, feasibility RCT with early health technology assessment and qualitative research. Up to 30 participants with acquired orbital or nasal defects will be recruited from the Maxillofacial Prosthetic Departments of participating NHS hospitals. All trial participants will receive 2 new facial prostheses manufactured using digital and conventional manufacturing methods. The order of receiving the facial prostheses will be allocated centrally using minimisation. The 2 prostheses will be made in tandem and marked with a colour label to mask the manufacturing method to the participants. Participants will be reviewed 4 weeks following the delivery of the first prosthesis and 4 weeks following the delivery of the second prosthesis. Primary feasibility outcomes include eligibility, recruitment, conversion, and attrition rates. Data will also be collected on patient preference, quality of life and resource use from the healthcare perspective. A qualitative sub-study will evaluate patients' perception, lived experience and preference of the different manufacturing methods. DISCUSSION: There is uncertainty regarding the best method of manufacturing facial prostheses in terms of clinical effectiveness, cost-effectiveness and patient acceptability. There is a need for a well-designed RCT to compare digital and conventional manufacturing of facial prostheses to better inform clinical practice. The feasibility study will evaluate key parameters needed to design a definitive trial and will incorporate early health technology assessment and a qualitative sub-study to identify the potential benefits of further research. TRIAL REGISTRATION: ISRCTN ISRCTN10516986). Prospectively registered on 08 June 2021,  https://www.isrctn.com/ISRCTN10516986 .

Digital database for nasal prosthesis design with a 3D morphable face model approach.

Designing nasal prostheses can be challenging because of the unpaired nature of the facial feature, especially in patients lacking preoperative information. Various nose model databases have been developed as a helpful starting point for the computer-aided design of nasal prostheses, but these do not appear to be readily accessible. Therefore, an open-access digital database of nose models has been generated based on a 3-dimensional (3D) morphable face model approach. This article describes the generation of the database, highlights steps for designing a nasal prosthesis, and points readers to the database for future clinical application and research.

Pilot study assessing 3D-printed teeth as a caries removal teaching tool.

INTRODUCTION: In UK universities, caries removal teaching utilises plastic teeth. This format does not enable students to learn how to distinguish between tooth layers and caries via tactile feedback. The aim of this study was to assess the applicability of a novel, 3D-printed carious tooth within caries removal teaching. MATERIALS AND METHODS: Single-material 3D-printed teeth containing simulated tactile caries were developed and 14 final-year undergraduates were briefed to remove caries and minimise damage to healthy tissue within the tooth. Students completed evaluation questionnaires for their opinion of 3D-printed teeth in comparison to plastic teeth and perceived confidence to subsequently treat patients. Cavity preparation perimeters were measured, using photographs with a standard protocol. Heat map analysis illustrated variation in location and extent of cavity preparations produced by the cohort. RESULTS: Student feedback indicated the 3D-printed caries exercise was positively received, 71.4% agreed 3D-printed teeth would have better prepared students for patient treatment; 78.6% rated their preclinical stress/anxiety as 'very high' or 'high' and 57.1% agreed that if preclinical teaching incorporated 3D-printed teeth, their stress/anxiety when treating their first caries patient would have been reduced. The average perimeter of cavity preparation indicated relative variation, with a maximum perimeter of 19.6 mm and a minimum of 10.7 mm, and a range of 8.9 mm. DISCUSSION: Introducing 3D-printed teeth into preclinical teaching would allow students to gain confidence in clinically relevant experience in tactile aspects of caries treatment earlier in their training than currently possible. CONCLUSION: This study demonstrates student acceptance of an alternative caries removal teaching method, with potential to increase aptitude in caries removal in a clinically relevant manner.

Outcome measures in facial prosthesis research: A systematic review.

STATEMENT OF PROBLEM: Facial prosthesis research uses a wide variety of outcome measures, which results in challenges when comparing the effectiveness of interventions among studies. Consensus is lacking regarding the most appropriate and meaningful outcome measures to use in facial prosthesis research to capture important perspectives. PURPOSE: The purpose of the systematic review was to identify and synthesize outcome measures used in facial prosthesis research. MATERIAL AND METHODS: Electronic searches were performed in 11 databases (including nonpeer-reviewed literature). The citations were searched, and expert societies were contacted to identify additional studies. Inclusion criteria comprised studies of participants with facial defects who required or had received prosthetic rehabilitation with an external facial prosthesis. Exclusion criteria comprised participants with ocular prostheses, case reports, case series with fewer than 5 participants, laboratory-based studies, and studies published before 1980. Study selection was performed independently by 2 reviewers. Discrepancies were resolved through discussion or by a third reviewer. Outcome measures were synthesized with a categorization approach based on the perspective, theme, and subtheme of the outcome measures. Quality assessment was performed with an appraisal tool that enabled evaluation of studies with diverse designs. RESULTS: Database searching identified 13 058 records, and 7406 remained after duplications were removed. After initial screening, 189 potentially relevant records remained, and 186 full texts were located (98% retrieval rate). After full-text screening, 124 records were excluded. Citation searches and contact with expert societies identified 4 further records. In total, 69 articles (grouped into 65 studies) were included. Studies were categorized as per the perspective of their outcome measures, with the following findings: patient-reported (74% of studies), clinical indicators (34%), clinician-reported (8%), multiple viewpoints (6%), and independent observer-reported (3%). Patient-reported outcome measures included tools to assess satisfaction, quality of life, and psychologic health. Variability in the choice of outcome measures was evident among the studies, with many self-designed, unvalidated, condition-specific questionnaires reported. A greater number of outcome measure themes emerged over time; themes such as service delivery and health state utility have recently been evaluated. CONCLUSIONS: Over the past 40 years, facial prosthesis research has focused on patient-reported outcome measures. Outcome measures relating to other perspectives have been used less frequently, although new themes appear to be emerging in the literature. Future research should use outcome measures with appropriate measurement properties for use with facial prosthetics.

Accuracy of capturing oncology facial defects with multimodal image fusion versus laser scanning.

STATEMENT OF PROBLEM: Fabrication of conventional facial prostheses is a labor-intensive process which traditionally requires an impression of the facial defect and surrounding tissues. Inaccuracies occur during the facial moulage because of soft-tissue compression, the patient's reflex movements, or the lack of support for the impression material. A variety of 3D imaging techniques have been introduced during the production of facial prostheses. However, the accuracy of the different imaging techniques has not been evaluated sufficiently in this clinical context. PURPOSE: The purpose of this in vitro study was to compare the difference in accuracy of capturing oncology facial defects with multimodal image fusion and laser scanning against a cone beam computed tomography (CBCT) reference scan. MATERIAL AND METHODS: Ten gypsum casts of oncology facial defects were acquired. To produce reference models, a 3D volumetric scan was obtained using a CBCT scanner and converted into surface data using open-source medical segmentation software. This model was cropped to produce a CBCT mask using an open-source system for editing meshes. The multimodal image fusion model was created using stereophotogrammetry to capture the external facial features and a custom optical structured light scanner to record the defect. The gypsum casts were also scanned using a commercial 3D laser scanner to create the laser-scanned model. Analysis of the best fit of each experimental model to the CBCT mask was performed in MeshLab. The unsigned mean distance was used to measure the absolute deviation of each model from the CBCT mask. A paired-samples t test was conducted to compare the mean global deviation of the 2 imaging modalities from the CBCT masks (α=.05). RESULTS: A statistically significant difference was found in the mean global deviation between the multimodal imaging model (220 ±50 µm) and the laser-scanned model (170 ±70 µm); (t(9)=2.56, P=.031). The color error maps illustrated that the greatest error was located at sites distant to the prosthesis margins. CONCLUSIONS: The laser-scanned models were more accurate; however, the mean difference of 50 µm is unlikely to be clinically significant. The laser scanner had limited viewing angles and a longer scan time which may limit its transferability to maxillofacial practice.

An in-vitro study to assess the feasibility, validity and precision of capturing oncology facial defects with multimodal image fusion.

AIM: Assess the feasibility, validity and precision of multimodal image fusion to capture oncology facial defects based on plaster casts. METHODS: Ten casts of oncology facial defects were acquired. To create gold standard models, a 3D volumetric scan of each cast was obtained with a cone beam computed tomography (CBCT) scanner (NewTomVG). This was converted into surface data using open-source medical segmentation software and cropped to produce a CBCT mask using an open-source system for editing meshes. For the experimental model, the external facial features were captured using stereophotogrammetry (DI4D) and the defect was recorded with a custom optical structured light scanner. The two meshes were aligned, merged and resurfaced using MeshLab to produce a fused model. Analysis was performed in MeshLab on the best fit of the fused model to the CBCT mask. The unsigned mean distance was used to measure the absolute deviation of each model from the CBCT mask. To assess the precision of the technique, the process of producing the fused model was repeated to create five models each for the casts representing the best, middle and worst results. RESULTS: Global mean deviation was 0.22 mm (standard deviation 0.05 mm). The precision of the method appeared to be acceptable although there was variability in the location of the error for the worst cast. CONCLUSION: This method for merging two independent scans to produce a fused model shows strong potential as an accurate and repeatable method of capturing facial defects. Further research is required to explore its clinical use.

Translucent zirconia in the ceramic scenario for monolithic restorations: A flexural strength and translucency comparison test.

OBJECTIVE: To compare three different compositions of Yttria-Tetragonal Zirconia Polycrystal (Y-TZP) ceramic and a lithium disilicate ceramic in terms of flexural strength and translucency. METHODS: Three zirconia materials of different composition and translucency, Aadva ST [ST], Aadva EI [EI] and Aadva NT [NT](GC Tech, Leuven, Belgium) were cut with a slow speed diamond saw into beams and tabs in order to obtain, after sintering, dimensions of 1.2×4.0×15.0mm and 15.0×15.0×1.0mm respectively. Blocks of IPS e.max CAD LT were cut and crystallized in the same shapes and dimensions and used as a reference group [LD]. Beams (n=15) were tested in a universal testing machine for three-point bending strength. Critical fracture load was recorded in N, flexural strength (σ in MPa), Weibull modulus (m) and Weibull characteristic strength (σ0 in MPa) were then calculated. Tabs (n=10) were measured with a spectrophotometer equipped with an integrating sphere. Contrast Ratios were calculated as CR=Yb/Yw. SEM of thermally etched samples coupled with lineal line analysis (n=6) was used to measure the tested zirconia grain size. Data were statistically analyzed. RESULTS: Differences in translucency, flexural strength and grain size were found to be statistically significant. CR increased and flexural strength decreased in the following order ST(σ 1215±190MPa, CR 0.74±0.01)>EI(σ 983±182MPa, CR 0.69±0.01)>NT(σ 539±66MPa, CR 0.65±0.01)>LD (σ 377±39Mpa, CR 0.56±0.02). The average grain size was different for the three zirconia samples with NT(558±38nm)>ST(445±34nm)>EI(284±11nm). CONCLUSIONS: The zirconia composition heavily influenced both the flexural strength and the translucency. Different percentages of Yittria and Alumina result in new materials with intermediate properties in between the conventional zirconia and lithium disilicate. Clinical indications for Zirconia Aadva NT should be limited up to three-unit span bridges.