The role of non-contact digitizer in geometrical evaluation of mandibular prostheses effect on facial asymmetry of mandibulectomy patients

Purpose: This study sought to geometrically evaluate the effect of a mandibular prosthesis on facial asymmetry in patients with one of two different types of mandibulectomy defect. Methods: Facial data from 20 participants (9 men and 11 women; mean age 68 years) with either a reconstructed segmental defect (segmental group,n = 10) or a marginal mandibulectomy defect (marginal group, n =10) were acquired with a non-contact three-dimensional (3D) digitizer. Facial asymmetry was evaluated by superimposing a facial scan onto its mirror scan using 3D evaluation software. Facial scans with and without the mandibular prosthesis in place were also superimposed to evaluate the effect of the mandibular prosthesis. Results: Facial asymmetry differed significantly between subjects with and without the prosthesis in the segmental group (P = 0.005) but not in the marginal group (P = 0.16). There was no significant difference in the effect of the prosthesis on facial appearance between the two groups (P = 0.052). The ratio of 3D deviation of facial asymmetry without the prosthesis and in the mirror scan with the prosthesis differed significantly between the two groups (P = 0.01). Conclusions: Placement of a mandibular prosthesis has a notable effect on facial asymmetry in patients with segmental mandibulectomy defects

Use of Digital Technologies in Maxillofacial Prosthetics in Japan

Purpose: This study investigated the use of digital technology in maxillofacial prosthetics among practitioners involved in maxillofacial prosthetic rehabilitation in Japan.Materials and Methods: A self-administered survey questionnaire with 24 closed-ended and multiple choice questions was used. A total of 300 questionnaires were distributed at the 32nd meeting of the Japanese Academy of Maxillofacial Prosthetics that was held in Tokyo, Japan in June 2015. The survey questionnaire was distributed in a pack that included an introduction letter explaining the research aims, objectives, and informed consent. The data obtained were analyzed by descriptive statistical methods and reported as frequency and range.Results: In total, 105 respondents (77 men (73.4%), 28 women (26.6%); median age, 40 years; age range 21-66 years) completed the questionnaire (response rate, 35%). The majority of respondents were dentists (75.2%), followed by dental technicians (21.9%). The median duration of work experience for the respondents in their specialty was 14 years, and 97% of respondents had interested and adopted digital technologies in maxillofacial prosthetics. Digital technologies were used significantly in patient and practice management, diagnostic, and patient's defect visualization (p < 0.001) but insignificant in treatment planning (p = 0.917). In contrast, there were significant increases in non-use of digital technologies in prosthesis design, prosthesis manufacturing, and patient and prosthesis evaluation (p < 0.001).Conclusion: Japanese dental practitioners are interested and willing to use digital technology in maxillofacial prosthetics. Most respondents use some or a substantial number of digital technologies in clinical practice. (Int J Maxillofac Prosthetics 2021;4:25-36

Effect of triangular mesh resolution on the geometrical trueness of segmented CBCT maxillofacial data into STL format.

OBJECTIVES To determine the optimal level of mesh reduction that would maintain acceptable levels of geometrical trueness while also minimizing the impact on other parameters such as file size and processing time. METHODS AND METHODS Intraoral and extraoral maxillofacial defects were created on 8 cadaver heads and scanned by using a CBCT scanner (NewTom 3D Imaging, Verona). DICOM data were segmented to produce head (n=8) and skull models (n=8) saved as standard tessellation language (STL) files. A further processing of head models was preformed to produce face (n=8) and ear models (n=8). A mesh reduction process was performed for each STL model (reference, R0) by generating 50% (R1), 75% (R2), and 90% (R3) reductions. The 3 datasets were compared to the R0 file using 3D evaluation software (GOM Inspect) using a global best-fit algorithm, to calculate the root mean square (RMS) deviations. Statistical analyses were performed at a level of significance of α=0.05. RESULTS There was no 3D deviation after the 50% triangular mesh reduction in the 4 datasets. Minor 3D deviations were observed after 75% reduction, in all groups. After 90% reduction, higher 3D deviations were observed, and especially in head and skull. Statistically significant increase in 3D deviations was observed with higher degrees of mesh reduction (p < 0.001). CONCLUSION The resolution of CBCT-based maxillofacial defect models can be reduced up to 50%, with neglectable concern to inaccuracy. CLINICAL SIGNIFICANCE Accurate maxillofacial models can be obtained from CBCT DICOM files after segmentation and export as STL files, even when the mesh resolution is reduced up to 50%. This information can be valuable for practitioners and researchers working with 3D models of maxillofacial defects

Triangular mesh reduction of digitized maxillectomy defects for prosthetic rehabilitation: A 3D deviation study.

OBJECTIVES To evaluate the effect of different amounts of triangular mesh reduction on the trueness of digitized complete-arch dentate and edentulous maxillectomy defects models. MATERIAL AND METHODS Twenty gypsum maxillectomy defect models (dentate and edentate group: n=10) were digitized using the Trios 3 intraoral scanner, scanning the teeth, mucosa and maxillectomy defect. These datasets (reference, R0) were saved as standard tessellation language (STL) files, and triangular mesh reduction was performed using Meshmixer's reduction tool. Digital test-datasets with file sizes reduced by 50%(R1), 75%(R2), and 90%(R3) were generated (each: n=20). Each test-dataset was compared to the R0 file using 3D evaluation software (GOM Inspect), applying automated pre-alignment followed by a global best-fit alignment, and root mean square (RMS) 3-dimensional (3D) deviations were calculated. Statistical analyses were performed, at a level of significance of α=0.05. RESULTS The number of triangles, and STL file size were synchronized with each other and inversely proportional to the amount of mesh reduction. The resulting mean percentages of the STL file sizes were 50.00% for R1, 24.93% for R2, and 10.00% for R3. There were no 3D deviations at 50% triangular mesh reduction. The 3D deviations increased with the amount of mesh reduction: at 75% reduction the median deviations were lower (dentate:0.0016mm, IQR:0.0015-0.0018; edentate:0.0016mm, IQR:0.0015-0.0016), than at 90% (dentate:0.004mm, IQR:0.0038-0.0041; edentate:0.003mm, IQR:0.0036-0.0039). A statistically significant increase in 3D deviations was observed with higher degrees of mesh reduction (p<0.001). CONCLUSIONS Triangular mesh reduction results in a significant increase in 3D deviations if the reduction is more than 75%. CLINICAL SIGNIFICANCE Digital models of patients with maxillectomy defects can be saved with a mesh reduction of 50% without affecting the trueness. The use of a 50% mesh reduction decreases the required storage capacity by 50%