A method based on 3D affine alignment for the quantification of palatal expansion

Divergence between CBCT and Optical Scans for Soft Tissue Analysis and Cephalometry in Facial Imaging: A cross-sectional study on healthy adults

BACKGROUND

Facial soft tissue analysis is becoming increasingly emphasized in orthodontic diagnosis and treatment planning. While traditional cephalometry primarily focuses on hard tissues, recent non-invasive imaging techniques offer the potential to comprehensively evaluate three-dimensional (3D) facial soft tissues. The aim of the study was to establish the geometrical 3D and cephalometric divergence between Cone Beam Computed Tomography (CBCT) derived images and scanned soft tissues. Crucial for enhancing orthodontic diagnosis, minimizing patient exposure to ionizing radiation and providing facial cephalometric parameters.

MATERIAL AND METHODS

A cross-sectional study was conducted from January 2020 to May 2023. CBCT and 3D facial scans were obtained simultaneously using a specialized imaging system. Reproducible landmark points were selected for both cephalometric and soft tissue analysis. Angular and linear measurements were recorded, and correlations between CT and facial scans were statistically assessed.

RESULTS

Comparisons between 10 CBCT-derived and 10 facial scan-based soft tissue representations resulted into 1.8mm mean root median square (RMS). Angular measurements, such as ANB, right gonial angle, and left gonial angle, exhibited a 0.9° of difference with their respective soft tissue variables. In contrast, linear measurements of total anterior facial height showed a lower correlation coefficient, equal to 0.51. The correlation between soft tissues and underlying hard tissues was more pronounced for gonial angles.

CONCLUSION

Facial soft tissue analysis using either 3D facial scans or CBCT-derived offers similar results for orthodontic diagnosis and treatment planning. These findings support the use of non-invasive diagnostic tools in orthodontics, although further investigations are needed to comprehensively understand the complexity of hard and soft tissue relationships.

An in vitro comparison of the dimensional stability of four 3D-printed models under various storage conditions

OBJECTIVES

To investigate the dimensional stability of various 3D-printed models derived from resin and plant-based, biodegradable plastics (PLA) under specific storage conditions for a period of up to 21 weeks.

MATERIALS AND METHODS

Four different printing materials, including Draft V2, study model 2, and Ortho model OD01 resins as well as PLA mineral, were evaluated over a 21-week period. Eighty 3D-printed models were divided equally into two groups, with one group stored in darkness and the other exposed to daylight. All models were stored at a constant room temperature (20°C). Measurements were taken at 7-week intervals using the Inspect 3D module in OnyxCeph software (Image Instruments GmbH, Chemnitz, Germany).

RESULTS

Dimensional change was noted for all of the models with shrinkage of up to 0.26 mm over the study period. Most contraction occured from baseline to T1, although significant further contraction also arose from T1 to T2 (P < .001) and T1 to T3 (P < .001). More shrinkage was observed when exposed to daylight overall and for each resin type (P < .01). The least shrinkage was noted with Ortho model OD01 resin (0.16 mm, SD = 0.06), and the highest level of shrinkage was observed for Draft V2 resin (0.23 mm, SD = 0.06; P < .001).

CONCLUSIONS

Shrinkage of 3D-printed models is pervasive, arising regardless of the material used (PLA or resin) and being independent of the brand or storage conditions. Consequently, immediate utilization of 3D printing for orthodontic appliance purposes may be preferable, with prolonged storage risking the manufacture of inaccurate orthodontic retainers and appliances.

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

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.