To investigate how the stress distribution and forces transmitted from orthodontic aligners to the tooth surface are affected by the geometry and extension of the trimming line. Thirty-six aligners were thermoformed from Zendura FLX sheets (0.75 mm thick) and divided into four groups based on the design of the trimming line: Scalloped, Scalloped extended, Straight and Straight extended. Fuji pressure-sensitive films were used for pressure measurement. The pressurized films were scanned and evaluated. Pressures and forces were measured over the entire facial surface of an upper right central incisor (Tooth 11) and at 7 different locations [cervical, middle, incisal, mesio-incisal, mesio-cervical, disto-incisal, and disto-cervical]. In addition, the thickness of the aligners at these 7 sites was measured with a digital caliper. The active force ranged from (2.2 to 6.9) N, and the average pressure was (1.6-2.7) MPa. The highest values were recorded for the (straight extended) design, while the lowest values were recorded for the scalloped design. The forces and stresses were not uniformly distributed over the surface. When the values in each area were compared separately, significant differences were found between the different designs in the cervical area, with the scalloped design transmitting the lowest cervical forces. Aligner thickness was drastically reduced (60-75% thinning) over the entire tooth surface after thermoforming. The straight extended design of aligner's trimming line exhibited more uniform force transfer and stress distribution across the surface than the other designs. The trimming line design could have a significant impact on the clinical outcome of orthodontic aligner treatment.

Objectives: To use the finite element method (FEM) to investigate the effect of various attachment configurations and trimming line designs of orthodontic aligners on their biomechanical performance.Method: A 3D upper jaw model was imported into 3D design software. The upper right central incisor tooth (Tooth 11) was made mobile, and its periodontal ligament (PDL) and bone structures were designed. Aligners were modelled with three distinct attachment configurations: No attachment, rectangular horizontal, rectangular vertical, and two trimming line designs; scalloped and straight extended, with a homogeneous thickness of 0.6 mm. These models were then imported into an FE software. Simulations were conducted for three different movements, including facial translation, distalization, and extrusion.Results: Forces were recorded at 1.3–2.6 N during facial translation, 1.4–5.9 N in distalization, and 0.0–2.0 N in extrusion. The straight extended trimming line consistently generated higher forces than the scalloped design. Attachments had no significant impact on force components during facial translation but were more effective in distalization and extrusion. The combination of a straight extended trimming line with horizontal attachments exhibited the least stresses at the apical third during distalization, and the highest stresses during extrusion, suggesting superior retention.Conclusions: Rectangular attachments offer limited benefits in facial translation, but horizontal rectangular attachments can intensify load in distalization and are crucial for force generation in extrusion. Horizontal attachments are preferred over vertical options. Additionally, the straight extended trim line enhances control of tooth movement and can replace attachments in certain cases.Clinical Relevance: These findings provide biomechanical evidence and an optimal protocol to guide clinical practice in planning diverse teeth movements. The emphasis is on the influence of attachment utilization and the specific design of aligner trimming lines to enhance control over tooth movement.

This research aims to investigate the influence of model height employed in the deep drawing of orthodontic aligner sheets on force transmission and aligner thickness. Forty aligner sheets (Zendura FLX) were thermoformed over four models of varying heights (15, 20, 25, and 30 mm). Normal contact force generated on the facial surface of the upper right central incisor (Tooth 11) was measured using pressure-sensitive films. Aligner thickness around Tooth 11 was measured at five points. A digital caliper and a micro-computed tomography (µ-CT) were employed for thickness measurements. The normal contact force exhibited an uneven distribution across the facial surface of Tooth 11. Model 15 displayed the highest force (88.9 ± 23.2 N), while Model 30 exhibited the lowest (45.7 ± 15.8 N). The force distribution was more favorable for bodily movement with Model 15. Thickness measurements revealed substantial thinning of the aligner after thermoforming. This thinning was most pronounced at the incisal edge (50% of the original thickness) and least at the gingivo-facial part (85%). Additionally, there was a progressive reduction in aligner thickness with increasing model height, which was most significant on the facial tooth surfaces. We conclude that the thermoplastic aligner sheets undergo substantial thinning during the thermoforming process, which becomes more pronounced as the height of the model increases. As a result, there is a decrease in both overall and localized force transmission, which could lead to increased tipping by the aligner and a diminished ability to achieve bodily movement.

To evaluate the biomechanical performance of various designs of cantilevered three-unit implant-supported prostheses, using two distinct prosthetic materials and under different loading conditions. Three mandibular models were created with varying implant positions to support a 3-unit prosthesis using two materials (Zirconia and PEKK), resulting in three different designs: distal cantilever (M1), fixed-fixed (M2), and mesial cantilever (M3). The geometric model was created by segmenting a CBCT scan of an edentulous mandible using Mimics software, followed by refinement in 3-Matic to generate a trabecular bone core encased by a 2 mm-thick cortical shell and a 1 mm-thick mucosal layer. Implant CAD files were integrated, and the models were processed in SolidWorks to finalize solid geometries. These were then imported into ANSYS for mesh generation and finite element analysis, with materials assumed to be isotropic and elastic. Models underwent 3 different static loading protocols (Vertical 100 N, 30° Oblique 50 N, 45° Oblique 50 N). Von Mises stress and total deformation were calculated. Model 2 demonstrated the best performance. Under vertical loading, PEKK prostheses showed lower stress than zirconia in the prosthetic body (10-45 %) and the cortical bone (3-40 %), but higher stresses in the implant (4-10 %). Compared to vertical loading, oblique loading generated higher stress but remained within a safe range without compromising function. The fixed-fixed design showed optimal biomechanical performance. The mesial cantilever was more favorable than the distal for stress distribution. Zirconia provided superior stress dissipation, while PEKK showed reduced stress in the prosthetic body but increased stress I the implant and bone. The study provides prosthodontists with evidence recommending design and materials for 3-unit implant-supported prostheses. Zirconia is ideal for cantilevered designs, resisting high bending forces and minimizing implant stress, while PEKK is more suitable for fixed-fixed designs with lower stress levels.