Lever arm on bracket vs. lever arm on archwire: A 3D finite element method study of mechanics of miniscrew-supported lingual en-masse retraction of maxillary anterior teeth.

OBJECTIVE: To compare the deformation of the main archwire and 3D movements of maxillary anterior teeth during miniscrew-supported en-masse retraction with the lever arm on the archwire and on the brackets in lingual orthodontic treatment in finite element analysis (FEM) simulation. MATERIAL AND METHODS: A 3D dental-alveolar model with bonded 0.018×0.025-inch slot lingual brackets and a 0.017×0.025-inch dimension stainless-steel archwire was created. Four FEM models were created based on a 3D dental-alveolar model: in Models A and C, the lever arms were attached to the lingual bracket, while in Models B and D, the lever arms were attached to the archwire. Meanwhile, in Models A and B, the miniscrews were placed in between the molars, while in Models C and D, the miniscrews were positioned on the palatal roof. After a 1.5N retraction force was applied from the miniscrew to the end of the lever arm, the initial movements in the sagittal, transversal, and vertical planes were recorded and analysed for maxillary anterior teeth. RESULTS: In Models B and D, smaller deformation of the main archwire and less prominent bowing effect were noticed in both sagittal and vertical directions compared to their counter groups. In Models C and D, the central incisors showed less torque loss in the sagittal direction and more canine intrusion vertically. CONCLUSIONS: For the same lever arm-miniscrew retraction configuration, the lever arm on the bracket showed less deformation of the main archwire and more body movement of the teeth than the lever arm on the archwire group. With the same level arm height, the transverse and vertical bowing effect is reduced when the lever arm was placed distal to the central incisor and the miniscrews placed next to the palatal suture.

3D-printed porous condylar prosthesis for temporomandibular joint replacement: Design and biomechanical analysis.

BACKGROUND: Customized prosthetic joint replacements have crucial applications in severe temporomandibular joint problems, and the combined use of porous titanium scaffold is a potential method to rehabilitate the patients. OBJECTIVE: The objective of the study was to develop a design method to obtain a titanium alloy porous condylar prosthesis with good function and esthetic outcomes for mandibular reconstruction. METHODS: A 3D virtual mandibular model was created from CBCT data. A condylar defect model was subsequently created by virtual condylectomy on the initial mandibular model. The segmented condylar defect model was reconstructed by either solid or porous condyle with a fixation plate. The porous condyle was created by a density-driven modeling scheme with an inhomogeneous tetrahedral lattice structure. The porous condyle, supporting fixation plate, and screw locations were topologically optimized. Biomechanical behaviors of porous and solid condylar prostheses made of Ti-6Al-4V alloy were compared. Finite element analysis (FEA) was used to evaluate maximum stress distribution on both prostheses and the remaining mandibular ramus. RESULTS: The FEA results showed levels of maximum stresses were 6.6%, 36.4% and 47.8% less for the porous model compared to the solid model for LCI, LRM, and LBM loading conditions. Compared to the solid prosthesis, the porous prosthesis had a weight reduction of 57.7% and the volume of porosity of the porous condyle was 65% after the topological optimization process. CONCLUSIONS: A custom-made porous condylar prosthesis with fixation plate was designed in this study. The 3D printed Ti-6Al-4V porous condylar prosthesis had reduced weight and effective modulus of elasticity close to that of cortical bone. The.

Biomechanical behavior of mandible with posterior marginal resection using finite element analysis.

This study aims to characterize biomechanical behavior of various designs of posterior mandibular marginal resection under functional loadings using finite element method. The ultimate goal of this work is to provide clinically relevant information to prevent postoperative fracture and to stipulate prophylactic internal fixation for planning of marginal mandibulectomy. A 3D mandibular master model was reconstructed from cone beam computed tomography images. Different marginal resection models were created based on three design parameters, namely, defect curvilinear radius, anterior-posterior defect width and residual height of the mandibular body. Functional loadings from incisors (60 N) and contralateral first molar area (200 N) were applied to designed models and stress patterns were compared of five groups with curvilinear radius from 0 (conventional rectangular shape), 2.5, 3.5, 5, and 6 mm. Models with 25, 35 and 45 mm defect width mimic defects varied from canine to 3rd molar were tested. Residual height range from 10 to 4 mm was assessed. The results show high stresses predominated in the occlusal area and the posterior inferior border near the resection corner. The average maximum stress decreased by 29.8% (r = 2.5 mm), 51.9% (r = 3.5 mm), 54.4% (r = 5 mm), and 59.3% (r = 6 mm) compared to the baseline of r = 0 mm. The results from the combined defect width/residual height models demonstrate the increase of defect width and the decrease in residual height resulted in the increase of maximum stress. Our data also confirm that the factor of residual height supersedes defect width in terms of prevention of postoperative fracture when considering resection design.

Evaluation of a custom-designed human-robot collaboration control system for dental implant robot.

BACKGROUND: The purpose of this study is to develop a methodology to better control a human-robot collaboration for robotic dental implant placement. We have designed a human-robot collaborative implant system (HRCDIS) which is based on a zero-force hand-guiding concept and a operational task management workflow that can achieve highly accurate and stable osteotomy drilling based on a surgeon's decision and robotic arm movements during implant surgery. METHOD: The HRCDIS brings forth the robot arm positions, exact drilling location, direction and performs automatic drilling. The HRCDIS can also avoid complex programing in the robot. The purpose of the study is to evaluate the accuracy of drilling resulting from our developed operational task management method (OTMM). The OTMM can enable the robot to switch, pause, and resume drilling tasks. The force required for hand-guiding in a zero-force control mode of the robot was detected by a 6D force sensor. We compared our force data to those provided by the manufacturer's manual. The study was conducted on a phantom head with a 3D-printed jaw bone to verify the validity of our HRCDIS. We appraised the discrepancies between free-hand drillings and the HRCDIS controlled drillings at apical centre and head centre of the implant and implant angulation to the baseline data from a virtual surgical planning model. RESULTS: The average required force used by hand-guiding to operate the robot with HRCDIS was near 7 Newton which is much less than the manufacturer's specification (30 Newton). The results from our study showed that the average error at implant head was 1.04 ± 0.37 mm, 1.56 ± 0.52 mm at the implant apex, and deviation of implant angle was 3.74 ± 0.67°. CONCLUSIONS: The results from this study validate the merit of the human-robot collaboration control by the HRCDIS. Based on the improved navigation system using HRCDIS, a robotic implant placement can provide seamless drilling with ease, efficiency and accuracy.

Biomechanical and Mechanostat analysis of a titanium layered porous implant for mandibular reconstruction: The effect of the topology optimization design.

A porous scaffold/implant is considered a potential method to repair bone defects, but its mechanical stability and biomechanics during the repair process are not yet clear. A mandibular titanium implant was proposed and designed with layered porous structures similar to that of the bone tissue, both in structure and mechanical properties. Topology was used to optimize the design of the porous implant and fixed structure. The finite element analysis was combined with bone "Mechanostat" theory to evaluate the stress and osteogenic property of the layered porous implant with 3 different fixation layouts (Model I with 4 screws, Model II with 5 screws and Model III with 6 screws) for mandibular reconstruction. The results showed that Model III could effectively reduce the stress shielding effect, stress within the optimized implant, defective mandible, and screws were respectively dropped 48.18%, 44.23%, and 57.27% compared to Model I, and the porous implant had a significant stress transmission effect and maintained the same stress distribution as the intact mandible after the mandibular defect was repaired. The porous implant also showed a significant mechanical stimulation effect on the growth and healing of the bone tissue according to the bone "Mechanostat" theory. The combination of porous structure with the topology technique is a promising option to improve the mechanical stability and osteogenesis of the implant, and could provide a new solution for mandibular reconstruction.

Experimental validation of finite element simulation of a new custom-designed fixation plate to treat mandibular angle fracture.

BACKGROUND: The objective of the study was to validate biomechanical characteristics of a 3D-printed, novel-designated fixation plate for treating mandibular angle fracture, and compare it with two commonly used fixation plates by finite element (FE) simulations and experimental testing. METHODS: A 3D virtual mandible was created from a patient's CT images as the master model. A custom-designed plate and two commonly used fixation plates were reconstructed onto the master model for FE simulations. Modeling of angle fracture, simulation of muscles of mastication, and defining of boundary conditions were integrated into the theoretical model. Strain levels during different loading conditions were analyzed using a finite element method (FEM). For mechanical test design, samples of the virtual mandible with angle fracture and the custom-designed fixation plates were printed using selective laser sintering (SLS) and selective laser melting (SLM) printing methods. Experimental data were collected from a testing platform with attached strain gauges to the mandible and the plates at different 10 locations during mechanical tests. Simulation of muscle forces and temporomandibular joint conditions were built into the physical models to improve the accuracy of clinical conditions. The experimental vs the theoretical data collected at the 10 locations were compared, and the correlation coefficient was calculated. RESULTS: The results show that use of the novel-designated fixation plate has significant mechanical advantages compared to the two commonly used fixation plates. The results of measured strains at each location show a very high correlation between the physical model and the virtual mandible of their biomechanical behaviors under simulated occlusal loading conditions when treating angle fracture of the mandible. CONCLUSIONS: Based on the results from our study, we validate the accuracy of our computational model which allows us to use it for future clinical applications under more sophisticated biomechanical simulations and testing.

Accuracy of dental implant surgery with robotic position feedback and registration algorithm: An in-vitro study.

BACKGROUND: The purpose of this study was to develop and validate a positioning method with hand-guiding and contact position feedback of robot based on a human-robot collaborative dental implant system (HRCDIS) for robotic guided dental implant surgery. METHODS: An HRCDIS was developed based on a light-weight cooperative robot arm, UR5. A three-dimensional (3D) virtual partially edentulous mandibular bone was reconstructed using the cone bone computed tomography images. After designing the preoperative virtual implant planning using the computer software, a fixation guide worn on teeth for linking and fixing positioning marker was fabricated by 3D printing. The fixation guide with the positioning marker and a resin model mimicking the oral tissues were assembled on a head phantom. The planned implant positions were derived by the coordinate information of the positioning marker. The drilling process using the HRCDIS was conducted after mimicking the experimental set-up and planning the drilling trajectory. Deviations between actual and planned implant positions were measured and analyzed. RESULTS: The head phantom experiments results showed that the error value of the central deviation at hex (refers to the center of the platform level of the implant) was 0.79 ± 0.17 mm, central deviation at the apex was 1.26 ± 0.27 mm, horizontal deviation at the hex was 0.61 ± 0.19 mm, horizontal deviation at the apex was 0.91 ± 0.55 mm, vertical deviation at the hex was 0.38 ± 0.17 mm, vertical deviation at the apex was 0.37 ± 0.20 mm, and angular deviation was 3.77 ± 1.57°. CONCLUSIONS: The results from this study preliminarily validate the feasibility of the accurate navigation method of the HRCDIS.

Topological optimization of 3D printed bone analog with PEKK for surgical mandibular reconstruction.

PURPOSE: The purpose of this study was to analyze mechanical behaviors of a topologically optimized and 3D-printed mandibular bone block with polyetherketoneketone (PEKK) for surgical mandibular reconstruction. MATERIALS AND METHODS: 3D virtual mandibular models were reconstructed from cone beam computed tomography images. A proposed mandibular resection of the mandibular body (40 mm anterior-posteriorly) was segmented. Internal structure of the resected bone was designed with topological optimization. Dental implants and implant-supported crowns were integrated into the design. A second 3D virtual model was created with the same size and location of the defect but was reconstructed with a fibular graft and implant-supported crowns. The biomechanical behaviors of the two models were compared by finite element method (FEM) under the same boundary constraints and three loading locations, namely, central incisors, lower left and right side first molar areas. RESULTS: The FEM results showed the maximum stresses and displacements of the topology optimized model were much lower than those of the model with fibular bone graft. The highest stress of the optimized mandibular model was located on the lower edge of the posterior border of bone analog, and fixation screws. The maximum displacement occurred at the lower edge of the proximal mandibular stump or the lower edge of the distal mandibular body on the contralateral site. Under the same three loading locations, the maximum stress of the optimized model significantly decreased by 67.9%, 71.9% and 68.6% compared to the fibular graft model. CONCLUSIONS: The 3D printed bone analog with topological optimization is patient-specific and has advantages over the conventional fibular bone graft for surgical mandibular reconstruction. The optimized PEKK bone analog model creates more normal stress-strain trajectories than the fibular graft model and likely provides better functional and cosmetic outcomes.

Bionic mechanical design and 3D printing of novel porous Ti6Al4V implants for biomedical applications.

In maxillofacial surgery, there is a significant need for the design and fabrication of porous scaffolds with customizable bionic structures and mechanical properties suitable for bone tissue engineering. In this paper, we characterize the porous Ti6Al4V implant, which is one of the most promising and attractive biomedical applications due to the similarity of its modulus to human bones. We describe the mechanical properties of this implant, which we suggest is capable of providing important biological functions for bone tissue regeneration. We characterize a novel bionic design and fabrication process for porous implants. A design concept of "reducing dimensions and designing layer by layer" was used to construct layered slice and rod-connected mesh structure (LSRCMS) implants. Porous LSRCMS implants with different parameters and porosities were fabricated by selective laser melting (SLM). Printed samples were evaluated by microstructure characterization, specific mechanical properties were analyzed by mechanical tests, and finite element analysis was used to digitally calculate the stress characteristics of the LSRCMS under loading forces. Our results show that the samples fabricated by SLM had good structure printing quality with reasonable pore sizes. The porosity, pore size, and strut thickness of manufactured samples ranged from (60.95± 0.27)% to (81.23±0.32)%, (480±28) to (685±31) µm, and (263±28) to (265±28) µm, respectively. The compression results show that the Young's modulus and the yield strength ranged from (2.23±0.03) to (6.36±0.06) GPa and (21.36±0.42) to (122.85±3.85) MPa, respectively. We also show that the Young's modulus and yield strength of the LSRCMS samples can be predicted by the Gibson-Ashby model. Further, we prove the structural stability of our novel design by finite element analysis. Our results illustrate that our novel SLM-fabricated porous Ti6Al4V scaffolds based on an LSRCMS are a promising material for bone implants, and are potentially applicable to the field of bone defect repair.

Digital design of scaffold for mandibular defect repair based on tissue engineering.

Mandibular defect occurs more frequently in recent years, and clinical repair operations via bone transplantation are difficult to be further improved due to some intrinsic flaws. Tissue engineering, which is a hot research field of biomedical engineering, provides a new direction for mandibular defect repair. As the basis and key part of tissue engineering, scaffolds have been widely and deeply studied in regards to the basic theory, as well as the principle of biomaterial, structure, design, and fabrication method. However, little research is targeted at tissue regeneration for clinic repair operations. Since mandibular bone has a special structure, rather than uniform and regular structure in existing studies, a methodology based on tissue engineering is proposed for mandibular defect repair in this paper. Key steps regarding scaffold digital design, such as external shape design and internal microstructure design directly based on triangular meshes are discussed in detail. By analyzing the theoretical model and the measured data from the test parts fabricated by rapid prototyping, the feasibility and effectiveness of the proposed methodology are properly verified. More works about mechanical and biological improvements need to be done to promote its clinical application in future.