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This study attempted to understand the biomechanics of using 3D-printed anatomical assembly thin bone plate (AATBP) and anterior star-shaped plating (ASP) under different patellar fractures. The transverse (C1), transverse plus second fragment (C2) and complex (C3) patella fractures were defined for performing the dynamic cyclic load test and finite element (FE) analysis. The AATBP was fixed onto the patella after adjusting the total fixation height using a ratchet mechanism and providing holding power hooks. The ASP contoured the plate/distal legs based on the patella surface curvature and generated an additional drill guide to avoid screw interference. The average ASP fixation fracture gaps were significantly larger than the AATBP fixation. FE analysis showed that the AATBP biomechanical performance was better than the ASP fixation for different patella fractures. The 3D-printed AATBP can be used effectively for different patella fractures without screw interference and demonstrated greater stability for comminuted patellar fractures.

Abstract Background This study aims to evaluate the optimal ratio of synthetic bone graft (SBG) material and platelet rich fibrin (PRF) mixed in a metal 3D-printed implant to enhance bone regeneration. Methods Specialized titanium hollow implants (5 mm in diameter and 6 mm in height for rabbit; 6 mm in diameter and 5 mm in height for pig) were designed and manufactured using 3D printing technology. The implants were divided into three groups and filled with different bone graft combinations, namely (1) SBG alone; (2) PRF to SBG in 1:1 ratio; (3) PRF to SBG in 2:1 ratio. These three groups were replicated tightly into each bone defect in distal femurs of rabbits (nine implants, n = 3) and femoral shafts of pigs (fifteen implants, n = 5). Animal tissue sections were obtained after euthanasia at the 8th postoperative week. The rabbit specimens were stained with analine blue, while the pig specimens were stained with Masson–Goldner’s trichrome stain to perform histologically examination. All titanium hollow implants were well anchored, except in fracture specimens (three in the rabbit and one fracture in the pig). Result Rabbit specimens under analine blue staining showed that collagen tissue increased by about 20% and 40% in the 1:1 ratio group and the 2:1 ratio group, respectively. Masson–Goldner's trichrome stain results showed that new bone growth increased by 32% in the 1:1 ratio PRF to SBG, while − 8% in the 2:1 ratio group. Conclusion This study demonstrated that placing a 1:1 ratio combination of PRF and SBG in a stabilized titanium 3D printed implant resulted in an optimal increase in bone growth.

Abstract Background Although minimally invasive surgeries have gained popularity in many orthopaedic fields, minimally invasive approaches for diaphyseal clavicular fracture have not been widely performed, which is attributed to difficulties in performing a closed reduction of fracture deformities of a curved bone in a three-dimensional space. The goal of this study was to investigate the radiographic parameters of fracture deformities in a three-dimensional space and to identify the risk factors for deformities. Methods The computed tomography images of 100 patients who sustained a clavicle fracture were included. Five parameters were used to analyze the deformities: change in clavicle length, fracture displacement, and fragment rotation around the X, Y, Z axes. The change in length was assessed using the length of the endpoint line. The displacement was assessed using the distance between the fracture midpoints. The rotation deformities were assessed using the Euler angles. The correlation between the parameters was evaluated with the Pearson correlation coefficient. The risk factors were evaluated using univariable analysis and multiple regression analysis. Results The average change in length was − 5.3 ± 8.3 mm. The displacement was 11.8 ± 7.1 mm. The Euler angles in the Z-Y-X sequences were -1 ± 8, 1 ± 8, and − 8 ± 13 degrees. The correlation coefficient between the change in length and the displacement was − 0.724 (p

Iliac vein compression syndrome (IVCS, or May–Thurner syndrome) occurs due to the compression of the left common iliac vein between the lumbar spine and right common iliac artery. Because most patients with compression are asymptomatic, the syndrome is difficult to diagnose based on the degree of anatomical compression. In this study, we investigated how the tilt angle of the left common iliac vein affects the flow patterns in the compressed blood vessel using three-dimensional computational fluid dynamic (CFD) simulations to determine the flow fields generated after compression sites. A patient-specific iliac venous CFD model was created to verify the boundary conditions and hemodynamic parameter set in this study. Thirty-one patient-specific CFD models with various iliac venous angles were developed using computed tomography (CT) angiograms. The angles between the right or left common iliac vein and inferior vena cava at the confluence level of the common iliac vein were defined as α1 and α2. Flow fields and vortex locations after compression were calculated and compared according to the tilt angle of the veins. Our results showed that α2 affected the incidence of flow field disturbance. At α2 angles greater than 60 degrees, the incidence rate of blood flow disturbance was 90%. In addition, when α2 and α1 + α2 angles were used as indicators, significant differences in tilt angle were found between veins with laminar, transitional, and turbulent flow (p < 0.05). Using this mathematical simulation, we concluded that the tilt angle of the left common iliac vein can be used as an auxiliary indicator to determine IVCS and its severity, and as a reference for clinical decision making.

Abstract Background Lumbar spinal fusion with rigid spinal fixators as one of the high risk factors related to adjacent-segment failure. The purpose of this study is to investigate how the material properties of spinal fixation rods influence the biomechanical behavior at the instrumented and adjacent levels through the use of the finite element method. Methods Five finite element models were constructed in our study to simulate the human spine pre- and post-surgery. For the four post-surgical models, the spines were implanted with rods made of three different materials: (i) titanium rod, (ii) PEEK rod with interbody PEEK cage, (iii) Biodegradable rod with interbody PEEK cage, and (iv) PEEK cage without pedicle screw fixation (no rods). Results Fusion of the lumbar spine using PEEK or biodegradable rods allowed a similar ROM at both the fusion and adjacent levels under all conditions. The models with PEEK and biodegradable rods also showed a similar increase in contact forces at adjacent facet joints, but both were less than the model with a titanium rod. Conclusions Flexible rods or cages with non-instrumented fusion can mitigate the increased contact forces on adjacent facet joints typically found following spinal fixation, and could also reduce the level of stress shielding at the bone graft.

The current tibiotalocalcaneal (TTC) nails used in ankle arthrodesis surgery have shortcomings leading to unfavorable clinical failures. This study proposes a novel nail design and fabricated by metal 3D printing that can enhance the global implant stability through finite element (FE) analysis and fatigue testing. A novel titanium nail was designed with trilobular cross-sectional design for increasing anti-rotation stability. This nail has three leads with different, increasing pitches that increase the self-compression effect in the fusion sites. Between the leads, there are two porous diamond microstructure regions that act as a bone ingrowth scaffold. The nail was fabricated by metal 3D printing and implanted into artificial ankle joint to evaluate the self-compression effects. The nonlinear FE analysis was performed models to compare the anti-rotation stability between trilobular nail (Tri-nail) and the conventional circular nail. The static and fatigue four-point bending tests were done to understand the mechanical strength of the novel nail. The experiment of self-compression effect showed that the three lead design provides two stages of significant compression effect, with a pressurization rate as high as 40%. FE simulated results indicated that the Tri-nail group provides significant tangent displacement reduction as well as reduction in the surrounding bone stress value and the stress distribution is more even in the Tri-nail group. Four-point test found that the Tri-nail yielding strength is 12,957 ± 577 N, which is much higher than the approved FDA reference (1026 N). One million cycles using 8% of the yielding strength (1036 N) were accomplished without Tri-nail failure. The proposed novel metal 3D printing Tri-nail can provide enough mechanical strength and is mechanically stable with superior anti-rotation ability and excellent fusion site self-compression effect.

This study aims to develop a generalizable method for designing a patient-specific reconstructive scaffold implant for a large distal lateral femur defect using finite element (FE) analysis and topology optimization. A 3D solid-core implant for the distal femur defect was designed to withhold the femur load. Data from FE analysis of the solid implant were use for topology optimization to obtain a ‘bone scaffold implant’ with light-weight internal cavity and surface lattice features to allow for filling with bone material. The bone scaffold implant weighed 69.6% less than the original solid-core implant. The results of FE simulation show that the bone repaired with the bone scaffold implant had lower total displacement (12%), bone plate von Mises stress (34%), bone maximum first principal stress (33%), and bone maximum first principal strain (32%) than did bone repaired with bone cement. The trend in experimental strain with increasing load on the composite femur was greater with bone cement than with the bone scaffold implant. This study presents a generalizable method for designing a patient-specific reconstructive scaffold implant for the distal lateral femur defect that has sufficient strength and space for filling with allograft bone.

This study developed a novel chair-side tongue pressure (TP) measuring instrument with a disposable positioning mouthpiece controlled using a smartphone application (APP), denoted as the TP wireless application (TPWA). The mouthpiece was designed with a palate-shaped air balloon containing a tongue contact bump and a plastic bite positioning tube. Fatigue load testing was performed to evaluate mouthpiece durability by applying 700 displacement cycles (50 times a day for one week during training, with twice the safety factor) on the air balloon. The main component used in developing this instrument was a silicon pressure sensor equipped with wireless Bluetooth connection. Young (52 adults; mean age = 20.23 ± 2.17) and elderly (40 adults; mean age = 72.60 ± 7.03) individuals participated in the test with the new instrument, with the results compared to those of a commercial device. The TPWA mouthpiece fatigue test showed that mean response pressures were maintained at 12 kPa. No significant (p > 0.05) differences were found during testing repetitions 0–10 and 701–710. There were no significant differences in the maximum TP values presented between the test sequences using different instruments for young and elderly participants. The TPWA results showed that TP values gradually decreased with increasing age (40.77 kPa for young and 16.55 kPa for elderly participants). The maximum TP for males (43.51 kPa) was significantly larger than that for females (35.14 kPa) in the young group, but an opposite trend was seen in the elderly group (12.97 for males and 17.59 for females). Thus, this study developed a novel chair-side TP measurement instrument with Bluetooth wireless mobile application control. A durable positioning oral mouthpiece was approved for measuring pressure sufficiently, reliably, and precisely for TP screening.

This study evaluates the biomechanical performance of a new multi-axial alveolar distractor using an animal study. The multi-axial alveolar distractor is designed with a ball and socket joint mechanism that can rotate up to 60° toward the buccal/lingual and mesial/distal sides intra-operatively to achieve vector control. The transport segment can be moved through activating the transport screw with 0.25 pitch, allowing 13 mm in distraction height. This distractor was fixed at the right angulus mandibular of experimental rabbits and adjusted 15° toward the mesial side and 25° toward the buccal side as Group TMB (toward mesial-buccal) (n = 3), and 15° toward the mesial side as Group TM (toward mesial) (n = 3). Group TC (control) was the control group. The distractors were activated 1 mm/day for 13 days. Living bone growth was observed at various periods. The total bone growth length at the angulus region and buccal side distraction thickness after distraction were calculated. The variations in bone growth geometric shape at the mandible angulus were also recorded. Fracture testing was performed to understand the variations in the mechanical strength between the distracted and intact bone specimens. The digital radiography results showed that the osteotomy areas at the mandible angulus were healed and the bone growth completed after surgery. The average bone growth length of Group TMB was 17.68 mm. This was greater than that of Group TM at 14.79 mm. The corresponding buccal side distractor thicknesses for Group TMB and TM after distraction were 5.12 ± 0.52 mm and 3.32 ± 0.37 mm, respectively. The tensile strengths of the bone specimens after distraction of Groups TMB, TM and TC were 172.13 N, 119.27 N and 304.24 N, respectively, and the percentage of distraction bone tensile strength to normal bone was 57% and 39% for Groups TMB and TM, respectively. This study concluded that this new multi-axial alveolar bone distractor can drive bones to grow in accordance with the direction/angle of the distraction plan. The bone growth healed gradually and presented insufficient mechanical strength.

This study developed a numerical simulation to understand bone mechanical behavior and micro-crack propagation around a fixation screw with severe mandibular defects. A mandible finite element (FE) model was constructed in a rabbit with a right unilateral body defect. The reconstruction implant was designed to be fixed using six screws distributed on the distal and mesial sides. The element death technique provided in FE analysis was combined with bone remodeling theory to simulate bone necrosis around the fixation screw in which the strain value reached the overload threshold. A total of 20 iterations were performed to observe the micro-crack propagation pattern for each screw according to the high strain locations occurring in each result from consecutive iterations. A parallel in vivo animal study was performed to validate the FE simulation by placing specific metal 3D printing reconstruction implants in rabbits to compare the differences in bone remodeling caused by radiation treatment after surgery. The results showed that strain values of the surrounding distal bone fixation screws were much larger than those at the mesial side. With the increase in the number of iteration analyses, the micro-crack prorogation trend for the distal fixation screws can be represented by the number and element death locations during the iteration analysis process. The corresponding micro-movement began to increase gradually and induced screw loosening after iteration calculation. The strained bone results showed that relatively high bone loss (damage) existed around the distal fixation screws under radiation treatment. This study concluded that the FE simulation developed in this study can provide a better predictive diagnosis method for understanding fixation screw loosening and advanced implant development before surgery.

This study developed a zygomaticomaxillary complex (ZMC) patient-specific repairing thin (PSRT) implant based on the buttress theory by integrating topology optimization and finite element (FE) analysis. An intact facial skeletal (IFS) model was constructed to perform topology optimization to obtain a hollow skeleton (HS) model with the structure and volume optimized. The PSRT implant was designed based on the HS contour which represented similar trends as vertical buttress pillars. A biomechanical analysis was performed on a ZMC fracture fixation with the PSRT implant and two traditional mini-plates under uniform axial loads applied on posterior teeth with 250 N. Results indicated that the variation in maximum bone stress and model volume between the IFS and HS models was 15.4% and 75.1%, respectively. Small stress variations between the IFS model and repairing with a PSRT implant (2.75–26.78%) were found for compressive stress at frontal process and tensile stress at the zygomatic process. Comparatively, large stress variations (30.67–96.26%) with different distributions between the IFS model and mini-plate models were found at the corresponding areas. This study concluded that the main structure/contour design of the ZMC repair implant according to the buttress position and orientation can obtain a favorable mechanical behavior.

This study proposes a novel titanium 3D printing patient-specific implant: a lightweight structure with enough biomechanical strength for a distal femur fracture with segmental large defect using nonlinear finite element (FE) analysis. CT scanning images were processed to identify the size and shape of a large bone defect in the right distal femur of a young patient. A novel titanium implant was designed with a proximal cylinder tube for increasing mechanical stability, proximal/distal shells for increasing bone ingrowth contact areas, and lattice mesh at the outer surface to provide space for morselized cancellous bone grafting. The implant was fixed by transverse screws at the proximal/distal host bone. A pre-contoured locking plate was applied at the lateral site to secure the whole construct. A FE model with nonlinear contact element implant-bone interfaces was constructed to perform simulations for three clinical stages under single leg standing load conditions. The three stages were the initial postoperative period, fracture healing, and post fracture healing and locking plate removal. The results showed that the maximum implant von Mises stress reached 1318 MPa at the sharp angles of the outer mesh structure, exceeding the titanium destruction value (1000 MPa) and requiring round mesh angles to decrease the stress in the initial postoperative period. Bone stress values were found decreasing all the way from the postoperative period to fracture healing and locking plate removal. The overall construct deformation value reached 4.8 mm in the postoperative period, 2.5 mm with fracture healing assisted by the locking plate, and 2.1 mm after locking plate removal. The strain value at the proximal/distal implant-bone interfaces were valuable in inducing bone grafting in the initial postoperative period. The proposed patient-specific 3D printed implant is biomechanically stable for treating distal femoral fractures with large defect. It provides excellent lightweight structure, proximal/distal bone ingrowth contact areas, and implant rounded outer lattice mesh for morselized cancellous bone grafting.

In this study, we evaluate the influence of implant neck wall thickness and abutment screw size on alveolar bone and implant component biomechanical responses using nonlinear finite element (FE) analysis. Twelve internal hexagon Morse taper implant–abutment connection FE models with three different implant sizes (diameters 4, 5, and 6 mm), secured with 1.4, 1.6, and 1.8 mm abutment screws to fit with three unilateral implant neck wall thicknesses of 0.45, 0.50, and 1.00 mm, were constructed to perform simulations. Nonlinear contact elements were used to simulate realistic interface fixation within the implant system. A 200 N concentrated force was applied toward the center of a hemispherical load cap and inclined 30° relative to the implant axis as the loading condition. The simulation results indicated that increasing the unilateral implant neck wall thickness from 0.45 to 1.00 mm can significantly decrease implant, abutment, and abutment screw stresses and bone strain, decreased to 58%, 48%, 54%, and 70%, respectively. Variations in abutment screw size only significantly influenced abutment screw stress, and the maximum stress dissipation rates were 10% and 29% when the diameter was increased from 1.4 to 1.6 and 1.8 mm, respectively. We conclude that the unilateral implant neck wall thickness is the major design factor for the implant system and implant neck wall thickness in effectively decreasing implant, abutment, and abutment screw stresses and bone strain.

This study established an in vitro model mimicking clinical peri-implant intra-bony defects. We investigated the effect of access limitation and the bactericidal effectiveness of erbium-doped yttrium, aluminum and garnet (Er:YAG) laser irradiation in shallow and deep peri-implant defects at different tooth positions. Reverse engineering, computer-aided design (CAD), and 3D-printing techniques were integrated to establish physical peri-implant intra-bony defect models at mandibular central incisor, first premolar, and first molar positions with shallow (2 mm depth) or deep (6 mm depth) defects and with 1.5 mm and 1.8 mm widths at the bottom and crestal portions of the alveolar process, respectively. Three-dimensional printed suites at the corresponding implant sites replaced experimental implant specimens for the investigation of bacterial adhesion in individuals. Dental implants with diameters of 3, 4 and 5 mm were utilized at the mandibular incisor, premolar, and molar positions, respectively. Bacterial adhesion of Gram (–) Escherichia coli on the exposed implant surfaces prior to sterilization was assessed. Sterilization with shallow and deep intra-bony defects was investigated by measuring the reduction of residual viable bacteria on implants after 60 s of irradiation with an Er:YAG laser. The adhesion rate of Gram (–) Escherichia coli on the investigated implant surfaces ranged from 1% to 3% (1.76 ± 1.25%, 2.19 ± 0.75% and 2.66 ± 1.26% for 3, 4, and 5 mm implants, respectively). With shallow peri-implant bony defects, the Er:YAG laser sterilization rates were 99.6 ± 0.5%, 99.3 ± 0.41% and 93.8 ± 7.65% at mandibular incisor, premolar, and molar positions, respectively. Similarly, sterilization rates in deep peri-implant defects were 99 ± 1.35%, 99.1 ± 0.98% and 97.14 ± 2.57%, respectively. A 3D-printed model with replaceable implant specimens mimicking human peri-implant intra-bony defects was established and tested in vitro. This investigation demonstrated effective sterilization using Er:YAG laser irradiation in both shallow and deep peri-implant intra-bony defects at different positions and diameters of dental implants.

A hybrid fixation method, using a combination of vertebroplasty and cement-augmented screws, has been demonstrated as a useful technique for securing osteoporotic burst fractures. The purpose of this study was to assess changes in the range of motion (ROM) and stress in the spine after treating a lumbar burst fracture with this hybrid method. Five finite element models were developed: (a) intact lumbar spine (INT), (b) INT with vertebroplasty at L3 (AwC), (c) two-segment fixation of AwC (AwC-TSF), (d) AwC-TSF model with cement-augmented screws (AwC-TSF-S), and (e) INT with an L3 burst fracture treated with two-segment fixation (TSF). After loading, the models were evaluated in terms of the ROM of each motion segment, stiffness of fusion segments, and stresses on the endplates and screws. The results showed that the TSF model has a larger ROM at the instrumented segments than both the AwC-TSF and AwC-TSF-S models. The stiffness at L2–L4 under extension and lateral bending in AwC-TSF, AwC-TSF-S and TSF was approximately nine times greater than the INT model. In conclusion, the hybrid fixation method (AwC-TSF-S) results in a stiffer construct and lower ROM at instrumented segments, which may also reduce the risk of fracture of adjacent vertebrae.

Background/purpose: The aims of this investigation were to describe the effect of different ceramic and remaining dentin thicknesses on substrate temperature during photocuring, and investigate whether the temperature increased by >5.5°C for different dentin/ceramic combinations. Materials and methods: Three groups of dentin thicknesses of 1.0 (D1.0), 1.5 (D1.5), and 2.0 mm (D2.0), and three groups of ceramic thicknesses of 1.5 (C1.5), 2.5 (C2.5), and 3.5 mm (C3.5) were examined. Temperature changes and the maximum temperature were observed under a high-intensity halogen light (QTH-Atralis 10 ECS program at 1200 mW/cm2 for 30 seconds, Ivoclar Vivadent AG, Schaan, Liechtenstein). Four groups, D1.0–C1.5 (+11°C), D1.5–C1.5 (+7.2°C), D1.0–C2.5 (+6.7°C), and D2–0C1.5 (+5.8°C), demonstrated temperature changes of >5.5°C. Results and Conclusions: A statistical analysis showed that separate individual thicknesses and combinations of dentin and ceramic had significant effects on temperature changes (P

In this study, we investigated the relative contributions of design factors to the fracture strength of provisional materials after repair. Materials and methods: The Taguchi method was used to investigate the optimal design with respect to four different design factors: subject material, repair material, repair design, and connector thickness. Each factor was assigned three levels. Using the Taguchi L9 orthogonal array, nine rectangular bar-shaped experimental specimens with different parameter combinations were fabricated (n= 5) and tested with a three-point bending test. The fracture load (in newtons) of each specimen group was recorded. The Taguchi method was employed to identify the significance of each design factor in controlling the fracture strength. The sensitivity of each design parameter was determined using an analysis of variance. Fractographic analysis was performed to identify the adhesive or cohesive failure mode for each specimen. Results: The mean effect of the design factors at each level was determined. The subject material, with a contribution percentage of as high as 33.48%, had the most dominant effect on the fracture strength of the repaired provisional restorations, followed by the repair material (31.88%), connector thickness (19.70%), and joint design (14.94%). The strongest subject material was bis-acryl Protemp 3 Garant. The polymethyl methacry late material, Tempron, was the preferred repair material. A 4-mm connector thickness was the best level. A 45º bevel joint was superior to the butt or fiber joint. The predicted fracture strength of the optimum parameter combination (Protemp 3 Garant/45º bevel joint/Tempron/4 mm connector thickness) was 173.34 N. From the fractographic analysis, different bonding abilities between the same and different resin materials were investigated. Fiber joint groups were nearly all in the cohesive mode without complete catastrophic fracture. Conclusion: Within the limitations of this study, these four design factors had different contributions to the fracture strength of repaired provisional restorations. Clinicians must be aware of the sequence of importance in determining better problem-solving methods.