Biomechanical interactions of endodontically treated tooth implant-supported prosthesis under fatigue test with acoustic emission monitoring.

BACKGROUND: This study investigated the biomechanical interactions in endodontically treated tooth implant-supported prosthesis (TISP) with implant system variations under dynamic cyclic loads monitored using the acoustic emission (AE) technique. METHODS: Macrostructure implants using a taper integrated screw-in (TIS; 2-piece implant) and a retaining-screw (RS; 3-piece implant) connected to an abutment were used for this investigation and their corresponding mechanical resistances in conformity with the ISO 14801 standard were evaluated. The endodontically treated TISP samples were constructed containing TIS and RS implants splinted to the second premolar with fatigue tests performed by applying occlusal force onto the premolar simulating the bending moment effect. The numbers of accumulated AE signals in the fatigue tests and failure modes for the sample were recorded to evaluate the mechanical resistance. RESULT: The maximum load in the static test for RS (3-piece) implant (797N) was significantly higher than that for the TIS (2-piece) implant (559N). Large deformations were found at abutment screws in both RS and TIS implants. Although the numbers of accumulated AE signals for the TIS implant (72511) were higher than those for the RS implant (437), statistical non-significant differences were found between TIS and RS implants. No obvious damage was noted in endodontically treated TISP samples using RS implants but two of the corresponding TIS implants fractured in the abutment screws. CONCLUSIONS: Splints with RS (3-piece) implant prosthesis produce better mechanical responses than the TIS (2-piece) implant when connected to an endodontically treated tooth restored with a post core and crown.

Designing an anatomical contour titanium 3D-printed oblique lumbar interbody fusion cage with porous structure and embedded fixation screws for patients with osteoporosis.

This study aimed to design an anatomical contour metal three-dimensional (3D)-printed oblique lateral lumbar interbody fusion (OLIF) cage with porous (lattices) structure and embedded screw fixation to enhance bone ingrowth to reduce the risk of cage subsidence and avoid the stress-shielding effect. Finite element (FE) analysis and weight topology optimization (WTO) were used to optimize the structural design of the OLIF cage based on the anatomical contour morphology of patients with osteoporosis. Two oblique embedded fixation screws and lattice design with 65% porosity and average pore size of 750 µm were equipped with the cage structure. The cage was fabricated via metal 3D printing, and static/dynamic compression and compressive-shear tests were performed in accordance with the ASTM F2077-14 standard to evaluate its mechanical resistance. On FE analysis, the OLIF cage with embedded screw model had the most stability, lowest stress values on the endplate, and uniform stress distribution versus standalone cage and fixed with lateral plate under extension, lateral flexion, and rotation. The fatigue test showed that the stiffnesses/endurance limits (pass 5 million dynamic test) were 16,658 N/mm/6000 N for axial load and 19,643 N/mm/2700 N for compression shear. In conclusion, an OLIF cage with embedded fixation screws can be designed by integrating FE and WTO analysis based on the statistical results of endplate morphology. This improves the stability of the OLIF cage to decrease endplate destruction. The complex contour and lattice design of the OLIF cage need to be manufactured via metal 3D printing; the dynamic axial compression and compressive-shear strengths are greater than that of the U.S. Food and Drug Administration (FDA) standard.

Biomechanical evaluation of an osteoporotic anatomical 3D printed posterior lumbar interbody fusion cage with internal lattice design based on weighted topology optimization.

In this study, we designed and manufactured a posterior lumbar interbody fusion cage for osteoporosis patients using 3D-printing. The cage structure conforms to the anatomical endplate's curved surface for stress transmission and internal lattice design for bone growth. Finite element (FE) analysis and weight topology optimization under different lumbar spine activity ratios were integrated to design the curved surface (CS-type) cage using the endplate surface morphology statistical results from the osteoporosis patients. The CS-type and plate (P-type) cage biomechanical behaviors under different daily activities were compared by performing non-linear FE analysis. A gyroid lattice with 0.25 spiral wall thickness was then designed in the internal cavity of the CS-type cage. The CS-cage was manufactured using metal 3D printing to conduct in vitro biomechanical tests. The FE analysis result showed that the maximum stress values at the inferior L3 and superior L4 endplates under all daily activities for the P-type cage implantation model were all higher than those for the CS-type cage. Fracture might occur in the P-type cage because the maximum stresses found in the endplates exceeded its ultimate strength (about 10 MPa) under flexion, torsion and bending loads. The yield load and stiffness of our designed CS-type cage fall into the optional acceptance criteria for the ISO 23089 standard under all load conditions. This study approved a posterior lumbar interbody fusion cage designed to have osteoporosis anatomical curved surface with internal lattice that can achieve appropriate structural strength, better stress transmission between the endplate and cage, and biomechanically tested strength that meets the standard requirements for marketed cages.

Development and Biomechanical Evaluation of an Anatomical 3D Printing Modularized Proximal Inter-Phalangeal Joint Implant Based on the Computed Tomography Image Reconstructions.

In this study, we developed a modularized proximal interphalangeal (PIP) joint implant that closely resembles the anatomical bone articular surface and cavity contour based on computed tomography (CT) image reconstruction. Clouds of points of 48 groups reconstructed phalanx articular surfaces of CT images, including the index, middle, ring, and little fingers, were obtained and fitted to obtain the articular surface using iterative closest points algorithm. Elliptical-cone stems, including the length, the major and minor axis at the stem metaphyseal/diaphyseal side for the proximal and middle phalanxes, were designed. The resurfacing PIP joint implant components included the bi-condylar surface for the proximal phalanx with elliptical-cone stem, ultra-high molecular weight polyethylene bi-concave articular surface for middle phalanx with hook mechanism, and the middle phalanx with elliptical-cone stem. Nine sets of modularized designs were made to meet the needs of clinical requirements and the weakness structure from the nine sets, that is, the worst structure case combination was defined and manufactured using titanium alloy three-dimensional (3D) printing. Biomechanical tests including anti-loosening pull-out strength for the proximal phalanx, elliptical-cone stem, and articular surface connection strength for the middle phalanx, and static/dynamic (25000 cycles) dislocation tests under three daily activity loads for the PIP joint implant were performed to evaluate the stability and anti-dislocation capability. Our experimental results showed that the pull-out force for the proximal phalanx implant was 727.8N. The connection force for the hook mechanism to cone stem of the middle phalanx was 49.9N and the hook mechanism was broken instead of stem pull out from the middle phalanx. The static dislocation forces/dynamic fatigue limits (pass 25000 cyclic load) of daily activities for piano-playing, pen-writing, and can-opening were 525.3N/262.5N, 316.0N/158N, and 115.0N/92N, respectively, and were higher than general corresponding acceptable forces of 19N, 17N, and 45N from the literatures. In conclusion, our developed modularized PIP joint implant with anatomical articular surface and elliptical-cone stem manufactured by titanium alloy 3D printing could provide enough joint stability and the ability to prevent dislocation.

Development of a Novel Hybrid Suture Anchor for Osteoporosis by Integrating Titanium 3D Printing and Traditional Machining.

The aim of this study is to develop a titanium three-dimensional (3D) printing novel hybrid suture anchor (HSA) with wing structure mechanism which can be opened to provide better holding power for surrounding osteoporotic bone. A screw-type anchor (5.5-mm diameter and 16-mm length) was designed with wing mechanism as well as micro dual-thread in the outer cortex bone contact area and macro single-thread in the anchor body. Both side wings can be opened by an internal screw to provide better bone holding power. The suture anchor and internal screw were manufactured using Ti6Al4V 3D printing and traditional machining, respectively. Static pullout and after dynamic 300-cyclic load (150 N) pullout tests for HSA with or without the wing open and commercial solid anchor (CSA) were performed (n = 5) in severely osteoporotic bone and osteoporotic bone to evaluate failure strengths. Comparison of histomorphometrical evaluation was performed through in vivo pig implantation of HSAs with the wing open and CSAs. The failure strengths of HSA with or without the wing open were 2.50/1.95- and 2.46/2.17-fold higher than those of CSA for static and after dynamic load pullout tests in severely osteoporotic bone, respectively. Corresponding values for static and after dynamic load pullout tests were 1.81/1.54- and 1.77/1.62-fold in osteoporotic bone, respectively. Histomorphometrical evaluation revealed that the effects of new bone ingrowth along the anchor contour for CSA and HSA were both approximately 20% with no significant difference. A novel HSA with wing mechanism was developed using 3D printing and the opened wing mechanism can be used to increase bone holding power for osteoporosis when necessary. Better failure strength of HSA than CSA under static and after dynamic load pullout tests and equivalence of bone ingrowth along the anchor contours confirmed the feasibility of the novel HSA.

Development and validation of a radiomics-based model to predict local progression-free survival after chemo-radiotherapy in patients with esophageal squamous cell cancer.

PURPOSE: To develop a nomogram model for predicting local progress-free survival (LPFS) in esophageal squamous cell carcinoma (ESCC) patients treated with concurrent chemo-radiotherapy (CCRT). METHODS: We collected the clinical data of ESCC patients treated with CCRT in our hospital. Eligible patients were randomly divided into training cohort and validation cohort. The least absolute shrinkage and selection operator (LASSO) with COX regression was performed to select optimal radiomic features to calculate Rad-score for predicting LPFS in the training cohort. The univariate and multivariate analyses were performed to identify the predictive clinical factors for developing a nomogram model. The C-index was used to assess the performance of the predictive model and calibration curve was used to evaluate the accuracy. RESULTS: A total of 221 ESCC patients were included in our study, with 155 patients in training cohort and 66 patients in validation cohort. Seventeen radiomic features were selected by LASSO COX regression analysis to calculate Rad-score for predicting LPFS. The patients with a Rad-score ≥ 0.1411 had high risk of local recurrence, and those with a Rad-score < 0.1411 had low risk of local recurrence. Multivariate analysis showed that N stage, CR status and Rad-score were independent predictive factors for LPFS. A nomogram model was built based on the result of multivariate analysis. The C-index of the nomogram was 0.745 (95% CI 0.7700-0.790) in training cohort and 0.723(95% CI 0.654-0.791) in validation cohort. The 3-year LPFS rate predicted by the nomogram model was highly consistent with the actual 3-year LPFS rate both in the training cohort and the validation cohort. CONCLUSION: We developed and validated a prediction model based on radiomic features and clinical factors, which can be used to predict LPFS of patients after CCRT. This model is conducive to identifying the patients with ESCC benefited more from CCRT.

Finite element and Weibull analyses to estimate failure risks in the ceramic endocrown and classical crown for endodontically treated maxillary premolar.

The present study evaluated the failure risks of an endodontically treated premolar with severely damaged coronal hard tissue and restored with either a computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic endocrown or a classical crown configuration. Two, three-dimensional finite element maxillary premolar models were designed with endodontic treatment and restored with either a chairside economic reconstruction of esthetic ceramic (CEREC) ceramic endocrown or a classical crown. The Weibull function was incorporated with finite element analysis to calculate the long-term failure probability relative to different load conditions. Additionally, an in vitro fatigue-load fracture experiment was performed to validate the numerical simulation results. The results indicated that the stress values on the dentin and luting cement for the endocrown restoration were lower than those for the crown configuration. Weibull analysis revealed that the individual failure probability in the endocrown dentin and luting cement diminished more than those for the crown restoration. While the overall failure probabilities for the endocrown and the classical crown were similar, fatigue fracture testing revealed that the endocrown restoration had higher fracture resistance than the classical crown configuration (1,446 vs. 1,163 MPa). This investigation implies that the endocrown can be considered as a conservative, aesthetic, and clinically feasible restorative approach for endodontically treated maxillary premolars.

A nomogram based on pretreatment CT radiomics features for predicting complete response to chemoradiotherapy in patients with esophageal squamous cell cancer.

PURPOSE: To develop and validate a nomogram model to predict complete response (CR) after concurrent chemoradiotherapy (CCRT) in esophageal squamous cell carcinoma (ESCC) patients using pretreatment CT radiomic features. METHODS: Data of patients diagnosed as ESCC and treated with CCRT in Shantou Central Hospital during the period from January 2013 to December 2015 were retrospectively collected. Eligible patients were included in this study and randomize divided into a training set and a validation set after successive screening. The least absolute shrinkage and selection operator (LASSO) with logistic regression to select radiomics features calculating Rad-score in the training set. The logistic regression analysis was performed to identify the predictive clinical factors for developing a nomogram model. The area under the receiver operating characteristic curves (AUC) was used to assess the performance of the predictive nomogram model and decision curve was used to analyze the impact of the nomogram model on clinical treatment decisions. RESULTS: A total of 226 patients were included and randomly divided into two groups, 160 patients in training set and 66 patients in validation set. After LASSO analysis, seven radiomics features were screened out to develop a radiomics signature Rad-score. The AUC of Rad-score was 0.812 (95% CI 0.742-0.869, p < 0.001) in the training set and 0.744 (95% CI 0.632-0.851, p = 0.003) in the validation set. Multivariate analysis showed that Rad-score and clinical staging were independent predictors of CR status, with p values of 0.035 and 0.023, respectively. A nomogram model incorporating Rad-socre and clinical staging was developed and validated, with an AUC of 0.844 (95% CI 0.779-0.897) in the training set and 0.807 (95% CI 0.691-0.894) in the validation set. Delong test showed that the nomogram model was significantly superior to the clinical staging, with p < 0.001 in the training set and p = 0.026 in the validation set. The decision curve showed that the nomogram model was superior to the clinical staging when the risk threshold was greater than 25%. CONCLUSION: We developed and validated a nomogram model for predicting CR status of ESCC patients after CCRT. The nomogram model was combined radiomics signature Rad-score and clinical staging. This model provided us with an economical and simple method for evaluating the response of chemoradiotherapy for patients with ESCC.

[Effect of Hematite on the Inhibition of Hydrogen Sulfide Formation and Its Mechanism During Anaerobic Digestion and Methanogenesis of Sulfate Wastewater].

In order to achieve the high value production of methane, this paper investigated the effect and mechanism of hematite on the inhibitation of the formation of hydrogen sulfide during the anaerobic digestion of high-concentration sulfate wastewater. Different dosages of hematite were added to artificially prepared sulfate wastewater to analyze the migration and transformation pathways of sulfur in the reaction system. The results showed that the delay time of the anaerobic digestion process and the hydrogen sulfide concentration in the control reactor were 1.64 times and 180 times those in the reactor with the optimal hematite dosage of 0.5 g·(30 mL)-1, respectively. Thus, the addition of hematite effectively shortened the delay time and reduced the concentration of hydrogen sulfide. Dynamic equilibrium analysis of sulfur in different anaerobic digestion reactors showed that the solid sulfur content in the reactor accounted for 96.9% of the total sulfur. XPS results further demonstrated that hematite mainly enhanced the fixation of S2- in the form of FeS2. Therefore, the addition of hematite can effectively accelerate the anaerobic digestion of sulfate wastewater while reducing the concentration of hydrogen sulfide in the reactor.

Anatomical Thin Titanium Mesh Plate Structural Optimization for Zygomatic-Maxillary Complex Fracture under Fatigue Testing.

This study performs a structural optimization of anatomical thin titanium mesh (ATTM) plate and optimal designed ATTM plate fabricated using additive manufacturing (AM) to verify its stabilization under fatigue testing. Finite element (FE) analysis was used to simulate the structural bending resistance of a regular ATTM plate. The Taguchi method was employed to identify the significance of each design factor in controlling the deflection and determine an optimal combination of designed factors. The optimal designed ATTM plate with patient-matched facial contour was fabricated using AM and applied to a ZMC comminuted fracture to evaluate the resting maxillary micromotion/strain under fatigue testing. The Taguchi analysis found that the ATTM plate required a designed internal hole distance to be 0.9 mm, internal hole diameter to be 1 mm, plate thickness to be 0.8 mm, and plate height to be 10 mm. The designed plate thickness factor primarily dominated the bending resistance up to 78% importance. The averaged micromotion (displacement) and strain of the maxillary bone showed that ZMC fracture fixation using the miniplate was significantly higher than those using the AM optimal designed ATTM plate. This study concluded that the optimal designed ATTM plate with enough strength to resist the bending effect can be obtained by combining FE and Taguchi analyses. The optimal designed ATTM plate with patient-matched facial contour fabricated using AM provides superior stabilization for ZMC comminuted fractured bone segments.

Biomechanical optimization of a custom-made positioning and fixing bone plate for Le Fort I osteotomy by finite element analysis.

This study integrates image-processing, finite element (FE) analysis, optimization and CAM techniques to develop a bone plate that can provide precise positioning and fixation for the Le Fort I osteotomy. Two FE 3D models using commercial mini-plate and continuous bone plates were generated by integrating computed tomography images and CAD system for simulations under the worst load condition. The goal driven optimization method was used to examine the system performance using certain minimum output values for relative micro-movement between the two maxillary bone segments and stress for the bone plate to seek maximum reduction volume in a continuous plate. The simulation results indicated that the maximum stress/relative micro-movement was 1269.20MPa/133.66µm and 418.37MPa/92.37µm for the commercial straight mini-plate and continuous fixation types, respectively. The optimal design plate found the volume reduction rate reach 24.3% compared to the continuous bone plate and the decreased variations in stress/relative micro-movement were 65.14% (442.36MPa) and 29.36% (96.53µm) when compared to values obtained from the commercial mini-plate plate. The optimal bone plate can be manufactured using a 5-axes milling machine and fixed onto the freed separate maxillary segments of a rapid prototyping model to provide precise positioning/fixation and present adequate strength/stability in the Le Fort I osteotomy.

Biomechanical interactions of different mini-plate fixations and maxilla advancements in the Le Fort I Osteotomy: a finite element analysis.

This study investigates the biomechanical interaction of different mini-plate fixation types (shapes/sizes and patterns) with segmental advancement levels on the Le Fort I osteotomy using the non-linear finite element (FE) approach. Nine models were generated under a standard 1-piece LeFort I osteotomy for advancement with 3, 6 and 9 mm distances and four mini-plates with three fixation patterns including LL, LI, and II patterns placed on the maxillae models by integrating computed tomography images and computer-aided design system. The axial and oblique occlusal forces were 250 N applied to each premolar/molar and 125 N applied at 30° inclination to the tooth long axis and from palatal to buccal, respectively. The relative micro-movement values between the two maxillary bone segments and maximum mini-plate stress increased obviously with maxilla advancement increment and the increasing trend can be fitted by exponential curve. The corresponding values in II mini-plate fixation presented apparently high values in all simulated cases. The mini-plate stress concentration locations were found at the bending regions to increase high fracture risk. The mini-plate yield strength can be mapped to a critical (limited) advancement for three types of fixations for safe consideration. This study concluded that L-shaped mini-plates with lateral fixation are recommended to provide better stability. The risk for mini-plate fracture and bone relapse increases when maxillary advancement is larger than a critical value of 5 mm in the Le Fort I osteotomy.

Mechanical response comparison in an implant overdenture retained by ball attachments on conventional regular and mini dental implants: a finite element analysis.

This study investigates the bone/implant mechanical responses in an implant overdenture retained by ball attachments on two conventional regular dental implants (RDI) and four mini dental implants (MDI) using finite element (FE) analysis. Two FE models of overdentures retained by RDIs and MDIs for a mandibular edentulous patient with validation within 6% variation errors were constructed by integrating CT images and CAD system. Bone grafting resulted in 2 mm thickness at the buccal side constructed for the RDIs-supported model to mimic the bone augmentation condition for the atrophic alveolar ridge. Nonlinear hyperelastic material and frictional contact element were used to simulate characteristic of the ball attachment-retained overdentures. The results showed that a denture supported by MDIs presented higher surrounding bone strains than those supported by RDIs under different load conditions. Maximum bone micro strains were up to 6437/2987 and 13323/5856 for MDIs/RDIs under single centric and lateral contacts, respectively. Corresponding values were 4429/2579 and 9557/5774 under multi- centric and lateral contacts, respectively. Bone micro strains increased 2.06 and 1.96-folds under single contact, 2.16 and 2.24-folds under multiple contacts for MDIs and RDIs when lateral to axial loads were compared. The maximum RDIs and MDIs implant stresses in all simulated cases were found by far lower than their yield strength. Overdentures retained using ball attachments on MDIs in poor edentulous bone structure increase the surrounding bone strain over the critical value, thereby damaging the bone when compared to the RDIs. Eliminating the occlusal single contact and oblique load of an implant-retained overdenture reduces the risk for failure.

Examination of ceramic restorative material interfacial debonding using acoustic emission and optical coherence tomography.

OBJECTIVE: CAD/CAM ceramic restorative material is routinely bonded to tooth substrates using adhesive cement. This study investigates micro-crack growth and damage in the ceramic/dentin adhesive interface under fatigue shear testing monitored using the acoustic emission (AE) technique with optical coherence tomography (OCT). METHODS: Ceramic/dentin adhesive samples were prepared to measure the shear bond strength (SBS) under static load. Fatigue shear testing was performed using a modified ISO14801 method. Loads in the fatigue tests were applied at 80%, 70%, and 60% of the SBS to monitor interface debonding. The AE technique was used to detect micro-crack signals in static and fatigue shear bond tests. RESULTS: The results showed that the average SBS value in the static tests was 10.61±2.23MPa (mean±standard deviation). The average number of fatigue cycles in which ceramic/dentin interface damage was detected in 80%, 70% and 60% of the SBS were 152, 1962 and 9646, respectively. The acoustic behavior varied according to the applied load level. Events were emitted during 60% and 70% fatigue tests. A good correlation was observed between crack location in OCT images and the number of AE signal hits. SIGNIFICANCE: The AE technique and OCT images employed in this study could potentially be used as a pre-clinical assessment tool to determine the integrity of cemented load bearing restored ceramic material. Sustainable cyclic load stresses in ceramic/dentin-bonded specimens were substantially lower than the measured SBS. Predicted S-N curve showed that the maximum endured load was 4.18MPa passing 10(6) fatigue cyclic.

Design, manufacture and in-vitro evaluation of a new microvascular anastomotic device.

INTRODUCTION: Many microvascular anastomoses have been proposed for use with physical assisted methods, such as cuff, ring-pin, stapler, clip to the anastomose blood vessel. The ring-pin type anastomotic device (e.g., 3M Microvascular Anastomotic System) is the most commonly used worldwide because the anastomotic procedure can be conducted more rapidly and with fewer traumas than using sutures. However, problems including vessel leakage, ring slippage, high cost and high surgical skill demand need to be resolved. The aim of this study is to design and manufacture a new anastomotic device for microvascular anastomosis surgery and validate the device functions with in-vitro testing. METHODS: The new device includes one pair of pinned rings and a set of semi-automatic flap apparatus designed and made using computer-aided design / computer-aided manufacture program. A pair of pinned rings was used to impale vessel walls and establish fluid communication with rings joined. The semi-automatic flap apparatus was used to assist the surgeon to invert the vessel walls and impale onto each ring pin, then turning the apparatus knob to bring the rings together. The device was revised until it became acceptable for clinical requires. An in-vitro test was performed using a custom-made seepage micro-fluid system to detect the leakage of the anastomotic rings. The variation between input and output flow for microvascular anastomoses was evaluated. RESULTS: The new microvascular anastomotic device was convenient and easy to use. It requires less time than sutures to invert and impale vessel walls onto the pinned rings using the semi-automatic flap apparatus. The in-vitro test data showed that there were no tears from the joined rings seam during the procedures. CONCLUSIONS: The new anastomotic devices are effective even with some limitations still remaining. This device can be helpful to simplify the anastomosis procedure and reduce the surgery time.

Finite element sub-modeling analyses of damage to enamel at the incisor enamel/adhesive interface upon de-bonding for different orthodontic bracket bases.

This study investigates the micro-mechanical behavior associated with enamel damage at an enamel/adhesive interface for different bracket bases subjected to various detachment forces using 3-D finite element (FE) sub-modeling analysis. Two FE macro-models using triangular and square bracket bases subjected to shear, tensile and torsional de-bonding forces were established using µCT images. Six enamel/adhesive interface sub-models with micro- resin tag morphology and enamel rod arrangement were constructed at the corresponding stress concentrations in macro-model results. The boundary conditions for the sub-models were determined from the macro-model results and applied in sub-modeling analysis. The enamel and resin cement stress concentrations for triangular and square bases were observed at the adhesive bottom towards the occlusal surface under shear force and at the mesial and distal side planes under tensile force. The corresponding areas under torsional force were at the three corners of the adhesive for the triangular base and at the adhesive bottom toward/off the occlusal surface for the square base. In the sub-model analysis, the concentration regions were at the resin tag base and in the region around the etched holes in the enamel. These were perfectly consistent with morphological observations in a parallel in vitro bracket detachment experiment. The critical de-bonding forces damaging the enamel for the square base were lower than those of the triangular base for all detached forces. This study establishes that FE sub-modeling can be used to simulate the stress pattern at the micro-scale enamel/adhesive interface, suggesting that a square base bracket might be better than a triangular bracket. A de-bonding shear force can detach a bracket more easily than any other force with a lower risk of enamel loss.

Biomechanical responses of endodontically treated tooth implant-supported prosthesis.

INTRODUCTION: This study was designed to investigate the biomechanical interactions in endodontically treated tooth implant-supported prosthesis with variations in implant system and load type by using the nonlinear finite element (FE) approach. METHODS: The computed tomography (CT), micro-CT image process, and computer-aided design systems were integrated to construct the FE models containing 1-, 2-, and 3-piece implants splinted to the second premolar. Realistic interface conditions within the implant system were simulated by using frictional contact elements, and mechanical responses in terms of von Mises stress were computed for all models. RESULTS: The simulated results indicated that splinting an endodontically treated tooth to a neighbor implant decreased stress values in dentin and post but increased stress of implant and bone. The oblique occlusal forces increased the stress values relative to those of axial analogs. A splinted system with a 2-piece implant increased stress on the bone and decreased stress on the prosthesis compared with that of the 1-piece implant. CONCLUSIONS: Splints with 1-piece implant prosthesis, without eccentric occlusal contacts, have better mechanical responses than those of 2- or 3-piece implants when connected to an endodontically treated tooth restored with post core and crown.