Maximum Principal Stress Values Research Articles

Evaluation of stress distributions in endodontically treated anterior incisors under occlusal and trauma-induced forces following various restoration treatments: A finite element analysis.

The aim of this study was to calculate the stress distribution of fiberglass post associated with resin composite crown restoration and fiberglass posts with zirconia restorations in mature and immature endodontically treated central maxillary incisor under various loading conditions. The study created six different study models in a virtual environment: healthy mature maxillary central teeth, intact immature maxillary central teeth, mature maxillary central teeth with fiberglass post associated with resin composite crown restoration, immature maxillary central teeth with fiberglass post associated with resin composite crown restoration, mature maxillary central teeth with fiberglass posts and zirconia restoration, and immature maxillary central teeth with fiberglass posts and zirconia restoration. Loading conditions simulating mastication, trauma, and bruxism were applied to each of the models at different angles and amounts. The von Mises and the maximum and minimum principal stress values in tooth structures (dentin) and support structures (bone, PDL) and materials were observed using finite element stress analysis. The highest stress values in the tissue and the restoration structure were observed for masticating force and crowns rehabilitated with zirconia restorations. None of the compared loading conditions and restorations showed destructive stress values on periodontal ligament or bone. The mature and immature endodontically treated central maxillary incisors can be better rehabilitated using fiberglass post associated with resin composite crown restoration and may be preferred to zirconia restorations in order to reduce the stresses on the surrounding tissues and teeth. However, further clinical studies are needed to fully explore this topic.

Evaluation of stress distribution of different marginal designs on PEEK and PEKK substructure materials, cortical and cancellous Bone:A finite element analysis

High-performance polymers are used in different fixed prosthesis treatments due to their many advantages such as biocompatibility, shock absorption ability, high fracture resistance. The effects of marginal design on the forces on high-performance polymers are unknown. This study aimed was to investigate the stress distribution of different marginal designs on Polyetheretherketone (PEEK) and Polyetherketoneketone (PEKK) substructure materials, cortical bone and cancellous bone by finite element analysis. A first maxillary molar tooth was modeled in 3D using the "3D Complex Render" method. Considering the ideal preparation conditions (Taper angle was 6°, step depth was 1 mm, occlusal reduction was 2mm), four different configurations were modeled by changing the marginal design (chamfer, deep chamfer, shoulder 90°, shoulder 135°). PEEK, PEKK substructure, and composite superstructure were designed on created models. A total of 150N oblique force from two points and a total of 300N vertical force from three points were applied from occlusall. and the maximum principal stress, minimum principal stress, von Mises stress findings in the cortical bone, spongiose bone, and substructure were examined. The study was carried out by static linear analysis with a three-dimensional finite element stress analysis method. The highest maximum principal stress value in the cortical bone was observed when the PEEK+Shoulder 135° step at vertical force. The highest minimum principal stress value in the cortical bone was observed when the PEEK+Shoulder 90° step, and PEEK+deep chamfer step at oblique force. The highest maximum principal stress value in spongiose bone was observed when the PEEK+Shoulder 90° step. The highest minimum principal stress value in spongiose bone was observed when the PEEK+deep chamfer step at vertical force. The highest von Mises stress value in the substructure was observed when the PEKK+Deep chamfer step at oblique force. The lowest maximum principal stress value in the cortical bone was observed when the PEKK+Shoulder 135° step at oblique force. The lowest minimum principal stress value in the cortical bone was observed when the PEEK+Shoulder 135° step, and PEKK+shoulder 135° step at vertical force. The lowest maximum principal stress value in spongiose bone was observed when the PEEK+Shoulder 90° step. The lowest minimum principal stress value in spongiose bone was observed when the PEEK+Shoulder 135° step and PEKK+Shoulder 135° step at vertical force. The lowest von Mises stress value in the substructure was observed when the PEEK+Deep chamfer step at vertical force. When cortical and spongiose bone stress were evaluated, no destructive stress was observed. Considering the stresses occurring in the substructure the highest stress was observed in the chamfer step.

A finite element model for predicting impact-induced damage to a skin simulant

A finite element model was developed for assessing the efficacy of rugby body padding in reducing the risk of sustaining cuts and abrasions. The model was developed to predict the onset of damage to a soft tissue simulant from concentrated impact loading (i.e., stud impact) and compared against a corresponding experiment. The damage modelling techniques involved defining an element deletion criterion, whereby those on the surface of the surrogate were deleted if their maximum principal stress reached a predefined value. Candidate maximum principal stress values for element deletion criteria were identified independently from puncture test simulations on the soft tissue simulant. Experimental impacts with a stud were carried out at three energies (2, 4 and 6 J), at three angular orientations (0°, 15° and 30°) and compared to corresponding simulations. Suitable maximum principal stress values for element deletion criteria settings were first identified for the 4 J impact, selecting the candidates that best matched the experimental results. The same element deletion settings were then applied in simulations at 2 and 6 J and the validity of the model was further assessed (difference < 15% for the force at tear and < 30% for time to tear). The damage modelling techniques presented here could be applied to other skin simulants to assess the onset of skin injuries and the ability of padding to prevent them.

Dental Versus Zygomatic Implants in the Treatment of Maxillectomy: A Finite Element Analysis.

This study analyzed the stress distributions on zygomatic and dental implants placed in the zygomatic bone, supporting bones, and superstructures under occlusal loads after maxillary reconstruction with obturator prostheses. A total of 12 scenarios of 3-dimensional finite element models were constructed based on computerized tomography scans of a hemimaxillectomy patient. Two obturator prostheses were analyzed for each model. A total force of 600 N was applied from the palatal to buccal bones at an angle of 45°. The maximum and minimum principal stress values for bone and von Mises stress values for dental implants and prostheses were calculated. When zygomatic implants were applied to the defect area, the maximum principal stresses were similar in intensity to the other models; however, the minimum principal stress values were higher than in scenarios without zygomatic implants. In models that used zygomatic implants in the defect area, von Mises stress levels were significantly higher in zygomatic implants than in dental implants. In scenarios where the prosthesis was supported by tissue in the nondefect area, the maximum and minimum principal stress values on cortical bone were higher than in scenarios where implants were applied to defect and nondefect areas. In patients who lack an alveolar crest after maxillectomy, a custom bar-retained prosthesis placed on the dental implant should reduce stress on the zygomatic bone. The stress was higher on zygomatic implants without alveolar crest support than on dental implants.

Static and dynamic stress analysis of different crown materials on a titanium base abutment in an implant-supported single crown: a 3D finite element analysis

BackgroundThis Finite Element Analysis was conducted to analyze the biomechanical behaviors of titanium base abutments and several crown materials with respect to fatigue lifetime and stress distribution in implants and prosthetic components.MethodsFive distinct designs of implant-supported single crowns were modeled, including a polyetheretherketone (PEEK), polymer-infiltrated ceramic network, monolithic lithium disilicate, and precrystallized and crystallized zirconia-reinforced lithium silicates supported by a titanium base abutment. For the static load, a 100 N oblique load was applied to the buccal incline of the palatal cusp of the maxillary right first premolar. The dynamic load was applied in the same way as in static loading with a frequency of 1 Hz. The principal stresses in the peripheral bone as well as the von Mises stresses and fatigue strength of the implants, abutments, prosthetic screws, and crowns were assessed.ResultsAll of the models had comparable von Mises stress values from the implants and abutments, as well as comparable maximum and minimum principal stress values from the cortical and trabecular bones. The PEEK crown showed the lowest stress (46.89 MPa) in the cervical region. The prosthetic screws and implants exhibited the highest von Mises stress among the models. The lithium disilicate crown model had approximately 9.5 times more cycles to fatique values for implants and 1.7 times more cycles to fatique values for abutments than for the lowest ones.ConclusionsWith the promise of at least ten years of clinical success and favorable stress distributions in implants and prosthetic components, clinicians can suggest using an implant-supported lithium disilicate crown with a titanium base abutment.

Biomechanical behavior of all-on-4 concept and alternative designs under different occlusal load configurations for completely edentulous mandible: a 3-D finite element analysis.

The aim of this study was to evaluate the effect of the All-on-4 design and 4 alternative implant-supported fixed prosthesis designs on stress distribution in implants, peri-implant bone, and prosthetic framework in the edentulous mandible under different loading conditions using three-dimensional finite element analysis (3D-FEA).Five different experimental finite element models (Model A (unsplinted 6), Model B (splinted 6), Model C (All-on-4), Model D (axial; 2 anterior, 2 posterior), and Model E (4 interforaminal)) were created. Three different loading conditions were applied (canine loading, unilateral I-loading, and unilateral II-loading). The highest minimum (Pmin) and the maximum (Pmax) principal stress values were acquired for cortical and trabecular bones; the highest von Mises (mvM) stress values were obtained for implants and metal frameworks. Model B and Model D showed the most favorable stress distribution. The All-on-4 design (Model C) also showed acceptable stress values close to those of Model B and Model D in the cortical and trabecular bones. In accordance with the stress values in the bone structure, the lowest stress values were measured in the implants and Co-Cr framework in Model B and Model D. The highest stress values in all structures were measured for unilateral loading- II, while the lowest values were found for canine loading. It was concluded that Model B and Model D experimental models showed better biomechanical performance in all structures. Furthermore, the use of a splinted framework, avoiding cantilevers, results in lower stress transmission. On the other hand, canine loading and unilateral loading-I exhibited the best loading conditions.

Dental versus zygomatic implants in the treatment of maxillectomy: a finite element analysis.

This study analyzed the stress distributions on zygomatic and dental implants placed in the zygomatic bone, supporting bones, and superstructures under occlusal loads after maxillary reconstruction with obturator prostheses. 12 scenarios of three-dimensional finite element models were constructed based on computed tomography scans of a patient who had hemimaxillectomy. Two obturator prostheses were analyzed for each model. A total force of 600 N was applied from the palatal to buccal bones at an angle of 45°. The maximum and minimum principal stress values for bone and also the von Misses stress values for dental implants and prostheses were calculated. When zygomatic implants were applied to the defect area, the maximum principal stresses were similar in intensity to the other models; however, the minimum principal stress values were higher than in scenarios without zygomatic implants. In models that used zygomatic implants in the defect area, von Misses stress levels were significantly higher in zygomatic implants than in dental implants. In scenarios where the prosthesis was supported by tissue in the non-defect area, the maximum and minimum principal stress values on cortical bone were higher than in scenarios where implants were applied to both defect and non-defect areas. In patients who lack an alveolar crest after maxillectomy, reduced stress on the zygomatic bone is expected if a custom bar-retained prosthesis is placed on the dental implant. The stress was higher on zygomatic implants without alveolar crest support than on dental implants.

The Distribution Law of Ground Stress Field in Yingcheng Coal Mine Based on Rhino Surface Modeling

The distribution law of the ground stress field is of great significance in guiding the design of coal mine roadway alignment, determining the parameters of roadway support, and preventing and controlling the impact of ground pressure in coal mines. A geostress inversion method combining Rhino surface modeling and FLAC3D 6.0 numerical simulation software is proposed. Based on the geological data of the coal mine and the results of on-site measurements, a three-dimensional geological model of Yingcheng Coal Mine is established for the geostress inversion, and the distribution law of the geostress field in Yingcheng Coal Mine is obtained. Research shows the following: (1) The horizontal maximum principal stress values of the Yingcheng Mine are between 33.9 and 35.3 MPa, the horizontal minimum principal stress values are between 23.6 and 25.4 MPa, and the direction of the horizontal maximum principal stress is roughly in the southwest to west direction; (2) the three-way principal stress magnitude relationship is σH &gt; σv &gt; σh, indicating that the horizontal stress dominates in the study area, which belongs to the slip-type stress state; (3) The maximum principal stress of No. 3 coal seam is 33.1–34.8 MPa, the middle principal stress is 27.5–29.2 MPa, and the minimum principal stress is 17.3–22.9 MPa. Due to the influence of topography and burial depth, there is a phenomenon of stress concentration in some areas. By comparing the inversion values with the measured values, the accuracy of the geostress inversion is high, and the initial geostress inversion method based on Rhino surface modeling accurately inverts the geostress distribution pattern of the Yingcheng coal mine.

Stress Distribution on Prepared Tooth With Shoulder and Radial Shoulder Margin to Receive Crowns of Three Different Materials: A Finite Element Analysis.

Aim and background This study aims to determine the stress distribution on the prepared tooth at the margins with shoulder and radial shoulder finish lines when an occlusal load of 300N was applied to ceramic, zirconia, and polyether ether ketone (PEEK) crowns. Materials and methods Six models of mandibular first molar teeth were fabricated. The tooth models were subdivided into two groups with shoulder and radial shoulder margins, respectively (n = 18). The teeth were restored with three different prosthetic crown materials (ceramic, zirconia, and PEEK). To simulate the typical forces experienced by a prosthetic crown material in a lower posterior tooth during chewing and biting, an occlusal load of 300N was applied to each of the samples, and the maximum principal stress (Pmax) and von Mises stress were calculated, respectively. These samples were then compared and evaluated to determine the material best suited as a prosthetic crown material of choice for a lower posterior tooth. Results Among the materials used, the maximum principal stress value was the least in PEEK crowns. The von Mises stress value was highest for the zirconia crown with shoulder margin and was least for the PEEK crown with a similar margin. Conclusion PEEK as a crown material was found to be a better choice for lower posterior teeth as there was the least maximum principal stress at the margin, irrespective of either shoulder or radial shoulder finish line used.

Mechanical behavior of endodontically treated teeth: A three-dimensional finite element analysis using displacement vector.

This study aimed to analyze the effects of core materials, remaining tooth structures, and interfacial bonding on stress distribution in endodontically treated teeth using finite element analysis (FEA). Three-dimensional FEA was conducted using a reverse engineering technique based on maxillary premolars scanned by micro-computed tomography. Six models were generated with or without ferrules and with one of the following three abutment systems: metal core, resin core, or resin core with fiber posts. In each model, bonding and debonding were assumed in the dentin and surrounding structures: bonded and debonded models. The maximum principal stress values were recorded, and stress distribution of the entire restored teeth and dentin was generated. Furthermore, the distribution of the displacement vector of the debonded models was generated. In comparing the bonded and debonded models, the debonded models showed larger values for tensile stresses than those in bonded models for all abutment models. The models without ferrules rotated around the center of the abutment, whereas those with ferrules did not show remarkable displacement in the analysis. FEA assuming fracture of adhesive interface proved to be an effective method to clarify the significance of ferrules. It prevents stress concentration in dentin by reducing the rotation of the abutment, even when the adhesive fails.

Effect of maximum applied cyclic stress on fretting fatigue stress distribution of flat-on-flat modified 9Cr-1Mo steel contact: Finite element analysis

Fretting fatigue experiments were conducted on a modified 9Cr-1Mo (P91) steel under flat-on-flat contact with maximum applied cyclic stress (σmax) levels of 450 MPa, 500 MPa and 550 MPa at a stress ratio of 0.3 and a contact pressure of 100 MPa. A decrease in the cyclic life was observed with an increase in σmax. Chaboche model with isotropic and kinematic hardening was employed in finite element analysis to evaluate the stress distribution near the contact pad and along the contact surface under fretting fatigue conditions. In addition, the contact-related parameters such as contact pressure, contact shear stress and relative tangential motion were also assessed. The relative tangential motion was found to increase with increasing σmax. Besides, the peak values of normal stress (parallel to the applied loading direction) and maximum principal stress were observed around the leading and trailing edges of the contact pad at the σmax. The amplitude of relative tangential motion and slip zone increases with σmax. The orientations of the principal plane and shear plane to the applied cyclic loading direction are −89.5° and −134.5°, irrespective of the σmax. The fracture surface of the failed specimen revealed that the direction of the crack was nearly perpendicular to the applied stress. Smith-Watson-Topper parameter was used for estimating the crack initiation life with σmax. It has been noticed that the fraction and dominance of crack initiation or propagation phase depend on the imposed cyclic condition for the steel.

Quantitative investigation of the cracking mechanism of 3D sand-printed rock containing a fold flaw

Natural discontinuities originating inside rocks are often distributed in folds rather than simple straights. To represent the details of fold-shaped flaws, rock-like specimens containing a fold flaw are created by 3D sand printing, and cases involving four undulation angles (α) are considered. Uniaxial compression tests, digital image correlation (DIC), and the extended finite element method (XFEM) on rock-like models are conducted to investigate the influence of undulation angles on the cracking mechanism of the specimens. The 3D sand-printed specimen has obvious advantages in simulating natural rocks. Two types of crack initiation modes are observed: tip cracking and nontip cracking. DIC-based measurements and XFEM simulations show that the maximum value of maximum principal stress and strain occur near when α = 0° and 10°, while they appear in the flaw inflexion when α = 20° and 30°, which explains the difference in crack initiation. Two types of cracks are identified based on the displacement vector analysis: tensile and horsetail cracks. The crack initiation position of these two cracks is precisely determined by extracting strain data around the flaw tip. The undulation angle cannot alter the final coalescence, which is induced by the connection of horsetail cracks with the flaw.

Biomechanical Effects of Different Load Cases with an Implant-Supported Full Bridge on Four Implants in an Edentulous Mandible: A Three-Dimensional Finite Element Analysis (3D-FEA).

The long-term success and predictability of implant-supported restorations largely depends on the biomechanical forces (stresses) acting on implants and the surrounding alveolar bone in the mandible. The aim of our study was to investigate the biomechanical behavior of an edentulous mandible with an implant-supported full bridge on four implants under simulated masticatory forces, in the context of different loading schemes, using a three-dimensional finite element analysis (3D-FEA). A patient-specific 3D finite element model was constructed using pre- and post-implantation computer tomography (CT) images of a patient undergoing implant treatment. Simplified masticatory forces set at 300 N were exerted vertically on the denture in four different simulated load cases (LC1-LC4). Two sets of simulations for different implants and denture materials (S1: titanium and titanium; S2: titanium and cobalt-chromium, respectively) were made. Stress outputs were taken as maximum (Pmax) and minimum principal stress (Pmin) and equivalent stress (Peqv) values. The highest peak Pmax values were observed for LC2 (where the modelled masticatory force excluded the cantilevers of the denture extending behind the terminal implants), both regarding the cortical bone (S1 Pmax: 89.57 MPa, S2 Pmax: 102.98 MPa) and trabecular bone (S1 Pmax: 3.03 MPa, S2 Pmax: 2.62 MPa). Overall, LC1-where masticatory forces covered the entire mesio-distal surface of the denture, including the cantilever-was the most advantageous. Peak Pmax values in the cortical bone and the trabecular bone were 14.97-15.87% and 87.96-94.54% higher in the case of S2, respectively. To ensure the long-term maintenance and longevity of treatment for implant-supported restorations in the mandible, efforts to establish the stresses of the surrounding bone in the physiological range, with the most even stress distribution possible, have paramount importance.

Effect of different implant locations and abutment types on stress and strain distribution under non-axial loading: A 3-dimensional finite element analysis

Background/purposeDental implants have been a popular treatment for replacing missing teeth. The purpose of this study was to investigate the impact of engaging (hexagonal) and non-engaging (non-hexagonal) abutments in various six-unit fixed prosthesis on the stress distribution and loading located in the implant neck, implant abutment, and surrounding bone. Materials and methodsThree implants were digitally designed and inserted parallel to each other in edentulous sites of the maxillary right canine, maxillary right central incisor, and maxillary left canine. Titanium base engaging abutments, non-engaging abutments and connecting screws were designed. Five distinct models of 6-unit fixed dental prosthesis were created, each featuring different combinations of various abutments. Forces (45-degree angle) were applied to the prosthesis, allowing for the analysis of the stress distribution on the implant neck and abutments, and the maximum and minimum principal stress values on the cortical and trabecular bone. ResultsVon Mises stress values and stress distributions located in the implant neck region due to the applied loading forces were analyzed. The overall stress values were highest while employing the hexagonal abutments. The maxillary left canine with a hexagonal abutment (model 5) reported the highest von mises value (64.71 MPa) while the maxillary right canine with a non-hexagonal abutment (model 4) presented lowest von mises value (56.69 MPa). ConclusionThe results suggest that both the various abutment combinations (engaging and non-engaging) on five different models have a similar influence on the distribution of stress within the implant system.

Assessment of biomechanical behavior of immature non-vital incisors with various treatment modalities by means of three-dimensional quasi–static finite element analysis

The objectives of this study were to evaluate the stress distribution and risk of fracture of a non-vital immature maxillary central incisor subjected to various clinical procedures using finite element analysis (FEA). A three-dimensional model of an immature central incisor was developed, from which six main models were designed: untreated immature tooth (C), standard apical plug (AP), resin composite (RC), glass-fibre post (GFP), regeneration procedure (RET), and regeneration with induced root maturation (RRM). Mineral trioxide aggregate (MTA) or Biodentine® were used as an apical or coronal plug. All models simulated masticatory forces in a quasi–static approach with an oblique force of 240 Newton at a 120° to the longitudinal tooth axis. The maximum principal stress, maximum shear stress, risk of fracture, and the strengthening percentage were evaluated. The mean maximum principal stress values were highest in model C [90.3 MPa (SD = 4.4)] and lowest in the GFP models treated with either MTA and Biodentine®; 64.1 (SD = 1.7) and 64.0 (SD = 1.6) MPa, respectively. Regarding the shear stress values, the dentine tooth structure in model C [14.4 MPa (SD = 0.8)] and GFP models [15.4 MPa (SD = 1.1)] reported significantly higher maximum shear stress values compared to other tested models (p < 0.001), while no significant differences were reported between the other models (p > 0.05). No significant differences between MTA and Biodentine® regarding maximum principal stress and maximum shear stress values for each tested model (p > 0.05). A maximum strain value of 4.07E−03 and maximum displacement magnitude of 0.128 mm was recorded in model C. In terms of strengthening percentage, the GFP models were associated with the highest increase (22%). The use of a GFP improved the biomechanical performance and resulted in a lower risk of fracture of a non-vital immature maxillary central incisor in a FEA model.

Multi-objective design optimization of bioresorbable braided stents

Background and objectivesBioresorbable braided stents, typically made of bioresorbable polymers such as poly-l-lactide (PLLA), have great potential in the treatment of critical limb ischemia, particularly in cases of long-segment occlusions and lesions with high angulation. However, the successful adoption of these devices is limited by their low radial stiffness and reduced elastic modulus of bioresorbable polymers. This study proposes a computational optimization procedure to enhance the mechanical performance of bioresorbable braided stents and consequently improve the treatment of critical limb ischemia. MethodsFinite element analyses were performed to replicate the radial crimping test and investigate the implantation procedure of PLLA braided stents. The stent geometry was characterized by four design parameters: number of wires, wire diameter, initial stent diameter, and braiding angle. Manufacturing constraints were considered to establish the design space. The mechanical performance of the stent was evaluated by defining the radial force, foreshortening, and peak maximum principal stress of the stent as objectives and constraint functions in the optimization problem. An approximate relationship between the objectives, constraint, and the design parameters was defined using design of experiment coupled with surrogate modelling. Surrogate models were then interrogated within the design space, and a multi-objective design optimization was conducted. ResultsThe simulation of radial crimping was successfully validated against experimental data. The radial force was found to be primarily influenced by the number of wires, wire diameter, and braiding angle, with the wire diameter having the most significant impact. Foreshortening was predominantly affected by the braiding angle. The peak maximum principal stress exhibited contrasting behaviour compared to the radial force for all parameters, with the exception of the number of wires. Among the Pareto-optimal design candidates, feasible peak maximum principal stress values were observed, with the braiding angle identified as the differentiating factor among these candidates. ConclusionsThe exploration of the design space enabled both the understanding of the impact of design parameters on the mechanical performance of bioresorbable braided stents and the successful identification of optimal design candidates. The optimization framework contributes to the advancement of innovative bioresorbable braided stents for the effective treatment of critical limb ischemia.

Effect of process parameters on crack characteristics in laser welding of Al2O3 ceramic

The crack of ceramic weld is a worldwide problem for brittle material, high energy laser beam is expected to solve this problem. In this paper, the crack of fiber laser welding of Al2O3 ceramics was studied. The weld crack rate was used to characterize the crack condition of weld, and the influences of laser power, welding speed and defocusing distance on crack characteristics were carried out. The results showed that Al2O3 ceramics weld has obvious crack tendency, and the cracks mainly appeared on the weld center line. When the crack appeared on the weld center line, there was crack-free on the base metal. When the defocusing distance increased from +3 mm to +20 mm, the number of cracks gradually decreased. When the defocusing distance was greater than +17 mm, cracks-free appeared on the weld and base metal. Abaqus software was used to simulate the relationship between crack and stress based on thermal elastoplastic theory. The high crack areas, few crack areas and free crack areas were divided according to the maximum principal stress value. No matter what welding conditions, as long as the maximum principal stress was less than 1576 MPa, there was crack-free on the weld and base metal.

Impact of different CAD/CAM materials on internal and marginal adaptations and fracture resistance of endocrown restorations with: 3D finite element analysis

PurposeTo assess and compare the impact of various computers aided design/manufacturing (CAD/CAM) materials on internal and marginal discrepancies, fracture resistance and failure probability of Endocrown restorations with 3D Finite Element analysis.Material and methodsForty devitalized human maxillary first molars were collected. After endodontic treatment, they classified into 4 groups (n = 10) based on the materials used for endocrown fabrication. Group V (Vita-Enamic), Group N (Nacera Hybrid), Group T (Translucent Prettau Zirconia) and Group P (Pekkton ivory). All samples were exposed to artificial aging method simulating one year of clinical service. Silicone replica technique and stereomicroscope (25X) utilized to evaluate the marginal and internal gaps of endocrowns at different areas. Fracture resistance test used for cemented specimens followed by qualitative investigation utilizing Stereomicroscopy. Four models representing four endocrown systems used for restoration of severely-damaged endodontically treated upper first molar were generated for finite element analysis (FEA). Axially and centrally static occlusal compressive load was applied. Modified Von Mises and maximum principal stress values on the remaining tooth structure, cement lines and restorative materials were assessed independently. Resulted data were statistically analyzed at P-value ≤ 0.05.ResultsIn the current study, the highest mean values of internal and marginal discrepancies (μm) among studied groups were reported for Zirconia group (100.300 and 102.650) respectively, while the lowest mean value of internal discrepancy (μm) was observed for Nacera group (69.275) and the lowest mean value of marginal discrepancy (μm) was observed for PEKK group (78.4750). Regarding internal discrepancy, Vita-Enamic and PEKK groups did not exhibit any statistically significant differences (P = 0.293), however zirconia and the other tested groups exhibited statistically significant differences in the mean values of the marginal gap region (p 0.05).On the other hand, PEKK group showed the highest mean value of fracture resistance (1845.20 N) and the lowest value was observed for Vita-Enamic group (946.50 N). Regarding to stress distributions through 3D FEA, and according to modified von Mises (mvM) analysis, the greatest possible stress values were noticed in PEKK model in relation to tooth structure, cement line, and flowable composite as the following: (93.1, 64.5, 58.4 MPa) respectively, while Zirconia revealed lower maximum stress values (11.4, 13.6, 11.6 MPa) respectively.ConclusionsStatistically excellent marginal and internal fit was observed for PEKK in relation to other used endocrown materials. Also, PEKK material explained fracture resistance comparable to zirconia value while the lowest value was detected for Vita Enamic material.

Energy Accumulation Characteristics and Induced Rockburst Mechanism of Roadway Surrounding Rock under Multiple Mining Disturbances: A Case Study

The source of energy release when rockburst occurs must be determined to understand the mechanisms underlying disaster formation and achieve accurate prevention and control. Although previous research has systematically investigated the energy source underlying rockburst from different perspectives, issues such as an unclear understanding of the energy accumulation state and inaccurate positioning of the energy release source remain to be resolved. In this study, the “1·17” major roof accident in the Danshuigou Mine was used as the background to evaluate and analyze the stress environment and energy accumulation characteristics of roadway surrounding rock under multiple mining disturbances, and the results showed that a super energy package occurs in the surrounding rock of the mining roadway. Subsequently, the evolution process of energy in this region and the mechanism of induced rockburst were elaborated. The results showed that the degree of stress concentration in the surrounding rock of the roadway will increase several times as the number of mining disturbances increases. Under the influence of multiple mining disturbances, the maximum principal stress peak of the surrounding rock of the roadway can reach 5–10 times the maximum principal stress value outside the mining-affected area. A large amount of elastic energy was accumulated in the rock surrounding the roadway, and super-high-density energy packages were formed locally. The maximum energy density value reached 50–185 times the value observed in areas outside the mining-affected zone. Thus, rockburst may be induced when the large amount of energy accumulated in the super energy package is suddenly and violently released; moreover, the degree of energy accumulation in the super energy package is likely closely related to the magnitude of rockburst. These results have important theoretical significance and application value for clarifying the mechanism of rockburst and improving the effectiveness of rockburst prediction and prevention.

Finite element analysis of endodontically treated premolars without ferrule restored with one-piece glass fiber post and core in combination with different inner shoulder retention form systems

ObjectiveThe current study was performed to explore the impact of post materials as well as the inner shoulder retention form (ISRF) design on the biomechanical behavior of endodontically treated premolars without ferrule restoration using a method of mathematical three-dimensional (3D) finite element analysis (FEA). MethodsBased on the tooth anatomy and our previous research, eight mandibular second premolar FEA models representing different restorative situations were built: teeth with (a) 2.0 mm height ferrule (DF), (b) no ferrule (NF), (c) 0.5 mm width and 0.5 mm depth ISRF (ISRFW0.5D0.5), (d) 0.5 mm width and 1.0 mm depth ISRF (ISRFW0.5D1.0), (e) 0.5 mm width and 1.5 mm depth ISRF (ISRFW0.5D1.5), (f) 1.0 mm width and 0.5 mm depth ISRF (ISRFW1.0D0.5), (g) 1.0 mm width and 1.0 mm depth ISRF (ISRFW1.0D1.0), (h) 1.0 mm width and 1.5 mm depth ISRF (ISRFW1.0D1.5). All groups were restored with prefabricated glass fiber post and resin composite core (PGF), one-piece glass fiber post-and-core (OGF) and cast Co-Cr alloy (Co-Cr) respectively, and the zirconia crown was restored. Load (180N) was subjected to the buccal cusp at 45° to the tooth's long axis. Stress pattern, maximum principal stress values (MPS), and maximum displacement values on root, post and core, cement layer were calculated for each model. ResultsStress distributions were similar while the values were different among groups. Regardless of restorative approaches, roots restored with PGF showed the highest MPS values, followed by OGF and Co-Cr groups. Regardless of post materials, NF groups resulted in the highest MPS values and maximum displacement values, while ISRF and DF groups exhibited similar results. Compared with PGF groups in association with ISRF, except for OGF with ISRFW0.5D0.5, the remaining OGF groups with ISRF and all Co-Cr groups in association with ISRF presented lower values than that of DF groups. And among different ISRF systems, roots restored with ISRFW1.0D1.0 presented the lowest stress (PGF: 32.96 MPa, OGF: 31.69 MPa, Co-Cr: 29.66 MPa). ConclusionsFor endodontically treated premolars without ferrule, restored with OGF in combination with ISRF preparation could effectively enhanced its load-bearing capacity. Furthermore, the ISRF with a depth and width of 1.0 mm is recommended.