Root Stress Distribution Research Articles

Stress Analysis of Periodontal Tissue in en Masse Retraction With Integration of Maxillary Anterior Teeth: A Three-Dimensional Finite Element Method Study.

To simulate the en masse traction technique with the integration (EMTI) of six maxillary anterior teeth using a finite element model (FEM) and explore various protocols for maxillary protrusion. The study aimed to investigate root displacement and stress distribution in the periodontal ligament (PDL) by varying the retraction position and direction of EMTI applied to the maxillary anterior teeth. No actual participants were involved. The FEM model included six teeth (central and lateral incisors and canines) with a PDL thickness of 0.3 mm. The model encompassing the alveolar bone (ALB) and EMTI had 180,528 elements and 47,836 nodes. The EMTI integrated six anterior teeth via a 0.9-mm-diameter stainless steel lingual wire, equipped with three moment arms extending toward the root apex: one midline (central arm) and two distal to the canines (lateral arms). The position and direction of the traction force applied to the three moment arms of the EMTI were varied to assess crown and apex displacement, as well as PDL stress. Lingual tipping was consistent across all protocols, emphasizing controlled incisor tipping. The application of horizontal traction at 10 mm and traction at 7 mm from the central and lateral arms of the EMTI, respectively, demonstrated the most uniform stress distribution across the PDL of all six anterior teeth. The FEM analysis results suggest that the new EMTI method, which retracts the maxillary anterior teeth as a unit, is effective for tooth movement and PDL stress distribution. The EMTI technique, with its specific traction protocols and emphasis on controlled tipping, appears to be a promising approach for addressing maxillary protrusions.

Comparative analysis of stress distribution in residual roots with different canal morphologies: evaluating CAD/CAM glass fiber and other post-core materials

BackgroundThe selection of post-core material holds significant importance in endodontically treated teeth, influencing stress distribution in the dental structure after restoration. The use of computer-aided design/computer-aided manufacturing (CAD/CAM) glass fiber post-core possesses a better adaptation for different root canal morphologies, but whether this results in a more favorable stress distribution has not been clearly established.Materials and methodsThis study employed finite element analysis to establish three models of post-core crown restoration with normal, oversized, and dumbbell-shaped root canals. The three models were restored using three different materials: CAD/CAM glass fiber post-core (CGF), prefabricated glass fiber post and resin core (PGF), and cobalt-chromium integrated metal post-core (Co-Cr), followed by zirconia crown restoration. A static load was applied and the maximum equivalent von Mises stress, maximum principal stress, stress distribution plots, and the peak of maximum displacement were calculated for dentin, post-core, crown, and the cement acting as the interface between the post-core and the dentin.ResultsIn dentin of three different root canal morphology, it was observed that PGF exhibited the lowest von Mises stresses, while Co-Cr exhibited the highest ones under a static load. CGF showed similar stress distribution to that of Co-Cr, but the stresses were more homogeneous and concentrated apically. In oversized and dumbbell-shaped root canal remnants, the equivalent von Mises stress in the cement layer using CGF was significantly lower than that of PGF.ConclusionsIn oversized root canals and dumbbell-shaped root canals, CGF has shown good performance for restoration of endodontically treated teeth.Clinical relevanceThis study provides a theoretical basis for clinicians to select post-core materials for residual roots with different root canal morphologies and should help to reduce the occurrence of complications such as root fracture and post-core debonding.

Efficient semi-analytic method for single tooth contact analysis of loaded spiral bevel gears

Accurately and fast calculation of single tooth load contact state of a gear pair is the basis for accurate calculation of multi-tooth load contact analysis. Therefore, this study proposed a semi-analytical quick single tooth load tooth contact analysis (Q-SLTCA) method. First, the ease-off tooth contact analysis (ease-off TCA) method was established, and a numerically stable initial contact stress distribution and contact ellipse analytical model was derived. Then, considering the influence of edge contact, the real-time division method of gear tooth slice was derived. Based on this, the equivalent principle of contact elliptical node and the load correction strategy were innovatively proposed. Then, the calculation method of the meshing characteristics of the tooth slice was established by coupling the boundary element method (BEM) with the equivalent cylindrical Hertz contact theory. The bending deformation, tooth root stress distribution, contact stress, contact deformation and meshing stiffness of the tooth slice were analyzed and calculated, and the instantaneous meshing stiffness of the single tooth was determined by combining the parallel method of the gear tooth stiffness. Finally, a single-tooth finite element method (FEM) meshing model was created for comparison with the method in this study, which verified the calculation accuracy and efficiency of the proposed method. This method can be easily developed into a quick multi-tooth load contact analysis algorithm, which can provide a new method for gear tooth crack and failure analysis.

Influence of gear–shaft interference fit assembly on the meshing characteristics of cylindrical gears considering comprehensive modifications

The interference fit assembly of shaft and gear has an important influence on the gear drive performance. In this work, the cylindrical gear active surfaces and fillet will be provided with comprehensive modifications including front and back end reliefs, tip and root reliefs, as well as a low-value lead crowning. The mathematical model of the gear flanks surfaces with the mentioned modifications has been developed. A finite element model of the gear set has been established to study the effect of the interference fit assembly of the gears with their shafts on the meshing characteristics of cylindrical gears with modified tooth surfaces. With the increment of the interference fit amount, the contact pattern is shifted towards the top edge of the gear flank. The increment of the interference fit amount also contributes to the shift of root stress distribution towards the root land of the tooth. The maximum value of root bending stress keeps a positive linear relationship with the amount of shaft–gear interference fit being considered.

Geometry optimisation of highly crowned gear couplings working in high misalignment applications to reduce tooth root stresses

Crowned gear couplings are mechanical components used to transmit power between misaligned rotating shafts. Their geometry is characterised by a significant longitudinal crowning to accommodate angular misalignment. Recent studies reveal that high misalignments drastically reduce the number of teeth in contact and lead to an uneven load distribution among engaged teeth. Consequently, tooth root fracture becomes a common failure mode. Current standards only address misalignment angles below 1.5°, treating applications with greater misalignments as special cases without design guidelines or stress prediction methods. This study proposes a procedure to optimize the design of crowned gear couplings working in high misalignment applications by determining tooth root stress distribution. The geometry is analytically generated, while finite element models are used to calculate the stress distribution. Experimental validation is performed using a dedicated test rig. The obtained results are very close to the ones from the numerical model, demonstrating the suitability of the method for crowned gear couplings operating under significant angular misalignments. The optimized design reduces tooth root stress by 50%, which will increase the fatigue life of the component or enable the application of higher torque values.

The Effect of Varying Occlusal Loading Conditions on Stress Distribution in Roots of Sound and Instrumented Molar Teeth: A Finite Element Analysis

IntroductionThis study aimed to investigate whether the direction of force applied to the occlusal surface influenced the pattern of tensile stresses in roots of sound and root canal–prepared mandibular molar teeth. The effect of obturation forces on the development of apical stress was also investigated. To this end, models were constructed using micro–computed tomographic imaging and investigated using finite element analysis. MethodsMicro–computed tomographic data established boundaries of internal and external model surfaces to allow finite element analysis. Individually segmented components were modeled based on mechanical properties in precedent literature. The following conditions were considered: axial force directed over the mesial marginal ridge, a mesial or a distal tipping force, a combination of both a torquing force and axial loading, and hydrostatic pressure. The maximum principal stresses were determined. ResultsThe highest root stress occurred in the cervical third of root surfaces (ie, not apically) under all loading conditions. Importantly, mesial tipping forces resulted in tension on distal roots, whereas distal tipping resulted in tension in the mesial roots. Intracanal pressures produced tensile stress on the internal root canal walls in the cervical third of the root. Stresses were calculated to be less than the fatigue tensile strength of dentin. ConclusionsStatic loading, under the conditions modeled, does not result in stress concentration at the root apices that would cause root fracture under normal masticatory loads. Stress patterns developing from mesial and distal tipping forces help to explain the appearance of vertical root fractures reported in sound nonrestored molar teeth.

Biomechanical Effects of Torquing on Upper Central Incisor with Thermoplastic Aligner: A Comparative Three-Dimensional Finite Element Study with and Without Auxillaries

Background and Objectives: This study was conducted to determine the effective method to torque the incisor with thermoplastic aligner using a three-dimensional (3D) finite element method. Materials and Methods: Three finite element models of maxilla and maxillary dentition were developed. In the first model, thermoplastic aligner without any auxiliaries was used. In the second and third models, thermoplastic aligner with horizontal ellipsoid composite attachment and power ridge were used, respectively. The software used for the study was ANSYS 14.5 FE. A force of 100 g was applied to torque the upper right central incisor. The resultant force transfer, stress distribution, and tooth displacement were evaluated. Results: The overall tooth displacement and stress distribution appeared high in the model with power ridge, whereas the root movement was more in the horizontal ellipsoid composite attachment model. The model without any auxillaries produced least root movement and stress distribution. Conclusion: Horizontal ellipsoid composite attachment achieved better torque of central incisor than the model with power ridge and model without any auxillaries.

Theoretical and Experimental Study on Contact Characteristics of Spiral Bevel Gears under Quasi-Static and Large Loading Conditions

The precise mathematical model for the tooth surface and transition surface of spiral bevel gears is derived. Taking a pair of spiral bevel gears of a heavy vehicle as an example of calculation and analysis, a finite element model of spiral bevel gears transmission system is established. Through the finite element tooth contact analysis under quasi-static loading and high loading condition, the influences of torque on the root stress distribution, contact stress, and transmission error are discussed, and the results are compared with the empirical formula results. Finally, a contact performance test bench of spiral bevel gear pair is developed, then the root bending stress, contact pattern, and transmission error tests are carried out. These experiment results are compared with analyzed ones, which showed a good agreement.

Transcatheter aortic valve implantation with the Portico and Evolut R bioprostheses in patients with elliptic aortic annulus.

To compare paravalvular leak (PVL) and device success rate of two self-expanding devices (Portico and Evolut-R) in patients with elliptic aortic annulus undergoing transcatheter aortic valve implantation (TAVI). This retrospective study included 374 patients submitted to TAVI with Portico (n=111) and Evolut-R (n=263), and available aortic annulus measurements at computed tomography angiography. Aortic annulus was defined elliptic if the index of eccentricity (IE=1-aortic annulus (minimum diameter)/(maximum diameter)) was >0.25. Device behavior to annulus eccentricity variations was measured by computational simulation in an idealized aortic root with three different IE (0, 0.25, and 0.5). An elliptic aortic annulus was found in 107 (28.6%) of 374 patients. Fewer rates of >moderate PVL were observed in Portico elliptic group compared to Evolut-R elliptic group (0.0% vs.15.2%; P=0.034). Device success in Portico elliptic group (100%) was significantly higher compared to that of Evolut-R elliptic group (84.8%; P=0.019). Eccentricity was a positive predictor of device success only in Portico patients (P=0.021). On computational simulation, Portico showed stable stent root interaction area, stress distribution, and regurgitant orifice area for IE=0.25 and 0.5. Portico showed good adaptability to annulus eccentricity variations and excellent PVL/device success rates in elliptic patients, compared to Evolut-R.

Altered stresses and dynamics after single and double annuloplasty ring for aortic valve repair.

OBJECTIVESAortic valve repair procedures for the treatment of isolated aortic valve insufficiency may be improved by stabilizing the functional aortic annulus using a double annuloplasty ring at the aortic annulus and sinotubular junction (STJ). The objective of this study was to compare the geometrical changes and aortic root stress distribution when using a single subvalvular ring and a double sub- and supravalvular ring in vivo.METHODSBoth the single- and double-ring procedures were performed successively in nine 80-kg pigs. Measurements were performed intraoperatively using sonomicrometry crystals in the aortic root to evaluate geometrical changes and annular and STJ force transducers measuring the segmental radial stress distribution.RESULTSThe total force in the STJ was significantly reduced after the double-ring procedure from 1.7 ± 0.6 to 0.04 ± 1.1 N (P = 0.001). The double-ring procedure significantly reduced the STJ area from 234.8 ± 37.6 to 147.5 ± 31.8 mm2 (P = 0.001) and expansibility from 17 ± 6% to 8 ± 3% (P = 0.001). With the single-ring procedure, the STJ shape was circular but became more oval with the double-ring procedure. The double-ring procedure did not affect stress distribution or geometry in the aortic annulus.CONCLUSIONSThe double-ring procedure stabilized the whole aortic root by reducing radial stress distribution in the STJ more efficiently than the single-ring procedure. Both area and expansibility were reduced with the double-ring procedure. These results confirm the importance of addressing the entire functional aortic annulus for optimal aortic valve repair procedures.

Influence of Different Fibreglass Post Geometries on the Stress Distribution and Pull-Out Bond Strength Before and After Mechanical Cycling.

Objective:There are no reports in the literature on whether FGP geometry influences the bond strength of the endodontically restored tooth. This study aimed to determine the stress distribution and the pull-out bond strength of different FGP geometries, before and after chewing loads simulation.Methods:One hundred and twenty root analogues were prepared and randomly distributed in six groups according to the post geometry. Half of the specimens were aged in water at 37 °C using a mechanical fatigue machine (84 N, 2 bar, 45°, 106 cycles, 4 Hz); while the remaining specimens were immediately submitted to the pull-out bond strength test. The specimens were tested in a universal testing machine and the bond strength in MPa was calculated. To assess the stress concentration, the finite element method was used simulating the same post geometries that were used in the in vitro test.Results:Two-way ANOVA (95%) showed no influence of post geometry on the bond strength (P=0.055) while fatigue cycling was statistical significant to reduce the bond strength values (P=0.000). The factors interaction was significant (P=0.019); however, TUKEY test (5%) showed no significant difference between post geometries after mechanical cycling. The tensile stress result showed critical areas in the post’s cervical region regardless of the design.Conclusion:The FGP geometry does not affect the root stress distribution and the long-term bond strength. However, FGP that allow a reduced cement layer thickness can improve the immediate pull-out bond strength value.

Stress distribution in dental roots restored with different post and core materials

Aim: The aim of this study was to investigate the stress distribution in models of maxillary central incisors restored with different post and core systems. Materials and Methods: A finite-element model of a maxillary central incisor was simulated in four different configurations – model 1: an intact tooth, Model 2: received gold cast metallic post and core, Model 3: received a fiberglass post and core, and Model 4: had a fiberglass post and the composite resin core. The restored tooth models were assumed to receive a ceramic crown simulating a clinical situation. After the preparation, the geometric models were exported in mesh to the analysis software (ANSYS 10.0, ANSYS Inc., Houston, USA). A 100 N static force at a 130° angle with respect to the longitudinal axis of the tooth was applied to the palatine surface of the model along equally distributed on the element nodes. The values and stress distribution were analyzed. Results: The stress distribution in the radicular structure of the models restored with three different post and core systems was like each other, but the gold cast metallic post and core system slightly improved the pattern of the stress distribution. Conclusions: The placement of post changes the stress distribution behavior, and the material with the highest elastic modulus showed the best performance in the stress distribution.

Effect of occlusal slope related to uneven attrition on root stress distribution and potential fracture

Background/purposeSeverely uneven occlusal attrition is thought to play an important role in the occurrence of spontaneous vertical root fracture (VRF), a frequent problem among Chinese people. This study evaluated the influence of occlusal slope related to uneven attrition on the root stress condition. Materials and methodsA finite element model of the mandibular first molar was established. Two different occlusal slope patterns were simulated in 5 models: (A) sound tooth, (B) 0.5–1.5 mm and (C) 2–3 mm attrition increased buccally, and (D) 0.5–1.5 mm and (E) 2–3 mm attrition increased distally. A static load of 200 N was applied vertically or angled at 45° to the longitudinal axis. The von Mises stress was evaluated. ResultsUnder vertical loading, more stress was transferred from the cervical to the middle root with attrition, especially the mesial root, while stress declined with attrition under oblique loading. Stress was mainly distributed in the buccal surface and mesial root with vertical loading, or in the lingual surface and distal root with oblique loading. The maximum von Mises with oblique loading was significantly higher than with vertical loading. ConclusionUneven occlusal attrition made the middle of the mesial root bear more stress, increasing fracture risk under vertical load. This finding suggests that timely restoration of the sloped occlusal morphology in teeth with severe attrition should be recommended to prevent VRFs. Lateral loading was not a risk factor of typical vertical root fractures, but the high stress could cause distal root cervical fracture.

Photoelastic analysis of stress distribution in mandibular second molar roots caused by several uprighting mechanics.

Mandibular molar uprighting is indicated when mesial inclination of the secondmolars occurs because of missing first molars. There are many methodologies to perform such movement. In this study, we aimed to analyze and compare the stress distributions in different molar uprighting techniques. Four photoelastic models were designed to evaluate different mandibular secondmolar uprighting techniques: a miniscrew positioned in the retromolar region, a beta-titanium alloy cantilever spring, a beta-titanium alloy wire with a T-loop spring, and an 0.018-in stainless steel archwire with an open-coil spring between the second premolar and the secondmolar. On the miniscrew test specimen, the greatest concentration of strains was observed in the cervical zone of the distal root. The cantilever spring had many strains in the cervical zone of the mesial root. On the T-loop spring test specimen, mainly the observed strains were in the apical zone of the mesial root. The open-coil spring specimen showed fringes in the cervical zone and the apical zone of the mesial root without formation of large sequences of strains. The miniscrew mechanical action had the least and the cantilever spring mechanical action had the greatest strain means on the roots of mandibular secondmolars.

Stress distribution of maxillary first molar PDL with highpull headgear traction; A finite element analysis

Statement of the problemHeadgear is most commonly used to correct anteroposterior discrepancies. Headgear can also be used to make more space for teeth to come in. In this instance the headgear is attached to the molars, via molar headgear bands and tubes, and helps to draw these molars backwards in the mouth, opening up space for the front teeth to be moved back using braces and bands. Stress on PDL of molars teeth and soreness of teeth when chewing, or when the teeth touch, is typical. Adults usually feel the soreness 12–24 h later, but younger patients tend to react sooner. PurposeApplication of heavy forces to maxillary dentition during treatment with headgear, induces high concentration of stresses in periodontal tissue. Quantification of this stress is of great concern in orthodontics. This study was designed to investigate the quantity and quality of stress response in the PDL of maxillary first molar which was subjected to highpull headgear traction using Finite Element Method. Materials and methodIn an experimental study, a three-dimensional finite element model of maxillary dentition, consisting of 17096 elements & 23013 nodes, was developed based on a young human skull. The forces were applied to the maxillary first molar in the stabilized arch by means of a rectangular full size arch wire in (022) slot bracket. Mechanical properties of this model were based on previous studies. A 350 g force was used for high pull headgear to affect the dentition (+30°) and stress distribution was investigated in buccal, palatal, mesial and distal side and in cervical, middle, apical sections of the PDL. The quantity of stresses were expressed as principal stresses, while the negative and positive signs indicated compressive and tensile stresses respectively. ResultsThe buccal surface of PDL of mesiobuccal root and the buccal, palatal, and distal surface in cervical regions of PDL of distobuccal root and the distal surface of the PDL of palatal root had received a great deal of stresses, in addition, the over all stress distribution in roots of molar had intrusive nature. ConclusionThe distribution of high stress concentration areas observed after using high pull headgear is limited to some root surfaces specially the distobuccal root.

Bending fatigue strength of case-carburized helical gears (In the case of large helix angles)

Case-carburizing enlarges the depth of the hardened layer at the tooth width end on the acute angle side of helical gears. For the helical gears with large helix angles (Exceeding 25°), this hardened layer may lower their bending fatigue strength. Therefore, we investigated the influence of this hardened layer on their bending fatigue strength through the bending fatigue tests. Our results suggest that this hardened layer might reduce the case-carburizing’s effect to enhance their bending fatigue strength. Thus, using only the maximum tooth root stress would be inadequate for evaluating their bending fatigue strength, and it would be necessary to consider the relationship between the hardened layer and the tooth root stress distribution (Especially, the stress applied at the tooth width end on the acute angle side) from the beginning of meshing to the end.

Comparison of in vitro flows past a mechanical heart valve in anatomical and axisymmetric aorta models

Flow characteristics past a bileaflet mechanical heart valve were measured under physiological flow conditions in a straight tube with an axisymmetric expansion, similar to vessels used in previous studies, and in an anatomical model of the aorta. We found that anatomical features, including the three-lobed sinus and the aorta’s curvature affected significantly the flow characteristics. The turbulent and viscous stresses were presented and discussed as indicators for potential blood damage and thrombosis. Both types of stresses, averaged over the two axial measurement planes, were significantly lower in the anatomical model than in the axisymmetric one. This difference was attributed to the lower height-to-width ratio and more gradual contraction of the anatomical aortic sinus. The curvature of the aorta caused asymmetries in the velocity and stress distributions during forward flow. Secondary flows resulting from the aorta’s curvature are thought to have redistributed the fluid stresses transversely, resulting in a more homogeneous stress distribution in the anatomical aortic root than in the axisymmetric root. The results of this study demonstrate the importance of modelling accurately the aortic geometry in experimental and computational studies of prosthetic devices. Moreover, our findings suggest that grafts used for aortic root replacement should approximate as closely as possible the shape of the natural sinuses.

Influence of inhomogeneous dental posts on stress distribution in tooth root and interfaces: Three-dimensional finite element analysis

Statement of problemIn post-and-core crown restorations, the use of flexible posts concentrates stresses at the dentin and the use of stiff posts concentrates stresses at the interfaces. A class of inhomogeneous materials (called functionally graded materials) has been proposed for posts to resolve the weaknesses of both flexible and rigid posts. PurposeThe purpose of this in vitro study was to design an inhomogeneous post and investigate its influence on the stress distribution of post-and-core crown restorations. Material and methodsAn extracted tooth was mounted, sectioned, and photographed to create a 3-dimensional model of the first premolar tooth. The post-and-core crown restoration was modeled with and without a ferrule. The surrounding tissues of the mandibular tooth, periodontal ligament, and cortical and trabecular bones were modeled. Fiber-reinforced composite (FRC), metallic, and inhomogeneous posts were investigated by finite element analysis and the stress distribution results compared. ResultsFRC posts resulted in the highest maximum tensile stress (MTS) at the remaining dentin (90.4 to 93.2 MPa), while inhomogeneous posts graded by index n=10 (FGM10) caused the lowest MTS, both with and without a ferrule (72.3 to 74.8 MPa). ConclusionsThe use of FRC posts concentrated more MTS at the dentin and less MTS at the dentin-adhesive interface than metallic posts. Inhomogeneous posts (FGM10) resolved the weaknesses of both flexible and rigid posts by simultaneously reducing stresses at the dentin and interface. The ferrule effect resulted in fewer dentin and interface stresses.

An analysis of the tooth stress distribution of forged bi-metallic gears

The work described in this paper is an evaluation of the contact characteristics of bi-metallic gears forged through a novel bi-metallic gear forging process. Finite element analysis of the contact characteristics of single material gears was first performed to validate the tooth contact and tooth root stresses with empirical American Gear Manufacturers Association and British Standard standards. Having verified the validity of the model, simulations were performed for gears comprising lightweight cores with teeth bounded by steel bands of uniform thicknesses, 1 mm, 2 mm, 4 mm, and 6 mm to evaluate the differences in stress distribution and compare to single material gear teeth. The forged profiles obtained experimentally by utilising 2 mm, 4 mm, and 6 mm thickness bands via the bi-metallic gear forging process are also discussed. The uniform thickness model is subsequently adapted to incorporate the experimental forged profiles in order to estimate the contact stress, root stress, and stress distribution within the teeth to identify performance differences between bi-metallic forged gears and traditional single material gears.

Stress Distribution in Roots Restored with Fiber Posts and An Experimental Dentin Post: 3D-FEA.

The aim of this study was to compare the stress distribution in radicular dentin of a maxillary canine restored with either a glass fiber post, carbon fiber post or an experimental dentin post using finite element analysis (3D-FEA). Three 3D virtual models of a maxillary canine restored with a metal-ceramic crown and glass fiber post (GFP), carbon fiber post (CFP), and experimental dentin post (DP) were obtained based on micro-CT images. A total of 180 N was applied on the lingual surface of the incisal third of each tooth at 45 degrees. The models were supported by the periodontal ligament fixed in three axes (x=y=z=0). The von Mises stress (VMS) of radicular dentin and the intracanal posts was calculated. The structures of all groups showed similar values (MPa) and distribution of maximum von Mises stress. Higher stress was found in the apical third of dentin while the posts presented homogeneous stress distribution along the axis. The fiber and dentin posts exhibited similar stress values and distribution. Thus, the experimental dentin post is a promising restorative material.