Effect of Different Cements on the Biomechanical Behavior of Teeth Restored with Cast Dowel‐and‐Cores—In Vitro and FEA Analysis

Purpose: To test the hypothesis that the type of cement used for fixation of cast dowel‐and‐cores might influence fracture resistance, fracture mode, and stress distribution of single‐rooted teeth restored with this class of metallic dowels. Materials and Methods: The coronal portion was removed from 40 bovine incisors, leaving a 15 mm root. After endodontic treatment and standardized root canal relief at 10 mm, specimens were embedded in polystyrene resin, and the periodontal ligament was simulated with polyether impression material. The specimens were randomly divided into four groups (n = 10), and restored with Cu–Al cast dowel‐and‐cores cemented with one of four options: conventional glass ionomer cement (GI); resin‐modified glass ionomer cement (GR); dual‐cure resin cement (RC); or zinc‐phosphate cement (ZP). Sequentially, fracture resistance of the specimens was tested with a tangential load at a 135° angle with a 0.5 mm/min crosshead speed. Data were analyzed using one‐way analysis of variance (ANOVA) and the Fisher test. Two‐dimensional finite element analysis (2D‐FEA) was then performed with representative models of each group simulating a 100 μm cement layer. Results were analyzed based on von Mises stress distribution criteria. Results: The mean fracture resistance values were (in N): RC, 838.2 ± 135.9; GI, 772.4 ± 169.8; GR, 613.4 ± 157.5; ZP, 643.6 ± 106.7. FEA revealed that RC and GR presented lower stress values than ZP and GI. The higher stress concentration was coincident with more catastrophic failures, and consequently, with lower fracture resistance values. Conclusions: The type of cement influenced fracture resistance, failure mode, and stress distribution on teeth restored with cast dowel‐and‐cores.     

Cortical Bone Stress Distribution in Mandibles with Different Configurations Restored with Prefabricated Bar‐Prosthesis Protocol: A Three‐Dimensional Finite‐Element Analysis

Purpose: To evaluate stress distribution in different horizontal mandibular arch formats restored by protocol‐type prostheses using three‐dimensional finite element analysis (3D‐FEA). Materials and Methods: A representative model (M) of a completely edentulous mandible restored with a prefabricated bar using four interforaminal implants was created using SolidWorks 2010 software (Inovart, São Paulo, Brazil) and analyzed by Ansys Workbench 10.0 (Swanson Analysis Inc., Houston, PA) to obtain the stress fields. Three mandibular arch sizes were considered for analysis, regular (M), small (MS), and large (ML). Three unilateral posterior loads (L) (150 N) were used: perpendicular to the prefabricated bar (L1); 30° oblique in a buccolingual direction (L2); 30° oblique in a lingual‐buccal direction (L3). The maximum and minimum principal stresses (σ_max, σ_min), the equivalent von Mises (σ_vM), and the maximum principal strain (σ_max) were obtained for type I (M.I) and type II (M.II) cortical bones. Results: Tensile stress was more evident than compression stress in type I and II bone; however, type II bone showed lower stress values. The L2 condition showed highest values for all parameters (σ_vM, σ_max, σ_min, ?_max). The σ_vM was highest for the large and small mandibular arches. Conclusion: The large arch model had a higher influence on σ_max values than did the other formats, mainly for type I bone. Vertical and buccolingual loads showed considerable influence on both σ_max and σ_min stresses.     

Evaluating the Effect of Oblique Ridge Conservation on Stress Distribution in an Endodontically Treated Maxillary First Molar: A Finite Element Study

IntroductionAlthough the maxillary first molar (MFM) has been frequently subjected to stress analysis in endodontic investigations, the available data about the effect of its oblique ridge are quite sparse. The aim of this study includes evaluating the effect of the residual oblique ridge on the stress distribution after preparing conservative access cavities.MethodsBased on the cone-beam computed tomographic data, the model of an intact MFM and 5 cavity designs were prepared for endodontic treatment, which were consequently filled with gutta-percha and dental resin composite (6 total models). All models were subjected to 4 types of occlusal loading; finite element analysis via ABAQUS CAE software (Dassault Systemes, Vélizy-Villacoublay, France) was accomplished, whereas other software programs such as (Mimics Research Materialise, Leuven, Belgium) and 3-Matic Research (Materialise) were also incorporated in different stages for detecting stress distribution.ResultsThe stress distribution on the MFM is not only dependent on the remaining width of the oblique ridge but also on the type of loading. The most stress on the cervical region was concentrated on the palatal root in some type of loading, whereas the least stress on the occlusal surface was recorded when the whole oblique ridge was replaced by the composite resin.ConclusionsWhen the occlusal contacts are occurring only on the palatal cusp, the stress distribution on the oblique ridge is noticeably affected by the cavity design.     

Influence of Material of Overdenture‐Retaining Bar with Vertical Misfit on Three‐Dimensional Stress Distribution

Purpose: This study evaluated the effects of different bar materials on stress distribution in an overdenture‐retaining bar system with a vertical misfit between implant and bar framework. Materials and Methods: A three‐dimentional finite element model was created including two titanium implants and a bar framework placed in the anterior part of a severely reabsorbed jaw. The model set was exported to mechanical simulation software, where displacement was applied to simulate the screw torque limited by 100‐μm vertical misfit. Four bar materials (gold alloy, silver‐palladium alloy, commercially pure titanium, cobalt‐chromium alloy) were simulated in the analysis. Data were qualitatively evaluated using Von Mises stress given by the software. Results: The models showed stress concentration in cortical bone corresponding to the cervical part of the implant, and in cancellous bone corresponding to the apical part of the implant; however, in these regions few changes were observed in the levels of stress on the different bar materials analyzed. In the bar framework, screw, and implant, considerable increase in stress was observed when the elastic modulus of the bar material was increased. Conclusions: The different materials of the overdenture‐retaining bar did not present considerable influence on the stress levels in the periimplant bone tissue, while the mechanical components of the system were more sensitive to the material stiffness.     

Effects of the Implant Design on Peri‐Implant Bone Stress and Abutment Micromovement: Three‐Dimensional Finite Element Analysis of Original Computer‐Aided Design Models

Background: Occlusal overloading causes peri‐implant bone resorption. Previous studies examined stress distribution in alveolar bone around commercial implants using three‐dimensional (3D) finite element analysis. However, the commercial implants contained some different designs. The purpose of this study is to reveal the effect of the target design on peri‐implant bone stress and abutment micromovement. Methods: Six 3D implant models were created for different implant–abutment joints: 1) internal joint model (IM); 2) external joint model (EM); 3) straight abutment (SA) shape; 4) tapered abutment (TA) shapes; 5) platform switching (PS) in the IM; and 6) modified TA neck design (reverse conical neck [RN]). A static load of 100 N was applied to the basal ridge surface of the abutment at a 45‐degree oblique angle to the long axis of the implant. Both stress distribution in peri‐implant bone and abutment micromovement in the SA and TA models were analyzed. Results: Compressive stress concentrated on labial cortical bone and tensile stress on the palatal side in the EM and on the labial side in the IM. There was no difference in maximum principal stress distribution for SA and TA models. Tensile stress concentration was not apparent on labial cortical bone in the PS model (versus IM). Maximum principal stress concentrated more on peri‐implant bone in the RN than in the TA model. The TA model exhibited less abutment micromovement than the SA model. Conclusion: This study reveals the effects of the design of specific components on peri‐implant bone stress and abutment displacement after implant‐supported single restoration in the anterior maxilla.     

Evaluation of Stress Distribution in Overdenture‐Retaining Bar with Different Levels of Vertical Misfit

Purpose: To evaluate the effects of different levels of vertical misfit between implant and bar framework on distribution of static stresses in an overdenture‐retaining bar system using finite element analysis. Material and Methods: A 3D finite element model (11,718 elements and 21,625 nodes) was created and included two titanium implants and a bar framework placed in the medial region of the anterior part of a severely reabsorbed‐jaw. All materials were presumed to be linear elastic, homogenous, and isotropic. Mechanical simulation software (NEiNastran 9.0) was used, where displacements were applied on the end of the bar framework to simulate the closure of the vertical misfits (5, 25, 50, 100, 200, and 300 μm) after tightening of the screws. Data were qualitatively evaluated using Von Mises stress given by the software. Results: The models showed stress concentration in cortical bone, corresponding to the cervical part of the implant, and in cancellous bone, corresponding to the apical part of the implant; however, in these regions few changes were observed in stress to the misfits studied. While in the bar framework, retaining‐screw neck, and implant platform, a considerable stress increase proportional to the misfit amplification was observed. Conclusions: The different levels of vertical misfit did not considerably influence the static stress levels in the peri‐implant bone tissue; however, the mechanical components of the overdenture‐retaining bar system are more sensitive to lack of passive fit.     

Influence of Cusp Inclination on Stress Distribution in Implant‐Supported Prostheses. A Three‐Dimensional Finite Element Analysis

Purpose: The aim of this study was to assess the influence of cusp inclination on stress distribution in implant‐supported prostheses by 3D finite element method. Materials and Methods: Three‐dimensional models were created to simulate a mandibular bone section with an implant (3.75 mm diameter × 10 mm length) and crown by means of a 3D scanner and 3D CAD software. A screw‐retained single crown was simulated using three cusp inclinations (10°, 20°, 30°). The 3D models (model 10d, model 20d, and model 30d) were transferred to the finite element program NeiNastran 9.0 to generate a mesh and perform the stress analysis. An oblique load of 200 N was applied on the internal vestibular face of the metal ceramic crown. Results: The results were visualized by means of von Mises stress maps. Maximum stress concentration was located at the point of application. The implant showed higher stress values in model 30d (160.68 MPa). Cortical bone showed higher stress values in model 10d (28.23 MPa). Conclusion: Stresses on the implant and implant/abutment interface increased with increasing cusp inclination, and stresses on the cortical bone decreased with increasing cusp inclination.     

Influence of Ferrule,Post System,and Length on Stress Distribution of Weakened Root-filled Teeth

Introduction

The aim of this study was to evaluate the influence of a ferrule, post system, and length on the stress distribution of weakened root-filled teeth.

Methods

The investigation was conducted by using 3-dimensional (3D) finite element analysis. A sound tooth and 8 3D models of a weakened root-filled central incisor were generated using computer-aided design/computer-aided manufacturing software. The models were created without a ferrule and with a 2.0-mm ferrule, restored with a relined glass fiber post or a cast post and core (Cpc), and 12.0- and 7.0-mm post lengths. Each 3D model was imported using ∗.STEP files to the finite element software for mesh generation. The models were subjected to 100-N oblique loading at the palatal surface, and the results were evaluated by von Mises criterion and maximum principal stress distribution.

Results

Finite element analysis showed that the Cpc models showed elevated stress levels in the root canal regardless of the presence of a ferrule. Relined glass fiber post models showed homogeneous stress distribution to the dentin external surface similar to the sound tooth model. Without a ferrule, Cpc with a 7- or 12-mm length promoted high levels of tensile stress inside the root canal.

Conclusions

Ferrule presence promoted more satisfactory stress distribution to the roots. Post length influenced the stress distribution only for the models restored with a cast post and core. High levels of tensile stress inside the root canals were verified with a cast post and core, which should be avoided to rehabilitate weakened roots, mainly in the absence of a ferrule.     

牙体缺损程度对后牙桩核冠修复牙本质应力影响的三维有限元分析

目的:比较上颌第一磨牙不同程度牙体缺损桩核冠修复后牙本质应力分布情况,探讨牙体剩余量与牙本质应力分布之间的关系。方法:通过磨片法建立上颌第一磨牙桩核冠有限元模型,比较上颌第一磨牙4种不同程度牙体缺损桩核冠修复后的牙本质应力分布情况。结果:后牙牙体水平向缺损量超过其牙冠牙体量1/2时,牙本质应力峰值较高,缺损量在牙冠牙体量1/2以内,对应力峰值无显著影响。结论:当水平向牙体剩余量大于1/2时,剩余牙体组织所受应力较大,上颌第一磨牙的腭根根分叉处是根折的危险区域。     

Mechanical behaviour of nickel‐titanium rotary endodontic instruments in simulated clinical conditions: a computational study

Aim To develop an accurate finite element (FE) model for studying rotary endodontic instruments and to demonstrate the usefulness of the FE method in improving the knowledge of the mechanical behaviour of these instruments during root canal preparation. Methodology An accurate geometrical model of a Ni‐Ti ProTaper F1 instrument was created. The interaction between the rotating instrument and differently shaped root canals during the insertion and removal procedure was studied using FE analyses. The complex thermo‐mechanical behaviour of the Ni‐Ti alloy was reproduced using an ad hoc computational subroutine. With the aim of demonstrating the enhanced performance of the shape memory alloy employment, the same analysis was performed on a ‘virtual’ ProTaper F1 made of stainless steel. Results The Ni‐Ti instrument operated in its pseudo‐elastic range and was able to recover its original shape and to follow the canal curvature without deviation. The radius and the position of the canal curvature are the most critical parameters that determined the stress in the instrument with higher stress levels being produced by decreasing the radius and moving from the apical to the mid root position. Conclusions The most demanding working conditions were observed in canals with sharp curves, especially in areas where the instruments had larger diameters. To prevent possible damage to instruments and fracture, it is advised that the instruments should be discarded following their use in such canals.     

截根术牙半切除术及术后不同修复设计对牙周膜内应力分布影响的研究——二维有限元分析

临床工作中常采用截根术半切除术以保留重度牙周炎及牙根纵裂的牙齿,本文利用二维有限元法分析了截根术、牙半切除术及术后不同修复设计治疗后患牙牙周膜内应力分布的变化情况.结果发现:牙半切除术较截根术更符合患牙的保健要求;术后进行合理的修复对患牙取得远期疗效有利.从而为临床工作中究竞采取何种术式及术后采取何种修复设计提供了理论基础.     

种植体螺纹形状对骨界面应力分布的影响

目的研究种植体表面不同螺纹形状对种植体-骨界面应力分布的影响,以供临床筛选合适的种植系统。方法采用三维有限元法,分别对种植体施加30牛顿垂直和斜向45°两种方向的集中载荷,对不同螺纹顶角螺纹形状分别为对称、上平下斜、上斜下平的种植体-骨界面进行应力分析。结果螺纹形状为上平下斜式种植体的应力峰值较小;各组模型的最大位移值相近,但螺纹形状对称、顶角为30°者位移极值最小,为3.84×10-4mm和85.61×10-4mm。结论螺纹形状对种植体-骨界面的应力分布有影响,设计和选择种植系统时应全面考虑。     

不同包绕度对桩冠箍效应影响的三维有限元分析

目的：研究桩冠修复中箍的不同包绕度与箍效应之间的相互关系及影响。方法：建立上颌中切牙烤瓷核桩冠三维有限元模型,模拟箍效应的4种包绕形式,通过三维有限元方法分析才本质受力情况。结果：①根管口周围余留牙本质壁完整,牙本质应力分布最好。②仅余留唇侧牙体时,须部牙本质应力水平明显升高。结论：随着箍包绕才体壁的减少,箍效应有所降低,但保留唇舌侧牙体和仅保留石侧牙体部可获得一定的箍效应。     

The Effects of Adhesive Type and Thickness on Stress Distribution in Molars Restored with All‐Ceramic Crowns

Purpose: This study investigated the effects of luting cement type and thickness on the stress distribution within all‐ceramic crowns using finite element analysis. Materials and Methods: An all‐ceramic crown restoration of the mandibular right first molar was prepared according to standard dental processes and scanned using micro‐computed tomography. Eight 3D FE models were then developed that accounted for two adhesive systems, each with cement thickness of 60 μm, 90 μm, 120 μm, and 150 μm. The models were subjected to four loading conditions, and stresses in the veneer and core layers were evaluated. Results: The stress distribution and maximum stresses in the veneer, core, and cement are presented in corresponding loading conditions. The cement with higher elastic modulus resulted in lower tensile stresses in the veneer and core layers, and the shear strength of the cement was critical to the intactness of the all‐ceramic crown. Conclusion: The cement thickness acts as a cushion between the crown and dentin substrate. Although there is an optimal thickness (approximately 90 μm) that can reduce the stress level in ceramic crowns, cement thickness is not very important to stresses in the core or veneer in most cases when compared to the influence of loading conditions or cement moduli.     

Influence of Tapered and External Hexagon Connections on Bone Stresses Around Tilted Dental Implants: Three‐Dimensional Finite Element Method With Statistical Analysis

Background: The purpose of this study is to analyze the tension distribution on bone tissue around implants with different angulations (0°, 17°, and 30°) and connections (external hexagon and tapered) through the use of three‐dimensional finite element and statistical analyses. Methods: Twelve different configurations of three‐dimensional finite element models, including three inclinations of the implants (0°, 17°, and 30°), two connections (an external hexagon and a tapered), and two load applications (axial and oblique), were simulated. The maximum principal stress values for cortical bone were measured at the mesial, distal, buccal, and lingual regions around the implant for each analyzed situation, totaling 48 groups. Loads of 200 and 100 N were applied at the occlusal surface in the axial and oblique directions, respectively. Maximum principal stress values were measured at the bone crest and statistically analyzed using analysis of variance. Stress patterns in the bone tissue around the implant were analyzed qualitatively. Results: The results demonstrated that under the oblique loading process, the external hexagon connection showed significantly higher stress concentrations in the bone tissue (P <0.05) compared with the tapered connection. Moreover, the buccal and mesial regions of the cortical bone concentrated significantly higher stress (P <0.005) to the external hexagon implant type. Under the oblique loading direction, the increased external hexagon implant angulation induced a significantly higher stress concentration (P = 0.045). Conclusions: The study results show that: 1) the oblique load was more damaging to bone tissue, mainly when associated with external hexagon implants; and 2) there was a higher stress concentration on the buccal region in comparison to all other regions under oblique load.     

Effects of Root Maturation and Thickness Variation in Coronal Mineral Trioxide Aggregate Plugs Under Traumatic Load on Stress Distribution in Regenerative Endodontic Procedures: A 3-dimensional Finite Element Analysis Study

IntroductionRegenerative endodontic procedures (REPs) are the best biological-based treatment choice for managing necrotic immature permanent teeth. This study aimed to evaluate the stress distribution of immature maxillary permanent incisors and periodontal tissues under a traumatic load after root maturation achieved by REP with thickness variation in coronal mineral trioxide aggregate (MTA) plugs.MethodsFive different mathematical 3-dimensional finite element analysis models of an immature permanent maxillary incisor were created. These involved immediate postoperative models after REP with varying coronal MTA plug thickness (model 1: 3-mm MTA and model 2: 5-mm MTA), postoperative models after REP with varying coronal MTA plug thickness with 15% volumetric root maturation (model 3: 3-mm MTA and model 4: 5-mm MTA), and a control model (model 5: a mature, healthy maxillary incisor). After the modeling procedures, a traumatic horizontal force load of 400 N was applied, and 3-dimensional finite element analysis was performed. The minimum principal, maximum principal, and von Mises stress criteria were calculated for evaluation.ResultsRegardless of the coronal MTA plug thickness, tensile stress in cervical root surfaces decreased with root maturation after REP. Using the 5-mm MTA plug reduced all types of stress in the middle third of the root. In bone tissue, the difference in MTA thickness did not affect stress values. However, stress decreased in most of the bony surfaces with root maturation after REP.ConclusionsUsing the 5-mm coronal MTA plug may help in providing biomechanical advantages regarding stress transmission. Also, because root maturation after REP provided a more favorable stress distribution as mentioned, regenerative treatments can be recommended for immature permanent maxillary incisors for a good prognosis.     

The influence of ferrule effect and length of cast and FRC posts on the stresses in anterior teeth

Objectives

The purpose was to assess the influence of ferrule effect and length of cast post and cores, and FRC posts on the strength of anterior teeth.

Materials and methods

The investigations were conducted by means of finite element analysis with the application of contact elements. Thirteen 3D models of maxillary first incisors were generated: model 1 was an intact tooth; 2A – a tooth with all-ceramic crown with ferrule effect, 2B–D a teeth restored with, ferrule and FRC posts of various lengths 13 mm, 8 mm, 4 mm, 3A – a tooth with ceramic crown without, ferrule effect, 3B and C teeth without ferrule and 10 mm, 5 mm length FRC posts, 4B–D teeth with ferrule, restored by cast posts and cores of 13 mm, 8 mm, 4 mm lengths and 5B and C teeth without ferrule, restored with cast posts and cores of 10 mm, 5 mm lengths. Each model was subject to a load with a total force of 100 N uniformly distributed under the lingual cingulum, at an angle of 130°. To evaluate, the strength of tooth tissues, ceramics and composites, the modified von Mises failure criterion was used, for FRC the Tsai-Wu criterion and for cast NiCr alloy the von Mises criterion. Contact stresses were calculated at the luting cement–tissue interface.

Results

Ferrule effect in teeth reduces mvM stresses in dentin, in posts and in luting cement. The contact tensile stresses around posts in teeth with ferrule effect were 1.7–3.0 times smaller than in, teeth without ferrule. Lower mvM stresses occurred in teeth with cast posts in comparison with FRC posts. The mvM stresses in teeth with posts of various lengths were similar, irrespective of post material.

Significance

Ferrule effect in teeth with posts and cores has a critical influence on stress reduction. Using posts and cores made of rigid materials leads to stress reduction in teeth. Post length has a small, effect on stress values in tooth structures.