A three-dimensional finite element analysis of the effects of restorative materials and post geometry on stress distribution in mandibular molar tooth restored with post-core crown

Mechanical and modal analysis of different implant strategies for loss of three teeth with bone atrophy in the maxillary posterior region

PURPOSE

This study aimed to evaluate the stress distribution and secondary stability involved in five implant strategies, including implant-supported prostheses (ISP) and tooth-implant-supported prostheses (TISP), used for bone atrophy in the maxillary posterior region with teeth loss using finite element analysis, and to explore the more desirable implant methods.

METHODS

Five implant strategies were made to analyze and compare: M1, implant-supported prosthesis consisting of a short implant with a regular implant; M2, implant-supported prosthesis consisting of a tilted implant with a regular implant; M3, cantilever structure; M4, tooth-implant-supported prosthesis consisting of a short implant with a regular implant; M5, tooth-implant-supported prosthesis consisting of a regular implant, and M6, with only the natural teeth as a control group. Dynamic loading of the above models was performed in finite element analysis software to assess the stress distribution of the bone tissue and implants using the von Mise criterion. Finally, the secondary stability of different models was evaluated by modal analysis.

RESULTS

The maximum stress distribution in the cortical bone in M1(60 MPa) was smaller than that in M2(97 MPa) and M3(101 MPa), The first principal strain minimum was obtained in M2 (2271μ ε ). M4 (33 MPa, 10085 Hz) with the best mechanical properties and highest resonance frequency. But increased the loading on the natural teeth.

CONCLUSIONS

Short implants and tilted implants are both preferred implant strategies, if cantilever construction is necessary, a tooth-implant-supported prosthesis consisting of a short implant and a regular implant is recommended.

Timing selection for loosened tooth fixation based on degree of alveolar bone resorption: a finite element analysis

Objective

This study aimed to evaluate timing of fixation to retard bone absorption using finite element analysis(FEA).

Methods

Volunteer CT images were used to construct four models of mandibles with varying degrees of alveolar bone resorption. By simulating occlusal force loading, biomechanical analysis was made on the periodontal membrane, tooth root and surrounding bone (both cancellous and cortical) of mandibular dentition.

Results

The von Mises stress value of the periodontal structures was positively related with the degree of alveolar bone resorption, and the von Mises stress at the interface between the periodontal membrane and tooth root was increased significantly in moderate to severe periodontitis models. The von Mises stress at the interface between the periodontal cortical bone and cancellous bone was increased significantly in the severe periodontitis model. And the von Mises stress value with oblique loading showed significantly higher than vertical loading.

Conclusion

Teeth with moderate to severe periodontitis, loosened tooth fixation can be used to retard bone absorption.

Investigation of stress distribution within an endodontically treated tooth restored with different restorations

Background/purpose

Recently, metal-free restoration has become the standard in prosthetic treatment. However, it is still unclear which combination is most effective in preventing root fracture and secondary caries. The purpose of this study was to evaluate the influence of different post systems, crown materials, crown thickness and luting agents on the stress distribution around the crown margins, cervical dentin and the tip of the post.

Materials and methods

Ninety-six mandibular first premolar models were developed and analyzed using finite element analysis (FEA). Two designs of crowns, six kinds of crown materials, four types of post and core systems and two kinds of luting agents were included and evaluated for the stress distribution within the abutment teeth. The Von Mises stress magnitudes were compared among all models.

Results

The stress at the tip of the post decreased as the young's modulus of luting agent decreased; The stress concentrated more at the cervical area (dentin and crown), as the physical properties of the crown material increased.

Conclusion

Crowns fabricated using polyetheretherketone (PEEK) can reduce the stress concentration at the cervical area, so it may be possible to reduce the amount of tooth reduction during abutment tooth preparation. The stress distribution around the post tip is affected by the post and core systems and luting agent, regardless of crown materials and thickness. When inserting a post of the higher Young's modulus such as zirconia post, methyl methacrylate luting cement can reduce the stress concentration at the tip of the post.

Mechanical and thermal stress evaluation of PEEK prefabricated post with different head design in endodontically treated tooth: 3D-finite element analysis

An endodontic post is required to retain and support the core restoration in case of insufficient remaining coronal dentin after root canal therapy. This study analyzed the biomechanical and thermal behavior of PEEK prefabricated post after choosing the head design that produces the least amount of stress on the core and remaining tooth structure. These results were compared with the most common commercially available prefabricated post, which is titanium and glass fiber post. Thus a CBCT scanning of a maxillary central incisor with its supporting structure was used to construct a 3D solid model of an endodontically treated teeth for finite element analysis (FEA). The restored tooth with the spherical head design of PEEK prefabricated post yielded a more benign stress distribution and repairable failure mode on the crown, luting cement, core, and dentin under both mechanical and thermal loads, followed by glass fiber post and titanium post respectively.

Influence of conservative endodontic access and the osteoporotic bone on the restoration material adhesive behavior through finite element analysis

Assess, using finite element analysis, the adhesive behavior of Class I restorations under physiological occlusal loads on an endodontically treated first upper premolar with conventional and conservative crown opening surrounded by alveolar bone in normal and osteoporotic conditions. For this, four virtual models were used: M1-conservative access/normal bone; M2-conventional access/normal bone; M3-conservative access/osteoporotic bone; M4-conventional access/osteoporotic bone. On enamel, under axial load, the highest peaks occurred on conventional models and, under oblique load, the highest peaks occurred on conservative opening models. The bone condition showed no influence on the adhesive behavior. On dentin, under axial load, the models showed similar behaviors, regardless of the bone condition; under oblique load, the highest incidence of forces occurred on the distal region of the palatal root canal entrance and the highest peak was observed in the conventional opening model with normal bone. Also, under oblique load, conventional opening models showed larger values on dentin for the normal bone and similar for the osteoporotic. The conclusions shows higher displacement tensile strength peaks were observed in the conventional models, which can lead to a greater risk of adhesive failure on class I restorations with this opening. Therefore, a conservative opening would be recommended to avoid opening clinical complications. The bone condition showed no significant influence on adhesive behavior, except for dentin under oblique load, where conventional models showed larger values relative to normal bone and similar to the osteoporotic bone.

Determination of the Optimum Material for an Endodontic Prefabricated Post Using a Sub-Problem Approximation Method

The success in the chewing process depends on the performance of the tooth used. Actually, taking care of the tooth and improving its performance can change our life. Therefore, the treatment process of the teeth has become more necessary in the life of a dental patient. Nowadays, a post plays an important vital role in this process. In the present work, analysis of the effect of the post material on the performances of the components of endodontically treated teeth (ETT) was carried out through the finite element analysis (FEA). The effects of post material on the von Mises stress component (Svon), shear stress, and displacement component (Usum) occurred on the all components of ETT were investigated. After that, the determination of the optimum material for an endodontic prefabricated post (EPP) was investigated through the sub-problem approximation method.

Effect of tapering internal coronal walls on fracture resistance of anterior teeth treated with cast post and core: In vitro study

When fabricating indirect post and core, internal coronal walls are tapered to remove undercuts and allow a better adaptation. To evaluate the fracture strength of anterior tooth reconstructed with post and core and crowned, with two different taper of internal coronal walls, 6° and 30° to the long axis, two groups of 30 clear plastic analogues simulating endodontically treated maxillary central incisors were prepared. The analogues crowned were subjected to a compressive load with a 1-kN cell at a crosshead speed of 0.05 mm/min at 130° to the long axis until fracture occurred. Data were analyzed by Lillifors and Mann–Whitney tests. Mean failure loads for the groups were as follows: group I 1038.69 N (standard deviation ±243.52 N) and group II 1231.86 N (standard deviation ±368.76 N). Statistical tests showed significant difference between groups (p = 0.0010 < 0.01). Increasing the taper of internal coronal walls appears to enhance the fracture resistance of anterior maxillary teeth post and core reconstructed.

The influence of experimental silane primers on dentin bond strength and morphology: a laboratory and finite element analysis study

STATEMENT OF PROBLEM

The inconsistency of dentin bonding affects retention and microleakage.

PURPOSE

The purpose of this laboratory and finite element analysis study was to investigate the effects on the formation of a hybrid layer of an experimental silane coupling agent containing primer solutions composed of different percentages of hydroxyethyl methacrylate.

MATERIAL AND METHODS

A total of 125 sound human premolars were restored in vitro. Simple class I cavities were formed on each tooth, followed by the application of different compositions of experimental silane primers (0%, 5%, 25%, and 50% of hydroxyethyl methacrylate), bonding agents, and dental composite resins. Bond strength tests and scanning electron microscopy analyses were performed. The laboratory experimental results were validated with finite element analysis to determine the pattern of stress distribution. Simulations were conducted by placing the restorative composite resin in a premolar tooth by imitating simple class I cavities. The laboratory and finite element analysis data were significantly different from each other, as determined by 1-way ANOVA. A post hoc analysis was conducted on the bond strength data to further clarify the effects of silane primers.

RESULTS

The strongest bond of hybrid layer (16.96 MPa) was found in the primer with 25% hydroxyethyl methacrylate, suggesting a barely visible hybrid layer barrier. The control specimens without the application of the primer and the primer specimens with no hydroxyethyl methacrylate exhibited the lowest strength values (8.30 MPa and 11.78 MPa) with intermittent and low visibility of the hybrid layer. These results were supported by finite element analysis that suggested an evenly distributed stress on the model with 25% hydroxyethyl methacrylate.

CONCLUSIONS

Different compositions of experimental silane primers affected the formation of the hybrid layer and its resulting bond strength.

On the ferrule effect and the biomechanical stability of teeth restored with cores, posts, and crowns

An abutment for a fixed partial denture may not contain enough tooth structure, such that the abutment does not provide an adequate ‘ferrule effect’. A crown or bridge dental prosthesis that is cemented onto such an abutment/s may undergo biomechanical failure. Here, the tooth, core, and post complex, on which the crown is cemented, may fracture off from the abutment, causing the crown to separate from the abutment, while the cement that bonds the crown to the tooth, core, and post complex remains intact, such that the tooth, core, and post complex remains inside the crown when the crown separates from the abutment. This article reviews the dentistry literature on the ferrule effect, and presents alternative definitions for terms such as ferrule, the ferrule effect, and the ferrule tooth structure. The article also explains how the use of a surgical operating microscope, or high magnification binocular surgical loupes of ×6-8, or greater magnification improve the ability of a dentist to assess how much ferrule tooth structure an abutment contains, compared to the use of unaided vision.

Effects of post core materials on stress distribution in the restoration of mandibular second premolars: a finite element analysis

STATEMENT OF PROBLEM

Previous studies have not resolved the question as to which post and core combination optimizes the stress distribution within the post restoration and tooth.

PURPOSE

The purpose of this study was to determine which post and core combination provides the most favorable stress distribution upon loading.

MATERIAL AND METHODS

Three-dimensional models of teeth were created with the Ansys program to simulate different materials used for post and cores (Ti, NiCr, AuPd, zirconia, zirconia post/composite resin core, glass fiber post/composite resin core, and carbon fiber post/composite resin core) and metal ceramic crowns (nickel chromium alloy [Group NiCr] and gold palladium alloy [Group AuPd]). A force of 400 N was applied to the occlusal surface, and von Mises equivalent stress values were calculated.

RESULTS

Carbon fiber post/composite resin core/metal ceramic crowns with NiCr alloy core had the highest stress values in the weakened root, tooth/post interface, and post. NiCr post/NiCr core/metal ceramic crowns with NiCr alloy core had the lowest stress values in the weakened root and post. The zirconia post and core had the lowest stress value in the tooth/post interface.

CONCLUSIONS

A post material with a high elastic modulus led to lower stress in the weakened root (approximately 6%) and tooth/post interface (approximately 12%) and to higher stress in the post (approximately 5 times). A composite resin core led to higher stress in the weakened root (approximately 11% to 17%) and lower deformation in the tooth/post interface (approximately 17.5%) and post materials (approximately 24%). Group AuPd resulted in lower stress in the root and high stress in the post (approximately 4.5% to 7%) and affected the amount of deformation in posts with a composite resin core.

Effect of the crown design and interface lute parameters on the stress-state of a machined crown-tooth system: a finite element analysis

The effect of preparation design and the physical properties of the interface lute on the restored machined ceramic crown-tooth complex are poorly understood. The aim of this work was to determine, by means of three-dimensional finite element analysis (3D FEA) the effect of the tooth preparation design and the elastic modulus of the cement on the stress state of the cemented machined ceramic crown-tooth complex. The three-dimensional structure of human premolar teeth, restored with adhesively cemented machined ceramic crowns, was digitized with a micro-CT scanner. An accurate, high resolution, digital replica model of a restored tooth was created. Two preparation designs, with different occlusal morphologies, were modeled with cements of 3 different elastic moduli. Interactive medical image processing software (mimics and professional CAD modeling software) was used to create sophisticated digital models that included the supporting structures; periodontal ligament and alveolar bone. The generated models were imported into an FEA software program (hypermesh version 10.0, Altair Engineering Inc.) with all degrees of freedom constrained at the outer surface of the supporting cortical bone of the crown-tooth complex. Five different elastic moduli values were given to the adhesive cement interface 1.8GPa, 4GPa, 8GPa, 18.3GPa and 40GPa; the four lower values are representative of currently used cementing lutes and 40GPa is set as an extreme high value. The stress distribution under simulated applied loads was determined. The preparation design demonstrated an effect on the stress state of the restored tooth system. The cement elastic modulus affected the stress state in the cement and dentin structures but not in the crown, the pulp, the periodontal ligament or the cancellous and cortical bone. The results of this study suggest that both the choice of the preparation design and the cement elastic modulus can affect the stress state within the restored crown-tooth complex.