Three-dimensional finite element modeling from CT images of tooth and its validation

Finite element models: A road to in-silico modeling in the age of personalized dentistry

OBJECTIVE

This article reviews the applications of Finite Element Models (FEMs) in personalized dentistry, focusing on treatment planning, material selection, and CAD-CAM processes. It also discusses the challenges and future directions of using finite element analysis (FEA) in dental care.

DATA

This study synthesizes current literature and case studies on FEMs in personalized dentistry, analyzing research articles, clinical reports, and technical papers on the application of FEA in dental biomechanics.

SOURCES

Sources for this review include peer-reviewed journals, academic publications, clinical case studies, and technical papers on dental biomechanics and finite element analysis. Key databases such as PubMed, Scopus, Embase, and ArXiv were used to identify relevant studies.

STUDY SELECTION

Studies were selected based on their relevance to the application of FEMs in personalized dentistry. Inclusion criteria were studies that discussed the use of FEA in treatment planning, material selection, and CAD-CAM processes in dentistry. Exclusion criteria included studies that did not focus on personalized dental treatments or did not utilize FEMs as a primary tool.

CONCLUSIONS

FEMs are essential for personalized dentistry, offering a versatile platform for in-silico dental biomechanics modeling. They can help predict biomechanical behavior, optimize treatment outcomes, and minimize clinical complications. Despite needing further advancements, FEMs could help significantly enhance treatment precision and efficacy in personalized dental care.

CLINICAL SIGNIFICANCE

FEMs in personalized dentistry hold the potential to significantly improve treatment precision and efficacy, optimizing outcomes and reducing complications. Their integration underscores the need for interdisciplinary collaboration and advancements in computational techniques to enhance personalized dental care.

Finite element analysis of fatigue life of commercially pure titanium clasps additively manufactured with different building orientations

The geometrical accuracy of additively manufactured pure titanium clasps depends on the building orientation. The aim of this study is to compare the geometrical accuracy and the fatigue lives predicted by finite element analysis (FEA) among three clasps manufactured with different building orientations. Besides, this paper proposed a calculation method of the moment of inertia of area and cross-sectional area along with the arm as the geometrical parameters. One of the clasps manufactured with a cylindrical chucking part for the fatigue test had almost the same geometrical parameters with the CAD design. Also, the authors' fatigue life prediction method using the CAD based FEA was verified through comparison with micro-CT image-based FEA. The other two clasps had larger geometrical parameters than the CAD design, resulting in longer fatigue lives. The results implied the importance of calculating the moment of inertia of the area in the design of the clasp arm.

Stress and movement trend of lower incisors with different IMPA intruded by clear aligner: a three-dimensional finite element analysis

BACKGROUND

During the intrusion of lower incisors with clear aligners (CAs), root disengagement from the alveolar bone often occurs, resulting in serious complications. This study aimed to determine the potential force mechanism of the mandibular anterior teeth under the pressure of CA, providing theoretical data for clinical practice.

METHODS

In this study, a 3D finite element model was established, including the CA, periodontal ligament, and mandibular dentition. Incisor mandibular plane angles were set as 5 groups: 90°, 95°, 100°, 105°, and 110°. The 4 mandibular incisors were intruded by 0.2 mm, while the canines were the anchorage teeth. The stress, force systems, and potential movement trends of mandibular anterior teeth were obtained.

RESULTS

The compressive stress of the incisors was concentrated in the lingual fossa, incisal ridge, and apex. With the increase in IMPA, the moment of central incisors changed from lingual crown moment to labial crown moment, with the turning point between 100° and 105°, but the center of resistance (CR) was always subjected to the force toward the lingual and intrusive direction. The force and moment toward the labial side of the lateral incisors were greater than those toward the central incisors. The canines always tipped distally and received extrusive force with no relationship with IMPA.

CONCLUSIONS

With the increase in the initial IMPA, the direction of labiolingual force on the mandibular incisors was reversed. However, the root of the lower incisors always tipped labially, which indicated fenestration and dehiscence.

Numerical Study of the Mechanical Behaviour of Wedge-Shaped Defect Filling Materials

This paper deals with direct restorations of teeth with non-carious cervical lesions (NCCL). NCCL defects are capable of gradual growth and are accompanied by the degradation of the surrounding tissue. Direct restorative treatment, in which the cavity is filled with a cementing agent, is considered to be an accessible and common treatment option. The study included simulations of the teeth without lesions, the teeth with V and U lesions and the tooth-restorative system. Parameterised numerical tooth models were constructed. Two cases with defect depths of 0.8 mm and ~1.7 mm and three variants with fillet radii of the defect end of 0.1, 0.2 and 0.3 mm were considered. The effect of two biomaterials for restorations was studied, namely Herculite XRV (Kerr Corp, Orange, CA, USA) and Charisma (Heraeus Kulzer GmbH, Hanau, Germany). The models were deformed with a vertical load of 100 to 1000 N from the antagonist tooth. The tooth-restorative system was considered, taking into consideration the contact interaction in the interface areas with the tooth tissues. Within the limits of the research, the character of the distribution of the deformation characteristics and their dependence on the level of loading, the depth of the defect and the radius of the curvature of the "wedge" were established.

Correlation of Bone Material Model Using Voxel Mesh and Parametric Optimization

The authors present an algorithm for determining the stiffness of the bone tissue for individual ranges of bone density. The paper begins with the preparation and appropriate mechanical processing of samples from the bovine femur and their imaging using computed tomography and then processing DICOM files in the MIMICS system. During the processing of DICOM files, particular emphasis was placed on defining basic planes along the sides of the samples, which improved the representation of sample geometry in the models. The MIMICS system transformed DICOM images into voxel models from which the whole bone FE model was built in the next step. A single voxel represents the averaged density of the real sample in a very small finite volume. In the numerical model, it is represented by the HEX8 element, which is a cube. All voxels were divided into groups that were assigned average equivalent densities. Then, the previously prepared samples were loaded to failure in a three-point bending test. The force waveforms as a function of the deflection of samples were obtained, based on which the global stiffness of the entire sample was determined. To determine the stiffness of each averaged voxel density value, the authors used advanced optimization analyses, during which numerical analyses were carried out simultaneously, independently mapping six experimental tests. Ultimately, the use of genetic algorithms made it possible to select a set of stiffness parameters for which the error of mapping the global stiffness for all samples was the smallest. The discrepancies obtained were less than 5%, which the authors considered satisfactory by the authors for such a heterogeneous medium and for samples collected from different parts of the bone. Finally, the determined data were validated for the sample that was not involved in the correlation of material parameters. The stiffness was 7% lower than in the experimental test.

Numerical Modeling of a New Type of Prosthetic Restoration for Non-Carious Cervical Lesions

The paper considers a new technology for the treatment of non-carious cervical lesions (NCCLs). The three parameterized numerical models of teeth are constructed: without defect, with a V-shaped defect, and after treatment. A new treatment for NCCL has been proposed. Tooth tissues near the NCCLs are subject to degradation. The main idea of the technology is to increase the cavity for the restoration of NCCLs with removal of the affected tissues. The new treatment method also allows the creation of a playground for attaching the gingival margin. The impact of three biomaterials as restorations is studied: CEREC Blocs; Herculite XRV; and Charisma. The models are deformed by a vertical load from the antagonist tooth from 100 to 1000 N. The tooth-inlay system is considered, taking into account the contact interaction. Qualitative patterns of tooth deformation before and after restoration were established for three variants of the inlay material.

Validated Finite Element Models of Premolars: A Scoping Review

Finite element (FE) models are widely used to investigate the biomechanics of reconstructed premolars. However, parameter identification is a complex step because experimental validation cannot always be conducted. The aim of this study was to collect the experimentally validated FE models of premolars, extract their parameters, and discuss trends. A systematic review was performed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Records were identified in three electronic databases (MEDLINE [PubMed], Scopus, The Cochrane Library) by two independent reviewers. Twenty-seven parameters dealing with failure criteria, model construction, material laws, boundary conditions, and model validation were extracted from the included articles. From 1306 records, 214 were selected for eligibility and entirely read. Among them, 19 studies were included. A heterogeneity was observed for several parameters associated with failure criteria and model construction. Elasticity, linearity, and isotropy were more often chosen for dental and periodontal tissues with a Young’s modulus mostly set at 18–18.6 GPa for dentine. Loading was mainly simulated by an axial force, and FE models were mostly validated by in vitro tests evaluating tooth strains, but different conditions about experiment type, sample size, and tooth status (intact or restored) were reported. In conclusion, material laws identified herein could be applied to future premolar FE models. However, further investigations such as sensitivity analysis are required for several parameters to clarify their indication.

Evaluation of cavity size, kind, and filling technique of composite shrinkage by finite element

Background:

Cavity preparation reduces the rigidity of tooth and its resistance to deformation. The purpose of this study was to evaluate the dimensional changes of the repaired teeth using two types of light cure composite and two methods of incremental and bulk filling by the use of finite element method.

Materials and Methods:

In this computerized in vitro experimental study, an intact maxillary premolar was scanned using cone beam computed tomography instrument (SCANORA, Switzerland), then each section of tooth image was transmitted to Ansys software using AUTOCAD. Then, eight sizes of cavity preparations and two methods of restoration (bulk and incremental) using two different types of composite resin materials (Heliomolar, Brilliant) were proposed on software and analysis was completed with Ansys software.

Results:

Dimensional change increased by widening and deepening of the cavities. It was also increased using Brilliant composite resin and incremental filling technique.

Conclusion:

Increase in depth and type of filling technique has the greatest role of dimensional change after curing, but the type of composite resin does not have a significant role.

Biomechanics of cervical tooth region and noncarious cervical lesions of different morphology; three-dimensional finite element analysis

OBJECTIVE

The present study aims to investigate the influence of presence and shape of cervical lesions on biomechanical behavior of mandibular first premolar, subjected to two types of occlusal loading using three-dimensional (3D) finite element method (FEM).

MATERIALS AND METHODS

3D models of the mandibular premolar are created from a micro computed tomography X-ray image: model of sound mandibular premolar, model with the wedge-shaped cervical lesion (V lesion), and model with saucer-shaped cervical lesion (U lesion). By FEM, straining of the tooth tissues under functional and nonfunctional occlusal loading of 200 (N) is analyzed. For the analysis, the following software was used: CTAn program 1.10 and ANSYS Workbench (version 14.0). The results are presented in von Mises stress.

RESULTS

Values of calculated stress in all tooth structures are higher under nonfunctional occlusal loading, while the functional loading is resulted in homogeneous stress distribution. Nonfunctional load in the cervical area of sound tooth model as well as in the sub-superficial layer of the enamel resulted with a significant stress (over 50 [MPa]). The highest stress concentration on models with lesions is noticed on the apex of the V-shaped lesion, while stress in saucer U lesion is significantly lower and distributed over wider area.

CONCLUSION

The type of the occlusal teeth loading has the biggest influence on cervical stress intensity. Geometric shape of the existing lesion is very important in the distribution of internal stress. Compared to the U-shaped lesions, V-shaped lesions show significantly higher stress concentrations under load. Exposure to stress would lead to its progression.

Reliability of FEA on the Results of Mechanical Properties of Materials

The present study evaluated the reliability of FEA on the results of different mechanical properties (E and v) of materials. Two 3D models of a maxillary canine with endodontic treatment, intracanal post, composite resin core and restored with porcelain-fused-to-metal crown were generated according to micro-CT images. Two groups with different E and ν values for porcelain, metal coping alloy, resin cement and composite resin were established. The materials' properties for group GL were based on literature data, while for group GIE the impulse excitation technique was used. A load of 180 N was applied at 45° on the incisal third of the lingual surface of the canine tooth. All models were supported by the periodontal ligament (x=y=z=0). The von Mises stress (VMS) was calculated. The stress values revealed differences between the groups for both VMS distribution and value. The porcelain (GL: 5.966 MPa; GIE: 7.478 MPa), metal coping (GL: 3.811 MPa; GIE: 0.973 MPa) and core (GL: 4.771 MPa; GIE: 0.026 MPa) were significantly affected. In conclusion, this study showed that the determination of mechanical properties (E and ν) of materials is essential for the reliability on the results of FEA.

Micron-scale phenotyping quantification and three-dimensional microstructure reconstruction of vascular bundles within maize stalks based on micro-CT scanning

Vascular bundles within maize (Zea mays L.) stalks play a key role in the mechanical support of plant architecture as well as in water and nutrient transportation. Convenient and accurate phenotyping of vascular bundles may help phenotypic identification of germplasm resources for breeding. Based on practical sample preparation procedures for maize stalks, we acquired serials of cross-sectional images using a micro-computed tomography (CT) imaging device. An image processing pipeline dedicated to the phenotyping of vascular bundles was also developed to automatically segment and validate vascular bundles from the cross-sectional images of maize stalks, from which phenotypic traits of vascular bundles, i.e. number, area, and spatial distribution, were calculated. More profound quantification of spatial distribution was given as area ratio of vascular bundles, which described the distribution of vascular bundles associated with the centroid of maize stalks. In addition, three-dimensional visualisation was performed to reveal the spatial configuration and distribution of vascular bundles. The proposed method significantly improves computation accuracy for the phenotypic traits of vascular bundles compared with previous methods, and is expected to be useful for illustrating relationships between phenotypic traits of vascular bundles and their function.

Modeling and validation of a 3D premolar for finite element analysis

Abstract Introduction The development and validation of mathematical models is an important step of the methodology of finite element studies. Objective This study aims to describe the development and validation of a three-dimensional numerical model of a maxillary premolar for finite element analysis. Material and method The 3D model was based on standardized photographs of sequential slices of an intact premolar and generated with the use of SolidWorks Software (Dassault, France). In order to validate the model, compression and numerical tests were performed. The load versus displacement graphs of both tests were visually compared, the percentage of error calculated and homogeneity of regression coefficients tested. Result An accurate 3D model was developed and validated since the graphs were visually similar, the percentage error was within acceptable limits, and the straight lines were considered parallel. Conclusion The modeling procedures and validation described allows the development of accurate 3D dental models with biomechanical behavior similar to natural teeth. The methods may be applied in development and validation of new models and computer-aided simulations using FEM.

Simulation of Low-Intensity Ultrasound Propagating in a Beagle Dog Dentoalveolar Structure to Investigate the Relations between Ultrasonic Parameters and Cementum Regeneration

The therapeutic effect of low-intensity pulsed ultrasound on orthodontically induced inflammatory root resorption is believed to be brought about through mechanical signals induced by the low-intensity pulsed ultrasound. However, the stimulatory mechanism triggering dental cell response has not been clearly identified yet. The aim of this study was to evaluate possible relations between the amounts of new cementum regeneration and ultrasonic parameters such as pressure amplitude and time-averaged energy density. We used the finite-element method to simulate the previously published experiment on ultrasonic wave propagation in the dentoalveolar structure of beagle dogs. Qualitative relations between the thickness of the regenerated cementum in the experiment and the ultrasonic parameters were observed. Our results indicated that the areas of the root surface with greater ultrasonic pressure were associated with larger amounts of cementum regeneration. However, the establishment of reliable quantitative correlations between ultrasound parameters and cementum regeneration requires more experimental data and simulations.

Mechanics analysis of molar tooth splitting

A model for the splitting of teeth from wedge loading of molar cusps from a round indenting object is presented. The model is developed in two parts: first, a simple 2D fracture mechanics configuration with the wedged tooth simulated by a compact tension specimen; second, a full 3D numerical analysis using extended finite element modeling (XFEM) with an embedded crack. The result is an explicit equation for splitting load in terms of indenter radius and key tooth dimensions. Fracture experiments on extracted human molars loaded axially with metal spheres are used to quantify the splitting forces and thence to validate the model. The XFEM calculations enable the complex crack propagation, initially in the enamel coat and subsequently in the interior dentin, to be followed incrementally with increasing load. The fracture evolution is shown to be stable prior to failure, so that dentin toughness, not strength, is the controlling material parameter. Critical conditions under which tooth splitting in biological and dental settings are likely to be met, however rare, are considered.

Analysis of the abfraction lesions formation mechanism by the finite element method

Introduction:

An abfraction lesion is a type of a non-carious cervical lesion (NCCL) that represents a sharp defect on the cervical part of tooth, caused by occlusal biomechanical forces. The largest prevalence of the NCCL is found on the mandibular first premolar. The goal of the study is, by means of a numerical method – the finite element method (FEM), in an appropriate computer program, conduct a stress analysis of the mandibular premolar under various static loads, with a special reference to the biomechanics of cervical tooth region.

Material and methods:

A three-dimensional model of the mandibular premolar is gained from a µCT x-ray image. By using the FEM, straining of the enamel, dentin, peridontal ligament and alveolar bone under axial and paraxial forces of 200 [N] is analyzed. The following software were used in the analysis: CT images processing–CTAn program and FEM analysis–AnsysWorkbench 14.0.

Results:

According to results obtained through the FEM method, the calculated stress is higher with eccentric forces within all tested tooth tissue. The occlusal load leads to a significant stress in the cervical tooth area, especially in the sub-superficial layer of the enamel (over 50 MPa). The measured stress in the peridontal ligament is approximately three times higher under paraxial load with regard to the axial load, while stress calculated in the alveolar bone under paraxial load is almost ten times higher with regard to the axial load. The highest stress values were calculated in the cervical part of the alveoli, where bone resorption is most commonly seen.

Conclusion:

Action of occlusal forces, especially paraxial ones, leads to significant stress in the cervical part of tooth. The stress values in the cervical sub-superficial enamel layer are almost 5 times higher in relation to the superficial enamel, which additionally confirms complexity of biomechanical processes in the creation of abfraction lesions.

Zygomatic Implants: The Impact of Zygoma Bone Support on Biomechanics

Maxillectomy and severely resorbed maxilla are challenging to restore with provision of removable prostheses. Dental implants are essential to restore esthetics and function and subsequently quality of life in such group of patients. Zygomatic implants reduce the complications associated with bone grafting procedures and simplify the rehabilitation of atrophic maxilla and maxillectomy. The purpose of this study was to compare, by means of 3-dimensional finite element analysis, the impact of different zygomatic bone support (10, 15, and 20 mm) on the biomechanics of zygomatic implants. Results indicated that maximum stresses within the fixture were increased by 3 times when bone support decreased from 20 to 10 mm and were concentrated at the fixture/bone interface. However, stresses within the abutment screw and the abutment itself were not significantly different regardless of the bone support level. Supporting bone at 10 mm sustained double the stresses of 15 and 20 mm. Fixture's deflection was decreased by 2 to 3 times when bone support level increased to 15 mm and 20 mm, respectively. It was concluded that zygomatic bone support should not be less than 15 mm, and abutment screw is not at risk of fracture regardless of the zygomatic bone support.

Role of multiple cusps in tooth fracture

The role of multiple cusps in the biomechanics of human molar tooth fracture is analysed. A model with four cusps at the bite surface replaces the single dome structure used in previous simulations. Extended finite element modelling, with provision to embed longitudinal cracks into the enamel walls, enables full analysis of crack propagation from initial extension to final failure. The cracks propagate longitudinally around the enamel side walls from starter cracks placed either at the top surface (radial cracks) or from the tooth base (margin cracks). A feature of the crack evolution is its stability, meaning that extension occurs steadily with increasing applied force. Predictions from the model are validated by comparison with experimental data from earlier publications, in which crack development was followed in situ during occlusal loading of extracted human molars. The results show substantial increase in critical forces to produce longitudinal fractures with number of cuspal contacts, indicating a capacity for an individual tooth to spread the load during mastication. It is argued that explicit critical force equations derived in previous studies remain valid, at the least as a means for comparing the capacity for teeth of different dimensions to sustain high bite forces.

Assessment of the Effect of Two Occlusal Concepts for Implant-Supported Fixed Prostheses by Finite Element Analysis in Patients With Bruxism

The aim of this study was to evaluate the effects of bruxing forces on implants configured under 2 different occlusal schemes by dynamic finite element analysis. A main model consisting of a 5-unit fixed partial denture supported by 3 implants was simulated with bone, implants, and superstructures. All calculations were made individually for each component, namely porcelain crowns, abutments, abutment screws, implants, and bone. Maximum stresses were found in the group-function occlusion. Group-function loading may result excess stresses on the components compared with canine-guidance loading. According to the results of this study, use of canine guidance is encouraged in bruxers with implant-supported prostheses.

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.

Stress analysis of occlusal forces in canine teeth and their role in the development of non-carious cervical lesions: abfraction

Non-carious cervical tooth lesions for many decades were attributed to the effects of abrasion and erosion mainly through toothbrush trauma, abrasive toothpaste, and erosive acids. However, though the above may be involved, more recently a biomechanical theory for the formation of these lesions has arisen, and the term abfraction was coined. The aim of this study was to investigate the biomechanics of abfraction lesions in upper canine teeth under axial and lateral loading conditions using a three-dimensional finite element analysis. An extracted human upper canine tooth was scanned by μCT machine (Skyscan, Belgium). These μCT scans were segmented, reconstructed, and meshed using ScanIP (Simpleware, Exeter, UK) to create a three-dimensional finite element model. A 100 N load was applied axially at the incisal edge and laterally at 45° midpalatally to the long axis of the canine tooth. Separately, 200 N axial and non-axial loads were applied simultaneously to the tooth. It was found that stresses were concentrated at the CEJ in all scenarios. Lateral loading produced maximum stresses greater than axial loading, and pulp tissues, however, experienced minimum levels of stresses. This study has contributed towards the understanding of the aetiology of non-carious cervical lesions which is a key in their clinical management.

Influence of crown ferrule heights and dowel material selection on the mechanical behavior of root-filled teeth: a finite element analysis

PURPOSE

This study used the 3D finite element (FE) method to evaluate the mechanical behavior of a maxillary central incisor with three types of dowels with variable heights of the remaining crown structure, namely 0, 1, and 2 mm.

MATERIALS AND METHODS

Based on computed microtomography, nine models of a maxillary central incisor restored with complete ceramic crowns were obtained, with three ferrule heights (0, 1, and 2 mm) and three types of dowels (glass fiber = GFD; nickel-chromium = NiCr; gold alloy = Au), as follows: GFD0--restored with GFD with absence (0 mm) of ferrule; GFD1--similar, with 1 mm ferrule; GFD2--glass fiber with 2 mm ferrule; NiCr0--restored with NiCr alloy dowel with absence (0 mm) of ferrule; NiCr1--similar, with 1 mm ferrule; NiCr2--similar, with 2 mm ferrule; Au0--restored with Au alloy dowel with absence (0 mm) of ferrule; Au1--similar, with 1 mm ferrule; Au2--similar, with 2 mm ferrule. A 180 N distributed load was applied to the lingual aspect of the tooth, at 45° to the tooth long axis. The surface of the periodontal ligament was fixed in the three axes (x = y = z = 0). The maximum principal stress (σ(max)), minimum principal stress (σ(min)), equivalent von Mises (σ(vM)) stress, and shear stress (σ(shear)) were calculated for the remaining crown dentin, root dentin, and dowels using the FE software.

RESULTS

The σ(max) (MPa) in the crown dentin were: GFD0 = 117; NiCr0 = 30; Au0 = 64; GFD1 = 113; NiCr1 = 102; Au1 = 84; GFD2 = 102; NiCr2 = 260; Au2 = 266. The σ(max) (MPa) in the root dentin were: GFD0 = 159; NiCr0 = 151; Au0 = 158; GFD1 = 92; NiCr1 = 60; Au1 = 67; GFD2 = 97; NiCr2 = 87; Au2 = 109.

CONCLUSION

The maximum stress was found for the NiCr dowel, followed by the Au dowel and GFD; teeth without ferrule are more susceptible to the occurrence of fractures in the apical root third.

Influence of customized composite resin fibreglass posts on the mechanics of restored treated teeth

AIM

To evaluate the mechanical behaviour of the dentine/cement/post interface of a maxillary central incisor using the finite element method and to compare the stresses exerted using conventional or customized post cementation techniques.

METHODOLOGY

Four models of a maxillary central incisor were created using fibreglass posts cemented with several techniques: FGP1, a 1-mm-diameter conventionally cemented post; CFGP1, a 1-mm-diameter customized composite resin post; FGP2, a 2-mm-diameter conventionally cemented post; CFGP2, a 2-mm-diameter customized composite resin post. A distributed load of 1N was applied to the lingual aspect of the tooth at 45° to its long axis. Additionally, polymerization shrinkage of 1% was simulated for the resin cement. The surface of the periodontal ligament was fixed in the three axes (X =Y = Z = 0). The maximum principal stress (σ(max) ), minimum principal stress (σ(min)), equivalent von Mises stress (σ(vM) ) and shear stress (σ(shear)) were calculated for the dentine/cement/post interface using finite element software.

RESULTS

The peak of σ(max) for the cement layer occurred first in CFGP1 (1.77 MPa), followed by CFGP2 (0.99), FGP2 (0.44) and FGP1 (0.2). The shrinkage stress (σ(vM) ) of the cement layer occurred as follows: FGP1 (35 MPa), FGP2 (34), CFGP1 (30.7) and CFGP2 (30.1).

CONCLUSIONS

Under incisal loading, the cement layer of customized posts had higher stress concentrations. The conventional posts showed higher stress because of polymerization shrinkage.