Finite-element modeling and analysis in nanomedicine and dentistry

Anterior provisional fixed partial dentures: A finite element analysis

PURPOSE

The aim of this study was to analyze the stress distribution of fiber-reinforced composite provisional fixed partial denture utilizing a finite element analysis model.

MATERIAL AND METHODS

Three anterior teeth were collected: upper right central, left central, and right lateral incisors. A fiber-reinforced composite strip was applied to the palatal surfaces of the teeth. Micro-computed tomographic scans were acquired of the models in order to generate three-dimensional geometrical replicas. Finite element analysis was used to assess the stress distribution of fiber-reinforced composite provisional fixed partial denture using different pontic types under static applied forces that were 100, 30, and 0 N.

RESULTS

The maximum stress values were found on the unprepared natural pontic. Stress values ranged from 92.2 to 909.8, 116.4 to 646.7, and 93.8 to 393.5 MPa for composite, naturally prepared, and natural unprepared pontic, respectively.

CONCLUSIONS

Using unprepared natural tooth pontic in anterior provisional fixed partial denture to replace missing central incisors is considered superior to other types in terms of stress distribution.

Fracture Resistance of Class II MOD Cavities Restored by Direct and Indirect Techniques and Different Materials Combination

This study aimed to evaluate the fracture resistance of class II MOD cavities restored using different techniques and materials. Sixty extracted maxillary molars were selected and standardized class II MOD cavities were prepared using a custom-made paralleling device. The specimens were divided into four groups based on the restoration technique used: Group 1 (direct resin composite), Group 2 (short-fiber-reinforced composite resin), Group 3 (composite polyethylene fiber reinforcement), and Group 4 (CAD/CAM resin inlays). Fracture resistance was assessed for each group after thermocycling aging for 10,000 cycles. The mode of fracture was assigned to five types using Burke's classification. To compare the fracture force among the tested materials, a paired sample t-test was performed. The significance level for each test was set at p < 0.05. Significant differences in fracture resistance were observed among the different restoration techniques. CAD/CAM inlays (2166 ± 615 N), short-fiber-reinforced composite resin (2471 ± 761 N), and composite polyethylene fiber reinforcement (1923 ± 492 N) showed superior fracture resistance compared to the group restored with direct resin composite (1242 ± 436 N). The conventional resin composite group exhibited the lowest mean fracture resistance. The choice of restoration material plays a critical role in the clinical survival of large MOD cavities. CAD/CAM inlays and fiber-reinforced composites offer improved fracture resistance, which is essential for long-term success in extensive restorations.

The effect of abutment material stiffness on the mechanical behavior of dental implant assemblies: A 3D finite element study

PURPOSE

This study aimed to evaluate the stress distribution and microgap formation in implant assemblies with conical abutments made of different materials under an oblique load.

MATERIALS AND METHODS

The mechanical behavior of an implant assembly with a titanium abutment was analyzed and compared with that of an assembly with a Y-TZP abutment using finite element analysis (FEA). A torque of 20 Ncm was first applied to the abutment screw, followed by oblique loads of 10 N-280 N applied to the prosthesis placed on the implant. The maximum stress in the abutment screw, the microgap formation process, and the critical load for bridging the internal implant space were evaluated.

RESULTS

No significant difference in stress distribution between the two cases was observed, with the stresses being mainly concentrated at the top half of the screw (the predicted maximum von Mises stress was approximately 1200 MPa at 280 N). The area in contact at the implant-to-abutment interface decreased with increasing load for both abutments, with the critical load for bridging the internal implant space being roughly 140 N. The maximum gap size being was approximately 470 μm with either abutment.

CONCLUSION

There was no significant difference in the stress distribution or microgap formed between implant assemblies with titanium and Y-TZP abutments having an internal conical connection.

A critical analysis of research methods and experimental models to study the load capacity and clinical behavior of the root filled teeth

The prognosis of root‐filled teeth depends not only on a successful root canal treatment but also on the restorative prognosis. This critical review discusses the advantages and limitations of various methodologies used to assess the load capacity or clinical survivability of root‐filled teeth and restorations. These methods include static loading, cyclic loading, finite element analysis and randomized clinical trials. In vitro research is valuable for preclinical screening of new dental materials or restorative modalities. It also can assist investigators or industry to decide whether further clinical trials are justified. It is important that these models present high precision and accuracy, be reproducible, and present adequate outcomes. Although in vitro models can reduce confounding by controlling important variables, the lack of clinical validation (accuracy) is a downside that has not been properly addressed. Most importantly, many in vitro studies did not explore the mechanisms of failure and their results are limited to rank different materials or treatment modalities according to the maximum load capacity. An extensive number of randomized clinical trials have also been published in the last years. These trials have provided valuable insight on the survivability of the root‐filled tooth answering numerous clinical questions. However, trials can also be affected by the selected outcome and by intrinsic and extrinsic biases. For example, selection bias, loss to follow‐up and confounding. In the clinical scenario, hypothesis‐based studies are preferred over observational and retrospective studies. It is recommended that hypothesis‐based studies minimize error and bias during the design phase.

Finite Element Analysis of effect of cusp inclination and occlusal contacts in PFM and PEEK implant-supported crowns on resultant stresses

BACKGROUND

Effect of prosthesis design on occlusal overload and long-term implant stability cannot be overstated. In Porcelain Fused to Metal (PFM) crowns, low cusp inclination and occlusal contacts limited to central fossa ensure axially directed forces on an implant but often pose esthetic and functional challenges. It is theorized that resilient Polyetheretherketone (PEEK) crowns have shock absorption capacity for favorable stress distribution. This study compared two implant crown materials and evaluated the effect of cusp inclination and occlusal contact distribution on resultant stresses.

METHODS

Thirty 3D finite element models of implant-supported PFM and PEEK crowns, generated using Solidedge 3D CAD solid modeling software (v19, Siemens PLM Software Inc.,US), were used to study the effect of 3 cups inclinations (0°, 15°, 30°) under five load conditions, with 300N force distributed over one, two, or three contact areas and exported to ANSYS (v18.1, ANSYS Inc. Pennsylvania, US) for stress analysis.

RESULTS

Maximum stress in both PFM and PEEK models was at the neck of the implant under Load 3(300N distributed over three contact areas: central fossa, buccal cusp tip, marginal ridge). Minimum stress in all models was under Load 1(300N applied at one contact area in central fossa). Maximum stresses were recorded for 30° cusp inclination in PFM models.

CONCLUSION

In both PFM and PEEK crown models, contact areas placed away from the implant axis generated greater implant and peri-implant stresses and had more effect on resultant stresses than that of increase in cusp inclination. The effect of cusp inclination on the resultant stresses was dependent on the crown material.

Novel Design and Finite Element Analysis of Diamond-like Porous Implants with Low Stiffness

The purpose of this study was to design porous implants with low stiffness and evaluate their biomechanical behavior. Thus, two types of porous implants were designed (Type I: a combined structure of diamond-like porous scaffold and traditional tapered thread. Type II: a cylindrical porous scaffold filled by arrayed basic diamond-like pore units). Three implant-supported prosthesis models were constructed from Type I, Type II and commercial implants (control group) and were evaluated by finite element analysis (FEA). The stress distribution pattern of the porous implants were assessed and compared with the control group. In addition, the stiffness of the cylindrical specimens simplified from three types of implants was calculated. The Type I implant exhibited better stress distribution than the Type II implant. The maximum stress between the cortical bone–Type I implant interface was 12.9 and 19.0% lower than the other two groups. The peak stress at the cancellous bone–Type I implant interface was also reduced by 16.8 and 38.7%. Compared with the solid cylinder, the stiffness of diamond-like pore cylinders simplified from the two porous implants geometry was reduced by 61.5 to 76.1%. This construction method of porous implant can effectively lower its stiffness and optimize the stress distribution at the implant–bone interface.

Finite element analysis of rotary nickel-titanium endodontic instruments: A critical review of the methodology

Finite element analysis has been a valuable research tool for rotary nickel-titanium endodontic files over the last two decades. This review aims to summarise and critique the methodology as used in currently available endodontic literature for finite element analysis of rotary nickel-titanium instruments. An electronic literature research in PubMed and Scopus databases was performed using the appropriate search terms, and the titles and abstracts were screened for relevance. The review revealed an inconsistent approach to the finite element method, particularly with regards to the boundary conditions in which the instruments are tested. Moreover, there is a lack of experimental data to validate in silico findings. A standardised protocol to finite element analysis of rotary endodontic instruments could be considered for future studies.

Effect of revascularisation and apexification procedures on biomechanical behaviour of immature maxillary central incisor teeth: a three-dimensional finite element analysis study

OBJECTIVES

This study aimed to assess the effects of revascularisation and apexification procedures on biomechanical behaviour of immature teeth using 3-dimensional finite element analysis (3D FEA).

MATERIALS AND METHODS

Five 3D FEA permanent maxillary incisor models were developed from CBCT scans and available literature data: Model MT: Mature tooth, Model IT: Immature tooth (Cvek's stage 3), Model AT: Apexified tooth-mineral trioxide aggregate (MTA) apexification, Model RTB: Revascularised tooth with blood, and Model RTS: Revascularised tooth with supplementary scaffold. Using FEA, a masticatory load of 240N at 120° was simulated, and the Von Mises and maximum principal stresses within the models were evaluated. Failure index (FI) and weakening% were also calculated for each model.

RESULTS

On dentinal stress analysis, model MT (96.16MPa) and IT (158.38MPa) had lowest and highest stress values, respectively. Among the experimental groups, model RTS (131.12MPa) had lower stresses than AT (136.33MPa) and RTB (133.7MPa), with no significant difference among the three. Peak dentinal stresses in all the models were observed in the cervical third of the root and near the apical opening in model IT. The extent of high dentinal stress area in model RTB and RTS was lesser than that of AT. The FI and weakening% values were highest for model AT followed by RTB and RTS, among the experimental groups. However, all these treatments strengthened an immature tooth by more than 20%.

CONCLUSIONS

AT, RTB, and RTS treatments lowered the stress values and risk of fracture in immature teeth with no significant difference among the three groups.

CLINICAL RELEVANCE

Stress distribution evaluation following revascularisation/apexification was essential, with potential to influence clinical decision-making. MTA apexification and revascularisation with blood clot/supplementary scaffold lowered the stresses in immature teeth, with no significant difference among the three.

Evaluation of deformation in the buccal lamellar bone with finite element analysis in alveolar ridge-splitting/expansion technique

PURPOSE

The aim of this study was to investigate deformation and stress distribution in the buccal lamellar bone via finite element analysis (FEA) in the application of alveolar ridge-splitting/expansion technique (ARST) in atrophic maxilla and mandible.

MATERIAL AND METHOD

Three-dimensional (3D) solid models of maxilla and mandible were formed using computer software, with an alveolar ridge thickness of 4 mm in the right first molar region. In both models, one horizontal and two releasing vertical osteotomies were made in the atrophic region. Vertical forces varying from 50 N to 1000 N were continuously applied on the midpoint of the horizontal osteotomy and then the axial and total deformation and von Mises stress distribution in the buccal lamellar bone was assessed by FEA.

RESULTS

The degrees of axial deformation and total deformation and the maximum von Mises stress value under a 50 N force were 0.22 mm, 0.23 mm, and 4.52 MPa in the maxillary buccal lamellar bone and were 0.04 mm, 0.06 mm, and 5.90 MPa in the mandibular buccal lamellar bone, respectively. Similarly, under a 1000 N force, the values were 4.44 mm, 4.75 mm, and 90.49 MPa in the maxillary buccal lamellar bone and were 0.96 mm, 1.1 mm, and 118.02 MPa in the mandibular buccal lamellar bone, respectively.

CONCLUSION

These findings implicate that the ARST used for implant placement or alveolar augmentation can be achieved with the application of lower amounts of force in the maxilla compared to the mandible. It was also revealed that in ARST, the maximum von Mises stress value was lower in the maxillary buccal lamellar bone than in the mandibular buccal lamellar bone. Based on these findings, we consider that the administration of ARST could be biomechanically more stable in the maxilla than in the mandible.

Application of bioengineering devices for stress evaluation in dentistry: the last 10 years FEM parametric analysis of outcomes and current trends

INTRODUCTION

Dentistry, therefore implantology, prosthetics, implant prosthetics or orthodontics in all their variants, are medical and rehabilitative branches that have benefited greatly from these methods of investigation to improve the predictability of rehabilitations. We will examine the Finite Element Method and Finite Element Analysis in detail. This method involves the simulation of mechanical forces from an environment with infinite elements, the real one, to a simulation with finite elements.

EVIDENCE ACQUISITION

The study searched MEDLINE databases from 2008 to 2018. Human use of FEM in vitro studies reported a contribution on oral rehabilitation through the use of FEM analysis. The initial search obtained 296 citations. After a first screening, the present revision considered the English-language works referred to human application of the FEM published in the last 10 years. Finally, 34 full texts were available after screening.

EVIDENCE SYNTHESIS

The ultimate aim of this review is to point out all the progress made in the field of bioengineering and therefore, thanks to this, in the field of medicine. Instrumental investigations such as FEM are an excellent tool that allows the evaluation of anatomical structures and any facilities for rehabilitation before moving on to experimentation on animals, so as to have mechanical characteristics and satisfactory load cycle testing.

CONCLUSIONS

FEM analysis contributes substantially to the development of new technologies and new materials in the biomedical field, being able to perform a large number of simulations without the need for patients or to perform human tests. Thanks to the 3D technology and to the reconstructions of both the anatomical structures and eventually the alloplastic structures used in the rehabilitations it is possible to consider all the mechanical characteristics, so that they can be analyzed in detail and improved where necessary. It is possible thanks to these methods to know what are the ideal characteristics of a material to promote an oral rehabilitation, so we know the characteristics, it remains only to take a step in the field of the industry for the construction of materials close to these characteristics.

Application of External Force Regulates the Migration and Differentiation of Adipose-Derived Stem/Progenitor Cells by Altering Tissue Stiffness

Large soft-tissue defects are challenging to reconstruct surgically. Expansion of soft tissue using an external volume expansion (EVE) device is a noninvasive method to improve such reconstruction; however, the underlying mechanism is unclear. In this study, we created fat flaps in Sprague-Dawley rats, applied an external force of 3 or 6 kPa using an EVE device, and investigated the migration and differentiation of adipose-derived stem/progenitor cells (ASCs). In addition, we performed finite element analysis to explore the stiffness of adipose tissue. An external force of 3 kPa promoted the migration and adipogenic differentiation of ASCs. By comparison, an external force of 6 kPa had a larger effect on migration of ASCs, but a smaller effect on adipogenic differentiation of ASCs. External force affected adipose tissue stiffness. In conclusion, external force generated by an EVE device increases the stiffness of adipose tissue, which influences the migration and differentiation of ASCs. The size of the external force can be altered according to the tissue stiffness required at particular time points to promote long-term adipose tissue regeneration. Impact Statement Stem cell therapy in clinic mostly requires the addition of exogenous stem cells, therefore the safety and controllability is always defective. In this study, the external force of external volume expansion regulates adipose-derived stem/progenitor cells (ASCs) migration and differentiation through tissue stiffness. Using tissue engineering without exogenous ASCs can promote long-term adipose tissue regeneration. The findings of this study provide theoretical support for clinical tissue engineering applications and improvements in stem cell therapy.

A three-dimensional topology optimization model for tooth-root morphology

To obtain the root of a lower incisor through structural optimization, we used two methods: optimization with Solid Isotropic Material with Penalization (SIMP) and Soft-Kill Option (SKO). The optimization was carried out in combination with a finite element analysis in Abaqus/Standard. The model geometry was based on cone-beam tomography scans of 10 adult males with healthy bone-tooth interface. Our results demonstrate that the optimization method using SIMP for minimum compliance could not adequately predict the actual root shape. The SKO method, however, provided optimization results that were comparable to the natural root form and is therefore suitable to set up the basic topology of a dental root.