Biomechanical behavior of endodontically treated premolars restored with different endocrown designs: Finite element study.

PURPOSE: Although endocrown is a successful restorative approach for endodontically treated molars, its survival rate in endodontically treated premolars with extensive loss of coronal structure has been debated. The aim of this study was to evaluate the biomechanical behavior of endodontically treated maxillary premolars restored with different lithium disilicate endocrown designs. MATERIALS AND METHODS: Based on cone-beam computed tomography (CBCT) of an intact maxillary premolar, five models were designed. Model A: fiber post, core, and crown; Model B: endocrown, 5 mm pulpal extension and butt margin; Model C: endocrown, 5 mm pulpal extension and axial extension; Model D: Endocrown, 3 mm pulpal extension and butt margin; Model E: Endocrown, 3 mm pulpal extension and axial extension. The bone geometry was simplified as a cylinder of compact and trabecular bone. All models were imported into finite element analysis (FEA) software, where the base of the bone cylinder was chosen as fixed support. Axial and oblique loads of 100 N each were applied separately to each model, and static structural analysis was performed. RESULTS: Regardless of the design of the endocrown, the resulting von Mises stresses were far below the yield strength of the tooth structure and the flexural strength of the ceramic material. The generated von Mises stresses on the restoration decreased by 15% in the models with 3 mm pulp extension (D and E) compared to the 5-mm pulpal extension models. In addition, the resulting von Mises stresses on the tooth structure decreased also by 15% in models C and E with the axial extension compared to models B and D with the butt margin. CONCLUSION: Endocrown is a suitable restoration for endodontically treated maxillary premolars. Furthermore, reducing the depth of the pulpal extension to 3 mm with the addition of an axial extension resulted in a more favorable stress distribution within the tooth-restoration interface.

Biomechanics in Removable Partial Dentures: A Literature Review of FEA-Based Studies.

The present study was aimed at reviewing the studies that used finite element analysis (FEA) to estimate the biomechanical stress arising in removable partial dentures (RPDs) and how to optimize it. A literature survey was conducted for the English full-text articles, which used only FEA to estimate the stress developed in RPDs from Jan 2000 to May 2021. In RPDs, the retaining and supporting structures are subjected to dynamic loads during insertion and removal of the prosthesis as well as during function. The majority of stresses in free-end saddle (FES) RPDs are concentrated in the shoulder of the clasp, the horizontal curvature of the gingival approaching clasp, and the part of the major connector next to terminal abutments. Clasps fabricated from flexible materials were beneficial to eliminate the stress in the abutment, while rigid materials were preferred for major connectors to eliminate the displacement of the prosthesis. In implant-assisted RPD, the implant receive the majority of the load, thereby reducing the stress on the abutment and reducing the displacement of the prosthesis. The amount of stress in the implant decreases with zero or minimal angulation, using long and wide implants, and when the implants are placed in the first molar area.

An in vitro / in vivo release test of risedronate drug loaded nano-bioactive glass composite scaffolds.

Three-dimensional (3D) matrices scaffolds play a noteworthy role in promoting cell generation and propagation. In this study, scaffolds prepared from chitosan/polyvinyl alcohol loaded with/without an osteoporotic drug (risedronate) and nano-bioactive glass (nBG) have been developed to promote healing of bone defects. The scaffolds were characterized by scanning electron microscopy (SEM), porosity test as well as mechanical strength. The pattern of drug release and ability to promote the proliferation of Saos-2osteosarcoma cells had also been reported. Osteogenic potential of the scaffolds was evaluated by testing their effect on healing critical-sized dog's mandibular bone defects. Increasing chitosan and nBG in the porous scaffolds induced decrease in drug release, increased the scaffold's strength and supported their cell proliferation, alkaline phosphatase (ALP) activities, as well as increased calcium deposition. Histological and histomorphometric results demonstrated newly formed bone trabeculae inside critical-sized mandibular defects when treated with scaffolds. Trabecular thickness, bone volume/tissue volume and the percentage of mature collagen fibers increased in groups treated with scaffolds loaded with 10% nBG and risedronate or loaded with 30% nBG with/without risedronate compared with those treated with non-loaded scaffolds and empty control groups. These findings confirmed the potential osteogenic activity of chitosan/polyvinyl alcohol-based scaffolds loaded with risedronate and nBG.

Pediatric Stainless-Steel Crown Cementation Finite Element Study.

OBJECTIVE: To study the effect of using different cement types under pediatric stainless-steel crown (SSC) around mandibular second primary molar using three-dimensional (3D) finite element analysis. MATERIALS AND METHODS: A 3D finite element model was built for pediatric mandibular molar by laser scanning of natural extracted tooth. Four types of cement (zinc phosphate, glass ionomer, resin-modified glass ionomer, and resin) of 200 µm layers thickness were tested under a stainless-steel crown of 130-µm thickness. Twelve case studies were reported within this research, as the applied load of 330 N was tested with three angulations: vertical, oblique at 45°, and laterally. RESULTS: Linear static stress analysis was performed. The resultant stresses and deformations' distribution patterns did not change with cement type, while the values were altered. All deformations and stresses were found within the normal range. CONCLUSIONS: Analysis results indicated that using stiffer cement material increases tooth structure stresses and reduces crown body stresses and deformations, while bone was nearly insensitive to cement type.

Comparing different bar materials for mandibular implant-supported overdenture: Finite-element analysis.

AIM: This study was conducted aiming to optimize the selection of bar material that can minimize stresses on mandibular bone. SUBJECTS AND METHODS: One finite-element model was created under ANSYS environment to evaluate the use of different materials as a bar-manufacturing material in mandibular implant-supported overdenture (OD). Model components were created on engineering computer-aided design software and then assembled under the finite-element package. A force of 200 N was unilaterally and vertically applied on the left second premolar area. RESULTS: Within these study conditions, the polyether ether ketone bar produced the lowest Von Mises stress on OD and the maximum value of deformation. Stainless steel bar produced the maximum OD total deformation. CONCLUSIONS: Cortical and spongy bones are not sensitive to the bar material. Increasing bar material stiffness increases Von Mises stresses in the bar itself and reduces its total deformation, in what is called overconstrained system.

Effect of ceramic translucency and luting cement shade on the color masking ability of laminate veneers.

BACKGROUND: The aim of this study was to evaluate the effect of ceramic material types, degree of veneer translucency, and luting cement shades on masking the underlying dark dental substrate to achieve best esthetics. MATERIALS AND METHODS: In this in vitro study, 56 specimens each of 0.5-mm thickness were fabricated from two esthetic veneer materials Vita Enamic and Vita Suprinity, with two different translucencies, i.e., HT and T. To simulate the color of a dark underlying dental structure, background discs with C3 shade were fabricated using resin composite. The ceramic specimens with varying translucencies were cemented on the dark background of the resin composite with A1 and opaque white shades of resin luting cement. Color difference (ΔE) values from a reference color (A1 shade) were calculated using a spectrophotometer. The results were then statistically analyzed using three-way ANOVA test (α = 0.05). RESULTS: The ΔE values of both ceramic systems were affected by both the degree of veneer translucency (P = 0.00) and the luting agent shade (P = 0.016). The use of an opaque luting agent and T translucency resulted in a decrease in the ΔE* values for all ceramics tested, regardless to the material type. Suprinity and Enamic showed similarity in the masking ability of dark substrate after cementation. CONCLUSION: None of the 0.5-mm veneers of the two ceramic systems could reach A1 shade without a detectable color difference after cementation. The change in degree of veneer translucency was more effective than the change in luting agent shade in masking the underlying dark substrate.

Stress analysis of mandibular implant overdentures retained with one, two, or four ball attachments: A finite element study.

BACKGROUND: The aim of this study is to compare stress patterns induced by ball attachments when used to retain mandibular overdentures supported by one, two, or four dental implants. MATERIALS AND METHODS: In this finite element study, three 3D models were prepared to simulate mandibular implant overdentures retained by one or two or four ball attachments of 3.5 mm diameter with collar height 1.6 mm. The geometric solid models were created by commercial engineering computer-aided design package then transferred to ANSYS as set of standard ACIS text files. Vertical load of 100 N was applied on the central fossa of the right molar. Stresses were evaluated at the areas of implant and attachment components, mucosa underlying overdentures, and cortical and cancellous bone adjacent to implants. RESULTS: The results of this study showed that the Von Mises stresses generated by the application of vertical loading varied according to the number of implants used to support the overdenture. Maximum Von Mises stress on cortical bone ranged between 1.15 and 1.77 MPa in all-studied cases. Mucosa was squeezed under the one implant model. Flexibility of the overdenture material played a significant role in distributing the load stress and deformation of all underlying structure. Caps deformation was the highest when using two implants. CONCLUSION: With increasing the number of implants, stresses and deformations of overdenture are reduced, but implants receive greater stresses and deformations. Using two implants in the canine region showed the best results when compared with using one or four implants, except for the caps.

3D FEA Study On Implant Threading Role on Selection of Implant and Crown Materials.

AIM: This study deeply investigates the effect of dental implant threading and material selection on the mandibular bone under two different crown materials (Translucent Zirconia and Porcelain fused to metal). METHODS: Two different designs of single piece dental implants were supporting dummy crown above simplified bone geometry in two finite element models. Models components were created by general-purpose CAD/CAM engineering package and then assembled inside ANSYS before meshing and assigning materials. Compressive loading of 100 N and 45º oblique loading of 50 N were tested. RESULTS: Twenty-four case studies were analysed, and their results were compared. Micro thread reduces implant maximum Von Mises stress by about 50 to 70% than regular thread one. Oblique loading of 50 N will produce 4 to 5 times more maximum Von Mises values on implant body than 100 N vertical loading. Zero or negligible effect on the cortical bone was recorded when exchanging the tested crown material. Although titanium implant can also reduce cortical bone, Von Mises stress by 50 to 100% in comparison to reinforced PEKK (poly ether-ketone-ketone) or PEEK (poly-ether-ether-ketone). CONCLUSIONS: Reinforced PEKK and PEEK implants can represent a good alternative to titanium implants. Zirconia crown distributes the applied load better than Porcelain fused to a metal one. Regardless of the implant material, an implant with the micro thread has superior behaviour in comparison to a regular one. Zirconia crown above titanium implant with the micro thread may represent the best option for patient bone.

Recent Advances in Material and Geometrical Modelling in Dental Applications.

This article touched, in brief, the recent advances in dental materials and geometric modelling in dental applications. Most common categories of dental materials as metallic alloys, composites, ceramics and nanomaterials were briefly demonstrated. Nanotechnology improved the quality of dental biomaterials. This new technology improves many existing materials properties, also, to introduce new materials with superior properties that covered a wide range of applications in dentistry. Geometric modelling was discussed as a concept and examples within this article. The geometric modelling with engineering Computer-Aided-Design (CAD) system(s) is highly satisfactory for further analysis or Computer-Aided-Manufacturing (CAM) processes. The geometric modelling extracted from Computed-Tomography (CT) images (or its similar techniques) for the sake of CAM also reached a sufficient level of accuracy, while, obtaining efficient solid modelling without huge efforts on body surfaces, faces, and gaps healing is still doubtable. This article is merely a compilation of knowledge learned from lectures, workshops, books, and journal articles, articles from the internet, dental forum, and scientific groups' discussions.

Advanced Computational Methods in Bio-Mechanics.

A novel partnership between surgeons and machines, made possible by advances in computing and engineering technology, could overcome many of the limitations of traditional surgery. By extending surgeons' ability to plan and carry out surgical interventions more accurately and with fewer traumas, computer-integrated surgery (CIS) systems could help to improve clinical outcomes and the efficiency of healthcare delivery. CIS systems could have a similar impact on surgery to that long since realised in computer-integrated manufacturing. Mathematical modelling and computer simulation have proved tremendously successful in engineering. Computational mechanics has enabled technological developments in virtually every area of our lives. One of the greatest challenges for mechanists is to extend the success of computational mechanics to fields outside traditional engineering, in particular to biology, the biomedical sciences, and medicine. Biomechanics has significant potential for applications in orthopaedic industry, and the performance arts since skills needed for these activities are visibly related to the human musculoskeletal and nervous systems. Although biomechanics is widely used nowadays in the orthopaedic industry to design orthopaedic implants for human joints, dental parts, external fixations and other medical purposes, numerous researches funded by billions of dollars are still running to build a new future for sports and human healthcare in what is called biomechanics era.

Angulated Dental Implants in Posterior Maxilla FEA and Experimental Verification.

AIM: This study aimed to evaluate the effect of different implant angulations in posterior maxilla on stress distribution by finite element analysis and verify its results experimentally. METHODS: Two simplified models were prepared for an implant placed vertically and tilted 25° piercing the maxillary sinus. Geometric models' components were prepared by Autodesk Inventor then assembled in ANSYS for finite element analysis. The results of finite element analysis were verified against experimental trials results which were statistically analysed using student t-test (level of significance p < 0.05). RESULTS: Implant - abutment complex absorbed the load energy in case of vertical implant better than the case of angulated one. That was reflected on cortical bone stress, while both cases showed stress levels within the physiological limits. Comparing results between FEA and experiment trials showed full agreement. CONCLUSION: It was found that the tilted implant by 25° can be utilised in the posterior region maxilla for replacing maxillary first molar avoiding sinus penetration. The implant-bone interface and peri-implant bones received the highest Von Mises stress. Implant - bone interface with angulated implant received about 66% more stresses than the straight one.

New dental implant selection criterion based on implant design.

OBJECTIVE: A comparative study between threaded and plain dental implant designs was performed to find out a new criterion for dental implant selection. MATERIALS AND METHODS: Several dental implant designs with a systematic increase in diameter and length were positioned in a cylindrical-shaped bone section and analyzed using finite element method. Four loading types were tested on different dental implant designs; tension of 50 N, compression of 100 N, bending of 20 N, and torque of 2 Nm, to derive design curves. RESULTS: Better stress distribution on both spongy and cortical bone was noted with an increase in dental implant diameter and length. With the increase in dental implant side area, a stress reduction in the surrounding bones was observed, where threaded dental implants showed better behavior over the plain ones. CONCLUSIONS: Increasing value of ratio between dental implant side area and its cross-sectional area reduces stresses transferred to cortical and spongy bones. The use of implants with higher ratio of side area to cross-section area, especially with weak jaw bone, is recommended.

Influence of Number of Implants and Attachment Type on Stress Distribution in Mandibular Implant-Retained Overdentures: Finite Element Analysis.

AIM: This study aimed to compare the stresses generated by using two or four root form dental implants supporting mandibular overdentures that were retained with ball and locator attachments. METHODS: Under ANSYS environment, four 3D finite element models were prepared. These models simulated complete overdentures supported by two or four implants with either ball or locator attachments as a connection mechanism. The models' components were created by CAD/CAM package then were imported to ANSYS. Load of 100 N was applied at the right premolar/molar region vertically and at an oblique angle of 110° from lingual direction. RESULTS: Within the conditions of this research, in all cases, it was found that cortical and cancellous bone regions were the least to be stressed. Also, the ball attachment produced higher stresses. CONCLUSION: Caps deformation and stresses are negligible in cases of using locator attachment in comparison to ball attachments. This may indicate longer lifetime and less repair/maintenance operations in implant overdentures retained by locator attachments. Although the study revealed that bone was insensitive to a number of implants or attachment type, it may be recommended to use two implants in the canine region than using four, where the locator attachments were found to be better.

Finite Element Study on Continuous Rotating versus Reciprocating Nickel-Titanium Instruments.

In the present study, GTX and ProTaper as continuous rotating endodontic files were numerically compared with WaveOne reciprocating file using finite element analysis, aiming at having a low cost, accurate/trustworthy comparison as well as finding out the effect of instrument design and manufacturing material on its lifespan. Two 3D finite element models were especially prepared for this comparison. Commercial engineering CAD/CAM package was used to model full detailed flute geometries of the instruments. Multi-linear materials were defined in analysis by using real strain-stress data of NiTi and M-Wire. Non-linear static analysis was performed to simulate the instrument inside root canal at a 45° angle in the apical portion and subjected to 0.3 N.cm torsion. The three simulations in this study showed that M-Wire is slightly more resistant to failure than conventional NiTi. On the other hand, both materials are fairly similar in case of severe locking conditions. For the same instrument geometry, M-Wire instruments may have longer lifespan than the conventional NiTi ones. In case of severe locking conditions both materials will fail similarly. Larger cross sectional area (function of instrument taper) resisted better to failure than the smaller ones, while the cross sectional shape and its cutting angles could affect instrument cutting efficiency.

Finite Element Study on Continuous Rotating versus Reciprocating Nickel-Titanium Instruments

Abstract In the present study, GTX and ProTaper as continuous rotating endodontic files were numerically compared with WaveOne reciprocating file using finite element analysis, aiming at having a low cost, accurate/trustworthy comparison as well as finding out the effect of instrument design and manufacturing material on its lifespan. Two 3D finite element models were especially prepared for this comparison. Commercial engineering CAD/CAM package was used to model full detailed flute geometries of the instruments. Multi-linear materials were defined in analysis by using real strain-stress data of NiTi and M-Wire. Non-linear static analysis was performed to simulate the instrument inside root canal at a 45° angle in the apical portion and subjected to 0.3 N.cm torsion. The three simulations in this study showed that M-Wire is slightly more resistant to failure than conventional NiTi. On the other hand, both materials are fairly similar in case of severe locking conditions. For the same instrument geometry, M-Wire instruments may have longer lifespan than the conventional NiTi ones. In case of severe locking conditions both materials will fail similarly. Larger cross sectional area (function of instrument taper) resisted better to failure than the smaller ones, while the cross sectional shape and its cutting angles could affect instrument cutting efficiency.

Resumo As limas rotativas GTX e ProTaper foram comparadas numericamente com as limas reciprocatórias WaveOne pela análise de elementos finitos, com o objetivo de baixar custos, comparação fiel e exata, além de pesquisar o efeito do projeto das limas e de seu material sobre a durabilidade. Dois modelos tridimensionais de análise de elementos finitos foram especialmente elaborados para esta comparação. Utilizou-se um sistema de engenharia CAD/CAM comercial para construir o modelo totalmente detalhado da geometria das estrias das limas. Materiais multi-lineares foram definidos na análise usando dados reais de deformação por estresse de NiTi e M-Wire. Procedeu-se à análise estática não linear para simular a ação do instrumento dentro do canal radicular em ângulo de 45° na região apical, submetido a uma torsão de 0.3 N.cm. As três simulações realizadas no presente estudo demonstraram que o M-Wire é um pouco mais resistente a falhas que o NiTi convencional. Por outro lado, ambos os materiais são bastante similares em condições de travamento severo. No caso da geometria das limas, os instrumentos de M-Wire podem ter vida útil mais longa que os de NiTi convencional. Em condições de travamento severo, ambos os materiais terão falhas similares. Maior área transversal (em função da conicidade do instrumento) resiste melhor a falhas que as áreas transversais menores, ao passo que a geometria da área transversal e seus ângulos de corte podem afetar a eficiência de corte das limas.

A finite element study on stress distribution of two different attachment designs under implant supported overdenture.

OBJECTIVE: This study aimed to evaluate stress patterns generated within implant-supported mandibular overdentures retained by two different attachment types: ball and socket and locator attachments. MATERIALS AND METHODS: Commercial CAD/CAM and finite element analysis software packages were utilized to construct two 3D finite element models for the two attachment types. Unilateral masticatory compressive loads of 50, 100, and 150 N were applied vertically to the overdentures, parallel to the longitudinal axes of the implants. Loads were directed toward the central fossa in the molar region of each overdenture, that linear static analysis was carried out to find the generated stresses and deformation on each part of the studied model. RESULTS: According to FEA results the ball attachment neck is highly stressed in comparison to the locator one. On the other hand mucosa and cortical bone received less stresses under ball and socket attachment. CONCLUSIONS: Locator and ball and socket attachments induce equivalent stresses on bone surrounding implants. Locator attachment performance was superior to that of the ball and socket attachment in the implants, nylon caps, and overdenture. Locator attachments are highly recommended and can increase the interval between successive maintenance sessions.

Influence of implant-abutment angulations and crown material on stress distribution on central incisor: a 3D FEA

Aim: To investigate the effect of implant-abutment angulation and crown material on stress distribution of central incisors. Finite element method was used to simulate the clinical situation of a maxillary rightcentral incisor restored by two different implant-abutment angulations, 15° and 25°, using two different crown materials (IPS E-Max CAD and zirconia). Methods: Two 3D finite element models were specially prepared for this research simulating the abutment angulations. Commercial engineering CAD/CAM package was used to model crown, implant abutment complex and bone(cortical and spongy) in 3D. Linear static analysis was performed by applying a 178 N oblique load.The obtained results were compared with former experimental results. Results: Implant Von Misesstress level was negligibly changed with increasing abutment angulation. The abutment with higherangulation is mechanically weaker and expected to fail at lower loading in comparison with thesteeper one. Similarly, screw used with abutment angulation of 25° will fail at lower (about one-third)load value the failure load of similar screw used with abutment angulated by 15°. Conclusions: Bone (cortical and spongy) is insensitive to crown material. Increasing abutment angulation from15° to 25°, increases stress on cortical bone by about 20% and reduces it by about 12% onspongy bone. Crown fracture resistance is dramatically reduced by increasing abutment angulation. Zirconia crown showed better performance than E-Max one.

A finite element study on the mechanical behavior of reciprocating endodontic files

To evaluate the mechanical behavior of reciprocating endodontic files, comparing nickel-titanium NiTi and stainless steel 316L St.St. 316L as manufacturing material for such instruments. METHODS: A three-dimensional finite element model was designed for this study. The simplified instrument model geometry was created on commercial CAD/CAM software. Real strain stress curves of St.St. 316L and NiTi were used in the analysis. Non-linear static analysis was performed to simulate the instrument inside root canal at an angle of 45° in the apical portion, and subjected to torsion of 0.3 N.cm. RESULTS: Non-linear NiTi material showed super elasticity and high functionality in such applications. Very high levels of stress appeared in the file at 3 mm from the tip close to yield point. CONCLUSIONS: St. St. 316L is not suitable for manufacturing reciprocating instruments. Modeling of the instrument with equivalent circular cross-sectional area did not affect results quality. Reciprocating instruments have short lifespan, thus manufacturers recommend using one file per tooth. Reciprocating instruments are recommended for less experienced dentist...

The Biomechanical Effect of Different Denture Base Materials on the Articular Disc in Complete Denture Wearers: A Finite Element Analysis.

AIM: The objective of the present study was to evaluate the effect of different denture base materials on the stress distribution in TMJ articular disc (AD) in complete denture wearers. MATERIAL AND METHODS: A three dimensional Finite Element (FEA) models of an individual temporomandibular joint (TMJ) was built on the basis CT scan. The FEA model consisted of four parts: the condyle, the articular disc, the denture base, and the articular eminence skull. Acrylic resin and chrome-cobalt denture base materials were studied. Static loading of 300N was vertically applied to the central fossa of the mandibular second premolar. Stress and strain were calculated to characterize the stress/strain patterns in the disc. RESULTS: The maximum tensile stresses were observed in the anterior and posterior bands of (AD) on load application with the two denture base materials. The superior boundaries of the glenoid fossa showed lower stress than those on the inferior boundaries facing the condyle. CONCLUSIONS: Within the limitations of the present study it may be concluded that: The denture base material may have an effect in stress-strain pattern in TMJ articular disc. The stiffer denture base material, the better the distribution of the load to the underling mandibular supporting structures & reducing stresses induced in the articular disc.