Effect of platform connection and abutment material on stress distribution in single anterior implant-supported restorations: A nonlinear 3-dimensional finite element analysis

The effect of different abutment and restorative crown materials on stress distribution in single-unit implant-supported restorations: A 3D finite element stress analysis

PURPOSE

To evaluate the effect of restorative materials with or without resin content, modeled on zirconia and titanium abutment materials, on the stress distribution on the alveolar bone, implant, and prosthetic crowns with a 3D finite element stress analysis.

MATERIAL AND METHODS

Titanium and zirconia abutments were combined with three implant-supported crown materials (polymer infiltrated hybrid ceramic (PICN), lithium disilicate (LD), and zirconia-reinforced lithium silicate (ZLS)) to create six experimental groups. The 40 × 30 × 20 mm alveolar bone, 3.75 × 10 mm implant, esthetic abutment, and maxillary first premolar crown bonded over the abutment were the components of the finite element models. On the lingual cusp of the crown, the 150 N occlusal loading was applied in the buccolingual direction at a 30° angle. Equivalent von Mises stress and maximum and minimum principal stresses were used for both the qualitative and quantitative evaluation of the stress distribution of the created models.

RESULTS

The von Mises stress in implant and abutment did not differ according to the crown materials. The use of a zirconia abutment resulted in higher von Mises stress values in the abutment but lower stress values in the implant. The highest stress values were obtained in ZLS (196.65 MPa) and LD (194.05 MPa) crowns. The use of titanium abutments, regardless of crown materials, resulted in higher von Mises stress values in restorative crowns than in zirconia abutments. The principal stress values in alveolar bone showed similar distribution and concentration in all models.

CONCLUSIONS

Changes in crown material did not affect stress distribution in the implant and peripheral bone. However, the zirconia esthetic abutment resulted in a lower stress concentration on the implant.

Mechanical behavior of titanium and zirconia abutments at the implant-abutment interface: A systematic review

STATEMENT OF PROBLEM

Zirconia has become popular for dental implant abutments in the esthetic zone but can damage the implant connection interface. Studies have been conducted to compare zirconia abutments with conventional titanium abutments; however, a consensus or systematic review is lacking.

PURPOSE

The purpose of this systematic review was to evaluate the performance of abutments made of zirconia and titanium in relation to wear and misfit at the implant-abutment interface.

MATERIAL AND METHODS

Electronic databases (PubMed/MEDLINE, Embase, Web of Science) were independently searched by 2 researchers for relevant studies published up to June 2021. The population, intervention, comparison, outcome (PICO) question was "Do zirconia abutments cause greater wear at the implant-abutment interface than titanium abutments under occlusal forces?" Eligible studies included in vitro studies that evaluated changes in the surface of external and/or internal connections and single and/or multiple, screwed and/or cemented prostheses rehabilitated with titanium and zirconia abutments submitted to mechanical cycling.

RESULTS

Nine studies were included for qualitative analysis. A total of 172 specimens were analyzed, 86 zirconia and 86 titanium abutments. In terms of wear on the implant connection surface, zirconia abutments caused more severe wear, more scratches, and more rounding of the hexagonal angles at the implant connection interface than titanium abutments. In terms of misfit at the connection interface, zirconia abutments showed greater misfit than titanium abutments.

CONCLUSIONS

Zirconia abutments produce more wear at the titanium implant connection interface, titanium abutments showed better fit to the implant connection interface, and the fit can be influenced by the abutment manufacturing method.

Biomechanical behavior of different designs of hybrid abutment-restoration on the posterior crown: a finite element analysis

This study aimed to evaluate the influence of material and crown design on the biomechanical behavior of implant-supported crowns with hybrid abutment (HA) through three-dimensional (3D) finite element analysis. The study factors were the type of material used as the mesostructure or crown (zirconia, lithium disilicate, and hybrid ceramic) and the crown design cemented to the titanium base (mesostructure cemented to the titanium base and a crown cemented on it (HaC); hybrid crown-abutment, the abutment and crown are manufactured as a single piece and cemented to the titanium base (HC); monolithic crown cemented on the titanium base and screwed to the implant (CS); and monolithic crown cemented on the titanium base (CC). Four 3D models were constructed using an implant with an internal connection, and an oblique load of 130 N was applied at 45° to the long axis of the implant. The models were evaluated using the von Mises stress for crown, abutment, screw, and implant and maximum principal stress for bone tissues. The lowest stresses occurred in the groups with a lower elastic modulus material, mainly hybrid ceramics, considered a material with greater resilience. The cemented crown group presented the lowest stress values. The stresses were concentrated in the cervical region of the crown at the titanium crown/base interface. Mesostructures made of materials with a higher elastic modulus exhibited a higher concentration of stress. The presence of a screw hole increased the stress concentration in the ceramic crown. Cemented ceramic crowns exhibited better biomechanical behavior than screw-retained crowns.

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.

Stress behavior of an anterior single implant restored with high-performance polymer abutments under immediate and delayed loading: A 3D FEA study

PURPOSE

To evaluate the stress generated on peripheral bone, implant, and prosthetic components while using polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) hybrid abutments in two different loading situations with nonlinear 3D finite element analysis.

MATERIALS AND METHODS

Standard tessellation language (STL) files of original components were used for the in-silico modeling of implant, standard titanium abutment, and hybrid abutments (PEEK and PEKK). The implant was placed in the bone block to imitate immediate loading, in which a friction coefficient of 0.3 was set between the bone and the implant interface, or delayed loading, where the bone-implant interface was assumed to be perfect. In all models, both a horizontal force (25.5 N) and a 30-degree oblique force (178 N) were applied to the long axis of the implant to the palatal surface of the restoration. The stress distribution was evaluated.

RESULTS

While more stress was observed in the prosthetic structures in the PEEK and PEKK models, the stresses on the implant and bone were similar in all models, regardless of the loading situation. Under immediate loading, PEEK hybrid abutments caused excessive stress accumulation on the titanium base abutment.

CONCLUSIONS

Even though abutment type did not affect the stresses on peripheral bone, PEEK and PEKK abutments generated greater stresses on the implant and the standard titanium abutment accumulated higher stresses. Oblique forces mostly generated greater stress than horizontal forces. Oblique forces on an immediately loaded implant led to stresses higher than the yield strength of a titanium implant when restored with PEEK hybrid abutment.

Implant deformation and implant-abutment fracture resistance after standardized artificial aging: An in vitro study

BACKGROUND AND PURPOSE

Zirconia abutments have been widely adopted in clinical implant practice. The unique mechanical properties of zirconia may significantly affect the long-term prognosis of implant treatments. The purpose of this study was to investigate the influence of abutment material on implant deformation and fracture resistance of internal conical connection implant-abutment complexes of two diameters after standardized artificial aging.

MATERIALS AND METHODS

Thirty original abutments (one-piece titanium, one-piece zirconia, zirconia with alloy base) with two diameters (regular, narrow) were connected to internal conical connection implants and subjected to a standardized artificial aging process consisting of thermal cycling and mechanical cyclic loading. Microcomputed tomography (μCT) scans of implant bodies were performed before and after aging. 3-dimensional images of implant bodies were generated from the μCT scans and aligned for before and after aging to calculate the volumetric deformation amount. Finally, fracture resistance was measured using a mechanical static loading test for the surviving aged and 30 brand-new specimens.

RESULTS

All specimens survived artificial aging. No significant difference in implant deformation was found in the regular groups (p = 0.095). In narrow groups, the one-piece zirconia group showed significantly less deformation (p < 0.0001). For fracture resistance, no significant decrease was observed after aging in any group (p > 0.05). One-piece zirconia abutments showed significantly lower strength than the other two materials for both diameters (p < 0.0001).

CONCLUSIONS

In the regular diameter system, abutment material had no significant influence on the tested mechanical property degradation after simulated long-term oral use. The mechanical performance of narrow diameter one-piece zirconia abutments differed from the other two materials. For optimal performance, one-piece zirconia abutments should be adopted only in anterior regions.

Hydrothermal aging affects the three-dimensional fit and fatigue lifetime of zirconia abutments

OBJECTIVE

Evaluate the effect of aging using two different methods on the three-dimensional fit of zirconia abutments at the implant-abutment connection and estimate the probability of survival of anterior crowns supported by straight and 17-degree angled abutments.

MATERIALS AND METHODS

Two different zirconia abutment designs, straight and 17-degree angled abutments (n = 63/group), were evaluated in the current study. The abutments were randomly allocated into three experimental groups according to laboratory aging condition (134°C, 2.2 bar, 20 h): (i) control, (ii) autoclave aging, and (iii) hydrothermal reactor aging. Crystalline content was determined by X-Ray diffraction (XRD) and Raman spectroscopy, and microstructure was analyzed using field-emission gun scanning electron microscope (FEG-SEM). Implant-abutment volume misfit was determined in the straight abutments by micro-computed tomography using the silicone replica technique. For fatigue testing, abutments were torqued to the implants and connected to standardized maxillary incisor zirconia crowns. The assemblies were subjected to step-stress accelerated life testing (SSALT) in water until fracture or suspension. The use level probability Weibull curves and probability of survival for a mission of 50,000 cycles at 50, 100, 150 and 200 N were calculated and plotted. Fractured samples were analyzed using a stereomicroscope and scanning electron microscope.

RESULTS

The crystalline spectra depicted a zirconia system primarily composed of the tetragonal phase. Laboratory aging yielded a 20%- and 37%-increase in the monoclinic content for abutments aged in autoclave and hydrothermal reactor relative to control, respectively. A fully crystalline matrix with a regular grain size was observed in the FEG-SEM for control abutments, with a considerable presence of intergranular defects. While autoclave aging triggered no significant alteration to the microstructure, defect population was reduced after hydrothermal reactor aging. Control abutments presented a significantly higher volume misfit (2.128 ± 0.54 mm3) relative to aged abutments using autoclave (1.244 ± 0.48 mm3) or hydrothermal reactor (1.441 ± 0.41 mm3). The beta (β) values indicated that failures were predominantly controlled by material strength rather than fatigue damage accumulation for all groups, except for straight control abutments. Irrespective of aging, the probability of survival of straight and angled zirconia abutments was up to 95% (95-100%) at 50 and 100 N. A 50N-increase in the load resulted in wider range of survival estimate, with straight autoclave abutments percentage significantly lower probability of survival (77%) than angled hydrothermal reactor abutments (99%). At 200N, angled hydrothermal reactor (97%) or autoclave (82%) aged abutments demonstrated the highest probability of survival, angled control (71%) and straight hydrothermal reactor (69%) abutments intermediate values, and straight autoclave (23%) and control (7%) abutments the lowest estimate. The failure mode predominantly involved abutment and/or abutment screw fracture for both straight and angled abutments.

CONCLUSIONS

Hydrothermal aging significantly influenced volume misfit, as well as the probability of survival of zirconia abutments at higher loads for both angled and straight abutments.

Biomechanical evaluation of different implant-abutment connections, retention systems, and restorative materials in the implant-supported single crowns using 3D finite element

This is an in silico study aimed to evaluate the biomechanical influence of different implant-abutment interfaces (external hexagon and Morse taper implants), retention systems (cement- and screw-retained), and restorative crowns (metal-ceramic and monolithic) using three-dimensional finite element analysis (3D-FEA). Eight 3D models were simulated for the maxillary first molar area using InVesalius, Rhinoceros, and SolidWorks and processed using the Femap and NEi Nastran softwares. Axial and oblique forces of 200 N and 100 N, respectively, were applied on the occlusal surface of the prostheses. Microstrain and von Mises stress maps were used to evaluate the deformation (cortical bone tissue) and stress (implants/fixation screws/crowns), respectively for each model. For both loadings, Morse taper implants had lower microstrain values than the external hexagon implants. The retention system did not affect microstrain on the cortical bone tissue under both loadings. However, the cemented prosthesis displayed higher stress with the fixation screw than the external hexagon implants. No difference was observed between the metal-ceramic and zirconia monolithic crowns in terms of microstrain and stress distribution on the cortical bone, implants or components. Morse taper implants can be considered as a good alternative for dental implant rehabilitation because they demonstrated better biomechanical behavior for the bone and fixation screw as compared to external hexagon implants. Cement-retained prosthesis increased the stress on the fixation screw of the external hexagon implants, thereby increasing the risk of screw loosening/fracture in the posterior maxillary area. The use of metal-ceramic or monolithic crowns did not affect the biomechanical behavior of the evaluated structures.

Hybrid abutment during prosthetic planning and oral rehabilitation

BACKGROUND

The present study aims to describe through a literature review, the characteristics and properties of hybrid abutments, as well as their proper use as a new rehabilitation strategy.

METHODS

A bibliographic search was conducted in the main health databases Pubmed (www.pubmed.gov) and Google Scholar (www.scholar.google.com.br), in which studies published from 2001 to 2020 were collected. Laboratory studies, case reports, systematic and literature reviews were included. Therefore, articles that do not adress the characteristics and properties of hybrid abutments were excluded. In addition, studies that did not report the use of hybrid abutments as a new rehabilitation strategy.

RESULTS

According to the inclusion and exclusion criteria, 80 research articles were selected and 20 were excluded, while 25 in vitro, 17 in vivo and 9 in silico studies were reviewed.

CONCLUSIONS

The literature demonstrates that hybrid abutments are an excellent alternative in cases of implant-supported rehabilitation, presenting high esthetic results, associated with good soft tissue response, periimplant marginal bone stability and adequate stress distribution during the masticatory loads dissipation.

Effect of fatigue loading and failure mode of different ceramic implant abutments

STATEMENT OF PROBLEM

Currently many options are available for restoring a dental implant, although the ideal implant abutment for withstanding the occlusal load and the restorative material for fulfilling the esthetic need remains unclear. Zirconia (Zir) abutments offer good esthetics, but concerns still remain regarding their fracture strength, complex fabrication, and higher cost as compared with those of titanium (Ti) base abutments offering lower cost, acceptable esthetics, and a straightforward procedure.

PURPOSE

The purpose of this in vitro study was to evaluate the fracture strength and failure mode of single-tooth Zir and Ti base implant abutments with fatigue loading.

MATERIAL AND METHODS

Forty restorations were included using 4 different types of abutment-restorations. Zir abutments with lithium disilicate crowns (ZirLd); titanium base abutments with custom Zir abutments and lithium disilicate crowns (TiZirLd); titanium base abutments with monolithic lithium disilicate abutment-crowns (TiLd); titanium base abutments with monolithic polymer-infiltrated ceramic abutment-crowns (TiEn). Specimens were subjected to a progressive cyclic loading by using a custom-made mastication simulator at a frequency of 1.4 Hz starting with a load of 88 N followed by stages of 170, 210, 250, and 290 N for a maximum of 20 000 cycles each or until fracture occurred. The number of cycles, maximum load, and failure modes were recorded. Statistical analysis was done by using the Mann-Whitney U test (α=.05).

RESULTS

Group TiEn showed a lower resistance to fatigue, with a mean ±standard deviation of 5054 ±123.3 cycles subjected to a mean force of 170 N. Groups ZirLd and TiLd resisted higher forces without fracture 13452.6 ±7094.3 cycles, and load of 178 ±16.9 N, followed by the TiLd group with a mean ±standard deviation of 25798.6 ±5498.7 cycles, and load of 202 ±16.9 N, while the TiZirLd group showed a mean of 48235.4 cycles subjected to a mean force of 258 N. The failure mode observed in the TiEn occurred only in the ceramic, whereas in the ZirLd and TiLd group, it was above the shoulder level of the Ti base abutment. Even though the TiZirLd group was able to withstand higher loads and a higher number of cycles, the failures were catastrophic and presented fractures of the titanium-base abutment and prosthetic screw.

CONCLUSIONS

The TiZirLd, ZirLd, and TiLd abutment-restorations have the potential to withstand the average physiological occlusal forces that occur in the anterior region. The group with the higher fatigue resistance was TiZirLd, although care should be taken with patients presenting parafunctional habits since the failure mode can be catastrophic. Also, polymer-infiltrated ceramic is not suitable for a Ti base abutment when subjected to oblique loading.

Effect of bone quality and bone loss level around internal and external connection implants: A finite element analysis study

STATEMENT OF PROBLEM

A consensus regarding the biomechanical effects of vertical bone loss in normal and osteoporotic bone tissue according to different implant-abutment interfaces is lacking.

PURPOSE

The purpose of this finite element analysis study was to evaluate the effect of vertical bone loss (without bone loss; with 1.5-mm bone loss; with 3-mm bone loss; and with 4.5-mm bone loss) in normal and osteoporotic bone that received a Ø4×10-mm implant with different implant-abutment connections (external connection [external hexagon] and internal connection [Morse taper]) by using 3D finite element analysis.

MATERIAL AND METHODS

Sixteen 3D models were simulated. Axial and oblique forces of 200 N and 100 N, respectively, were applied on the occlusal surfaces of the prostheses. Maximum principal stress and microstrain were determined from the bone tissue of each model. von Mises stress analysis was used to evaluate the stress distribution in implants and prosthetic components (fixation screws, abutment, and crown).

RESULTS

The results showed higher stress concentrations in models with bone loss as increased vertical bone loss contributed to higher stress and microstrain in the bone tissue, regardless of the quality of bone and implant-abutment connection. Osteoporotic bone contributed to increase in microstrain in the trabecular bone. The internal connection showed lower stress than the external connection implants only in models without marginal bone loss. Furthermore, higher stress concentrations were observed in the implants and fixation screws in models with increased bone loss and external connection implants, mainly under oblique loading. Osteoporotic bone did not affect stress distribution in the implants and prosthetic components.

CONCLUSIONS

Progressive bone loss contributed to higher stress in the bone tissue, implants, and prosthetic components. The osteoporotic bone affects only the microstrain in the trabecular bone, but not the stress in the implants and prosthetic components. The internal connection implants showed lower stress in the cortical bone only in models without bone loss, while external connection implants exhibited higher stress in the implants and screws under oblique loading.

Evaluation of the clinical behavior of 2 different materials for implant-supported interim fixed partial prostheses: A randomized clinical trial

STATEMENT OF PROBLEM

Clinical studies about interim implant-supported prostheses made of polymethylmethacrylate (PMMA) and polyoxymethylene (POM) have been limited to clinical reports or studies on the survival of implants subjected to immediate loading without evaluating the influence of the material used.

PURPOSE

The purpose of this randomized clinical trial was to evaluate the clinical performance of posterior resin interim implant-supported fixed partial dentures (FPDs) made of 2 different computer-aided design and computer-aided manufactured (CAD-CAM) materials: PMMA and POM.

MATERIAL AND METHODS

A total of 21 participants received 49 interim implant-supported FPDs. The same participant received the PMMA as part of the control group and the POM as part of the experimental group. The restorations were evaluated at 1 week and 3 and 6 months after their placement, using the California Dental Association (CDA) quality-evaluation index. Their functional wear and color stability were also evaluated. Data were analyzed by using nonparametric statistics (α=.05).

RESULTS

The CDA criteria showed that the PMMA group performed better than the POM group in the surface and color parameter (P<.05). Fractures at the implant connection level were observed in 10 prostheses. The number of fractures was significantly higher in internal conical connection implants (P<.05). The statistical analysis of color stability showed values of ΔE*ab of 7.18 for PMMA and 8.58 for POM, without significant differences between materials. Concerning the wear evaluation, a significant increase in the wear of both materials was found at 6 months of functioning (P<.05). No significant differences were found within materials.

CONCLUSIONS

Within a 6-month observation period, PMMA interim implant-supported FPDs performed better than POM in the surface and color parameter. Entirely polymer posterior implant-supported FPDs with internal conical connection implants appear to be more susceptible to fracture.

3D finite element model based on CT images of tooth

Aim: This study aimed the description of a protocol to acquire a 3D finite element (FE) model of a human maxillary central incisor tooth restored with ceramic crowns with enhanced geometric detail through an easy-to-use and low-cost concept and validate it through finite element analysis (FEA). Methods: A human maxillary central incisor was digitalized using a Cone Beam Computer Tomography (CBCT) scanner. The resulted tooth CBCT DICOM files were imported into a free medical imaging software (Invesalius) for 3D surface/geometric reconstruction in stereolithographic file format (STL). The STL file was exported to a computer-aided-design (CAD) software (SolidWorks), converted into a 3D solid model and edited to simulate different materials for full crown restorations. The obtained model was exported into a FEA software to evaluate the influence of different core materials (zirconia - Zr, lithium disilicate - Ds or palladium/silver - Ps) on the mechanical behavior of the restorations under a 100 N applied to the palatal surface at 135 degrees to the long axis of the tooth, followed by a load of 25.5 N perpendicular to the incisal edge of the crown. The quantitative and qualitative analysis of maximum principal stress (ceramic veneer) and maximum principal strain (core) were obtained. Results: The Zr model presented lower stress and strain concentration in the ceramic veneer and core than Ds and Ps models. For all models, the stresses were concentrated in the external surface of the veneering ceramic and strains in the internal surface of core, both near to the loading area. Conclusion: The described procedure is a quick, inexpensive and feasible protocol to obtain a highly detailed 3D FE model, and thus could be considered for future 3D FE analysis. The results of numerical simulation confirm that stiffer core materials result in a reduced stress concentration in ceramic veneer.

Biomechanical Evaluation of Initial Stability of a Root Analogue Implant Design with Drilling Protocol: A 3D Finite Element Analysis

Background: The aim of this study was to biomechanically evaluate the initial stability of a patient-specific root analogue implant (RAI) design with drilling protocol by comparing it to designs without drilling protocol through a 3D finite element analysis (FEA). Methods: A 3D surface model of an RAI for the upper right incisor was constructed. To evaluate the effect of root apex drilling, four modified RAI shapes were designed with the press-fit implantation method: Non-modified, wedge added at root surface, lattice added at root surface, and apex-anchor added at root apex (AA). Each model was subjected to an oblique load of 100 N. To simulate the initial stability of implantation, contact conditions at the implant–bone interface were set to allow for the sliding phenomenon with low friction (frictional coefficient 0.1–0.5). Analysis was performed to evaluate micro-displacements of the implants and peak stress on the surrounding bones. Results: Under all low frictional coefficient conditions, the lowest von Mises stress level on the cortical bone and fewest micro-displacements of the implant were observed in the AA design. Conclusion: In view of these results, the AA design proved superior in reducing the stress concentration on the supporting cortical bone and the micro-displacement of RAI.

Effect of Implant Platform Connection and Abutment Material on Removal Torque and Implant Hexagon Plastic Deformation

Objectives  The aim of this study was to evaluate the plastic deformation of the hexagonal connection, and the removal torque of the implant-abutment joint of two dental implants combined with internal or external hexagonal connection implants after mechanical cycling.

Materials and Methods  Twenty-four dental implants were used in the study. Half of the implants had internal hexagonal connections (IH; Titamax II Plus) and the other half had external hexagonal connections (EH; Titamax Ti Ex). Four groups of two types of dental implant abutments (titanium: Ti, UCLA II Plus and zirconia: Zr, fabricated by CAD/CAM; n = 6) were investigated. The abutments received a metallic crown and the settings were submitted to mechanical cycling (MC; 10 ⁶ cycles, axial load, 120N). The connection surface area was measured by scanning electron microscope (SEM) images. The removal torque was evaluated and the plastic deformation of the hexagonal surface of the implant was measured by comparing the images before and after MC.

Statistical Analysis  Paired- t test was used to analyze the data statistically at a significance level of α = 0.05.

Results  The torque values decreased for all groups after MC, and the hexagonal surface area decreased due to plastic deformation for IH and EH associated with Zr abutments.

Conclusions  Zirconia abutments showed the worst plastic deformation of the implant connection surface and torque loosening when associated with IH implant.

Analysis of stress distribution in ceramic and titanium implants in alveolar sockets of the anterior region of the maxilla

Background

In the routine of dentistry, knowing the biomechanical properties of implant systems and their inherent stress distribution under force loading is an essential step to predict structural damage and biological responses. This study aimed to investigate stress distribution in zirconia and titanium implants and their biomechanical response in alveolar sockets of the anterior region of the maxilla through tridimensional finite element analysis.

Material and Methods

From computed tomography scans of a reference patient, three models of the maxillary dental arch were designed with Rhinoceros 5.0 software (McNeel Europe™, Barcelona, Spain). In each model, a dental implant replaced the maxillary left central incisor. The implants consisted of M1) Zirconia Pure Ceramic Implant Monotype; M2) Zirconia Pure Ceramic ZLA; and M3) Titanium Bone Level - Roxolid SLA. Ceramic crowns were installed in all the implants. Implants and prostheses were loaded with 50N oblique and axial forces. Von-Mises and Mohr Coulomb criteria were used to assess stress distribution in the implant systems and perimplantar bone, respectively.

Results

Traction was detected in the cervical region of the palatal bone surface of all the models. Oppositely, compression was found in the cervical region of the vestibular bone surfaces.

Conclusions

Zirconia Pure Ceramic Implant Monotype had the best response under oblique force loading. Ceramic implants may be an alternative to replace titanium implants in fresh alveolar sockets in the anterior region of the maxilla. Key words:Finite elements, implants, stress, ceramic, titanium.

Influence of different implant-abutment connections on stress distribution in single tilted implants and peripheral bone: A three-dimensional finite element analysis

BACKGROUND

The load transfer between the implant-bone interface depends on various factors, including loading type; material properties of the implant and prosthesis; and implant geometry, length, diameter, and shape.

OBJECTIVE

The purpose of this study was to evaluate stress distribution in single tilted bone-level implants with different connections and peripheral bone under vertical and oblique loads using three-dimensional (3D) finite element analysis (FEA).METHOS.3D models of four different implant systems and their abutments were created from the data (computer-aided design) of original implants and abutments scanned with an optical scanner. The implants were placed in the bone block at degrees of 0°, 15°, and 30°. Then, a 3D model of the metal-ceramic crown was created and a 100-N total load was applied vertically and obliquely.

RESULTS

Stress analyses showed variable results depending on the connection design and tilting angle; however, the tube in tube (TIT) connection type exhibited lower stress values in most loading and tilting simulations.

CONCLUSIONS

Increase in tilting angle showed variable results in each connection design. The TIT connection design was found to be more successful in terms of stress distributions in the implant components and the peripheral bone.

The effect of adhesive failure and defects on the stress distribution in all-ceramic crowns

OBJECTIVES

To explore the effect of adhesive failure and defects between the crown and cement on the stress distribution within all-ceramic crowns and the corresponding risk of failure.

METHODS

An IPS e.max crown of lithium disilicate produced by CAD/CAM for a first mandibular molar was modeled using finite element analysis based on X-ray micro-CT scanned images. Predefined debonding states and interfacial defects between the crown and cement were simulated using the model. The first principal stress distribution of the crown and cement was analyzed under a vertical occlusal load of 600 N. A concept of failure risk was proposed to evaluate the crown.

RESULTS

Stress concentrations in the crown were identified on the occlusal surface surrounding the region of loading, beneath the area of loading and at the margin of the interior surface. Stress concentrations in the cement were also evident at the boundary of the debonded areas. The lower surface of the crown is safe to sustain the 600 N vertical load, but the top surface of the cement would undergo cohesive failure. According to the evaluation of failure risk of the crown, the conditions of highest risk corresponded to the conditions with highest percentage of cement damage. The risk of failure is not only associated with debonding between the crown and cement, but also associated with its distribution.

CONCLUSIONS

Debonding related defects and cementing defects are more deleterious to the interfacial stress than debonding itself. The axial wall plays a critical role in maintaining the principal tensile stress of the crown at an acceptable level.

Evaluation of stress distribution in bone and three-unit fixed implant-supported prostheses with zirconia and titanium abutments: A 3D finite element analysis

Background. For esthetic considerations in anterior regions, abutments with high-strength ceramics such as alumina and zirconia have been developed as substitutes for titanium abutments. The present study was designed to investigate the distribution of stress in prosthesis and bone components of an implant-supported FPD with different abutments by using 3D finite element analysis. Methods. Ceramic FPDs were made from the canine to the upper left second premolar with titanium fixtures. In order to investigate the stress distribution, forces of 100 and 300 N were applied at angles of 0, 15 and 35 degrees to the central fossa of the second premolar and pontic, as well as the cingulum of the canine crown. Force loading was static. After analyzing the mechanical properties of the materials, boundary conditions and loading were performed according to the existing averages, and subsequently, the results obtained from this analysis were analyzed. Results. The highest level of stress was observed in the distal crest of the posterior implant (23.20 MPa) under lateral forces (15 and 35 degrees) in a model with both titanium abutments. Conclusion. Lateral forces induced higher accumulation of stress in the implant and surrounding bone, while abutment change did not affect the distribution of stress.

Influence of Metal and Ceramic Abutments on the Stress Distribution Around Narrow Implants: A Photoelastic Stress Analysis

PURPOSE

This study aimed to compare, through photoelastic analysis, the distribution of stresses around narrow implants with external hexagon (EH) and Morse taper (MT) connections, when single crowns made with metal and ceramic abutments were used.

MATERIALS AND METHODS

Six photoelastic models were prepared, simulating the use of narrow EH and MT implants replacing a lateral incisor. These 2 groups received 3 different abutments: prefabricated metal abutments, customized metal abutments, and customized zirconia abutments. All crowns were identical and made with a leucite reinforced glass-ceramic. Vertical loads of 0 to 100 N were applied on the palatal surface of the crowns, and the photoelastic stress fringes developed in each model were captured in a high-definition video, and digital photographs were taken at 100 N.

RESULTS

The abutment type and material influenced the stress distribution patterns around narrow implants with EH and MT connections. Stresses were generated mainly around the apical and lingual regions of the implants.

CONCLUSIONS

For both connections, the prefabricated metal abutments presented better stress distribution around the implants when compared to customized metal and zirconia abutments because low stress levels were developed in smaller areas around the implants.

Mechanical properties of resin glass fiber-reinforced abutment in comparison to titanium abutment

Purpose:

So far, definitive implant abutments have been performed with high elastic modulus materials, which prevented any type of shock absorption of the chewing loads and as a consequence, the protection of the bone-fixture interface. This is particularly the case when the esthetic restorative material chosen is ceramic rather than composite resin. The adoption of an anisotropic abutment, characterized by an elastic deformability, could allow decreasing the impulse of chewing forces transmitted to the crestal bone.

Materials and Methods:

According to research protocol, the mechanical resistance to cyclical load was evaluated in a tooth-colored fiber-reinforced abutment (TCFRA) prototype and compared to that of a titanium abutment (TA), thus eight TCFRAs and eight TAs were adhesively cemented on as many titanium implants. The swinging that the two types of abutments showed during the application of sinusoidal load was also analyzed.

Results:

In the TA group, both fracture and deformation occurred in 12.5% of samples while debonding 62.5%. In the TCFRA group, only debonding was present in 37.5% of samples. In comparison to the TAs, the TCFRAs exhibited a greater swinging during the application of sinusoidal load. In the TA group, the extrusion prevailed, whereas in the TCFRA group, the intrusion was more frequent.

Conclusion:

The greater elasticity of TCFRA to the flexural load allows absorbing part of the transversal load applied on the fixture during the chewing function, thus reducing the stress on the bone-implant interface.