•The effect of machining on fatigue strength of CAD/CAM ceramics was evaluated.•Machining reduces the flexural fatigue strength of CAD/CAM ceramics.•Y-TZP showed the greatest reduction in the fatigue ...strength due to machining.•Either soft machining or hard machining can be deleterious.•Higher values of roughness may be expected after machining.
To assess the effect of machining on the flexural fatigue strength and on the surface roughness of different computer-aided design, computer-aided manufacturing (CAD/CAM) ceramics by comparing machined and polished after machining specimens.
Disc-shaped specimens of yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP), leucite-, and lithium disilicate-based glass ceramics were prepared by CAD/CAM machining, and divided into two groups: machining (M) and machining followed by polishing (MP). The surface roughness was measured and the flexural fatigue strength was evaluated by the step-test method (n=20). The initial load and the load increment for each ceramic material were based on a monotonic test (n=5). A maximum of 10,000 cycles was applied in each load step, at 1.4Hz. Weibull probability statistics was used for the analysis of the flexural fatigue strength, and Mann-Whitney test (α=5%) to compare roughness between the M and MP conditions.
Machining resulted in lower values of characteristic flexural fatigue strength than machining followed by polishing. The greatest reduction in flexural fatigue strength from MP to M was observed for Y-TZP (40%; M=536.48MPa; MP=894.50MPa), followed by lithium disilicate (33%; M=187.71MPa; MP=278.93MPa) and leucite (29%; M=72.61MPa; MP=102.55MPa). Significantly higher values of roughness (Ra) were observed for M compared to MP (leucite: M=1.59μm and MP=0.08μm; lithium disilicate: M=1.84μm and MP=0.13μm; Y-TZP: M=1.79μm and MP=0.18μm).
Machining negatively affected the flexural fatigue strength of CAD/CAM ceramics, indicating that machining of partially or fully sintered ceramics is deleterious to fatigue strength.
Highlights • The feldspathic and polymer infiltrated ceramics (Enamic) have completely different microstructures. The former present crystals while the latter is amorphous. • The lithium dissilicate ...and the Zirconia-reinforced lithium silicate presented greater susceptibility to stress corrosion than the other ceramics. • The zirconia present in the lithium silicate is tetragonal zirconia.
•A masticatory load may result in different mechanical responses on the crown and cement layer according to the implemented restorative material.•It is necessary for the clinician to consider the ...biomechanics when selecting the monolithic material for the restoration.•Stress concentration can be calculated based on the stress peak value to the average stress value in the concerned region.
To investigate the influence of different materials for monolithic full posterior crowns using 3D-Finite Element Analysis (FEA).
Twelve (12) 3D models of adhesively-restored teeth with different crowns according to the material and its elastic modulus were analysed: Acrylic resin, Polyetheretherketone, Composite resin, Hybrid ceramic, pressable and machinable Zirconia reinforced lithium silicate, Feldspathic, Lithium disilicate, Gold alloy, Cobalt–Chromium alloy (Co–Cr), Zirconia tetragonal partially stabilized with yttria, and Alumina. All materials were assumed to behave elastically throughout the entire deformation. Results in restoration and cementing line were obtained using maximum principal stress. In addition, maximum shear stress criteria was used for the cementing line.
Restorative materials with higher elastic modulus present higher stress concentration inside the crown, mainly tensile stress on an intaglio surface. On the other hand, materials with lower elastic modulus allow stress passage for cement, increasing shear stress on this layer. Stiffer materials promote higher stress peak values.
Materials with higher elastic modulus such as Co–Cr, zirconia and alumina enable higher tensile stress concentration on the crown intaglio surface and higher shear stress on the cement layer, facilitating crown debonding.
Purpose
To determine the elastic properties of five ceramic systems with different compositions (lithium disilicate vs. feldspathic ceramics) and processing methods and compare the stress ...distribution in premolars in the interface with inlays made with these systems loaded with the maximum normal bite force (665 N) using 3D finite element analysis (FEA).
Materials and Methods
The elastic properties of five ceramic restoration materials (IPS e.max Press, IPS e.max CAD, Vita PM9, Vita Mark II, Vita VM7) were obtained using the ultrasonic pulse‐echo method. Three‐dimensional FEA simplified models of maxillary premolars restored with these ceramic materials were created. The models were loaded with a load at the two nodes on the occlusal surface in the middle of the tooth, 2 mm from the outside of the tooth, simulating a loading ball with a radius of 6 mm.
Results
The means values of density (g/cm³), Young's modulus (GPa), and Poison's ratio was 2.6 ± 0.3, 82.3 ± 18.3, and 0.22 ± 0.01 for IPS e.max Press; 2.3 ± 0.1, 83.5 ± 15.0, and 0.21 ± 0.01 for IPS e.max CAD; 2.5 ± 0.1, 44.4 ± 11.5, and 0.26 ± 0.08 for PM9; 2.4 ± 0.1, 70.6 ± 4.9, and 0.22 ± 0.01 for Vitamark II; 2.4 ± 0.1, 63.3 ± 3.9, and 0.23 ± 0.01 for VM7, respectively. The 3D FEA showed the tensile stress at the interface between the tooth and the inlay was dependent on the elastic properties of the materials, since the Vita PM9 and IPS e.max CAD ceramics presented the lowest and the highest stress concentration in the interface, respectively.
Conclusions
The elastic properties of ceramic materials were influenced by composition and processing methods, and these differences influenced the stress concentration at the bonding interface between tooth and restoration. The lower the elastic modulus of inlays, the lower is the stress concentration at the bonding interfaces.
Implant-retained custom-milled framework enhances the stability of palatal obturator prostheses. Therefore, to evaluate the mechanical response of implant-retained obturator prostheses with bar-clip ...attachment and milled bars, in three different materials under two load incidences were simulated. A maxilla model which Type IIb maxillary defect received five external hexagon implants (4.1 x 10 mm). An implant-supported palatal obturator prosthesis was simulated in three different materials: polyetheretherketone (PEEK), titanium (Ti:90%, Al:6%, V:4%) and Co-Cr (Co:60.6%, Cr:31.5%, Mo:6%) alloys. The model was imported into the analysis software and divided into a mesh composed of nodes and tetrahedral elements. Each material was assumed isotropic, elastic and homogeneous and all contacts were considered ideal. The bone was fixed and the load was applied in two different regions for each material: at the palatal face (cingulum area) of the central incisors (100 N magnitude at 45°); and at the occlusal surface of the first left molar (150 N magnitude normal to the surface). The microstrain and von-Mises stress were selected as criteria for analysis. The posterior load showed a higher strain concentration in the posterior peri-implant tissue, near the load application side for cortical and cancellous bone, regardless the simulated material. The anterior load showed a lower strain concentration with reduced magnitude and more implants involving in the load dissipation. The stress peak was calculated during posterior loading, which 77.7 MPa in the prosthetic screws and 2,686 με microstrain in the cortical bone. For bone tissue and bar, the material stiffness was inversely proportional to the calculated microstrain and stress. However, for the prosthetic screws and implants the PEEK showed higher stress concentration than the other materials. PEEK showed a promising behavior for the bone tissue and for the integrity of the bar and bar-clip attachments. However, the stress concentration in the prosthetic screws may represent an increase in failure risk. The use of Co-Cr alloy can reduce the stress in the prosthetic screw; however, it increases the bone strain; while the Titanium showed an intermediate behavior.
Abstract Objective To investigate the microstructural properties and reliability of zirconia partially stabilized by yttrium oxide (Y-TZP) for use in monolithic form (Vita YZ HT, Vita Zahnfabrik, ...Germany) after different clinical adjustment protocols simulation. One-hundred and sixty two Y-TZP discs of high translucency were divided into 6 groups (n = 27), according to simulated adjustments: S-Y-TZP as sintered; G-glazed Y-TZP; DbG-Y-TZP with diamond bur adjustment simulation followed by glaze application; GDb-glazed Y-TZP adjusted with diamond bur; DbDrG-Y-TZP with adjustment simulation with diamond bur and polishing kit (diamond rubber), followed by glaze; GDbDr-glazed Y-TZP with adjustment simulation with diamond bur followed by polishing kit. Methods After monotonic testing under biaxial flexure (n = 3), remaining specimens were distributed into 3:2:3 ratio and tested under step-stress accelerated life testing. Specimens were evaluated in a stereomicroscope and SEM. Microstructure was analyzed by X-ray diffraction and mean surface roughness (Ra). Survival data were used to calculate Weibull's beta value (β) and reliability for missions of 300,000 and 600,000 cycles at 200 N. Ra data were statistically analyzed by 1-way ANOVA and Tukey’s test (both, a = 5%). Results The untreated HT zirconia (S) presented a lower probability of survival after 600,000 cycles at 200 N, compared to HT zirconia adjusted with diamond bur and glazed (DbG), and after final polishing with polishing kit (GDbDr). Final polishing with diamond rubber (GDbDr) resulted in a more homogeneous surface compared to glazed samples (G, DbG and DbDrG). Significance HT zirconia is more likely to present increased survival when glazed after diamond adjustments (DbG) or when it is finished with polishing kit (GDbDr).
•The RPD clasp material influences on its durability, retention force and enamel damage.•The polyamide material presented suitable mechanical performance when used in higher undercuts.
This study ...aimed to evaluate the effect of different materials and undercut on the removal force and stress distribution in the supporting tooth and in the circumferential clasp used in removable partial prosthesis.
Upper molars prepared for Akers circumferential clasp with retention and opposing arm were modeled, scanned, elaborated with CAD software and the geometries imported in FEA and analyzed. Six different materials were selected for the clasp (Polyamide, Polyoxymethylene, Polyetheretherketone - PEEK, Gold alloy, Titanium and CoCr) and 3 different undercuts (0.25, 0.50 and 0.75mm), totaling 18 groups.
The clasps presented greater stress in their structure and potentially greater damage to the dental enamel when made with rigid materials and with more undercut; however, they presented greater ability to remain in position.
Polyamide with a higher undercut is an esthetic alternative to rigid metallic clasps. It showed promising behavior because it strongly reduces the damage to the enamel, and even with an undercut of 0.75, the retention is lower than for CoCr with a 0.25 undercut, and this retention might still be sufficient. Polyoxymethylene and Polyetheretherketone (PEEK) are not suitable materials for the clasps, because the maximum stress occurring during removal with higher undercuts is higher than the material strength.
•The LTD also significantly increased the fracture resistance of zirconia.•The fracture resistance was significantly lower in all groups that were glazed.•The groups were treated with rubber ...polishers alone presented the highest resistance.•Phase transformations in ultra-translucent zirconia were not observed.•Finishing and polishing induced phase transformation.
To investigate the effect of different surface finishing and polishing regimes and low temperature degradation on flexural strength, phase transformation and surface topography of ultra-translucent ZrO2 ceramic.
300 (n=15/group) of conventional zirconia (Z: Ice Zirkon Transluzent) and ultra-translucent zirconia (UT: Prettau Anterior) bar-specimens were made and divided according to the "Finishing/Polishing" - (C — Control, B — diamond rubber polishers, P — adjusting with burs, PB — adjusting with burs+diamond polishers, PG — adjusting with burs+glaze), "Low temperature Degradation (LTD)" (with or without a treatment at 127°C, 1.7bar/24h). Then, a 3-point mini flexural test was performed in a universal testing machine (1mm/min, 500kgf load cell). SEM, EDS, XDR, AFM, optical profilometry and Weibull analysis were performed. Data were analyzed by 3-way ANOVA and Tukey’s post-test (5%).
Groups ZPBD (1670±253MPa), ZBD (1664±217MPa), and ZB (1655±3678MPa) showed significantly higher flexural strength than the UTPG group (372±56MPa). The Weibull modulus was significantly higher for the ZPD group compared to the UB, UCD, UPD and UPBD, while UTB, UTCD and UTPD had the lowest value. Monoclinic phases were observed only in the conventional zirconia groups and were more evident after LTD. Diamond rubber polishers presented less roughness for both zirconias.
The use of diamond rubber polishers is the most suitable finishing/polishing method for zirconia ceramic restorations and that final glazing reduces the fracture resistance of these materials.
Highlights • We used a staircase method for evaluating cyclic loads-to-failure of crowns. • We compared the results from cyclic and monotonic testing. • 50 μm was more favorable for the structural ...performance of the crowns than 500 μm.
Background/Aims
Mouthguards (MGs) are devices that can reduce the risks of facial trauma. However, the large variety of MG types and thicknesses raises the question of which type is the most ...effective and beneficial for the athletes. The aim of this study was to evaluate stress distribution in the skull, teeth, and jaws as a consequence of a direct impact.
Material and Methods
Using modeling software, a human skull was modeled and a human jaw was created with all teeth inserted into the respective alveolus. The models were divided according to the MG type (custom‐made or stock) and thickness (1, 2, and 4 mm). Two models without MG were evaluated with and without teeth contact. The geometries were exported to analysis software and the materials were considered ideal. Fixation occurred at the base of the foramen magnum. The load (500 N) was applied on the canine tooth with a ball. Maximum principal (MPa) and Von‐Mises results were obtained.
Results
Without any protection, the generated tensile stress was of greater magnitude causing more damage in the absence of teeth contact. The presence of a MG significantly reduced the generated stress in all structures, and the customized/individualized type was more efficient than stock MGs.
Conclusions
In extreme situations when it is impossible to use a MG, keeping the teeth in maximum intercuspal position is less harmful. Despite this, the use of any MG is beneficial and assists in dampening the generated stress. The thicker the device, the greater the capacity for decreasing the damage in all structures. The use of individual protectors for each patient is even more beneficial for preventing trauma during at‐risk activities of impact.
PDF
