Dimorvan Bordin

Fatigue Failure of Narrow Implants with Different Implant-Abutment Connection Designs

PURPOSEnTo evaluate the reliability of narrow diameter dental implants (NDIs) with similar macrogeometry and 3 implant-abutment connection designs.nnnMATERIALS AND METHODSnEighty-four NDIs (3.5 × 10 mm) were selected and divided into 4 groups (n = 21/group) according to implant-abutment connection design, as follows: EH - external hexagon, IH - internal hexagon, IC - internal conical, and IC-M - internal conical connected to a monolithic titanium abutment. Identical abutments were torqued to the implants, and standardized maxillary incisor crowns were cemented and subjected to step-stress accelerated life testing (SSALT) in water. Use of level probability Weibull curves, and reliability for a mission of 50,000 cycles at 75 N and 200 N were calculated.nnnRESULTSnThe beta (β) values were: 1.48 for IC, 1.40 for IC-M, 8.54 for EH, and 1.98 for IH, indicating that damage accumulation was an acceleration factor for failure of all groups. At 75 N the probability of survival was not significantly different between groups. A decrease in reliability was observed for all groups at 200 N with no significant differences between IC (81.71%) and IC-M (94.28%), or between EH and IH (0%) which presented the lowest values. EH failures were primarily restricted to the screw, while IH involved screw and implant fracture. IC and IC-M were restricted to prosthetic failures (fracture and bending).nnnCONCLUSIONSnNarrow implants with external or internal hexagon connections presented the lowest reliability at high loads compared to internal conical connections. Failure modes differed among connections.

Fracture strength and probability of survival of narrow and extra-narrow dental implants after fatigue testing: In vitro and in silico analysis

PURPOSEnTo assess the probability of survival (reliability) and failure modes of narrow implants with different diameters.nnnMATERIALS AND METHODSnFor fatigue testing, 42 implants with the same macrogeometry and internal conical connection were divided, according to diameter, as follows: narrow (Ø3.3×10mm) and extra-narrow (Ø2.9×10mm) (21 per group). Identical abutments were torqued to the implants and standardized maxillary incisor crowns were cemented and subjected to step-stress accelerated life testing (SSALT) in water. The use-level probability Weibull curves, and reliability for a mission of 50,000 and 100,000 cycles at 50N, 100, 150 and 180N were calculated. For the finite element analysis (FEA), two virtual models, simulating the samples tested in fatigue, were constructed. Loading at 50N and 100N were applied 30° off-axis at the crown. The von-Mises stress was calculated for implant and abutment.nnnRESULTSnThe beta (β) values were: 0.67 for narrow and 1.32 for extra-narrow implants, indicating that failure rates did not increase with fatigue in the former, but more likely were associated with damage accumulation and wear-out failures in the latter. Both groups showed high reliability (up to 97.5%) at 50 and 100N. A decreased reliability was observed for both groups at 150 and 180N (ranging from 0 to 82.3%), but no significant difference was observed between groups. Failure predominantly involved abutment fracture for both groups. FEA at 50N-load, Ø3.3mm showed higher von-Mises stress for abutment (7.75%) and implant (2%) when compared to the Ø2.9mm.nnnCONCLUSIONSnThere was no significant difference between narrow and extra-narrow implants regarding probability of survival. The failure mode was similar for both groups, restricted to abutment fracture.

Influence of platform diameter in the reliability and failure mode of extra-short dental implants

PURPOSEnTo evaluate the influence of implant diameter in the reliability and failure mode of extra-short dental implants.nnnMATERIALS AND METHODSnSixty-three extra-short implants (5mm-length) were allocated into three groups according to platform diameter: Ø4.0-mm, Ø5.0-mm, and Ø6.0-mm (21 per group). Identical abutments were torqued to the implants and standardized crowns cemented. Three samples of each group were subjected to single-load to failure (SLF) to allow the design of the step-stress profiles, and the remaining 18 were subjected to step-stress accelerated life-testing (SSALT) in water. The use level probability Weibull curves, and the reliability (probability of survival) for a mission of 100,000 cycles at 100MPa, 200MPa, and 300MPa were calculated. Failed samples were characterized in scanning electron microscopy for fractographic inspection.nnnRESULTSnNo significant difference was observed for reliability regarding implant diameter for all loading missions. At 100MPa load, all groups showed reliability higher than 99%. A significant decreased reliability was observed for all groups when 200 and 300MPa missions were simulated, regardless of implant diameter. At 300MPa load, the reliability was 0%, 0%, and 5.24%, for Ø4.0mm, Ø5.0mm, and Ø6.0mm, respectively. The mean beta (β) values were lower than 0.55 indicating that failures were most likely influenced by materials strength, rather than damage accumulation. The Ø6.0mm implant showed significantly higher characteristic stress (η = 1,100.91MPa) than Ø4.0mm (1,030.25MPa) and Ø5.0mm implant (η = 1,012.97MPa). Weibull modulus for Ø6.0-mm implant was m = 7.41, m = 14.65 for Ø4.0mm, and m = 11.64 for Ø5.0mm. The chief failure mode was abutment fracture in all groups.nnnCONCLUSIONSnThe implant diameter did not influence the reliability and failure mode of 5mm extra-short implants.

The effect of DLC-coating deposition method on the reliability and mechanical properties of abutment's screws

OBJECTIVEnTo characterize the mechanical properties of different coating methods of DLC (diamond-like carbon) onto dental implant abutment screws, and their effect on the probability of survival (reliability).nnnMETHODSnSeventy-five abutment screws were allocated into three groups according to the coating method: control (no coating); UMS - DLC applied through unbalanced magnetron sputtering; RFPA-DLC applied through radio frequency plasma-activated (n=25/group). Twelve screws (n=4) were used to determine the hardness and Youngs modulus (YM). A 3D finite element model composed of titanium substrate, DLC-layer and a counterpart were constructed. The deformation (μm) and shear stress (MPa) were calculated. The remaining screws of each group were torqued into external hexagon abutments and subjected to step-stress accelerated life-testing (SSALT) (n=21/group). The probability Weibull curves and reliability (probability survival) were calculated considering the mission of 100, 150 and 200N at 50,000 and 100,000 cycles.nnnRESULTSnDLC-coated experimental groups evidenced higher hardness than control (p<0.05). In silico analysis depicted that the higher the surface Youngs modulus, the higher the shear stress. Control and RFPA showed β<1, indicating that failures were attributed to materials strength; UMS showed β>1 indicating that fatigue contributed to failure. High reliability was depicted at a mission of 100N. At 200N a significant decrease in reliability was detected for all groups (ranging from 39% to 66%). No significant difference was observed among groups regardless of mission. Screw fracture was the chief failure mode.nnnSIGNIFICANCEnDLC-coating have been used to improve titaniums mechanical properties and increase the reliability of dental implant-supported restorations.

Biomechanical Behavior of the Dental Implant Macrodesign.

PURPOSEnThe aim of this study was to evaluate the influence of implant macrodesign when using different types of collar and thread designs on stress/strain distributions in a maxillary bone site.nnnMATERIALS AND METHODSnSix groups were obtained from the combination of two collar designs (smooth and microthread) and three thread shapes (square, trapezoidal, and triangular) in external hexagon implants (4 × 10 mm) supporting a single zirconia crown in the maxillary first molar region. A 200-N axial occlusal load was applied to the crown, and measurements were made of the von Mises stress (σvM) for the implant, and tensile stress (σmax), shear stress (τmax), and strain (εmax) for the surrounding bone using tridimensional finite element analysis. The main effects of each level of the two factors investigated (collar and thread designs) were evaluated by one-way analysis of variance (ANOVA) at a 5% significance level.nnnRESULTSnCollar design was the main factor of influence on von Mises stress in the implant and stresses/strain in the cortical bone, while thread design was the main factor of influence on stresses in the trabecular bone (P < .05). The optimal collar design able to produce more favorable stress/strain distribution was the microthreaded design for the cortical bone. For the trabecular bone, the triangular thread shape had the lowest stresses and strain values among the square and trapezoidal implants.nnnCONCLUSIONnStress/strain distribution patterns were influenced by collar design in the implant and cortical bone, and by thread design in the trabecular bone. Microthreads and triangular thread-shape designs presented improved biomechanical behavior in posterior maxillary bone when compared with the smooth collar design and trapezoidal and square-shaped threads.

Influence of Polishing System on the Surface Roughness of Flowable and Regular-Viscosity Bulk Fill Composites

This study evaluated the influence of polishing protocols on the surface roughness of flowable and regular bulk fill composites. Five bulk fill composites were tested: SureFil SDR Flow (SDR), Tetric EvoFlow Bulk fill (TEF), Filtek Bulk Fill Flowable (FIF), Tetric EvoCeram Bulk Fill (TEC), and Filtek Bulk Fill Posterior (FIP). Two polishing protocols were tested: Sof-Lex and Astropol. Astropol created a smoother surface for FIP (P < .05); however, the polishing protocol did not influence surface roughness on TEC (P > .05). SDR, TEF, and FIF exhibited rougher surfaces when polished. Sof-Lex created rougher surfaces for bulk fill composites. It was concluded that surface roughness was related to material composition rather than the polishing system.

Residual stress of porcelain-fused to zirconia 3-unit fixed dental prostheses measured by nanoindentation

OBJECTIVEnTo evaluate the residual stress (nanoindentation based on hardness) of fatigued porcelain-fused to zirconia 3-unit fixed dental prostheses (FDP) with different framework designs.nnnMETHODSnTwenty maxillary 3-unit FDP replacing second-premolar (pontic) were fabricated with conventional framework-design (even-thickness of 0.5mm and 9mm2 connector area) and modified framework-design (thickness of 0.5mm presenting lingual collar connected to proximal struts and 12mm2 connector area). Connector marginal ridges were loaded and the fractured and suspended FDPs were divided (n=3/each) into: (1) Fractured zirconia even-thickness (ZrEvenF); (2) Suspended zirconia even-thickness (ZrEvenS); (3) Fractured zirconia with modified framework (ZrModF); (4) Suspended zirconia with modified framework (ZrModS); (5) Non-fatigued FDP with conventional framework design (Control). The FDPs were nanoindented at 0.03mm (Region of Interest (ROI) 1), 0.35mm (ROI 2) and 1.05mm (ROI 3) distances from porcelain veneer outer surface with peak load 4000μN. The Linear Mixed Analysis of Variance (ANOVA) Model on ranks and Least Significant Difference Test on ranks (95%) were used.nnnRESULTSnHighest rank hardness values were found for Control group and ZrModS, whereas the lowest values were found in ZrModF. Statistical differences (p=0.000) were found among all groups except for comparison between ZrModS and Control group (p=0.371). Hardness between ROIs were statistically significant different (p<0.001) where ROI 1 presented the lowest values.nnnSIGNIFICANCEnFramework-design modification did not influence the residual stress of porcelain-fused to zirconia fatigued 3-unit FDP. Whereas fractured FDPs showed the highest residual stress compared to suspended and control FDPs. Residual stress increased as nanoindented away from framework.