The Effect of Implant Length and Diameter on Stress Distribution around Single Implant Placement in 3D Posterior Mandibular FE Model Directly Constructed Form In Vivo CT.

A three-dimensional (3D) finite element (FE) model of the mandibular bone was created from 3D X-ray CT scan images of a live human subject. Simulating the clinical situation of implant therapy at the mandibular first molar, virtual extraction of the tooth was performed at the 3D FE mandibular model, and 12 different implant diameters and lengths were virtually inserted in order to carry out a mechanical analysis. (1) High stress concentration was found at the surfaces of the buccal and lingual peri-implant bone adjacent to the sides of the neck in all the implants. (2) The greatest stress value was approximately 6.0 MPa with implant diameter of 3.8 mm, approx. 4.5 MPa with implant diameter of 4.3 mm, and approx. 3.2 MPa with implant diameter of 6.0 mm. (3) The stress on the peri-implant bone was found to decrease with increasing length and mainly in diameter of the implant.

Effect of accelerated aging on the fracture toughness of zirconias.

STATEMENT OF PROBLEM: Low temperature degradation (LTD) of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is of concern. PURPOSE: The purpose of this in vitro study was to assess the effect of accelerated aging on the Vickers hardness and fracture toughness of a newly developed Y-TZP and 2 primary Y-TZPs. MATERIAL AND METHODS: Two primary 3 mol% Y-TZP, Lava (LA), Everest Zirconium Soft (EV), and a new 3 mol% Y-TZP, ZirTough (NZ) were assessed. Specimens (n=30 each brand) of 10 × 10 × 3 mm were hydrothermally treated for accelerated aging to examine LTD. Five conditions were used (n = 5 per condition) as follows: control group (no aging); 5 hours at 134°C/0.2 MPa (5h-134°C); 100 hours at 134°C/0.2 MPa (100 h-134°C); 5 hours at 180°C/1.0 MPa (5 h-180°C); and 20 hours at 180°C/1.0 MPa (20 h-180°C). Fracture toughness was measured by using the indentation fracture (IF) method under a loading of 294 N and calculated from the obtained measurements. To observe differences in particle composition and fracture patterns, mirror-polished test specimens (n=5 each brand) were re-sintered at 1200°C for 1 hour as a thermal etching process, and a Vickers indenter was pressed into the test specimens according to the IF method. Test piece surfaces and cracks were observed with scanning electron microscopy (SEM). One-way ANOVA and the post- hoc (Scheffé test were used to examine) interlevel significant differences (α=.05). RESULTS: The Vickers hardness and fracture toughness were as follows: 1319 HV and 7.36 MPa · m(1/2) for LA, and 1371 HV and 6.76 MPa · m(1/2) for EV in no aging; 1334 HV and 7.02 MPa · m(1/2) for LA, and 1346 HV and 6.07 MPa · m(1/2) for EV in 5h-134°C. No significant differences were found between no aging and 5h-134°C for LA and EV for Vickers hardness and fracture toughness. Measurements could not be made for LA and EV for 100 h-134°C, 5h-180°C, or 20 h-180°C because of fractures in the surface layer. For NZ, Vickers hardness and fracture toughness were as follows: 1261 HV and 15.60 MPa · m(1/2) in no aging; 1217 HV and 14.98 MPa · m(1/2) in 5h-134°C; 1231 HV and 15.13 MPa · m(1/2) in 100 h-134°C; 1252 HV and 15.51 MPa · m(1/2) in 5h-180°C; 1224 HV and 15.01 MPa · m(1/2) in 20 h-180°C. No significant differences were shown in the Vickers hardness and fracture toughness. SEM observations after the thermal etching processing of NZ showed zirconia particles and scattered alumina particles. CONCLUSION: Measurements with LA and EV could only be made for no aging and 5h-134°C, and no significant differences were found in Vickers hardness and fracture toughness. Measurements were made with NZ under all conditions and no significant differences were found in Vickers hardness and fracture toughness.

Structural stability of posterior retainer design for resin-bonded prostheses: a 3D finite element study.

The purpose of this in vitro study was to compare the stress distribution and natural frequency of different shape and thickness retainer designs for maxillary posterior resin-bonded prostheses using finite element (FE) method. A 3D FE model of a three unit posterior resin-bonded prosthesis analysis model was generated. Three different shaped retainer designs, viz. C-shaped (three axial surface wraparounds), D-shaped (three axial surface wraparounds with central groove) and O-shaped (360° wraparounds), and three different thicknesses, viz., 0.4, 0.8, and 1.2 mm, resin-bonded prostheses were used in this study. The resin-bonded prosthesis analysis model was imported into an FE analysis software (ANSYS 10.0, ANSYS, USA) and attribution of material properties. The nodes at the bottom surface of the roots were assigned fixed zero displacement in the three spatial dimensions. A simulated angle of 45° loading of a 100 N force was applied to the node of the pontic lingual cusp surface. The stress distributions and corresponding natural frequencies were analyzed and resolved. The C-shaped retainer for 0.4 mm thickness recorded the greatest von Mises stresses of 71.4 MPa for all three groups. C-shaped, D-shaped and O-shaped retainer presented natural frequencies 3,988, 7,754, and 10,494 Hz, respectively. D-shaped retainer and O-shaped retainer increased natural frequencies and structural rigidity over the traditional C-shaped retainer. The maximum von Mises stresses values of the remaining tooth and prosthesis decreased with greater retainer thickness. D-shaped retainer and O-shaped retainer increased natural frequencies and structural rigidity over the traditional C-shaped retainer.

Three-dimensional finite element analysis of Aramany Class IV obturator prosthesis with different clasp designs.

The purpose of this study was to evaluate the stress distribution on the alveolar bone surrounding abutment teeth and the displacement of the Aramany Class IV obturator prosthesis with two different clasp designs. Three-dimensional finite element models of an Aramany Class IV maxillary defect were constructed. Two different clasp designs on an obturator prosthesis (double Akers clasps and multiple Roach clasps) and two different load conditions (vertical and horizontal) were compared. Finite element analysis was used to calculate the equivalent stress. The difference in the clasp design of the Aramany Class IV obturator prosthesis affected the stress distribution of the alveolar bone surrounding the abutment teeth and the displacement of the obturator prosthesis. Multiple Roach clasps reduced the stress distribution on the alveolar bone surrounding the abutment teeth and the displacement of the Aramany Class IV obturator prosthesis compared to double Akers clasps.

Effects of coloring agents applied during sintering on bending strength and hardness of zirconia ceramics.

The effects of coloring agents (Vita in-ceram 2000 YZ coloring liquid (VL) and IPS e.max ZirCAD (IS)) and shades (1, 3, and 5) applied during sintering on the bending strength and fracture toughness of zirconia ceramics was examined. No differences in the bending strength or fracture toughness were observed for the type of coloring agent used. Moreover, the bending strength and Vickers hardness of the zirconia ceramics decreased, while the crack length and fracture toughness did not change with the different coloring agents. The marginal borders of the indentations formed were clear and linear, and no damage, including chipping, was observed. Therefore, clinical application of zirconia ceramics can be recommended because the coloring agents and shades applied during sintering have the same effect as an opaque layer and cause no significant deterioration of the mechanical properties of the zirconia ceramics.

Effects of rotating fatigue on the mechanical properties of microhybrid and nanofiller-containing composites.

The objective of this study was to assess and compare the flexural strength and Vickers hardness of five nanofiller-containing composites (Filtek Supreme XT, Gradia Forte, Luna-Wing, GNH400N, GCUC) against five microhybrid composites (Meta Color Prime Art, Solidex, Estenia C&B, Ceramage, Clearfil Majesty) before and after rotating fatigue test (RFT). For each resin composite, 16 rectangular beam specimens (2 mm × 2 mm × 25 mm) were prepared and half of which were subjected to 1 × 10(4) cycles in RFT. Flexural strength was determined using a three-point bending test. Vickers hardness measurements were carried out on specimens which failed after the three-point bending test. When under the influence of rotating fatigue, the flexural strength of all composites was affected by multiple factors. In contrast, rotating fatigue had no significant influence on the Vickers hardness of both microhybrid and nanofiller-containing composites.

Effect of loading conditions on the fracture toughness of zirconia.

PURPOSE: A Vickers hardness indenter was pressed into yttria-stabilized zirconia (Y-TZP) by the indentation fracture method (IF method). METHODS: The effect on the calculated Vickers hardness, fracture toughness values, and indentation fracture load (9.8, 49, 98, 196, and 294 N) was examined to deduce the optimum conditions of the IF method. Calculated Vickers hardness and fracture toughness values were analyzed with one-way analysis of variance and then multiple comparisons (Scheffe). The appearance of on indentation and cracks was also evaluated using a scanning electron microscopy (SEM). RESULTS: Indentation of Y-TZP was generated by 9.8 and 49 N of indentation fracture load, however cracks could not be confirmed with the microscope attached to the Vickers hardness tester. Both indentation and cracks were observed at 98, 196 and 294 N of indentation fracture load obtained values of 7.1 and 6.8 MPam(1/2). Cracks noted at the 98 N were not clear, whereas the 196 and 294 N showed especially clear cracks. Due to the hardness of zirconia and the light loads, fracture toughness values for 9.8, 49, and 98 N could not be calculated. There was no significant difference between 196 and 294 N, when calculated fracture toughness values were analyzed with multiple comparisons. SEM revealed clear indentation and cracks, that extended linearly, but no chips or fractures were observed. Surface changes were observed at 196 and 294 N that are presumed to be accompanied by phase transition around the cracks. CONCLUSIONS: Optimum experimental conditions of the indentation fracture load in the IF method were determined as 196 and 294 N.

Effect of water temperature on cyclic fatigue properties of glass-fiber-reinforced hybrid composite resin and its fracture pattern after flexural testing.

PURPOSE: To evaluate in vitro the influence of dynamic loading applied to a glass-fiber-reinforced hybrid composite resin on its flexural strength in a moist, simulated oral environment. MATERIALS AND METHODS: Three-point flexural strength specimens were subjected to cyclic loading in water at 37°C and 55°C to investigate the influence of immersion temperature on impact fatigue properties. Specimens were subjected to cyclic impact loading at 1 Hz for up to 5 × 105 cycles to obtain the number of cycles to failure, the number of unbroken specimens after 5 × 105 cycles, and the residual flexural strength of unbroken specimens. Maximum loads of 100, 200, and 300 N were chosen for both the non-reinforced and the glass-fiber reinforced hybrid composite resins. RESULTS: The mean residual flexural strength for 100 N impact loading at temperatures of 37°C and 55°C was 634 and 636 MPa, respectively. All specimens fractured at fewer than 5 × 105 cycles for loads of 200 and 300 N. CONCLUSION: Reduced numbers of cycles to fracture and lower fatigue values were observed as both the maximum load and immersion temperature increased.

Accuracy of three-dimensional finite element modeling using two different dental cone beam computed tomography systems.

The aim of this study is to evaluate the accuracy of dental ceramic object three dimensional (3D) finite element model constructed directly from two different dental cone beam computed tomography (CT) systems. CT scanned one 10.0 × 10.0 × 20.0 mm block and one 8.0 × 10.0 × 40.0 mm block of an 8-step wedge. All 3D finite element (FE) models were created from CT images. Each 3D FE model measured the length of the directions X, Y, and Z that corresponded to an original specimen using the measurement function between two points on the Mechanical Finder software package. The measurements and practical value were compared with the CT image and the accuracy of the reproduced measurements was examined. No significant differences were found between Alphard-3030 on the Z axis and ProMax 3D on the Y axis of the block. In addition, there were also no significant differences observed between Alphard-3030 on the Y axis and ProMax 3D on the X axis compared with Alphard-3030 on the Z axis and ProMax 3D on the Y axis for the step-wedge. The results suggest that measurement of the dimensions of cone beam CT images could be useful in applications where both good reproducibility and accuracy of FE models are required.

Finite element analysis to compare stress distribution of gold alloy, lithium-disilicate reinforced glass ceramic and zirconia based fixed partial denture.

AIM: Clinical data indicate that veneer chipping of zirconia core is more likely than with ceramic-fused-to-metal structures. The purposes of this simulation study were to: (a) use two-dimensional finite element modeling to simulate stresses at the interface of three-unit posterior fixed partial dentures (FPDs) made with three different core materials; and (b) to investigate the influence of three different veneer thicknesses on the stress distribution within the veneer-core complex. METHODS: A mesio-distal cross-section of a three-unit FPD was digitized and used to create two-dimensional models of the teeth, supporting bone, different core materials (gold alloy, zirconia and lithia-disilicate reinforced glass ceramic), and different pontic preparation configurations (occlusal veneer thickness 1.0, 1.5, and 2.0 mm). A simulated 100 N vertical occlusal load was applied to the standardized pontic element. Compression stress and tensile stress values were calculated by finite element analysis along the veneer-core interface and compared. RESULTS: The veneer-core interfacial stress of zirconia-based FPD is greater than that of gold alloy and lithium-disilicate reinforced glass ceramic core. The veneer-core interface stress value decreased with increasing occlusal veneer thickness. CONCLUSIONS: Finite element modeling revealed differences in tensile and compressive stresses between different pontic preparation configurations and core materials. In general, gold alloy and lithium-disilicate reinforced glass ceramic core provided more even stress distribution at the connector and pontic of fixed partial denture than a zirconia framework.

Effect of nanofiller on wear resistance and surface roughness of resin composites.

OBJECTIVE: To compare the wear resistance and surface roughness of nanofiller-containing composites and microhybrid composites after simulated wear. METHODS: Five microhybrid composites and five nanofiller-containing resin composites were included in the study. Six cylindrical specimens with a diameter of 10 mm and a thickness of 6 mm for each material were prepared. The volume loss, vertical loss and the surface roughness (Ra) were determined after 800 cycles of simulated chewing motion. One specimen of each material was analysed by scanning electron microscopy (SEM) to compare the morphology of the wear surfaces. The microhybrid composites group and nanofiller-containing composites group were tested using the Mann-Whitney U test with a significance level of α = 0.05. RESULTS: For all microhybrid composites, the average wear volume loss and vertical loss were 56.44 mm3 and 730.6 µm, respectively, while the average wear losses of nanofiller-containing composites were 40.15 mm3 and 528.17 µm, respectively. The nanofiller containing composite GNH400N showed the least roughness (Ra = 0.346 ± 0.076 µm), while the conventional microhybrid composite Ceramage showed the highest roughness (Ra = 0.699 ± 0.214 µm). However, wear resistance and surface roughness for the two groups showed no statistical difference. SEM micrographs of the nanofiller-containing composites after wear testing showed smoother and more uniform wear surfaces than for the microhybrid composites. CONCLUSION: Nanofillers did not significantly influence the wear resistance of resin composites, but might improve the surface roughness of resin composites.

Measuring the effects of water immersion conditions on the durability of fiber-reinforced hybrid composite resin using static and dynamic tests.

The present study was designed to measure the durability of glass fiber-reinforced hybrid resins (FRC) in clinical applications. Accordingly, we studied the effects of static and dynamic loading as well as temperature changes inside the oral cavity, a moist environment, on the bending strength of FRC. The bending strength was measured using several tests, including an open-air bending strength test (AE), a 24-h water immersion test (WC1D), a 2-year water immersion test (WC2Y), a thermal cycling test (TC), a repeated in-water impact test at 37°C/10(5) (WI37), and a repeated in-water impact test at 55°C/10(5) (WI55). The following tests are ordered from greatest to least with respect to GF's bending strength: AE, WI37, WI55, WC1D, WC2Y, and TC. Likewise, the following tests are ordered from greatest to least with respect to EV's bending strength: AE, WC1D, WC2Y, WI37, WI55, and TC.

Effects of mechanical properties of adhesive resin cements on stress distribution in fiber-reinforced composite adhesive fixed partial dentures.

Using finite element analysis (FEA), this study investigated the effects of the mechanical properties of adhesive resin cements on stress distributions in fiber-reinforced resin composite (FRC) adhesive fixed partial dentures (AFPDs). Two adhesive resin cements were compared: Super-Bond C&B and Panavia Fluoro Cement. The AFPD consisted of a pontic to replace a maxillary right lateral incisor and retainers on a maxillary central incisor and canine. FRC framework was made of isotropic, continuous, unidirectional E-glass fibers. Maximum principal stresses were calculated using finite element method (FEM). Test results revealed that differences in the mechanical properties of adhesive resin cements led to different stress distributions at the cement interfaces between AFPD and abutment teeth. Clinical implication of these findings suggested that the safety and longevity of an AFPD depended on choosing an adhesive resin cement with the appropriate mechanical properties.

Finite element analysis to compare stress distribution of connector of lithia disilicate-reinforced glass-ceramic and zirconia-based fixed partial denture.

This study used finite element method to analyze the stress distribution in connector of ceramic-based bilayer structures, in simulation of dental crown-like structures with a functional but weak veneer layer bonded onto a strong core layer. The purpose of this study was to evaluate the stress distribution at veneer/core interface of 2 different core materials [Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and lithia disilicate-reinforced glass-ceramic] using three-dimensional finite element analysis. Within the limitations of this study, finite element analysis showed that stress concentrations were located at the veneer/core interface of the connector in Y-TZP core models. The general observation was that compared with Y-TZP, lithia disilicate-reinforced glass-ceramic showed a relatively stable stress value and had a minor effect on the stress concentration susceptibility.

In vitro evaluation of the bonding durability of self-adhesive resin cement to titanium using highly accelerated life test.

The purpose of this in vitro study was to evaluate the bonding durability of three self-adhesive resin cements to titanium using the Highly Accelerated Life Test (HALT). The following self-adhesive resin cements were used to bond pairs of titanium blocks together according to manufacturers' instructions: RelyX Unicem, Breeze, and Clearfil SA Luting. After storage in water at 37°C for 24 h, bonded specimens (n=15) immersed in 37°C water were subjected to cyclic shear load testing regimes of 20, 30, or 40 kg using a fatigue testing machine. Cyclic loading continued until failure occurred, and the number of cycles taken to reach failure was recorded. The bonding durability of a self-adhesive resin cement to titanium was largely influenced by the weight of impact load. HALT showed that Clearfil SA Luting, which contained MDP monomer, yielded the highest median bonding lifetime to titanium.

Three-dimensional finite element analysis of posterior fiber-reinforced composite fixed partial denture Part 2: influence of fiber reinforcement on mesial and distal connectors.

The aim of this study was to evaluate the influence of connectors under two different loading conditions on displacement and stress distribution generated in isotropic hybrid composite fixed partial denture (C-FPD) and partially anisotropic fiber-reinforced hybrid composite fixed partial denture (FRC-FPD). To this end, two three-dimensional finite element (FE) models of three-unit FPD from mandibular second premolar to mandibular second molar - intended to replace the mandibular first molar - were developed. The two loading conditions employed were a vertical load of 629 N (applied to eight points on the occlusal surface) and a lateral load of 250 N (applied to three points of the pontic). The results suggested that the reinforcing fibers in FRC framework significantly improved the rigidity of the connectors against any twisting and bending moments induced by loading. Consequently, maximum principal stress and displacement generated in the connectors of FRC-FPD were significantly reduced because stresses generated by vertical and lateral loading were transferred to the reinforcing fibers.

High volume individual fibre post versus low volume fibre post: the fracture load of the restored tooth.

OBJECTIVES: The purpose of this study was to evaluate the fracture loads of post-and-core systems with two different individually formed fibre post designs and polymerization conditions. METHODS: Totally seventy-two (n=8/group) bovine teeth were cut and made up the root length of 15.0mm. They were divided into 3 main groups (Group A, B, C). A: one glass fibre post was light-cured before cementation, B: fibres were bundled to fill the entire root canal opening and light-cured before cementation, C: one unpolymerized glass fibre post was inserted into cement-filled root canal and light-cured with luting cement (ParaCem). Moreover specimens of each group were divided into 3 subgroups according to the post length: subgroup 1: 10mm; subgroup 2: 7.5mm; subgroup 3: 5.0mm. After cementation, the core was built up, and then made the composite resin crown (Filtek Z250). Fabricated specimen was loaded from 45° of palatal side at a crosshead speed of 1.0mm/min. The first load drop and maximum fracture loads were statistically analyzed by ANOVA and Tukey's test. RESULTS: Maximum fracture load of Group B (433 N) and C (418 N) are significantly higher than Group A (284 N) (p<0.01). Short post (5mm) provided higher fracture loads in all main groups, especially in Group C. CONCLUSIONS: Using short and thick fibre post system (the same diameter as the root canal) showed higher strength than one fibre post only. In addition, by curing the cement and the fibre material simultaneously, the strength of the restored tooth was increased.

Effect of cyclic impact load on shear bond strength of zirconium dioxide ceramics.

PURPOSE: To investigate the influence of cyclic impact load and the number of load cycles on compressive shear bond strength under the three different cements. MATERIALS AND METHODS: The following materials were used: Super Bond C&B (SB) and Panavia Fluoro Cement (PF) as adhesive resin cements, Fuji Luting (FL) as a resin-modified glass-ionomer cement, and zirconium dioxide ceramics as adherend. Before the shear bond test, three different impact loading conditions (compressive direction, shear direction, and no impact) and the number of load cycles (1 to 106 cycles), were performed. A total of 189 specimens (n = 3/group) were randomly assigned to groups and tested. A cyclic impact test was performed by applying a load of 98N at a distance of 40 mm and a loading cycle frequency of 1 Hz. All results were statistically analyzed with two-way ANOVA and Tukey's multiple comparison test. RESULTS: Shear bond strengths of SB, PF, and FL subjected to no cyclic impact load were 21.6 to 53.8 MPa in SB, 27.0 to 63.6 MPa in PF, and 20.0 to 35.9 MPa in FL. The shear bond strength of SB and PF increased to a certain degree from one to 105 cycles, while FL did likewise from one to 104 cycles. CONCLUSION: The shear bond strengths of SB, PF, and FL were greatest without cyclic impact, followed by compressive and then shear cyclic impact.

Stress and strain analysis of the bone-implant interface: a comparison of fiber-reinforced composite and titanium implants utilizing 3-dimensional finite element study.

This study analyzed stress and strain mediated by 2 different implant materials, titanium (Ti) and experimental fiber-reinforced composite (FRC), on the implant and on the bone tissue surrounding the implant. Three-dimensional finite element models constructed from a mandibular bone and an implant were subjected to a load of 50 N in vertical and horizontal directions. Postprocessing files allowed the calculation of stress and strain within the implant materials and stresses at the bone-to-implant interface (stress path). Maximum stress concentrations were located around the implant on the rim of the cortical bone in both implant materials; Ti and overall stresses decreased toward the Ti implant apex. In the FRC implant, a stress value of 0.6 to 2.0 MPa was detected not only on the screw threads but also on the implant surface between the threads. Clear differences were observed in the strain distribution between the materials. Based on the results, the vertical load stress range of the FRC implant was close to the stress level for optimal bone growth. Furthermore, the stress at the bone around the FRC implant was more evenly distributed than that with Ti implant.

The effect of surface treatment on bond strength of layering porcelain and hybrid composite bonded to zirconium dioxide ceramics.

PURPOSE: The purpose of this study was to investigate the differences between Rocatec (as surface treatment) and #600 polishing (as control) on shear bond strength of layering porcelain and hybrid composite to zirconium dioxide ceramics. METHODS: Manufactured zirconia blocks used in this study were yttrium partially stabilized zirconia (YTZ(®)), and veneering materials were NobelRondo Zirconia Dentin A2 High Value (NZR) and Estenia C&B (ES). Total 48 zirconia blocks were fabricated (10 mm × 10 mm × 20 mm). The blocks of 24 each were treated by Rocatec and #600 paper, respectively. Surface treated zirconia blocks were divided into two groups, according to veneering materials of NZR and ES. NZR was fired and ES was polymerized to zirconia. The fabricated specimen was fixed to mounting jig and applied shear force using the universal testing machine at a crosshead speed of 0.5 mm/min. All results were statistically analyzed by two-way ANOVA and Tukey's test. EPMA analysis and SPM analysis of specimen interface were carried out. RESULTS: Mean shear bond strength of each condition was: NZR/#600; 23.3 (S.D. ±7.0) MPa, NZR/Rocatec; 26.9 (S.D. ±7.0) MPa, ES/#600; 10.7 (S.D.±2.4) MPa, ES/Rocatec; 12.5 (S.D.±0.8) MPa. CONCLUSIONS: From the results of this study, shear bond strength of layering porcelain to zirconia was higher than that of restorative hybrid resin. However the more study will be needed, the appropriate choice of materials became the gides to the expansion of the applied cases of metal-free prothesis.