Carolina Guimarães Castro

Finite element analysis and bond strength of a glass post to intraradicular dentin: Comparison between microtensile and push-out tests

OBJECTIVE This study tested the hypothesis that the stress distribution and bond strength of glass posts to intraradicular dentin is influenced by the mechanical testing methodology. METHODS Thirty single rooted endodontically treated teeth were prepared for luting of tapered fiber-glass posts (Reforpost, Angelus, Londrina, PR, Brazil) with a conventional adhesive system and resin luting cement (Adper Scotchbond Multi-purpose, Rely X ARC, 3M ESPE, St. Paul, MN, USA). The teeth were randomly divided (n=10 per group) into micro-push-out (Mpo), hourglass- (Mh) and rectangular stick-shaped (Ms) microtensile testing groups before sectioning each root into five 1-mm-thick specimens. During specimen preparation for microTBS testing 46/50 stick and 4/50 hourglass specimens prematurely failed; therefore, the Ms group could not be included in the mechanical testing. The remaining specimens were tested at 0.5 mm/min until bond failure. Stress distribution within each specimen type for the three mechanical test methods was analyzed by finite element analysis (FEA). Qualitative analyses were carried out through Von Mises, XY and Sy criterion. RESULTS Mpo and Mh had a mean microTBS of 11.89+/-6.55 and 14.98+/-12.72 MPa, respectively, which was not significantly different (p=0.1311). The push-out test demonstrated a more homogenous stress distribution by FEA and less variability in mechanical testing. SIGNIFICANCE Therefore, the recommended testing method for determining the bond strength of glass posts to intraradicular dentin is by Mpo.

The influence of cavity design and glass fiber posts on biomechanical behavior of endodontically treated premolars.

The aim of this study was to evaluate the effect of cavity design and glass fiber posts on stress distributions and fracture resistance of endodontically treated premolars. Fifty extracted intact mandibular premolars were divided into 5 groups (n = 10): ST, sound teeth (control); MOD, mesio-occlusal-distal preparation + endodontic treatment (ET) + composite resin restoration (CR); MODP, mesio-occlusal-distal + ET + glass fiber post + CR; MOD2/3, mesio-occlusal-distal + two thirds occlusal-cervical cusp loss + ET + CR; and MODP2/3, mesio-occlusal-distal + two thirds cusp loss + ET + glass fiber post + CR. The specimens were loaded on a cusp slope until fracture. Fracture patterns were classified according to four failure types. Stress distributions were evaluated for each group in a two-dimensional finite element analysis. The fracture resistance of the MODP, MOD2/3, and MODP2/3 groups was significantly lower than the ST and MOD groups (p < 0.05). The loss of dental structure and the presence of fiber post restoration reduced fracture resistance and created higher stress concentrations in the tooth-restoration complex. However, when there was a large loss of dental structure (MODP2/3), the post reduced the incidence of catastrophic fracture types.

Surface Treatment of Glass Fiber and Carbon Fiber Posts: SEM Characterization

Morphology, etching patterns, surface modification, and characterization of 2 different fiber posts: Gfp, Glass fiber post; and Cfp, carbon fiber were investigated by SEM analysis, after different surface treatments. Thirty fiber posts, being 15 Gfp and 15 Cfp were divided into a 5 surface treatments (n = 3): C‐alcohol 70% (control); HF 4%‐immersion in 4% hydrofluoric acid for 1min; H3PO4 37%‐immersion in 37% phosphoric acid for 30s; H2O2 10%‐immersion in 10% hydrogen peroxide for 20 min; H2O2 24%‐immersion in 24% hydrogen peroxide for 10 min. Morphology, etching patterns, surface modification and surface characterization were acessed by SEM analysis. SEM evaluation revealed that the post surface morphology was modified following all treatment when compared with a control group, for both type of reinforced posts. HF seems to penetrate around the fibers of Gfp and promoted surface alterations. The Cfp surface seems to be inert to treatment with HF 4%. Dissolution of epoxy resin and exposure of the superficial fiber was observed in both post groups, regardless the type of reinforcing fiber, H2O2 in both concentrations. Relative smooth surface area was produced by H3PO4 37% treatment, but with similar features to untreated group. Surface treatment of fiber post is a determinant factor on micromechanical entanglement to resin composite core. Post treatment with hydrogen peroxide resulted strength of carbon and glass/epoxy resin fiber posts to resin composite core. Microsc. Res. Tech., 2011.

Two‐Dimensional FEA of Dowels of Different Compositions and External Surface Configurations

PURPOSE The degree of stress generated in the endodontically treated and restored tooth can be influenced by the composition and configuration of the dowels used for the restoration. Using two-dimensional (2D) finite element analysis (FEA), this study tested the hypothesis that the characterization of the stress distribution can be influenced by which evaluation method is employed: protrusion loading and 4-point flexural strength test or varying the type of material (carbon and glass fiber) or the external configuration of the dowel (smooth and serrated). MATERIALS AND METHODS For simulation of the protrusion load test, models were generated with Mechanical-AutoCAD V6 software from an image of an anatomical plate, one maxillary central incisor, and two dowels and exported to Ansys 9.0. The bone region model was fixed, and a tangential load of 1 N with a 135 degrees inclination to the tooth longitudinal axis was applied at the level of the palatal surface of the crown. In the simulation of a 4-point flexural strength test, a 1 N perpendicular load was applied in two points to the dowel. The dental materials and structures were considered elastic, isotropic, homogeneous, and linear, with the exception of the dowel, which was assumed to exhibit orthotropic behavior. Mechanical properties were defined based on a review of the literature, and the model was meshed with an eight node tetrahedral element. RESULTS The stress results from both tests were analyzed according to von Mises criteria and principal stresses (Sx). Data from the 4-point flexural strength test simulation showed that, for the serrated dowels, a higher stress concentration was found; however, no difference in the occlusal load for material or dowel configuration was found. CONCLUSIONS These results suggest that although the external configuration of the dowel influences direct loading, when the dowel is integrated to the tooth and setting material, the influence on biomechanical behavior disappears.

Effect of periodontal therapies on indirect restoration: a scanning electron microscopic analysis

The aim of this study was to evaluate the influence of different periodontal therapies on the integrity of indirect restorations by scanning electron microscopy (SEM). Sixty single-rooted bovine teeth were selected and randomly assigned to 12 groups. Inlay cavities were prepared in the cervical region on the center of the cementoenamel junction, and were restored with laboratory processed resin and luted with a resin cement. Twelve periodontal therapies were used (n= 5): C: control (no treatment); MS: manual scaling with Gracey curettes; US: ultrasonic scaling; PP: prophylaxis with prophylactic paste; PS: prophylaxis with pumice-stone; SBJ: sodium bicarbonate jet; MS/PP; MS/PS; MS/SBJ; US/PP; US/PS; US/SBJ. The specimens were prepared and analyzed by SEM. SEM micrographs at x100 to x1000 magnification were obtained from the surface of the laboratory resin and the interface of the indirect restorations. The images were evaluated by 3 skillful, calibrated, blinded observers as to the presence of grooves, microcavities and fracture of margins. The results showed that PS produced groves on restoration surface. MS and US produced groves and marginal fractures on the restorations. SBJ resulted in resin cement degradation. These results suggest that except for PS, all procedures had deleterious effects on the marginal integrity of indirect restorations.

Strain analysis of different diameter Morse taper implants under overloading compressive conditions

The aim of this study was to evaluate the amount of deformation from compression caused by different diameters of Morse taper implants and the residual deformation after load removal. Thirty Morse taper implants lacking external threads were divided into 3 groups (n = 10) according to their diameter as follows: 3.5 mm, 4.0 mm and 5.0 mm. Two-piece abutments were fixed into the implants, and the samples were subjected to compressive axial loading up to 1500 N of force. During the test, one strain gauge remained fixed to the cervical portion of each implant to measure the strain variation. The strain values were recorded at two different time points: at the maximum load (1500 N) and 60 seconds after load removal. To calculate the strain at the implant/abutment interface, a mathematical formula was applied. Data were analyzed using a one-way Anova and Tukeys test (α = 0.05). The 5.0 mm diameter implant showed a significantly lower strain (650.5 μS ± 170.0) than the 4.0 mm group (1170.2 μS ± 374.7) and the 3.5 mm group (1388.1 μS ± 326.6) (p < 0.001), regardless of the load presence. The strain values decreased by approximately 50% after removal of the load, regardless of the implant diameter. The 5.0 mm implant showed a significantly lower strain at the implant/abutment interface (943.4 μS ± 504.5) than the 4.0 mm group (1057.4 μS ± 681.3) and the 3.5 mm group (1159.6 μS ± 425.9) (p < 0.001). According to the results of this study, the diameter influenced the strain around the internal and external walls of the cervical region of Morse taper implants; all diameters demonstrated clinically acceptable values of strain.

Effect of a bonding resin layer associated with a self-etching adhesive system on the bond strength of indirect restorations

The aim of this study was to evaluate the influence of a low-viscosity bonding resin applied over a self-etching adhesive system on the microtensile bond strength (μTBS) of indirect restorations. Comparisons were made using One Up Bond F (OB) self-etching adhesive system, Single Bond (SB) one-bottle adhesive system and Scotchbond Multi Purpose Plus (SMP) bonding component. Thirty bovine incisors were extracted and decoronated at the cementoenamel junction. The labial surfaces were ground so that superficial dentin and deep dentin were exposed. The specimens were randomized to three groups (n=10): G1- OB; G2- OB + SMP; G3- SB. In G2, a layer of the SMP bonding was applied over the OB adhesive system. Indirect composite restorations were bonded using dual-cure cement under 500 g load for 5 min. The specimens were serially sectioned with a bonding area of ± 1.0 mm2 in 3 regions: enamel (E), superficial dentin (SD) and deep dentin (DD). The sticks were fixed with cyanoacrylate adhesive and submitted to μTBS test at a crosshead speed of 0.5 mm/min in a mechanical testing machine (EMIC DL 2000). The fractured specimens were examined under scanning electron microscopy to determine the failure mode. Data were analyzed by one-way ANOVA followed by Tukeys test (p<0.05). μTBS means (in MPa) were: G1/E: 15.5 ± 3.5b; G1/SD: 22.7 ± 7.6a; G1/DD: 19.4 ± 9.4a; G2/E: 15.9 ± 5.8b; G2/SD: 19.9 ± 6.9a; G2/DD: 15.3 ± 4.9a; G3/E: 23.2 ± 7.3a; G3/SD: 20.4 ± 8.2a; G3/DD: 19.1 ± 8.7a. The results showed that the use of a low viscosity bonding resin did not affect the μTBS means when associated with a self-etching adhesive system. The self-etching adhesive system was significantly more efficient in dentin than in enamel, while the one-bottle system was significantly more efficient in enamel when compared to the self-etching adhesive system.

Influence of the Prosthetic Index on Fracture Resistance of Morse Taper Dental Implants

PURPOSE Manufacturers have inserted a prosthetic index, an internal hexagon to guide prosthetic components inside Morse taper implants. However, it is still unclear if this mechanism could decrease the mechanical strength of Morse taper implants. The aim of this study was to evaluate the influence of the prosthetic index inside Morse taper implants on fracture resistance compared with nonindexed implants. MATERIALS AND METHODS Fifty-seven Morse taper implants, with 11.5-degree angulation of the internal conical portion, were divided into three groups: implants without the prosthetic index and solid Morse taper universal post (group 1), implants with the prosthetic index and solid Morse taper universal post (group 2), and implants and abutments with the prosthetic index (group 3). All groups were modeled for finite element stress analysis (FEA), simulating force application of a perpendicular load to the abutments. Fracture resistance (n = 10) was determined under the same condition. Dynamic loading (n = 9) was also performed. The statistical analysis was performed using one-way analysis of variance (ANOVA), and the Tukey test was applied (α = .05). The metallographic analysis was used to identify the fracture distribution and the microstructure of the titanium alloy. RESULTS There was no statistically significant difference between the values of all tested groups. According to the FEA, the prosthetic index region was out of stress. The mean fracture resistances and loading test were 353.7 N and 200 N for group 1, 397.3 N and 170 N for group 2, and 372.0 N and 160 N for group 3, respectively. Metallographic analysis showed a macroscopic failure pattern just as demonstrated by FEA. CONCLUSION The presence of the prosthetic index on Morse taper implants did not decrease its resistance to fracture for the tested implants.