Marcelo Ferraz Mesquita

The effect of thermal cycling on the bond strength of low-fusing porcelain to commercially pure titanium and titanium–aluminium–vanadium alloy

OBJECTIVES Titanium-ceramic restorations are currently used in spite of the pending problem of titanium-ceramic bonding, which has only been partially solved. In addition, some titanium-ceramic systems appear to be susceptible to thermal cycling, which can cause weaker bond strength. The objective of this study was to evaluate the bonding characteristics of titanium porcelain bonded to commercially pure titanium (Ti-Cp) or titanium-aluminum-vanadium (Ti-6Al-4V) alloy as well as the effect of thermal cycling on bond strength. METHODS A three-point-flexure-test was used to evaluate the bond strength of titanium porcelain bonded to commercially pure titanium and Ti-6Al-4V alloy according to DIN 13.927. To evaluate the effect of thermal cycling on the samples, half were thermal cycled in temperatures ranging from 4 degrees C (+/-2 degrees C) to 55 degrees C (+/-2 degrees C). Results were compared with palladium-silver (Pd-Ag) alloy bonded to conventional porcelain (control). Scanning electron microscope (SEM) photomicrographs were taken to characterize the failed surfaces in the metal-ceramic interface. Anova and Tukeys multiple comparison tests were used to analyze the data at a 5% probability level. RESULTS Thermal cycling did not significantly weaken the bond strength of porcelain to titanium interfaces. There was no significant difference in bond strength between commercially pure titanium (23.60 MPa for thermal cycled group and 24.99 MPa for non-thermal cycled group) and Ti-6Al-4V groups (24.98 and 25.60 MPa for thermal cycled and non-thermal cycled groups, respectively). Bond strength values for the control group (47.98 and 45.30 MPa, respectively) were significantly greater than those for commercially pure titanium and Ti-6Al-4V combinations. SIGNIFICANCE The bond strength of low fusing porcelain bonded to cast pure titanium or Ti-6Al-4V alloy was significantly lower than the conventional combination of porcelain-Pd-Ag alloy. Thermal cycling did not affect the bond strength of any group.

Influence of Material of Overdenture-Retaining Bar with Vertical Misfit on Three-Dimensional Stress Distribution

PURPOSE This study evaluated the effects of different bar materials on stress distribution in an overdenture-retaining bar system with a vertical misfit between implant and bar framework. MATERIALS AND METHODS A three-dimentional finite element model was created including two titanium implants and a bar framework placed in the anterior part of a severely reabsorbed jaw. The model set was exported to mechanical simulation software, where displacement was applied to simulate the screw torque limited by 100-microm vertical misfit. Four bar materials (gold alloy, silver-palladium alloy, commercially pure titanium, cobalt-chromium alloy) were simulated in the analysis. Data were qualitatively evaluated using Von Mises stress given by the software. RESULTS The models showed stress concentration in cortical bone corresponding to the cervical part of the implant, and in cancellous bone corresponding to the apical part of the implant; however, in these regions few changes were observed in the levels of stress on the different bar materials analyzed. In the bar framework, screw, and implant, considerable increase in stress was observed when the elastic modulus of the bar material was increased. CONCLUSIONS The different materials of the overdenture-retaining bar did not present considerable influence on the stress levels in the periimplant bone tissue, while the mechanical components of the system were more sensitive to the material stiffness.

The Effect of Aging by Thermal Cycling and Mechanical Brushing on Resilient Denture Liner Hardness and Roughness

PURPOSE The purpose of this study was to investigate the effects of aging on resilient denture liners. The aging effects were produced by using thermal cycling and mechanical brushing and were quantified as changes to surface hardness and roughness of resilient denture liners. MATERIAL AND METHODS A plasticized acrylic resin (Dentuflex) and two silicone-based (Molloplast-B, Sofreliner MS) resilient denture liners were examined. Pre- and post-test roughness and hardness measurements were recorded using a Surfcorder SE 1700 and Shore A durometer Teclock GS-709, respectively. Sixty specimens were manufactured; half were subjected to 3000 cycles in the thermal cycler (5 and 55 degrees C). The remaining specimens received 30,000 strokes applied by a mechanical brushing machine followed by 3000 thermal cycles. Representative specimens from each group were observed under scanning electron microscope (SEM). Data were examined by multiple ANOVA, split-plot analysis, and Tukey test (alpha= 0.05). RESULTS Shore A hardness values for Dentuflex, Molloplast-B, and Sofreliner MS soft liners were different from each other (p < 0.05) before (79 +/- 2.9; 40 +/- 1.4; 33 +/- 0.7) and after (80 +/- 3.1; 40 +/- 1; 34 +/- 0.9) thermocycling. The surface roughness (in mum) of the same soft liner materials was significantly different (p < 0.05) at the start (2.2 +/- 0.4; 1.6 +/- 0.6; 0.2 +/- 0.1) but it was not different (p > 0.05) after tooth brushing (1.7 +/- 0.3; 1.7 +/- 0.4; 1.9 +/- 0.8) or thermocycling (1.6 +/- 0.5; 1.6 +/- 0.6; 1.5 +/- 0.5). CONCLUSION Thermal cycling promoted increased hardness for Sofreliner MS and Dentuflex. Mechanical brushing promoted wear abrasion in Sofreliner MS and Dentuflex materials. Molloplast-B experienced no deleterious effects from either of the tests.

Fracture resistance of endodontically treated teeth restored with intra-radicular post: the effects of post system and dentine thickness.

To investigate the influence of post system and amount of remaining root tissue on the fracture resistance of endodontically treated teeth. Seventy upper canine teeth were divided into seven groups (n=10), one control (sound teeth) and six experimental groups resulting from the interaction between the two study factors: post system (FB, fiber post; FPC, fiber post relined with resin composite; CPC, cast Ni-Cr alloy post and core) and amount of remaining root tooth tissue (2 or 1mm of thick root). All teeth were restored with metal crowns and exposed to 250,000 cycles in a controlled chewing simulator. The samples were submitted to the fracture resistance test in a universal testing machine, at an angle of 135° and speed of 0.5mm/min, until fracture occurred. Failure modes were observed, and the data of fracture resistance, in Newtons, were submitted to the analysis of variance (ANOVA), followed by Tukeys test (α=0.05). Roots restored with FPC had the highest fracture strength of the experimental groups, being statistically similar to the intact teeth group (P>0.05). FP and CPC did not differ statistically (P>0.05) and were statistically lower than those of FPC (P<0.05). No statistically significant difference was observed between amounts of remaining root tooth tissue to the same post systems (P>0.05). A prevalence of irreparable failures was observed in specimens restored with CPC, whereas FP and FPC posts showed more repairable failures. The post system had an influence significant on fracture resistance. However, the remaining dentine with 2- or 1-mm thickness was not an important factor for the fracture resistance.

Effect of retorque on loosening torque of prosthetic screws under two levels of fit of implant-supported dentures

This study evaluated the influence of retorque on loosening torque (Lt) of prosthetic screws in implant-supported dentures with different fit levels. Ten mandibular implant-supported dentures were fabricated and then 20 cast models were then prepared using prosthetic structures to create 2 fit levels: passive fit (Pf) and misfit (Mf). Two tightening techniques were also evaluated: initial torque only (T1); and initial torque and retorque after 10 min (T2). Gold or titanium screws were used, resulting in 4 groups to each one: Pf/T1, Pf/T2, Mf/T1, Mf/T2. The Lt was measured 24 h after the tightening torque using digital torque meter. Data were analyzed statistically by two-way ANOVA and Tukeys test (alpha=0.05), separately for each screw material. For titanium screws, no significant difference (p>0.05) was found between Pf/T1 and Pf/T2, or between Pf/T2 and Mf/T2. However, statistically significant difference (p<0.05) was found between Pf/T1 and Mf/T1, and between Mf/T1 and Mf/T2. Mf reduced the Lt using T1, while and T2 increased the Lt for Mf. Retorque and fit were shown to have no significant influence on the Lt of the gold screws. Retorque application made insignificant the misfit effect on the Lt of the titanium screws, suggesting that this procedure should be performed routinely during the screw tightening in multi-unit dentures.

The service life of implant-retained overdenture attachment systems.

STATEMENT OF PROBLEM Implant-retained overdentures are a treatment option for patients who are not satisfied with conventional complete dentures. Although implant-retained overdentures are widely used, little data are available or provided by implant manufacturers about retentive strength and wear of attachments. PURPOSE The purpose of this study was to evaluate retentive strength and fatigue resistance of 4 overdenture bar-and-clip attachment systems. MATERIAL AND METHODS Forty bar-and-clip attachment system specimens were tested (n=10): Conexão Bar Clip (polymer clip), Sterngold Hader Bar (polymer clip), 3i Gold Hader Type Clip (metal clip), or SIN Clipo (metal clip). Specimens immersed in artificial saliva were tested to 5500 cycles at 0.8 Hz using a servohydraulic universal testing machine. Retention strength values (N) were recorded initially and after 1100, 2200, 3300, 4400, and 5500 insertion and removal cycles during the tensile test using a speed of 1 mm/min and a load cell of 1 kN. Data were submitted to a 2-way repeated-measures ANOVA and the Tukey A post hoc test (alpha = .05). RESULTS An increase in retention strength values was observed during the fatigue test after 5500 cycles of insertion and removal. No significant difference in retentive strength was observed in the groups using polymer clips (Conexão Bar Clip and Sterngold Hader Bar) (P=.729); the same occurred with metal clip systems (SIN Clipo and 3i Gold Hader Type Clip) (P=.068). The SIN Clipo system demonstrated the smallest retention strength values, which were significantly different from the other 2 attachment systems, the Sterngold Hader Bar (P<.01) and the Conexão Bar Clip (P<.01). Although the 3i Gold Hader Type Clip did not differ significantly, in terms of retentive strength, from the Sterngold Hader Bar (P=.258), its retentive strength was significantly lower than the retentive strength of the Conexão Bar Clip system (P=.030). CONCLUSIONS The systems evaluated demonstrated satisfactory retention for all time periods tested, as retention strengths from 5 to 7 N should be sufficient to stabilize overdentures. No component fracture or compromise in retention was found for any of the systems tested.

Evaluation of low-fusing ceramic systems combined with titanium grades II and V by bending test and scanning electron microscopy

The bond strength by three point bending strength of two metal substrates (commercially pure titanium or grade II, and Ti-6Al-4V alloy or grade V) combined to three distinct low-fusing ceramic systems (LFC) and the nature of porcelain-metal fracture by scanning electron microscopy (SEM) were evaluated. The results were compared to a combination of palladium-silver (Pd-Ag) alloy and conventional porcelain (Duceram VMK68). Sixty metal strips measuring 25x3x0.5mm were made - 30 of titanium grade II and 30 of titanium grade V, with application of the following types of porcelain: Vita Titankeramik, Triceram or Duceratin (10 specimens for each porcelain). The porcelains were bonded to the strips with dimensions limited to 8x3x1mm. The control group consisted of ten specimens Pd-Ag alloy/Duceram VMK68 porcelain. Statistical analyses were made by one-way analysis of variance (ANOVA) and Tukey test at 5% significance level. Results showed that the bond strength in control group (48.0MPa ± 4.0) was significantly higher than the Ti grade II (26.7MPa ± 4.1) and Ti grade V (25.2MPa ± 2.2) combinations. When Duceratin porcelain was applied in both substrates, Ti grade II and Ti grade V, the results were significantly lower than in Ti grade II/Vitatitankeramik. SEM analysis indicated a predominance of adhesive fractures for the groups Ti grade II and Ti grade V, and cohesive fracture for control group Pd-Ag/Duceram. Control group showed the best bond strength compared to the groups that employed LFC. Among LFC, the worst results were obtained when Duceratin porcelain was used in both substrates. SEM confirmed the results of three point bending strength.

Effect of framework material and vertical misfit on stress distribution in implant-supported partial prosthesis under load application: 3-D finite element analysis

Abstract Objective. This study evaluated the influence of framework material and vertical misfit on stress created in an implant-supported partial prosthesis under load application. Materials and methods. The posterior part of a severely reabsorbed jaw with a fixed partial prosthesis above two osseointegrated titanium implants at the place of the second premolar and second molar was modeled using SolidWorks 2010 software. Finite element models were obtained by importing the solid model into an ANSYS Workbench 11 simulation. The models were divided into 15 groups according to their prosthetic framework material (type IV gold alloy, silver-palladium alloy, commercially pure titanium, cobalt-chromium alloy or zirconia) and vertical misfit level (10 µm, 50 µm and 100 µm). After settlement of the prosthesis with the closure of the misfit, simultaneous loads of 110 N vertical and 15 N horizontal were applied on the occlusal and lingual faces of each tooth, respectively. The data was evaluated using Maximum Principal Stress (framework, porcelain veneer and bone tissue) and a von Mises Stress (retention screw) provided by the software. Results. As a result, stiffer frameworks presented higher stress concentrations; however, these frameworks led to lower stresses in the porcelain veneer, the retention screw (faced to 10 µm and 50 µm of the misfit) and the peri-implant bone tissues. Conclusion. The increase in the vertical misfit resulted in stress values increasing in all of the prosthetic structures and peri-implant bone tissues. The framework material and vertical misfit level presented a relevant influence on the stresses for all of the structures evaluated.

Effects of Horizontal Misfit and Bar Framework Material on the Stress Distribution of an Overdenture-Retaining Bar System: A 3D Finite Element Analysis

PURPOSE To evaluate the influence of horizontal misfit change and bar framework material on the distribution of static stresses in an overdenture-retaining bar system using finite element (FE) analysis. MATERIALS AND METHODS A 3D FE model was created including two titanium implants and a bar framework placed in the anterior part of a severely resorbed jaw. The model set was exported to mechanical simulation software, where horizontal displacement (10, 50, 100, and 200 μm) was applied simulating the settling of the framework, which suffered shrinkage during laboratory procedures. Four bar materials (gold alloy, silver-palladium alloy, commercially pure titanium, and cobalt-chromium alloy) were also simulated in the analysis using 50 μm as the horizontal misfit. Data were qualitatively evaluated using von Mises stress, given by the software. RESULTS The misfit amplification presented a great increase in the stress levels in the inferior region of the bar, screw-retaining neck, cervical and medium third of the implant, and cortical bone tissue surrounding the implant. The higher stiffness of the bar presented a considerable increase in the stress levels in the bar framework only. CONCLUSION The levels of static stresses seem to be closely linked with horizontal misfit, such that its amplification caused increased levels of stress in the structures of the overdenture-retaining bar system. On the other hand, the stiffness of the bar framework presented a lower effect on the static stress levels.

Effects of Thermocycling on the Tensile Bond Strength of Three Permanent Soft Denture Liners

PURPOSE This study investigated the effect of in vitro accelerated aging reproduced with thermocycling on the bond strength of three commercially available permanent denture soft liners (PermaSoft, Dentuflex, Ufi-gel) with one heat-polymerized polymethyl methacrylate resin denture base (QC-20) by tensile test. MATERIAL AND METHODS Ten specimens were prepared for control and test groups of each material for a total of 60 specimens. All controls were stored in water (37 degrees C) for 24 hours before testing. All test groups received 3000 thermal cycles consisting of 1 minute at 5 degrees C and 1 minute at 65 degrees C. All specimens were submitted to a tensile test using a universal testing machine at a crosshead speed of 5 mm/min. Results were statistically analyzed (ANOVA, p < or = 0.05, Tukeys post-hoc test). RESULTS The mean bond strength of control specimens was (MPa): 0.32 (Ufi-gel), 0.49 (PermaSoft), and 1.19 (Dentuflex). There was no statistical difference (p > 0.05) between Ufi-gel and PermaSoft, but both were statistically different (p < 0.05) when compared to Dentuflex. After thermocycling, the mean bond strength was (MPa): 0.18 (Ufi-gel), 0.81 (PermaSoft), and 3.32 (Dentuflex). All materials were statistically different (p < 0.05). Ufi-gel had the lowest value and Dentuflex the highest in both control and test groups. Dentuflex presented only adhesive failure; in the remaining groups, there was no predominant failure mode, except Ufi-gel control with no adhesive failure. CONCLUSIONS Despite presenting greater bond strength, thermocycling had a deleterious effect in Dentuflex; Ufi-gel may be adequate for short-term use.