Soldering and remelting influence on fatigue strength of cobalt-chromium alloys

Statement of problem. For laboratory production, it would he economically advisable to reuse excess cobalt-chromium alloys in manufacturing partial denture frameworks. Furthermore, discrepancies in tit, modifications, repairs, and also economic factors could lead to soldering procedure on the metal frameworks. Purpose. This study evaluated the influence of soldering and remelting procedures on the fatigue strength of Steldent, Dentorium, and Biosil cobalt-chromium alloys, as new alloys and in a mixture of new and previously casted alloy and when submitted or not submitted to conventional soldering procedure. Material and methods. The soldering procedure was conducted in rod specimens 1.7 mm in diameter made with new, or with a mature of new and reused alloy (n = 10 per group). The results were compared with those of intact rods. The fatigue strength was carried out with a cyclic testing machine simulating the insertion and the removal of partial dentures. After failure, the fracture surface was examined with a scanning electron microscope. Results. The soldered specimens revealed 1119 loading cycles before fracture. These means differed statistically from those of intact alloys, which disclosed 2733 cycles before failure (p 0.05), which suggested that it may be possible to reuse excess cobalt-chromium alloys without compromising the fatigue strength of the framework.78214615

Retention force and fatigue strength of overdenture attachment systems

This study evaluated retention force and fatigue resistance of two overdenture attachment systems. Twenty samples (O-ring and Bar-Clip) from two manufacturers (Conexao Sistemas de Protese and Lifecore Biomedical) were prepared and divided into four groups: (i) Conexao/O-ring; (ii) Conexao/Bar-Clip; (iii) Lifecore/O-ring and (iv) Lifecore/Bar-Clip, with five samples in each group. They were submitted to mechanical fatigue test using a servohydraulic machine performing 5500 cycles of insertion and removal (f=0.8 Hz), immersed in artificial saliva. Retention force values were obtained three times (0, 3000 and after 5500 cycles) simulating the clinical service, using a tensile strength at 1 mm min(-1) and load cell of 1 kN. Data were analysed with analysis of variance and Tukey's test at 5% level. Results showed that Conexao/Bar-Clip specimens had significantly higher retention values than Lifecore/Bar-Clip (44.61 and 18.44 N, respectively), Conexao/O-ring specimens had significantly lower values than Lifecore/O-ring (13.91 and 19.75 N, respectively). Conexao/Bar-Clip values were always significantly higher than those of Conexao/O-ring group (44.61 and 13.91 N, respectively). Lifecore (O-ring and Bar-Clip) presented similar values (19.75 and 18.44 N, respectively). The systems evaluated showed satisfactory retention force values, before and after fatigue testing. Conexao/Bar-Clip specimens presented the highest values. A 5-year simulation of insertion and removal did not decrease retention values or fracture components.31988488

The effect of surface modifications on titanium to enable titanium-porcelain bonding

Objectives. Titanium-ceramic restorations are currently used, despite the pending problem of titanium-ceramic bonding, which has only been partially solved. The surface treatment of the metal proposed by the manufacturer promotes lower bond strength between titanium and porcelain when compared to the conventional metal-ceramic systems. The objective of this study was to evaluate the influence of acid and caustic baths on the bonding characteristics of specific titanium porcelain bonded to cast commercially pure titanium (CP Ti). Methods. Eighty strips of cast CP Ti were obtained in dimensions of 25 mm x 3 mm x 0.5 mm, and divided into eight groups (n=10) which were subjected to surface treatment by immersion in one of the follow solutions-group HF: HF 10%; group NaOH+HF: NaOH 50%-CuSO4 center dot 5H(2)O 10% followed by HF 10%; group HCl: HCl 35%; group NaOH+HCl: NaOH 50%-CuSO4 5H(2)O 10% followed by HCl 35%; group HNO3: HNO3 35%-HF 5%; group NaOH+HNO3: NaOH 50%-CuSO4 center dot 5H(2)O 10% followed by HNO3 35%-HF 5%; control group: treated according to the manufacturer's instructions; NaOH + control group: treated according to the manufacturer's instructions followed by immersion in NaOH 50%-CuSO4 center dot 5H(2)O 10%. Low fusion porcelain (Vita Titankeramik) was applied to the center of one of the sides of each CP Ti sample with dimensions of 8 mm x 3 mm x 1 mm. All groups were submitted to a three-point flexure test. Scanning electron microscopy (SEM) photomicrographs were taken to characterize the failed surfaces at the titanium-porcelain interface. Anova and Tukey's multiple comparison tests were used to analyze the data at a 5% probability level. Results. All groups treated with NaOH 50%-CuSO4 center dot 5H(2)O 10% solution showed significant superior values when compared to groups treated exclusively with acid solution. There were no significant differences between HF (21.2 MPa) and HCl (23.4 MPa) groups; control (25.2 MPa), HCl (23.4 MPa) and HNO3 (26.6 MPa) groups; NaOH + HF (29.9 MPa) and NaOH + HCl (30.8 MPa) groups; NaOH + HNO3 (34.8 MPa) and NaOH + control (32.1 MPa) groups. SEM analysis indicated a combination of cohesive and adhesive fractures in NaOH + HNO3 and NaOH + control groups, while mainly adhesive fractures were found in the other groups. Significance. Bond strength between porcelain and cast CP Ti can be increased by use of a caustic bath prior to porcelain firing. (c) 2007 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.241283

Evaluation of varying amounts of thermal cycling on bond strength and permanent deformation of two resilient denture liners

Statement of problem. Two problems found in prostheses with resilient liners are bond failure to the acrylic resin base and increased permanent deformation due to material aging. Purpose. This in vitro study evaluated the effect of varying amounts of thermal cycling on bond strength and permanent deformation of 2 resilient denture liners bonded to an acrylic resin base. Material and methods. Plasticized acrylic resin (PermaSoft) or silicone (Softliner) resilient lining materials were processed to a heat-polymerized acrylic resin (QC-20). One hundred rectangular specimens (10 X 10-mm(2) cross-sectional area) and 100 cylindrically-shaped specimens (12.7-mm diameter X 19.0-mm height) for each liner/resin combination were used for the tensile and deformation tests, respectively. Specimen shape and liner thickness were standardized. Specimens were divided into 9 test groups (n=10) and were thermal cycled for 200, 500, 1000, 1500, 2000, 2500, 3000, 3500, and 4000 cycles. Control specimens (n=10) were stored for 24 hours in water at 37degreesC. Mean bond strength, expressed as stress at failure (MPa), was determined with a tensile test using a universal testing machine at a crosshead speed of 5 mm/min. Analysis of failure mode, expressed as a percent (%), was recorded as either cohesive, adhesive, or both, after observation. Permanent deformation, expressed as a percent (%), was determined using ADA specification no. 18. Data from both tests were examined with a 2-way analysis of variance and a Tukey test (alpha=.05). Results. For the tensile test, Softliner specimens submitted to different thermal cycling regimens demonstrated no significantly different bond strength values from the control; however, there was a significant difference between the PermaSoft control group (0.47 +/- 0.09 MPa [mean +/- SD]) and the 500 cycle group (0.46 +/- 0.07 MPa) compared to the 4000 cycle group (0.70 +/- 0.20 MPa) (P<.05). With regard to failure type, the Softliner groups presented adhesive failure (100%) regardless of specimen treatment. PermaSoft groups presented adhesive (53%), cohesive (12%), or a combined mode of failure (35%). For the deformation test, there was no significant difference among the Softliner specimens. However, a significant difference was observed between control and PermaSoft specimens after 1500 or more cycles (1.88% +/- 0.24%) (P<.05). Conclusions. This in vitro study indicated that bond strength and permanent deformation of the 2 resilient denture liners tested varied according to their chemical composition.92328829

Corrosion-fatigue life of commercially pure titanium and Ti-6Al-4V alloys in different storage environments

Statement of problem. Removable partial dentures are affected by fatigue because of the cyclic mechanism of the masticatory system ansi frequent insertion and removal. Titanium and its alloys have been used in the manufacture of denture frameworks; however, preventive agents with fluorides are thought to attack titanium alloy surfaces. Purpose. This study evaluated, compared, analyzed the corrosion-fatigue life of commercially pure titanium and Ti-6Al-4V alloy in different storage environments. Material and methods. For each metal, 33 dumbbell rods, 2.3 mm in diameter at the central segment, were cast in the Rematitan system. Corrosion-fatigue strength test was carried out through a universal testing machine with a load 30% lon er than the 0.2% offset yield strength and a combined influence of different: environments: in air at room temperature, with synthetic saliva, and with fluoride synthetic saliva. After failure, the number of cycles were recorded, and fracture surfaces were examined with on SEM. Results. ANOVA and Tukey's multiple comparison rest indicated that Ti-6Al-4V alloy achieved 21,269 cycles (SD = 8,355) against 19,157 cycles (SD = 3,624) for the commercially purr Ti. There were no significant differences between either metal in the corrosion-fatigue life for dry specimens, but when the solutions were present, the fatigue life was significantly reduced, probably because of the product-ion of corrosion pits caused by superficial reactions.84327427

THE SERVICE LIFE OF IMPLANT-RETAINED OVERDENTURE ATTACHMENT SYSTEMS

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)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): Conexao Bar Clip (polymer clip), Sterngold Hader Bar (polymer clip), 3, 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 I 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 (Conexao Bar Clip and Sterngold Hader Bar) (P=.729); the same occurred with metal clip systems (SIN Clipo and 31 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 Conexao Bar Clip (P<.01). Although the 31 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 Conexao 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. (J Prosthet Dent 2009;102:74-80)10227480Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conexao Sistemas de Proteses, LtdaFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [04112515-6

Surface roughness and fatigue performance of commercially pure titanium and Ti-6Al4V alloy after different polishing protocols

Statement of problem. Surface quality of cast metal is directly related to service performance under fatigue stress. Surface heterogeneities resulting from either finishing or polishing processes or by corrosive agents Such as fluoridated solutions, can negatively affect fatigue life. Cast titanium frameworks arc difficult to polish, and ail accepted polishing protocol has not been established. Purpose. This study evaluated and compared surface roughness of cast commercially pure titanium (CP Ti) and Ti-6Al-4V alloy submitted to conventional or electrolytic polishing, correlating the results with corrosion-fatigue strength testing performed in artificial fluoridated saliva. Specimens were also tested in air at room temperature to evaluate the effectiveness of the corrosion-fatigue test model. Material and methods. For cacti metal, 40 dumb-bell-shaped rods, 2.3 mm in diameter at the central segment, were cast. Conventional polishing was performed on 20 specimens of cacti metal following the manufacturer's instructions. A Source of continuous electrical current was used for electrolytic polishing of the other 20 specimens of each metal, which were immersed in an electrolytic solution containing 5% fluoridric acid, 35% nitric acid, and 60% distilled water. Surface roughness, Ka (mu m), was measured with a profilometer, and fatigue tests were carried out with a universal testing machine using a load 30% lower than the 0.2% offset yield strength. After failure, the fractured surfaces were examined using scanning electron microscopy. Surface roughness means were analyzed with a 2-way analysis of variance and the Tukey multiple comparisons test (alpha=.05). Results. Electrolytic polishing (0.24 +/- 0.05 mu m) provided significantly (P <.05) lower surface roughness values than conventional polishing (0.032 +/- 0.06 mu m). Regardless of the polishing protocol, surface roughness of Ti-6Al-4V alloy (0.25 +/- 0.06 mu m) was significantly lower (P <.05) than that of CP Ti (0.31 +/- 0.05 mu m), and the fluoridated environment did not influence fatigue performance. There was no correlation between fatigue performance and surface roughness. Conclusion. Surface roughness of Ti-6Al-4V was significantly lower than that of CP Ti. For cast titanium frameworks, the electrolytic polishing regimen was found to be more effective than the manufacturer's polishing instructions with abrasives and rotary instruments. After polishing, differences in surface roughness values did not affect corrosion-fatigue performance.93437838

Over-refractory casting technique as an alternative to one-piece multi-unit fixed partial denture frameworks

Statement of problem. Soldering has been suggested to achieve acceptable fit of multi-unit fixed partial denture (FPD) frameworks of 3 or more elements. However, distortion of the entire framework may occur. Purpose. The purpose of this study was to evaluate marginal fit in 1-piece-casting FPD frameworks comparing 2 casting techniques: the conventional technique (CT) and the over-refractory, technique (ORT). The techniques were evaluated on castings made from commercially pure titanium (CP Ti; Tritan), titanium-aluminum-vanadium (Ti-6AI-4V), and nickel-chromium (Ni-Cr; VeraBond II) alloys. Material and methods. A metal master cast including 3 preparations was created to simulate a 5-unit FPD. The metal cast was duplicated in vinyl polysiloxane for fabrication of 60 working casts. For the CT, 0.7-mm-thick patterns were waxed on the casts using an electrical wax-clipping unit. Patterns were removed from the preparations before investing. For the ORT, the silicone impressions were poured with an investment material (Rematitan for CP Ti and Ti-6Al-4V, and Talladium for Ni-Cr). The patterns were waxed on the refractory casts, and the assembly, was invested. Both CT and ORT (n=10), CP Ti, and Ti-6Al-4V frameworks were cast using an arc-melting titanium vacuum-casting machine. The Ni-Cr frameworks were cast using an automated centrifugal-casting machine. The mean marginal discrepancies of the frameworks were measured at the mesial, distal, buccal, and lingual interfaces. Marginal gap measurements were recorded 3 times for each surface to the nearest 0.5 mu m using a traveling microscope (X50). The data were analyzed with 2-way analysis of variance, followed by the Tukey HSD test (alpha=.05). Results. Marginal discrepancies for the ORT specimens (82.8 +/- 1.7 mu m for CP Ti; 64.4 +/- 1.3 mu m for Ti-6Al-4V; and 77.2 +/- 1.5 mu m-for Ni-Cr) were significantly lower than those obtained for the CT specimens (106.3 +/- 2.6 mu m for CP Ti; 75.7 +/- 0.8 mu m for Ti-6Al-4V; 101.9 +/- 1.7 mu m for Ni-Cr) (P <.05). For both techniques, marginal discrepancies were significantly different among the alloys evaluated, presenting the following order firorn greatest to least marginal discrepancy: CP Ti, Ni-Cr alloy, and Ti-6AI-4V (P <.05). Conclusion. The ORT for multi-unit FPD frameworks demonstrated significantly lower marginal discrepancies than the CT.95324324

Stress-relieving and porcelain firing cycle influence on marginal fit of commercially pure titanium and titanium-aluminum-vanadium copings

Objectives. This study evaluated: (1) the marginal fit of copings fabricated from commercially pure titanium (cp Ti) and titanium-aluminum-vanadium alloy (Ti-6Al-4V) after each firing cycle for a recommended porcelain; and (2) the effectiveness of a stress-relieving treatment on the fit. The results were compared with copings made with Pd-Ag alloy submitted to the recommended porcelain firing protocol. Methods. Bovine teeth were machined for metal-ceramic crowns and die casts were obtained for waxing patterns. The firing cycle of titanium porcelain was performed on cp Ti and Ti-6Al-4V copings obtained using the Rematitan System. A stress-relieving treatment (cp Ti treated and Ti-6Al-4V treated groups) was performed on original invested castings at the first porcelain firing temperature (800 degreesC). Fit (mum) was measured in the 'as cast' condition and after each porcelain firing cycle with a traveling microscope. The values were compared using the analysis of variance and Tukey's test (P < 0.05), the Pd-Ag group was compared to titanium groups using Dunnett's test (P < 0.05). Results. The marginal fit values in the as-cast condition (initial) were 84.43 mum for Ti-6Al-4V not treated, 76.35 mum for Ti-6Al-4V treated, 86.09 mum for cp Ti not treated, 97.66 mum for cp Ti treated and 58.11 mum for Pd-Ag group. The Ti-6Al-4V, cp Ti, and Pd-Ag groups exhibit significant differences in marginal fit values when the as-cast condition (initial) was compared with those after the recommended porcelain firing protocol (by Tukey's test at 5% probability level). No significant differences were observed between stress-relieving treated and not treated groups. Significance. The firing cycles used for porcelain build-up may worsen the fit of titanium copings to values that suggest no inferences to the detriment of clinical applications. (C) 2003 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.19768669

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 4degreesC (+/-2degreesC) to 55degreesC (+/-2degreesC). 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 Tukey's 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-6AI-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. 2003 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.19879079