Cast Cobalt-chromium Alloy Research Articles

Application of digital impression and model in removable partial dentures for Kennedy classⅠandⅡdentition defects.

This study aimed to evaluate the application of digital impression and resin model technology in removable partial dentures (RPD) for Kennedy classⅠandⅡdentition defects. Patients with Kennedy classⅠorⅡdental defect were selected and grouped in accordance with the following denture production processes: digital impression/resin model/cast cobalt-chromium alloy framework group (group A), digital impression/resin model/laser printed titanium framework group (group B), alginate impression/plaster model/cast cobalt-chromium alloy framework group (group C), and alginate impression/plaster model/laser printed titanium framework group (group D), with 40 cases in each group. The final RPD was examined in place in the mouth, and the evaluation indicators included the retention force of clamp ring, the tightness of connector and base, and the accuracy of occlusion. The evaluation scores of each index were used for analysis on the Kruskal-Wallis rank-sum test. No statistically significant difference in the score of each index was found among the four groups in RPD. The cast cobalt-chromium alloy and laser-printed titanium framework RPD using digital impression and resin model can meet the clinical restoration requirements of patients with Kennedy classⅠandⅡdentition defects.

Comparison of Bond Strength Between Two Resin Cement Types and Additive Manufacturing or Cast Cobalt-Chromium Alloys.

To compare the bond strength of two types of resin cement to that of additive manufacturing (AM) or cast cobalt-chromium (Co-Cr) alloys. Two types of resin luting cement, composite resin and methyl methacrylate (MMA), were bonded to AM or cast Co-Cr alloys, and shear bond tests were performed after seven days of storage in distilled water at 37°C. Co-Cr alloy adhesive elements AM to the enamel surface of the labial aspect of a bovine mandibular central incisor crown were bonded with two types of resin luting cement and subjected to 1,000 cycles of storage in water for one day and 28 days or thermal cycling, followed by shear bonding tests. Residual cement on the metal and enamel surfaces after the bonding tests was evaluated using an optical microscope. The normality of the results was evaluated using statistical software Statcel4, analysis of variance, or Kruskal-Wallis test, depending on normality, and multiple comparison tests were performed using the Tukey-Kramer or Steel-Dwass tests. After one day, the shear bond strength (SBS) was 25.9 MPa for Panavia V5 (PV; Kuraray Noritake Dental Corporation, Niigata, Japan) and 23.5 MPa for Super-Bond (SB; Sun Medical Corporation, Shiga, Japan), with no significant difference between the two cement types (P > 0.05). After 28 days, the SBS decreased to 4.1 MPa for PV and 6.7 MPa for SB, showing a significant difference between the two cements (P < 0.05). Following 1,000 thermal cycles, the SBS was 2.0 MPa for PV and 5.6 MPa for SB, with SB exhibiting a significantly higher value (P < 0.05). The adhesive strength was significantly lower after 28 days of storage and thermal cycling compared to after one day of storage (P < 0.05). The Co-Cr alloy exhibited more residual cement on the enamel surface due to interfacial fracture with the resin cement. The Co-Cr alloy showed more residual cement on the enamel surface due to interfacial fracture with the resin cement. MMA-based resin cement showed optimal bond strength and may be suitable for clinical use in computer-aided design (CAD)/computer-aided manufacturing (CAM) orthodontic appliances.

Strength of Polyether Ether Ketone Composite as a Major Connector Material for Removable Partial Dentures

PEEK composite was tested mechanically as a maxillary removable partial denture (RPD) framework material instead of cast cobalt chromium alloy. Methods: Partial edentulous upper jaw cast was scanned using structured-light 3D scanner, palatal strap (PS) designs for RPD were designed by a designing dental laboratory software. CAD/CAM machine fabricated PSs patterns using their designs’ STL software files. PSs were made from poly-ether-ether ketone (PEEK) reinforced by ceramic fillers using thermal injection press technique and Co-Cr alloy using centrifugal casting, each material group was subdivided into two subgroups according to storage conditions (stored and non-stored subgroups), storage took place in deionized water for about 180 days at 37.5 ± 2 o C. All specimens were subjected to fracture resistance test using universal testing machine then maximum compression load (MCL) result values were subjected to statistical analysis. PEEK composite specimens were scanned by field emission microscope (FEM) and energy dispersive spectroscopy. Storage water of PEEK composite was analyzed using atomic absorption spectroscopy (AAS). Results: In either stored or non-stored subgroups of PEEK composite straps they showed significant lower mean MCL values than corresponding alloy subgroups (p=0.0001). FEM scanning showed fillers agglomerations in non-stored PEEK composite and their nearly absence from stored PEEK composite specimens. AAS detected Al element in PEEK composite storage water. Conclusion: Mechanically thermally injected ceramic reinforced PEEK composite could not replace cast Co-Cr alloy as PSs material for maxillary RPD. Biocompatibility concerns raised in this study due to suspected Al leaching and ceramic fillers dissolution from PEEK composite matrix.

Marginal Accuracy of Milled Versus Cast Cobalt Chromium Alloys in Long Span Implant-Supported Frameworks: A Systematic Review and Meta-analysis

Aim: To assess if milled cobalt chromium (Co-Cr) alloy offers significantly better marginal accuracy than cast Co-Cr alloy for screw-retained long-span dental implant framework. Materials and Methods: A search PICO was formulated using suitable keywords and an electronic search was initiated. The databases of PubMed, Cochrane Library, Google Scholar and Embase were searched for related articles. Bibliographies of randomised control trials and reviews, identified in the electronic search, were analysed for studies published outside the electronically searched journals. Electronic search identified 26 studies. A total of 16 studies were eliminated after reading the abstracts. Out of the remaining 10 studies, 3 were eliminated based on the inclusion and exclusion criteria, and finally 7 studies were finalised for systematic review. Results Data were extracted from the included studies and analysed. The obtained data were suitable for meta-analysis, which showed an overall effect size z = 4.97 ( P &lt; .001) at 95% CI showing a significant statistical difference between milled and cast Co-Cr frameworks. Conclusion: Milled cobalt chromium frameworks are significantly more accurate than cast frameworks for long-span implant-supported frameworks used in dental prosthetic rehabilitation. More randomized controlled trials need to be conducted with a larger sample size to get a more authentic conclusion in a clinical scenario.

Comparative evaluation of wear resistance of CAD-CAM zirconia and cast cobalt chromium alloy for indirect restorations against human enamel - An In Vitro study.

To comparatively evaluate the wear resistance of two different posterior indirect restorative materials against human enamel. Two different posterior indirect restorative materials of ten in each Group-I (Monolithic zirconia) (n = 10) and Group-II (Cast cobalt chromium) (n = 10) were formed into disc and used as a substrate for the wear test. Freshly extracted mandibular first premolars were used as a pin (antagonist) (n = 20). Pin-on-disc wear testing machine was used to simulate the masticatory parameters and evaluation of the wear parameters was done after 1,20,000 cycles, with load of 40N for specific duration. Data related to wear testing procedure were tabulated and evaluated. Results were statistically analyzed using Mann-Whitney test and Wilcoxon signed rank test. Mean surface roughness value (Ra value) obtained for Group-I disc test samples showed no statistical significance (P value < 0.05). Mean wear rate value of test disc samples was statistically significant between Group-I and Group-II (P value < 0.05). Mean surface roughness value was statistically significant between Groups-I and II before and after wear test (P value < 0.05). From the results obtained, it was found that the Group-I (Monolithic zirconia) exhibited higher wear resistance than Group-II (cast cobalt chromium) and causes less wear to the opposing enamel antagonist.

Effect of thermo-mechanical cycling on the shear bond strength of porcelain to milled and cast cobalt-chromium alloys

Statement of problem: Most of the failures in metal-ceramic restorations occurs at the interface between the two materials. For long term clinical performance, these restorations should have adequate bond strength between metal and ceramic. Few data is available in regards to the metal-ceramic bond strength of Cobalt Chromium (Co-Cr) alloys fabricated by computer aided designing design/computer aided manufacturing CAD/CAM technology.Purpose of the study: The purpose of this in vitro study was to explore the influence of Co-Cr fabrication techniques on shear bond strength of porcelain to milled and cast Co-Cr alloys and to evaluate failure mode with & without thermo-mechanical cycling.Materials & Methods: A total of 20 disc samples (10 mm diameter x 4 mm thickness) were fabricated of Co-Cr alloy and divided into two groups (10 discs each) according to their fabrication technique: Group I: fabricated by CAD/CAM milling and Group II: fabricated by conventional casting. Then porcelain build up for all discs (10 mm diameter x 2mm thickness) was done using feldspathic porcelain. Each group was subdivided according to discs’ exposure to thermo-mechanical cycling into two sub-groups (5 discs each). Sub-group A : without thermo-mechanical cycling and Sub-group B: with thermo-mechanical cycling. All the disc samples were subjected to the shear bond strength (SBS) test and the failure mode was investigated under digital microscope at 40 X. Data were statistically analyzed using Independent sample t-test and Two-way ANOVA test (P ≤ 0.05).Results: The results showed that the fabrication techniques were statistically insignificantly affecting the SBS of both CAD/CAM milled and conventional casting groups. Regarding the thermo-mechanical cycling, the CAD/CAM milled and conventional casting groups without thermo-mechanical cycling showed a statistically significantly higher SBS than those with thermo-mechanical cycling. Failure mode was mixed type for all disc samples.Conclusions: Fabrication technique of Co-Cr alloy had no significant effect on SBS. Thermo-mechanical cycling of milled and cast Co-Cr samples significantly affecting SBS with the superiority of the non-thermo-mechanical cycled samples. All the tested samples showed SBS values within the clinically acceptable levels. CAD/ CAM fabricated Co -Cr may be considered a promising alternative to conventional cast Co-Cr for metal ceramic prosthesis in terms of SBS.

Cavitation erosion resistance of a non-standard cast cobalt alloy: Influence of solubilizing and cold working treatments

The wear behavior of a non-standard cast cobalt chromium alloy (Co30Cr19Fe), during vibratory cavitation test, was investigated. Low stacking fault energies (SFE) cobalt alloys deform by complex plastic deformation mechanisms, which enhance the cavitation erosion (CE) resistance, since the onset of localized stress, leading to fatigue failure and material removal, is delayed. The purpose of this work is to characterize the main operating deformation mechanisms during cavitation erosion testing of the non-standard Co30Cr19Fe alloy. As cast, solution treated, and 15% and 30% cold rolled specimens were tested. The as cast microstructure consisted of ~2 mm fcc alpha grains and hcp epsilon-martensite. The 1473 K solubilization treatment led to primary recrystallization and formation of 250 µm new grains. The 15% cold worked microstructure consisted of heavily deformed fcc phase containing deformation twins and epsilon-martensite. Ultrasonic cavitation testing was carried out, during 40 h, according to ASTM G32-09. The solubilized specimens presented the worst behavior, whereas, the 30% cold worked specimens were the most CE resistant. The CE results are discussed based on the microstructural parameters: amount of alpha fcc and epsilon-hcp phases, grain sizes, relative amounts of twinning, slip lines and strain induced martensite formation.

Formation of a nanocrystalline recrystallized layer during microabrasive wear of a cobalt-chromium based alloy (Co-30Cr-19Fe)

The tribological behavior of a cast cobalt-chromium alloy, during microabrasion testing, was investigated. The alloy's microstructure contains coarse grains of fcc cobalt rich dendrites, interdendritic segregations and almost no precipitates. The tests were done using a 0.1 g/cm3 Al2O3/distilled water slurry, 0.3 N applied load and 20 rpm rotational speed. Two-body abrasion (grooving wear) was the dominating wear micromechanism. A severely deformed nanocrystalline layer containing random oriented ∼20 nm grains was observed, immediately below the worn surface. Finite element modeling of a single Al2O3 particle scratching the Co-Cr alloy surface showed that severe plastic deformation occurs in a region 1–2 μm beneath the worn surface, giving rise to the observed nanocrystalline layer.

A comparative evaluation of shear bond strength of porcelain fused to metal substructure fabricated using conventional and contemporary techniques: an in vitro study

Base metal alloys due to their low cost, are being used more often as the substructure because of their good mechanical properties, excellent metal ceramic bonding and biocompatibility. The bonding of porcelain to metal is an important point to be considered for the success of the restoration. Aim: To compare and evaluate the shear bond strength of porcelain fused to metal substructure fabricated using conventional and contemporary techniques. Methods and Material: Thirty sample discs were fabricated – 10 of cast nickel chromium alloy, 10 of cast cobalt chromium alloys and 10 of laser sintered cobalt chromium alloy. Conventionally used feldspathic porcelain was used and fired over the metal discs. These samples were placed in a specially fabricated jig, which was held in a universal testing machine. The samples were subjected to shear stress until they fractured and the readings were noted. The fractured surface of the sample was then viewed under stereomicroscope. Results: The mean shear bond strength was highest in group C (porcelain fused to laser sintered cobalt chromium), followed by group A (porcelain fused to cast nickel chromium) and group B (porcelain fused to cast cobalt chromium) which was the least. The level of significance was fixed at p < 0.05. After applying Student’s Unpaired ‘t’ test there is no significant difference in shear bond strength in group A compared with group B, highly significant in group A and group C and very highly significant in group B and group C. Conclusions: All the three groups showed adequate, but laser sintered cobalt chromium alloy had the highest shear bond strength to porcelain. Nickel chromium alloy fabricated by conventional casting method showed lesser values of the shear bond strength, followed by cobalt chromium alloy fabricated by conventional casting, which had the least shear bond strength.

The marginal fit of selective laser melting–fabricated metal crowns: An in vitro study

The selective laser melting technique is attracting interest in prosthetic dentistry. The marginal fit is a key criterion for fixed restorations. The purpose of the study was to evaluate the marginal fit of cast cobalt-chromium alloy crowns versus the fit of selective laser melting-fabricated crowns. The marginal gap widths of 36 single crowns (18 selective laser melting-fabricated cobalt-chromium metal crowns and 18 cobalt-chromium cast crowns) were determined with a silicone replica technique. Each crown specimen was cut into 4 sections, and the marginal gap width of each cross section was evaluated by stereomicroscopy (× 100). The Student t test was used to evaluate whether significant differences occurred in the marginal gap widths between the selective laser melting-fabricated and cast cobalt-chromium metal crowns (α=.05). The mean marginal gap width of the cast crowns (170.19 μm) was significantly wider than that of the selective laser melting-fabricated crowns (102.86 μm). Selective laser melting-fabricate cobalt-chromium dental crowns found improved marginal gap widths compared with traditional cast crowns.

Biotribological study of multilayer coated metal-on-metal hip prostheses in a hip joint simulator

Metal-on-metal (MOM) hip joint bearings have demonstrated low wear rates and nowadays this contact pair has being considered as an alternative to metal-on-polymer (MOP) joint replacements. However, wear of MOM joints is a concern due to the toxicity and biological reaction of wear debris and metallic corrosion. This has motivated to investigate the possibility to apply thin hard coatings on metallic heads to reduce the wear and metallic ion release. The aim of the present study was to investigate the wear properties of metal-on-metal hip prostheses with surface engineered femoral heads using a multilayer coating (TiN/CrN)×3, in comparison with metal-on-metal pairs in a hip joint simulator. Different surface PVD coatings were applied on surgical grade wrought cobalt–chromium alloy femoral heads: multilayer (TiN/CrN)×3, CrN single layer and diamond-like carbon (DLC). These femoral heads were tested against high carbon content cast cobalt–chromium alloy acetabular cups using a three-axial multi-station hip joint simulator (FIME II). During the wear tests three directions of motion were applied with the following amplitudes: flexion–extension (FE) ±23°, abduction–adduction (AA) ±23° and internal–external (IER) ±8°. All components were tested at 1.2Hz under a Paul-type loading curve and bovine calf serum solution as lubricant. Results showed that both; the PVD coatings protects the femoral heads reducing wear up to 5 times in the case of the DLC coating and 28 and 55 times in the case of (TiN/CrN)×3 and CrN respectively compared with the MOM femoral heads.

Cyclic fatigue properties of cobalt-chromium alloy clasps for partial removable dental prostheses

Cast cobalt-chromium (Co-Cr) alloy clasps have been widely used for prosthodontic treatment, but long-term retentiveness of these clasps is not clear. The purpose of this study was to investigate the residual retentive force of 3 types of cast Co-Cr alloy clasps in relation to their proportional limits. Thirty half-round straight clasps and 30 circumferential clasp assemblies were made from 3 Co-Cr alloys (Hardalloy, Regalloy, and Vera PDN) (n=10). All of the straight clasps were subjected to a compression-deformation test to obtain data for displacement/load at the proportional limit. Two undercut depths (0.25 mm and 0.50 mm, n=5) were included in a cyclic fatigue test. Each circumferential clasp assembly was subjected to an insertion/removal test on a metal abutment tooth for 7200 cycles to simulate 5 years of clinical use. The residual retentive force was measured after 360 cycles; thus, the retentive force of each clasp was recorded 21 times throughout the test. The data were subjected to repeated-measures ANOVA (α=.05) to compare the retentive force of each group of clasps for different periods of fatigue testing. The ANOVA. The Student t test (α=.05) was used for analysis of clasps fabricated with the same alloy but with different undercuts. A linear correlation analysis (α=.05) was used to test the correlation between retentive forces and cycling sequences. The mean values of displacement at the proportional limit for the 3 Co-Cr alloys varied from 0.30 mm to 0.36 mm. The mean retentive forces of each alloy group decreased dramatically after the first cycling phase (P<.05). Thereafter, the decrease was more gradual but was still significantly different compared to the original retentive forces (P<.05). Compared to clasps in the 0.25-mm undercut group, those in the 0.50-mm undercut group exhibited greater mean retentive forces before the cyclic fatigue test (P<.05), as well as a greater decrease in the retentive force at the end of the test (P<.05). A negative correlation was found between the retentive force of cast Co-Cr alloy clasps and the logarithm of cycling sequences. After a test simulating 5 years of service, cast Co-Cr alloy clasps exhibited a residual retentive force to satisfy the requirements for clinical use.

Cyclic fatigue test of cobalt-chromium alloy cast clasps

To investigate the change of retentive forces of cast cobalt-chromium (Co-Cr) alloy clasp in cyclic fatigue test. Samples of three types of cast Co-Cr alloy (Group A: Hardalloy; B: Regalloy™; C: Vera PDN™) clasps were fabricated and placed at undercut depths of 0.25 mm, 0.50 mm. The clasps were drawn from the model molar cyclicly to simulate 5 years of clinical use in an universal testing machine. Retentive force were record at 21 different time point for each clasp during the whole fatigue testing process. Data were subjected to ANOVA, Chi-square test and linear regression analysis. All clasps showed decreasing retention during the cyclic fatigue test. Clasps engaged in 0.50 mm undercut depth exhibited greater initial retentive force [Group A: (8.714 +/- 1.104) N, B: (9.072 +/- 0.653) N, C: (9.588 +/- 1.980) N] as well as greater loss of retention [Group A: (4.408 +/- 0.662) N, B: (3.484 +/- 0.494) N, C: (3.290 +/- 1.484) N] at the end of the test than clasps engaged in 0.25 mm undercut did [initial forces were (7.940 +/- 0.357), (7.834 +/- 1.308) and (8.156 +/- 1.067) N for Group A, B, C, respectively; loss of retention were (2.444 +/- 0.736) N, (2.954 +/- 1.048) N and (1.832 +/- 1.180) N for group A, B, C, respectively]. Negative correlation was found between the clasp retention and the logarithm of cycling times. Co-Cr alloy cast clasp could provide adequate retentive force for 5 years of clinical use.

Interface interactions between porous titanium/tantalum coatings, produced by Selective Laser Melting (SLM), on a cobalt–chromium alloy

Porous titanium and tantalum coatings were produced on cast cobalt–chromium alloy substrate plates (Co-28 Cr-6 Mo ASTM designation F75)) using the additive manufacturing process Selective Laser Melting (SLM). Both tantalum and titanium coatings where successfully produced, however, a poor interface bond was observed with the titanium coatings on the cobalt–chrome alloy. This was due to a eutectic reaction leading to the formation of a low melting point phase βTi(CoCr) which cracks during cooling, rather than the formation of titanium carbide, as previously reported. This cracking makes titanium an unsuitable material to coat cobalt–chromium alloys using SLM. Tantalum coatings, however, showed considerably improved performance in terms of interface compatibility when compared to titanium and therefore a Co–Cr/Ta system would seem feasible for the manufacture of porous structured devices when a bi-material approach is required. This would allow the advantages of a highly biocompatible structured coating to be combined with the mechanical performance of a less biocompatible substrate.

A laboratory investigation of the role of guide planes in the retention of cast cobalt-chromium alloy partial denture frameworks

This in vitro study examined the resistance to displacement offered by guide planes and the displacement mechanics of a bilateral bounded saddle cast cobalt chrome alloy removable partial denture framework under conditions simulating an average initial fit.

Improve the Retention of Your Partials?

A Laboratory Investigation of the Role of Guide Planes in the Retention of Cast Cobalt-chromium Alloy Partial Denture Frameworks. M. Ali, N.E. Waters, R.I. Nairn, F. West and M. Sherriff. Journal of Dentistry 2001; 29: 291–299

A laboratory investigation of the role of guide planes in the retention of cast cobalt-chromium alloy partial denture frameworks

Objectives: This in vitro study examined the resistance to displacement offered by guide planes and the displacement mechanics of a bilateral bounded saddle cast cobalt chrome alloy removable partial denture framework under conditions simulating an average initial fit. Methods: A specially designed model mouth jig fitted with strain gauges to monitor the forces across the guiding plane/guiding surface interfaces was used. Guiding planes of enamel, silver tin amalgam and dental composite with seven combinations of guide planes and three angles of withdrawal were examined. Guiding plane size was also examined for dental enamel. Results: A statistically significant difference in retention was found for all factors examined. Retention increased with increasing angle of withdrawal. Size effects were found but considered unreliable. Conclusions: It was concluded that with a tight fit guiding plane retention may be readily predicted for any given material, combination of mesial, distal and lingual guiding planes and angulation conditions by the application of mechanical principles providing the basic parameters are known. Attention is drawn to the reasons for further work to fully understand the clinical situation.

Custom endoprostheses for limb salvage: a historical perspective and imaging evaluation.

Downloaded from www.ajronline.org by UCLA Digital Coll SVCS on 05/06/15 from IP address 149.142.243.67. Copyright ARRS. For personal use only; all rights reserved PictorialEssay Custom Endoprostheses for Limb Salvage: A Historical Perspectiveand ImagingEvaluation Leanne L. Seeger1, Sheila Farooki1, Lawrence Yao1'2, J. Michael Kabo3, Jeffrey J. Eckardt3 H istorically, primary bone malig nancies were treated with amputa tion. Since the mid l970s, several limb salvage reconstruction techniques have cast steel alloys. Early titanium single-piece components were machined (Fig. 2). Early knee devices were rigid hinges [1] (Fig. 2). Since the late l980s, the single-component endoprosthesis has been replaced by modular systems that use a rotating-hinge knee joint been developed, including resection arthrode sis, allografts and allograft composites, en doprostheses, and rotationplasty [1—3].These have evolved in conjunction with radiation therapy and adjuvant chemotherapy protocols that have dramatically improved patient sur vival [3, 41. Limb salvage reconstruction has three goals: The local recurrence rate should be no greater than that with amputation, the procedure should not delay the administrationof adjuvantor neo adjuvant therapy, and the reconstruction should be enduring and not associated with many local complications I [ I , 2]. Endoprosthetic limb salvage is most often undertaken for primary bone sarcomas. Less frequent indications include aggressive or multiply recurrent benign bone tumors; bone metastases; soft-tissue sarcoma involving bone; failed primary joint replacement; and recalcitrant, chronic nonunions [2—4](Fig. I). Evolution of Prosthetic Design The first endoprosthesis was implanted in I940. but this technique was not used routinely until the late I 970s. Original custom-designed single-piece Fig.1.—Indications fortotalfernoralendoprosthesisin Fig.2.—Evolution ofdistalfernoralendoprostheses.From 73-year-oldwomanwho had previouslyundergonesix procedures for arthroplasty fixation. Although en doprosthetic reconstruction is usually performed for primarybonetumors,other indicationsinclude chronic nonunionsthat are recalcitrant to conventionaltreat ment.Anteroposterior radiograph offemurshowsnon leftto right Waldius(Howmedica,Rutherford,NJ) distal fernoral replacementmadewith cast cobalt chromium alloy and rigid metal-on-metalhinge knee mechanism (thisdeviceis nolongerused);cast cobaltchromiumdis tal fernoralreplacementwith KinematicRotatingHinge Knee(Howrnedica)mechanism;Lewis ExpandableAd unionat level of midshaft. justableProsthesis distalfernoralreplacement (Wright Medical,Arlington,TN);modulardistalfemoralreplace rnentwithforgedcobaltchromiumfemoralstem,360° po rous ingrowth material,modulartitanium segment,and cobalt chromium condylar component using rotating hingekneemechanism(Howmedica). prostheses were components of ReceivedMarch17,1998;acceptedafterrevisionApril20,i998. t Department of Radiological Sciences, UCLA School of Medicine, 200 UCLA Medical Plaza, Ste. i65-57, Los Angeles, CA 90095-6952. Address correspondence to L L Seeger. 2Presentaddress:Departmentof Radiology,GeorgetownUniversityMedicalCenter,3800ReservoirRd.,NW.,2ndFloor,CCC,Washington,DC20007-2197. 3Departmentof OrthopaedicSurgery,UCLASchoolof Medicine,10833LeConteAve.,76-i16CHS,LosAngeles,CA90095-6902. AJR1998;ili:1525—1529 036i—803X/98/i7i6—1525 ©AmericanRoentgenRaySociety AJR:i71, December 1998

Effect of water and artificial saliva on the low cycle fatigue resistance of cobalt-chromium dental alloy

Statement of problem. Fatigue of denture clasp alloys causes clasp failures and decreases the retention of removable partial dentures. Little information is available on how the environment (dry, water, artificial saliva) effects the fatigue behavior of cast cobalt-chromium alloy clasps. Purpose. This study determined the effect of water and the artificial saliva on the resistance of cast cobalt-chromium alloy to the deflection fatigue. Material and methods. Test bars (n = 10) were tested either dry, in water, or in artificial saliva (Fusayama type) with a constant deflection fatigue test. The number of loading cycles before fracture was registered as resistance to fatigue. To establish whether there were indications of alloy corrosion occurring during the fatigue test, the testing liquid was analyzed retrospectively with an atomic absorbance spectroscopy. To determine elemental composition of the fracture surface, fracture surfaces of the test bars were analyzed with a scanning electron microscope and energy dispersive spectroscopy. Results. The bars that were tested dry had a mean fatigue resistance of 78,000 loading cycles, whereas test specimens tested in artificial saliva had a resistance of 59,000 loading cycles and 36,000 for those tested in water. Atomic absorbance spectroscopy revealed small amounts of cobalt (Co) in testing water and in artificial saliva. Energy dispersive spectroscopy analysis revealed differences in elemental composition of a fatigue fracture surface compared with that of a 1-bend fracture. Conclusions. The results suggest that both water and artificial saliva reduce the fatigue strength of cobalt-chromium alloy, explained by corrosion of the alloy in the wet environment. (J Prosthet Dent 1998;80:708-13.)

The distortion of cast cobalt-chromium alloy partial denture frameworks fitted to a working cast

Purpose. This in vitro study examined the distortion of 10 identically designed cast cobalt-chromium alloy frameworks, individually constructed, and adjusted by 10 technicians to fit one of 10 replicated stone working casts. Material and methods. The distortion was measured with a specially developed strain gauge apparatus when the frameworks were seated on the maxillary metal analog, the stone working cast, or a stone duplicate cast. Results. A statistically significant difference between the distortion of each of the frameworks was observed. A significant difference in the distortion was also observed for the frameworks when placed on each of the three casts. The distortion was the least when the frameworks were seated on the stone working cast and the greatest when seated on the metal analog. Conclusion. This study demonstrated that the distortion of a framework is not related to its closeness of fit as observed by the presence or absence of gaps between the framework components and the teeth. (J Prosthet Dent 1997;78:419-24.)