Larger diameter bearings reduce wear in metal-on-metal hip implants.

Metal-on-metal hip arthroplasty has the longest clinical history of all total arthroplasties. We asked whether large diameter femoral heads would result in less wear than those with small diameters. We also asked if there is a threshold diameter that ensures good wear behavior. We tested three batches of cast high-carbon cobalt-chromium-molybdenum hip implants (28 mm, 36 mm, and 54 mm diameters) in a hip simulator for 5 million cycles. We used bovine serum as lubricant and weighed the samples at regular intervals during testing. The 28-mm configuration had almost twice the wear of the 54-mm configuration, but we observed no difference between the 36-mm and the 54-mm configurations. The similarity in the wear performances of the larger configurations supports the presence of a threshold diameter that ensures good wear behavior.

Surface characterization and debris analysis of ceramic pairings after ten million cycles on a hip joint simulator.

This study was aimed at characterizing the ceramic wear particles produced during tests on a hip joint wear simulator of up to 10 million cycles. Alumina and alumina-zirconia composites were studied as commercial or potential hip joint products respectively. No ceramic particles could be observed, even after a careful isolation procedure. This confirms the low wear rate found for these materials in previous works (of the order of tenths of milligrams per million cycles). Surface characterization was conducted by means of scanning electron microscopy. It confirms the low wear regime of ceramic pairings and allows ceramic wear debris morphology to be defined. The effect of microstructure on surface wear is discussed.

Cusp fracture resistance in composite-amalgam combined restorations.

OBJECTIVE: To evaluate the in vitro resistance to fracture and microleakage in composite-amalgam combined restorations. METHODS: Seventeen Class I cavities with unsupported enamel walls prepared in extracted permanent molar teeth were treated with a bonding agent (Scotchbond MP, 3M Dental), the buccal cusps were reinforced with a composite resin (Z-100, 3M Dental) and the cavities were then restored with amalgam (Permite, Oral B). All teeth were load tested using a special fatigue-stress apparatus, immersed in a dye solution and then sectioned for examination by stereomicroscopy and scanning electron microscopy (SEM). RESULTS: Fractures in enamel supported by composite were present in 11 cases while 12 specimens included fractures in enamel supported by bonded amalgam. Microleakage was observed in 16% of the enamel-amalgam interfaces, 10% of the dentin-amalgam interfaces, 7% of the amalgam-composite interfaces, 4% of the composite-enamel interfaces and 11% of the composite-dentin interfaces. CONCLUSIONS: Bonded amalgam appears to be as effective as bonded composite in supporting undermined enamel in terms of resistance to fracture, but composite may have better marginal adaptation to enamel compared to bonded amalgam. Good marginal adaptation may be observed between amalgam and composite in composite-amalgam restorations.

Design-related fretting wear in modular neck hip prosthesis.

An accelerated cyclic loading corrosion test was used to determine the corrosion behavior of a commercial (GSP) and a prototype titanium hip prosthesis each with a modular neck. Four GSP and four prototype stems were subjected to a 2-Hz cyclic load ranging between 200 and 2,100 N for 1,000,000 cycles. Three stems were tested in an environment of FeCl3 solution, three stems were tested in Ringer's solution, and two stems were tested in air. After cyclic loading, the specimens were carefully examined with optical and scanning electron microscopy (SEM). None of them showed macroscopic or microscopic signs of corrosion, regardless of the environment to which the specimens were subjected. However, macroscopic evidence of mechanical fretting was present at the neck-stem modular junction, primarily concentrated at the medial contact point between stem and neck, especially for the prototype stems. SEM analysis confirmed these observations. The appreciable differences observed between the two designs suggest that the problem can be minimized or eliminated with an accurately designed taper fitting.

[The marginal leakage of amalgam and Vitrebond restorations after an occlusal load test]. / Infiltrazione marginale di restauri in amalgama e Vitrebond dopo test da carico occlusale.

The use of adhesive liners in amalgam fillings and restorations is a recent form of conservative dentistry. The aim of our study was to assess marginal microleakage in amalgam and Vitrebond restorations after occlusal load test. Using extracted teeth, we prepared 16 class II amalgam restorations, (Valiant ICQ, Caulk). Adhesive liner, (Vitrebond, 3M USA), was used in half of these. The samples then had first a cyclic load test, (27 kg per 7,000 cycles), followed by a microleakage test, (sample immersed in 2% erythrosin solution for 24 hours). The results showed that, in samples with adhesive liner, color penetrated to a statistically lesser extent than in the control group without Vitrebond.

Stability of glucose oxidase and catalase adsorbed on variously activated 13X zeolite.

The use of 13X zeolite (0.1-0.4-mm granules), treated with 2N and 0.01N HCI, 0.01M citric acid, 0.1M citric-phosphate buffer (pH 3.6), and in untreated form to adsorb glucose oxidase of fungal origin and microbial catalase was examined. Physicochemical analysis of the support demonstrated that its crystalline structure, greatly altered by the HCl and buffer, could be partially maintained with citric acid. The specific adsorption of the enzymes increased with decreasing pH and proved to be considerable for all the supports. The stability with storage at 25 degrees C is strictly correlated with the titrable acidity of the activated zeolite expressed as meq NaOH/g and with pH value of the activation solution. It proved to be lower than 55 h for both enzymes if adsorbed on zeolite treated with 2N HCl, and 15-fold and 30-fold higher for glucose oxidase and catalase adsorbed, respectively, on zeolite treated with the 0.1M citric-phosphate buffer and 0.01M citric acid. The specific adsorption of glucose oxidase and catalase was, respectively, 1840 U/g at pH 3.0 and 6910 U/g at pH 5.0. Their half-life at 25 degrees C with storage at pH 3.5 for the former and at pH 5.0 for the latter was 800 and 1560 h vs. 40 and 110 h for the corresponding free enzymes.