PubMed · 3333886
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G A Nolasco, E H Souza, J S da Silva, L Nakama, M S Betiol. [Alternative casting alloys].. https://pubmed.ncbi.nlm.nih.gov/3333886/
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Hydrogen embrittlement of Ni-Ti superelastic alloy in a fluoride solution (0.2% APF) has been investigated by means of a tensile test (after immersion) and hydrogen thermal desorption analysis. Upon immersion, the tensile strength of the alloy decreased to the critical stress level of martensite transformation. Hydrogen desorption of the immersed specimens appeared with a peak at around 500 degrees C. The amount of absorbed hydrogen in the alloy ranged from 100 to 1000 mass ppm when immersed in the fluoride solution for 2 to 24 h. The immersion in the fluoride solution led to the degradation of mechanical properties due to hydrogen embrittlement. The results of the present study imply that one reason that Ti and its alloys fracture in the oral cavity is the fact that hydrogen is absorbed in a fluoride solution, such as prophylactic agents.
Most methods of immediate loading of implants reported in the literature involve retrofitting a pre-existing denture to the implants. This article describes and illustrates clinical and laboratory procedures for immediate loading of implants in the edentulous mandible with the use of a laboratory-processed, provisional, screw-retained, implant-supported fixed complete denture that incorporates a cast metal reinforcement.
STATEMENT OF THE PROBLEM: Acetyl resin removable partial denture (RPD) direct retainers may provide an esthetic alternative to conventional metal direct retainers. The effect of repeated stress on acetyl resin direct retainers is unknown. PURPOSE: This study compared deformation of acetyl resin and metal alloy RPD direct retainers after repeated dislodgments over a test die. MATERIAL AND METHODS: Ten acetyl resin (Thermoflex) and 10 metal alloy (Ticonium Premium 100) RPD direct retainers, fabricated to manufacturers' specifications, were dislodged over a stainless steel die by means of a laboratory test apparatus for a simulated 3-year period (5000 cycles). Occlusal and facial digital images made before and after cycling were measured (mm) for direct retainer deformation by using computer-imaging software (Scion Image 1.62). Student t tests (alpha=.05) were performed for statistical comparisons. RESULTS: A significant difference in deformation between acetyl resin and metal alloy direct retainers occurred in the occlusal view (P=.045), but not in the facial view (P=.832). Average deformation varied but was greatest in the occlusal view: 0.09 +/- 0.8 mm for acetyl resin direct retainers compared with 0.01 +/- 0.9 mm for metal alloy direct retainers. Average facial view deformations revealed no significant differences: 0.039 +/- 0.6 mm for metal alloy and 0.033 +/- 0.7 mm for acetyl resin direct retainers. CONCLUSION: Within the limitations of this in vitro study, significantly greater deformation resulted with acetyl resin compared with metal alloy direct retainers after 3 years of simulated use.