PubMed · 6572679
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
A I Hamilton. 1983. Conserving scarce materials.. https://doi.org/10.14219/jada.archive.1983.0414
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
OBJECTIVES: The aim of the study is to investigate the stress-strain response of different dental materials, especially dental brittle materials, and compare them with enamel. METHODS: A nano-based indentation system (Ultra Micro-Indentation System, UMIS-2000, CSIRO, Australia) was used to determine the indentation stress-strain response of two kinds of dental ceramics (Cerec 2 Mark II and Vita VM9), one kind of dental alloy (Wiron 99) and healthy enamel. A spherical indenter was used to test the materials with nanometer and micro-Newton displacement and force resolution. Assuming the elastic modulus remained constant, a plot of contact pressure versus contact strain, H-a/R, of each material was obtained. RESULTS: By comparing the H-a/R curve of the different materials with enamel, it can be concluded that only the metallic alloy, has similar stress-strain response as enamel. Dental ceramics showed much higher yield stress response than enamel. VM9, a porcelain veneer component of crown/bridge structure, is slightly softer than its core, Mark II. The yield point for Mark II and VM9 are nearly 10 and 7GPa, respectively, and approximately 2GPa for Wiron alloy and enamel. SIGNIFICANCE: H-a/R curves provide a new method to compare the mechanical properties of different dental materials. From the standpoint of structural reliability, strong and tough materials with primarily elastic response, such as toughened ceramics are required to enable dental crown/bridges to have long term reliability. On the other hand, materials with too high hardness or yield response may damage opposing teeth during occlusal contact. Future studies may establish a relationship between stress and strain property and abrasive wear of dental material.
OBJECTIVES: The objective of this investigation was to determine the materials used in metallic post and core construction and investigate and the modes of failure that occurred resulting in post fracture. METHODS: Eighty-five fractured metal posts were clinically retrieved over a 5-year period. The tooth with the fractured post, and relevant clinical details were recorded. Investigation of the fractured posts was undertaken to determine their constituent elements and modes of fracture using scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). RESULTS: The results showed that 77% of the posts were cast and 23% wrought. The modes of fracture were ductile (67%) or brittle (52%) although some posts exhibited both within the same specimen. In addition, evidence of fatigue was present in 20% of posts and porosity in 48%. CONCLUSIONS: A large variety of materials were used in the construction of post and cores although low-gold silver-palladium alloy most commonly encountered. Their failure was predominantly ductile in nature although a significant amount of brittle fracture was also noted. Porosity within castings also appeared to be a contributory factor in some cases and this was particularly evident in high-palladium castings. Evidence of fatigue was noted in a minority of posts.
OBJECTIVES: Permanent deformation is one of the most common mechanical complications that affect denture clasps. This can lead to loss of retention and stability of the prosthesis. The purpose of this study was to apply and validate a nonlinear finite element model for permanent deformation prediction in cast denture clasps. Such a model can enhance the process of design optimization and contribute to minimizing the possibility of this problem. METHODS: Cast clasps made from Ti-6Al-7Nb, Co-Cr and Type IV gold alloys were loaded in three different directions (outside, inside and outside inclined 30 degrees ), and the resulting permanent deformation values were recorded. Nonlinear finite element analysis simulations based on the maximum distortion energy criterion for yielding, were conducted for clasp models that were reproduced according to the dimensions of each experimental specimen. Linear regression analysis for the results of the experiment and simulation was performed to verify the validity of the mathematical models. RESULTS: Deflections required to produce specific amounts of permanent deformation were in close agreement with those recorded experimentally. The R2 value for all bending tests was 0.985 and the linear regression equation expressed in micrometers was [DeflectionFEA=0.976 (DeflectionReal)+34]. SIGNIFICANCE: Permanent deformation behavior in the cast clasps with a relatively wide range of deflections (0-2 mm) can be predicted using the proposed model, which shall enhance the design optimization process of cast clasps for denture prostheses.