Podcast
Questions and Answers
What is the primary reason for documenting the use of dental alloys?
What is the purpose of taking metal shavings from intraoral restorations?
What is the primary method of corrosion in dental alloys?
Why is corrosion of dental alloys a concern from a biocompatibility standpoint?
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What is a common method for measuring corrosion in dental alloys?
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What is the significance of identifying and quantifying released elements in dental alloys?
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What is the purpose of EDX analysis in dental alloys?
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What is the accuracy of analyzing dental alloys using scanning microscopy and EDX?
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What is an alloy typically composed of?
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What is a characteristic of dental alloys?
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Why has the composition of dental alloys evolved over time?
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What is a challenge in understanding the biocompatibility of dental alloys?
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How many elements from the periodic table are used in today’s dental alloys?
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What is the most common way to express the composition of dental alloys?
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Why is atomic percentage a better predictor of an alloy’s biological properties?
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What is a key difference between weight percentage and atomic percentage?
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What is a necessary condition for an alloy to have adverse biological effects?
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What influences the biological response to an alloy?
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What is a factor that influences the corrosion of dental alloys?
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What is true about elemental release and corrosion from alloys?
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What influences the lability of an element?
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What is the primary consequence of thermal treatment on a ceramic alloy?
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What is the role of metal oxides generated during the firing process?
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What can modify the lability of an element?
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What reduces the lability of copper in dental alloys?
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Why may exposed oxides at the crown margin increase the toxicity of the alloy?
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What reduces the lability of titanium?
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What is the consequence of recasting base metal alloys?
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What is the problem with placing a gold surface coating on a nickel-based or cobalt-based alloy?
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Why should gold surface coating of nickel-based or cobalt-based alloys be discouraged?
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What happens to the release of ions from alloys over time?
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What is the effect of solders on dental alloys?
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What is the primary factor influencing the accumulation of elements locally around dental alloys?
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What is unique about the corrosion properties of brass in the mouth?
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In which tissue have elevated copper levels been demonstrated in dogs adjacent to crowns composed of brass?
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What is the significance of the study on patients with inflamed gingiva adjacent to various dental alloys?
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What is the general trend observed in the levels of alloy components in human gingival tissues adjacent to dental alloys?
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What is the main reason why elements released from nonamalgam dental alloys do not contribute significantly to the systemic body burden of elements?
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What is the primary source of metal intake in the body?
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What is the significance of Table 8.3 in the context of dental alloys?
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Study Notes
Basic Material Properties
- An alloy is a mixture of two or more metals or non-metals (elements).
- Dental alloys typically contain at least four metals and often six or eight different metals, making them metallurgically complex.
- Alloy compositions are diverse and have evolved over the past 20 years, with many types of alloys emerging that were unknown just a few years ago.
- Most dental alloys were previously based on gold, but today's alloys may be based on silver, gold, palladium, nickel, cobalt, or titanium.
Alloy Composition
- The composition of dental alloys can be expressed in two ways: weight percentage (wt.%) or atomic percentage (at.%).
- Weight percentage is the most common way to describe an alloy's composition, but atomic percentage is better for predicting the number of atoms available to be released.
- The wt.% and at.% of an alloy may be substantially different from one another.
Analysis of Dental Alloys
- Dental alloys are classified as medical devices, and their use must be documented by the dentist and laboratory technician.
- Information about an alloy's composition is available in the literature or from manufacturers.
- Metal shavings can be taken from intraoral restorations and analyzed using scanning microscopy and energy-dispersive x-ray (EDX) analysis to determine the alloy's composition.
Corrosion and Release of Elements
- Corrosion is the primarily electrochemical process of alloys involving the ionization of elements that are released into the environment.
- Elements that are initially uncharged lose electrons and become positively charged ions as they are released into solution.
- Corrosion is a chemical property of an alloy that influences other properties, including esthetics and strength.
- The release of elements from an alloy is necessary for an alloy to have adverse biological effects such as toxicity, allergy, or mutagenicity.
- Factors that influence the corrosion of dental alloys include:
- Composition of the alloy (particularly at the surface)
- Phase structure of the alloy
- Surface structure (roughness, presence of oxides)
- Crevices, pits
- Thermal treatment/history
- Combinations of alloys (gold coating, soldering)
- Time in service
Factors Influencing Element Release
- The composition of an alloy is a fundamental factor that influences element release.
- Certain elements, such as copper, zinc, and nickel, have higher tendencies to be released than elements such as gold and palladium.
- The lability of an element may be substantially modified by other elements around it.
- The phase structure of the alloy and thermal treatment can also influence element release.
Clinical Practice Advice
- Gold surface coating of nickel-based or cobalt-based alloys should be discouraged because the combination of the alloys and their permanent contact may enhance corrosion rather than retard it.
- Only those solders or alloy combinations should be used that have a low tendency for corrosion.
Nonimplanted Dental Alloys
- Elements released from nonimplanted dental alloys may or may not gain access into the body.
- There is some evidence that elements from dental crowns and other alloys gain access to local gingival tissues or the oral mucosa.
- However, there is little evidence to demonstrate that elements released from nonamalgam dental alloys contribute significantly to the systemic body burden of elements.
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Description
Learn about the composition and properties of dental alloys, including their metallurgically complex nature and diverse compositions.