Dental Materials Chemistry Quiz

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Questions and Answers

Which of the following metals is commonly used in dentistry for its unique properties?

Aluminum

Titanium (correct)

Lead

Copper

What property of metals allows them to conduct electricity?

Free electrons (correct)

High density

Valence electrons

Thermal expansion

Which of the following is NOT a shaping process used for metals in dentistry?

Electroforming

Casting

Sintering

Translating (correct)

What is the primary reason metals have high strength and hardness?

Strong metallic interatomic bonding Signup and view all the answers

In the lost wax technique used in dental casting, what is primarily formed from molten metal?

A mold Signup and view all the answers

Which process involves the bonding of solid particles by heat without any liquid?

Sintering Signup and view all the answers

What characteristic is typical of metals that allows them to be hammered into sheets?

Ductility Signup and view all the answers

What sound do metals typically produce when struck?

A metallic ring Signup and view all the answers

What is the primary reason pure metals are unsuitable for dental applications?

They are too soft and ductile. Signup and view all the answers

What happens when 5% copper is alloyed with gold?

The material becomes harder and stronger. Signup and view all the answers

Which of the following best describes tarnish?

It is surface discoloration of the metal. Signup and view all the answers

What is a cause of corrosion in metals used in dental applications?

Chemical reactions in a wet environment. Signup and view all the answers

Which type of corrosion occurs without the presence of water?

Chemical (dry) corrosion. Signup and view all the answers

What is necessary for electrochemical corrosion to continue?

Transportation of electrons. Signup and view all the answers

Which is an example of chemical corrosion?

Silver sulfide formation on silver. Signup and view all the answers

What should be avoided to provide good shelf life for dental alloys?

Exposure to humidity and high temperatures. Signup and view all the answers

What initiates the process of crystallization in a molten alloy?

Formation of nuclei at the super cooling point Signup and view all the answers

What is the primary difference between single crystal and polycrystalline structures?

Single crystals are rare, while polycrystals consist of many grains Signup and view all the answers

What occurs at grain boundaries in a metal?

There is a transition between different crystal orientations Signup and view all the answers

Which type of defect involves the movement of a row of atoms within the crystal lattice?

Line defect Signup and view all the answers

What type of defect results from the presence of foreign atoms in a crystal lattice?

Substitutional defects Signup and view all the answers

What happens to the atoms in a crystal lattice when the proportional limit is exceeded?

They become permanently deformed and cannot return Signup and view all the answers

Which of the following best describes the role of dislocations in improving metal strength?

They inhibit the motion of dislocations Signup and view all the answers

Which of the following correctly describes impurities within a crystal structure?

They distort the crystal lattice Signup and view all the answers

What occurs at the anode of an electrochemical cell?

Free electrons are liberated. Signup and view all the answers

What characterizes galvanic corrosion?

It occurs due to contact between dissimilar metals. Signup and view all the answers

In stress cell corrosion, what role do the stressed areas of a metallic restoration play?

They act as the anode. Signup and view all the answers

Which of the following best describes concentration cell corrosion?

It results from variation in electrolyte composition. Signup and view all the answers

What is the effect of cathodic reactions in an electrochemical cell?

They produce more electrons than the anode. Signup and view all the answers

What substance acts as the electrolyte in dental galvanic corrosion, as mentioned in the examples?

Saliva Signup and view all the answers

During an electrochemical reaction, what happens to the cathode?

It gains electrons and remains intact. Signup and view all the answers

What is one method listed for protecting against corrosion?

Applying varnish coatings. Signup and view all the answers

Study Notes

Metals and Corrosion in Dental Biomaterials

Dental biomaterials frequently use gold, platinum, silver, copper, and titanium.
Metals in dentistry exhibit properties like positive ionization in solutions, luster due to free electron light reflection, and high strength/hardness/melting temperatures.
Metals like Hg and gallium are liquid at room temperature; H₂ is a gaseous metal.
Metals are malleable (hammered into sheets) and ductile (drawn into wires), producing a metallic ring sound when struck.
All metals conduct heat and electricity because they contain free electrons.
Metal density correlates with atomic weight and lattice structure.

Shaping of Metals

Casting involves melting metal and shaping it in a mold.
Dental casting often uses a wax pattern embedded in an investment that is then burned out, creating a mold for molten metal.
Cold working, also called wrought metals, involves shaping solid metal blocks into rods, wires, or tubes through hammering or pulling with dies.
Electroforming uses electrolysis to plate a metal onto a conducting surface, essentially reversing the corrosion process.
Common plated die materials include silver and copper.

Sintering (Powder Metallurgy)

Sintering bonds solid particles by heat.
It involves agglomeration and eliminating initial porosity (gaps) for enhanced density.
Sintering processes often require high pressure and contraction.
Amalgam tablets can be produced through sintering.

Metal Solidification

Metal solidification typically happens through a two-step mechanism:
- Nuclear Formation: A molten alloy cools, approaching its freezing temperature, at which point atoms aggregate to form initial crystallization points (nuclei) at a supercooling point.
- Crystallization: As cooling continues, crystallization nuclei grow independently in three dimensions (forming dendrites or treelike crystalline structures) until they touch adjacent crystals.
The growth stops upon crystal contact.
Tightly packed crystals form grains, with their boundaries called grain boundaries.

Grain Boundary

Grain boundaries are transitional regions between differently oriented adjacent crystal grains.
These form when growing crystals meet, marking a transition zone.

Crystal Imperfections

Real crystals usually have varied defects.
Defects like point, line, or plane defects considerably impact metal properties.

Point Defects

Impurities: Interstitial or substitutional impurities may distort the crystal lattice.
Vacancies: Vacancies allow atoms to move within the crystal lattice, thus affecting its behavior.

Line Defects (Dislocations)

Dislocations arise from atom rows' movement within the lattice, causing deformation.
Dislocations deform material in single steps across the crystal structure and eventually leave the crystal.

Deformation of Metals

Stress below the proportional limit results in reversible atom displacement, like stretching a bond, as stress is released, original crystal structure is maintained
Exceeding the proportional limit leads to permanent deformation (dislocation), where the structure does not revert to its original shape after the load is released.
Continued deformation leads to atom separation and fracture (loss of cohesion).

Alloys

Pure metals are too soft for dentistry.
Alloys (metal mixtures) improve mechanical properties.
- For example, alloying gold with 5% copper creates a harder, stronger material.
Most alloys solidify over a range of temperatures, rather than at a singular temperature like pure metals.

Tarnish and Corrosion

Tarnish refers to discoloration or surface finish loss of metal, often stemming from pigment-producing bacteria, drugs that leave stains, food debris, dental plaque, and calculus deposited on restorations, and the formation of thin films (oxides, sulfides, chlorides) on the surface.
Tarnish serves as a precursor to the more extensive corrosion.

Corrosion

Corrosion involves a metal or alloy degrading through chemical or electrochemical reactions with its environment.
Oral environments (containing water, salt, oxygen, bacteria, proteins, and ions like chloride and hydroxide) contribute to metal corrosion in the oral cavity.
Corrosion types include:
- Chemical Corrosion (dry corrosion): Can occur due to direct combination of metallic and non-metallic elements, forming compounds through reactions (oxidation, halogenation, or sulfurization). Sulfur, for example, can cause silver sulfide formation. Oxidation also happens among silver-copper amalgam materials, thus demanding careful storage in cool, dry environments.
- Electrochemical Corrosion (wet corrosion): Requires water or electrolytes and pathways for electron transport.

Electrochemical Cell Components

Anode: Electrode with lower potential; oxidation occurs, forming +ions and releasing electrons.
Cathode: Electrode with higher potential; reduction occurs, consuming electrons to create +ions.
Electrolyte: Substance supplying ions for current flow between the electrodes.

Types of Electrochemical Corrosion

Galvanic Corrosion: Dissimilar metals in contact form an electrochemical cell with one metal becoming the anode (corroding) and the other the cathode. An example of this is dental amalgam (anode), gold alloy restorations (cathode) and saliva as an electrolyte. Galvanic shock can be alleviated with a varnish coating.
Stress Corrosion: Stress in metals, like cold working, raises internal energy, increasing corrosion tendency, often leading to specific regions of the metal being preferentially affected.
Concentration Corrosion (Crevice Corrosion): Uneven oxygen concentration in the oral environment results in localized corrosion, often in pits (regions of low oxygen), leading to pits or crevice corrosion.

Protection from Corrosion

Passivation: Formation of a stable surface oxide layer prevents oxidation/metal degradation and protects the metal.
Polishing: High polishing of oral metal alloys create smooth, glossy surfaces, reduces crevice corrosion by making them difficult for fluids and bacteria to collect.
Decreasing Anode/Cathode Ratio: Increasing the ratio of anodes to cathodes lowers the corrosion rate.

Effect of Corrosion

Corrosion products can weaken restorations and damage appearance.
Metal ions from corrosion can affect patient health, causing metallic taste sensations and potentially causing toxicity
Corrosion may roughen surfaces, increasing plaque accumulation and creating bad odors.
Corrosion may cause pain and swelling, without visible infection.
Corrosion can lead to migration, targeting other body parts and causing inflammation.

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Description

Test your knowledge on the properties and applications of metals in dentistry. From the lost wax technique to corrosion, this quiz covers various aspects of dental materials and their unique characteristics. Perfect for dental students and professionals looking to refresh their understanding of metal usage in dental applications.