Dental Materials Quiz

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Questions and Answers

What is a primary advantage of high copper alloys compared to low copper alloys?

  • Reduction in creep (correct)
  • Higher tendency to corrode
  • Smaller particle size
  • Increased expansion due to moisture

Which shape of silver alloy particles has the highest compressive strength?

  • Irregular shape
  • Spherical shape (correct)
  • Admixed shape
  • Cubic shape

What happens to amalgam during its setting process in terms of dimensional changes?

  • Initial contraction followed by expansion (correct)
  • Only expansion occurs
  • Only contraction occurs
  • No dimensional changes happen

Which of the following metals is defined as a noble metal?

<p>Palladium (C)</p> Signup and view all the answers

What characteristic makes gold particularly useful in dental applications?

<p>Excellent resistance to corrosion (D)</p> Signup and view all the answers

What is creep in the context of amalgam?

<p>Permanent deformation over time due to stress (D)</p> Signup and view all the answers

Which of the following base metals is known for having a high tendency to corrode?

<p>Copper (C)</p> Signup and view all the answers

What is an important consideration when using amalgam due to its mercury content?

<p>It should be avoided due to slow elimination from the body (B)</p> Signup and view all the answers

What primarily affects the setting time of alginate materials?

<p>Temperature and water to powder ratio (A)</p> Signup and view all the answers

Which factor contributes to the loss of accuracy in alginate impressions over time?

<p>Evaporation of moisture (B)</p> Signup and view all the answers

What is the main consequence of under mixing alginate materials?

<p>Decreased tear strength (D)</p> Signup and view all the answers

How does the strain rate dependence of impression materials affect their mechanical response?

<p>Higher strain rates result in higher values of modulus (B)</p> Signup and view all the answers

What is the primary reason for adding palladium to gold in dental applications?

<p>To enhance hardness and white color. (C)</p> Signup and view all the answers

What is the role of sodium phosphate in alginate materials?

<p>Controls the working time (C)</p> Signup and view all the answers

What characterizes high noble metals?

<p>Contain more than 60% noble metal and 40% gold. (D)</p> Signup and view all the answers

What happens to the elastic recovery of an alginate impression material when the amount of deformation increases during removal?

<p>It results in permanent deformation (D)</p> Signup and view all the answers

What is the primary mechanical property that distinguishes ceramics from metals and polymers?

<p>Brittleness (A)</p> Signup and view all the answers

What is a significant disadvantage of using alginate for impressions?

<p>Limited surface detail (D)</p> Signup and view all the answers

What outcome occurs when the coefficient of thermal expansion (CTE) of a veneer is greater than that of the supporting ceramic material?

<p>The veneer remains in tension and may fracture (D)</p> Signup and view all the answers

How does the melting range of an alloy differ from a single melting temperature?

<p>It allows for a range between liquidus and solidus temperatures. (C)</p> Signup and view all the answers

Which method can help minimize wear of ceramic restoration surfaces?

<p>Using a smooth restoration surface (D)</p> Signup and view all the answers

Which of the following properties is crucial for preventing restoration failure under occlusal forces?

<p>High modulus of elasticity. (A)</p> Signup and view all the answers

What effect does an increase in temperature have on the working and setting times of alginate materials?

<p>Shortens both times (D)</p> Signup and view all the answers

What type of crown uses a porcelain layer fused to a metal base?

<p>Porcelain fused to metal (PFM) crown (A)</p> Signup and view all the answers

What is the primary composition of predominantly base metal alloys?

<p>Minor amounts of noble metals and complex compositions. (B)</p> Signup and view all the answers

What is a common issue with nickel and cobalt based dental alloys?

<p>They exhibit questionable biocompatibility. (C)</p> Signup and view all the answers

What characteristic should be matched to prevent failure at the bond between ceramic and alloy materials?

<p>Coefficient of thermal expansion (CTE) (B)</p> Signup and view all the answers

What effect does heat treatment have on the hardness of alloys?

<p>It can increase hardness. (B)</p> Signup and view all the answers

Why are ceramics considered biocompatible?

<p>They have minimal adverse effects on biological tissue (C)</p> Signup and view all the answers

What is the definition of 'yield strength' in the context of dental alloys?

<p>The maximum stress that can be applied without permanent deformation. (B)</p> Signup and view all the answers

Which factor is a critical aspect in enhancing the bond strength between ceramic and alloy in restorations?

<p>Roughening the surface interface (A)</p> Signup and view all the answers

What happens when a ceramic experiences expansion at a higher rate than the supporting alloy due to differing CTEs?

<p>The bond may fail due to tension (A)</p> Signup and view all the answers

What is the main difference in composition between cp-Ti and Ti-6Al-4V?

<p>cp-Ti contains 99% titanium, while Ti-6Al-4V contains 90% titanium, 6% aluminum, and 4% vanadium. (D)</p> Signup and view all the answers

What determines the grade of cp-Ti alloy?

<p>The amount of oxygen present in the alloy. (A)</p> Signup and view all the answers

What protective feature does titanium implants exhibit due to exposure to air?

<p>A spontaneously formed oxide layer. (D)</p> Signup and view all the answers

Which dental cement type is generally stronger for providing mechanical support in a restoration?

<p>High strength resin bases. (D)</p> Signup and view all the answers

Which of the following cements is categorized as a Type II dental cement?

<p>Cements for restorative materials. (B)</p> Signup and view all the answers

Which material often provides thermal protection for the pulp in a dental restoration?

<p>High strength resin bases. (D)</p> Signup and view all the answers

What is a significant property of Ti-6Al-4V that makes it widely used in medical implants?

<p>Superior biocompatibility and mechanical properties. (C)</p> Signup and view all the answers

How does the oxide layer on titanium implants contribute to their functionality?

<p>It inhibits low-charge transfer and prevents corrosion. (A)</p> Signup and view all the answers

What types of waxes are classified under natural dental waxes?

<p>Animal-based, plant-based, and mineral-based (A)</p> Signup and view all the answers

How do waxes generally change when temperature increases past their melting point?

<p>They transition to a liquid state with decreased viscosity (B)</p> Signup and view all the answers

What is the effect of applied force on the viscosity of waxes?

<p>Waxes exhibit shear-thinning behavior under force (A)</p> Signup and view all the answers

What does the term 'residual stress' in waxes refer to?

<p>Stress remaining from manipulation during various processes (A)</p> Signup and view all the answers

What is the typical behavior of waxes regarding flow at room temperature?

<p>They should exhibit little or no flow (C)</p> Signup and view all the answers

What happens to the molecular structure of waxes under long-term stress?

<p>They may exhibit time-dependent deformation (D)</p> Signup and view all the answers

What is a characteristic of agar compared to other waxes based on wettability?

<p>It has a small contact angle promoting good wettability (D)</p> Signup and view all the answers

What does the term 'flow' refer to in the context of waxes?

<p>Change in shape under applied force (D)</p> Signup and view all the answers

Flashcards

Amalgam composition effects

The amount of copper in an amalgam affects its properties. High copper amalgams are stronger, resist corrosion better, and don't expand as much as low copper amalgams.

Amalgam shape & properties

The shape of silver alloy particles in amalgam affects its properties. Spherical particles give higher compressive strength, while irregular particles provide more interlocking strength and higher surface area.

Amalgam dimensional change

During the setting of amalgam, there is a contraction phase followed by an expansion phase.

Amalgam creep

Creep is the slow deformation (bending) of amalgam under constant stress over time.

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Amalgam brittleness

Amalgam is a brittle material, and the risk for fracture is higher in the early restorations.

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Noble metals (dental)

Noble metals like gold, palladium, and platinum are highly resistant to corrosion in the oral environment.

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Base metals (dental)

Base metals like silver and copper have a higher tendency to corrode in the oral environment compared with noble metals.

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Amalgam Toxicity

Mercury is toxic and should be handled carefully. Amalgam generates little mercury vapor, but minimizing its usage is preferred.

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Noble Metal Alloy Classification

Categorization of alloys based on gold and noble metal content.

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High Noble Alloy

Alloy with more than 40% gold and more than 60% noble metals.

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Noble Alloy

Alloy with more than 25% noble metal (can be without gold).

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Predominantly Base Metal Alloy

Alloy with less than 25% noble metals (can be without gold).

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Melting Range

Casting alloys don't melt at a single temperature. Instead, they have a melting range.

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Liquidus Temperature

Temperature where all the alloy begins to melt (upper range).

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Solidus Temperature

Temperature where all the alloy solidifies (lower range).

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Hardness in Alloys

Measure of how easily an alloy can be indented or polished.

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Cp-Ti

A type of titanium with 99% titanium content. Its strength varies depending on the oxygen content, with grade 1 having the lowest and grade 4 having the highest.

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Ti6Al4V

An alloy composed of 90% titanium, 6% aluminum, and 4% vanadium. It has excellent corrosion resistance and is widely used as an implant biomaterial due to its biocompatibility, mechanical strength, and ability to integrate with bone.

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Titanium Biocompatibility

Titanium's biocompatibility is due to the spontaneous formation of a self-healing oxide layer when it is exposed to air or body fluids. This oxide layer inhibits corrosion, prevents low-charge transfer, and makes it biocompatible.

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Dental Cements: Type I

Luting agents used to bond permanent and temporary tooth structures. They come in water-based (glass ionomer), oil-based (ZOE), and resin-based (RMGI) varieties.

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Dental Cements: Type II

Used to support restorative materials. They are categorized by strength, where high strength is more suitable as a foundation and low strength is better for liners.

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Dental Cements: Type III

Liners or bases placed within the cavity preparation. They provide protection and support for the tooth's pulp. High strength materials like glass ionomer, RMGI, and zinc phosphate are suitable for this purpose.

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Base vs. Cement: Strength

Bases are generally stronger than cements. They provide mechanical support and thermal protection for the restoration, especially important for metal restorations due to their high thermal conductivity.

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Dental Cement Types & Uses

Dental cements have different types with distinct applications and compositions. They are crucial for various procedures in dentistry and their understanding is necessary for optimal treatment.

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Alginate setting time

The time it takes for the chemical reaction in alginate to be complete and the material to solidify.

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Alginate working time

The time you have to mix and work with the alginate before it starts to set.

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How does temperature affect alginate?

Higher temperatures shorten both the setting time and working time of alginate.

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Why is water/powder ratio important for alginate?

Changing the water/powder ratio affects both the setting time and strength of alginate. A thinner mix sets slower and is weaker.

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What is elastic recovery in alginate?

The ability of alginate to return to its original shape after being compressed or stretched.

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What is permanent deformation?

The amount of change in shape that remains after the compression force is removed from an alginate impression.

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Strain rate dependence

The mechanical response of a material (like alginate) depends on how quickly it is loaded or deformed.

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Creep

The slow deformation of a material under constant stress over time.

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What is the effect of increased hardness on alginate?

As the hardness of a material increases, the amount of contact it has with alginate decreases. This is because harder materials are less likely to deform and mold to the alginate.

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How does water affect the hardness of materials?

Materials tend to be harder when dry compared to when they are wet. Water can soften materials by allowing their molecules to move more freely.

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What is the key factor for good detail reproduction with dental stones?

Good wetting between the alginate and gypsum is essential for accurate reproduction of detail in dental casts. This allows the gypsum to flow into the contours of the alginate impression.

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What is the difference between waxes and dental stones regarding wetting?

Waxes like agar have a small contact angle, indicating good wettability and detail reproduction, while addition silicone (non-water based) and gypsum have limited reproduction due to poor wettability.

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What is the melting range of wax?

Waxes do not melt at a single temperature due to their varying composition. Instead, they have a melting range, meaning they transition from solid to liquid over a specific temperature interval.

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What is the significance of wax flow in dentistry?

Flow is the ability of wax to change shape under force. Dental waxes should exhibit considerable flow at the time of preparing the wax pattern for easy manipulation. However, they should have minimal flow at room temperature for stability.

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What is residual stress in wax and how does it occur?

Residual stress is stress present in wax as a result of manipulation like heating, cooling, or bending. These stresses are released over time as the wax warms up and its molecules move more freely.

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What factors influence wax flow?

The flow of wax is influenced by temperature, time, and the applied force. Higher temperatures, longer times, and greater forces generally lead to increased flow.

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Slip Casting

A ceramic forming technique where a liquid slip (a suspension of ceramic powder in water) is poured into a plaster mold. As the plaster absorbs water from the slip, a layer of ceramic solid forms on the inside of the mold, creating the desired shape.

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Sintering

A process where powder particles are heated to a high temperature, causing them to bond together and form a solid mass. The heat facilitates diffusion between particles, leading to densification and strengthening of the material.

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CTE (Coefficient of Thermal Expansion)

A measure of how much a material expands or contracts in size per unit length when heated or cooled by one degree Celsius.

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Debonding due to CTE Difference

When two materials with different CTE values are bonded together, heating or cooling can lead to strain differences, potentially causing the bond to break. The material with a higher CTE will expand more, putting stress on the bond.

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Biocompatible Ceramics

Ceramics that are safe and compatible with biological tissue. They minimally trigger adverse reactions in the body, allowing for integration with bone and tissues.

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Ceramics in Restorations (PFM and All Ceramic)

Ceramics are used in dental restorations in various forms. Porcelain fused to metal (PFM) crowns use a metal framework covered with porcelain, while all-ceramic crowns are entirely made of ceramic.

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Ceramic-Alloy Bonding

The bond between ceramic and metal in PFM crowns is achieved through chemical reactions and mechanical interlocking. The oxide layer on the metal surface chemically bonds with the ceramic, while roughening the surface further enhances the bond strength.

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Failure in Ceramic-Alloy Bonding

Failure can occur if the oxide layer on the metal is inadequate, or if there's a significant difference in thermal expansion between the ceramic and metal, causing stress during heating or cooling.

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Study Notes

General Guidelines

  • Review all lectures, including online and in-class sessions.
  • Exams are cumulative. Refer to previous guidelines for midterm information.
  • Follow the recommended textbook pages listed in the course syllabus.
  • Use the "Self-Test Questions" at the end of each chapter to aid in studying.

Adhesion and Bonding

  • Understand the types of bonds in dentistry (mechanical and chemical).
  • Mechanical interlocking relies on rough surfaces creating a bond between materials.
  • Chemical bonding uses chemical reactions to create a bond.
  • Acid etching removes the smear layer without demineralization.
  • 37% phosphoric acid and EDTA can be used to remove the smear layer.
  • Self-etching systems use monomers like 10-MDP, 4-META, and phenyl-P.
  • Bonding agents, primers, and resins use specific compounds like HEMA and 4-META; Mneumonic is facebook primed us for scoail media and is now called meta, You see hema on social media.
  • Understand the different bonding strategies (etch and rinse, self-etch, and universal) and the steps involved.
  • Bonding agents include Bis-GMA, UDMA, and TEGDMA. These are unfilled/lightly filled monomers. Think like the CIA are agents and GMA, UDMA, and TEGDMA sound like agents.
  • Understand the differences between bonding strategies (etch and rinse, self-etch, and universal) and the number of steps/bottles.

Challenges of Bonding to Dentin

  • Retention is critical for the bond to last the duration of service.
  • Leaks or bacteria penetrating the interface can lead to sensitivity, failure, staining, secondary caries, and inflammation.
  • Biomaterial degradation can also affect retention.
  • Proper material preparation, technique, and handling are important.
  • Lamp calibration is crucial for biomaterial performance.
  • The presence of water and organic components influence surface energy of dentin.
  • Keeping collagen expanded is important.
  • Chlorohexidine is mentioned as a clean/disinfectant.
  • Gluma used as a collagen crosslinking agent.

Amalgam

  • Amalgam is made of silver alloy, mercury and small quantities of zinc and palladium.
  • Amalgamation involves the dissolution of the components into mercury.
  • The crystallization of new products continues until all the liquid mercury is consumed.
  • There are three gamma phases in low copper amalgam: Gamma Y1 is silver-mercury, Gamma Y2 is tin-mercury
  • High copper alloys have higher strength, less corrosion, less creep, and better longevity at the margins but low copper alloys are less expensive with longer-term expansion issues due to moisture and have been largely replaced by high copper amalgams which are stronger and don't expand as much.

Metals - Amalgam (Composition and Chemical Reaction)

  • Identify the gamma phases (1, 2).
  • Silver powder composition, types, influences on properties.
  • Silver powder composition in amalgam includes silver + tin + copper.
  • The amount of copper changes the properties of amalgam.

Metals and Alloys

  • Noble metals are resistant to corrosion, good malleability, and have low melting points.
  • Gold is the most well-known of dental metals, excellent resistant to corrosion.
  • Palladium has excellent resistance to corrosion, medium melting point, and a harder element than gold.
  • Platinum is harder than palladium but is rarely used due to cost.
  • High noble metal alloys contain greater than 40% gold content and more than 60% noble metals. Predominantly base metals do not have to have any gold but less than 25% noble metals are used.
  • High noble alloys are expensive, contain higher densities, and often have copper and silver added to increase hardness and strength. Titanium alloys are extensively used as implant biomaterial due to suitable biocompatibility, mechanical properties, and osteointegration. Ti6Al4V is an example

Ceramics

  • Identify the composition, phases (crystal and glass) of dental ceramics.
  • Glass-dominated ceramics are used mostly for aesthetics, such as veneers, but have low strength.
  • Crystal-dominated ceramics have improved strength but are more opaque.
  • Crystalline ceramics are the strongest.
  • Crystal base materials like leucite, fluorapatite, spinel, zirconia, alumina, lithium disilicate, and lithium silicate, and the glassy phase comprises silica(quartz).
  • Different manufacturing methods for ceramics include stacking, pressing, milling, additive manufacturing, and slip casting

Ceramics (Manufacturing Methods)

  • Detail the different ways ceramics are made (stacking, pressing, machining, and slip casting.)

Ceramics (Properties)

  • Understand the properties of ceramics, including mechanical and thermal properties.
  • Ceramics are hard, have high compressive strength and moduli, and have low tensile strength.
  • Briefly describe the coefficient of thermal expansion (CTE).

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