chapter 43: Restorative and Esthetic Dental Materials

Amalgam is the technical name for

"silver fillings"

dual-cured

A composite resin material that has both light-cure and auto-cure properties

alloy

A mixture of two or more metals that dissolved with each other when in liquid state

Nonmercury Alloys

A nonmercury alloy called Galloy, composed of gallium, indium, and tin, was approved by the American Dental Association (ADA), but has not been researched for its potential because of the advancement of composite resins.

force

A push or a pull

16. What item is used to determine the color of composite for a procedure?

A shade guide is used to determine the color of composite.

gold

A soft, yellow, corrosive-resistant metal that is used in the making of indirect restorations

22. What material would you use to prepare for provisional coverage?

Acrylic resin or composite resin would be used to prepare for provisional coverage.

malleability

Ability of a material to withstand deformation under compressive stress without permanent damage

9. What does copper provide to an amalgam restoration?

Copper provides strength and corrosion resistance to amalgam.

coupling agent

Agent that strengthens resin by bonding filler to the resin matrix

Trituration

Also known as amalgamation, trituration is the process by which mercury and alloy powders are mixed together to form the mass of amalgam needed to restore the tooth. The preloaded capsule of amalgam alloy and mercury contains a pestle, which aids in the mixing process. Before the capsule is placed into the amalgamator, many types of capsules require the use of an activator, which breaks the separating membrane (Fig. 43.12). The activated capsule is placed into the amalgamator, and the cover is closed to prevent mercury vapors from escaping during trituration.The amalgamator is set to operate for the length of time specified in the manufacturer's directions (Table 43.2). In a proper mix, the mass of amalgam is free of dry alloy particles and holds together as a single unit. The mix is placed from the capsule into an amalgam well; the pestle is removed, and the mix is loaded into the amalgam carrier. TABLE 43.2

The Application of Dental Amalgam Preparation

Amalgam is supplied by the manufacturer in sealed single-use capsules with the proper ratio of alloy powder in one side of the capsule and mercury in the other side, separated by a thin membrane. This ensures an accurate ratio and reduces the possibility of exposure to any of the materials. Immediately after use, the capsule is reassembled and is discarded with nonregulated waste. Capsules are available in three sizes: 400 mg and 600 mg of alloy, which are the appropriate amounts for a Class I or Class II conservative restoration, and 800 mg of alloy, which is the appropriate amount of material for a multisurface restoration (Fig. 43.11). If more than this amount of amalgam is required, additional capsules are placed within the setup and triturated as needed.

11. How is the amalgam triturated?

Amalgam is triturated in an amalgamator.

10. Where do you dispose of amalgam scraps?

Amalgam scraps are placed in a wide-mouthed, air-tight container marked "Noncontact Amalgam Waste for Recycling". When the container is full, it is sent to a recycler.

amalgam

An alloy, with one of the constituents being mercury.

Electrical Properties

An electrical current (also referred to as galvanic action or shock) can take place in the oral cavity when two different or dissimilar metals are present (Fig. 43.3). Conditions that can create these electrical currents include the following: • Saliva contains salt, which makes it a good conductor of electricity. • Two metallic components of different composition (two different types of metals in the restorations or a metal object such as a fork placed in the mouth) can act as the battery.

galvanic

An electrical current that takes place when two different or dissimilar metals come together

pestle

An object that is moved vertically to pound or pulverize a material

esthetic

Artistically pleasing and beautiful appearance

Commercial Examples of Composite Resins

Classification Brand Microfilled Durafill, Renamel, Matrixx, Epic, Heliomolar, Ivoclar, Vivadent, Virtuoso, Sculptable Hybrids Herculite, Prodigy, Spectrum, Charismas Microhybrid Filtek, Synergy, Gradia, Point 4, Renamel, Tetric, Venus Nanofilled Premise, Aelite Esthetic Enamel, Clearfill Majesty, Artiste

Shade Selection

Color matching is one of the most critical aspects when working with composite resins. If the correct shade is not selected, this will be apparent to the patient after the restoration is in place. A shade guide is always used when determining the correct shade for application The composite kit may include its own shade guide; most manufacturers cross-reference their shades with those of the VITA Shade Guide, which is a universally adopted shade guide. The following are tips for choosing a shade: • Determine tooth shades if possible in daylight or with standardized daylight lamps and not under normal ambient lighting. • The entire surroundings should be kept free from bright colors. If necessary, ask the patient to remove lipstick and to cover brightly colored clothing. • Make your choice quickly; always accept the first decision because the eyes begin to tire after approximately 5 to 7 seconds.

Composite Resins

Composite resins have become the most widely accepted and used material of choice by dentists and patients (Fig. 43.15). Composite resins are now being placed throughout the mouth; in anterior teeth because of their esthetic qualities, but with new advances in their makeup, they are being placed in posterior teeth as well.Initially composite resins were not as strong as amalgams or gold alloy restorations, but they are now designed to meet the needs of a specific area of a tooth or mouth. This tooth-colored material is versatile, with many indications.

Corrosive Properties

Corrosion is the reaction that occurs within a metal when it is exposed to corrosive factors such as temperature, humidity, 717and saline. Certain foods contain metallic forms that cause corrosion of a dental material. The surface discoloration that we see in older amalgam restorations in the mouth is referred to as tarnish (Fig. 43.4). Most corrosion, however, involves surface discoloration and can be removed easily with the use of polishing agents.

wetting

Covering or soaking something with a liquid

Composition of Dental Amalgam

Dental amalgam is the end result of mixing approximately equal parts of mercury (43 to 54 percent) and an amalgam alloy powder (46 to 57 percent) (Fig. 43.8). The alloy powder is a combination of metals. Amalgam alloy powder is composed of the following metals: • Silver, which gives it its strength • Tin, for its workability and strength• Copper, for its strength and corrosion resistance • Zinc, to suppress oxidationThe main differences in the composition and classification of dental amalgam alloy powders are based on (1) alloy particle shape and size, (2) copper content, and (3) zinc content.

8. Would dental amalgam be placed in anterior or posterior teeth?

Dental amalgam would be placed in posterior teeth. Composite resins are used in anterior teeth due to esthetics.

15. When composite resins are light-cured, what factors might contribute to the need for a longer curing time for the material?

Depth of restoration and color might contribute to the need for a longer curing time.

Direct Restorative and Esthetic Materials

Direct restorative and esthetic materials are applied to a tooth or teeth while the material is pliable and can still be adapted, carved, and finished. Materials selected for these types of restorative and esthetic procedures are amalgam, composite resins, glass ionomers, temporary restorative materials, and tooth-whitening products.

strain

Distortion or change produced as a result of stress

Application Properties

FLOW- Dental materials are designed to have a certain amount of flow for placement; this allows the material to fill in the preparation of the tooth. ADHESION-Without proper adhesion, microleakage can occur, and the restoration could come out. Characteristics of dental materials that can affect the adhesion process are wetting, viscosity, surface characteristics, and film thickness. Wetting is the ability of a liquid to flow over the surface and come into contact with the small irregularities that may be present. For example, water has high wetting ability because it flows easily. Viscosity is the property of a liquid that causes it not to flow easily. A liquid with high viscosity, such as maple syrup, does not flow easily and is not effective in wetting a surface. The surface characteristics that are important in wetting are the chemical nature of the tooth surface and how the dental material flows on that surface. An example of this is how rain on your windshield runs, but when a chemical is added to the windshield to help repel the rain, the rain beads up. For adhesion to take place and remain permanent, the cement must have a thin film thickness of 25 microns or less to join the tooth and restoration. It is important to remember that the thinner the film thickness, the stronger the adhesive junction. RETENTION-they will not adhere to each other naturally. For example, amalgam (silver fillings) and cast metals will not naturally adhere directly to tooth structure.Because amalgam and tooth structure do not adhere to each other, a traditional cavity preparation must include a retention form within the tooth structure. The dentist will use a bur or a hand (manual) cutting instrument to produce this retention form (creating a crevice in the tooth that the material can lock into). Even though retention holds the material in place, it does not completely seal the two structures together. Micro-leakage can still occur between the material and the tooth if an additional material such as a bonding material is not placed to create a seal. CURING-

Pigments

For a composite material to match a tooth color, coloring must be added. Most often, the coloring comes from an inorganic substance.

matrix

Foundation that binds a substance together; continuous phases (organic polymer) in which particles of filler are dispersed in composite resin

18. What are some of the most common uses of glass ionomer materials?

Glass ionomer materials are commonly used as restorative materials, liners, bonding agents, and permanent cements.

25. What type of restoration is made in the dental laboratory?

Indirect restorations are made in the dental laboratory.

Glass Ionomers

Glass ionomers represent one of the most versatile dental materials available. This material has been shown to have an excellent biocompatibility within the oral environment. The adaptability of the glass ionomer by altering the chemical properties allows the material to be used for different purposes within the mouth. This chapter discusses glass ionomers used in the restorative sense such as for restorations, for core buildups, and as sealants. Chapters 44 and 45 introduce glass ionomers used as liners, bonding agents, and cements. Because glass ionomers have the ability to adhere chemically (not mechanically) to teeth, the need to prepare the tooth structure is not as extensive as the preparation for an amalgam or composite resin. The most unique feature of glass ionomers is the release of fluoride after the final setting. This provides the added advantage of inhibiting decay. This type of material is especially desirable for the following applications: • Primary teeth: Because of the fluoride release and minimal cavity preparation requirement, glass ionomers are the material of choice for the restoration of carious primary teeth. • Final restorations in nonstressed areas such as class V and root surfaces: This material is widely used to restore lost tooth structure such as occurs as a consequence of decay or cervical abrasion. • Sealants: The material is mixed to a more fluid consistency to allow flow into the depths of the pits and fissures of the posterior teeth. • Core material for buildups: Some dentists favor glass ionomers over amalgam because of ease of placement, adhesion, fluoride release, and thermal qualities. • Provisional (longer term temporary) restorations. In the term glass ionomer, the word glass actually refers to a combination of glass, ceramic particles, and a glassy matrix. From this special glass combination, the material derives its translucency and prolonged fluoride release. Ionomer refers to ion-cross-linked polymers, such as acrylic acid, tartaric acid, and maleic acid (common materials found in most dental cements). The type of polymer and its molecular weight ensure excellent adhesion and resistance to acid erosion.

ceramic

Hard, brittle, heat- and corrosive-resistant material such as clay.

auto-cured

Hardened or set by a chemical reaction of two materials

High-Copper Alloys

High-copper alloys, frequently used in dentistry, are named this because they contain a higher percentage of copper than previous alloys. High-copper alloys are classified according to their particle shape: spherical (round particles) or irregular (rough, lathe-cut particles) (Fig. 43.9). These particle shapes influence the trituration and working characteristics (condensing and carving) of the resulting amalgam mixture. A high-copper alloy is made up of 40 to 70 percent silver, 8 to 28 percent copper, and 15 to 30 percent tin. The percentages are expressed as percentages of the composition by weight. Table 43.1 describes the composition and classification of dental amalgam alloy powder

14. Which filler type of composite resin is recommended because of its versatility?

Hybrid resin is recommended for its versatility.

21. How could IRM be utilized in a pediatric practice?

IRM can be utilized in a pediatric practice to restore primary teeth that are about to be replaced by permanent teeth.

20. What does the abbreviation IRM stand for?

IRM stands for intermediate restorative material.

Application of Composites

Important differences in the application or technique of an amalgam restoration versus a composite restoration include the following: • The cavity preparation for a composite resin is designed to hold the resin material by means of a bonding system rather than by retention added into the preparation. • Some dental materials cannot be used with composite resins. • The matrix system will vary with the composite resins. • Placement of composite resin may be accomplished in increments if it is a large restoration; light-curing is performed before additional increments are added.

Filler

Inorganic fillers used in composite resins include quartz (a hard rock-forming mineral), glass, silica (white or colorless crystalline compound) particles, and colorants. These fillers add the strength and other characteristics needed in a restorative material. The ability of these materials to reflect light creates an esthetically pleasing restoration. The amount of filler, the particle size, and the types of fillers used are important factors in determining the strength and wear-resistant characteristics of the material (Fig. 43.16). These factors also influence the polished finish of the restoration. Composites are classified by particle size as megafill, macrofill, midifill, minifill, microfill, and nanofill. Composites that have a combination or mixed range of particle sizes are referred to as hybrids (Fig. 43.17).Macrofilled composites, also known as conventional or traditional composites, were used primarily in the 1960s and 1970s. This type of composite contained the largest of filler particles, providing the greatest strength, but its use resulted in a duller, rougher surface. Macrofilled composites are self-cured and were used in areas where greater strength was required to resist fracture. Microfilled composites came about in the 1980s; the main difference noted with this type of composite resin was that it contained inorganic fillers that were much smaller than those in a macrofilled composite. Microfilled composite resins are light-cured and are capable of producing a highly polished finished restoration; they were used primarily in anterior restorations, for which smoothness and esthetics were of primary concern. Hybrid composites are used most often today. They contain a mixed range of particle sizes. Hybrid composites are cured with a visible light-curing method and can be polished smoother than macrofilled composites, yet they have greater strength than is seen with microfilled composites. Hybrid composites also have high wear resistance and excellent shading characteristics. Flowable composites are supplied as a hybrid or nanofilled composite with enough filler included to make the material wear resistant. Flow is the key term in describing this type of composite. The material is designed to flow more easily into the more conservative preparation. An example would be a class V noncarious lesion caused by toothbrush abrasion. Flowable composites are provided in a syringe-like device that permits precise placement of the material in the cavity preparation. Sealant composites resemble flowable composites but have the viscosity to allow the material to flow into the pits and fissures of the tooth surface. No preparation with the handpiece or hand instruments is needed for placement, but the tooth surface is etched to prepare for application of the material (see Chapter 59 for the application).

filler

Inorganic material that adds strength and other characteristics to composite resins

Application

Light-cured composite resins are supplied in a single-paste, lightproof syringe. These resins do not require mixing and are used directly from the syringe with the addition of a syringe tip. The paste contains both the photo initiator and the amine activator and will not polymerize until it is exposed to the curing light. The material is supplied in a kit that includes varying shades of the composite resin, along with an etching and bonding system that works specifically for the application process of that material (Fig. 43.19). FIG. 43.19 Composite resin kit. (Courtesy 3M ESPE, St Paul, MN.) Traditional composite resin materials were placed incrementally in layers and cured before placing another increment. With the advancement in makeup of composites, bulk-filling for posterior composites through a syringe tip allows for precise application and a reduction in time.

microleakage

Microscopic space located at the interface of the tooth structure and the sealant or restoration

7. What metals make up the alloy powder in amalgam?

The alloy powder in amalgam contains silver, tin, copper, and zinc.

Best Management Practices for Mercury Amalgam

Noncontact (Scrap) Amalgam • Place noncontact, scrap amalgam in a wide-mouthed, airtight container that is marked "Noncontact Amalgam Waste for Recycling." • Make sure the container lid is well sealed. • When the container is full, send it to a recycler. Amalgam Capsules • Stock amalgam capsules in a variety of sizes. • After mixing amalgam, place the empty capsules in a wide-mouthed, airtight container that is marked "Amalgam Capsule Waste for Recycling." • Capsules that cannot be emptied should likewise be placed in a wide-mouthed, airtight container that is marked "Amalgam Capsule Waste for Recycling." • Make sure the container lid is well sealed. • When the container is full, send it to a recycler. Disposable Chairside Traps • Open the chairside unit to expose the trap. • Remove the trap and place it directly into a wide-mouthed, airtight container that is marked "Contact Amalgam Waste for Recycling." • Make sure the container lid is well sealed. • When the container is full, send it to a recycler. • Traps from dental units dedicated strictly to hygiene may be placed in with the regular garbage. Reusable Chairside Traps • Open the chairside unit to expose the trap. • Remove the trap and empty the contents into a wide-mouthed, airtight container that is marked "Contact Amalgam Waste for Recycling." • Make sure the container lid is well sealed. • When the container is full, send it to a recycler. • Replace the trap into the chairside unit. (Do not rinse the trap under running water as this could introduce dental amalgam into the waste stream.) Vacuum Pump Filters • Change the filter according to the manufacturer's recommended schedule. Note: The following instructions assume that your recycler will accept whole filters; some recyclers require different handling of this material, so check with your recycler first. • Remove the filter. • Put the lid on the filter and place the sealed container in the box in which it was originally shipped. When the box is full, the filters should be recycled. Amalgam Separators • Select an amalgam separator that complies with ISO 11143. • Follow the manufacturer's recommendations for maintenance and recycling procedures. Line Cleaners • Use nonbleach, nonchlorine-containing line cleaners, which will minimize amalgam dissolution, such as those listed in the Additional Resources section of this document.

irregular

Not straight, uniform, or symmetric

Resin Modified

Over the past several years, glass ionomer materials have improved in terms of physical properties and esthetic qualities through the addition of resin. Resin gives the material better strength, greater wear resistance, and an improved esthetic quality. The resin component also allows the material to be light-cured, auto-cured, or both.

Viscosity

Physical property of fluids responsible for resistance to flow

Polymerization

Polymerization is the process by which resin material is changed from a pliable state (in which it can be molded or shaped) into a hardened restoration. Polymerization occurs through auto-curing or light-curing. The light-curing process uses either a high-intensity blue light source, which is a combination of tungsten and a halogen, or an light-emitting diode (LED) curing light. The exact curing time depends on the following: • Composite manufacturer's instructions (most often, 20-60 seconds) • Thickness and size of the restoration (when larger quantities of the material are being placed) • Shade of the restorative material used (the darker the shade, the longer the required curing time)

The Application of Dental Amalgam

Preparation Amalgam is supplied by the manufacturer in sealed single-use capsules with the proper ratio of alloy powder in one side of the capsule and mercury in the other side, separated by a thin membrane. This ensures an accurate ratio and reduces the possibility of exposure to any of the materials. Immediately after use, the capsule is reassembled and is discarded with nonregulated waste. Capsules are available in 600 mg of alloy, which is the appropriate amount of material for a small or single-surface restoration, or 800 mg of alloy, which is used for a larger restoration (Fig. 43.11). If more than this amount of amalgam is required, additional capsules are placed within the setup and triturated as needed. Trituration Also known as amalgamation, trituration is the process by which mercury and alloy powders are mixed together to form the mass of amalgam needed to restore the tooth. The preloaded capsule of amalgam alloy and mercury contains a pestle, which aids in the mixing process. Before the capsule is placed into the amalgamator, many types of capsules require the use of an activator, which breaks the separating membrane (Fig. 43.12). The activated capsule is placed into the amalgamator, and the cover is closed to prevent mercury vapors from escaping during trituration. The amalgamator is set to operate for the length of time specified in the manufacturer's directions (Table 43.2). In a proper mix, the mass of amalgam is free of dry alloy particles and holds together as a single unit. The mix is placed from the capsule into an amalgam well; the pestle is removed, and the mix is loaded into the amalgam carrier. Amalgam should appear soft, pliable, and easily shaped when first triturated. At this stage, amalgam is transferred to the dentist in the amalgam carrier to be placed and condensed into the prepared tooth. Once it hardens, amalgam forms a very strong restoration that can withstand the mechanical properties mentioned. See Procedure 43.1: Mixing and Transferring Dental Amalgam. Condensation The amalgam is carried to the tooth by the amalgam carrier and is placed in increments into the prepared tooth, and each increment is condensed immediately with the use of an amalgam condenser. The purpose of condensation is to pack the amalgam tightly into all areas of the prepared cavity and to aid in removing any excess mercury from the amalgam mix (Fig. 43.13). Carving and Finishing With the use of hand carving instruments, the dentist is able to carve back the amalgam material to the tooth's normal anatomy, which was removed during cavity preparation (Fig. 43.14). A burnisher is used to smooth the amalgam, making sure that no irregularities are present in the restoration. Once most of the carving has been completed, the patient is instructed to bite down lightly on articulating paper. This allows the dentist to check how the new restoration occludes with the opposing tooth, and then final carvings can be made.

cured

Preserved or finished by a chemical or physical process

4 What is a source of galvanic action?

Saliva (salt conducting electrical currents) and two metals (acting as battery) are sources of galvanic action.

palladium

Soft, steel-white, tarnish-resistant metal that occurs naturally with platinum

Solubility

Solubility is the degree to which a substance will dissolve in a given amount of another substance. For example, sand has low solubility because it does not dissolve easily; sugar has high solubility because it does dissolve easily. The solubility of a dental material placed in the mouth is a matter of concern (Fig. 43.5). A material that dissolves easily in the oral environment is of limited use because it will wash away and leave the tooth structure exposed.

2. How long would you triturate Sybraloy?

Sybraloy is triturated for 13 seconds.

When a new dental material is developed, the product undergoes a strict evaluation and assessment before it is marketed to the profession.

The Council on Dental Materials, Instruments, and Equipment was formed as a subcommittee by the American Dental Association (ADA)

Condensation

The amalgam is carried to the tooth by the amalgam carrier and placed in increments into the prepared tooth, with each increment condensed immediately with the use of an amalgam condenser. The purpose of condensation is to pack the amalgam tightly into all areas of the prepared cavity and to aid in eliminating any excess mercury from the amalgam mix (Fig. 43.13).

Mercury-to-Alloy Ratios

The appropriate mercury-to-alloy ratio is very important. The ratio must contain just enough mercury to make the mix workable without containing an excessive amount of mercury. A 1:1 mercury-to-alloy ratio, also known as the Eames technique, is widely used. This ratio is one portion of mercury to one portion of alloy by weight.

Metal Reinforcement

The blend of spherical silver-tin alloy with glass ionomer produces a strong, abrasion-resistant dental material. The glass component provides a desirable balance between working and setting times, together with sustained fluoride release. The particles are a polymer of acrylic acid, which provides toughness and resistance to acid erosion. The level of metal addition also provides an optimal level of radiopacity. This product is extremely versatile in its clinical application for core buildups; for repair of fractured cusps and amalgam fillings in class I, II, and V cavities; as a base; and as an abutment for overdentures.

13. What is the common term used for dimethacrylate?

The common term for dimethacrylate is BIS-GMA.

Composition of Composite Resins

The composition of composite resins is a chemical mix that includes (1) an organic resin matrix, (2) inorganic fillers, (3) a coupling agent, and (4) tooth-colored pigments.

Coupling Agent

The coupling agent is important because it strengthens the resin by chemically bonding the filler to the resin matrix. To achieve this, filler particles are coated with an organosilane compound. The silane portion of the molecule bonds with the quartz, glass, and silica filler particles. The organic portion bonds with the resin matrix, thus bonding the filler to the matrix.

17. What is the final step in finishing a composite resin?

The final step in finishing a composite resin is the use of a polishing paste.

Finishing and Polishing

The finishing and polishing of composite resins are much different from the completion steps in an amalgam procedure. Because composite materials go from a soft pliable state to being completely hardened by polymerization, the dentist is not able to carve or make adjustments with hand instruments. Finishing burs and abrasive materials are used to contour and polish a finished composite resin. Steps in Finishing a Composite Resin • Reduction of the material is completed by the use of a white stone or a finishing diamond. • Fine finishing is performed with carbide finishing burs, then with diamond burs. • Polishing the resin begins with medium discs and finishes with superfine discs. • Finishing strips assist in polishing of the interproximal surfaces. • Polishing paste applied to a rubber cup completes the step.

23. How many drops of monomer per tooth are recommended when acrylic resin is mixed for a provisional restoration?

The recommended amount is 10 drops of monomer per tooth.

Resin Matrix

The resin matrix component of composite is a fluid-like material called dimethacrylate, also referred to as BIS-GMA. This fluid, which is the monomer, is used to make synthetic resins. BIS-GMA is the foundation of resins. By itself, it is not strong enough to be used as a restorative dental material. The addition of fillers and coupling agents provides the strength needed for the material to withstand the forces of mastication. Additional additives included in this process are the initiator, the accelerator, the retarder, and the ultraviolet (UV) light stabilizers.

24. What are the three noble metals used in dentistry?

The three noble metals used in dentistry are gold, palladium, and platinum.

Thermal Change

These thermal changes are of major concern for two reasons: (1) contraction and expansion, and (2) the need to protect the pulp from thermal shock from extreme differences in temperature. When temperature changes occur, each type of dental material will contract or expand at its own rate. It is essential that the tooth structure and the restorative material have, as nearly as possible, the same rate of contraction and expansion. Significant changes in the degree of contraction and expansion can cause a dental material to pull away from the tooth, which can result in microleakage, or a faulty restoration. This microscopic separation of material and tooth can allow oral fluids, debris, and microorganisms to enter between the restoration and the wall of a cavity preparation. The term for this process is percolation.

Mechanical Properties

This averages out to 28,000 pounds of pressure per square inch (psi) on a single cusp of a molar tooth. Dental materials used in restoring posterior teeth must have sufficient strength to withstand such force. • Tensile stress and strain pulls and stretches the material. Think about tug-of-war as an example (Fig. 43.2, A). • Compressive stress and strain results from two forces directed toward each other. An example would be chewing (Fig. 43.2, B). • Shear stress and strain occurs from the two forces of material parallel to each other sliding in opposite directions. Think about cutting a piece of paper with scissors. The blades of the scissor are parallel but work in opposite directions

Ductility and Malleability

This is a measure of a metal's ability to withstand permanent deformation by either tensile or compressive forces. Ductility is the measure of the capacity of a metal to be stretched or drawn out by a pulling or tensile force without fracturing. This property allows a metal to be made into a thin wire. Malleability is the measure of the capacity of a metal to be extended in all directions by a compressive force, such as rolling or hammering. This property allows a metal to be shaped into a thin sheet or plate.

Hardness

This is a measure of the resistance of a metal to indentation, scratching, or abrasion. It is an indication of strength and wear-ability.

tarnish

To discolor; to stain

restorative

To restore or bring back to its natural appearance

adhere

To stick or glue two items together

Amalgamation Time

Types of Amalgam Setting Time (Seconds) Dispersalloy M-2 13 Tytin M-2 4-5 Sybraloy M-2 13 Spheralloy M-2 15 Valiant M-2 13 Valiant PhD M-2 15 Velvalloy M-2 20 Amalgam should appear soft, pliable, and easily shaped when first triturated. At this stage, amalgam is transferred to the dentist in the amalgam carrier to be placed and condensed into the prepared tooth. Once it hardens, amalgam forms a very strong restoration that can withstand the mechanical properties mentioned. See Procedure 43.1: Mixing and Transferring Dental Amalgam.

19. What could contaminate the setting of glass ionomers?

Water could contaminate the setting of glass ionomers and should be avoided.

Fabrication and Application When supplied as a powder and a liquid for ce

When supplied as a powder and a liquid for cement, glass ionomers are manually mixed together on a treated paper pad, with the powder incorporated into the liquid in several increments (Fig. 43.20). The material must be completely mixed in less than 45 seconds. FIG. 43.20 Setup for mixing glass ionomer liquid and powder. For restorative purposes, glass ionomers are supplied in light-protected tubes, cartridges, tubs, or premeasured capsules (Fig. 43.21). The material can be either manipulated with a spatula and placed in the applicator, or triturated and then placed in the applicator, applied to the tooth, and light-cured. FIG. 43.21 Glass ionomers are supplied in capsules, cartridges, and individual powder and liquid bottles. (Courtesy GC America Inc., Alsip, IL.)

Carving and Finishing

With the use of hand carving instruments, the dentist is able to carve back the amalgam material to the tooth's normal anatomy, which was removed during cavity preparation (Fig. 43.14). A burnisher is used to smooth the amalgam, making sure that no irregularities are present in the restoration. Once most of the carving has been completed, the patient is instructed to bite down lightly on articulating paper. This allows the dentist to check how the new restoration occludes with the opposing tooth, and then final carvings can be made.

6 How does an auto-cured material harden or set up?

a chemical reaction of the materials being mixed together.

2 What type of reaction does a dental material undergo when distortion occurs?

stress

1 Which professional organization evaluates a new dental material?

ada

5 What are the four properties that must be considered in the application of a dental material?

are flow, adhesion, retention, and curing.

3 What happens to a dental material when it is exposed to hot and cold?

contraction and expansion

porcelain

hard, white, translucent ceramic material fabricated by firing and then glazing it to match the tooth color

stress

internal resistance to an external load

Criteria for a New Dental Material

must not be poisonous or harmful to the body. • It must not be harmful or irritating to the tissues of the oral cavity. • It must help protect the tooth and tissues of the oral cavity. • It must resemble the natural dentition as closely as possible so as to be esthetically pleasing. • It must be easily formed and placed in the mouth to restore the mouth's natural contour. • It must conform and function despite limited access, wet conditions, and poor visibility.

spherical

round

platinum

sliver-white noble metal that does not corrode in air

percolation

the process of a liquid slowly passing through a porous substance

The restorative and esthetic dental materials used most commonly in dentistry today include the following:

• Amalgam • Composite resin • Glass ionomer • Temporary restorative materials • Tooth-whitening products • Gold alloy • Ceramic castings

Cautions for Placing Glass Ionomers

• Avoid water contamination/contact with the material. • Be aware that when the material's glossy appearance has disappeared, the setting stages have begun. • Protect the matrix band from the material; the material will adhere to a metal band.

Indications for Using Dental Amalgam

• Primary and permanent teeth • Stress-bearing areas of the mouth • Small to medium-sized cavities in the posterior teeth • Severe destruction of tooth structure • As a foundation for cast-metal, metal-ceramic, and ceramic restorations • When a patient's commitment to personal oral hygiene is poor • When moisture control is problematic • When cost is an overriding patient concern

Indications for Using Composite Resins

• Restoration of class I, II, III, IV, and V restorations • Restoration of surface defects such as hypocalcification, attrition, abrasion, and congenital abnormalities • Closure of diastema • Esthetic recontouring of teeth such as peg laterals

Contraindications to the Use of Dental Amalgam

• When esthetics is particularly important, such as in the anterior teeth or in facial surfaces that can be viewed • With patients who have a history of allergy to mercury or other amalgam components • When a large restoration is needed and the cost of other restorative materials is not a significant factor in the treatment decision

Contraindications for Using Composite Resins

• With patients who have a high caries incidence • Poor oral hygiene habits, especially in the posterior area • Teeth affected with an abnormal or heavy occlusal stress • The cost of the restorative materials