Chapter 43 Notes
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Criteria for a New Dental Material
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•It 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.
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Properties of Dental Materials
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The types of dental materials used to restore teeth must respond to and withstand specific factors associated with oral conditions. The following characteristics enhance the ability of dental materials to withstand the oral environment and allow for easy application.
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Materials used in restoring posterior teeth must have sufficient strength to withstand such force.
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A force is any push or pull on matter. In turn, force can create a stress and a strain. Stress is the reaction within the material that can cause distortion. Strain is the change produced within the material that occurs as the result of stress.
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Types of Stress and Strains
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Types of Stress and Strain •Tensile stress pulls and stretches the material. A tug-of-war is an example of tensile stress. •Compressive stress pushes the material together. Chewing is an example of compressive stress. •Shear stress is the breakdown of material as the result of something sliding over two areas. Cutting with scissors is an example of shear stress.
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Thermal change
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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.
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Electrical Properties
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An electrical current (also referred to as galvanic action) can take place in the oral cavity when two different or dissimilar metals are present (Fig. 43-2). Conditions that allow these electrical currents include the following: •Saliva contains salt, which makes it a good conductor of electricity. •Two metallic components of different composition (two restorations or a metal object such as a fork placed in the mouth) can act as the battery. •Galvanic action, or shock, is the coming together of all these conditions.
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Corrosion is the reaction of metals that occurs within a metal when it is exposed to corrosive factors such as temperature, humidity, and saline.
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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.
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Characteristics of dental materials that can affect the adhesion process are wetting, viscosity, surface characteristics, and film thickness.
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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.
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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.
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Surface characteristics influence the wetting ability of the material.
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Retention is the ability to hold two things firmly together when they will not adhere to each other naturally.
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dental restorations, casting, and appliances must be held in place with the use of materials and retention methods.
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Curing is a setting process of a dental material that is initiated by a chemical reaction or by light in a blue wave spectrum.
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An auto-cured or self-cured material hardens as the result of a chemical reaction of the materials once mixed together.
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A light-cured material does not harden until it has been exposed to a curing light (Fig. 43-5). This allows a more flexible working time.
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With a dual-cured material, some curing takes place as the material is mixed. However, the final cure does not occur until the material has been exposed to a curing light.
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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 used in these types of restorative and esthetic procedures are amalgam, composite resins, glass ionomers, temporary restorative materials, and tooth-whitening products.
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Indications for Using Dental Amalgam
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•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
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Contraindications to the Use of Dental Amalgam
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•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
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Amalgam alloy powder is composed of the following metals:
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•Silver, which gives it its strength •Tin, for its workability and strength •Copper, for its strength and corrosion resistance •Zinc, to suppress oxidation
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The main differences in the composition and classification of dental amalgam alloy powders are based on:
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(1) alloy particle shape and size, (2) copper content, and (3) zinc content.
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High-copper alloys are classified according to their particle shape: spherical (round particles) or irregular (rough, lathe-cut particles)
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Mercury-to-Alloy Ratios
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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.
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The controversy has evolved in the following two directions:
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(1) potential harm to patients from the mercury within the amalgams placed in their teeth, and (2) the toxicity level of mercury vapors affecting dental personnel exposed over a long period.
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ADA and the National Institute of Health-Nations Administration have agreed that there is no basis for claims that amalgam is a significant health hazard.
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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.
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Trituration
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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.
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The mix is placed from the capsule into an amalgam well; the pestle is removed, and the mix is loaded into the amalgam carrier.
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Amalgam should appear soft, pliable, and easily shaped when first triturated.
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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.
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A burnisher is used to smooth the amalgam, making sure that no irregularities are present in the restoration.
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Composite resins have been placed mainly in anterior teeth because of their esthetic qualities, but with new advances in their makeup, they are increasingly being placed in posterior teeth as well.
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Commercial Examples of Composite Resins
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•Aurafil •Command •Durafil •Estilux •Finesse •Herculite •Prisma-Fil •Prodigy •Profile •Silar •Silux •Visar
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Composite resins are not as strong as amalgams or gold alloy restorations, but they are designed to meet the needs of a specific area of a tooth or mouth.
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Indications for Using Composite Resins
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•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.
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Contraindications for Using Composite Resins
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•When esthetics is not an important factor •With patients who do not have daily proper oral hygiene habits, especially in the posterior area •When the cost of the restorative materials is a significant factor in the treatment decision.
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Composition of Composite Resins
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The composition of composite resins is a chemical mix, which includes (1) an organic resin matrix(2) inorganic fillers(3) a coupling agent, and (4) pigments.
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The resin matrix component of composite is a fluid-like material called dimethacrylate, which is also referred to as BIS-GMA.
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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 allows polymerization to take place. Additional additives included in this process are the initiator, the accelerator, the retarder, and the ultraviolet (UV) light stabilizers.
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Inorganic fillers used in composite resins include quartz (a hard rock-forming mineral), glass, silica (white colorless crystalline compound) particles, and colorants. These fillers add the strength and other characteristics that are needed in a restorative material.
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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
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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.
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Composites are classified by particle size as megafill, macrofill, midifill, minifill, microfill, and nanofill.
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Composites that have a combination or mixed range of particle sizes are referred to as hybrids.
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Macrofilled composites
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This type of composite contained the largest of filler particles, providing the greatest strength, but its use resulted in a duller, rougher surface. self-cured and were used in areas where greater strength was required to resist fracture.
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Microfilled composites
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contained inorganic fillers that were much smaller than those in a macrofilled composite. 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.
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Hybrid composites
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used most often today. They contain a mixed range of particle sizes. cured with a visible light-curing method and can be polished smoother than macrofilled composites. high wear resistance and excellent shading characteristics.
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Flowable composites
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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.
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Sealant composites
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resemble flowable composites but have even more viscosity to allow the material to flow into the pits and fissures of the tooth surface.
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The coupling agent is important because it strengthens the resin by chemically bonding the filler to the resin matrix.
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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.
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Pigments For a composite material to match a tooth color, coloring must be added. Most often, the coloring comes from an inorganic substance.
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Important differences in the application or technique of an amalgam restoration versus a composite restoration include the following:
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•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 composite resins. •Placement of composite resin is accomplished in increments; light-curing is performed before additional increments are added.
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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.
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Tips When Choosing a Shade
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•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, etc., 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.
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The light-curing process uses a high-intensity blue light source that provides an effective curing of resins. The blue light source is a combination of tungsten and a halogen lighting system. The exact curing time depends on the following:
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•Composite manufacturer's instructions (most often, 20 to 60 seconds) •Thickness and size of the restoration (when larger quantities of the material are being placed, each increment is cured before the next is placed) •Shade of the restorative material used (the darker the shade, the longer the required curing time)
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Finishing burs and abrasive materials are used to contour and polish a finished composite resin.
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Steps in Finishing a Composite Resin
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•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 disks and finishes with superfine disks. •Finishing strips assist in polishing of the interproximal surfaces. •Polishing paste applied to a rubber cup completes the step.
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Glass ionomers represents one of the most versatile dental materials available.
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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.
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This type of material is especially desirable for the following applications:
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•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
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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.
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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.
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The blend of spherical silver-tin alloy with glass ionomer produces a strong, abrasion-resistant dental material.
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The particles are a polymer of acrylic acid, which provides toughness and resistance to acid erosion.
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Cautions for Placing Glass Ionomers
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•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 the metal band.
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The type of material selected for a temporary restoration is designed to maintain or restore function and keep the patient comfortable for a limited time
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Temporary restorative materials are used for the following reasons:
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•To reduce the sensitivity and discomfort of a tooth to determine its diagnosis •To maintain the function and esthetics of a tooth until a permanent restoration can be placed •To protect the margins of a prepared tooth that will receive a permanent casting at a later time •To prevent shifting of adjacent or opposing teeth caused by an open space
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The type of temporary restorative material selected depends on the location and amount of the tooth structure that needs to be restored. If a tooth has lost a filling or has a small pit within the enamel, an intermediate restorative material would be selected. If a cusp is gone, or if the dentist has prepared the tooth for a cast restoration involving the gingival margin, a provisional coverage material would be selected.
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An intermediate restoration is frequently recommended by the dentist as a short-term restoration.
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IRM is a reinforced zinc oxide-eugenol composition. The eugenol has a sedative effect on the pulp, and fillers are added to improve the strength and durability of the material.
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Common uses of IRM include the following:
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•Restoration of primary teeth (when permanent teeth are 2 years or less from eruption) •Restorative emergencies •Caries management programs
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IRM is supplied as a powder and a liquid, which are mixed manually on a treated paper pad, or as premeasured capsules that are activated and then triturated.
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A provisional restorative material is designed to cover the major portion, if not the entire clinical portion, of a tooth or several teeth for a longer period.
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Acrylic resins are supplied in several applications: as a liquid/powder, in premeasured tubes, and in automix cartridges.
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Tooth whitening, also referred to as bleaching, is one of the most popular and cost-effective ways of restoring the esthetic appearance of teeth.
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Whitening products can be found in many everyday items such as toothpaste, fluoride, mouth rinses, and even chewing gum.
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Peroxide-based solutions are supplied in different concentrations. Peroxide-based whitening products work deep within the enamel to remove staining and discoloration that have come from years of accumulated stain and aging.
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Teeth become discolored and stained for many reasons, most commonly aging; consumption of staining substances such as coffee, tea, colas, and tobacco; trauma; use of tetracycline (antibiotic); excessive fluoride; nerve degeneration; and aging of restorations.
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Most in-office bleaching procedures use a bleaching agent that is carbamide peroxide, which breaks down in the mouth to form hydrogen peroxide.
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A newer choice for in-office whitening is power or light-accelerated bleaching, also referred to as laser bleaching.
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A power bleaching treatment typically involves isolation of soft tissue with a resin-based, light-curable barrier; application of a professional dental-grade hydrogen peroxide whitening gel (25 percent to 38 percent hydrogen peroxide); and exposure to the light source for 6 to 15 minutes.
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Commercial Examples of Bleaching Products
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•Contrast PM •Dental Lite •Illumine •Nite White •Nupro Gold •Opalescence •Prestige •Zaris
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indirect restoration is one that is fabricated outside the mouth by a dental laboratory technician
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restorations, also referred to as castings, involve a sequence of procedures that include preparing the tooth, taking a final impression, waxing a pattern, investing the pattern, casting the restoration, finishing and polishing the casting, and cementing the restoration in place.
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Noble metals used for cast restorations consist of gold (Au), palladium (Pd), and platinum (Pt). All other metals in the alloys that are not classified as noble metals are considered to be base metals.
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base metal is a metal of relatively low value that has inferior properties such as lack of resistance to corrosion and tarnish. Iron, tin, and zinc are examples of base metals.
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Gold alloys are described according to their hardness, malleability, and adaptability. With the use of this descriptive system, the four types of gold alloys are as follows:
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•Soft, type I alloys have 83 percent noble metals and are used for casting inlays, which are subject to slight stress during mastication. •Medium, type II alloys have 78 percent noble metals and can be used for almost all types of cast inlays and posterior bridge abutments. •Hard, type III alloys have 77 percent noble metals and are acceptable for inlays, full crowns, three-quarter crowns, and anterior or posterior bridge abutments. •Extra hard, type IV alloys have 75 percent noble metals and are also referred to as partial denture alloys; they are designed for crowns, bridges, and cast-removable partial dentures.
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Ceramic is a type of material that is similar to that used in the dishes or pottery in your home.
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Ceramics are compounds, which are combinations of metallic and nonmetallic elements.
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Combinations of ceramic-metal restorations include the following:
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•Porcelain fused to metal (PFM) •Porcelain bonded to metal (PBM) •Ceramico-metal (C/M) •Porcelain-metal (P/M)
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The type of ceramic most often used in dentistry is porcelain.
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Porcelain material is chosen for the following reasons:
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•The shading of colors matches tooth color well. •Porcelain improves the esthetic appearance of anterior teeth. •The material has the strength of metal. •Porcelain is a good insulator. •The material has a low coefficient of thermal expansion.
