Composites, Glass Ionomers, and Compomers Chapter 6

Direct-Placement Materials Direct-placement materials are those that can be placed directly into the cavity preparation or bonded directly onto the tooth surface. Esthetic materials are tooth-colored Composite resin Glass ionomer cement Resin-modified glass ionomer (hybrid ionomer) Compomer

Composite Resin A composite is a mixture of two or more materials that has properties superior to any single component. Composite resins are tooth-colored. They can be used in both anterior and posterior teeth. Composite resin is composed mainly of organic resin matrix and inorganic fillers joined together by a silane coupling agent.

Composite Resin (cont’d) Composite resins are joined together by a silane coupling agent that sticks the particles to the matrix. Also added are initiators and accelerators that cause the material to set. Pigments give the material color.

Resin Components The most commonly used resin for the matrix of composites is bis-GMA. Another is urethane dimethacrylate. These resins are thick liquids made up of two or more organic molecules. To reduce viscosity and allow the loading of filler particles, a low molecular weight monomer is added.

Filler Particles Filler particles are added to the organic resins to make them stronger. Fillers are also added to control handling characteristics. Fillers help to reduce shrinkage. Fillers used in composite resins are made up of inorganic particles such as quartz, silica, and glass.

Filler Particles (cont’d) The higher the filler content, the stronger the material will be. One important factor to keep in mind when choosing a composite resin material is the size of the filler particles. Particle size will affect the wear resistance and polish-ability of the material.

Particle Size The amount of filler in the resin and the amount of resin between the particles are related to how the material wears. Large filler particles tend to get plucked from the resin matrix at the surface when the restoration is under function. Larger particles cause the finished restoration to appear dull or rough.

Particle Size (cont’d) Smaller particles are not as easily pulled from the resin and therefore cause fewer voids that contribute to wear. Smaller particles are packed more closely together, thereby exposing less of the resin matrix to wear. The smaller the particles, the smoother is the surface.

Coupling Agent To provide a stronger bond between the organic fillers and the resin matrix, a coupling agent is used. This coupling agent is silane, which reacts with the surface of the inorganic filler. Good adhesion of the two is necessary to minimize loss of filler particles and reduce wear.

Pigments Pigments are inorganic materials that are added in various amounts to approximate the basic shades of tooth enamel. To get an accurate color match, a shade guide is used.

Polymerization Polymerization is the chemical reaction that occurs when low molecular weight molecules called monomers join together to form long-chain, high molecular weight molecules called polymers. Chemicals that cause the polymerization reaction to begin are initiators and activators.

Types of Composites Three types of composite materials are used in dentistry. Each composite material has its advantages and disadvantages: Chemical cure Light cure Dual cure

Chemical Cure Chemically cured composite resins, also called self-cured composite resins, represent a two-paste system. They are supplied in jars or syringes. One paste is called the base; the other is called the catalyst. Equal parts of the two are dispensed and mixed together.

Chemical Cure (cont’d) With this type of system, the operator has a limited amount of working time before the material starts to set. When the materials are mixed together, it is important that they be spatulated to a homogenous mixture to allow a thorough cure. Air is introduced during the mixing process; this may cause voids in the restoration.

Light Cure Light-cured composite materials are the most common type of composite used in dentistry. The operator has ample working time to manipulate the material to its desired form. The material is set with the use of a curing light in the blue wavelength. Care must be taken with the operatory light so that it does not begin to set the material prematurely.

Dual Cure Dual-cured composite resins utilize both visible light and chemical reactions to cure the material. These resins are available in a two-paste system or may be dispensed from a syringe. The initial set is made by the curing light, and the chemical reaction finishes the process.

Types of Filled Materials Composite resins have steadily improved in quality over the years. Filler particle size has decreased, the number of filler particles has increased, and polymerization shrinkage has decreased. Fillers are available in three classifications: Macrofilled Microfilled Hybrid

Macrofilled Materials First generation of composite resin material Conventional composite containing the largest of the filler particles Provides greater strength Duller, rougher surface Absorbs stains more easily

Microfilled Materials Developed to overcome the problems associated with the larger particle size Contain much smaller particles Not as strong as macrofilled materials Polish to a glossy finish Do not absorb stains as easily

Hybrid Contain both macro and micro particles Easily polished Greater strength than microfilled products High wear resistance Microhybrids, which are a combination of small particles and microfine particles, are considered the newest generation.

Flowable Composites Flowable composites are low-viscosity, light-cured resins that are lightly filled. These composites flow readily and can be delivered directly into the preparation by small needles on syringes. These typically are utilized in conservative-type procedures.

Pit and Fissure Sealants Low-viscosity resins that vary in filler size Used to prevent caries Contain little or no filler Similar to flowable composites

Physical Properties Important physical properties of composites include the following: Biocompatibility Strength Wear Polymerization Shrinkage Thermal conductivity Water sorption Radiopacity

Biocompatibility Newly placed composite resins can release chemicals that, in deep cavity preparations, could pass through the dentinal tubules into the pulp, causing inflammation. When the tubules are sealed by dentin bonding agents and/or a base is placed, sensitivity is reduced or eliminated.

Strength Composites with larger filler particles (macrofilled) are stronger in both tensile and compression than are microfilled materials. Macrofilled materials still are not as strong as amalgam, but they are stronger than glass ionomers.

Wear Composites wear faster than amalgams. Recent improvements in material are closing that gap in strength.

Polymerization Shrinkage Term refers to the shrinkage that occurs when the composite resin is cured The matrix, when cured, usually shrinks away from the cavity walls. Material cures toward the center of the bulk of material, which pulls the material away from the interface. Curing in small increments (1 to 2 mm) decreases shrinkage.

Thermal Conductivity Composite resin has a thermal conductivity close to that of natural tooth structure. It is much lower than that of metal. Composite resin is a biologically protective material for the pulp.

Coefficient of Thermal Expansion Ideally the coefficient of thermal expansion (CTE) of the filling material would be the same as that of the tooth structure. In the case of composite, the CTE is greater and will have a greater change in dimension than will the adjacent tooth structure. This can result in debonding and leakage of the restoration.

Elastic Modulus The elastic modulus (also referred to as the e-modulus, or Young’s modulus) is the stiffness of the composite and is determined by the amount of filler. The greater the volume of the filler, the stiffer (higher elastic modulus) and more wear resistant is the restoration.

Water Sorption The resin matrix absorbs water from the oral cavity. The greater the resin content, the more water is absorbed. Microfills and flowables have greater water sorption. Water softens the resin matrix, which gradually degrades the material.

Radiopacity Metals such as lithium, barium, or strontium are added to the filler to make the restoration more opaque when viewed on a radiograph. Older materials did not have these fillers, and most appear radiolucent.

Selection of Materials Several criteria can be used to determine the best material to use in a particular situation. In the anterior teeth (non–stress-bearing areas), selection is usually based on color matching and ability to finish to a natural, glossy appearance. Stress-bearing areas use the stronger hybrid or microhybrid materials.

Shade Guides Many manufacturers include a shade guide with color tabs that can be used to help in shade selection. Remember to use a natural light source when viewing shades. Always check the shade before work begins, so the teeth are fully hydrated.

Other Factors Shelf life Dispensing and cross-contamination Finishing and polishing Dental prophylaxis/scaling

Glass Ionomers Self-cured or light-cured, tooth-colored, fluoride-releasing cements that bond to tooth structures Used to cement crowns, bridges, veneers, and orthodontic appliances Also may be used as a liner, base, or core For restorations at the cervical portion of the tooth

Physical Properties of Glass Ionomers Biocompatible Bond to tooth structure Release fluoride ion High water solubility in the first 24 hours Thermal expansion similar to that of natural teeth Good insulators Moderate compressive and tensile strength Wear faster Radiopaque

Hybrid Ionomers To improve the physical properties of glass ionomers, resins have been added to the material. These resins have some properties of composites and some properties of glass ionomers. They are stronger than regular glass ionomers, are easier to polish, and are more wear resistant.

Compomers Composite resins that have been modified with polyacid Release fluoride but are not the same as glass ionomers Good color-matching ability Polish well Medium wear rate

Indirect Restorations Indirect restorations are fabricated outside of the mouth. They include Inlays Onlays Veneers Crowns with porcelain or ceramic facings

Summary Composite resins are direct-placement restorative materials that have a wide variety of uses. Glass ionomer cements also have a wide variety of uses but are not as strong as composite resins.