A composite filling is a tooth-colored plastic and glass mixture used to restore decayed teeth.
Following preparation, the dentist places the composite in layers; typically using a light specialized to harden each layer.
This type of composite is cured outside the mouth, in a processing unit that is capable of delivering higher intensities and levels of energy than handheld lights can. Aesthetics are the main advantage of composites, since dentists can blend shades to create a color nearly identical to that of the actual tooth. For the first half of the twentieth century, amalgam and gold were the primary restorative materials for posterior teeth. Now, with the capability of bonding restorative materials to tooth structure, advances in esthetic materials and techniques have improved the ability of the dental team to deliver the esthetic results that patients demand. This chapter describes the physical and mechanical properties, clinical applications, and shortcomings of directly placed esthetic materials. Direct-placement esthetic materials are those that can be placed directly into the cavity preparation or onto the tooth surface by the clinician without first being constructed outside of the mouth. A composite is a mixture of two or more materials with properties superior to any single component. The most commonly used resin for the matrix of composites is bis-GMA (bisphenol-A-glycidyl dimethacrylate), produced by reacting glycidyl methacrylate with bisphenol-A.
Monomers are organic molecules (that make up the oligomers) with double carbon bonds that link together by an addition reaction to form a polymer. FIGURE 6-1 Variety of filler sizes that are combined in the composite resins and contribute to their classification names.
The fillers used in many composite resins are composed of glass, quartz, silica, or ceramic.
Important factors for the durability of the composite resin are the size of the filler particles and the ratio or weight of the filler to the matrix. Composites can be classified by the size of the filler particles they contain (Figure 6-1).
A coupling agent is used to provide a stronger bond between the inorganic fillers and the resin matrix.
Opposing occlusion has worn the composite down, and numerous pits have developed as bits of the composite have fractured out. Inorganic pigments are added in varying amounts to develop a variety of colors that approximate the basic colors of teeth or specialized colors. Polymerization is the chemical reaction that occurs when low molecular weight resin molecules called monomers join together to form long-chain, high molecular weight molecules called polymers. Chemically cured composite resins, or self-cured composites, are two-paste systems supplied in screw-type syringes or cartridges. Composites in cartridges come with mixing tips that automatically mix the two pastes as they are extruded from the cartridge (see Figure 6-11). Light-cured composites are the most common type of composite resin used in private practice. Tetric EvoCeramBulk Fill nano-hybrid composite material is for fast, efficient bulk placement of direct posterior composite restorations. A fast setting bulk fill posterior composite, x-tra base allows curing of 4 mm layers in only 10 seconds when using the universal shade. Sofreliner Tough S addition-cured silicone material for relining dentures on patients that require relief on upper or lower, partial or full dentures has been added to the Sofreliner Tough Series. Using both chemical and mechanical adhesion, PermaCem 2.0 permanent cement is said to provide an exceptionally strong bond to zirconium restorations. Second generation resin modified GC FujiCEM2 glass ionomer luting cement is powered by F2 Flex Fuse technology. Featuring proprietary MDP, there is reportedly no need for a bonding agent when using Panavia SA Cement.
Composites are also used for cosmetic improvements of the smile by changing the color of the teeth or reshaping disfigured teeth. Polymerization is accomplished typically with a hand held curing light that emits specific wavelengths keyed to the initiator and catalyst packages involved. Indirect composites can have higher filler levels, are cured for longer times and curing shrinkage can be handled in a better way. Composites bond to the tooth to support the remaining tooth structure, which helps to prevent breakage and insulate the tooth from excessive temperature changes. Some anterior teeth also had metal restorations that were visible when the patient smiled, in the form of gold margins of three-quarter crowns, class III gold foils, or class V gold foils and inlays or amalgams.
The dental team must keep current with the rapid changes that occur with materials and techniques. These materials include composite resins, glass ionomer cements, resin-modified glass ionomer cements, and compomers. Indirect-placement esthetic materials are those materials that are constructed outside of the mouth, and then cemented in place. Composite resins are tooth-colored restorative materials that are used in both the anterior and posterior parts of the mouth.
When the polymerization reaction goes to completion, the result is a cured composite resin. As a general rule, the higher the filler content, the stronger and more wear resistant the restoration will be and the less it will shrink when polymerized.
Wear of the composite is related to the filler particle size, the amount of filler in the resin, and the amount of resin between particles.

This coupling agent is silane, which reacts with the surface of the inorganic filler and with the organic matrix to allow the two to adhere to each other.
Pigmented resins (also called coloring resins) can be used to cover discolorations or dark dentin, or to hide the graying effect of a metal post in a root canal–treated tooth. For composite resins, activation of the polymerization process can be done chemically (chemical-cured), or by light (light-cured), or by a combination of the two (dual-cured). When side groups of adjacent polymer chains share electrons, they form covalent bonds that link (called cross-linking) the chains together (Figure 6-4).
This “automixing” greatly reduces the introduction of air into the mixed composite and provides the correct proportions of each material. Many clinicians prefer light-cured composite resin, because it requires no mixing and the operator can control the working time by deciding when to apply the curing light.
Restorations can be placed with one material in a single increment without specific dispensing equipment. The 75% filled material has a low shrinkage stress and low shrinkage combined with high compressive strength (350 MPa) and flexural strength (133 MPa). It is said to deliver a Shore A hardness of 24 for up to 18-month relief of irritated tissue for first-time denture wearers, after surgery, or following teeth extraction or implant procedures. It features new high-elastic crosslinking monomers with a modified filler-surface treatment to increase strength. It is optimized to offer a 35-minute intraoral work time and a mouth removal time of 2 minutes 30 seconds. The cement blends with the color of the patient’s teeth, crowns or other surfaces around it. The light green color of DryZ contrasts nicely with gingiva, blood and tooth structure, making it easy to detect where the material has been placed.
When using a curing light, the light should be held as close to the resin surface as possible, a shield should be placed between the light tip and the operator's eyes, and that curing time should be increased for darker resin shades.
Silicate cement, introduced in 1873, was the first tooth-colored restorative material but was not widely used until the early 1900s.
Good listening skills are needed to determine the types of esthetic services the patient is requesting so that the dental team and the patient are working in concert toward the same goal.
They are composed mainly of an organic resin matrix and inorganic filler particles joined together by a silane coupling agent that sticks (adheres) the particles to the matrix.
These resins are thick liquids made up of two or more types of organic molecules called oligomers.
By reducing the amount of resin, fillers help to reduce the amount of shrinkage that occurs when the resin matrix polymerizes, or sets.
To make the composite resin restoration show up (appear radiopaque) on radiographs, heavy metal ions of barium, boron, zinc, zirconium, or ytterbium may be added to the filler particles. The amount of filler in a composite resin usually is reported by the manufacturer as the percent of filler by weight (weight %) in the resin.
Large filler particles tend to get pulled from the resin matrix at the surface (called plucking) when the restoration is under function or abraded by food and tooth brushing, resulting in wear of the remaining resin matrix and a rough surface. Good adhesion of the two is necessary to minimize loss of filler particles and to reduce wear. Pigments are also used to characterize a restoration when the tooth being restored or adjacent teeth have white spots as with mild fluorosis (see Chapter 7 [Preventive and Desensitizing Materials]) or other special characteristics. During polymerization, regardless of method, an activator (chemical or light) causes an initiator molecule to form free radicals (highly charged molecules that have unpaired electrons).
Cross-linking of polymers produces a much stronger, stiffer material than is formed with single-chain polymers.
The other paste, called the catalyst, contains composite and a tertiary amine as an activator.
The composites most commonly found in cartridges are those used as core materials for crowns. Shrinkage Stress Relievers ensure optimal marginal integrity, Polymerization Boosters within the initiator system enable 4 mm thick layers to be cured in 10 seconds and Light-Sensitivity Filters provide extended working time under ambient light. It can be used in the open and closed sandwich technique, features a self-leveling effect for easy adaptation to cavity walls and is highly radiopaque. Formulated for easy clean-up, the optimized viscosity and no-drip formulation provide for fast and easy removal of excess, resulting in less stress and chair time for the clinician.
Indicated for indirect restorations, including all types of metal-, resin-, alumina- and zirconia-based inlays, onlays, crowns and bridges, it is said to deliver optimal bond strength and allows for completion of more restorations in less time. It is said to be easy to apply, clean up and remove and provides exceptional retention strength.
During clean-up, the cement is said to be easy to remove at the margins, leaving no room for damage to the gum tissue or the restoration. Although it was somewhat esthetic, it was relatively soluble in the mouth and washed out over time. Esthetic materials must be carefully selected so that their properties are compatible with the patient’s oral condition and occlusion.
Guidelines for selection of the shade of these materials to obtain satisfactory cosmetic results also are discussed. Also added are initiators and accelerators that cause the material to set and pigments that give color to the material and match tooth colors. To reduce viscosity and allow loading with filler particles, a low molecular weight monomer, such as TEGDMA (triethylene glycol dimethacrylate), is added. Fillers can also be used to control the translucency of the composite by their effect on the scattering of light.

Smaller particles are not as easily plucked from the resin and therefore cause fewer voids that contribute to wear. The silane is applied to the filler surface before the filler is added to the resin monomer. Equal parts of these two pastes are mixed together, and the polymerization reaction begins. Blue light with a wavelength of about 470 nanometers (nm) activates an initiator (camphorquinone) that, in the presence of an accelerator (an organic amine), causes the resin to polymerize. DryZ also is great for tissue management when you’re seating restorations, placing rubber dams, bleaching teeth and restoring subgingival cavities. In the latter half of the twentieth century, various direct-placement tooth-colored restorative materials were introduced.
Dental hygienists and dental assistants must understand the properties of these materials, so that as important members of the dental team they can help the dentist to assess the performance of the restorations and can alert the dentist when they perceive that a restoration may be failing. Composite resins are commonly called composites and also can be referred to in the dental literature as resin composites. The amount of filler and the size and shape of the filler will affect the viscosity of the composite and how it handles. Smaller particles can be packed closer together, thereby exposing less of the resin matrix to wear (Figures 6-2 and 6-3) and increasing the number of filler particles that can be added to the resin matrix. The free radicals break one of the carbon-to-carbon double bonds to form a single bond and another free radical.
The reaction could go to completion very quickly, but chemicals called inhibitors are added to each paste to slow down the reaction. Some core materials are supplied in syringes that have two chambers (one for base and one for catalyst). These components are both present in the composite but do not react until the light triggers the reaction.
It controls seepage that may contaminate a sensitive, restorative material, allowing you to do optimal restorative dentistry. Initially, chemical-cured, unfilled acrylic resins were used, but they leaked, wore down quickly, and became discolored. They need to be familiar with the physical properties of the materials so that they do not damage the restorations during routine oral hygiene, coronal polishing, and preventive procedures.
Reducing the amount of resin by adding filler reduces thermal expansion and contraction and decreases water sorption (uptake) that softens the resin and makes it more likely to wear.
They are leached slowly from the composite by dietary acids and by application of acidulated phosphate fluoride in the dental office.
The smaller the particles, the smoother the surface of the composite will be after finishing and polishing and the longer it will be able to retain its luster.
That free radical can cause the same reaction with another monomer to add to the polymer chain (called addition polymerization).
The operator has a limited amount of time (working time—usually about 2 minutes in the mouth) to place the restoration before it becomes too stiff to manipulate. Inhibitors are also present to reduce the effects of the operatory light on a premature setting. In 1955, Michael Buonocore introduced the acid etch technique for bonding the acrylic to enamel. They need to know the handling characteristics of the esthetic materials so that they can assist the dentist in their placement or can perform steps in their placement, finish and polish as permitted by state dental practice acts. As the monomers link together into chains, the volume of resin decreases, so the net result is shrinkage (called polymerization shrinkage).
Once the initial set occurs, the material should not be manipulated or the properties of the restoration will be degraded. A small delivery tip can be added to the mixing tip to deliver the mixed composite directly into the preparation. Disposable mixing sticks are usually supplied with the composite contained in screw-type syringes.
The operator may choose to turn the operatory light away from the mouth when placing the composite.
Because the two pastes must be manually mixed, air can be incorporated into the material, causing voids or porosity in the restoration. Silica particles were added to bis-GMA to reinforce it, and this became the basis of the composite resin. The early composite resins were available in a very limited number of shades, were rough and worn out quickly, discolored, and shrank excessively when they cured. Resin bonding agents had not been developed yet, so postoperative sensitivity and recurrent caries were common occurrences.
In an effort to have more control over the working time, composites cured by ultraviolet light were developed.
Composites have been continually improved on ever since by making them more durable, esthetic, and color stable.
Other materials such as glass ionomer cements and compomers have also been developed and improved on, providing the dental team with a wide selection of esthetic materials and colors for the restoration of carious or damaged teeth and for cosmetic enhancement. Choosing the type of material depends, in part, on the extent of damage to the tooth, the stresses that will be placed on the restoration, and the esthetic requirements of the patient.

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