By John O. Burgess, DDS, MS, and Jessica M. Davidson, BS
Editor's Note: The first part of this article appeared in the March/April issue of Dental Equipment & Materials.
After the bonding agent is applied and cured, the composite resin is placed. There are three methods for placing the composite resin. Incremental placement and curing is controversial and may not reduce marginal opening and microleakage resulting from polymerization shrinkage. However, incremental placement and curing of composite resin with visible light thoroughly polymerizes each increment, and is advocated at this time. Increments, no greater than 2 mm thick, should be placed to ensure complete polymerization. Incremental placement of composite resin does not eliminate stress at the marginal areas of the resin restoration; however, it will ensure complete polymerization of the composite. High-intensity curing units (such as plasma arc curing lights like Virtuoso or Sapphire, Den-Mat, and Wave Light, Schein Dental) shorten curing times but do not significantly increase curing depths. High-intensity curing lights speed curing of each increment and decrease the total time required to place a composite resin restoration. A small glass ionomer base may be placed on thin areas of dentin to decrease postoperative sensitivity. The incremental placement technique with total etch is indicated for patients with low or normal caries risk.
A second technique for placing posterior composite resins is the bulk filling technique where the preparation is completely filled and composite resin is polymerized in one increment. This technique, often called trans-tooth curing, places the composite resin in bulk into the preparation, cures the composite through the tooth from the facial and lingual and then from the occlusal. This technique is somewhat popular but has no clinical studies evaluating its effectiveness; therefore, it is not recommended as a routine technique.
In the third technique, the open sandwich technique, a fluoride-releasing material is applied in the proximal box from the gingival margin to just below the contact point of the adjacent tooth. Resin-modified glass ionomers (Fuji II LC, GC America, or Vitremer, 3M ESPE), are the most effective fluoride-releasing and recharging restorative materials. They release fluoride that is absorbed by the adjacent tooth structure, especially the gingival margin. In this technique, the resin-modified glass ionomer is injected into the proximal box of the preparation from the gingival area to just below the proximal contact of the adjacent tooth. A wear-resistant composite resin is applied over the fluoride-releasing material. A five-year clinical study showing the success of this technique has recently been published with excellent results. Since two in vivo studies have reported decreased caries associated with glass ionomer restorations, it is prudent to use this technique with higher caries risk patients.
Flowable composite resins. These materials are sometimes advocated as thin liner under the initial increment of composite resin for posterior composite resin restorations. Flowables are less highly filled, shrink more, have greater water uptake and staining, and have lower mechanical properties than more highly filled composite resin. Flowable resins, when used as a liner, are acceptable if used as a thin layer but no clinical studies have documented that these materials produce better restorations than not using them.
Finishing posterior composite resin restorations requires carbide burs (7901, 7801 and 7404 Brasseler) and XT Sof-Lex disks (3M ESPE), a series of four disks are recommended in the Snap on and large size. A number 12 B blade on a bard parker handle is a must for removing flash at the gingival margin. The AstroPol (Ivoclar) or the Enhance polishing kit (Caulk) is recommended to smooth the restoration. All these instruments are used to form the occlusal embrasures and develop occlusal anatomy and proper contours. Aluminum oxide polishing paste (Caulk) is recommended as a final polishing agent for the restoration.
Rebonding. After the composite resin is inserted and finished, the margins are etched with phosphoric acid for 10 seconds, rinsed, and a surface penetrating resin (Fortify, BISCO) is painted onto the margin and the composite resin and cured. One clinical study has shown less occlusal wear after a single application of Fortify at five-year recall. In addition to less wear, Fortify penetrates and improves marginal seal. After rebonding, the restoration is complete.
Composite resin also has a successful history for the esthetic restoration of fractured or carious anterior and posterior teeth. Early composite resin materials were tooth-colored but lacked color stability and polishability due to their large filler particle size. As materials developed, color stability and wear improved. However, many modern hybrids and microhybrids lose surface luster with time. Polish is dependent on the intrinsic filler particle size and fillers larger than .4 micron produce surfaces that dull after the polished surface is exposed to the oral environment. Even when the initial polish produces a glossy composite resin surface, the composite resin dulls. Microfilled composite resins maintain their polish since they have a mean filler particle size of .04 micron. Unfortunately, microfilled composite resins have inherent problems. The filler loading is lower, producing a weaker material that is unable to withstand the occlusal forces produced in large Class IV restorations.
An early and still very popular method for restoring Class IV (incisal edge) fractures uses a sandwich technique of an initial layer of hybrid composite resin over the tooth for strength, and covering this with a highly polishable microfilled composite resin. Often Renamel hybrid and microfil (Cosmedent) is used in this method. In the sandwich technique the microfil is used to provide polish longevity while the hybrid is used as a stronger reinforcing opaque dentin layer. The shades of the microfilled and hybrid composite resin must be identical to blend composite resins but the opacities of the microfil and the hybrid composite resins must vary to produce excellent esthetic dentistry. Since the sandwich technique uses two composite resins that are expensive and have limited shelf life, it is desirable to have one composite resin that is esthetic, maintains its polish, is easy to manipulate, and has different opacities.
Another technique for producing esthetic anterior restorations uses one composite, a hybrid, to replace missing tooth structure, even though hybrid composite resins are less polishable than microfilled composite resins. Kerr introduced a successful layering technique to the dental community with the introduction of Herculite XRV. This composite resin kit had dentin, enamel, and incisal shades to more closely duplicate missing tooth structure. The dentin shades were more opaque and were intended to replace missing dentin while enamel shades were more translucent and designed to replace the enamel covering the dentin in natural tooth structure. If the tooth had significant translucency, then an incisal shade was placed on the incisal edge. In general, shade layering composite produced lifelike restorations. As materials have improved, easier composite resin systems have been introduced to produce more predictable esthetic anterior restorations.
Several excellent new composite resin kits have recently been introduced which provide improved esthetic restoration of anterior teeth. These kits use microhybrid resins with smaller mean filler particles, which claim to produce good marginal integrity, lifelike restorations, and long-lasting polish with a single material. One of these kits (EsthetX, Caulk) uses a unique shade guide — three opacities of composite resin (enamel, body, and gingival) to produce esthetic restorations.
Miris (Coltene/Whaledent) uses seven base dentin shades, four effects shades, and six enamel shades as layers to produce esthetic anterior restorations. The mean filler particle size of Miris is 0.6 microns and the particle distribution range is from 0.1 to 2.5 microns. The Miris kit has a unique shade guide. The dentin shade of the tooth is taken using the dentin shade and an enamel shell is used to match the enamel. After the dentin shade is coated with a liquid, it is then placed into the enamel shell to visualize the over layering effect.
The most recent material to be introduced as an esthetic restorative material is Filtek Supreme (3M ESPE). This material is a blend of nanofiller, nanoclusters, and conventional microhybrid filler particles, and it is designed to produce easier polishing and impart a long-lasting polish. The 30 shades for this material are based on the Vita shade guide with enamel, dentin, body, and translucent opacities.
In short, while some manufacturers claim to match tooth structure with many different shades and opacities of the composite resin, others have attempted to simplify the process by supplying an opaque dentin. The opaque dentin is an effects layer to provide special coloring and a very translucent enamel shade. All have attempted to improve color matching and long-term polish, but each has done this in different ways. These advancements need to be evaluated independently in a comparative study to determine their effectiveness at maintaining polish, matching tooth color, and providing a wear-resistant durable restoration.
Cavity preparation
Beveling the facial margin is suggested to enhance acid-etching, enamel bonding, and provide a more esthetic restoration. The long bevel or chamfer provides a transition of materials from the tooth to the composite, making the transition almost imperceptible. Esthetic masking of underlying intrinsic staining may require deeper preparation, allowing for adequate restorative material blending.
Layering
A thin layer of opaque dentin is placed to form the lingual wall of the restoration. After this is cured, a thin layer of body is applied and cured. Following this a thin layer of enamel is placed and scalloped, then an incisal or translucent shade is placed and cured to establish the final incisal edge color and shape. Incisal may not be necessary if the adjacent teeth are not very translucent.
Carbide finishing burs will be used to remove gross excess, followed by finishing strips and disks (Sof-Lex, 3M ESPE) and the Enhance (Caulk) finishing system.
Dr. John O. Burgess is chairman of the operative dentistry and biomaterials department and director of clinical research at Louisiana State University Health Sciences Center's School of Dentistry in New Orleans. Jessica Davidson is clinical research coordinator at Louisiana State University School of Dentistry. They may be reached at (504) 670-2730.
