Inside Dentistry
Nov/Dec 2007
Volume 3, Issue 10

Question-When a Class 2 Composite Resin is Planned and the Cervical margin is on dentin or a root, is a resin adhesive flowable composite a better choice than a glass-ionomer sandwich in that region?

Gary Alex, DMD; Joel Berg, DDS; Jeff Brucia, DDS

It is quite common to find recurrent decay in the box (dentin/cementum) areas of failed Class 2 composite restorations. Certainly the long-term clinical success of direct-composite resins is contingent on many factors, not the least of which is the ability to resist microleakage in these vulnerable areas where no enamel is present. Inadequate marginal sealing can contribute to secondary caries, marginal staining, sensitivity, pulpal involvement, breakdown of the adhesive interface, and eventual restoration failure. While current adhesive techniques and materials have the potential to virtually eliminate microleakage at the enamel/restoration interface, long-term management of microleakage at the dentin/restoration interface is still a significant clinical challenge. While part of the problem is almost certainly related to clinical technique, a more insidious concern might be that dentin bonding agents are just not as good as we think, at least over the long haul. The literature is replete with long-term studies, both in vitro and in vivo, that demonstrate a worrisome trend toward potential degradation of the dentin/adhesive interface over time. Microleakage, nanoleakage, hydrolysis, dentin permeability, pulpal pressure, shrinkage stress, “water tree” formation, insufficient hybrid layer formation, phase separation, dentin tubule orientation, occlusion, enzymes released by bacteria, and operator error have all been implicated as potential contributors to this deterioration.

Three common clinical techniques used when placing direct composites are:

1. Use of flowable composites. A flowable (ie, a lightly filled composite) is placed in a thin layer after a dentin bonding agent is placed but before placement of a more heavily filled composite restorative.

2. Placement of a resin-modified glass ionomer (RMGI) restorative. A RMGI restorative is placed as a thick initial layer (in either an open- or closed-sandwich technique) followed by a dentin bonding agent and composite restorative.

3. Placement of a RMGI liner. A RMGI liner is placed in a thin layer followed by a dentin bonding agent and a composite restorative.

My personal opinion is that long-term microleakage is best controlled by the placement of a RMGI restorative or a RMGI liner before placing a dentin bonding agent. The literature is replete with in vivo and in vitro studies demonstrating the superiority of RMGIs vs dentin bonding agents/flowable composites in terms of controlling microleakage. My personal preference is the use of RMGI liners. RMGI liners have the intrinsic ability to both micromechanically and chemically interact with dentin. They are simple to mix and place, release high sustained levels of fluoride, have significant antimicrobial properties, evidence very low solubility, and exhibit a favorable modulus of elasticity and coefficient of thermal expansion and contraction (similar to that of dentin). They also have a low elastic modulus that may help attenuate shrinkage stress from subsequently placed heavily filled composites. My opinion is that RMGIs offer distinct advantages over flowable composites and my preference is the routine use of a RMGI liner under composite restoratives.

When deciding on whether to use a glass-ionomer material or a flowable composite at the gingival seat of a Class 2 restoration, several factors must be taken into account. Clinicians like flowable composites because they “flow.” There is indeed good adaptability to the margin when one can visualize, and therefore verify, that all surfaces are covered and are void-free. This is the distinct advantage of using a flowable resin composite. On the other side are the RMGI products. These materials offer the advantage of being relatively hydrophilic, and therefore more tolerant of any residual moisture that may be present on the surface. They also possess a dentin-like coefficient of thermal expansion, and will release fluoride along the marginal interface and also at the contact point to potentially affect the adjacent tooth. If there is a proximal lesion present on the tooth in question, then the juxtaposing tooth must also be affected, although perhaps with a lesion so small that it is not clinically detectable. The subtle but persistent (when recharged from daily toothpaste exposure) fluoride release from glass ionomer has been shown in laboratory studies to allow remineralization and prevention of demineralization to occur.  

There also is the issue of technique sensitivity in application. The adhesive procedural steps before placing a resin composite—flowable or otherwise—are demanding and must be strictly followed to achieve predictable results. With glass-ionomer materials—resin modified or otherwise—newer products allow the simple placement of an acidic primer, after which the glass-ionomer material is placed. This is simplified over the resin-composite technique. On the other hand, the actual placement of available glass-ionomer products themselves is a little trickier than the placement of the flowable resins. Glass ionomers are sticky, and the clinician must practice his/her technique to get things right. In the end, handling is a key element that will determine the clinician’s choice. I believe glass ionomers offer a unique advantage in all “sandwich” technique situations.

When removing decay or an existing restoration that extends interproximally beyond the cementoenamel junction, the restorative margin will be placed on either dentin or cementum. Long-term clinical results have demonstrated that a well-done cast gold restoration placed over a gingival bevel still remains the standard of care. This is not always the choice of the patient. A Class 2 direct composite restoration can provide years of service if special attention is given to the technique. Composite resin placement has proven to adhere well to dentin and cementum if good materials and techniques are used. The concern is that even though the bond can be adequate, the seal has been shown to be very poor. The use of flowable composites or compomers has shown no improvement in the seal. The only direct material that can reduce leakage in this area has been shown to be a glass-ionomer material.

The technique, an open-sandwich restoration, can work very well in this situation. After caries removal and matrix placement, the area is conditioned with a 10% polyacylic acid gel for 10 seconds. After rinsing, a conventional glass ionomer or a RMGI is placed to the margin and built up vertically until there is an enamel margin present. Ideally, the contact should not be in this material and the marginal ridge should have 1.5 mm of composite under it for support. Once the glass-ionomer material has set, this material along with the tooth may be etched and adhesive applied followed by an incremental placement of a composite material. This technique has proven to work well when these steps are practiced.

Gary Alex, DMD
Private Practice
Huntington, New York
Joel Berg, DDS
Lloyd and Kay Chapman
Chair for Oral Health
Department of Pediatric Dentistry
The University of Washington
Seattle, Washington
Jeff Brucia, DDS
Private Practice
San Francisco, California
Assistant Professor Department of Dental Care 
A. Dugoni School of Dentistry
The University of the Pacific
San Francisco, California

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