One of the best “well-kept secrets” in this day of dentin adhesive dentistry is the use of glass ionomer cements (GICs) in both the direct and indirect restorative processes. Since their discovery, GICs have been one of the most widely researched of all dental materials. In many countries, GIC presents the restorative material of choice because of its low cost and anticariogenic properties. According to Dr. Hien Ngo, glass ionomer cement forms a “chemically fused seal to dentin” that many regard as superior to dentin adhesive technology.

Universal dentin replacement

There is some truth behind the high regard. Some argue that the dentin bond hydrolyzes with time, allowing microleakage to occur. Others even say the dentin bond doesn’t work, or that restorative material bonded to enamel has to be cut off, while material bonded to dentin can be “popped off.” This is partly true.

However, an important clinical distinction should be made: There is “good” dentin for bonding, as well as “bad” dentin. Good dentin is dentin close to the dentinoenamel junction that has fewer dentinal tubules per square millimeter, therefore leaving more peritubular dentin to demineralize through the acid-etch process. In turn, this creates a very good micromechanical surface for bonding adhesive resins. On the other hand, bad dentin includes deeper excavated areas close to the dental pulp, Class V cervical areas, sclerotic dentin and deep Class II proximal boxes without an “enamel rim.” These all are areas where the dentin bond does not perform as well, leading to the possibility of recurrent decay and marginal failure of the restorative material.

As a clinician, it is important to differentiate between good and bad dentin when choosing a material to seal a restorative interface. It is well accepted that glass ionomer cements seal bad dentin better than dentin bonding systems, and in areas of good dentin, dentin adhesives perform very well. Therefore, the key is to use the appropriate material where it performs best. Because of the challenges associated with the placement and finishing of glass ionomer materials and the resulting esthetics, it may be easy to overlook GIC as a direct restorative. However, as a liner or base (dentin replacement), GIC is difficult to beat. Its coefficient of thermal expansion is the same as dentin, so GIC expands and contracts at the same rate as dentin.

The following presents some of the uses of glass ionomer cement in the fabrication of direct and indirect dental restorations.

Base/liner under restorations

Glass ionomer cements have been widely used as bases under restorative materials for some time. Some evidence suggests that glass ionomers, when placed over decalcified dentin substrate, can promote remineralization—even in carious areas. For this reason alone, many practitioners may desire to place glass ionomer in areas of deep carious excavation before placing restorative material.

Also, GICs will bond to dentin without etching or removal of the smear layer. Some practitioners believe this may limit post-operative sensitivity in deep posterior carious lesions. It makes sense, then, that GIC would make an optimal liner or base under restorative materials; in fact, this so-called “sandwich technique” has been employed for many years.

Nonetheless, the use of glass ionomer cements as bases always has been a bit technique-sensitive. Finding that precise consistency of the cement base for packing traditionally has proven a challenge, because of the very short window of opportunity for handling the material prior to setting. Through the use of automix technology and the optimal handling characteristics of materials including Fuji II LC and Fuji IX (GC America), placing glass ionomer bases has been greatly simplified. As a liner, a light-cured GIC, such as Fuji II LC, can be placed over all dentin surfaces in a thin layer, then cured, as in Figs. 1-3.

For more bulk replacements of dentin, a material such as Fuji IX will present increased compressive strength at greater thicknesses1-4 (note Figs. 4-6).

Sandwich technique

	SANDWICH TECHNIQUE
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	(4) Fuji IX GP is syringed into a deep Class II cavity preparation in tooth No. 14 as a dentin replacement prior to composite restoration. (5) A non-serrated amalgam plugger is used to manipulate the GIC into position. (6) After complete set, the material is modified with a bur to conform to the requirements of an ideal cavity. (7) Occlusal view of the completed composite restoration.

The patient presented with an amalgam restoration that required replacement on tooth No. 14 because of recurrent decay on the occlusal and mesial proximal surfaces. It will be restored using composite resin with glass ionomer cement underneath as a “dentin substitute.”

Procedure

1. Remove the existing amalgam restoration along with any recurrent decay.

2. Condition the preparation using Fuji conditioner and rinse thoroughly with water.

3. Activate and mix the automix capsule per manufacturer’s instructions, and syringe the Fuji IX directly into the cavity preparation (Fig. 4).

4. Pack GIC material into the floor of the preparation with a non-serrated amalgam plugger (Fig. 5). Allow it to set.

5. Remove excess material using a bur and handpiece, and recreate the optimal internal form to the cavity preparation (Fig. 6). The material stays in the deep excavated areas of the preparation.

6. Etch the preparation with 37% phosphoric acid for 10-15 seconds, then rinse with water.

7. Evacuate excess moisture using high-volume suction, taking care not to desiccate any remaining dentin not covered by the GIC base.

8. Place the 7th generation bonding resin (G-Bond, GC America) into the cavity preparation and agitate it using the microbrush. This ensures penetration into the demineralized tooth structure.

9. Evaporate the solvent (carrier) by directing air spray across the cavity preparation, then light cure the adhesive for 20 seconds.

10. Incrementally place the composite restorative material (Gradia Direct, GC America). Next, using a plastic filling instrument, sculpt the material to proper occlusal form. Note: Use an artist’s brush dipped in resin to further smooth and pull the composite material toward the cavosurface margins. This step reduces the amount of marginal finishing with carbide burs because of the ready adaptation of the resin-tooth interface.

11. Light cure the facial increment per manufacturer’s instructions. Afterward, sculpt both facial and lingual increments, smooth them with an artist’s brush and light cure them.\

12. Remove the rubber dam and check the occlusion with articulation paper. In this case, a minor adjustment is made using an interproximal composite finishing diamond.

13. Polish the restoration using rubber abrasive polishing points. In this case, the final polishing step is accomplished using an Occlubrush (Kerr Hawe).

14. Re-etch, rinse and dry the restoration, and brush on composite surface sealant. Light cure the sealant to complete the restorative process. Figure 7 shows the completed restoration of tooth No. 14, based with Fuji IX and restored with composite resin Gradia Direct.