Glass Ionomer Cement

Glass ionomer cements are classified as either conventional glass ionomer cements, which are water-based without any resin, or resin-modified glass ionomer, which has about 10% resin added to improve physical properties. Both types of glass ionomer cements are adhesive to enamel and dentin via ionic bonding of the glass ionomer to the calcium and phosphate ions of the tooth. It usually takes 24 hours for the final adhesive values to be attained. Besides being self-adhesive through chemical bonding to tooth structure, glass ionomers have the additional benefit of leaching fluoride to the adjacent tooth structure, which provides some protection against recurrent caries. Both types of glass ionomer cement have low solubility.

Conventional glass ionomer is provided as a powder and liquid that can either be hand dispensed for mixing on a mixing pad with a cement spatula or used in a preloaded capsule that is mixed on a mechanical mixer (amalgamator, triturator). The capsule has a dispensing tip, and the cement is syringed using an applicator gun onto the restoration and preparation. Applicator guns are usually manufacturer specific. When using a conventional glass ionomer cement, the excess cement at the margins should be protected from moisture and dried using a coating agent or an unfilled bonding resin. It is advisable not to clear away excess cement until it is fully set.

Resin-Modified Glass Ionomer Cement

Resin-modified glass ionomer (Figure 23-1) (also referred to as resin-reinforced and hybrid ionomer) is supplied as a powder-liquid, a paste-paste, or a unit-dose mixing capsule with a dispensing tip. It is easier to mix than the conventional powder-liquid glass ionomer and has improved physical properties while retaining the properties of self-adhesion and fluoride release. Some resin-modified glass ionomer cements provide a dentin conditioner to improve adhesive bonding. It is acceptable to clear away excess resin-modified glass ionomer cement when it reaches the gel stage or after complete setting. Resin-modified glass ionomer cements are less vulnerable to the effects of early moisture.

FIGURE 23-1 Step-by-step cementation of a porcelain-metal fixed partial denture with a resin-modified glass ionomer cement. A, Preparations for porcelain-metal fixed partial denture. B, Porcelain-metal fixed partial denture being cemented with resin-modified glass ionomer cement (FujiCEM, GC America, Alsip, Illinois) using an active force when cementing by having the patient bite down on a saliva ejector. C, Cleaning away the set cement from the crown margins. D, Completed cementation of porcelain-metal restoration.

Indications for Water-Based Cements

The primary clinical indications for either type of glass ionomer cement are all-metal and porcelain-metal restorations, alumina or zirconia core-type all-ceramic restorations, implant-supported crowns and fixed partial dentures, and metal posts. It is this author’s primary cement for use in cementing all-metal and porcelain-metal restorations. The tooth must not be overly desiccated and dried when using this class of dental cement. One usually wets the dentin using a microapplicator or a damp cotton pellet so the dentin is slightly glossy with no water pooling on the surface. When glass ionomer cements were first introduced there was concern for postoperative sensitivity after cementation,⁷ but not all studies have found this to be a problem.^8–10

Composite Resin Cements

In recent years the number of composite resin cements has grown significantly. Within this class of resin-based luting agents are those that require a separate adhesive application and those that are self-adhesive. In most cases the indications for these types of dental cement are the same, but the ease of application differs. Adhesive resin cements typically use an etch-and-rinse bonding adhesive, whereas self-adhesive resin cements eliminate the need for the separate phosphoric acid etching and application of a separate resin adhesive to tooth structure before cementation. Various initiators and packaging are used to promote resin polymerization. Composite resin cements are supplied as powder-liquid and paste-paste hand-mixing formulas, a double-barreled syringe with automixing tips, and a unit-dose dispensing and mixing system.

All cements in this category are relatively insoluble compared with other dental cements. They have the highest mechanical physical properties, including high compressive strength, high flexural strength, good fracture toughness, low coefficient of thermal expansion and contraction, and highest stiffness of any dental cement.^1,18,23 Composite resin cements are based on the chemistry of direct placement restorative composite resins and are resistant to wear and abrasion.

This class of cement offers more toothlike translucency. These cements are often available in several shades to permit better matches to adjacent tooth structures. Adhesion of this class of cement to not only tooth structure but also etched porcelain and sand-blasted metal has been demonstrated.^24–27 The interface and bond between etched porcelain and composite resin when the porcelain has been treated with a ceramic primer (silane) strengthens the porcelain and eliminates the propagation of microcracks and fractures between the porcelain, composite resin, and enamel.^28,29 In terms of handling, composite resin cements have easy flow, spread readily over the surface being cemented, are not tacky, can be polished, and have a chameleon effect relative to surrounding tooth structure.

Etch-and-Rinse (Total-Etch) Adhesive Resin

The resin cements in this category require the use of separate tooth etching with phosphoric acid combined with the application of a separate resin bonding agent. When bonding to dentin, these cements use the adhesive as the bonding interface with the composite cement. The cements can be classified as self-cure (autopolymerizing), dual-cure (light cure and self-cure), and light cure. Autopolymerizing and dual-cure composite resin cements can be used for all cementation applications, including all-metal, porcelain-metal, and all-ceramic (fritted porcelain, pressed porcelain, alumina and zirconia porcelain cores) restorations (Figure 23-2).

FIGURE 23-2 A porcelain-metal crown cemented with a dual-cure composite resin cement A, Porcelain-metal crown preparation being cleaned with a prophylaxis cup with a pumice-water paste. B, Inside of porcelain-metal crown being air abraded to improve adhesion of composite resin cement. C, After 15 seconds of etching with phosphoric acid, rinsing, and drying, a dual-cure adhesive resin (Tenure, Den-Mat, Santa Maria, California) was applied to the tooth preparation. D, Cementation of porcelain-metal crown with a dual-cure composite resin cement using a Profin reciprocating handpiece (Dentatus USA, New York, New York) with a wooden insert and PDS/MJ2 tip (Dentatus) to fully seat crown with mechanical force. E, Completed cementation of porcelain-metal crown.

The use of etch-and-rinse adhesive light-cure composite resin (Figure 23-3) cements should be limited to porcelain veneers and pressable ceramic crowns that allow the curing light to penetrate the porcelain so photopolymerization of the cement under the translucent veneer or crown occurs. The differences in the polymerization mechanism are based on the chemical type of initiator. Self-cure composite resin cements use a peroxide-amine initiator-accelerator; dual-cure composite resin cements use a combination of amine and photoinitiator; and light-cure resin cements use a photoinitiator only. Self-cure composite resin cements can be used to cement all types of indirect restorations, but because of potential problems with color stability, translucent all-ceramic restorations and all-ceramic crowns and veneers should be placed with light-cure composite cements.^30–32 When light-cure-only composite resin cements are used with all-ceramic veneers or crowns, the light-curing time should be increased when polymerizing through porcelain thicknesses of 0.5 to 2.0 mm.¹⁹

FIGURE 23-3 Restoration with pressed ceramic crowns and veneers, using an/>

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