Chapter 23 Cements
The number of choices for laboratory-fabricated restorations has increased significantly over the past decade. When planning treatment to replace missing teeth with fixed or removable partial dentures or implants, full-coverage crowns, or partial-coverage inlays and onlays and when restoring the endodontically treated tooth with cast posts and cores and prefabricated posts, the options include cast metals, ceramics, metal-ceramic, and computer-aided design and manufacture (CAD-CAM)–based restorative materials. With these developments, the types of cements have also changed. The cementation or luting of restorations is an extremely critical phase in placing laboratory-fabricated restorations. The surface treatments for the various adhesive cements differ, so it is critical that the clinician and the chairside assistant understand the requirements and steps needed to optimize clinical success with any given cement.
In the past (and still), the term “permanent cement” has been used to describe the use of a cement for final, definitive cementation of indirectly placed laboratory-fabricated restorations. Unfortunately the term as it relates to restorative procedures is inaccurate and gives patients a false sense of security and expectation. In the future of fixed prosthodontics, cementation in restorative dentistry should focus on the placement-cementation so that the restoration cannot be removed later. Currently, a more proper term for cementation is “definitive cementation.”1
This chapter describes all types of dental cements for definitive cementation and includes their composition, properties, and indications. A class of dental cements used for cementation of provisional restorations is described but not covered in detail. Currently the most widely used dental cements, glass ionomer and resin, adhere to the dentin for full-coverage restorations and to the enamel and dentin for partial-coverage restorations and porcelain veneers. These same cements can be used successfully to cement cast metal posts and cores, ceramic posts and cores, prefabricated metal posts, and resin-fiber–reinforced posts.
The treatment procedures for laboratory-fabricated restorations generally require two or more patient visits and a series of treatment decisions to achieve the final restoration. During treatment the clinician will spend significant time with tooth preparation (or implant placement), soft tissue management, impression making, fabrication of provisional restorations, and selection of the tooth shade for esthetic restorations. At a later appointment the clinician will perform the try-in and adjustment of the restoration and cementation. Preparing for these restorations might also involve a diagnostic wax-up to preview and plan the case, or more involved occlusal therapies may be needed during the provisional restoration phase. Over the course of treatment, cementation of the restoration requires less than 5% of the overall time spent on clinical steps. In terms of cost for these restorations, whether single crown, inlay or onlay, a more involved multi-unit fixed partial denture or multiple restorations for numerous teeth for esthetic reasons (such as a large porcelain veneer case), the practitioner may use an adhesive cementation system costing less than $20 (US), or for a single unit less than $2 (US), yet the durability of the restoration depends on this agent.
Improper and incorrect cement selection for the restorative material being cemented or poor technique during cementation can lead to premature failure of the costly restoration. Financial considerations include the cost to the practitioner in laboratory fees, cost to the patient for the restoration, and sometimes cost to the practitioner’s reputation and the staff’s perception of the success or lack of success with certain procedures.
Other factors are equally as vital as the selection of cement type for clinical success. For example, during the laboratory fabrication of cast and ceramic restorations, some steps can lead to marginal discrepancies and gaps between the restoration and tooth preparation. Today’s contemporary cements provide excellent marginal integrity to compensate for these discrepancies.2–5 An inherent aspect of retention is the taper of the tooth preparation with different cements.6 Zidan and Ferguson6 found that the retentive values of the adhesive resin cements for a tooth preparation with a 24-degree taper were 20% higher than the retentive values of the conventional cements (zinc phosphate and conventional glass ionomer) for a tooth preparation at a 6-degree taper. The use of resin luting agents yielded retention values double those of zinc phosphate or conventional glass ionomer cement. The type of bur or diamond rotary instrument used to prepare for crowns can also affect the retention of a crown placed with different cements.7
A significant issue after cementation is the presence of postoperative sensitivity. Conventional glass ionomer cements have higher rates of postoperative sensitivity than other cements,8 although reports show that when a manufacturer’s recommendations are followed, postoperative sensitivity is the same for zinc phosphate cement and glass ionomer cement.9–11 Before cementation, the tooth must be clean and dried to a level compatible with the cement being used. To err on the side of caution, some recommend avoiding desiccation of the dentin surface of the preparation before cementation12 to decrease the likelihood of postoperative sensitivity after cementation. Other studies describe the use of desensitizing agents and dentin sealers as part of the cementation process.13–17 However, certain desensitizing techniques can have a negative impact on adhesion. Although use of a 5% glutaraldehyde sealer15,16 or a resin desensitizer-sealer14,16,17 is not detrimental to multistep etch and rinse adhesive resin cements or glass ionomer cements, oxalate desensitizers are incompatible with glass ionomer luting agents.18
If there were one cement for all clinical situations, it would have to be easily mixed and go through its setting reaction either quickly for a single crown or inlay or onlay or be adjustable to set more slowly for multi-unit, more involved cementation cases. Unfortunately this “holy grail” of cements is not available. However, certain factors and properties can guide the choice of cement for a given situation. In the search for an all-purpose cement, specific physical properties and handling characteristics have been quantified.19–21 The ideal properties of an all-purpose cement include the qualities listed in Box 23-1.
Box 23.1 Desirable Properties of an All-Purpose Cement
Dental cements can be classified based on their chemistry and applications19–21 (Table 23-1). All cements must have a film thickness and consistency compatible with cementation, as described in American Dental Association (ADA) specification No. 96 and International Organization for Standardization (ISO) specification 9917. The three categories of dental cements are water-based, resin-based, and oil-based definitive and temporary cements. Examples of each cement type are listed in Table 23-2. This chapter focuses on glass ionomer and adhesive composite resins.
|TYPE OF CEMENT||APPLICATIONS|
|Conventional glass ionomer|
|Conventional Glass Ionomer|
|Fuji I||GC America|
|Resin-Modified Glass Ionomer|
|RelyX Luting Plus||3M ESPE|
|RelyX Luting||3M ESPE|
|Fuji Plus||GC America|
|Hy-Bond zinc phosphate||Shofu|
|Etch-and-Rinse Resin Cement (Can Be Dual-Cure or Self-Cure)|
|RelyX ARC||3M ESPE|
|CLEARFIL ESTHETIC and DC BOND||Kuraray|
|Variolink II||Ivoclar Vivadent|
|Dual Cement||Ivoclar Vivadent|
|Duo Cement Plus||Coltène/Whaledent|
|Self-Etch Self-Adhesive Resin Cement|
|RelyX Unicem||3M ESPE|
|Veneer Cements (Light Cure)|
|Variolink veneer||Ivoclar Vivadent|
|RelyX veneer||3M ESPE|
|CLEARFIL ESTHETIC CEMENT||Kuraray|
Water-based cements typically undergo an acid-base setting reaction and are acidic during cementation. These cements are either non-adhesive or have a low bond strength to tooth structure. Some water-based cements provide for fluoride release. Examples of water-based cements are glass ionomer, resin-modified glass ionomer, zinc phosphate, and zinc polyacrylate.
Resin-based cements are chemically similar to composite resins. They have higher bond strengths to tooth structure when bonded to dental adhesives. In some cases these cements are self-adhesive to dentin. For some resin-based cements, surface treatments of the restoration combined with primers and monomers allow adherence to dental metallic alloys or ceramics. Although these cements have stronger physical properties, they are generally more technique sensitive to use.22
Oil-based cements are typically used for the cementation of temporary (provisional) restorations. In the past most contained eugenol, but there are now eugenol-free oil-based cements. Typically these cements have a greater film thickness than water-based and resin-based cements and much lower physical properties. In cementing provisional restorations with these agents, the tooth must be thoroughly cleaned before the definitive cement is applied.
Each category of cement presents challenges to achieving clinical success. Within each class, these cements have physical properties that allow for a consistency favorable to cementation and a film thickness that will allow for complete seating of a restoration. There is variability in the handling characteristics of each class of cement and even differences within the same class of cement. A recent survey of usage of definitive fixed prosthodontic cements noted that conventional glass ionomer was used 24% of the time, resin modified glass ionomer 46% of the time, composite resin cements 8% of the time, zinc phosphate cement 10% of the time, and zinc polycarboxylate 12% of the time.23 Generally the clinician should not assume that cements within the same class are mixed and manipulated in the same way. The dentist and chairside assistant must read the manufacturer’s instructions relative to material dispensing and mixing before using any cement on a restoration.1,18,23
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 (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.
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
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.
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