2. Selection of Luting Agents
The various types of luting agents with common examples are shown in Figure 1 [1,5,16,17,18]. Water-based luting cements release fluoride, such as glass-ionomer, resin-modified glass-ionomer, and zinc phosphate and zinc polycarboxylate cements , while resin cements are chemically similar to composite resins, which provide maximum strength to the tooth and indirect restoration when bonded with dental adhesives [19,20]. In addition, the surface etching of the restoration can provide micromechanical retention with resinous cement. Despite the physical properties of these cements, they are usually more sensitive to the cementation process [5,21]. Namely, metal copings, frameworks, or partial restorations are usually fixed with water-based cements, while composite cements are indicated when it is necessary to provide stronger adhesive bonding between the dental structure and restorative material .
There are different performances between cements and even between different manufacturers that claim to produce the same product. Therefore, before applying the luting cements, it is extremely important to follow the manufacturer’s instructions for use , as well as to perform all the suitable surface treatments on the restoration and substrate. Cements can also be divided into two groups: adhesive and non-adhesive (Table 1). Non-adhesive cements provide mechanical retention and are commonly based on water and reactive filler, while adhesive cements form an adhesive bonding with both tooth hard tissues and restoration, they consist of anhydrous-silanized non-reactive fillers [7,21].
The ideal dental cements maintain and protect the tooth’s hard structures, are highly resistant to tensile and compression stresses, fatigue resistant, and mechanically stable, present low shrinkage and strong bond strength to the tooth tissues and dental biomaterials, and prevent the development of caries in the adhesive interface. The basic properties of various dental luting agents are shown in Table 2. Ideally, the dental cements should be biocompatible, possess antimicrobial activity, provide marginal sealing, create a minimum film thickness, be easy to apply, be less soluble, present translucency and radiopacity, and have optimal working and curing time. In addition, they must have high fracture strength, optimal wettability (small wetting angle), and sufficient viscosity for complete spreading, as well as be esthetic when used in combination with a restorative material. Moreover, removing the excess material should be easy [5,16,22].
The cementation steps are as remarkable as other aspects of restorative dentistry since the incorrect choice of cement can result in impaired marginal integrity, esthetic issues, and malocclusion ; moreover, any wrongly performed step could compromise the final bond strength. The cement selection depends on the preparation type and restorative material that will be cemented . Conventional cements were commonly used for metal alloys and fixed partial dentures. Zinc phosphate luting cements have been applied for many years. However, in more invasive preparations or for patients with a history of pulp hypersensitivity, a more biocompatible cement, e.g., polycarboxylate, should be used [16,25]. Some restorations require adhesive systems that are characterized by more complex applications [23,24]. In general, the stability and longevity of luting cements are not always predictable, as cement dissolution can lead to marginal caries. These problems are less pronounced with the use of resin-based and glass-ionomer cements due to their more predictable adhesive bonding and strength [23,26]. Furthermore, resin cements are especially preferable when the tooth is prepared following the principles of minimally invasive dentistry and all preparation margins are accessible . The crowns cemented with zinc phosphate, polycarboxylate, and glass-ionomer cements can be cautiously removed in case of necessity, reducing the risk of damaging the prepared tooth. However, in order to remove a restoration adhesively cemented, it must be sectioned.