CS2-25 Resin Cements PDF

1 Assoc. Prof. Dr. Özay ÖNÖRAL LUTING CEMENTS In indirect restorations such as crowns, bridges, inlays, onlays, and posts, luting cement plays a vital link between the restoration and the tooth. Although the retention of crowns, bridges, inlays, and onlays depends primarily on friction between the w...

1 Assoc. Prof. Dr. Özay ÖNÖRAL LUTING CEMENTS In indirect restorations such as crowns, bridges, inlays, onlays, and posts, luting cement plays a vital link between the restoration and the tooth. Although the retention of crowns, bridges, inlays, and onlays depends primarily on friction between the walls of the preparation and the internal surface of the restoration, the cement is still an integral part of the indirect restoration assembly. In dentistry, cements can be used as cavity base material, cavity lining material, restorative material or as an adhesive agent. The final stage after the completion of the production processes of fixed prosthetic restorations is cementation. For this purpose, luting cements are preferred. Since cementation can be done for temporary or permanent purposes; luting cements are basically divided into two as temporary and permanent cements. In accordance to their chemistries, there are 6 luting cement groups: (i) Zinc oxide eugenol, (ii) Zinc phosphate, (iii) Zinc poly-carboxylate, (iv) Glass ionomer, silicate, and resin cements. RESIN CEMENTS Resin cements are the newest types of cements used to lute and bond indirect restorations. They have higher compressive, tensile, and flexural strength and wear resistance compared to the conventional luting cements. They come in different shades and are virtually insoluble in oral fluids providing better marginal seal than any other cement types. These categories of cements can be used for all types of restorative materials (porcelain, metal, porcelain fused to metal, laboratory composites). Resin cements should bond both to the tooth structure and the internal surface of the restoration. Near East University, Faculty of Dentistry 2 Assoc. Prof. Dr. Özay ÖNÖRAL The term adhesion refers to the establishment of molecular interactions between a substrate (adherend) and an adhesive brought into close contact, creating an adhesive joint. Cohesion is used to describe the interaction of similar atoms and molecules within a material, involving primary (i.e., covalent or ionic) or strong secondary forces (i.e., hydrogen bonding). Wettability is the result of molecular interactions between the adhesive and the substrate, as well as the cohesion forces of the adhesive, particularly its surface tension. Liquids tend to form spheres when placed on a surface because that is the shape with the lowest surface area and, therefore, the minimum surface energy. Wetting is usually evaluated by the contact angle (θ), that is, the internal angle between the liquid and the substrate. Generally, small contact angles are achieved when a low surface tension liquid is placed on a high-energy surface substrate. Contact angles less than 90 degrees indicate a favorable wetting of the surface. Ideal wetting occurs when the liquid spreads over the surface with θ ≈ 0 degrees. Surface roughness increases the wettability of the surface by liquids. Viscosity influences the contact of the adhesive with the substrate. It should be low enough to allow the adhesive to flow readily and penetrate into the details of the substrate surface, without leaving porosities at the interface. In current clinical practice, there are three available resin cements in the market classified according to their adhesive characteristics. These are the etch-and-rinse resin cements, also called Near East University, Faculty of Dentistry 3 Assoc. Prof. Dr. Özay ÖNÖRAL total-etch cements, the self-etch resin cements, and the self-adhesive resin cements. Numerous terminologies pertaining to these three types of cements can be found in books and journals, which add to the confusion in classification. Some authors call the etch-and-rinse cements and self-etch cements conventional resin cements (CR cements) as they require adhesive pretreatment of the tooth surface, i.e., etching, priming, and bonding. The self-adhesive resin cements are sometimes referred to as simply adhesive resin cements (AR) or true adhesive cements as they can bond to the tooth surface on their own without the need for prior etching and bonding. Generally, etch and rinse resin cements yield the highest bond strengths to enamel, while self-etch resin cements show higher bond strengths to dentin. Self-adhesive resin cements have lower bond strengths than the total etch and self-etch resin cements. 1. Etch-And-Rinse Resin Cements These cements are those that use etch-and-rinse or total-etch adhesives. The enamel and dentin surface is etched with 36–37 % phosphoric acid followed by an application of a single layer of the single-bottle self-priming adhesive (dentin-bonding agent or DBA) prior to cementation with the resin cement. These cements, depending on the brand, can be self-cured, dual cured, or light cured. Advantages are: (I) Higher bond strengths to the enamel and other highly calcified Near East University, Faculty of Dentistry 4 Assoc. Prof. Dr. Özay ÖNÖRAL tooth structures (sclerotic dentin, fluorosed enamel, etc.), (ii) High bond strength to dentin if used properly, strict attention to details, and (iii) Usually come in many shades—good shade matching. Disadvantages are: (I) Multistep, (ii) Technique-sensitive, (iii) Possibility of postoperative sensitivity if not used properly on dentin surfaces (etching not more than 20 sec), and (iv) Dentin is less calcified than the enamel, and prolonged phosphoric acid etching can lead to decrease in bond strengths. Indications of these cements are: ✓ Restorations where the predominant tooth structure present is the enamel such as in the case of veneers. ✓ Preparations on highly calcified tooth structures (fluorosis, sclerotic dentin, arrested dentin). ✓ Enamel margins of inlays and onlays (using the selective etch technique). The selective etch technique involves etching with phosphoric acid the enamel margins only for 20 s. The etchant is then washed off and the tooth dried, and a self-etch adhesive is then applied on both the enamel and dentin. ✓ Cementation of low-strength ceramics (feldspathic porcelains) as high bond strengths can strengthen the low-strength ceramic. ✓ Maryland bridges. Near East University, Faculty of Dentistry 5 Assoc. Prof. Dr. Özay ÖNÖRAL Total-etch resin cements either come in two-paste systems or paste-powder systems and with their corresponding etchant and single-bottle dentin-bonding agents. A self-cured activator is also included with the kit. The dual-cured activator serves as a barrier between the acidic single-bottle DBA and the amines of the dual-cured or self-cured resin cement. The porcelain etchant (HF acid) and silane used for pretreatment of the ceramics and laboratory composites are sold separately. Some total-etch resin cements can be completely self-cured. These cements are not recommended for veneers as there is limited working time to properly fi t and seat the veneers due to their self-curing mode. Furthermore, because of their self-cured mechanism, they contain an amine initiator which has a yellowing effect during aging causing color shift. Total-etch dualcured resin cements come in two-paste systems (base paste and catalyst paste). When the base and catalyst pastes are mixed together, they set by both self- and light-cured mechanisms. To make the cement set only by light curing, such as in the case of veneer cementation, only the base paste is used. Light-cured resin cements specifically veneer or aesthetic cements come in a single syringe and can only polymerize with the application of light. These cements come in different shades. Since etch-and-rinse cements involve etching the enamel and dentin with phosphoric acid, they yield the highest bond strengths to the enamel among all resin cements. When used properly, they yield high bond strengths to dentin (Casseli and Martins 2006). In summary, the keys to successful cementation and preventing postoperative sensitivity with etch-and-rinse resin cements are as follows: ✓ Do not over-dry the tooth, especially after etching. The surface should appear glossy. ✓ Limit etching time to 15 s only on dentin. ✓ Ensure adequate sealing of the dentinal tubules through proper application of the dentin-bonding agent. ✓ Ensure proper tooth isolation, preferably with a rubber dam. ✓ When using self- or dual-cured resin cement, use a self-cured activator to prevent incompatibilities between the amine initiator of the cement and the acidic DBA. ✓ Tooth isolation is of paramount importance with these cements. Near East University, Faculty of Dentistry 6 Assoc. Prof. Dr. Özay ÖNÖRAL Near East University, Faculty of Dentistry 7 Assoc. Prof. Dr. Özay ÖNÖRAL 2. Self-Etch Resin Cements These cements are simpler to use as phosphoric acid etching is eliminated. Instead, the composed etchant, of monomers and acidic phosphate esters, is combined with the primer, thus the name selfetch primers. Common acidic monomers include 10-MDP found in Panavia F (Kuraray), 4-META, and GPDM. The adhesive to pretreat the tooth surface for most self-etch resin cements comes in two bottles, which are dispensed in equal amounts and are thoroughly mixed. These cements are mostly dual cured. Advantages are: (I) Good bond strength to the dentin, (ii) Ease of use (no need for a separate phosphoric acid etching step, rinsing and drying), (iii) Less risk of over-etching the dentin, (iv) Less risk of postoperative sensitivity, and (v) The smear layer is not removed, preventing the inflow and outflow of fluid from the dentinal tubules. Disadvantages are: (I) Relatively weaker bonds to the enamel and highly calcified tooth structures, (ii) May still cause postoperative sensitivity if adhesive is not airdried, (iii) Most self-etch resin cements need refrigeration as acidic monomers degrade with heat, and (iv) Less available shades compared to total-etch resin cements. Indications of these cements are: ✓ Crowns and bridges with a lot of healthy dentin exposed ✓ When retention is compromised: • Short crowns with less than 4 mm height • Crown tapers of more than 14° ✓ Crowns and other fixed prostheses that have repeatedly come off ✓ Inlays and onlays, especially those with deep cavities and few walls remaining Near East University, Faculty of Dentistry 8 Assoc. Prof. Dr. Özay ÖNÖRAL Most self-etch resin cements come in two-paste systems and are dual cured. These cements are very specific as to the type of adhesive that should be used in conjunction with them to avoid any incompatibilities. The self-etch adhesive usually comes in two bottles. Equal amounts of each liquid are dispensed in a mixing well and mixed thoroughly for 5–10 s to ensure good chemical reaction. The adhesive is then applied on the bonding surfaces of the tooth using a light rubbing motion for 20 s or as per manufacturer’s instructions. The adhesive is lightly air-dried with oil-free air for a minimum of 20 s. The air-drying removes the solvents and excess water leaving a thin but well-infiltrated hybrid layer. The adhesive is then light cured to stabilize the hybrid layer. Pastes A and B of the resin cement are dispensed in equal amounts on a mixing pad. Some self-etch resin cements come in twist tubes where each twist of the tube is marked by a line to ensure that exact amounts of base and catalyst pastes are dispensed. The pastes are then mixed with a plastic spatula using folding strokes to ensure that there are no air bubbles entrapped. Some self-etch resin cements come in an auto-dispenser to ensure that equal amounts of cements are dispensed. In summary, the keys to successful cementation with these cements are as follows: ✓ Data shows that self-etch resin cements yield comparable, if not higher dentin bond strengths to total-etch resin cements. Generally, however, bond strengths to the enamel are weaker than that of total-etch systems. They bond better to the dentin than to the enamel. This can be attributed to the weaker etchants in self-priming systems (acidic monomer vs. phosphoric acid). ✓ There is less risk of over-etching the dentin as the acid is weaker, decalcification of the dentin is less, and a thinner but well-infiltrated hybrid layer is formed. This explains why dentin bonds for self-etch resin cements are higher than that of total-etch cements in some studies. ✓ A common step usually ignored in self-etch adhesives is the air-drying after adhesive application. The adhesive should be air-dried for about 5–10 s as drying removes the residual acidic hydrogen ions and ethanol. If not air-dried, the hydrogen and ethanol remain in the set adhesive layer. The residual hydrogen will cause continuous etching, while the ethanol can cause hydrolysis of the bonds, which is clinically seen as brownish discoloration on the margins. ✓ Self-etch resin cements are usually stored under refrigeration and away from sunlight as heat degrades the acidic monomers. Near East University, Faculty of Dentistry 9 Assoc. Prof. Dr. Özay ÖNÖRAL Near East University, Faculty of Dentistry 10 Assoc. Prof. Dr. Özay ÖNÖRAL 3. Self-Adhesive Resin Cements The self-adhesive resin cements are the newest in this category. Also called one component “universal adhesive cements,” these cements do not require a separate bonding procedure on the tooth as phosphoric acid is grafted in the resin in the form of phosphoric esters. The phosphoric acid reacts with the composite fillers forming a cross-linked polymer, and it also reacts chemically and micromechanically with the dentin. These cements are dual cured. Advantages are: (I) Good alternatives to the more complicated-to-use and techniquesensitive total-etch and self-etch resin cements, and (ii) They can be used for most restoration types, regardless of the restoration material except veneers. Disadvantage is that when retention is the main issue and there is a lot of dentin exposed, the self-etch resin cements should take precedence over the self-adhesive cements as self-etch cements have higher bond strengths and are more durable. Indications are: ✓ They are the resin cements of choice for high-strength ceramics such as zirconia and alumina. ✓ They are also indicated over conventional luting cements, when retention is compromised such as too tapered preparations, short crowns, and onlay preparations with little tooth structures and walls remaining and isolation and time constraints are a problem. Self-adhesive resin cements come in a special double-barreled dispenser that makes it possible for the base and catalyst paste to be dispensed simultaneously and equally onto an auto-mix tip that enables the operator to apply it directly to the restoration and preparation margins. As self-adhesive resin cements contain acidic monomers that degrade with heat, they should be refrigerated and kept away from sunlight. The self-adhesive resin cements produce adequate bonds to the dentin and enamel. However, comparing them with etch-and-rinse and self-etch resin cements, they show lower bond strengths. Initially high bond strengths also tend to decrease with time. As less clinical steps are needed for these cements, there is less risk of contamination, and hence these cements are not as technique sensitive as the etch-and-rinse cements. Some authors recommend their use for areas of the mouth that are difficult to isolate such as the posterior segments. Although there are reports of clinical success with these self-adhesive resin cements, long-term observation of their clinical success is needed as they are relatively new Near East University, Faculty of Dentistry 11 Assoc. Prof. Dr. Özay ÖNÖRAL Near East University, Faculty of Dentistry 12 Assoc. Prof. Dr. Özay ÖNÖRAL Illustrations and Tables Near East University, Faculty of Dentistry 13 Assoc. Prof. Dr. Özay ÖNÖRAL Near East University, Faculty of Dentistry 14 Assoc. Prof. Dr. Özay ÖNÖRAL Near East University, Faculty of Dentistry 15 Assoc. Prof. Dr. Özay ÖNÖRAL Near East University, Faculty of Dentistry 16 Assoc. Prof. Dr. Özay ÖNÖRAL References 1. Jeffrey Platt. McDonald and Avery's Dentistry for the Child and Adolescent (Tenth Edition) 2016, Pages 206-220, https://doi.org/10.1016/B978-0-323-28745-6.00012-0. 2. https://pocketdentistry.com/12-other-dental-cements-2/ 3. Ronald Sakaguchi and John Powers. Craig’s Restorative Dental Materials, 13. Edition, Chapter 13. 4. Stephen Rosentsiel, Martin Land, and Junhei Fujimoto. Contemporary Fixed Prosthodontics, 5. Edition, Chapter 30. 5. Michello Sunico Segarra and Armin Segarra. A Practical Clinical Guide to Resin Cements. Part II-Chapter 3, 2015. Near East University, Faculty of Dentistry