April 3, 2019
by Chad C. Duplantis, DDS, FAGD
Cementation has a lengthy history in dentistry, with varied amounts of success along the way. As clinicians, we have seen numerous changes to formulations over the years. Each change is designed to improve our clinical results. However, misunderstanding the processes can compound the clinical applications. The intent of this article is to make the cementation protocol more efficient for the practitioner and team. Following reading, the clinician will better understand how to use the available cementation options.
It is often that practitioners choose a dental cement because it was recommended by a colleague or a sales representative. While there is not a “wrong” way to go about selecting a cement or cementation protocol, education provides the practitioner with knowledge to aid in decision-making. The knowledge gained through proper education is invaluable in assisting the clinician in proper cement selection. When it comes to cementation, the clinician must be aware of certain desirable characteristics in cements that provide consistent and predictable results.
In addition to the desired characteristics of the cements, the clinician must understand the indirect materials being cemented. Each of these materials have different qualities that influence the type of cements to be used. The materials must be handled and treated differently to achieve optimal results with the cements.
Once the cements and materials are understood, the clinician should be able to make a better decision on cementation based upon indications. The clinical armamentarium should include cements for multiple indications. The intent of this article is to assist the clinician in cement selection, thereby making the process more efficient.
What Should A Clinician Look for in a Cement?
Cementation is a generic term that refers to a broad range of products and techniques. Prior to differentiating the cements, it is important to understand that there are two main categories that encompass all dental cements. The first category is “luting” and the second is “bonding.” Luting, or a luting cement refers to a cement that is a substance that fills a space and holds the two items together.1,2 Bonding differs from luting in that a chemical reaction occurs enhancing the adhesion to the tooth or crown by the cement.1,3 Cements from both categories still have a place in modern day dentistry.
The characteristics below should be considered when choosing a cement:
Film thickness – Film thickness refers to the thickness of the cement when applied. This is especially important to allow for complete seating of our restorations. A minimal film thickness (≤25 µm) is desired for dental cements.4,5,6
Retention – Although retention is mentioned as a property of the cement, retention is really a property of the preparation. For a cement to be retentive, the preparation must have retentive properties. This factor is partially dependent upon the practitioner and partially on the clinical presentation of the tooth. All clinicians should strive to incorporate parallelism, length and surface area to improve retention and resistance. Axial grooves and other anatomical enhancements can also aid to prevent dislodgment of the restoration by functional and parafunctional stresses.7
Water solubility – One of the most important properties of a cement is the water solubility or resistance to oral fluids. Water sorption (uptake) is also important. Due to the environment in which these restorations are placed, it is imperative that a cement has a low water sorption and solubility. The possession of both characteristics will prevent washout of the cement, ultimately leading to leakage and failure.8
Ease of clean-up – A cement that cleans easily is preferable. It can be rather difficult to remove the excess material for some cements following the seating of the restoration. A cement that can be tack cured can make the clean-up process faster and much easier.
Ease of delivery – The days of powder and liquid are gone. These processes can be very sensitive if the proper ratios aren’t adhered to. Many cements are now available in quick caps (which may involve trituration) and a paste/paste syringe with a mixing tip. The paste/paste syringe ensures consistent mixing and an efficient delivery process.
Color stability – Colour stability is particularly important for thin, ceramic restorations. Studies have shown that many resin cements are subject to color degradation over time. This is especially the case of most dual-cure cements. Light-cure cements are less prone to color degradation yet can be more technique sensitive.9
Pulpal irritation – The acidity of the cements can cause pulpal irritation if not handled properly. Sensitivity is caused by movement of fluids within the exposed dentinal tubules.10 Post-operative sensitivity was seen to be reduced with the introduction of resin modified glass ionomer cements (RMGI), due to the ease of use and that there is no need to use an etchant prior to placement.11 It has further been shown that by use of proper techniques, sensitivity between RMGI and resin cements has been similar.11,12 Resin cements can be effective and produce minimal post-operative sensitivity if a hybrid layer of both resin and tooth is formed with the collagen fibers to create resistance to exposure of the tubules.13
Adhesion – Adhesion refers to the ability to form a bond between the cement and a substrate. The bond values differ between dentin, enamel, and the restorations. The cements discussed – RMGI, self-adhesive resin cements (SARC), and adhesive resin cements (ARC) – vary in bond strength. In addition, the bond strength of the ARC is dependent upon the bonding agent ultimately utilized. This must be investigated by the dentist to determine if the strength of the proposed cement satisfies the requirements of each indication.
Although no one cement will perform perfectly in all categories, it is important to choose a cement that is favorable in as many as possible. Cements which fall under the same classification can behave somewhat differently in each of the categories.
Dental cements have various uses in dentistry, and the quest for a “perfect cement” dates to the mid-1800’s. The first cement to be introduced for clinical usage was a zinc oxide eugenol (ZOE) cement. Minor formulary changes over time have allowed this cement to be more useful as a permanent cement, however, this cement is mainly used as a temporary cement.4 There were several classifications of ZOE cements, and many of us still use ZOE regularly in our office in the form of IRM (Immediate Restorative Material, Dentsply Sirona). So, although this cement is not used for permanent cementation, it still has a value in clinical dentistry.
Following ZOE, Zinc Phosphate was introduced in the late 1800’s. This cement is still used by clinician’s today and is often considered “the gold standard” for dental cementation due to its success.4 The cement was composed of a phosphoric acid liquid and a zinc oxide powder. Although set time, fluidity, and film thickness were in its favor, it was fairly water soluble. In addition, pulpal irritation was an issue due to the acidity.14
In progression, the cements all lacked adhesive properties until approximately 1960. The first cement to exhibit adhesion was polycarboxylate cement, which was composed of zinc oxide, magnesium oxide, bismuth, aluminum oxide and a polyacrylic acid. This cement exhibited a property called chelation through bonding calcium ions to the tooth. The biocompatibility was favorable, however there were excessive de-cementations over time. Today, the cement is mainly used as a temporary cement.
Following polycarboxylate, a new classification with promising properties was introduced. This classification is today referred to as conventional glass ionomer cements (GI). The GI cements were created by utilizing the polyacrylic acid in the polycarboxylates and modifying the powder to create a flouroaluminosilicate glass powder. This was a powder-liquid mix that was capable of releasing fluoride over time. The new formula lead to widespread use over time with success, and multiple indications.15 The bond strength was stronger than polycarboxylates, but more was desired from cements for clinical usage. Ultimately, these minor changes lead to advancements which created the three most commonly used cements today: Resin modified glass ionomer cements, adhesive resin cements, and self-adhesive resin cements.
Resin Modified Glass Ionomer Cements
Resin modified glass ionomer (RMGI) cements were introduced in the early 1990’s. These cements represent an improvement over traditional GI cements with the addition of methacrylate monomers, thereby increasing adhesive properties.16 They have an improved flexural strength, are biocompatible, and provide a greater bond (although classified as a luting cement) than traditional GI cements. RMGI cements are attractive by releasing the fluoride ion, are self-adhesive, and have little or no post-operative sensitivity.17,18
These cements have multiple indications; however, caution must be exercised as reports indicate that leucite and feldspathic restorations have an incidence of fracture if luted with RMGI. Proper
retention and resistance form must be adhered to for successful cementation with RMGI cements.4
The traditional formulations of GI cements were a powder/liquid mix which was rather technique sensitive. More recently, however, manufacturers have worked on improving the physical properties to the paste-paste syringe-based RMGI cement options. This recent innovation of paste-to-paste RMGI cements (Meron Plus QM, VOCO) also features added resin, which increases the fluoride release but slightly decreases the fluoride release. The additional resin in the newer formulation also leads to a higher bond strength than other cements with lithium disilicate restorations.19 The newer delivery systems are also advantageous in that they clean up easier as compared to the previous versions. RMGI cements were one of the first cements that had demonstrated positive performance in many of the desired characteristics (Fig. 1).
Performance of Meron Plus QM against other RMGI cements.
Resin cements encompass a broad classification of cements. This general classification is the most widely used classification of cements in modern dentistry.4 The delivery mechanism can be complicated, but it can also be quite simple. The two sub-categories that will be addressed are adhesive and self-adhesive cements.
Adhesive Resin Cements
Adhesive resin cements represent the longer standing of the two sub-categories. These cements have been used widely in dentistry for years, with multiple indications. There are multiple component systems, as well as dual component syringe mixed systems. In addition, the cements under this category are available in self-cure, dual-cure, or light-cure versions.
When selecting an adhesive resin cement, it is imperative that the clinician follow the appropriate bonding protocol outlined by the manufacturer for an optimal result. This bonding protocol consists of proper preparation of both the tooth and the restoration. An adhesive bonding agent and a silane coupling agent are necessary for success.20 Multiple shades of resin cements are available, as well as corresponding try-in pastes dependent upon the manufacturer.
Adhesive resin cements have a high flexural bond strength; therefore, they resist deformation. The ultimate shear bond strength is determined by the adhesive agent used.21 The recent addition of universal bonding agents has made the process of using adhesive resin cements more efficient. These bonding agents were introduced into the dental world in 2011. Universal bonding agents are mostly light-cure, self-etching, dentinal adhesives that contain MDP. The MDP assists in the preparation of the intaglio surface of the restoration and acts as a silane coupling agent. These bonding agents are entirely flexible in their usage, and can be used with any (self-, total-, selective) etching preference. It is important to note that some manufacturers recommend a dual-cure activator for usage with a dual- cure cement.22 Once again, it is imperative to verify the compatibility of the adhesive with the cement. It is also recommended to stay within manufacturer lines (adhesive and resin cement) to ensure compatibility. With an appropriate resin based adhesive and adherence to instructions, these cements can perform well in a given situation.
Self-adhesive Resin Cements
Self-adhesive resin cements are often-times referred to as “universal” cements. With an initial pH of 2.1 to 2.3, they are acidic enough to “etch” the tooth alone.23 They also have monomers that enhance the bond strength without applying a separate priming or bonding agent. In fact, etching is not recommended by the majority of manufacturers. Most of these are dual-cure. Although bond strengths are not as high as those of the adhesive resin cements, they do increase when light initiates the set.23 The indications are vast: crowns, bridges, inlays and onlays of all materials. Veneers are not recommended as an indication by most manufacturers as the long-term color stability can be an issue with these cements.
When considering bonding of self-adhesive resin cements, the dentinal bond strength is favorable. The bond strength to enamel is the weaker link in these cements.24 With a less favorable bond to enamel over dentin, caution should be exercised if using a self-adhesive resin cement on a prep with a large amount of enamel.
Self-adhesive resin cements are easy to use, easy to deliver, and easy to clean-up. Studies have indicated that self-adhesive cements exhibited the highest water sorption of all resin cements. This is due to an acid monomer content, which can cause hydroscopic expansion stress. This expansion may cause a threat to certain restorations. Water sorption should be less than 40 µg/mm3 and water solubility should be less than 7.5 µg/mm3 (Fig. 2).21
Water sorption of various resin cement.
Selection of Cement for Various Indications
One must realize that each patient and each restoration present different clinical situations that must be addressed. It is for this reason that we must be equipped with the aforementioned cements for each situation. In a perfect world, all preps would be supragingival with no oral moisture, no saliva, no contaminants, and one restoration would be suitable for all. We all know that these “unicorn-like” situations don’t exist, so we must properly assess each situation.
As far as materials are concerned, the number one requested restoration is a zirconia restoration (either full or porcelain layered), a distant second is lithium silicate and disilicate, and a metal (gold, precious, or semiprecious) coping is third.25 Each of these materials should be treated differently for successful cementation. We will discuss cement selection for zirconia (and metal) based restorations and glass and particle-filled ceramic restorations in detail.
Prior to discussing restorations, it is important to analyze the retentiveness of each preparation, and possible cements for that particular situation. Having recommended three main forms of cement, the author recommends ranking the cements in the following order: RMGI, SARC, and ARC. The reason behind this is based upon two key factors: ease of use and bond strength.
Zirconia-Based and Metal-Based Restorations
Since their introduction over 10 years ago, zirconia or zirconium oxide restorations compromise the fastest growing and most widely used restoration amongst U.S. dentists.25 These restorations are a subcategory of the general classification “polycrystalline restorations.”26 These restorations have numerous indications in dentistry, including full coverage crowns, inlays, onlays, veneers, and bridges. The zirconium is often monolithic but can be veneered with a veneering ceramic. The veneering of an additional ceramic will not affect cementation in most instances, seeing as the entire intaglio surface is zirconia-based.
Zirconia restorations are non-silica-based, metal-free restorations. The composition requires them to be treated differently than conventional ceramics. Retentive analysis of the preparation is a must in cement selection. If the prep is retentive, these may be cemented with conventional “luting” cements (RMGI).27 RMGI requires no special preparation other than a clean intaglio surface. The intaglio surface should be treated via sandblasting, with a 50-60 µm aluminum oxide below 2 bar (≤29psi). No additional surface treatment of the restoration is needed. Optimal performance of the cement, however, requires a clean prep. The prep should be cleaned with an antibacterial agent. A 2% Chlorhexidine rinse such as Consepsis® (Ultradent, South Jordan, UT) is a suitable agent for this purpose.
If the prep is deemed non-retentive, research supports that a bond is capable if treated correctly. Dr. Marcus Blatz has coined the “APC zirconia bonding concept”. In this concept, the intaglio surface should be treated via sandblasting, as detailed above, followed by treatment with a primer suitable for zirconia or alumina. Examples of suitable zirconia primers include Ceramic Bond (VOCO, Cuxhaven, Germany), Z Prime Plus (Bisco, Schaumburg, IL), Z-Bond (Danville Materials, Carlsbad, CA), and Monobond Plus (Ivoclar Vivadent, Amherst, NY), amongst others. The final step is to utilize a dual or self-cure resin cement. It is important to not use a light-cure only cement, as the cement will not fully polymerize.28 When utilizing a SARC cement, the prep should once again be cleaned with an antibacterial agent.
If so desired, a dual or self-cure ARC cement can be used. In this case, the intaglio surface of the restoration must be sandblasted and treated with a primer suitable for zirconia. Following the previous steps, both the restoration and the tooth must be treated according to manufacturer’s recommendations dependent upon bonding agent and cement selected. This should provide a predictable bond; however, ARC cement should only be necessary if the prep lacks retentive features for zirconia and metal restorations.
Although metal-based restorations do not comprise a large percentage of dental restorations today, they are still utilized in dentistry and deserving of consideration.25 Although variations in metal composition exist, these materials are handled in a similar fashion to the zirconia-based restorations. RMGI or dual or self-cured resin cements can be used with success.29 If a clinician selects a resin cement, the use of metal primers is debatable, but does not provide a deleterious effect.30,31,32
For both zirconia and metal restorations, it is important to not use a light-cure only cement, as the cement will not fully polymerize.28
Predominantly Glass Ceramics and Particle-Filled Glass Ceramics
Predominantly glass ceramics are composed of feldspar minerals and aluminum oxides. These ceramics are generally referred to as feldspathic ceramics, and a common example is Empress (Ivoclar Vivadent). These are highly esthetic with multiple indications: porcelain jacket crowns, inlays, onlays, and veneers. Due to their low strength and fracture resistance, it is recommended to cement these restorations with adhesive resin cements, thus bonding the restorations.26 In order to effectively bond these restorations, it is recommended that the intaglio surface be treated with 9.6% HF Acid for a minimum of 1 minute (maximum of 2.5 minutes), followed by ceramic (MDP containing) primer (silane) application for one minute then air dried.26,33 Following the previous steps, both the restoration and the tooth must be treated according to manufacturer’s recommendations dependent upon bonding agent and cement selected.
Particle-filled glass ceramics, once again, represent a broader classification composed of lithium disilicate (e.max, Ivoclar Vivadent), lithium silicate (Obsidian, Glidewell Laboratories, Newport Beach, CA) and glass-infiltrated alumina (In-Ceram Alumina, Vita, Yorba Linda, CA). These ceramics are filled with various types of particles, of varying size and amount, in a glassy matrix. Their strength is determined by the number of particles included and a lesser amount of glassy matrix. The three rank in strength (lowest to highest) based upon filler content in the order presented. These materials may be used for crowns, veneers, inlays, and onlays. These materials need to be understood, as they are each recommended to be treated differently than feldspathics prior to cementation.26
It is the author’s recommendation to adhesively bond all of these restorations if they are anterior, thin or partial coverage. All full coverage posterior restorations may be cemented with SARC or RMGI (dependent upon shade of cement or translucency of restoration.) For instance, a translucent restoration should not be cemented with an opaque or off-color cement, unless the desire is to alter the final shade of the restoration. When in doubt, a try-in paste of desired color is indicated.
For the lithium disilicate or lithium silicate restoration, a 5% HF acid etch for 20 seconds is recommended. The restoration is then to be treated with a ceramic silane primer. It is important to note the difference in strength of the HF acid, as compared to that for feldspathic porcelain. The tooth must be clean and free of contaminants. An antibacterial rinse will help maintain a clean tooth surface for bonding. The restoration should then be bonded according to manufacturer’s recommendations of cement and bonding agent selected.
For the glass-infiltrated alumina, air abrasion with either aluminum oxide or a silica coated oxide particle (Cojet, 3M, St, Paul, MN) is indicated.26 It is the author’s opinion that the glass-infiltrated alumina are also best cemented adhesively (with either adhesive or self-adhesive resin); however, it is possible to cement these two classifications with RMGI, and the use of a silane primer may not be indicated.
This is a patient with a monolithic, milled zirconia restoration, which was the initial placement of a full coverage restoration on tooth #3. This patient had a large, failed composite resin restoration that necessitated full coverage. The patient had also been experiencing some cold sensitivity.
As a reminder, zirconia restorations can be placed with RMGI, SARC, or ARC cements. For zirconia, following assessment of the retentiveness of the preparation, a RMGI cement is the first choice of the author. This is especially the case on a tooth that has a history of sensitivity.
This prep featured adequate height, and minimally tapered walls. Although there were no slots or grooves, the prep design was deemed to be retentive enough for RMGI cement (Fig. 3).
Following adjustment and polishing of the restoration, the restoration was air abraded with 50 µm aluminum oxide particles (Buffalo Dental, Syosset, NY) and cleaned with Ivoclean (Ivoclar Vivadent). The prep was rinsed with water, and cleansed with Consepsis 2% Chlorhexidine (Ultradent, South Jordan Utah) utilizing a cotton pellet (Figs. 4 & 5).
Meron Plus QM was chosen as the RMGI cement (VOCO). The cement was placed into the restoration, then the restoration placed on the clean prep. The marginal cement was tack-cured for 10s on both the buccal and palatal aspects. Following tack-curing the restoration, the excess was cleaned off with an explorer (Figs. 6-9).
The restoration was allowed to set for an additional minute after cleaning the excess. Once the material had set enough, an ASAP Direct Polisher (Clinician’s Choice, Ontario, CA) was used to ensure a final polish and clean any additional residual cement at the margins. The final cleaned restoration can be seen in Figure 10.
An IPS e.max pressed restoration (particle-filled glass, lithium disilicate, Ivoclar Vivadent) was chosen to replace a failed PFM crown on tooth #13. Although this particular restoration can be cemented utilizing RMGI cement, the author recommends a self-adhesive resin cement, or an adhesive resin cement. Bonding of lithium disilicate restorations with adhesive resin cements offers increased adhesion over SARC cements. Utilizing an ARC cement helps to compensate for the lesser strength of the restoration as opposed to zirconia-based restorations.
This restoration was etched with 5% HF acid for 20 seconds, and the intaglio surface of the restoration was then cleaned with alcohol. It is important not to over-etch; therefore, make sure that the lab has not etched prior to etching. If the lab has etched the restoration, there is no need to re-etch. Ceramic Bond (VOCO America) was then applied and allowed to air dry for 60 seconds. Prior to cement application, oil free air was blown for five seconds to ensure no pooling of adhesive (Fig. 11).
The tooth was anesthetized prior to cementation to decrease any sensitivity prior to and during cementation. Following administration of infiltrated anesthetic, the tooth was cleansed with Consepsis® (2% Chlorhexidine rinse, Ultradent) (Fig. 12). Although optional, it has been shown that this product is antimicrobial and does not interfere with bond strength. Furthermore, chlorhexidine can actually enhance bond strength by blocking the MMP formation due to etching, if etching is desired.34 Futurabond U (VOCO) was then applied for 20 seconds and gently air dried for five seconds (Fig. 13).
Following preparation of the restoration and the tooth, cement was placed into the restoration (Bifix QM, VOCO). The restoration was then placed on the tooth with gentle pressure (Fig. 14). Once seated, a tack cure (two seconds) was performed (Fig. 15). The excess cement was removed utilizing an explorer (Fig. 16). The cement was then allowed to cure for three minutes. The final restoration was then polished utilizing a porcelain polishing paste (Luminescence Plus, Premier) and rubber cup (Dialite, Brasseler USA). The final result is seen in Figures 17 and 18.
In conclusion, cementation of indirect restorations requires a systematic approach to cements, materials, and prep design. In clinical dentistry, often times the cement choice is ultimately based upon the preference of the practitioner. Although personal preference is not always wrong, it just may not be the best for every situation. Cementation is by no means a “one size fits all” process. The clinician must rely on proper education to make this an efficient and predictable process. Preparedness and proper knowledge are paramount for success in clinical
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About The Author
Chad Duplantis received his D.D.S. degree from The University of Texas Health Science Center at San Antonio, Dental School in 1999. He continued with postdoctoral training at Baylor College of Dentistry, earning a certificate in Advanced Education in General Dentistry in 2000. He has also applied for and has been confirmed for his Fellowship degree from the Academy of General Dentistry this coming July. He has been in private practice since 2000 in the North Fort Worth, Texas area. In private practice, he treats all ages with an emphasis on restorative and aesthetic dentistry.
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