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Overview: Self-adhesive Cements Karl F. Leinfelder, DDS, MS & Douglas A. Terry, DDS

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Traditional Cements
Based upon the mechanism by which cementing occurs, luting agents generally can be divided into two categories. The most traditional cements depend upon micromechanical retention. Due to a low viscosity and reduced film thickness the cement flows into all microscopic defects both on the internal surfaces of the restoration as well as the prepared tooth. Examples of this type of cement include zinc phosphate cement (1879), polycarboxylate cement (1969) and zinc oxide and eugenol (1870). The second category of cements are more sophisticated in terms of adhesion to the preparation. Some of them adhere by chelation whereas others depend upon infiltration of microscopic spaces surrounding the collagenous structures. Examples include glass ionomers, self-etching resins and resin cements.

It is of interest to note that the carboxylate cements (Durelon) exhibit two different mechanisms by which they bond to the surface of tooth structure (dentin and enamel). Recognized as the first adhesive cement to be introduced to the profession they exhibit a lowered film thickness which allows the agent to flow into microscopic defects. In addition it actually bonds to tooth structure through a process of chelation. Bond strengths generally average about five megapaschals.

Polycarboxylate cements sometimes have been selected as the cement of choice over zinc phosphate cement because they are believed to be more kind to the pulpal tissue. The apparent reduction in post-operative sensitivity associated with them is probably related to the fact that they seal the dentinal tubules. This in turn reduces the potential for fluid flow over the odontoblastic process which in turn minimizes the potential for post restorative sensitivity. While the carboxylate cements offer some advantage over zinc phosphate cement they have been reported (University of Michigan) to exhibit a lesser longevity in terms of retention.

Glass Ionomers
Glass ionomers apparently adhere to tooth structure through the formation of ionic bond at the tooth-cement interface. The bonding results from a chelation of the carboxyl groups in the acid with calcium and/or phosphate ions in the apatite. Resin modified glass ionomers (10 percent resin added to the formula) have the same mechanism of adhesion as the straight glass ionomer. Bond strengths incidentally of the resin modified glass ionomers are relatively higher than the regular glass ionomer formulation.

Composite Resin Cements
The composite resin cements are made up of the same basic components as composite resin restorative materials. The filler content however is lower so as to favorably influence viscosity and film thickness. If the preparation is first hybridized the composite resin cement will bond to the enamel and dentin, thereby increasing the potential for adhesion of the restoration.

As compared to traditional cements, resin luting agents exhibit a higher flexural strength, low coefficient of thermal expansion, and higher stiffness (modulus) of any dental cement. Furthermore they have the ability to bond to multiple substrates, possess the potential for shade matching, increased retentive capabilities, improved marginal wear resistance and protection against microleakage.

On the negative side of the ledger they generally have a short working time, undergo polymerization shrinkage (potential for post-operative sensitivity) and offer no anticariogenic effect. Also, depending upon the product, the cementing procedure might be somewhat complicated.

Examples of composite resin luting agents include:
• Calibra (Dentsply/Caulk): Versatility and opaquers.
• Lute IT (Pentron Clinical Technologies): Versatility, opaquers, cost.
• Nexus 2, 3 (Sybron/Kerr): Historical performance.
• Variolink II (Ivoclar): Most wear resistant.

Composite resin cements are excellent for ceramic restorations, particularly feldspatic resins which are weaker than alumina and zirconium ceramic materials. Ceramic agents such as Empress (Ivoclar) should always be bonded with a composite resin cement after the preparation is hybridized. Silinating the internal surface of the porcelain is also good protocol since such a procedure not only encourages the influx of the luting agent into the irregularities created by the etching agent but also generates a chemical union between the porcelain and the cement.

Self-etching or Self-adhesive Cements
This new class of cements is rapidly growing in popularity by the dental profession. The uniqueness of this class of materials is its simplicity. Excellent cementation can be achieved routinely without dealing with some of the complexities associated with other systems. The first self-etching system to be introduced to the clinicians was Unicem (3M ESPE).

Consisting of a disposable capsule, the powder and liquid are separated by a foil packet. Activation consists of two steps. The first consists of a device which ruptures the liquid containing foil packet. At this point the cement is triturated either with an amalgamator or the device developed by the company for the mixing process. At the end of the mixing procedure the capsule is put into a centrifugal mode for two seconds which accomplishes two objectives. The first is to force all the freshly mixed cement towards the ejection end of the capsule. The second is to eliminate or minimize any porosities (voids or bubbles) in the mix. Next the mixed glass ionomer is ejected from the end of the capsule onto the inner surface of the restoration to be placed. The shear bond strength of Unicem when mixed as just described is 23 MPa. This value is more than twice that of most other self-adhesive systems. Also available in a hand-held device (Clicker) the material is automatically mixed and then dispensed in fixed amounts. The shear bond strength using this system is around 20 MPa.

The next device to be introduced to the dental profession is the Maxcem. The device for mixing and dispensing consists of two barrels in a hand-held device; one for the base and the other the catalyst. After forcing the two systems through the mixing device the material is syringed onto the surface of the restoration. All of the subsequently introduced materials possess shear bond strengths of 10 megapaschals or less. Some of them might be only six to eight megapaschals.

Some of the self-adhesive cements currently on the market include the following:
• Unicem (3M ESPE)
• Breeze (Pentron Clinical Technologies)
• Monocem (Shofu)
• iCem (Heraeus Kulzer)
• Embrace (Pulpdent)
• Sprint (Ivoclar)
• G-Cem (GC America)

Self-adhesive cements have become popular for several reasons. The first and foremost relates to the fact that they are easy and fast to use. Specifically the preparation is washed and then air dried or air dispersed for a couple of seconds. The cement is applied to the internal surfaces of the restoration followed by seating. Incidentally, rather than injecting the cement into the restoration another procedure should be considered. After mixing, the cement should be ejected onto a paper pad. The cement is picked up and delivered with a microbrush. The surface of the restoration should be lightly coated uniformly with the brush. Such a procedure assures complete covering of the restoration and the surface of the preparation. It also facilitates complete seating of the restoration.

Self-adhesive cements are self-etching. No etching of the preparation with phosphoric acid is required. Apparently the reduced pH causes a dissolution of the mineral phase of the dentin and superficially replaces it with the resin itself. Hybridizing the dentin and sealing the tubules might account for the reason that post-operative sensitivity is generally nonexistent. In addition to this the cement exhibits a low film thickness, good aesthetics and is easy to clean up. Furthermore these cements are insoluble in oral fluids, exhibit high strength characteristics and they offer moderate to good adhesion. Finally, these cements exhibit a two-minute working time, three to five minute setting time. Incidentally, self-adhesive cements exhibit a limited number of contraindications. They should not be used to bond ceramic veneers (elevated water sorption of the cement), feldspatic ceramic restorations, low fusing all-ceramic restorations and Maryland Bridge.

It should be pointed out that the self-adhesive cements actually bond to a number of substrates. One study (Baylor) has demonstrated that Maxcem and Unicem exhibited shear bond strengths of approximately 18 MPa to Empress. Bond strengths for the same two cements to gold alloy were 8 MPa while 9 MPa to Lava zirconia. While clinical usage has been increasing and most physical and mechanical properties quite positive, it should be pointed out that there is little or no clinical data available on the overall performance of these luting agents.
Author’s Bio
Dr. Karl F. Leinfelder earned both his Doctor of Dental Surgery and Master of Science (dental materials) degrees from Marquette University. In 1983, he joined the School of Dentistry at the University of Alabama and is the recipient of the Joseph Volker Chair. He also served as Chairman of the Department of Biomaterials until 1994. Presently he holds positions at both universities; adjunct professor at University of North Carolina and Professor Emeritus at the University of Alabama. Dr. Leinfelder has published more than 275 papers on restorative materials, authored more than 150 scientific presentations, two textbooks on restorative systems and has lectured nationally and internationally on Clinical Biomaterials.

Dr. Douglas A. Terry received his DDS from the University of Texas Health Science Center, Houston Dental Branch, in 1978. He has lectured internationally on aesthetic dentistry and is an active consultant for several dental manufacturers in the area of new product development and refinement. He is an Assistant Professor in the Department of Restorative Dentistry and Biomaterials at the University of Texas Health Science Center in Houston, Texas, and an adjunct faculty member at the University of California Los Angeles Center for Esthetic Dentistry. He has earned his fellowship in the Academy of General Dentistry and the International Academy for Dental- Facial Esthetics. Dr. Terry is the founder and CEO of the Institute of Esthetic and Restorative Dentistry. He maintains a private practice in Houston, Texas, emphasizing aesthetic and restorative dentistry.
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September 2025
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