Deliverance: Trends in permanent luting cement

By Mark Konings, PhD, MBA; and Daniel Krueger, 3M ESPE

Through the years, scientific and technological advancements have contributed to the development of innovative cementation solutions tailored to meet the ever-increasing demands of the market. The main trends in new cement products are evident - materials that are stronger, less soluble, more adhesive, more esthetic, and easier to use. Aside from the main advantages and disadvantages, each type of cement provides its own challenges that must be overcome to achieve clinical success.

This article will review the development of permanent luting cements and contemporary materials, as well as the latest advancements in delivery systems that benefit the practicing clinician.

The evolution of permanent luting cements

For more than a century, zinc phosphate served as the “gold standard” of luting cements, and was accepted by dental professionals as the best material available for luting mechanically retentive metal-based restorations. Polycarboxylate cements, in turn, enjoyed state-of-the-art status when they were introduced 40 years ago. These were the two primary materials of the category before conventional glass ionomer cements were launched just more than 25 years ago. Conventional glass ionomers, featuring fluoride release and limited self-adhesive properties, experienced widespread recognition. When used as indicated, each can help provide excellent results.

Despite a sustained clinical history and reasonable costs, these three classes of luting cements exhibited low strength, poor esthetics, difficult mixing protocol, potential for sensitivity, limited adhesion, and high solubility. Although these materials comprise about one-third of all applications, they continue to experience an eroding market share as newer technologies meet the high standards of modern clinical application.

A fourth major class of permanent luting cements, resin-modified glass ionomer, was introduced in 1994 with Vitremer™ Luting Cement (renamed RelyX™ Luting Cement in 1999) from 3M ESPE. The category of resin-modified glass ionomer cements, which includes RelyX™ Luting Plus Cement from 3M ESPE and Fuji PLUS™ and FujiCEM™ Cement from GC America, boasts easy cleanup, improved adhesion to tooth structure and higher strength to aid in retention, lower solubility to virtually eliminate washout from margins, and low rates of postoperative sensitivity while maintaining high levels of fluoride ion release associated with conventional glass ionomer cements.

Composite resin cements, as the title indicates, are modified composite restorative materials that boast superior strength and adhesion, low solubility, and esthetics. There are three subtypes of composite resin cements: 1) total-etch systems - including Variolink® II from Ivoclar Vivadent, Calibra® from Dentsply, C&B Metabond® from Parkell, and RelyX™ Veneer Cement from 3M ESPE; 2) self-etching primer systems - including Panavia™ F from Kuraray; and 3) self-adhesive systems - including RelyX™ Unicem Self-Adhesive Universal Resin Cement from 3M ESPE, Maxcem™ Self-Etch/Self-Adhesive Resin Cement from Kerr, and Embrace™ Wetbond™ Universal Resin Cement from Pulpdent.

However, total-etch cement systems and self-etching primer cements have their share of weaknesses, including technique sensitivity and lack of moisture tolerance. Adding water or oral fluids at any point during the multi-step bonding procedure can lead to microleakage and reduced bond strengths, which introduces the potential for post-operative sensitivity and limits clinical application. As a result, total-etch and self-etching primer cements are not indicated in clinical situations where rigorous moisture control cannot be achieved.

Introduced in 2002, self-adhesive cements are the newest and most popular type of composite resin cement. The first product, RelyX Unicem cement, has already become the No. 1 cement in the United States. Kerr (Maxcem cement) and Pulpdent (Embrace Wetbond cement) recently introduced self-adhesive cements. Additional entries in this rapidly growing category are sure to follow.

These dual-cure cements effectively eliminate the separate etching, priming, and bonding steps needed with other composite resin cement systems. By combining strength, adhesion, and esthetics with a simple procedure, these self-adhesive systems are considered the first cements recommended for virtually all indications. Unlike other resin cement types, self-adhesive cements offer unique, moisture-tolerant chemistry with a low risk of postoperative sensitivity.

Along with the evolution of contemporary cements, developments in techniques and equipment provide today’s clinician with an abundance of tools to solve any combination of clinical challenges. A brief overview of various cement delivery systems follows.

The evolution of delivery systems

Until the 1970s, clinicians had one choice in cement form and delivery systems - hand mixing powders and liquids. Although this remains the least expensive delivery system and most popular method, hand mixing powders and liquids have long since been surpassed by innovative systems that have proven to be worth their value in ease and efficiency.

A recent survey identified “achieving a consistent mix” as the most important criterion in a cement’s delivery system for the practicing clinician. This was trailed - in order - by ease of use, ability to dispense desired amount of material, minimum amount of waste, and price per application. Although hand mixing powders and liquids may still be a viable alternative, primarily because of their low prices, dentists are using them less as contemporary systems continue to advance. Today, dentists have more options from which to choose than ever before, each with its own advantages and challenges.

Paste-paste delivery systems

To address the difficult mixing protocol and inconsistent properties obtained with powder-liquid cements, paste-paste delivery systems for resin-modified glass ionomer cements were introduced in 2001. These systems, including the Clicker™ Dispenser from 3M ESPE and the PastePak™ Dispenser from GC, hold and dispense two pastes simultaneously. They still require hand mixing. The variability of powder-liquid systems comes from inaccuracies in dispensing separate drops of liquid and scoops of powder, and from the difficulty of incorporating the powder into the liquid. The paste-paste systems automatically dispense the correct ratio of the two pastes, which are much easier to mix than a powder and liquid. These cement systems are about twice the cost per application of powder-liquid cements and continue to gain popularity.

Capsules

Capsule delivery systems for powder-liquid cements were introduced in the 1970s. Currently, they include polycarboxylate, glass ionomer, resin-modified glass ionomer, and self-adhesive resin cements. The capsules offer consistent, predictable results in a convenient unit-dose capsule at the push of a button. They do require, however, some hardware, especially a capsule mixer. Additionally, the capsules must be activated properly to ensure consistent results. They run about three to four times the cost per application of powder-liquid cements and, like paste-paste delivery systems, continue to grow in popularity.

Auto-mix syringes

The hand-held, dual-barrel syringe with auto-mix tip offers the potential for the ultimate in convenience and ease of use, albeit at a price. These systems require no additional hardware, no hand mixing, and are attractive to many dentists. Because the mix tips are so small and the volume of dispensed material is so low (as little as 0.05 mL), the performance of these delivery systems depends greatly on the ability of manufacturers to precisely control the quality of syringe filling. Any air in the syringe can result in poorly mixed cement and compromised cement properties. This is no small matter when cementing expensive, laboratory-fabricated restorations. Because of the excessive waste of material in the mix tip (up to two-thirds of the cement is discarded), cements in auto-mix syringes are the most expensive option - about five to 10 times the cost per application of powder-liquid cements. Nevertheless, their popularity continues to grow.

Conclusion

A full range of permanent luting cements exists, each of which is designed to meet a specific clinical need. Advances in cement technology and delivery systems have led to improved efficiency for the clinician, and a simpler procedure to benefit the patient. Not all types of cements are available in every delivery system, although the choices are increasing. As with any product, it is only through correct technique and use of the material that the fullest potential can be realized.

References available upon request.

Mark Konings (left) has been with 3M ESPE since 1990. He led the development and commercialization of Imprint II impression materials and RelyX Veneer cement. Daniel Krueger has worked four years in 3M’s Specialty Chemicals Division and 18 years in the Dental Products Division, where he has gained extensive product-testing experience.