Practical Restorative Progress, Self-Etching Primers By: Michael R. Razzano, DDS

In 1955, Dr. Michael Buonocore stirred and challenged dentistry with his, to some, “unreasonable” idea that tooth structure could be “etched” to produce a surface that actually enhanced the “retaining” of restorative materials. Dr. Buonocore and his colleagues discovered that etching enamel with phosphoric acid created microscopic surface irregularities that resin filling materials could flow into—and, that this material/tooth surface interlock demonstrated an enhanced “bonding” and retentive strength. Many consider this epoch-making work of Dr. Buonocore the birth of adhesive dentistry, with the introduction soon after of phosphoric acid etching/resin bonding agents for patient care.

And, then there was…
…the investigation and search for ways to improve the new enamel bonding systems, with the goal being a chemical adhesion rather than mechanical interlocking alone. Kuraray, a global chemical company, succeeded in developing the first chemically adhesive dental monomer, Phenyl-P, a phosphate monomer, in the mid-70s. Then, in 1978, Kuraray introduced Clearfil Bond System F, the first dental bonding system to provide both mechanical and chemical adhesion to enamel and dentin.

Soon after introducing this epoch-making adhesive bonding product, Kuraray introduced the “total etch” concept developed by Dr. Takao Fusayama, a legendary restorative dental pioneer and researcher. Dr. Fusayama’s “total etch” technique etched both enamel and dentin simultaneously with phosphoric acid followed by the application of the adhesive monomer. “Total etch” is today an accepted procedure and is an integral part of the “wet- bonding” technique.

As a normal result of their continuing search for ever-improving technologies and materials, Kuraray developed and introduced in 1981 a new adhesive phosphate monomer that they named MDP. This new monomer, MDP, was incorporated into the newly introduced products called Clearfil New Bond and Clearfil Photo Bond. In-vitro testing of the products containing MDP demonstrated that, in addition to improved bond strength to enamel and dentin, a significant adhesion to metals was also noted. This adhesion to metal finding led to the development of Panavia dental adhesive cement, which in turn opened the way for new restorative techniques that rely on strong adhesion to metals and porcelains.

Thus, the development of reliable bonding systems that adhere to both enamel and dentin, leading to the increased popularity and use to composite resin restorative materials. However, the products in this “generation” of bonding systems, were found to exhibit relatively weak adhesion to dentin, a problem that has serious implications for restorations with margins in dentin or cementum, such as root surface restorations. Kuraray scientists therefore focused their efforts on improving dentin adhesion, resulting in the development of the Clearfil Liner Bond System. This new system was developed with the following very specific, targeted objectives:

1. Avoid any damage to the dentin (especially the supporting collagen) that is caused by phosphoric acid.

2. Achieve optimal conditioning of dentin (such as “wetting”) with particular attention to the collagen network.

3. Simplify the conditioning procedure by allowing simultaneous treatment of enamel and dentin.

To accomplish these objectives, Kuraray scientists developed first CA Agent, a citric acid-based solution that provides milder and yet very effective etching. And second, they developed SA Primer, which restores the decalcified, partially collapsed collagen fibrils to their original height, thus allowing the MDP bonding monomer to penetrate more completely. The clinical performance of the Clearfil Liner Bond System exceeded expectations of the Kuraray scientists, including demonstrating a very high bond strength to dentin.

However, Kuraray scientists never seem to be satisfied and almost immediately continued their search for the ideal adhesive technology––one that was easier and faster to use, cost less, and eliminated any patient postoperative sensitivity or discomfort problems.

And, now most are using…
…the latest epoch-making development from Kuraray––self-etching primers.

While the Clearfil Liner Bond System is very successful clinically, its two-stage conditioning procedure required too many procedural steps. Kuraray introduced the next epoch-making adhesive system, Clearfil Liner Bond 2, in late 1993. Liner Bond 2 simplified the application procedure, maintained a gentle yet effective dentin conditioning—and, was a first self-etching, light cure bonding system. Based on technology developed for the Panavia 21 ED Primer, the LB2 System featured the new self-etching primer called LB primer. LB Primer uses the acidic phosphate monomer, Phenyl-P, combined with water and other ingredients to duplicate the gentle etching effects of CA Agent plus the conditioning affects of SA Primer, all in one step.

During this same time period, other manufacturers and clinicians began embracing the total etch technique and introduced systems that combined a phosphoric acid etchant with a “one-bottle” bond material. These “one-bottle” systems popularized the “wet bonding” technique, but are actually a slight misnomer since they still require two steps, acid etching with phosphoric acid then the bond material application.

While the “wet-bonding” technique uses a “one-bottle” bond (combining primer and bond), Kuraray’s self-etching and priming system combines etching and priming in one bottle. Both procedures, self-etching and wet bonding, produce excellent bond strengths.

However, Kuraray’s self-etching system has several advantages:

• Gentler etching, no phosphoric acid
• Elimination of the water rinse step
• Enhanced dentin sealing that eliminates post-operative sensitivity
• Faster, easier, less technique sensitive procedure (more predictable).

The cautions and shortcomings of the “one-bottle” wet bonding techniques include:

• Potential for excessive dentin decalcification
• Careful attention required for moisture control to assure consistent strong bond
• Incidence of post-operative sensitivity
• Increased technique steps.

Kuraray is totally committed to self-etching technology. While Kuraray was the first to introduce “total-etch”, and still provides an excellent “total-etch” bonding system, there seems to be little reason for not using self-etching products. Kuraray’s newest self-etching bonding systems, Clearfil Liner Bond 2V and Clearfil SE Bond, provide two choices for using self-etching bonding systems in virtually any clinical situation, including indirect restorative procedures. Clearfil SE Bond is designed for light-cure restorations only, and offers a fast, easy, economical solution. Clearfil Liner Bond 2V provides the versatility of a dual-cure product that can be used in any clinical situation, including indirect restorative procedures.

For more information on Kuraray’s family of self-etch products visit them online at www.kurarayamerica.com or call toll-free 888-587-2729. Reprinted from “Adhesive Technology Solutions”.