Adhesive resin restorations have made enormous strides in the second half of the 20th century. Kuraray Co., Ltd. (Kuraray Medical Inc, Japan) has played a major role in adhesive resin material development, and it is not too much to say that its history describes some of the major focal and transition points of adhesive resin restorations.
This history began in 1978 with the introduction of CLEARFIL™ BOND SYSTEM-F. This was the world’s first total-etch system, in which a solution of phosphoric acid was applied to enamel and dentin simultaneously. Phenyl-P (2-methacryloyloxyethyl phenyl phosphoric acid) was used as the adhesive resin monomer.1 Later, MDP (10-methacryloyloxydecyl dihydrogen phosphate) was developed as a replacement for Phenyl-P, and CLEARFIL NEW BOND was created. With the introduction of catalysts for visible light curing, CLEARFIL PHOTO BOND was developed. Each time adhesive systems were modified, adhesion to dentin continued to improve.
In the 1980s, understanding of the hybrid layer—first described by Professor Nobuo Nakabayashi—began to improve.2 Much research was performed to advance knowledge of adhesive mechanisms. Primers, which are important for promoting good dentin adhesion, were invented and introduced under the guidance of Professor Hiroyasu Hosada and his group—leading to the introduction of the CLEARFIL LINER BOND SYSTEM.
Adhesive resin monomers, such as Phenyl-P, MDP, or 4-META (4-methacryloyloxyethyl trimellitic acid anhydride) are acidic monomers that contain either carboxylate or phosphate groups in the monomer molecule. Acidity of a monomer can affect polymerization, but these acidic groups are necessary for good adhesion to tooth substrates when using resin-based adhesives.
With the great efforts of Kuraray R&D, an epoch-making technique of the “self-etching primer” was introduced to the dental profession in 1993. The first Kuraray products using this method were CLEARFIL LINER BOND 2 adhesive and PANAVIA 21 resin luting cement. In the next development, self-etching primer components were changed and polymerization improved. In 1999, CLEARFIL SE BOND, consisting of a one-bottle self-etching primer and one-bottle light-cured bonding agent, was introduced.
The self-etching primer in CLEARFIL SE BOND contains MDP, which is the active acidic monomer for demineralizing enamel and dentin. In addition, the self-etching primer solution contains HEMA as a hydrophilic resin, a dimethacrylate resin, catalyst, and water to permit ionization of the acidic monomers. Its pH is 2, which allows simultaneous etching of dentin and enamel; there is no washing step required. After drying with a gentle air stream to remove excess primer, the filled bonding resin is applied and light-cured. The components of the bonding resin are similar to the primer, but it does not contain water and has a much greater amount of hydrophobic resin and fillers to ensure a good bond to the resin composite filling material.
What is important for adhesion to dentin is the infiltration of adhesive resin monomers, which have excellent adhesion properties to tooth structure, particularly dentin, as well as adequate polymerization. For good resin infiltration, an acidic treatment with either phosphoric acid or self-etching primer is necessary to dissolve the smear layer that is produced on a tooth surface during dental cutting procedures. Regions produced after acid treatment—in other words, demineralized areas—even if only slight, must be hardened and protected by bonding resin infiltration. If not, the area devoid of resin at the adhesive interface will affect the long-term durability of the bond.
It has been reported that compared with the self-etching systems, strong acidic treatment such as phosphoric acid-etching decreased bond strength significantly in durability of adhesion to dentin over the long-term.3,4 Phosphoric acid-etching to dentin adhesion creates structural defects—layers of exposed denatured collagen in the adhesive interface, where bonding resin cannot infiltrate. On the other hand, CLEARFIL SE BOND does not create such structural defects. Successive interfacial structures have been formed from resin composite, bonding resin, hybrid layer to dentin where etching effects do not reach.
Because of its recognized adhesive ability, CLEARFIL SE BOND is highly regarded, clinically accepted, and widely used internationally. It is considered a gold standard—especially for its adhesion to dentin—by academic and dental associations concerned with adhesive dentistry.
A strong interfacial bond can be formed5 to the enamel after mild etching with sophisticated adhesive resin monomers, such as MDP, but this is still not widely recognized, possibly because the self-etching materials do not exhibit the typical etching pattern of enamel prisms that is formed after phosphoric acid-etching.
Perhaps it will be the responsibility of university researchers and clinicians to reflect on this matter and improve our knowledge and evidence base to demonstrate the clinical advantages of the self-etch system philosophy.
Over the past 10 years, CLEARFIL SE BOND has gained an excellent reputation among clinicians throughout Japan—thus the use of total etching with phosphoric acid has virtually become a treatment method of the past. In this field, Kuraray Medical Inc has played an extremely important and active role to create one of the world’s top bonding agents and introduce the self-etching adhesive system concept.
CLEARFIL SE BOND was created by concentrating and connecting very important techniques of adhesive resins, including those from the history of adhesive resin material development. For students and researchers who will one day become leaders in their respective fields, understanding the developmental steps that led to the creation of CLEARFIL SE BOND is an excellent means to learn about the inception of present day dental adhesion. It is hoped by this knowledge, future versions of adhesive resin materials will be developed that are superior to our present day systems.
1. Fusayama T, Nakamura M, Kurosaki N, et al. Non pressure adhesion of a new adhesive restorative resin. J Dent Res. 1979;58:1364-1370.
2. Nakabayashi N. The promotion of adhesion by the infiltration of monomers into tooth substrates. J Biomed Mater Res. 1982;16:265-273.
3. Nakajima M, Okuda M, Ogate M, Pereira PNR, Tagami J, Pashley DH. The durability of a flouride-releasing resin adhesive system to dentin. Oper Dent. 2003;28:186-192.
4. Okuda M, Pereira PNR, Nakajima M, Tagami J, Pashley DH. Long term durability of resin dentin interface: Nanoleakage versus microtensile bond strength. Oper Dent. 2002;27:289-296.
5. Shimada Y, Tagami J. Effect of regional enamel and prism orientation on resin bonding. Oper Dent. 2003;28:20-27.
The original document was summarized by Kuraray America. For a copy of the complete article by Dr. Junji Tagami, please contact Kuraray at 800-879-1676 or email info@kuraraydental.com
