As Bioactivity and Other Advancements Improve Bond Strength, Understanding of Chemistry and Proper Technique Gain Importance
Gary Alex, DMD
The development of practical adhesive dentistry can be traced to Michael Buonocore who, in 1955, discovered that he could increase the retention of acrylic-based restoratives by first treating the enamel with phosphoric acid. Subsequent research by Buonocore, Gwinnett, and Matsui elucidated the mechanism of adhesion as micromechanical attachment via resin infiltration and tag formation within the acid demineralized enamel.
Although long-term bonding to phosphoric acid-etched enamel surfaces has proven to be highly reliable and predictable, long-term bonding to dentin has been considerably more problematic. The primary reason for this is that enamel is a hard, crystalline, and highly mineralized non-vital tissue that is generally uniform throughout, whereas dentin is a vital, dynamic, and highly variable substrate. Superficial, middle, and deep dentin can vary significantly in structural, physical, and chemical composition. This, coupled with the relatively high water and collagen content of dentin, presents a significant challenge for consistent and reliable long-term adhesion.
Early dentin adhesive systems were extremely limited and generally ineffective, in part, because they bonded directly to the smear layer and the bond strength was limited by the smear layer's low intrinsic cohesive strength and low surface energy. Eventually, it was recognized that the smear layer needed to be removed, modified, or bypassed in some fashion so that adhesive primers and resins could interact directly with the acid-conditioned and demineralized dentin. This led to the development of the so-called total-etching and self-etching adhesive systems that dentists use today.
With all of these developments, just how good are the current adhesive systems and what can clinicians do to optimize their performance? What is our understanding of the factors affecting long-term bond durability, and how can bond strength be improved? With a growing number of great adhesive systems available on the market today, many dentists are realizing that the way forward lies in improving their understanding of the chemistry of their chosen system as well as the precision of their technique.
Gary Alex, DMD, maintains a private practice in Huntington, New York, and lectures nationally and internationally on adhesive and cosmetic dentistry, dental materials, comprehensive dentistry, and occlusion. He is an accredited member of the American Academy of Cosmetic Dentistry (AACD) and a past president of the AACD New York chapter. With a background in chemistry and adhesive technology, he is a consultant for numerous dental manufacturers and a member of the International Association of Dental Research. He has written and published numerous scientific articles and papers and is the co-founder of the "Long Island Center for Advanced Dentistry," which provides advanced continuing education training for dentists.