Wednesday, February 02, 2005

The Ever-changing World of Dentinal Adhesives

A nice review article on Dentinal Adhesives:

The Ever-changing World of Dentinal Adhesives
Karl F. Leinfelder, DDS, MS shares his expertise about the seven generations of bonding adhesives
By: Karl F. Leinfelder, DDS, MS

The mechanism of retention for all direct restorative materials traditionally has been through preparation design. Specifically, amalgam, silicate cement and the early resins achieved retention by means of undercutting portions of the preparation as well as converging the walls towards the enamel surface. Furthermore, the traditional use of well-defined internal line angles was considered mandatory.

Bonding to enamel has been clinically employed since the beginning of the 1970s.1-5 The first applications of this concept involved the restoration of fractured incisal edges and the use of pit and fissure sealants.6 Interestingly, the ability to restore incisal edges not only lead to a more conservative type of preparation design but also an abandonment of the many types of pins formerly necessary to retain the restoration. And on a more subtle note, the need for internal line angles also diminished.

Although enamel acid etching techniques have been part of the treatment plan for over three decades, the same is untrue for the adhesion to dentin. It is notable that the quest for an adhesive to dentinal structure began many years before anyone tried to find a means for bonding to enamel.7-10 Ironically, the discovery that resin could be bonded to enamel put the search for a dentinal adhesive on the “back burner”. It was by serendipity that Michael Buonocore11 discovered that zinc phosphate cement liquid blanched the surface of enamel. This in turn created a microporous surface, which permitted him to fasten acrylic splints to periodontally involved teeth without mechanical retention. Historically, it took nearly a decade and a half before his discovery became an accepted part of clinical procedures. With few modifications in technique, the principles of bonding to enamel have remained relatively constant over the years.

Considerably greater efforts have been associated with the quest for a dentin adhesive. The first endeavors towards finding this goal centered on the development of a chemical agent or radical that would bond directly to the collagenous structure.12-13 While many attempts were made to reach this goal, none of them came to fruition. Instead, a mechanism of adhesion was found once again with phosphoric acid; and strangely enough, like its enamel counterpart, the mechanism was micromechanical.14-18 Instead of dealing with porous defects on the ends of enamel rods, the one associated with dentin involved individual bundles of collagenous fibers. The commonality between the two was indeed micromechanical retention.

Read the remaining article here.

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