EARLY HISTORY OF DENTIN BONDING AND EVOLUTION OF MMA/TBB ADHESIVE RESIN Early history of dentin bonding

Early history of dentin bonding Attempts to develop an adhesive system which bonds acrylic resins to the tooth structure started in the early 1950s. In 1949, an adhesive system capable of bonding acrylic resin to the tooth structure was invented by Hagger; it was composed of glycerophosphoric acid dimethacrylate (GPDM) and sulfinic acid as the catalyst. In his patent, shear bond strengths of acrylic resin to porcelain, ivory, gold, steel, aluminum, and glass were presented, but not that of bonding to teeth. In the original first Swiss patent (No. 278946) Hagger applied for in July 21, 1949, titled “Method of Bonding Surface” (Verfahren zum Verkleben Flächen), no bonding to teeth was mentioned. In 1950, patent applications filed with other European countries, including the UK, Germany, and France, bonding to teeth was mentioned. In British patent specification No. 687299, titled “Unsaturated Esters”, applied for on July 17, 1950 and published on February 11, 1953, the following statement was included: This invention relates to unsaturated esters which are polymerizable liquid organic adhesives and particularly to such esters suitable for bonding a selfsetting cast filling of synthetic resin to a tooth cavity. However, this statement was not found in the Swiss patent published on February 16, 1952. Therefore, to be exact, dental bonding technology began in 1950 when Hagger proposed using an acidic monomer to achieve bonding to teeth. The bonding agent thus developed was marketed as Sevriton Cavity Seal® (Amalgamated Dental Co.). It contained 10% GPDM and methacrylic acid, and 80% methyl methacrylate (MMA), and used in conjunction with a chemically cured resin, Sevriton® (Amalgamated Dental Co.), in restorative dentistry1). In 1952, Buonocore et al.2) used a qualitative screening test to evaluate the adhesive capability of many of the then-available dental acrylic resins to dentin. The results indicated that, with one exception, acrylic resins had very little or no adhesion to wet dentin surfaces. One material which produced better adhesion was Sevriton® filling resin. Based on these preliminary test results, Buonocore et al.2) prepared an experimental adhesive mixture consisting of Sevriton Cavity Seal®, MMA monomer and polymer, and Sevriton® catalyst and measured its adhesive strength to wet dentin surfaces. Initial bond strength and that after 3 months of water immersion were 28 kgf/cm2 and 15 kgf/ cm2 respectively. A thin layer of adhesive material remained bonded to the dentin, and a marked alteration occurred in the staining reactions of the dentin layers adjacent to the adhesive. At the same time in 1952, histological studies performed by Kramer and McLean3) showed alterations in a narrow staining zone of about 3 μm thickness in the dentin layers adjacent to the adhesive. They thus proposed that the adhesive produced a molecular attachment between the resin and dentin. In 1958, a histological study of the bond area between an adhesive resin and dentin by Buonocore and Quigley4) also revealed a zone of altered staining characteristics in the dentin, which was 3to 10-μm wide. They suggested that bond formation was due to physical penetration of the adhesive material into dentin, a chemical interaction of adhesive constituents with dentin organic matter, or both. The altered staining zone was an intermediate layer that was formed after a GPDM-containing adhesive of about pH 2.5 penetrated dentin. This zone could be referred to as a resin-dentin interdiffusion zone5) formed by a “self-etching” bonding agent. Therefore, Review of methyl methacrylate (MMA)/tributylborane (TBB)-initiated resin adhesive to dentin