Methods and factors involved in bonding orthodontic attachments to enamel.

It is quite evident that in the practice of orthodontics, much time could be saved and much tedious labor could be avoided if a method were available to attach a bracket directly to a tooth surface. The object of this investigation was to determine if this could be accomplished by using Eastman 910 [6], a cyano-acrylate, as a bonding agent. This material is a thin , colorless liquid with a low viscosity and fast setting time, whose vapors in sizable amounts are irritating to mucous membranes. Initially, it was thought that an epoxy resin would be suitable for this purpose , but investigation showed that the epoxy resins do not have a setting time which would enable them to be of any practical value. SADLER [10], using commercial adhesives, attempted to bond edgewise brackets to extracted human teeth. He determined that for the most part, the adhesives surveyed showed a lack of adhesion to the metal brackets. He stated that in their present state, none of the adhesives tested were capable of bonding metal attachments directly to the teeth with a stability required for clinical orthodontics. In an attempt to find a method of bonding acrylic to tooth material , BUONOCORE [2] tested over onehundred commercial resin compositions. He determined that from all aspects, Eastman 910 adhesive rated best for this purpose . Earlier work with resin cements by SCHOUBOE, et al. [11], showed that the resin cements expand on absorption of water, and they suggest that this may be responsible for the resin cements not adhering to tooth structures under mouth conditions. A rough . screening test for adhesion was employed to find out if any of the resin cements used with a direct filling resin were actually adhesive to enamel and dentin under conditions of use. All of the resins showed an initial adhesion to the tooth tissues and, if the tooth and resin were kept dry, the adhesion was so strong that usually the tooth would be broken if an attempt were made to remove the resin. After soaking the tooth with the resin on it in water, however, this adhesion was lost. There were no exceptions and zinc phosphate cement adhered as long as the resin cements. After twenty-four hours of soaking in water, most of the cements could be dislodged easily and after one week, all of them could. Many acrylic and zinc phosphate cements were used by ROSE, et al. [ 9 ], to determine whether they could be used as bonding agents to enamel and/or dentin. Some materials which gave zero readings after five minutes immersion in water required as