Bonding Agents In Orthodontic

Bonding Agents In Orthodontic

Write a short note on bonding agents.
Answer.

Bonding Agents

Bonding agents in orthodontics are used to attach brackets to the tooth/teeth. Currently, bonding agents bond to enamel and dentin.

• First generation (1950–1970): Mineral acids were used to etch enamel. Dentin etching was not applicable because of the belief that it may harm pulp. Glycerophosphoric acid methacrylate is used. It is a bifunctional molecule. Hydrophilic phosphate reacts with calcium ions of hydroxyapatite. Hydrophobic methacrylate groups bonded to acrylic restorative resin. The major disadvantage was their low bond strength, i.e. 2–6 MPa.

“Importance of bonding agents in attaching orthodontic brackets”

• Second generation (1970s): Developed as adhesive agents for composite resins which had by then replaced acrylic restorations. One system used NPG-GMA (N-phenyl glycine glycidyl methacrylate). It was proposed that the NPG portion bonded to the calcium of the tooth by chelation. Other products included phenyl-P and 2-methacryloxy phenyl phosphoric acid. Bond strengths achieved were three times more than the earlier generations. Disadvantage: Bond strengths were still low. The adhesion was short term and the bond eventually hydrolyzed. Examples are: Prisma, Universal Bond, Clearfil, and Scotch Bond.

“Global trends in orthodontic bonding technology”

• Third generation (1980s): Third-generation bond agents deal with the smear layer which is formed when dentin is cut. It was believed that the smear layer prevented proper bonding to the underlying dentin. Complete removal by aggressive etching was contraindicated because it was believed that it protect the pulp by preventing direct contact with the monomer. The third-generation bond agents had bond strengths comparable to that of resin to etched enamel. Thus bond strengths improved to 12 to 15 MPa. Examples are: Tenure, Scotch Bond 2, Prisma, Universal Bond, Mirage Bond, etc.

“Treatment implications of orthodontic bonding agents”

• Fourth generation (early 1990s): Fourth-generation systems were possible because of some important ideological breakthroughs like the total-etch technique and the development of the hybrid zone. Research showed that acid etching of dentin did not significantly harm the pulp as long as bacterial contamination and microleakage were avoided. Thus the total-etch technique was introduced. These bonding agents were applied in multiple steps. Examples are: All Bond 2, Scotch Bond multipurpose, Optibond, etc.
• Fifth generation (the mid-1990s): The fifth generation combined the primer and adhesive into one bottle (self-priming adhesive). Examples of fit-generation self-priming adhesives are Single Bond (SM ), One Step (BISCO), Prim,e, and Bond (Dentsply).

“Complications of outdated orthodontic bonding agents”

• Sixth generation (mid to late 1990s): In this system, a separate etchant is not required. These are 2 botte systems. Two varieties are seen, i.e. Type 1 and Type 2.
  • Type 1 2 bottle 2-step system. Etchant and primer are combined in one bottle (called self-etching primer). Other bottles contain adhesive. Examples are Clearfil SE bond (Curare), Adhese (Ivoclair), Optibond solo plus (Kerr), Nano bond (Pentron), etc.
  • Type 2 2 bottle 1 step system. Liquid A contains the primer. Liquid B contains a phosphoric acid-modified resin (self-etching adhesive). Both liquids are mixed just before application. For example, Xeno 3 (Dentsply), Adper prompt L-pop (3M), Tenure imbibed (Dent Mat), etc.
• Seventh generation (early 2000): Attempts to combine all three (etchant, primer, and adhesive) into a single product. Thus, seventh-generation adhesives may be characterized as ‘no mix self-etching adhesives. Examples include iBond (Heraeus Kulzer), G bond (GC), Xeno 6 (Dentsply) (glass ionomer based), Clearfi; and S3 (Curare). Still, the efficacy of the newer systems is to be determined.