Dentin Bonding

Dentin Bonding

Write a short note on dentin bonding agents.
Answer:

Dentin bonding agents are described under various generations which are as follows:

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 hydroxylapatite. Hydrophobic methacrylate groups bonded to acrylic restorative resin. The major disadvantage was their low bond strength, i.e. 2 to 6 MPa.

Second generation (1970s): Developed as adhesive agents for composite resins which had by then replaced acrylic restorations. One system used N-phenyl glycine glycidyl methacrylate (NPGGMA).

It was proposed that the NPG portion bonded to the calcium of the tooth by chelation. Other products included phenyl-P and 2-methacrylate 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: Prisma, universal bond, clear, scotch bond.

Third generation (1980s): The 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: Tenure, scotch bond 2, prisma, universal, bond, mirage bond, etc.

Fourth generation (early 1990s): The 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: All bond 2, scotch bond multipurpose, options, etc.

Fifth generation (the mid-1990s): The fifth generation combined the primer and adhesive into one bottle (self-priming adhesive). Examples of the fifth-generation self-priming adhesives are single bond (SM), one step (Bisco), prime, and bond (Dentsply).

• Advantages:
  • Application steps were reduced.
  • Less technique is sensitive as it can bond to moist dentin.
  • Higher bond strength.

Sixth generation (the 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 I and Type II. Type I—two-botte two-step system. Etchant and primer are combined in one bottle (called self-etching primer). Another bottle contains adhesive.

• Examples are Clearfi SE bond (Curare), Adhese (Ivo-clair), Optibond solo plus (Kerr), Nano-bond (Pentron), etc.
• Type II—two-bottle one-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 III (Densply), 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 IV (Dentsply) (glass ionomer based), Clearfi S3 (Curare). Still, the efficacy of the newer systems is to be determined.