Which material relies on bonding to tooth structure rather than mechanical retention?

• A. Composite
• B. Amalgam
• C. Gold
• D. Glass ionomer

Answer: (A)

The key idea is adhesive bonding to tooth structure is the main retention mechanism. In composite restorations, bonding to etched enamel and dentin is what holds the restoration in place. The enamel is roughened by etching to create micro-porosities, and a dentin/etch adhesive penetrates and, once it cures, forms a hybrid layer with resin tags that arrest the material in place. This bond provides retention and seals margins, rather than relying on mechanical lock or undercuts alone.

In contrast, other materials are primarily held in by mechanical means: amalgam depends on the cavity design to provide undercuts that lock the material in, and gold restorations rely on precise fit and cementation rather than bonding to tooth structure. Glass ionomer does form a chemical bond to tooth structure, but the classic emphasis in this context is the adhesive bonding approach used with composites, which is why bonding to the tooth is highlighted for this material.