# Dental composite resin restorations are retained by:
A. Cohesion
B. True bonding
C. Mechanical interlocking
D. Atomic forces
The correct answer is C. Mechanical interlocking.
- Surface irregularities are produced by acid etching enamel with 37% to 50% phosphoric acid.
- The primer flows into these irregularities and resin tags are formed providing mechanical interlocking providing micromechanical bonding.
- The microtags formed are 2 to 5 micrometers in length.
- Bond strength is in the range of 18 to 22 MPa.
- Composites increase resistance form by bonding and strengthening tooth structure.
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