Which statement about bonding is true for retention in composite restorations?

• A. Bonding to tooth structure is the primary mechanism for retention in composites.
• B. Dovetails are always necessary.
• C. Increasing occlusal clearance improves retention.
• D. Bevels alone provide retention.

Answer: (A)

Retention in composite restorations comes mainly from forming a strong bond between the resin and the tooth structure using adhesive systems. When enamel is etched, the resin can flow into the created microscopic pores and form resin tags that lock the material to the tooth. Dentin bonding adds a hybrid layer where resin interacts with exposed collagen, providing micromechanical interlocking and a seal that resists dislodgement. This adhesive interface is the primary source of retention, not a particular shape feature of the cavity.

Dovetails or other macro-mechanical undercuts aren’t universally required to keep a composite in place, because the dominant factor is the adhesive bond to tooth structure. Increasing occlusal clearance doesn’t inherently boost retention and can actually compromise tooth structure without improving bonding. Bevels enhance the bonding surface on enamel and aid marginal integrity, but they do not by themselves provide retention without a good adhesive bond.

So, bonding to tooth structure with proper etching and adhesive use is the best explanation for how composites achieve retention.