What is the primary purpose of retaining grooves in an amalgam prep?

• A. To reduce the depth of the cavity.
• B. To provide mechanical retention and resist dislodgement of the restoration.
• C. To increase esthetics of restoration.
• D. To improve color stability.

Answer: (B)

Retention form in an amalgam prep is about creating features that lock the restoration in place. Retaining grooves produce undercuts in the cavity walls so the condensed amalgam mechanically interlocks with the tooth structure. Because amalgam doesn’t bond chemically to dentin, it relies on this mechanical retention to resist dislodgement from chewing and lateral forces. The grooves increase resistance to pulling out and help keep the restoration stable over time. They aren’t intended to change depth, aesthetics, or color stability, which aren’t achieved by retention grooves.