What is the purpose of undercutting in cavity preparation?

The purpose of undercutting in cavity preparation is to lock filling material into place. When a cavity is prepared for a restorative material, undercuts create a mechanical retention feature. This means that the filling material can grip onto the tooth structure more securely, preventing it from being dislodged under forces such as chewing or biting. This technique ensures that the restoration remains stable and durable over time, enhancing the longevity of the treatment.

In contrast, the other options do not align with the primary function of undercutting. While cleaning the cavity and smoothing the cavity surface are important steps in the overall preparation process, they do not specifically involve the undercutting technique. Similarly, increasing the cavity size is not a goal of undercutting; rather, it focuses on improving retention without necessarily enlarging the cavity unnecessarily. This distinction emphasizes the unique role that undercutting plays in effective cavity preparation.