Which line angle serves as a retention groove for a glass V posterior amalgam preparation?

The axio-gingival line angle serves as a retention groove in a glass ionomer posterior amalgam preparation because it provides additional mechanical retention. In restorative dentistry, line angles are critical for ensuring that the filling material adheres properly to the tooth structure. Specifically, the axio-gingival line angle is formed at the intersection of the axial wall and the gingival floor of the cavity prep.

When creating a preparation for an amalgam restoration, the retention groove placed at this specific angle helps to lock the restorative material into the preparation, preventing it from dislodging over time due to occlusal forces. The geometry of the axio-gingival angle is conducive to creating a space that can hold the restorative material in place, which is particularly vital in posterior teeth that endure significant masticatory forces.

In contrast, the other line angles, such as axio-mesial, pulpo-gingival, and axio-lingual, do not provide the same effective mechanical retention for the glass ionomer and do not typically serve the same purpose in this context. Thus, understanding the role of the axio-gingival line angle in retention helps clarify how effective cavity preparation can enhance the longevity and effectiveness of restorative materials.