Which statement is true about the placement of a glass ionomer base in a deep oblique amalgam preparation?

The correct statement is that the base is placed on dentin surfaces only. Glass ionomer is a biocompatible material that not only provides thermal insulation but also releases fluoride, which can be beneficial for the tooth structure. In the context of a deep oblique amalgam preparation, the base is specifically used to protect the pulp and provide support for the coronal structure.

When a glass ionomer base is applied, it is important that it only contacts dentin because the interface between the base and dentin is crucial for bonding. Dentin is a softer and more porous tissue than enamel, which means that placing the base solely on dentin allows for optimal adhesion and minimizes the risk of any potential displacement during the condensation of amalgam.

If the base were to extend to the gingival cavosurface or into retentive features, it could interfere with the proper seating and condensation of the amalgam, potentially compromising the final restoration. Moreover, glass ionomer bases do not rely solely on mechanical retention; they also feature a chemical bond to dentin that is vital for stability and longevity. Thus, focusing on the placement on dentin surfaces aligns with best practices in restorative dentistry.