American Board of Orthodontics (ABO) Practice Exam

The suggestion that immobile and upright abutments with shallow overbite are appropriate for planning resin bonded or cantilevered fixed partial dentures in cases of agenesis of the upper second incisors (U2's) is based on the stability and alignment needed for these types of restorations. Immobile abutments ensure that the forces applied during function do not compromise the integrity of the bond between the restoration and the teeth. Additionally, upright abutments help in distributing the occlusal forces evenly, which is vital for the long-term success of the prosthesis.

A shallow overbite also plays a significant role as it reduces the risk of excessive occlusal forces acting on the restoration during functional movements, which can lead to debonding or failure. The combination of stable abutments and a favorable occlusal relationship makes this choice particularly suited for the mentioned situations, ensuring optimal performance and longevity of the fixed partial denture.