A patient has a recurrent apical infection and requires enucleation of an apical cyst. Which instrument would be used?

Mitchell's trimmer is an instrument designed specifically for shaping and smoothing the preparation of dental cavities, particularly in the context of endodontic procedures. When dealing with a recurrent apical infection and an apical cyst, enucleation involves careful removal of the cyst without damaging surrounding tissues. Mitchell's trimmer allows for precision and control during this delicate procedure, making it suitable for sculpting the bone or tooth structure involved.

The other instruments have specific roles that may not apply to enucleation. For instance, a barbed broach is mainly used for removing the pulp tissue in endodontic treatment rather than for cyst removal. A rotary paste filler is typically employed for packing root canals with filling material, which is not necessary during enucleation. Similarly, a periosteal elevator is utilized to separate tissue from the bone, which may assist in the procedure but is not the primary instrument for enucleating a cyst. Therefore, the choice of Mitchell's trimmer is indicated due to its effectiveness in managing the contours and details of the surgical site.