Which of the following describes a factor that can complicate RPD design?

Abutment tooth mobility is a significant factor that can complicate the design of a removable partial denture (RPD). When abutment teeth are mobile, they lack the necessary stability and support that is crucial for an effective and functional prosthesis. The presence of mobile teeth can lead to complications such as improper seating of the RPD, discomfort for the patient, increased stress on the remaining teeth, and potential failure of the denture due to inadequate retention and support. In designing an RPD, the stability of the abutment teeth is paramount; thus, addressing mobility is essential to ensure the long-term success of the prosthetic solution.

In contrast, a perfectly aligned arch shape, the absence of recession of periodontal tissues, and the presence of all natural teeth do not complicate RPD design. Instead, these factors generally contribute to a more straightforward design process. A well-aligned arch provides better retention and alignment for the prosthesis, healthy periodontal tissues are indicative of solid support for RPDs, and having all natural teeth minimizes gaps that need to be addressed in the design. Therefore, abutment tooth mobility stands out as a complicating factor in the context of RPD design.