Preparing fixed partial denture abutments such that they provide a path of placement free of undercuts

The abutments of a fixed partial denture (FPD) should provide a path of placement, so that the denture may be seated onto the abutment without tooth structure blocking the margin or intaglio surface. This article presents a literature review concerning the path of placement (also referred to as the path of insertion or the path of draw). In addition, the article presents clinical techniques for verifying an undercut-free path of placement for a prepared abutment and describes how to determine if a laboratory technician can fabricate a clinically acceptable FPD for an abutment that features undercuts within the path of placement. The article provides definitions of terms such as "path of placement" and "undercut" and explains concepts such as "parallelism of multi-unit fixed partial denture abutments" and also what a dentist means when the dentist says that an abutment "is undercut." The author suggests that dentists use high magnification loupes (6-8X magnification or greater) or a surgical operating microscope to examine abutments for microscopic undercuts and to ensure that bridge abutments are aligned with a path of placement.