Reaction of the anterior abutment of a Kennedy Class II removable partial denture to various clasp arm designs: an in vitro study.

Five clasp arm designs were selected for in vitro testing of the anterior abutment of a Kennedy Class II removable partial denture. The clasps were a circumferential clasp with the cast retentive arm placed at the survey line, a circumferential clasp with a cast retentive arm placed into a mesiofacial undercut of 0.01 inch, a circumferential clasp with a wrought wire retentive arm placed into a mesiofacial undercut of 0.01 inch, a buccal I-bar placed at the greatest facial curvature into a 0.01 inch undercut, and a half T-bar buccal arm placed into a 0.01 inch distofacial undercut. The relative movement of the abutments was recorded by a polygraph on a line from a point of force in the extension and through the rest seat of the anterior abutment, 90 degrees from the first direction, and vertically in the long axis of the abutment. The amount of movement of the abutment tested varied relative to the clasp design and the directions recorded. The cast circumferential arm placed at the survey line consistently showed less movement, and a cast circumferential arm placed into an undercut showed the greatest total movement. The decision to use any of these clasp arm designs should be correlated with other clinical conditions that are present for a specific patient.