Measurement (in vitro) of the amount of force required to dislodge specific clasps from different depths of undercut.

A fundamental principle in clasp selection for a specific abutment is the reduction of the transmission of excessive forces to that abutment. The flexibility of a clasp was believed to directly affect the reduction of such forces. This study compares the average measurements of forces required to dislodge two kinds of circumferential clasps in different amounts of undercuts: one with a half-round retentive arm and the other with a round retentive arm under tensile load. Three commonly used undercuts were created on six cast crowns, premolars, and molars. Each clasp was exposed to adequate tensile load until dislodgment occurred. The test was run six times for the same clasp. The means of tensile load required to dislodge each of the different clasps were compared statistically. However, no significant difference was detected for the main effects of the three variables studied: tooth type, undercut, and amount and clasp type. Findings indicated the possible use of cast round clasps where advantages of clinical fit and reduction of transmitted forces to the abutments can be gained.