Key with Claw attached to Circular Bolster
The bolster, acting as the pivot, could cause significant damage to adjacent gums, teeth and bone during a forceful key extraction. Wrapping the bolster in a soft piece of linen or leather was advisable. With an aim towards minimizing injury, a variety of bolster shapes and sizes appeared, and some were movable. The earliest designs were deep and flat, and, in 1798, the bolster’s deficiency was attributed to its excessive depth, which raised the tooth in too high an arc and not in the desired perpendicular direction. Oval, barrel-shaped, cylindrical, pear-shaped, circular, egg-shaped, spherical, bullet-shaped, concave, and saddle-shaped were tried during the 100-year quest to design the elusive innocuous bolster!
Reversible Circular Bolster KeyWood-handled key (A147.162); a thumbscrew attaches the reversible circular bolster to the shaft.
University of the Pacific Permanent Collection, Donor: Maurice J. Owens, DDS
Thumbscrew and BolsterThe thumbscrew attaching the reversible circular bolster to the shaft.
Screw Pin and ClawA screw pin attaches the claw to the bolster.
Claw and Bolster CurvatureWith the curve of the claw conforming to that of the bolster, a more perpendicular arch is achieved during extraction of any sized tooth.