Adding a distinct second bend in the key shaft brought the bolster (fulcrum) in line with the middle of the handle and the axis of motion perpendicular to the tooth being extracted. In addition, a double bend shaft cleared anterior teeth more readily, making posterior tooth extractions less damaging.
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Improved Construction Key Illustration
This shaft modification was introduced in 1795 and called a key of "Improved Construction."
Courtesy of Martino Publishing, Eastford, CT — Colyer, 2006
Double-Bend Shaft
The late-1700s "improved" key (A147.168) shown here has a double-bend shaft...
University of the Pacific Permanent Collection,
Donor: Maurice J. Owens, DDS
Cross-Hatched Ebony Handle
The late-1700s "improved" key (A147.168) shown here has a double-bend shaft, a carved ebony handle with cross-hatched design and waisted ends...
Cylindrical Bolster
The late-1700s "improved" key (A147.168) shown here has a double-bend shaft, a carved ebony handle with cross-hatched design and waisted ends, a cylindrical bolster, and...
Double-Notched Claw Tip
The late-1700s "improved" key (A147.168) shown here has a double-bend shaft, a carved ebony handle with cross-hatched design and waisted ends, a cylindrical bolster, and a double-notched claw attached to the shaft head by a screw pin.
