| 摘要 |
A percussive dental crown extractor comprises a hook 16 attached by an arm 14 to the front end of a tube 12 which encloses a cylindrical, notched hammer 44 and a spring 50 urging the hammer to the rear end of the tube, remote from the hook. The tube is telescoped into an outer cylinder 10. The tube and cylinder are held together by an axial post 38, one end of which is attached to the bottom 32 of the cylinder, the other end of which extends through an opening in the rear 36 of the tube and has a captivating cap 40 inside the tube. A spring 42 around the post urges the tube and cylinder apart. A sear 52 mounted in a boss 20 in the side of the tube, engages a notch 46 on the hammer when the hammer is moved to the front end 34 of the tube by compressing the cylinder and tube. When the cylinder and tube are relaxed, the hammer and its spring are held cocked by the sear. When the sear is pulled out of the hammer by a finger release 22, the hammer flies back to hit the post cap, which in turn hits the rear end of the tube, causing the tube, and hence the hook, to jolt rearwardly.
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