220 MECHANICAL APPLIANCES 



The way in whicli Mr. Harrison makes use of 

 compressed wood, is by taking a piece of dry 

 willow, or any fine-grained wood, that is as free 

 from resin as possible, and compressing it, by 

 screwing it up between the jaws of a parallel vice 

 for about forty-eight hours, occasionally, as it 

 becomes compressed, screwing the vice up more. 



A bone-piece is fitted to the mouth, and behind 

 the tooth to be brought forward is cut a slot, or 

 groove, the width of the tooth ; the edges of the 

 groove are slightly undercut, to retain the wood 

 in position ; that end of the groove which approxi- 

 mates to the gum is cut somewhat deeper : con- 

 sequently, when a piece of compressed wood of 

 equal thickness is slid into the groove, with the 

 fibre of the wood parallel with the tooth, on 

 absorbing moisture it expands, and the pressure 

 comes first on the edge of the tooth, where it can 

 exert the greatest amount of power. When it has 

 pressed the tooth out as far as it possibly can, 

 another and thicker piece of wood is substituted, 

 and so on, until it may be found requisite to fit 

 another bone-piece to the retreating tooth, and 

 continuing the same plan. 



The way in which the compressed wood is 

 used for drawing a tooth back, is by cutting 

 a small recess on the lingual surface of the 

 bone-piece behind the tooth to be drawn back. 

 Into the recess is placed the wood, the fibre 

 parallel with the tooth, and over the wood a small 



