. The science and practice of dental surgery. d, or by creating a new bend or step asdescribed by Case. Lengthening may be pro-duced by pinchuig the «ire at intervals througli-out its length as described by Angle. Each ofthese methods is an example of discontinuousforce. The only agent commonly used that combinesin its application continuous and discontmuousforce is the fibrous or silk ligature. When firsttiglitly applied it acts in the same way as aw ire ligature, but absorption of moisture causesshortening of the ligature, and m this waycontmuous force for a limited period is super-imposed o
. The science and practice of dental surgery. d, or by creating a new bend or step asdescribed by Case. Lengthening may be pro-duced by pinchuig the «ire at intervals througli-out its length as described by Angle. Each ofthese methods is an example of discontinuousforce. The only agent commonly used that combinesin its application continuous and discontmuousforce is the fibrous or silk ligature. When firsttiglitly applied it acts in the same way as aw ire ligature, but absorption of moisture causesshortening of the ligature, and m this waycontmuous force for a limited period is super-imposed on discontinuous. The great efficiencyof sUk ligatures, even of very fine calibre,probably depends upon this combination offorces. Auotlier method by which continuousand discontinuous action miglit be combinedwould be to make part of the length of a tractionscrew slightly sinuous or helical. By this meansthe screw could be screwed up more tightly andthe extensional elasticity of the helical rodbrought into play, so that the risk of damage by. Fig. 334.—A diagram to show tho effect of tying teethto a flexible wire bow. The bow is pulled in wherethe ligatures are tied, and bulges out in theintervals; tliis results in a constant effort onthe part of the bow to resume its normal shape,and so also, in the movement of tho teeth that aretied. {Dental Record.) over-tightenmg would be reduced. The elas-ticity of a wire bow in combination with ascrew acts in a similar way. The Principle of Buccal or Labial Movement of aTooth by Fixed Appliances.—When fixed appli-ances are used and ^^•ire ligatures are employedto connect the teeth and bow, it must not bethought that the ligatures are the importantfactor in tooth movement; they are little morethan tlie means whereby force is transmittedfrom the wire bow to the teeth. Take for ex-ample the laljial movement of a central bow is adjusted in the buccal tubes onthe anchor bands, so that the nuts engage thefront of the tubes and
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectdentistry, bookyear19
