By Dr.Swathi Pai on Friday 28 January 2011 with 0 comments

1.     Size of the abrasive particles:
The larger the size of the particles, deeper is the penetration on the surface of the work. Hence rapid removal of material occurs with coarse grit burs compared to medium or fine grit burs.

  1. Shape of the abrasive particles:

             The abrasive particles should be irregular in shape for greater efficiency. Irregular particles will present a sharp edge where as round smooth particles will present a flat face to the work. Hence the former cuts well.

  1. Density of the abrasive particles;

             Density of the particle refers to the no.of abrasive particles /unit area. In instruments with high density, the particles are closely spaced whereas in those with low density, the particles are widely spaced. Therefore at constant loads, a greater force will be exerted on each particle of the substrate, when particles are widely spaced, increasing the grinding efficiency. Coarse grit burs have a low density compared to fine grit burs.

  1. Hardness of the abrasive particles:

For the bur to be efficient, the hardness of the abrasive particle should be greater than the hardness of the work in which it is to be used, only then can the abrasive indent the surface & remove the material.

  1. Clogging of the abrasive surface:

Clogging of the spaces between the particles by grinding debris affects grinding because this partially blocks the penetration of the abrasive particle into the surface. Clogging enhanced when particles are close together and when under cut is present on the protruding part of the particle. Use of coolants during grinding may wash away the debris, thus preventing clogging. Hence cleaning is always recommended after each use of bur.
MICROSCOPIC examination suggests that debris accumulation may be more detrimental to cutting efficiency than are wear & diamond chip loss from the surface of the bur.

  1. Speed & pressure: similar to bladed burs.

Proper speed & pressure are major factors in determining the life of the bur. Usual cause of failure of abrasive instrument is when excessive pressure is applied onto them to increase their cutting rate at inadequate speed which leads to loss of diamond & in turn decreasing the cutting efficiency.

Category: Conservative and Endodontics Notes , Dental Materials Notes



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