The effect of rotary cutting instruments and hand instruments on the cavo surface margins of Class II amalgam restorations :

Abstract

Cl. II amalgam restorations are routinely inserted by dentists from almost every country. Amalgam is considered to be the most used restorative material in dentistry. Cavity preparation is usually based on the principles as outlined by G.V. Black. Few people have investigated the effect of cutting instruments to enamel. Boyde has conducted a study in which an attempt was made to investigate the surface morphology following the use of cutting instruments. In this particular study, an in vitro experiment was conducted on extracted human teeth to determine the effect of the most commonly used cutting instruments to the cavo-surface margins. A total of 24 teeth were prepared by means of a diamond bur, tungsten carbide bur and hand instruments. The cavities were restored with amalgam and the restorations finished by means of several methods. All these manipulations were examined in a scanning electron microscope. The results indicate that a diamond bur produced irregular and grooved cut surfaces but produced an acceptable gingival floor. Carbide burs produced the best and smoothest enamel. Some chipping was observed however at the exit margin. Hand instruments caused fracturing and chipping of enamel margins and left an irregular and gouged surface. It is therefore recommended that hand instruments are used for intra-coronal structures only and not for cavo-surface line-angles. It was observed that with an adequate matrix-wedge system amalgam overhangs may still occur. These overhangs can easily be removed from buccal and lingual margins, but create a problem at the gingival interproximal margins. Even careful condensation of amalgam caused voids in the condensed amalgam restoration. The use of an amalgam finishing strip produced a burnished like amalgam surface with well adapted margins. The use of an amalgam finishing strip in combination with pumice was an adequate method to polish interproximal amalgams. The findings indicate that the best rotary cutting devices are carbide burs. This study points toward a need for a careful evaluation of existing operative procedures. Many methods and techniques are taken for granted and practiced routinely without the realization as to the microscopic damage that may occur to tooth structure.