The diamond burs were specially designed and tested experimentally for preparation of round and straight bevels of composite resin restorations in posterior teeth.
The shape and size of the bur was so designed that both the width and depth of the bevel should be prepared to be 0.5 mm when it is used when guiding is acquired with tooth surface and cavity wall.
Extracted human anterior and posterior primary teeth were used for experimentation. The cavities were prepared on the labial surface of anterior primary teeth and the occlusal surface of posterior primary teeth and the bevels were placed on the margin of the cavity with the above mentioned bevel-preparing burs. The cavity of each tooth was observed labially or occlusally, and its duplicated plaster model was also examined sectionally with the stereo-microscope.
As a result, the bevels with the use of the bevel-preparing burs were found to be relatively uniform and well prepared.
Next, the thermal cycling test was carried out after composite resin restorations in those prepared cavities. The relationship between marginal form of the cavity and the marginal sealing effect was examined using the dye penetration test.
It was concluded that the cavity with a round bevel showed the most excellent results for marginal sealing.