The dulling of twist drills during pin channel placement

Dull twist drills used for pin channels have been cited as an etiology for dentinal cracks. This investigation examined the dulling phenomenon after repeatedly using twist drills. Inspection of the twist drills in the SEM for metal deformation revealed no alteration of the cutting edges but an accumulation of a smear debris was noted behind the cutting edges of the cone-shaped drill. Debris was also recorded on the land and flute spiral surfaces with morphological changes on the dentinal walls. These surfaces progressed serially from a rough surface to a smooth, plaque-like surface with fine striations oriented toward the drill rotation. The timing of the changes coincided with dentinal cracking reported by others. Dulling of twist drills in dentin can be attributed to adherence of byproducts rather than a loss of the cutting edge.