Finishing Lines for Prosthodontics Using a Novel, Atraumatic, Ultrasonic Instrument

Objective: This in vitro study compared the accuracy of crown margins finished with new ultrasonic instruments with margins finished using conventional rotary instruments. Methods: Extracted human canine teeth were prepared for crowns. A split tooth model was used to refine the margins: half of each margin was finished with conventional rotary instruments, the other with ultrasonic instruments. The shape and finish of the margins were compared using scanning electron microscopy (SEM), and a qualitative comparison of surface roughness was obtained using profilometric analysis software. Results: The margins finished with the ultrasonic instruments exhibited a better-defined axial wall/margin angle, and a smoother marginal surface. Rotary instruments produced a sharper and more continuous finishing line. The margin produced with the ultrasonic instruments had a less pronounced smear layer, a condition that might favour bonding. Conclusions: The margins produced with the new ultrasonic instruments are comparable to the current standard and appear to have some practical advantages.