The Effect of Ultrasonic Instrumentation on Finish Line Integrity

Purpose: Ultrasonic scaler is frequently used for temporary cement remnants removal from abutment teeth. A major concern is the alteration of the structural integrity of the abutment finishing line by the ultrasonic scaler. The current study evaluates the influence of ultrasonic scaling on the integrity of the finish line. The effect of finish line design (chamfer or feather edge), and its location (dentin or enamel) was also evaluated. Methods: Intact 22 human extracted molars were divided into 2 groups: finish line was prepared on enamel (n=11) and dentin (n=11), and further subdivided to finish line configuration groups (chamfer or knife-edge). Preparation of finish line was preformed following a standard repetitive procedure. 3D scans of the same tooth before and after ultrasonic instrumentation were performed. Pre and post scaling images were superimposed. The finish line alterations were evaluated and measured. The significance of the differences was evaluated using Students’ t-test. Results: The average alteration at the finish line area following ultrasonic scaling was 71.5 ± 24.6 μm. Higher alterations were found for enamel and for chamfer finish lines compared to dentin and knife edge, 134.4 ± 61.4 μm and 30.3 ±11.7 μm respectively. The highest change (228.6μm) was found for chamfer finish line located on enamel. The differences between groups were statistically significant (p<0.05). Conclusion: Ultrasonic scaling alters the topography of the finish line area of abutment teeth and thus may compromise marginal fit and integrity of the final restoration.