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Effect of loading on the vibration characteristics of thin magnetostrictive ultrasonic scaler inserts.

BACKGROUND
The ultrasonic scaler market has seen an increase in availability of thin inserts for periodontal pocket access. While such thin inserts may have advantages in negotiating the periodontal pocket, the relatively narrow structure may be prone to damping under load. The purpose of this study was to assess the vibration characteristics under load of thin, straight, ultrasonic scaler inserts.


METHODS
Five types of thin inserts were each obtained from three manufacturers and were operated using an ultrasonic generator at medium power and low water. The displacement amplitude of the scaling tip was measured via a scanning laser vibrometer (SLV). Increasing forces up to 1.0 N were applied either to the base of the tip (up through its center) or while it was loaded from the side. Displacement measurements were obtained using the SLV under these loading conditions.


RESULTS
Under loading, there was a drop in displacement amplitude of all tips. Furthermore, loading of the tips resulted in large variations of displacement amplitudes recorded. The mean tip displacements recorded ranged from 10 to 30 microm when unloaded and 7 to 25 microm when loaded. The fundamental frequency of the ultrasonic tips' oscillation was at 30 kHz. However, loading resulted in the production of additional subharmonic frequencies in the region of 6 to 10 kHz.


CONCLUSIONS
Thin ultrasonic scaler tips are susceptible to loading. This results in a reduction in the displacement amplitude that shows variation not only between tips of different design but also between those of the same design made by the same manufacturer. Clinicians and researchers should be aware of this variability, which may influence both clinical procedures and future research with thin ultrasonic scaling tips.