The ultrasonic dental scaler is an invaluable tool in the fight against dental calculus and periodontal disease. The purpose of this study was to assess the natural frequency of the straight internal ultrasonic scaler insert 30K FSI-SLI-10S (Dentsply International, York, USA) and to measure the displacement observed at the tip when operated under different generator settings. Two approaches were used: finite element analysis and scanning laser vibrometry. The Finite Element Analysis method was employed to calculate the expected modes of vibration of the insert. Scanning laser vibrometry was used to measure displacements of the tip during operation. It was found the insert had two modes of vibration around the operating frequency of 30 kHz; these modes were first order bending in two orthogonal planes.