During a root canal treatment, fluid streaming and acoustic effects generated by irrigation tip’s oscillation, in combination with root canal irrigant dissolve tissue and kill microbes effectively. For a gentle passive ultrasonic irrigation, the frequencies and displacement amplitudes as well as the tip’s temperature increase are required to predict streaming effects and the device’s fatigue behaviour. As an initial step an operating deflection shape analysis was performed to understand the free vibration behaviour of irrigation tips. The operating frequency and the three-dimensional displacement of two specimens of irrigation tips (IRRI S 21/25, VDW) driven by an ultrasonic irrigation device were measured by means of scanning laser vibrometry. Both irrigation tips oscillated sinusoidally at a frequency of 30 kHz. With growing power level the maximum deflection increased up to 30 μm at the tip’s free end. This study can be seen as preliminary investigations of the vibration characteristic of a metallic endodontic tip and will be used to design further experiments under realistic conditions.