Intra-vascular thrombosis associated with dental ultrasound.

Ultrasonic instruments used in dentistry generally operate at frequencies of 25 to 42 kHz. A wire oscillating at these ultrasonic frequencies immersed in a liquid produces local flow patterns termed acoustic microstreaming. Large shear forces are produced which are able to rupture erythrocytes and platelets both in vitro and in vivo. This results in activation of the blood coagulation system with subsequent thrombus formation. The probe tip of an ultrasonic scaler was positioned to touch a mammalian mesenteric artery. The probe was operated for 10 to 20 s at a displacement amplitude of 15 micron. Acoustic microstreaming occurred which disturbed blood flow and this microstreaming ceased when the power was switched off. After continued operation of the probe, thrombi were formed against the vessel wall with fragments embolising downstream. These thrombi eventually grew to occlude the vessel. Furthermore, an in situ model demonstrated that acoustic energy was transmitted through the tooth during typical ultrasonic scaling procedures. As a consequence of these observations, it is possible that acoustic microstreaming fields may be generated within the blood vessels entering the tooth apex which are large enough to induce platelet damage. Therefore there is a potential hazard from the use of the ultrasonic scaler which may induce similar thrombi formation within the pulpal or perapical tissues of the teeth. If this were to occur it could result in tooth death which might not become evident until a long time after the ultrasonic exposure.