Centrifugal deflection device intended to be fitted to a surgical or dental handpiece to prevent the penetration of foreign matter that results from an operation, the centrifugal deflection device including a ring coupled in rotation either directly or via a tool shank to a drive shaft of the handpiece. This device is characterized in that the ring is covered by a sleeve secured to the front end of the body of the handpiece and which, with the ring, delimits an ejection chamber. The ejection chamber includes an inlet that communicates with a rear area of the handpiece and an outlet that communicates with the external environment, the ring having a first diameter at the outlet of the ejection chamber and a second diameter at the inlet of the ejection chamber, the first diameter of the ring being larger than the second diameter of the ring.