Mechanism for reclining chairs (1) reclinable up to the Trendelenburg position, preferably dental chairs, comprising a headrest (20), a backrest (2) movable with respect to a seat (3), and wherein said backrest is supported by a reclining mechanism comprising an arc (6) fastened to pads (8) sliding in guiding plates (9), actuated by a motoreducer (17), characterized in that it comprises:- at least a mobile trapezoidal lever (5) working as support for- a pair of vertically superimposed rollers (12), of which the bottom roller is stationary and the top roller is integral to the frame of the seat, each roller sliding on the lower and top edge of said trapezoidal lever (5)；- said at least one lever being mobile backwards and forwards in the direction of the longitudinal axis of said chair together with said pads；- said lever being oriented with its two opposed convergent lateral edges in the direction of chair longitudinal axis, the rollers (12) being pivotable around parallel axes and perpendicular to the chair longitudinal axis, so that simultaneously with the shifting of pads (8) along guiding plates (9) forward and backward, respectively, the frame of the seat performs a rheonomous tilting movement, upwards or downwards of its end corresponding to the anterior end of the chair seat.
