Trapdoor-insert assembly comprising a trapdoor comprising: - a front side and a back side: - a fixed frame suitable for being fixed to a wall in a wall opening, - a movable frame disposed in the fixed frame, - a panel mounted on said movable frame, and - connection means, which are arranged at the back side of the trapdoor and connect the movable frame to the fixed frame so that the movable frame can be moved between an opening position and a closing position; wherein at least one of said frames (1, 2) comprises at least one section (3a, 3b) having a longitudinal seat defined by a bottom wall and by two sidewalls; wherein the assembly comprises an insert which is connected to the section and comprises an operation portion and a coupling body; characterized in that said two sidewalls comprise two projecting wings in opposite parallel position that extend for the entire length of the section and define a narrowed inlet giving access to the longitudinal seat; whereby said coupling body comprises two retaining teeth that extend along opposite directions and are engaged under the two projecting wings; wherein said coupling body is configured in such a way that: - the retaining teeth can be moved closer to each other until they reach a position wherein said retaining teeth can pass through the narrowed inlet along a coupling direction that is incident to the bottom of the section; and - the retaining teeth can be moved apart in order to be engaged under the projecting wings. - a front side and a back side: - a fixed frame suitable for being fixed to a wall in a wall opening, - a movable frame disposed in the fixed frame, - a panel mounted on said movable frame, and - connection means, which are arranged at the back side of the trapdoor and connect the movable frame to the fixed frame so that the movable frame can be moved between an opening position and a closing position; wherein at least one of said frames (1, 2) comprises at least one section (3a, 3b) having a longitudinal seat defined by a bottom wall and by two sidewalls; wherein the assembly comprises an insert which is connected to the section and comprises an operation portion and a coupling body; characterized in that said two sidewalls comprise two projecting wings in opposite parallel position that extend for the entire length of the section and define a narrowed inlet giving access to the longitudinal seat; whereby said coupling body comprises two retaining teeth that extend along opposite directions and are engaged under the two projecting wings; wherein said coupling body is configured in such a way that: - the retaining teeth can be moved closer to each other until they reach a position wherein said retaining teeth can pass through the narrowed inlet along a coupling direction that is incident to the bottom of the section; and - the retaining teeth can be moved apart in order to be engaged under the projecting wings. - the retaining teeth can be moved closer to each other until they reach a position wherein said retaining teeth can pass through the narrowed inlet along a coupling direction that is incident to the bottom of the section; and - the retaining teeth can be moved apart in order to be engaged under the projecting wings.