A controller for use with an oral care device; wherein the controller is configured to estimate the location of the oral care device relative to an interdental space in a mouth, using predetermined data and current use data, the current use data relating to at least one of: actions of a user during use of the oral care device, operations of the oral care device; and generate a control signal based on the outcome of the estimation, wherein the control signal, during use, controls the oral care device to jet fluid and/or emit powder when it is estimated that the oral care device is proximate to or at or inside an interdental space in the mouth; and wherein the current use data comprises at least one of: a position of the oral care device relative to teeth; an orientation of the oral care device relative to teeth; a brushing force applied to the oral care device; a drivetrain current of the oral care device; a vibration frequency of the oral care device; a strain exerted on the oral care device; a deflection of a brush head of the oral care device; a light intensity generated by or of the oral care device; a sound intensity generated by or of the oral care device; a fluid backpressure of a fluid delivery system of the oral care device; a speed or velocity of the oral care device; a fluid delivery related sensor signal; and the predetermined data is produced using location data indicating locations of interdental spaces and training use data relating to at least one of: actions of the user during use of the oral care device, operations of the oral care device, wherein the predetermined data is based on a correlation between location data indicating locations of interdental spaces and training use data relating to at least one of: actions of the user during use of the oral care device, operations of the oral care device. the controller is configured to estimate the location of the oral care device relative to an interdental space in a mouth, using predetermined data and current use data, the current use data relating to at least one of: actions of a user during use of the oral care device, operations of the oral care device; and generate a control signal based on the outcome of the estimation, wherein the control signal, during use, controls the oral care device to jet fluid and/or emit powder when it is estimated that the oral care device is proximate to or at or inside an interdental space in the mouth; and wherein estimate the location of the oral care device relative to an interdental space in a mouth, using predetermined data and current use data, the current use data relating to at least one of: actions of a user during use of the oral care device, operations of the oral care device; and generate a control signal based on the outcome of the estimation, wherein the control signal, during use, controls the oral care device to jet fluid and/or emit powder when it is estimated that the oral care device is proximate to or at or inside an interdental space in the mouth; and wherein the current use data comprises at least one of: a position of the oral care device relative to teeth; an orientation of the oral care device relative to teeth; a brushing force applied to the oral care device; a drivetrain current of the oral care device; a vibration frequency of the oral care device; a strain exerted on the oral care device; a deflection of a brush head of the oral care device; a light intensity generated by or of the oral care device; a sound intensity generated by or of the oral care device; a fluid backpressure of a fluid delivery system of the oral care device; a speed or velocity of the oral care device; a fluid delivery related sensor signal; and the predetermined data is produced using location data indicating locations of interdental spaces and training use data relating to at least one of: actions of the user during use of the oral care device, operations of the oral care device, wherein the predetermined data is based on a correlation between location data indicating locations of interdental spaces and training use data relating to at least one of: actions of the user during use of the oral care device, operations of the oral care device.