An electric toothbrush (100; 600), comprising: a body comprising a gripping part (10; 610) and a stem (11; 611) extending from the gripping part (10; 610); a brush unit (20; 620) detachably coupled to the body, the brush unit (20; 620) having an outer surface including a front surface having a plurality of tooth cleaning elements (22; 622) extending therefrom; a motor located within the body and operably coupled to an eccentric shaft (13; 613) to oscillate the brush unit (20; 620); a light emitting element (24; 624) configured to emit light from the brush unit (20; 620); a light receiving element (25, 26; 625) configured to receive reflected light of the light emitted from the light emitting element (24; 624); a fluid dispensing system comprising a reservoir for storing a fluid and a fluid conduit (27; 627) extending from the reservoir to an outlet; a controller (50; 650) operably coupled to the motor, the light emitting element (24; 624), the light receiving element (25, 26; 625), and the fluid dispensing system, the controller (50; 650) receiving data indicative of an amount of the reflected light received by the light receiving element (25, 26; 625); and wherein the controller (50; 650) controls operation of the fluid dispensing system based on the amount of the reflected light detected by the light receiving element (25, 26; 625); characterized in that the stem (11; 611) comprises an internal cavity, a first window (23a; 623a) that provides visibility from an outer surface of the stem (11; 611) into the internal cavity of the stem (11; 611), and a first hole (21a; 621a) extending from the outer surface of the stem (11; 611) to the internal cavity of the stem (11; 611); and further in that the brush unit (20; 620) comprises a second window (23; 623) that provides visibility into an interior cavity of the brush unit (20; 620), and a second hole (21; 621) extending from the outer surface of the brush unit (20; 620) to the interior cavity of the brush unit (20; 620), the brush unit (20; 620) coupled to the body so that the first and second windows (23, 23a; 623, 623a) and the first and second holes (21, 21a; 621, 621a) are aligned, optionally wherein the outlet is formed by the first hole (21a; 621a) in the stem and the second hole (21; 621) in the brush unit (20; 620). a body comprising a gripping part (10; 610) and a stem (11; 611) extending from the gripping part (10; 610); a brush unit (20; 620) detachably coupled to the body, the brush unit (20; 620) having an outer surface including a front surface having a plurality of tooth cleaning elements (22; 622) extending therefrom; a motor located within the body and operably coupled to an eccentric shaft (13; 613) to oscillate the brush unit (20; 620); a light emitting element (24; 624) configured to emit light from the brush unit (20; 620); a light receiving element (25, 26; 625) configured to receive reflected light of the light emitted from the light emitting element (24; 624); a fluid dispensing system comprising a reservoir for storing a fluid and a fluid conduit (27; 627) extending from the reservoir to an outlet; a controller (50; 650) operably coupled to the motor, the light emitting element (24; 624), the light receiving element (25, 26; 625), and the fluid dispensing system, the controller (50; 650) receiving data indicative of an amount of the reflected light received by the light receiving element (25, 26; 625); and wherein the controller (50; 650) controls operation of the fluid dispensing system based on the amount of the reflected light detected by the light receiving element (25, 26; 625); characterized in that the stem (11; 611) comprises an internal cavity, a first window (23a; 623a) that provides visibility from an outer surface of the stem (11; 611) into the internal cavity of the stem (11; 611), and a first hole (21a; 621a) extending from the outer surface of the stem (11; 611) to the internal cavity of the stem (11; 611); and further in that the brush unit (20; 620) comprises a second window (23; 623) that provides visibility into an interior cavity of the brush unit (20; 620), and a second hole (21; 621) extending from the outer surface of the brush unit (20; 620) to the interior cavity of the brush unit (20; 620), the brush unit (20; 620) coupled to the body so that the first and second windows (23, 23a; 623, 623a) and the first and second holes (21, 21a; 621, 621a) are aligned, optionally wherein the outlet is formed by the first hole (21a; 621a) in the stem and the second hole (21; 621) in the brush unit (20; 620).