Two different industries share a name. The world's manual toothbrushes come overwhelmingly from Hangji, near Yangzhou in Jiangsu, roughly one in three, a plastics-and-bristle craft town. The electric toothbrush is a different animal: a sealed electronics product, motor, PCB, lithium cell, induction coil, sometimes Bluetooth, and it is designed and built in Shenzhen, not Hangji.
The reference design is the drive. Houses compete on the motor: sonic, a vibrating armature at roughly 30,000 to 40,000 strokes a minute; magnetic-levitation sonic, a contactless maglev motor that runs quieter and lasts longer, the premium tier; and rotating-oscillating, the round Oral-B-style head. Around it sit IPX7 sealing, inductive charging, pressure sensors, multiple modes, and increasingly colour screens and app pairing.
You buy a platform, not a project. These are full-lifecycle ODMs: ID and CMF, motor and electronics, in-house tooling and CNC, automated assembly and QC. They hold the patents and offer a catalogue of twenty-plus ready models for low-MOQ private label, with water flossers, UV sanitisers and replacement heads alongside. For export they carry CE/FCC/RoHS, FDA as an oral-care device, and PSE for Japan.
This is the layer below the famous brands. usmile and Soocas (own-brand Guangdong players), and the Western incumbents Oral-B and Philips Sonicare, are not on this list, it maps the houses you hire, not the brands you compete with.