Deposits of plaque build up between the tooth and the gum.
牙菌斑的沉积物在牙齿和牙龈间形成。
《柯林斯英汉双解大词典》
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Valve deposits. If the fuel has excessive amounts of gum in it, some of this gum may be deposited on the intake valve as the air-fuel mixture passes the valve on the way to the engine cylinder.