Ultreo, the competitor, plans to contest P&G claims that it is misleading customers with its marketing.
The oral-care company's advertising literature claims that the Ultreo Ultrasound toothbrush creates micro-bubbles capable of removing stubborn plaque.
P&G alleges that its own clinical study shows that the brush removes more plaque with the ultrasound feature turned off.
The personal care giant claims that Ultreo has provided no clinical studies on customers that support its claim that the ultrasound technology removes plaque.
Paul Warren, a P&G executive said: "Ultreo has provided no clinical proof that the ultrasound makes any difference in plaque removal."
Ultreo disputed these claims in a statement, saying that strong scientific evidence and a number of human clinical studies demonstrate the effectiveness of the ultrasound technology.
The company claimed that a recent study indicated that eight out of 10 consumers who used Ultreo would switch to Ultreo from their current power toothbrush.
"While we prefer to compete in the marketplace, we are prepared for a vigorous legal response to P&G's complaint," said a spokesperson in a statement.
The lawsuit was filed on 27 September, a day before the launch of P&G's Oral-B Triumph, at the American Dental Association Annual Session.
P&G claims claims that its Oral-B toothbrush can tell users through a wireless display when they are brushing too hard and when to move to the next part of the mouth.
P&G filed the suit in the US district court for southern New York.