UPDATE 2-US FDA clears Vivos Therapeutics' oral device for sleep apnea

(Adds shares in paragraph 2, study data in paragraph 6 and background throughout)

Nov 29 (Reuters) - Vivos Therapeutics said on Wednesday the U.S. health regulator has cleared its oral device for severe obstructive sleep apnea (OSA), leading a massive rally in the company's shares before the bell.

Shares of the medical device maker more than doubled to $9.12 in premarket trading.

The clearance is the first ever for an oral appliance, along with a mode of respiratory ventilation or exercise training program for the muscles around face, mouth and tongue, to treat moderate and severe OSA in adults.

OSA is the most common sleep-related breathing disorder, which occurs when throat muscles intermittently relax and block the airway during sleep.

According to Vivos, its treatment is an alternative to therapy devices made by companies such as Philips and ResMed that send pressurized air into a patient's nose and mouth during sleep as well as to surgically placed implants that send electrical signals to the brain.

The U.S. Food and Drug Administration's (FDA) move was supported by study data that tested 73 severe OSA patients and showed at least a 50% improvement in the index used to determine the presence and severity of the disease.

Vivos said its appliance therapy gradually repositions the hard and soft tissues that define the airway, opening it up and optimizing its function and flow.

Under the clearance process, the FDA conducts a review of safety and performance data to determine if a new device is considerably equivalent to the one that is already on the market. (Reporting by Pratik Jain in Bengaluru; Editing by Shilpi Majumdar)