Generally, when recommending masks for those who breathe through their mouth while sleeping (including people who have stuffy noses from colds), a full face mask is typically recommended. A full-face mask is also better suited for higher pressure settings. If you regularly suffer from congestion or sinusitis but prefer a nasal or nasal pillows mask, please consider the Dreamwear system which has interchangable masks. 

Oral CPAP masks deliver airflow only to the mouth (the nasal openings are closed with nose plugs), so they are suited to individuals who cannot breathe through their nose at all due to a severely deviated septum, nasal congestion or facial injury. In such circumstances, the user may find the delivery of the CPAP air stream through the mouth preferable to a full face mask, which delivers air to both the nose and mouth.

If you are using an oral mask, it is highly recommended to use a heated humidifier. Most users find there is a period of adjustment while becoming accustomed to an oral delivery mask. Please note, an oral mask should only be used if recommended by your respiratory physician.