Just wanted to say your post is striking. The clearness in your post is quite spectacular and I can take for granted you are an expert on this field….

CPAP is the gold standard for the treatment of sleep apnea, because it can be titrated or individually set on the optimum pressure to preserve your father’s upper airways at night. The brand of CPAP machine isn’t as important as having a quality titration done to arrive at the proper pressure for him, and finding the right mask type that makes him the most comfortable and likely to wear the system consistently all night, every night.

Oral devices are for very mild cases of sleep apnea. However, I would be very wary of any devices that are mail-order/internet. These devices are usually prescribed and fitted by a dentist or ENT specially trained in their use. Any device that is ‘plug and play’ without being fitted is a scam.