Certainly the most comfortable condition of sleeping if there is no appliance in the mouth. The reason we prescribe dental sleep appliances is because there is a sleep disorder. The aim is to protect the airway size during sleep. This protection can be passive and active. Once we are prescribing a dental sleep device we will compromise patient comfort.
From the comfort aspect the best appliance will be the lightest, the slimmest giving the tongue enough space and the one that gives maximum patient comfort at full occlusion. These requirements by only a fully digitally fabricated appliance will be met that gives a fully equilibrated occlusal surface. Once we need a dental sleep appliance we will want to give the most possible to our patients. What can be more than a fully comfortable lightweight 3D appliance that keeps the airway open passively during the night?