Abstract: Oral appliances that may include a supporting shell member having concave geometry for receiving at least a portion of a dental arch of a wearer into the concave geometry; and, a tongue guide member extending from said supporting shell member and into contact with an underside of a tongue of said wearer when the portion of the dental arch is received into the concave geometry. This oral appliance may be utilized in methods for treating various sleep and breathing disorders (“SBD”), for treating sleep apnea, treating airway obstruction, for upper and/or lower jaw reshaping, for airway reshaping, for mandibular advancement, for tongue-retaining, and for providing myofunctional therapy to encourage and help train the tongue to have the proper tongue posture for nasal breathing and discourage mouth breathing.