A medical mouthpiece (100; 1100; 2100; 3100; 4100), comprising: a generally U-shaped first member (110; 1110; 2110; 4110) having a tubular portion (126; 1111; 2111) extending anteriorly therefrom, the first member (110; 1110; 2110; 4110) including an upper surface (12; 1112; 2112; 3112) configured to contact an upper dentition of a patient spaced apart from a lower surface (14; 1114; 2114; 3114) configured to contact a lower dentition of the patient; wherein the first member (110; 1110; 2110; 4110) includes a posterior central orifice (130; 1130) extending anteriorly to posteriorly through the first member (110; 1110; 2110; 4110) along a medial line; wherein the first member (110; 1110; 2110; 4110) forms at least one lateral interocclusal passageway (116; 1116A, 1116B; 3116; 4116A) configured to be positioned within a lateral interocclusal space of a patient, the at least one lateral interocclusal passageway (116; 1116A; 3116; 4116A) extending anteriorly to posteriorly through the first member (110; 1110; 2110; 4110) between the upper surface (12; 1112; 2112; 3112) and the lower surface (14; 1114; 2114; 3114); and a second member (180; 1180; 4180) slidably received within the tubular portion (126; 1111; 2111), the second member (180; 1180; 4180) including a perimeter ring defining an outwardly-facing surface configured to be in facing engagement with an inner surface of the tubular portion (126; 1111; 2111); wherein the second member (180; 1180; 4180) includes an anterior central orifice (188; 1128; 4128) extending anteriorly to posteriorly through the second member (180; 1180; 4180) along the medial line, the anterior central orifice (188; 1128; 4128) cooperating with the posterior central orifice (130; 1130) to form a central passageway extending through the mouthpiece (100; 1100; 2100; 3100; 4100); wherein the second member (180; 1180; 4180) includes one or more anterior apertures and at least one lateral interocclusal passageway (1116B; 4116B) passing through the perimeter ring anteriorly to posteriorly from the one or more anterior apertures. a generally U-shaped first member (110; 1110; 2110; 4110) having a tubular portion (126; 1111; 2111) extending anteriorly therefrom, the first member (110; 1110; 2110; 4110) including an upper surface (12; 1112; 2112; 3112) configured to contact an upper dentition of a patient spaced apart from a lower surface (14; 1114; 2114; 3114) configured to contact a lower dentition of the patient; wherein the first member (110; 1110; 2110; 4110) includes a posterior central orifice (130; 1130) extending anteriorly to posteriorly through the first member (110; 1110; 2110; 4110) along a medial line; wherein the first member (110; 1110; 2110; 4110) forms at least one lateral interocclusal passageway (116; 1116A, 1116B; 3116; 4116A) configured to be positioned within a lateral interocclusal space of a patient, the at least one lateral interocclusal passageway (116; 1116A; 3116; 4116A) extending anteriorly to posteriorly through the first member (110; 1110; 2110; 4110) between the upper surface (12; 1112; 2112; 3112) and the lower surface (14; 1114; 2114; 3114); and a second member (180; 1180; 4180) slidably received within the tubular portion (126; 1111; 2111), the second member (180; 1180; 4180) including a perimeter ring defining an outwardly-facing surface configured to be in facing engagement with an inner surface of the tubular portion (126; 1111; 2111); wherein the second member (180; 1180; 4180) includes an anterior central orifice (188; 1128; 4128) extending anteriorly to posteriorly through the second member (180; 1180; 4180) along the medial line, the anterior central orifice (188; 1128; 4128) cooperating with the posterior central orifice (130; 1130) to form a central passageway extending through the mouthpiece (100; 1100; 2100; 3100; 4100); wherein the second member (180; 1180; 4180) includes one or more anterior apertures and at least one lateral interocclusal passageway (1116B; 4116B) passing through the perimeter ring anteriorly to posteriorly from the one or more anterior apertures.