A device for treatment of sleep apnea or snoring of a user, comprising: a first oral splint adapted for an upper jaw of the user, curved and essentially U-shaped with two legs, one adapted for the left side of the upper jaw and one adapted for the right side of the upper jaw, wherein the first oral splint comprises two adjustment devices for adjusting the positions of the abutment elements, one on each leg of the first oral splint positioned on the outer lateral side of the respective leg, each adjustment device of the first oral splint comprising an upper abutment element (40a; 140a; 240a; 340a), and a second oral splint adapted for a lower jaw of the user, curved and essentially U-shaped with two legs, one adapted for the left side of the upper jaw and one adapted for the right side of the upper jaw, wherein the second oral splint comprises two adjustment devices for adjusting the positions of the abutment elements, one on each leg of the second oral splint positioned on the outer lateral side of the respective leg, each adjustment device of the second oral splint comprising a lower abutment element (40; 140; 240; 340), wherein each of the lower abutment elements is adapted to cooperate with a respective one of the two upper abutment elements to bring the second oral splint forward relatively to the first oral sprint during closing of the mouth of the user, wherein each of the adjustment devices comprises a fixation element for adjustable and detachable fixation of an abutment element (40; 140; 240; 340), wherein the positions of the abutment elements of the lower oral splint are slightly forward of the positions of the abutment elements of the upper oral splint, and wherein each of the adjustment devices comprises an attachment element (30; 600) adapted to receive the fixation element, wherein each of the attachment elements (30; 600) exhibits a groove (32, 610) running in parallel with the length of the attachment element (30; 600), and wherein each abutment element (40; 140; 240; 340) can be fixed in a desired position in the groove of the attachment element (30; 600) of said adjustment devices. a first oral splint adapted for an upper jaw of the user, curved and essentially U-shaped with two legs, one adapted for the left side of the upper jaw and one adapted for the right side of the upper jaw, wherein the first oral splint comprises two adjustment devices for adjusting the positions of the abutment elements, one on each leg of the first oral splint positioned on the outer lateral side of the respective leg, each adjustment device of the first oral splint comprising an upper abutment element (40a; 140a; 240a; 340a), and a second oral splint adapted for a lower jaw of the user, curved and essentially U-shaped with two legs, one adapted for the left side of the upper jaw and one adapted for the right side of the upper jaw, wherein the second oral splint comprises two adjustment devices for adjusting the positions of the abutment elements, one on each leg of the second oral splint positioned on the outer lateral side of the respective leg, each adjustment device of the second oral splint comprising a lower abutment element (40; 140; 240; 340), wherein each of the lower abutment elements is adapted to cooperate with a respective one of the two upper abutment elements to bring the second oral splint forward relatively to the first oral sprint during closing of the mouth of the user, wherein each of the adjustment devices comprises a fixation element for adjustable and detachable fixation of an abutment element (40; 140; 240; 340), wherein the positions of the abutment elements of the lower oral splint are slightly forward of the positions of the abutment elements of the upper oral splint, and wherein each of the adjustment devices comprises an attachment element (30; 600) adapted to receive the fixation element, wherein each of the attachment elements (30; 600) exhibits a groove (32, 610) running in parallel with the length of the attachment element (30; 600), and wherein each abutment element (40; 140; 240; 340) can be fixed in a desired position in the groove of the attachment element (30; 600) of said adjustment devices.