Computer-implemented method of designing an intra-oral device including the steps of: obtaining an electronic image of a patient's dental arch including the teeth on the maxilla and the teeth on the mandible, characterized by processing the electronic image to: determine a retention portion (7161, 7261) on a crown region of at least a portion of one or more teeth; calculate a retention profile based on the determined retention portion (7161, 7261) to spread a load of retention across the portion of the one or more teeth available for gripping, wherein an area of the retention profile in the retention portion (7161, 7261) that is located over a tip of a cusp of the one or more teeth has a reduced first cusp thickness compared to a second thickness of an area between the tips of the cusp of the one or more teeth; determine an undercut portion of the portion of the one or more teeth and calculate an undercut portion of the retention profile, wherein the undercut portion of the portion of the one or more teeth is determined on the basis of the apex (a) of the sidewall of the portion of the one or more teeth and of a minimum distance to the gingival part of the portion of the one or more teeth, and wherein a thickness of the retention profile is calculated on the basis of the determined undercut portion of the portion of the one or more teeth so as to provide elastic gutter side walls adapted to clip on the portion of the one or more teeth; and design the intra-oral device to include at least one of an upper splint and a lower splint, wherein the at least one of the upper splint and the lower splint includes the calculated retention profile. obtaining an electronic image of a patient's dental arch including the teeth on the maxilla and the teeth on the mandible, characterized by processing the electronic image to: determine a retention portion (7161, 7261) on a crown region of at least a portion of one or more teeth; calculate a retention profile based on the determined retention portion (7161, 7261) to spread a load of retention across the portion of the one or more teeth available for gripping, wherein an area of the retention profile in the retention portion (7161, 7261) that is located over a tip of a cusp of the one or more teeth has a reduced first cusp thickness compared to a second thickness of an area between the tips of the cusp of the one or more teeth; determine an undercut portion of the portion of the one or more teeth and calculate an undercut portion of the retention profile, wherein the undercut portion of the portion of the one or more teeth is determined on the basis of the apex (a) of the sidewall of the portion of the one or more teeth and of a minimum distance to the gingival part of the portion of the one or more teeth, and wherein a thickness of the retention profile is calculated on the basis of the determined undercut portion of the portion of the one or more teeth so as to provide elastic gutter side walls adapted to clip on the portion of the one or more teeth; and design the intra-oral device to include at least one of an upper splint and a lower splint, wherein the at least one of the upper splint and the lower splint includes the calculated retention profile. determine a retention portion (7161, 7261) on a crown region of at least a portion of one or more teeth; calculate a retention profile based on the determined retention portion (7161, 7261) to spread a load of retention across the portion of the one or more teeth available for gripping, wherein an area of the retention profile in the retention portion (7161, 7261) that is located over a tip of a cusp of the one or more teeth has a reduced first cusp thickness compared to a second thickness of an area between the tips of the cusp of the one or more teeth; determine an undercut portion of the portion of the one or more teeth and calculate an undercut portion of the retention profile, wherein the undercut portion of the portion of the one or more teeth is determined on the basis of the apex (a) of the sidewall of the portion of the one or more teeth and of a minimum distance to the gingival part of the portion of the one or more teeth, and wherein a thickness of the retention profile is calculated on the basis of the determined undercut portion of the portion of the one or more teeth so as to provide elastic gutter side walls adapted to clip on the portion of the one or more teeth; and design the intra-oral device to include at least one of an upper splint and a lower splint, wherein the at least one of the upper splint and the lower splint includes the calculated retention profile.