A computer-implemented method for determining at least one removable orthodontic appliance, the method comprising: obtaining a digital impression (200A, 200B) of at least part of a dentition of a patient; obtaining, based on the digital impression (200A, 200B), at least one characteristic relating to at least one tooth; comparing the at least one characteristic with corresponding characteristics associated with a set of predefined removable orthodontic appliances; characterised by the steps of: comparing the digital impression (200A, 200B) of the patient and information associated with the patient to digital impressions, removable orthodontic appliances and information associated with a plurality of previously treated patients stored in a database; determining, based on the comparison with previously treated patients, at least one previously treated patient that correlates with or resembles the patient's case; and determining at least one suitable removable orthodontic appliance among the set of predefined removable orthodontic appliances based on the comparison of the at least one characteristic with corresponding characteristics associated with the set of predefined removable orthodontic appliances and on using the information of the determined at least one previously treated patient's case. obtaining a digital impression (200A, 200B) of at least part of a dentition of a patient; obtaining, based on the digital impression (200A, 200B), at least one characteristic relating to at least one tooth; comparing the at least one characteristic with corresponding characteristics associated with a set of predefined removable orthodontic appliances; characterised by the steps of: comparing the digital impression (200A, 200B) of the patient and information associated with the patient to digital impressions, removable orthodontic appliances and information associated with a plurality of previously treated patients stored in a database; determining, based on the comparison with previously treated patients, at least one previously treated patient that correlates with or resembles the patient's case; and determining at least one suitable removable orthodontic appliance among the set of predefined removable orthodontic appliances based on the comparison of the at least one characteristic with corresponding characteristics associated with the set of predefined removable orthodontic appliances and on using the information of the determined at least one previously treated patient's case. comparing the digital impression (200A, 200B) of the patient and information associated with the patient to digital impressions, removable orthodontic appliances and information associated with a plurality of previously treated patients stored in a database; determining, based on the comparison with previously treated patients, at least one previously treated patient that correlates with or resembles the patient's case; and determining at least one suitable removable orthodontic appliance among the set of predefined removable orthodontic appliances based on the comparison of the at least one characteristic with corresponding characteristics associated with the set of predefined removable orthodontic appliances and on using the information of the determined at least one previously treated patient's case.