A removable dental appliance comprising: an appliance body configured to at least partially surround a plurality of teeth of a dental arch of a patient, the appliance body comprising a unitary material defining a shell shaped to receive at least one tooth of the patient and a spring member integrally formed with the shell, and an attachment configured to affix to the at least one tooth, wherein the spring member is configured to receive the attachment and to allow movement of the attachment, and wherein the spring member is configured to apply a spring force to the attachment to cause at least one of a rotation, a translation, a tipping, a torqueing, an extrusion, or an intrusion of the at least one tooth toward a desired position of the tooth when the removable dental appliance is worn by the patient, wherein the spring member comprises a first elongate recess extending through the body, shaped and positioned to apply the spring force to the attachment in a selected direction and with a selected magnitude, and a second elongate recess extending through the body, shaped and positioned relative to the first recess to apply the spring force to the attachment in the selected direction and with the selected magnitude, the spring member including a portion of the appliance body defining an interstitial space separating the second recess from the first recess, and the second recess is configured to reduce at least one of compression, strain, and tension otherwise present in the material of the spring member as the spring member deforms when the first recess is engaged with the attachment, the engagement configured to deform a portion of the spring member including the interstitial space into the second recess. an appliance body configured to at least partially surround a plurality of teeth of a dental arch of a patient, the appliance body comprising a unitary material defining a shell shaped to receive at least one tooth of the patient and a spring member integrally formed with the shell, and an attachment configured to affix to the at least one tooth, wherein the spring member is configured to receive the attachment and to allow movement of the attachment, and wherein the spring member is configured to apply a spring force to the attachment to cause at least one of a rotation, a translation, a tipping, a torqueing, an extrusion, or an intrusion of the at least one tooth toward a desired position of the tooth when the removable dental appliance is worn by the patient, wherein the spring member comprises a first elongate recess extending through the body, shaped and positioned to apply the spring force to the attachment in a selected direction and with a selected magnitude, and a second elongate recess extending through the body, shaped and positioned relative to the first recess to apply the spring force to the attachment in the selected direction and with the selected magnitude, the spring member including a portion of the appliance body defining an interstitial space separating the second recess from the first recess, and the second recess is configured to reduce at least one of compression, strain, and tension otherwise present in the material of the spring member as the spring member deforms when the first recess is engaged with the attachment, the engagement configured to deform a portion of the spring member including the interstitial space into the second recess. <EOS>