A method for designing a dental appliance, the method comprising: identifying an intended outcome of at least a portion of a dentition of a patient at an end of at least one stage of a treatment plan, wherein the treatment plan comprises a plan to treat the at least the portion of the dentition; identifying one or more forces implemented on the at least the portion of the dentition during the at least one stage of the treatment plan; identifying one or more clinical acceptability criteria for the at least one stage, the one or more clinical acceptability criteria providing criteria to evaluate compliance with the intended outcome; gathering an aligner model for the at least one stage, wherein the aligner model comprises a model of an aligner for the at least the portion of the dentition at a beginning of the at least one stage and the aligner model has a thickness parameter to represent a thickness of at least a portion of the aligner model; iteratively modeling application of the one or more forces to the at least the portion of the dentition at the beginning of the at least one stage using the aligner model with the thickness parameter at iteratively reduced thicknesses until a resulting thickness is found for the thickness parameter, the resulting thickness being less than or equal to a starting thickness, and the resulting thickness being associated with a satisfactory outcome of the at least the portion of the dentition at the end of the at least one stage, the satisfactory outcome satisfying the one or more clinical acceptability criteria; and providing instructions to manufacture the dental appliance using the aligner model with the resulting thickness assigned to the thickness parameter. identifying an intended outcome of at least a portion of a dentition of a patient at an end of at least one stage of a treatment plan, wherein the treatment plan comprises a plan to treat the at least the portion of the dentition; identifying one or more forces implemented on the at least the portion of the dentition during the at least one stage of the treatment plan; identifying one or more clinical acceptability criteria for the at least one stage, the one or more clinical acceptability criteria providing criteria to evaluate compliance with the intended outcome; gathering an aligner model for the at least one stage, wherein the aligner model comprises a model of an aligner for the at least the portion of the dentition at a beginning of the at least one stage and the aligner model has a thickness parameter to represent a thickness of at least a portion of the aligner model; iteratively modeling application of the one or more forces to the at least the portion of the dentition at the beginning of the at least one stage using the aligner model with the thickness parameter at iteratively reduced thicknesses until a resulting thickness is found for the thickness parameter, the resulting thickness being less than or equal to a starting thickness, and the resulting thickness being associated with a satisfactory outcome of the at least the portion of the dentition at the end of the at least one stage, the satisfactory outcome satisfying the one or more clinical acceptability criteria; and providing instructions to manufacture the dental appliance using the aligner model with the resulting thickness assigned to the thickness parameter.