An orthodontic apparatus for repositioning a patient's teeth and to evaluate performance of the orthodontic apparatus, the apparatus comprising: an aligner body comprising a plurality of teeth receiving cavities shaped to reposition the patient's teeth from an initial arrangement towards a target arrangement, the aligner body having an engagement site comprising an opening or concavity formed through the aligner body; an attachment configured to be bonded to the patients teeth and to engage with the engagement site on the aligner body; a sensor configured to generate sensor data, wherein the sensor comprises a pressure, motion and/or force sensor; a processor comprising one or more of: a memory, a wireless communications circuit, and a timer, the processor configured to receive the sensor data from the sensor and do one or more of: store, analyze and transmit the received sensor data in order to evaluate performance of the orthodontic apparatus; and a first electrical contact on the attachment and a second electrical contact on the aligner body, wherein the first electrical contact and the second electrical contact form an electrical connection when the attachment is engaged with the engagement site; wherein the sensor is on either the attachment or the aligner body and wherein the sensor is in electrical communication with the processor through the electrical connection formed by the first electrical contact and the second electrical contact when the attachment is engaged with the engagement site, wherein the processor is configured to evaluate a performance of the orthodontic appliance, or to transmit to a remote processor to evaluate a performance of the orthodontic appliance, using the sensor data to determine one or more of: an amount of force or pressure applied to the patient's teeth, a distribution of force or pressure on the patient's teeth, an amount of movement of the patient's teeth, or a movement rate of the patient's teeth. an aligner body comprising a plurality of teeth receiving cavities shaped to reposition the patient's teeth from an initial arrangement towards a target arrangement, the aligner body having an engagement site comprising an opening or concavity formed through the aligner body; an attachment configured to be bonded to the patients teeth and to engage with the engagement site on the aligner body; a sensor configured to generate sensor data, wherein the sensor comprises a pressure, motion and/or force sensor; a processor comprising one or more of: a memory, a wireless communications circuit, and a timer, the processor configured to receive the sensor data from the sensor and do one or more of: store, analyze and transmit the received sensor data in order to evaluate performance of the orthodontic apparatus; and a first electrical contact on the attachment and a second electrical contact on the aligner body, wherein the first electrical contact and the second electrical contact form an electrical connection when the attachment is engaged with the engagement site; wherein the sensor is on either the attachment or the aligner body and wherein the sensor is in electrical communication with the processor through the electrical connection formed by the first electrical contact and the second electrical contact when the attachment is engaged with the engagement site, wherein the processor is configured to evaluate a performance of the orthodontic appliance, or to transmit to a remote processor to evaluate a performance of the orthodontic appliance, using the sensor data to determine one or more of: an amount of force or pressure applied to the patient's teeth, a distribution of force or pressure on the patient's teeth, an amount of movement of the patient's teeth, or a movement rate of the patient's teeth.