A tooth-attach wearable device (C1, C2) having a tooth attachment (P1, P2) corresponding to a shape of a tooth, the wearable device comprising: a sensor head configured to couple with one surface of the tooth attachment, to be exposed inside the oral cavity, and to sense a temperature of a patient; and a time measurer configured to measure an amount of time in which the tooth attachment is attached to the tooth, based on the temperature sensed at the sensor head; wherein a thermoelement is provided to the sensor head, the thermoelement generates electricity and supplies the generated electricity to the time measurer only when the temperature sensed at the sensor head is between 35 °C and 38 °C; wherein the time measurer measures and accumulates the amount of time only in response to receiving the electricity being supplied from the thermoelement; and wherein the wearable device further comprises a sensor chip configured to couple with the sensor head, to fix to the tooth attachment (P1, P2), and to supply electricity to the sensor head; wherein the wearable device comprises a communication controller provided to the tooth attachment (PI, P2), and configured to store temperature information of the patient sensed at the sensor head, and to transmit the stored temperature information, wherein the communication controller comprises a data storage configured to store the temperature information of the patient sensed at the sensor head as data; and a data transmitter configured to remotely transmit the data stored in the data storage; wherein the thermoelement is exposed outside the tooth attachment (P1, P2) and a portion of the thermoelement is coated with a hydrophobic film which is suitable for directly contacting with a tooth. a sensor head configured to couple with one surface of the tooth attachment, to be exposed inside the oral cavity, and to sense a temperature of a patient; and a time measurer configured to measure an amount of time in which the tooth attachment is attached to the tooth, based on the temperature sensed at the sensor head; wherein a thermoelement is provided to the sensor head, the thermoelement generates electricity and supplies the generated electricity to the time measurer only when the temperature sensed at the sensor head is between 35 °C and 38 °C; wherein the time measurer measures and accumulates the amount of time only in response to receiving the electricity being supplied from the thermoelement; and wherein the wearable device further comprises a sensor chip configured to couple with the sensor head, to fix to the tooth attachment (P1, P2), and to supply electricity to the sensor head; wherein the wearable device comprises a communication controller provided to the tooth attachment (PI, P2), and configured to store temperature information of the patient sensed at the sensor head, and to transmit the stored temperature information, wherein the communication controller comprises a data storage configured to store the temperature information of the patient sensed at the sensor head as data; and a data transmitter configured to remotely transmit the data stored in the data storage; wherein the thermoelement is exposed outside the tooth attachment (P1, P2) and a portion of the thermoelement is coated with a hydrophobic film which is suitable for directly contacting with a tooth.