[Study on determination of the imaginary axis of the tooth crown in anterior teeth: 1]

1. The state of inclination and the change under various conditions of the imaginary axis of the tooth crown of upper jaw anterior teeth can be determined by the image measuring system and method of this study. 2. The measurement error of this system was not more than 0.3 degree. This value was sufficient for the purpose of this study. 3. The imaginary axis of the tooth crown of anterior teeth was determined on the study cast with 1 to 3 degrees in mesiodistal direction and 2 to 4 degrees in labiopalatal direction as standard deviation. 4. The imaginary axis of the tooth crown of anterior teeth was determined toward labial in the random position and toward patient's right and palatal in Standing Posture. 5. It was confirmed that the determination of the imaginary axis of tooth crown was effected by the position of the patient relative to the operator, limitation or direction of view, and approach direction.