Cephalometric Measurement of Lower Incisor Position Relative to the Jaws

What is this test?

Measurement of the lower incisor perpendicular to the Nasion-B Point line is a cephalometric examination that analyzes a lateral skull X-ray to determine the position of the lower incisor (front lower tooth) relative to the upper and lower jaw bones. This measurement is a specialized test commonly used in orthodontics and maxillofacial surgery, helping doctors evaluate the relationship between the teeth and the jaws and understand how the face has developed.

Why is this examination needed?

This examination is mainly used for: 1) diagnosis and treatment planning before orthodontic treatment, helping doctors decide whether tooth extraction or other corrective approaches are needed; 2) evaluating whether jaw development is normal; 3) facial proportion analysis and aesthetic assessment; 4) preoperative evaluation and comparison of results after surgery; 5) monitoring treatment progress and predicting treatment outcomes.

What happens during the examination?

The examination requires a lateral skull X-ray. You will stand or sit upright with your head held in a standard position while a side-view X-ray is taken. The process is quick and painless, and the radiation dose is very low. After the X-ray is taken, a specialist will mark the Nasion point, the B Point, and the edge of the lower incisor on the film, then measure the angles and distances between them.

How should I prepare for the examination?

Before the examination, please remove metal items such as earrings, necklaces, and hairpins, as they can interfere with the image. If there is any chance you may be pregnant, please tell your doctor. During the examination, you will need to keep your head still and follow the technician's instructions to maintain the correct position. The entire process usually takes only a few minutes.