For quadrant dentistry, anesthetizing the inferior alveolar nerve is essential. This nerve block is achieved by targeting the nerve as it passes towards the mandibular foramen.

The area of injection can be established by three parameters:

1. Height of injection
2. Anteroposterior placement of the needle
3. Depth of penetration

The height of the injection should be based on the pterygomandibular raphe. The posterior border of the mandibular ramus is approximated by using the pterygomandibular raphe as it bends vertically upwards.

This location can be estimated by placing your thumb in the coronoid notch, while placing your index finger on the outside of the patient’s face on the posterior border of the ramus. Placement of the needle can then be better estimated based between these two points (the posterior border of the ramus and the coronoid notch).

The anteroposterior site of the injection relies on the intersection of two points:

Point 1 is along a horizontal line as described above – from the coronoid notch to the deepest part of the pterygomandibular raphe just as it ascends vertically.

Point 2 is along a vertical line through point 1 – 3/4ths the distance from the anterior border of the ramus.

The depth of the injection relies on contacting bone, and is generally 20-25 mm. This is about the length of 2/3rds of a long injection needle. If the bone is contacted less than half of the length of a long dental needle, this means that the needle is located too far anteriorly and is contacting the ramus too soon.

References:

https://www.researchgate.net/figure/Photograph-of-the-mandible-where-the-needle-tip-is-directed-toward-the-area-of-bone-just_fig2_51455298

Malamed, S. F. (2019). Handbook of local anesthesia. St. Louis, MO: Elsevevier.