Mental nerve blocks

A few thoughts about the technique behind mental nerve blocks:
- The path of the IDN through the mandible starts at the mandibular foramen. This is the ideal site for the deposition of anaesthetic for an IDB. as the nerve approaches from superiorly and posteriorly a higher chance of success is gained from injection most posterior and superior. However, too posterior may result in affecting the facial nerve which lies just posterior to the ramus of the mandible. Too far anteriorly will stop the spread on anaesthesia due to a ligamentous attachment to the lingula (sphenomandibular ligament)
- Upon entering the mandible, the IDB tracks anterior through the bones near the apices of the lower teeth. At the molar region (if I recall correctly), it sits more to the lingual cortical plate and it shifts to a more buccal position at around the premolar region. This and the denser quality of the bone is why infiltrations have a poorer success rate on lower posterior teeth. At the site of the mental foramen, the nerve splits into two terminal branches: The mental nerve which exits the bone and supplies the soft tissues of the lip and chin with sensation and the incisive nerve which remains in the bone and continues medially to supply the bone and anterior teeth of the ipsilateral side.
-As the mental nerve is one that supplies soft tissue only, the term mental nerve block is a misnomer. Technically if you aim to numb the lower anterior teeth by depositing anaesthetic at the mental foramen site you wan to perform a block of the incisive nerve not the mental nerve however the mental nerve block is the commonly used terminology.
-You do not have to enter the mental foramen with your needle tip. Deposition between the apices of the premolar teeth is usually sufficient to produce anaesthesia of the mental and incisive nerves however there is huge variation in its position. it may be at or abone the apices of the premolars. Or it may be much lower down in the mandible. Anterior-posteriorly I have seen it anywhere between the mesial surface of the lower 6s to the distal surface of the canine.
-Clinically, you can palpate intra and extraorally (before injection) to find a dimple in the bone that is painful to press. This is the location of the mental nerve.
-Articaine may be helpful in allowing the anaesthetic to penetrate the bone in non ideal injection sites to produce profound anaesthesia
-An opg is very helpful in locating the mental foramen. Sometimes it is hard to track the position of the mental nerve on the opg and it may be superimposed over the roots of the premolar teeth. I find it helpful to locate the mandibular foramen and follow the corticated borders anteriorly till it terminates. This is the location of the mental nerve. It may be helpful to change the contrast of the film to assist you.
- The mental foramen opens facing slightly posteriorly in most cases, therefore, injecting slightly posteriorly rather than anteriorly may give you improved success. This will allow anaesthetic to flow easier into the foramen and it targets the IDN at a higher point. Therefore you are more likely to affect both the mental and incisive branches.