Radiographic Assessment of Third Molars

Radiographic assessment of third molars is crucial – not just for the clinician planning on removing the tooth but also for any dentist looking to refer a patient. This post will primarily focus on lower third molars.

Why is radiographic assessment of third molars important?

By carrying out proper assessment of the third molar, it enables us to do the following:

• Inform patients more accurately about their clinical situation – we can advise them on potential complexity of the extraction and risks they may want to know about. We can also give them more information regarding the likely method of extraction i.e. surgical vs routine.
• Increase our confidence when it comes to carrying out the procedure – if you are carrying out the procedure, proper assessment will help you plan the procedure more confidently e.g. planning sectioning or bone removal.
• Identify and predict potential complications – this is important as we can forewarn a patient, as compared to informing them once the complication occurs and we seem like we are making excuses.

How to carry out radiographic assessment of third molars

In order to carry out assessment of lower third molars, I like to use the mnemonic CRAP:

Let’s look at each of these individually.

Crown

We want to look at the crown of the tooth on the radiograph. Assess for:

• Caries
• Restorations
• Size – is it bulbous or abnormal looking?

Caries, for example, may increase the risk of fracture of the tooth during extraction.

Roots

When assessing the roots, we should consider the following things:

• The number of roots – multiple roots may increase the difficulty
• The stage of development – are they fully developed roots?
• Any ankylosis – this may increase the difficulty and require more bone removal
• Any abnormalities of shape of roots – e.g. bulbosity, bends, hooks – these will often increase risk of fracture and complications

Angulation

In angulation, we are focusing on the direction of the wisdom tooth. Majority of wisdom teeth are impacted when it comes to extracting them. We can assess this using the terms below:

Third molars can also be transverse, i.e. sat across the arch. These are rare but can be quite difficult to remove. Distally impacted wisdom teeth are also generally more difficult to remove as the roots are usually pushed against the second molar, with a lack of space to work in.

We can also assess the nature of impaction:

• Bone
• Soft tissue
• Tooth
• A combination

Inferior Alveolar Nerve

This is likely the most important part of the assessment as damage to this nerve may have significant implications on the patient. It is probably the risk that patients would want to know most about.

We can assess the position of the inferior alveolar nerve based on the location of the inferior alveolar canal. This is seen as white tramlines on a radiograph. The position of this is demonstrated on the OPT below.

When we assess this canal, there are certain features we look for that may indicate an increased risk of damage to the inferior alveolar nerve:

• Narrowing of the canal or the roots
• Radiolucency where the roots cross the canal
• Loss of cortication of the tramlines
• Deviation of the roots or the canal

If one of these features is noted, it is worth having a detailed discussion with the patient about potential risk to the nerve. This may open up discussion regarding further imaging, such as a CBCT, or other management methods including coronectomy.

Pathology

In pathology, we want to look at any pathology surrounding the tooth, including periapical pathology, cysts etc. These may increase the complications or difficulties with removing the tooth.

Peripherals

With peripherals, we want to look at a few other aspects surrounding the wisdom tooth. The first that is helpful to look at is the quantity and quality of bone surrounding the wisdom tooth. If there is a lot of bone or an increased density of bone surrounding the tooth, then this may increase the difficulty of extraction.

It is also helpful to assess the lower second molar to essentially determine its restorability. If it isn’t restorable, then it may be easier to extract this first to improve access to the lower third molar.

Example of radiographic assessment

In this example, we have a section of an OPT demonstrating a lower left third molar. 

If we work through the mnemonic:

• Crown – no obvious caries and unrestored. The morphology looks normal.
• Roots – there are two obvious roots – a straighter distal root and a slightly curved mesial root. There are no other obvious hooks or bends.
• Angulation – the tooth is distally impacted, with the mesial root pressed against the lower second molar. There is also a lack of distal boneloss, so the nature of impaction is likely a combination of bone and soft tissue.
• Alveolar nerve – there is radiolucency where the roots cross the inferior alveolar canal.
• Pathology – no obvious pathology is evident.
• Peripherals – the bone looks normal in quality and quantity. The lower second molar is unrestored and there is a question of distal caries.

Therefore, from this report, the patient can be advised that there are a couple of factors that may make the surgical removal more difficult – distally impacted, no boneloss and potential interaction with the inferior alveolar canal.

Summary

• Radiographic assessment of third molars is crucial to help inform the patient, increase operator confidence and predict complications
• The mnemonic CRAP can be used to help assess the radiographs
• Assessment of the inferior alveolar nerve is a crucial part of this assessment

Useful Links & Recommended Reading

• Essentials of Dental Radiography and Radiology
• Master Dentistry: Volume 1: Oral and Maxillofacial Surgery, Radiology, Pathology and Oral Medicine, 3e
• Single Best Answer Questions for Dentistry