Coronectomy: solution when wisdom teeth are close to the nerve

Sometimes wisdom teeth are born too close to the lower dental nerve, which can cause problems and pain for the patient. Dr. Maizcurrana, specialist in Oral and Maxillofacial Surgery, explains how to proceed in these cases.

When is a wisdom tooth considered to be too close to the lower dental nerve?

There are two lower dental nerves: one right and one left. The inferior dental nerve is a nerve that passes through the interior of the mandibular bone, until it superficializes and emerges through the gum, normally located between the first and second premolar.

The proximity or contact between the wisdom tooth and the inferior dental nerve is usually suspected by analyzing its radiological study with orthopantomography. This suspicion should also be confirmed or ruled out with a computed tomography (CT) scan. Thus, orthopantomography is an ideal radiological test to evaluate wisdom teeth but it has a limitation: it is a test that provides two-dimensional information (width and height) but not three-dimensional (width, height and depth). This information is obtained with a computerized tomography (CT), since the three-dimensional information is what allows us to locate exactly where the inferior dental nerve is with respect to the wisdom tooth (anterior, posterior, interradicular, intraradicular), and also to determine the degree of proximity or contact, which can be close but without contact, with slight contact, with great contact, intimate contact, with thinning of the canal, etc. The greater the contact, the greater the risk of injury.

It should be noted, however, that the performance of a CT scan does not minimize or eliminate the risk of injury to an inferior dental nerve, it simply provides more information for its corroboration.

What can happen if this nerve is touched when extracting the tooth?

It is important to note that the inferior dental nerve has a sensory function, not a motor function, that is, it provides sensitivity to a very specific area (lower lip and chin), but it is not responsible for the movement of that area of the face.

The lesion of the inferior dental nerve can produce a quantitative alteration (by excess: hyperesthesia; or by defect: hypoesthesia, anesthesia), or qualitative (paresthesia), of sensitivity of the lower lip and chin on the damaged side. Thus:

  • Hyperesthesia is a painful increase in sensitivity.
  • Hypoesthesia is a partial lack of sensitivity and is usually related to a partial nerve lesion.
  • Anesthesia is the total absence of sensation and is usually the result of a complete nerve injury.
  • Paresthesia is an abnormal sensation in the form of tingling, tingling, burning, prickling, itching or numbness.
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Injury to the inferior dental nerve usually results in a combination of hypoesthesia and paresthesia of the lower lip and chin on the damaged side. These sensory disturbances may be temporary (recoverable on their own) or permanent (irrecoverable).

What exactly is a coronectomy and why can it be useful in these cases?

A coronectomy is a surgical technique within wisdom teeth surgery. It has been applied for more than 15 years and consists of removing the crown of the tooth and leaving its roots. In this sense, the tooth must be cut at the precise junction between the crown and the roots, so that the crown can be removed and the roots are immobilized within the maxillary bone.

Coronectomy is intended to solve a problem (the symptoms caused by the impacted crown on the neighboring tooth) but also to avoid a new problem (injury to the lower dental nerve).

The surgical procedure is similar to the one carried out for the complete extraction of a complex tooth. There are hardly any differences in the duration of both the surgical procedure and the post-surgical recovery and, in both cases, the criteria for selecting the type of anesthesia to be applied (local anesthesia, intravenous sedation, general anesthesia) are the same.

What happens if the roots are left “inside the gum”?

Rather than “inside the gum”, it would be more accurate to say “inside the bone”. Normally, any tooth or molar is born correctly, with its most superficial part (crown) being visible, and its deepest part or root being hidden, anchored in the thickness of the maxillary bone. The gum covers and protects the maxillary bone which, in turn, houses the dental root.

Voluntarily leaving the roots inside the bone does not usually cause any problems, either in the short or long term. Once the coronectomy is performed, the body activates the healing process (identical to the healing process that occurs when the entire tooth is extracted) and, after a few months, the hole left by the extracted crown is filled by new bone. As the roots are in a lower plane, this new bone acts as a “rigid cover” over the roots, preventing their mobility.

It is necessary not only for the “cover” to be formed, but also for it to acquire the appropriate degree of hardness. Therefore, it is essential that the patient strictly follows the immediate post-surgical recommendations, since a large part of the success or failure in achieving the formation of this rigid covering resides in the correct initiation of the healing process.