Nerve of pterygoid canal

Causes

The main causes of damage to the NAS are:

• implantation (doctor’s errors, lack of a full preliminary examination);
• removal of dystopic “eights” on the lower jaw;
• errors when performing conduction anesthesia;
• exit of the filling material beyond the root apex into the nerve canal;
• infectious lesion of the periapical region of the lower row.

But the most common reason is the first reason - damage as a result of implant installation, usually in the chewing area.

First signs of damage

The first symptoms of nerve damage are discomfort in the gums, cheeks, and lower lip. Manifestations of the problem are:

• paresthesia, that is, a change in the level of sensitivity without pain;
• dysesthesia with pain in the affected area, a feeling of “pins and needles”, changes in the general sensitivity of the area;
• anesthesia - complete loss of sensation in a certain area.

In some cases, the lingual nerve, which runs from the side of the tongue into the gum tissue, may be affected. This is usually observed as a result of the removal of "eights" (in approximately 2.1% of all cases). When implanted, this nerve is affected less frequently. If this situation occurs, the following symptoms appear:

• salivation becomes profuse;
• involuntary biting of the tip of the tongue appears;
• diction disorders;
• burning sensation, numbness in the tongue;
• loss, change in taste;
• swallowing is impaired.

In 90% of cases, the problems go away on their own within seven to ten weeks; no special treatment is required.

Anatomy of the nerves in the cheek area

The location of the infraorbital foramen in the cheek area is critical to prevent neuropraxia. Damage may occur due to an infraorbital nerve . Fortunately, most fillers include lidocaine, which reduces the need for n. infaorbitalis in this zone. However, such anesthesia may be necessary for upper lip augmentation. Injecting an anesthetic into the eye socket, as well as too strong massage after injection of filler, can lead to:

• diplopia;
• dysesthesia;
• paresthesia.

There are known cases of Bell's palsy after injections of dermal fillers. In most patients, improvement occurs spontaneously (71%), but in a fairly large percentage of victims, residual weakness of one half of the face persists for life.

You may also be interested in: First aid for central retinal artery occlusion after filler injections

Emergency treatment for Bell's palsy is a short course of oral steroids. Surgical decompression and other treatments such as electrography, physical therapy and acupuncture are not supported by sufficient evidence.

Classification

In accordance with Seddon's classification, the following types of NAS injuries are distinguished:

1. Neuropraxia. This injury is reversible; the sheath of the nerve fibers does not suffer, that is, there is no development of degeneration. After treatment, the problem goes away, which usually takes a couple of weeks.
2. Axonotmesis. A reversible type of lesion, for which long-term, intensive treatment is prescribed - from three to six months. The development of degeneration and fiber damage are observed.
3. Neurotmesis. A serious disorder affecting all structures, including fibers and connective membranes. Scar tissue develops, and surgery is indicated to correct the problem.

In accordance with the generally accepted WHO classification, there are five categories of NAS injuries:

• compression, nerves are not damaged;
• swelling of tissues;
• partial rupture of fibers;
• complete ruptures of the NAS are observed;
• post-traumatic fibrosis develops.

Assessment methods

To determine the cause and extent of the disorder, diagnostics are required. For this purpose they prescribe:

• mechanoceptive methods, in which the response to mechanical irritation and stimulation is recorded;
• nociceptive, allowing to determine sensitivity to painful stimulation.

The first type of research includes tests of the following types:

• tests with a brush, during which the Patient’s lip is passed with a brush and asked to determine the direction of movement;
• two-point irritation using a probe.

The second diagnostic method includes:

• pin tests;
• Temperature tests for sensations of cold or heat.

Tests are also carried out for the presence of deficits in the sense of taste, and data from the right and left sides of the maxillofacial apparatus are compared. The accuracy of the research should be no more than 1 mm.

Treatment

The following regimens are used for therapy:

• observation of the Patient at intervals of 2, 3, 4, 6 months;
• drug therapy;
• unscrewing, removing the implant;
• microsurgical intervention.

There is no strict protocol; tactics are determined individually in each case. But there are limitations to surgical intervention - it will be effective only in the first year, after which this method is considered ineffective.

Drug therapy includes:

• taking painkillers;
• use of hydrogen pump blockers;
• prescription of anti-inflammatory drugs (glucocorticosteroids are prescribed);
• therapy for sensory impairment.

If symptoms appear in the first 1.-1.5 days after installation of the implant, its removal may be indicated. During this period, the prognosis is favorable, but over a longer period of time, removing the artificial root will no longer bring a noticeable improvement. The reason is irreversible changes in nerve fibers.

Surgery is indicated in cases where all previous measures have not brought the expected effect. To do this, the doctor must determine the location of the NAS and evaluate sensitivity disorders. The effectiveness of the operation is influenced by the following factors:

• time between injury and surgery;
• severity, type of lesion;
• blood supply;
• Preparation;
• tension zone;
• Patient's age, health status.

Predictions and prevention

Treatment has an uncertain prognosis; with microsurgical intervention, the positive result is in the range of 55-82%. If the damage is severe, complete recovery does not occur with any treatment method. According to some experts, complications such as pain persist even after the intervention. It is also worth noting that the success of treatment depends entirely on the extent of the lesion. It is impossible to guarantee a high result in any situation, that is, the forecasts are uncertain.

To avoid complications, prophylaxis is recommended. This is a mandatory full examination before the implantation procedure. The specialist will determine the exact location of the nerve, the topography of the nerve trunks and the maxillofacial system. This allows you to exclude the development of pathology and conduct conduction anesthesia correctly, without the risk of complications.

The main preventive measures include:

• competent selection of implantation system;
• diagnostics, including CT, production of a surgical template, computer modeling;
• planning the procedure for introducing an artificial root;
• determining the paths of nerve trunks, ensuring the distance between them and implants is not less than 2 mm;
• when drilling, it is necessary to avoid excessive force;
• When immersing a drill or implant, stoppers are used to limit the depth and ensure safety.

Treatment of damage to the mandibular nerve during implantation requires the doctor to have high qualifications and experience. But even under such conditions, the success rate does not exceed 82%. Some complications may remain, such as numbness or soreness.

Features of local anesthesia for double socket nerve

Mandibular anesthesia, as the main method of anesthetizing teeth in the lower jaw, has been known since the end of the nineteenth century. The very principle of its implementation has remained unchanged, but the technique has undergone a number of changes.

Thus, classical mandibular anesthesia is performed in the area of ​​the mandibular foramen (Halsted method, 1885; Fischer, 1911; Egorov). “High” methods of blocking the inferior radial nerve have become more modern, during which an anesthetic depot is created in the area of ​​the torus of the lower jaw (Weisbrem, 1940), the notch of the lower jaw with the patient’s mouth closed (Vizirani, 1960, - Akinozi, 1977), and the articular process mandible (Gow-Gates, 1973). Such a variety of methods makes us think that there is a problem in carrying out local conduction anesthesia of the teeth of the lower jaw. According to a number of researchers, mandibular anesthesia is ineffective in 10-15% of cases [12].

One of the reasons for its ineffectiveness is the anatomical variations in the structure of the mandibular nerve and canals [13].

There are studies confirming that mandibular anesthesia is in most cases ineffective when the patient has a double mandibular canal. It was noted that after its implementation in this group of patients, the pain sensitivity of the dental tissues remains, at the same time, there is a feeling of numbness of the lower lip and chin on the corresponding side of the anesthesia [7, 8, 12, 13, 16, 17].

Anatomy of the inferior alveolar nerve

The mandibular nerve is a continuation of the third branch of the trigeminal nerve and is located in the thickness of the lower jaw along the length from the mandibular to mental foramina. According to a number of authors, the mandibular nerve along its entire length forms three main branches: the retromolar branch, the molar branch, and the incisive branch [1-3]. Throughout its entire length, the mandibular nerve can run as one main bundle, but can be divided into two [4] or even three branches [5].

In terms of prevalence, double inferior alveolar canal occurs in less than 1% of the population. Thus, according to Grover PS and Lorton L., when studying 5000 orthopantomograms, a double lower alveolar canal was observed in 4 cases (0.08%) [7]. According to other authors, a study of 6000 OPTG revealed double mandibular canals in 57 cases (0.95%) [6].

Classification of double mandibular canals

Having studied 3612 OPTGs, Notje et al. identified the following variations in the structure of the double mandibular canal: type 1 - two canals that begin through a single opening; type 2 - branch of the small canal at the level of the second and third molars; type 3 - two canals begin from different foramina, but unite at the level of the molars [6]. Heasman proposed a classification of the position of the canal in relation to the roots of the teeth: 67.7% - type 3 (average), 15.6% - type 2 (high), 5.2% (low), type 4 (mixed) - 11.5 % [8].

The most famous is the Langlais classification of double canals of the lower jaw (Fig. 1): type 1 - bifurcation at the level of the third molar (0.367%), type 2 (0.517%) - bifurcation within the jaw ramus or beyond, then union, type 3 - mixed (0.03333%): on the one hand type 1, on the other - type 2, type 4 (0.03333%) - two channels that begin with different holes [9].

Rice. 1. Classification of double mandibular canals according to Langlais.

Formation of a double channel

Of course, the double alveolar nerve is an anatomical variation in the structure of the jaws, which is formed during the prenatal period of development. Johansson et al. found that the development of the mandibular nerve proceeds from three independent canals, which then combine into one canal. [10]. Chaves et al., studying preparations of the jaws of prenatal children, found that the mandibular canal is divided into three independent highways that innervate a certain group of teeth. Thus, the first canal approaches the rudiments of the incisors and canines, the second - to the premolars, the third - to the molars of the lower jaw. This fact largely explains why, in primary adentia, the lesion affects a certain group of teeth on each side of the lower jaw [11].

During the development of the lower jaw, intramembranous ossification, three independent canals with nerve trunks are combined into a canal with the nerve of the same name. Currently, there is no consensus on the reason for the formation of the double mandibular canal. However, it can be assumed that changes in the mineralization of the jaws during the developmental stages of the child may prevent the approximation of the main branches of the mandibular nerve, which leads to the development of several independent canals.

Tactics of local anesthesia for double inferior alveolar nerve

Before starting dental treatment, it is necessary to conduct an additional X-ray examination, such as orthopantomography. It allows you to evaluate the position of the mandibular foramen in relation to the occlusal surface of the molars, the number of canals, and their topography according to Langlais.

For anesthesia of the teeth of the lower jaw with a double mandibular canal, “high” methods of anesthesia are recommended (torusal, Gou-Gates, Vizirani-Akinozi). Of course, it is not advisable to do OPTG for each patient before mandibular anesthesia, but it is worth thinking about performing it in cases where the patient himself complains about the “ineffectiveness” of pain relief during dental treatment. It is safe to say that there is a group of patients with an unfavorable history in relation to local anesthesia, for whom X-ray diagnostics, up to computed tomography, are actually indicated to identify the reasons for the ineffectiveness of local anesthesia.

For anesthesia of the teeth of the lower jaw with a double mandibular canal, “high” methods of anesthesia (torusal, Gou-Gates, Vizirani-Akinozi) are recommended. They ensure the creation of an anesthetic depot above the mandibular foramen, thereby resolving the issue of an anomaly in its position with a double mandibular canal.

If the doctor prefers classical mandibular anesthesia, its effectiveness should be assessed after an average of 10 minutes. If the patient notes a feeling of numbness of the chin, but there is no anesthesia of the pulp, the anesthetic depot has been created correctly and there is no need for repeated mandibular anesthesia. Repeated mandibular anesthesia should be carried out using the “high” type and only if the patient does not have a feeling of numbness in the chin and lower lip. As an additional method of pain relief, it is recommended to carry out intraligamentary or intraosseous anesthesia, which is guaranteed to lead to anesthesia of a specific tooth.

Clinical case

Patient V., born in 1982, complained of periodic pain in tooth 37. Objectively: 38 - partially erupted with a mesioangular position. DS: Dystopia 38. During the examination, an OPTG was performed, which revealed a double mandibular canal, presumably starting with one mandibular foramen, then running separately along the entire length of the ramus and body of the mandible and ending with two foramina (type 2 according to Langlais) (Fig. 2, 3). The patient was recommended to remove 38. From the anamnesis, it was found that during previous dental interventions there were often problems with pain relief.

For the operation of removing tooth 38, mandibular anesthesia was performed by palpation (1.8 ml Ubistesin 1:100000 3MESPE) and buccal infiltration anesthesia (0.5 ml Ubistesin 1:100000 3MESPE). 5 minutes after anesthesia, the patient noticed a feeling of numbness in the edge of the lower lip on the left. During the creation of surgical access and partial odontopreparation, patient 38 experienced pain. As an additional anesthesia, intraligamentary anesthesia (0.8 ml Ubistesin 1:100000 3MESPE) was performed, the tooth was removed painlessly.

Discussion

In this clinical example, the patient received standard anesthesia used for the extraction of lower jaw teeth. However, in this case, there was no complete anesthesia of the pulp 38. The authors of the article suggest that this problem is associated with the presence of a double mandibular canal in the patient. The double mandibular canal contains both nerves and vessels responsible for the blood supply to the mandible [6].

It is believed that the main canal, which opens at the level of the occlusal surface of the molars and has a larger diameter, always contains the mandibular nerve. The additional canal, which has a smaller diameter, in most cases starts from the main mandibular foramen. There are double mandibular canals, which begin with two independent openings, while the additional opening can be located either above the main one, closer to the base of the articular process, or below the main one, in the distal part of the jaw branch.

The main canal, which opens at the level of the occlusal surface of the molars and has a larger diameter, always contains the mandibular nerve. According to the literature, the additional canal of the lower jaw may contain branches of the mylohyoid nerve (n. myelohyoideus), which is closest in topographic-anatomical relation to the mandibular nerve . The mylohyoid nerve is not amenable to anesthesia during standard mandibular anesthesia due to the fact that the anesthetic cannot diffuse through the sphenomandibular ligament, through which the mylohyoid nerve passes [14].

According to Wilson, this is explained by the fact that the mylohyoid nerve branches from the mandibular nerve 14.7 mm above the mandibular foramen, i.e., this zone may be outside the range of action of the local anesthetic solution [15]. Lew et al. described a clinical case of ineffective local anesthesia of the mandibular teeth in a patient with a double mandibular canal [13], DeSantis et al. described a similar case [17], in this article the authors also encountered this problem. At the same time, there is evidence of the effectiveness of mandibular anesthesia in patients with a double mandibular canal [16].

Conclusion

A double mandibular canal may cause failure of mandibular anesthesia. This is largely due to the dislocation of the additional mandibular foramen and the innervation of the teeth from the mylohyoid nerve. Additional x-ray diagnostics (OPTG, CT) allows us to find out the reason for the ineffectiveness of anesthesia of the lower jaw. When identifying double mandibular canals using an x-ray, you can determine their topography, choose the technique of conduction anesthesia and the planned location for creating a local anesthetic depot.

LITERATURE

1. Oikarinen VJ. The inferior alveolar artery. SuomHammaslaToim 1965;61(Suppl 1):1–131.
2. Poirot G, Delattre JF, Palot C, Flament JB. The inferior alveolar artery in its bone course. SurgRadiolAnat 1986;8:237–244.
3. Zoud K, Doran GA. Microsurgical anatomy of the inferior alveolar neurovascular plexus. SurgRadiolAnat 1993;15:175–179.
4. Northje, C.J.; Farman, A.G.; Grotepass, FW Variations in the normal anatomy of the inferior dental (mandibular) canal: a restrospective study of panoramic radiographs from 3,612 routine dental patients. Brit. J. oral Surg., Edinburgh, v. 15, p. 55-63, 1977.
5. Auluck, A.; Keerchilatha, MP Trifid mandibular nerve canal. Dentomaxillofac. Rad., London, v. 34, no. 4, p. 259, Jul., 2005.
6. Northje, C. J.; Farman, A.G.; Joubert, JJV The radiographic appearance of the inferior dental canal: an additional variation. Brit. J. oral Surg., Edinburgh, v. 15, p. 171-2, 1977.
7. Grover, PS & Lorton, L. Bifid mandibular nerve as a possible cause of inadequate anaesthesia in the mandible. J. Oral Maxillofac. Surg., 41:111–9, 1983.
8. Heasman, PA Variation in the position of the inferior dental canal and its significance to restorative dentistry. J. Dent., Chengtu, v. 16, no. 1, p. 36—7, Feb., 1988.
9. Langlais, R. P. Broadus, R. Glass, B. Bifid mandibular canals in panoramic radiographs. Journal of the American Dental Association (1985), Vol 110, Issue 6, 923-926.
10. Johansson CS, Hildebrand C, Poulsen B (1992). Anatomy and developmental chronology of the rat inferior alveolar nerve. AnatRec 234:144–152.

A complete list of references is in the editorial office.