Foreign body surgery in the inferior alveolar nerve canal following endodontic treatment

Introduction

Root canal treatment is a commonly employed modality of treatment undertaken by dental practitioners to treat and preserve teeth that have lost vitality. Endodontic therapy involves the removal of the dental pulp, the subsequent shaping, cleaning, and irrigating of the root canals, and the obturation (filling) of the decontaminated canals. Filling of the cleaned and decontaminated canals is undertaken with an inert filling such as gutta-percha and sealed with the aid of a cement, typically eugenol-based.¹

This material acts as a lubricant as it aids in the progression of the principal obturation material (core) during the compaction phase, allowing the material to be advanced to the required degree, and compressed and compacted to achieve a dense filling of the canal space. Furthermore, it also aids in the filling of the lateral and accessory canals, which would otherwise be impossible to fill with a single core of gutta-percha. These sealant materials usually bear antimicrobial properties,² generally in the form of holding a prolonged alkaline pH,³ as well as its solubility into hard tissue structures.^4,5 However, these properties can also result in damage to biological structures. Root canal cement can be extruded beyond the apex of a tooth during obturation.

Periapical tissues may become irritated as a result of the sealant material and its properties. Generally, any irritant effect is short lived as the leaching of toxic substances from within the cement diminishes rapidly,⁶ with subsequent reabsorption of the excess material, leading to complete healing in a few months.⁷ However, more significant cytotoxicity has been reported with extrusion of canal sealants, which can result in periapical inflammation and necrosis of the periodontal ligaments.⁸ The cytotoxic effects of canal sealants can result in more long-term irritation, dependent on the sealant used and its pH, as well as the type of biological structure with which it is in contact.^9,10

Controversy exists regarding the overfilling of root canals and extrusion of material beyond the apex, when considering the need for adequate canal filling and apical seal versus the potential for damaging biological structures with extrusion. There are no uniformly accepted guidelines relating to the overfilling of root canals and extrusion of materials, although it is generally accepted that precision in the obturation and filling of the canal space in line with measured dimensional parameters is best followed.¹¹

Case report

A 53-year-old female patient was referred to the Department of Oral and Maxillofacial Surgery at Salisbury District Hospital by her general dental practitioner (GDP) after developing a painful dysaesthesia following a suspected nerve injury to the left inferior alveolar nerve. The patient had undergone root canal treatment of the lower left second molar (LL7) tooth 1.5 years previously due to loss of vitality. Immediately following the root canal treatment, the patient began to experience the onset of a paraesthesia associated with the distribution of the left inferior alveolar nerve distribution anterior to the LL7 region. Having re-visited her GDP on several occasions for review, no further treatment was undertaken and the situation was monitored. However, the symptoms did not subside, and began to progress and evolve into a partial anaesthesia of the nerve, which, unfortunately, was coupled with a painful dysaesthesia.

Following several months of monitoring and reviews, a referral was made to the Department of Oral and Maxillofacial Surgery. At the consultation appointment, the patient reported a significant effect on her quality of life as she was experiencing continual dysaesthesia in the left inferior alveolar nerve distribution. The patient recounted how this appeared to have manifested after root canal treatment. Clinical examination did not reveal any soft tissue anomalies, the oral cavity appeared healthy and there was no lymphadenopathy.

A full orthopantomograph (OPG) was obtained (Figure 1), which demonstrated recent root canal treatment of the lower left second molar (LL7). A well-defined and highly radio-opaque region was noted immediately beyond the apex of the LL7, consistent with root canal sealant material. Reviewing the anatomical landmarks, the inferior alveolar nerve canal bore a normal appearance and passage through the mandible. However, in the immediate vicinity of the inferior alveolar nerve canal, the root canal sealant appeared to be within the canal and had spread centrally in keeping with the passage of the canal through the mandible.

Based on the history, symptoms, clinical examination and radiographic findings, the working diagnosis of ‘dysaesthesia by virtue of dental material in contact with the inferior alveolar nerve’ was reached.

It was agreed with the patient to undertake further investigations in the form of cone beam CT (CBCT) scanning to more accurately localize the foreign body within the mandible and to ascertain the precise relationship and proximity of the inferior alveolar nerve to the LL7 tooth.

CBCT scanning was performed and provided coronal, sagittal and axial sectional imaging of the field in question (Figure 2). This demonstrated a clear area of high attenuation within the left body of the mandible and within the left inferior alveolar nerve canal. The regions of high attenuation were consistent with the extruded dental sealant seen on the OPG.

Following the CBCT scanning and discussion of the findings, it was concluded that the working diagnosis fit the history and symptoms, and hence the extruded dental sealant was deemed responsible for the on-going dysaesthesia. Owing to the cytotoxic nature of dental sealants and their resultant effects on biological soft tissue, continued presence of the sealant material within the inferior alveolar nerve canal was likely to be causing the sustained symptoms.

During the investigations and reviews, various drugs were tried in an effort to mitigate the dysaesthesia, including amitriptyline and gabapentin. However, these proved unsuccessful. Having discussed the various remaining options with the patient, the surgical option was explored. In select cases, surgery to directly access the field is often the sole remaining option for management, and has been shown to improve symptoms.¹²

The proposition was made and the patient consented to surgical access to the left inferior alveolar nerve by osteotomizing the mandible. This would then allow for direct visualization of the nerve and to debride and remove the dental sealant material in the field. It was clearly explained to the patient that the anaesthesia and dysaesthesia she was experiencing may not fully be corrected by the surgery and, indeed, the anaesthesia may not change. However, the patient was in agreement with us that mitigation of the dysaesthesia component of her symptoms was the principal aim and would have the greatest positive effect on her quality of life.

Surgery was undertaken on an elective basis under general anaesthesia. Intra-operative local anaesthesia was delivered and initial soft tissue access was in keeping with that used for a bilateral sagittal spilt osteotomy (BSSO). Soft tissue incisions were carried out using a Colorado monopolar needle. The incision was made halfway up the anterior border of the ramus of the mandible and advanced inferiorly along the external oblique ridge to the mesial of the lower left first molar. A V-shaped retractor was placed along the external oblique ridge and all soft tissue attachments were retracted as superior onto the coronoid process as possible. Subperiosteal dissection continued inferiorly down the external oblique ridge and to the mesial aspect of the lower left first molar. Soft tissues were retracted and protected with a Howarth's elevator specifically being placed on the medial aspect of the ramus of the mandible at the level of the lingula to retract and protect the inferior alveolar dental nerve.

Once the soft tissue approach was completed, the osteotomy was carried out as a Hunsuck modified sagittal split. A bony cut was made on the medial aspect of the ramus of the mandible just above the lingula. The cut was then extended anteriorly down the external oblique ridge to the level of the second molar. A further bony cut was then made vertically along the buccal cortex at the level of the lower left second molar and advanced inferiorly through the inferior border of the mandible. The cut above the lingula did not involve the posterior border of the ramus of the mandible.

Smith's spreaders were placed to hold the mandible apart while the extruded dental cement material was debrided from the LL7 roots using a Mitchell's trimmer. After all of the dental cement material was removed from the roots, cellulose ‘eye-spears’ were used for nerve brushing. Once the nerve was directly visualized, it was apparent that a significant mass of dental cement material was in direct contact with the nerve and, in fact, enveloped it. This was carefully removed by brushing and the nerve lateralized to ensure complete access was achieved to removal all the material.

Once the dental cement material was removed and the field cleansed, the mandible was plated using a single 2-mm load sharing four-hole plate via a transbuccal approach and the soft tissue incisions sutured (Figure 3).

The patient had an uneventful recovery and was discharged home the following day. Once the intra-operative local anaesthesia wore off, the patient reported an immediate improvement in her symptoms, and that the painful dysaesthesia had abated. Early follow up 1 week post-operatively continued to show encouraging signs of improvement. The patient had experienced no further dysaesthesia symptoms and felt her quality of life was improved as the unabating, constant pain/discomfort she had previously experienced was gone. As further time passed, the patient had no resurgence of her dysaesthesia symptoms and the region of anaesthesia was reducing.

Discussion

Neuropathic pain is defined as pain originating from the nervous system by virtue of a dysfunction of the system itself.¹³ Neuropathic pain is multifactorial; however, continuous and unabating neuropathic pain is often seen with foreign bodies, particularly with intra-osseous entrapment of foreign bodies, wherein chronic irritation and inflammation will persist and can lead to foreign body granuloma formation.¹⁴

Within the mandible, the environment exists to host an intra-osseous foreign body and its potential for contact with nerve tissue in the inferior-alveolar nerve canal. The presence of a cytotoxic, irritant material within this environment would undoubtedly result in a reaction. Irritated nerves frequently give rise to paraesthesia, which patients often describe as a burning, prickling or partial numbness sensation.¹⁵ This can change over time and, in some patients, the manifestation of a painful dysaesthesia can occur, particularly in cases of on-going irritation such as with a foreign body and continual irritation/inflammation.¹⁶

Although extrusion of sealant material can occur, the incidence of causing a dysaesthesia is relatively low because the nerve's usual position is sufficiently distant from the root apices. However, in the event a sealant material such as zinc oxide eugenol, or calcium hydroxide does contact the nerve, it is likely that immediate post-operative symptoms would manifest.¹² The high pH combined with bio-toxic properties makes these materials deleterious to organic soft tissue, and their maintained pH and toxic properties over time lead to symptoms that are persistent and difficult to control.¹⁷ Loss of mechano-sensory function, paraesthesia and dysaesthesia related to nerve injury can have a significant impact on quality of life.¹⁸ Disruption of normal speech, eating and sleep can manifest as a result of trigeminal nerve injuries^12,18 and, without treatment by an appropriate specialist service, approximately 80% of cases may continue to experience ongoing symptoms.¹²

Our case demonstrated the unabating and progressive nature of neuropathic pain with the continual irritation of the inferior alveolar nerve. The dental cement material being in direct contact with the inferior alveolar nerve resulted in an on-going effect. Having diagnosed the patient with dental cement material in the inferior alveolar nerve canal, and having excluded other modalities of neuropathic pain, our decision to operate was the agreed option to undertake. Surgical exposure of the nerve and manual removal of the material was the only way to cleanse the field of the on-going irritation and remove the dental cement.

Conclusion

Patients who present with neuropathic pain symptoms must be assessed carefully. Previous surgeries, no matter how routine or simple should be recorded and considered. Detailed examination and radiological investigations are vital to ensure the entire picture is seen as well as to aid in excluding the many different causes of neuropathic pain. One should always consider foreign bodies as a possible cause of pain, particularly if the nature of the said pain is persistent and evolving. Timely referral is also key in improving the outcomes of cases requiring surgery.