From Volume 12, Issue 1, January 2019 | Pages 22-24
This case report describes the management of a 16-year-old female patient who presented with mental nerve paraesthesia which developed during orthodontic treatment. The diagnosis was determined based on history taken, clinical and radiographic examination. Treatment involved removal of fixed appliances in the lower right quadrant, a referral to the Oral and Maxillofacial Surgery department and regular follow-ups until full resolution of symptoms.
A fit and well 16-year-old female patient was referred to a local Specialist Orthodontist by her General Dental Practitioner (GDP) to correct her moderate upper arch crowding and mesiolabially rotated upper left lateral incisor. She presented with Class II division 2 malocclusion on a Class I skeletal base with average vertical proportions. There was no crowding in the lower arch and the lower left lateral incisor was absent. The orthodontic treatment commenced with upper and lower 3M Victory pre-adjusted edgewise fixed appliances and band placement on the upper and lower first molars. Glass Ionomer Cement (GIC) bite planes on the upper first molars were utilized to prevent occlusal interference. Upper 0.012” NiTi and lower 0.014” NiTi archwires were placed for initial alignment. Treatment continued with regular follow-up appointments and a progression of increasing diameter archwire and appliance adjustments according to the treatment plan. Five months into treatment the lower second molars were bonded with molar tubes and included in the 0.016” NiTi archwire.
At the follow-up appointment 6 months later, a lower 0.019” x 0.025” NiTi archwire was placed. Three days later, the patient's mother phoned the Specialist Practice with concerns that her daughter was experiencing tingling sensations in her lower right lip following the recent archwire change. The patient was reviewed the next day by the Specialist Practitioner, whereupon she complained of a tingling sensation over the cutaneous distribution of the right mental nerve, including the gingivae of the lower right quadrant. This had originally been noted by the patient in the evening following the archwire change.
An Orthopantomograph (OPG) (Figure 1) suggested an intimate relationship between the inferior dental canal and the root apices of the lower right second premolar and first and second molars. These findings were discussed with the patient and the fixed appliance in the lower right posterior segment was removed immediately. At the one month follow-up appointment with the Specialist Practitioner there was an improvement of symptoms, with a reduced area of paraesthesia affecting only the lower right lip and an up-to-date OPG confirmed no obvious pathology. A referral to the Oral and Maxillofacial Surgery (OMFS) department was then generated to investigate this episode further.
The patient was seen at a New Patient OMFS clinic in Salisbury District Hospital 3 months later, where she was still complaining of paraesthesia of the lower right lip. Clinical examination was unremarkable, with the patient being able to discern sharp, blunt brush strokes and a two point discrimination of a sharp stimuli. A conservative approach was recommended as there was an improvement in her symptoms following the isolated removal of fixed appliances. A further follow-up appointment was arranged for two months later. A request for a second opinion regarding the reporting of the OPG finding was made to the radiology department. This confirmed the close proximity of the root apices of the lower right posterior teeth to the Inferior Dental Canal (IDC). Later the same month, the patient reported her sensation of the lower right lip had resolved back to normal.
Her treatment is currently ongoing, excluding the teeth in the lower right quadrant. Retention will be provided with full coverage Essix retainers on both arches.
Changes in facial sensation in the head and neck region can be the first manifestation of a serious pathology and therefore should be acted upon promptly. Sensory deficits can be sequelae of a single nerve disease or multiple nerve pathology1,2 and can present as the following:
Depending on the anatomical position of the lesion,1 extracranial or intracranial, the presenting signs and symptoms may vary. Extracranial lesions are considered to be more prevalent; examples include bone disease and trauma. Cerebrovascular disease, neoplasms and infections are examples of intracranial causes and, whilst considered to be more serious, are uncommon.1
The intramandibular course of the Inferior Dental Nerve (IDN) and its neurovascular structures has been widely explored.3,4,5,6,7-8 Its location is of vital importance when treatment planning for several dental and surgical procedures in the mandible.
In 1971, Carter and Keen classified the location of the IDN within the canal into three main types:3
Their results agreed with previous beliefs that the mandibular canal contained the whole of IDN, which was represented in the 60% of cases in this study, whereas there was no distinct canal and the branches of the nerve were spread out in the remaining 40% of cases.
Kim et al investigated the buccolingual location of the IDC and carried out topography of its neurovascular structures,4 providing the following summary:
The results interestingly showed Type 1 to be predominant at 70%. More fascinating is the fact that the vascular bundle travelled superiorly in relation to the nerve in 80% of cases; with, in the remaining 20% of cases, the vessel being located buccally. The author speculated that trauma to the superior part of the IDC may stress the inferior alveolar vessel, resulting in haematoma formation and subsequent pressure on the neural tissue, thus suggesting a possible explanation for the temporary paraesthesia/anaesthesia symptoms due to the resolution of haematoma.
Others have looked at the histology of the IDN in addition to its intrabony anatomy and found that the nerve consisted of two separate larger branches.5 The branches were twisted around each other, whilst each one was wrapped in an individual perineural sheath. Similar observations were made by Starkie and Stewart, suggesting the presence of two nerve plexuses.6
Despite considerable research into the intramandibular course of IDN, the anatomical variations and uncertainty regarding a precise intranetwork of the neurovascular structures within the canal are still evident. This stimulates the need for further research in this field.
Mental nerve paraesthesia is a symptom which is always taken very seriously and must be thoroughly investigated. Development of a mental nerve paraesthesia during orthodontic treatment is uncommon. A literature review using PubMed database identified five other cases of mental nerve paraesthesia as a result of orthodontic treatment.9,10,11-12 Of these, two cases were related to a second premolar tooth,9,10 one was attributed to a first premolar tooth10 and the remaining cases11,12 were associated with a lower second molar tooth.
In this case report, it is difficult to attribute the exact cause of the mental nerve paraesthesia to a single tooth. One can speculate that the origin of that symptom was as a result of any one tooth or a group of teeth in that quadrant. It would have been of interest to carry out a Cone Beam Computerized Tomography (CBCT) scan to determine a three-dimensional view of the IDC and its course within the mandible. However, since the resolution of symptoms without any active treatment, it became unnecessary to carry out any additional investigations.
This case is brought to the attention of all dental and medical clinicians to raise awareness of this rare complication during the orthodontic treatment. The location of the IDC and the IDN comprise a vital part in treatment planning of oral surgical procedures, such as dental extractions, implant placement and orthognathic surgery. In addition, it is an important consideration during certain dental procedures, such as endodontic therapy. Ultimately, the risks of potential nerve damage, however small, must always be discussed with the patient. The question raised is, should the potential nerve damage be included in the discussion along with other risks when consenting patients for orthodontic treatment?
