Implant-related nerve injuries

 

Nerve injuries related to dental implant treatment is becoming an increasing problem. The incidence of implant related inferior alveolar nerve (IAN) nerve injuries varies from 0-40%. 25% of edentulous patients present with a degree of altered IAN function, thus reinforcing the guidelines on the necessity of preoperative neurosensory evaluation.

 

Some hints for you as the patient:

 

• Great care must be taken when selecting your clinician (avoid non specialists for complicated treatments and if you are in doubt contact the general dental council. We also suggest caution in seeking ‘cheap’ implant treatment abroad!). 

• You should be advised regarding alternative treatments before you go ahead with implants

• You should have at least 2 visits including written and explicit consent that you should fully understand before signing

• You should be assessed using xrays and sometimes special scans to see exactly where the nerve is and whether there is enough bone for the implant

 

Scanning now available in many specialist practises and dental hospitals provides improved imaging for planning implant treatment with little radiation exposure. However CT evaluation can be less effective in identifying the IAN canal with poorer sensitivity and specificity compared with 'pantomogram radiography'; (big Xray).

 

Endodontics, or root canal treatment

 

Any tooth requiring endodontic therapy that is in close proximity to the IAN canal should have special attention given by the clinician. If the canal is 'over prepared' or the apex opened, chemical nerve injuries from irrigation of canal medicaments is possible. Endodontic nerve injuries are not be limited to those teeth close to the IAN canal ,but may occur in maxillary teeth as well.

 

The risk factors for endodontic inferior alveolar nerve injury include;

 

• Proximity of the tooth to the mandibular canal

• Over instrumentation

• Overfill

• Chemical nerve injury (including sodium hypochlorite)

  

Third molar surgery related inferior alveolar nerve injury is reported to occur in up to 3.6 % of cases permanently and 8% of cases temporarily. Factors associated with IAN injury are age, difficulty of surgery and proximity to the IAN canal. If the tooth is closely associated with the IAN canal radiographically; ie. superimposed on the IAN canal, darkening of roots, loss of lamina dura of canal, deviation of canal Figure 8 (Howe and Poynton 1969; Rood et al., 1983; 1986; Rud 1988) then 20% of patients having these teeth removed are at risk of developing temporary IAN nerve injury and 1-4% are at risk of permanent injury (Howe and Poynton 1969; Rood et al., 1983; 1986; Rud 1988; Renton et al 2005).

 

Radiographs illustrating 2 cases of ‘high risk’ mandibular third molars. In both cases the lower thord molar is crossing the IAN canal completely, there is darkening of the tooth roots and loss of lamina dura of the canal roof and floor.

 

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Again caution is advised when selecting treatment. Oral surgery specialists, registered as such on the General Dental Council list, are best trained to carry out this work.

 

Therefore the prevention of inferior alveolar nerve injuries in relation to third molar surgery is paramount and should ask: do you need the wisdom tooth removed? The National Institute of Clinicial Excellence has guidelines about whether wisdom teeth needs removal.

 

A clinical decision that the tooth needs to be extracted should be based on NICE guidelines. Prophylactic surgery should only be undertaken when specifically indicated i.e. pre radiotherapy, pre chemotherapy or pre IV bisposphonates, none of which are included in NICE guidelines.

 

• The clinician specialist must identify mandibular teeth at high risk of IAN injury based on plane radiographic features and/ or cone beam CT scanning. If deemed at high risk the patient must be made aware of the increased nerve injury incidence (increased risk 2% permanent and 20% temporary) and perhaps offered alternative procedures that may in course reduce the risk of injury. 

• If the tooth is in close proximity to the IAN on plain film then;

• You should be warned of higher nerve injury risk (up to 10 times higher=20% temporary and 2% permanent compared with 2% temporary and 0.2% permanent form low risk wisdom teeth)

• You may be sent for Cone beam CT scanning which may further elucidate the relationship between IAN and tooth roots. If the tooth is non vital, or pathology associated with it, then tooth removal has to take place and the roots should be sectioned appropriately to minimise trauma to the adjacent IAN.

• You may be offered a coronectomy procedure rather than removal of the tooth if appropriate (link to BDJ coronectomy paper)

 

The clinician should be aware that any mandibular tooth (lower 8,7,6,5 or 4) that if the tooth root is crossing the IAN canal, and displays the radiographic signs is associated with increased risk of IAN injury, there is increased possibility of damageto the IAN on removal of the tooth. The the patient must be assessed accordingly, consented and treated similarly to high risk third molar teeth. The same assessment should be applied for these high risk teeth as above.

 

Local anaesthetic injections (deep dental injections)

 

 

Injuries to inferior alveolar and lingual nerves are caused by local analgesia block injections and have an estimated injury incidence of between 1:26,762 to 1:800,000 inferior alveolar nerve blocks (Pogrel and Thamby, 2000; Haas and Lennon, 1995). More recently the incidence of nerve injury in relation to IDBs has been calculated as 1:609,000 but with a sig increase in injury rate with 4% agents (Gaffen & Haas 2009). These injuries are associated with a 34% incidence of neuropathic pain which is high when compared with other causes of peripheral nerve injury (Pogrel and Thamby, 2000). However the true incidence is difficult to gauge without large population surveys. The problem with these injuries that the nerve will remain grossly intact and surgery is not appropriate as one cannot identify the injured region.