What is the etiology of nerve injuries?
- Odontectomy (removal of impacted tooth) - 3rd molars most concern because closest to IAN and PSA
- Trauma - fracture of jaw
- Implants - near inferior alveolar canal
- Reconstruction - removal of cysts, tumors –> nerves get resected sometimes
- Other (injection injury, root canal therapy, I & D) - root canal treatment can sometimes pass the apex of the tooth
What nerve is hard to visualize/detect?
The lingual nerve is hard to see because it’s very close to the alveolar crest and it’s usually low and medial. 20% of patients could also have it above the crest. The IAN is at least detectable radiographically.
When you extract 3rd molars what nerves should you be careful of?
IAN is always at risk for permanent parenthesia but also the lingual nerve
What kind of bony impact is the most likely to have altered sensation in patient after extraction?
Fully bony impaction > partial bony impaction > soft tissue impaction > erupted
What is the most common cause of nerve injuries?
Iatrogenic, most often because of dental treatment
Post-operation nerve injuries are more frequent in which nerve?
IAN
Nerve injuries after a year from surgery is most common in which nerve?
Lingual nerve
Patient comes in with an impacted third molar near the canal. The patient is asymptomatic, do we extract? Why?
No we do not need to extract. This is because if it is near the IAN canal and patient is asymptomatic there is no need to take the risk
When should we extract a 3rd molar near the IAN canal?
If there is a pathology or the position of the tooth will impact the long-term health of the 2nd molars
True or false: possible anterior crowding is indicative of 3rd molar extraction
False - 3rd molars will not cause anterior crowding
What is a partial odontectomy?
It is the resection of crown below CEJ – the residual root surface established at 3-4mm below Buccal and lingual alveolar crest.
You side step the risk of leaving the portion of the tooth near the nerve alone – incidence of infection is a little higher than taking the whole teeth out but still not that high.
Migration of teeth occurs within the first 12months, the remaining root migrates up
True or false: taking out the implant that has breached the IAN site will help alleviate some effects?
False - you will probably tear up the nerve even more
What are some possible injuries that occur due to implant therapy?
- Mental nerve trauma associated with ridge incision (edentulous mandibles)
- Mental nerve injuries associated with retraction (to get access to procedure)
- ***Most common is direct mechanical trauma – drill is longer than implant so much take into consideration
- Thermal injury - drilling on top of IAN so heat is transferred to the nerve
- IAN transposition/lateral inaction procedures
What are the different mechanisms/possiblities of nerve injury through injections?
Injection injury is mechanical injury from the needle that can result/stem from:
- Intra-neural hematoma formation
- Extra-neural hematoma formation
- Local anesthetic toxicity
- higher concentration LA more toxic than others (septocaine)
- relationship of position of lingual nerve and landmarks when we use IAB are highly variable which often results in trauma to lingual nerve.
What nerve is damaged more from an IAB?
Lingual nerve
True or false: if you want to avoid possible nerve damage, sealants are non-toxic to nerves with endodontic therapy?
False - sealants are highly toxic and causes inflammation
How does endodontic therapy result in possible nerve damage?
Sealants are often used to stop bacteria but if you perforate through the apex and apply a sealant then the sealant has a direct path to the nerve which is bad.
If patient feels numb/pain, need to get patient to OR or could have neuropathy
How do you take history for trigeminal nerve injury?
- Date of injury
- Mechanism of injury
- it is important to know mechanism because if it’s endo and there is an injured nerve you need to treat ASAP vs. impacted 3rd molar - Symptom history
- History of prior treatment and response
- time does matter, you can’t go back and fix nerves if they have been disconnected for a long time - Functional deficit
- Psychological impact
What examination must you give after a surgical procedure that involves risk to nerves?
Sensory nerve examination – challenge patient with different stimuli to see how nerve is working
What different types of clinical exams can you give the patient to test nerves?
- Static light pressure (slow adapting mechoreceptors)
- Pin prick nocieception (small diameter fibers – A delta, C)
- Tinsel sign - shooting sensation or pain distally upon palpation of the injury site
- Directional determination - specific receptors innervated by larger myelinated fibers (A delta, B) and rapidly adapting mechanoreceptors
- Two point discrimination - large myelinated axons innervating pacinian corpucles
- Diagnostic nerve block – failure of a peripheral nerve block to alleviate pain suggests a psychosocial, sympathetic or centrally mediated pain process
- Somatosensory evoked potentials (SEP) - quantitative assessment of nerve integrity
What are the 3 classifications of neural injuries?
- Neuropraxia
- Axonotmesis
- Neurotmesis
What is neuropraxia?
- Immediate deficit in nerve conduction
- Anatomic continuity maintained
- No wallerian degeneration (when nerve is cut or crushed that the axon is separated from neurons cell body and degenerates)
- Spontaneous recovery
***like falling asleep on your arm, 100% recovery, no need surgery
What is axonotmesis?
- Contusion or crush injury
- Basic architecture of endoneural sheath is maintained
- Wallerian degeneration distal to the point of injury
- May recover spontaneously within 2-6 months but the quality and degree of regeneration varies
We want to try and give them back some sensation and have them pain free
What is neurotmesis?
- Physical disruption of the nerve trunk
- Wallerian degeneration distal to the point of injury
- Prognosis for regeneration depends on the quality of the transection and the orientation of the distal and proximal nerve segements
