PARESTHESIA - A CLINICAL STUDY

Paresthesia of the mandibular
nerve caused by implants

Extract from original paper by

P. Luigi Mondani – P. Maria Mondani

Institute of Dentistry, University of Modena
Specialisation School in Odontostomatology

Head: Prof. B. Vernole


Epineurium: careolar connective tissue surrounding the fasciculi.
Perineurium: sheath of connective tissue enclosing all the bundles of nerve fibres.
Endoneurium: thin connectival membrane ensheathing each nerve fibre. It is also called Henle's sheath or Key and Retzius's sheath. The endoneurium is profoundly joined to the Schwann cells which are its major constituent. Lastly, the endoneurium is closely connected to the perineurium giving a certain elasticity to the nerve bundle, which is extremely important for implantology.


When stretched, the elasticity of the epineurium and the two nerve fibres inside the fasciculi allow a degree of stretching that is tolerated by the nerve trunk, but the extent to which it can be extended depends on the elasticity of the perineurium.
Recent research has identified 20% as the maximum limit of extension, whereas 30% leads to structural laceration.
Other leading authors have given 6% as the maximum limit of extension, but it is important to note that the slower the nerve is stretched, the greater extension is supported by the nerve bundle.
Paresthesia of the mental nerve is an annoying complication for the patient and is occasionally reported in deep implants from the seventh to the lower quarter. The chin region remains anesthetised while the areas innervated by the vestibular, incisive and lingual nerve are perfectly normal.
Paresthesia may be caused by the implant pressing on the nerve or by bone particles disturbed by the implant that irritate and compress the nerve, or by hemorrhage of the artery or vein which was resected during surgery.
Numerous tests have been defined to evaluate alterations to sensitivity which when repeated over time allow us to monitor the evolution of the area in question using image-documented skin maps.



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Thermal evaluation test

1- Minnesota Thermal Disk.
The patient must recognise four disks made from materials with different thermal conductivity: polyvinyl chloride, stainless steel, copper, glass.

2- Thermal stimulation test.
Thermal stimuli starting from 34° are applied as required.

3- Path test.
Comparison between two contralateral areas during stimulation of the altered zone using thermoelectrodes



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Mechanoceptive tests

1- Weinstein’s tactile discrimination test. Evaluates the capacity to recognise contact with nylon filaments of decreasing diameter.

2- Sliding direction test. Capacity to recognise the direction in which a filament slides over the skin.

3- Weber's test. Capacity to identify the contact of one or two individual points identified as such. Normal 7-14 mm.

4- Nishiok's test: discrimination between 2 points. Capacity to identify the points of a compass based on its aperture. Normal 0-14 mm.

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Electric stimulation test

Comparison between the threshold value of electric stimulation in the area in question compared to the contralateral zone.

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Nociceptive discrimination test

Comparison between the threshold value of electric stimulation in the area in question compared to the contralateral zone.

1- The skin is stimulated with increasing pressures that become painful after 15 grams, 100 grams are the value of anesthesia (irreversible)

2- Thermal stimulation test. Evaluation of reaction capacity using thermoelectrode.


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Chemical test - Ninhydrin 3%

If the chin area in question is under anesthesia owing to the interruption of a nerve, and therefore has no sudation owing to the lack of sudomotor fibre stimulus, paper soaked in Ninhydrin will not turn violet. This test reveals the presence of permanent and transient interruptions.

Central or Peripheral electrophysiological analysis

This involves the electrophysiological analysis of the nerve through the central or peripheral recording of somatosensory evoked potentials using invasive and non-invasive methods.
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Masseter silent gap test


Evaluation of the lesion through the absence or diminution of the latency period.


Complete anesthesia of the mental part may appear after a couple of months and after several studies, Simpson concluded that anesthesia of the chin is rarely permanent. He also documented that over 50% of inferior alveolar nerve lesions heal spontaneously in eleven weeks, whereas recovery in less than six weeks was minimal. Before inserting a deep inferior implant in zone 7, 6, 5, 4 it is important to ensure that the patient is aware of the possible after-effects. Explain that in 80% of cases the symptoms of paresthesia are transient, and once consent has been given, perform the implant. In our profession of implantologists, very few patients withdraw consent when informed of a probable paresthesia. Those patients affected after five or six months have always reported that the paresthetic damage was reduced by 80-90%. Most affirm that the damage has disappeared completely. A very small number, less than 10, still complain of small traces of paresthesia, but it is well tolerated compared to the discomfort of a mobile plate.
It is important to underline that in rare case the damage may persist and be more severe, but occasionally the patient is not satisfied with the results of the implant and wants to claim compensation at the expense of the surgeon, exaggerating symptoms that are non-existent or almost and bringing the case to court. This is a trend that is become increasingly widespread in all fields of medicine

P. Luigi Mondani
P. Maria Mondani

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