the relationship of the anatomical structures in the retromolar region makes 
 any procedures executed in this region very complex , the extraction of the mandibular 
 third molar being the most frequent surgical intervention accomplished there .
many 
 times , this procedure is executed by professionals who are not specialists in oral 
 and maxillofacial surgery , which puts the integrity of the lingual nerve ( ln ) at 
 risk .
the ln , one of the mandibular nerve branches , third division of the trigeminal 
 nerve , presents fibres of the chorda tympani nerve , a branch of the facial nerve , 
 responsible for the sensitive innervations of the anterior two thirds of the tongue 
 and for the parasympathetic innervations of the sublingual and submandibular glands 
 . according to fign
, the chorda tympani 
 nerve is an extensive communicated branch , between the facial and lns , which has 
 sensory taste fibres , relating to the anterior two thirds of the tongue and from 
 the palatal vault , and parasympathetic secretor fibres going to the submandibular 
 and sublingual glands .
these anastomoses explain the loss of taste in the lesions 
 of the ln . in the infratemporal fossa ,
the lingual and inferior alveolar nerves 
 are crossed by the maxillary artery , which runs horizontally , around the medial 
 condyles head , followed by the maxillary vein .
the mandibular third molar is situated at the end of the body of the mandible 
 where it is connected with the relatively thin ramus .
so , there is a high risk of ln damage using the lingual split technique or 
 elevating the third molar flap medially to the distoangular recess .
furthermore , injury to the nerve might occur iatrogenically by direct injury 
 caused by the tooth dislocation to the submandibular region during extraction or 
 for excision of the nerve during the removal of a tumor of the submandibular gland , 
 followed by trauma , orthognathic surgery , third molar extraction due to the intubation 
 procedures of general anesthesia , endodontic treatment of the posterior teeth , tooth 
 implants , intra - osseous lesions curettage , partial or total resection of the tongue 
 or mandibular and periodontal procedures [ 4 - 8 ] beyond local anesthesia 
 .
the present study aimed to describe the anatomic relationship of the ln with 
 the nearby structures in the retromolar region and in the third molar socket , disclosing 
 its pathway from the retromolar region until the point that it runs along the floor 
 of the mouth , crossing with the submandibular gland duct .
the 
 third molar had completely erupted and it was not possible to determine the gender , 
 since the samples were detached from the body .
the exploration of the ln was accomplished through a 
 four centimeter incision in the retromolar region until the point that it adopted 
 a horizontal pathway moving away from the lingual plate , at the point that it crosses 
 with the submandibular duct .
the point at the oblique line in the retromolar region was defined as point a. 
 the central point in the lingual gingival margin that corresponds to the third molar 
 socket was identified as point b. the point at which the submandibular duct intersects 
 the ln in the sublingual region was identified as point c. the proper nerve at the 
 retromolar region was defined as point d. the point of the ln , at the level of the 
 third molar mandibular socket , nearest the lingual cortical and that intersects 
 an imaginary line parallel to the long axis of the socket was defined as point e. the following measurements were taken : the retromolar region ( a ) to the point 
 nearest the ln ( d ) ; the third molar socket ( b ) to the ln point in the retromolar 
 region ( d ) ; the distance between the alveolar rim ( b ) and the point at which the 
 submandibular duct intersects the ln in the oblique direction ( c ) ; the distance 
 from the third molar socket ( b ) to the ln ( e ) in a horizontal direction and vertical 
 direction .
the measurements were taken from the most superior aspect of the ln ( figure 1 ) .
project representing the reference points adopted for the measures : a = retromolar region ; b = third molar socket ; c = intersection point between ln and submandibular duct , d = ln at retromolar region and e = the point of ln , at the level of the third molar mandibular socket , nearest lingual cortical and that intersects an imaginary line paralled to the long axis of the socket .
all of the measurements were realized by the same examiner through a manual caliper 
 and analyzed by the spss 16.0 program , through a descriptive analysis via the measurement 
 of the medium - position and the measure of the standard deviation ( sd ) variability .
the mean distance between point a to point d was 7.2 mm ( sd 1.7 mm ) .
the b to 
 d distance , on average , was 9.4 mm ( sd 1.8 mm ) .
point b to point c was , on average , 
 22.6 mm ( sd 6.6 mm ) .
the relationship of point b to point e , in a horizontal direction , 
 which represents the distance of the lingual plate to the nerve was 4.4 mm ( sd 2.4 
 mm ) , ranging from 11 mm to 2 mm .
the distance between points b and e , in the vertical 
 direction , which represents the relationship between the nerve and the lingual alveolar 
 rim , was 16.8 mm ( sd 5.7 mm ) , ranging from 29 mm to 12 mm . at the point
that the 
 ln intersects the submandibular duct , there was no constant position relative to 
 the nerve and the duct . in this study
, 15 side heads presented the submandibular 
 duct ( wartons duct ) and passed over the ln , and in 9 cases , the duct crossed below 
 the nerve . from the 24 parts analyzed in this study ,
seven presented healthy mandibular 
 third molar teeth , 12 parts also had the inferior second molar , and 3 parts also 
 presented the maxillary third molar .
in this study , the distance between the retromolar region ( a ) and the ln ( d ) , 
 in the retromolar region , was 7.2 mm ( sd 1.7 mm ) and the distance between the ln 
 ( d ) in the retromolar region , and the third molar socket ( b ) was 9.4 mm ( sd 1.8 
 mm ) ( figure 1 ) .
this distance does not provide security or comfort 
 to the surgeon to accomplish large incision maneuvers and detachment of the nearby 
 tissue , since some cases require extensive detachment , and point a limits the ln 
 position in this region . according to the pell and gregory classification
, this distance tends to be closer 
 in the level 3 position - the mandibular third molar in the mandibular ramus in 
 which the nerve runs nearest to the retromolar region , presenting vulnerability 
 during surgical procedures in this region .
pogrel et al . 
  found one case where the nerve passed above the mandibular 
 lingual plate . in this position ,
the ln is vulnerable to trauma , may suffer injury 
 during gingival detachment in the retromolar region and is difficult to reach even 
 in procedures that dont involve sharpened instruments in the lingual plate of the 
 mandible .
the distance between the alveolar rim , at the level of the third molar region 
 ( b ) , and the sublingual region at the intersection point between the ln and the 
 submandibular gland duct ( c ) was found to be 22.6 mm ( sd 6.6 mm ) ( table 
 1 and figure 1 ) , and was located in the premolars region . 

it is important to observe the relationship between the nerve and the duct of the 
 submandibular gland ( wartons duct ) , because the position of both structures is 
 not always maintained the same .
this relationship is very important during surgical 
 procedures involving the submandibular gland . in this study , in 62.5% of the cases , 
 the duct passed above the nerve and in 37.5% the nerve passed below the duct .
hlzle 
 and wolff   investigated the relationship of the ln with the 
 adjacent structures in the atrophic jaws .
they found that in most cases the wartons  
 duct passed above the ln , and of a total of 34 samples , they found in 4 cases the 
 wartons duct running deeply in the floor of the mouth , which they did not find 
 with the ln ( figure 2 ) .
average and standard deviation by type of measure of the distances between lingual nerve ( ln ) and the adjacent structures in the inferior third molar region image showing the intersection point between ln ( yellow ) and the submandibular gland duct ( black ) .
with respect to the horizontal distance ( be ) , 4.4 mm ( sd 2.4 mm ) was found between 
 the ln and the mandibular plate , at the level of the third molar socket ( figure 
 3 and table 1 ) .
( 2.06 mm ; sd 1.1 mm ) and by hlzle and wolff   ( 0.86 mm ; sd 
 1 mm ) .
kiesselbach and chamberlain   found a horizontal distance 
 of 0.59 mm ( sd 0.9 mm ) between the ln and the mandibular lingual plate .
.   found this same relationship with 2.53 mm ( sd 1.48 mm ) . 

this can be justified 
 for the size of our sample , since in the behnia et al .
study  
 it involved 669 lns in 430 corpses with a maximum of 24h post - mortem .
our specimens 
 were conserved by immersion in 10% formaldehyde , with a time of immersion varying 
 from 2 to 5 years , which might cause changes in the tissue volume of the analyzed 
 parts .
diagram of the vertical and horizontal relationship between ln and lingual plate of the mandible , measured from the most external surface of the nerve .
the vertical average distance found was 16.8 mm ( sd 5.7 mm ) and the horizontal one was 4.4 mm ( sd 2.4 mm ) . another fact that might have contributed to the divergence of our result in the 
 horizontal measure was the method used . in the research of pogrel
and in the hlzle and wolff   studies , the ln was measured 
 taking the retromolar region as a reference , and not the third molar socket , as 
 was done in our study .
the measure found in this study highlights the relationship 
 between the ln and the mandibular lingual plate - 4.4 mm , representing great vulnerability 
 to the nerve . during dental sectioning ,
this surgical step must be completed by the 
 introduction of a straight extractor and the dental division is achieved by movements 
 of rotation inside the tooth .
when the vertical relationship between the ln ( e ) and the mandibular lingual 
 plate in the third molar region ( b ) was analyzed , a distance of 16.8 mm ( sd 5.7 
 mm ) was found ( figure 3 and table 1 ) .
( 8.32 mm ; 
 sd 4.05 mm ) , by behnia et al .  
( 3.01 mm ; sd 0.42 mm ) , by 
 hlzle and wolff   ( 7.83 mm ; sd 1.65 mm ) , by kiesselbach and 
 chamberlain   ( 2.28 mm ; sd 0.9 mm ) and miloro et al .  

and hlzle and wolff  
 carried out measures with the retromolar region as a reference and not the third 
 molar socket .
the study executed by behnia et al .   involved 
 the greatest sample in the literature , totaling 669 nerves .
they found that in 14.05% 
 of the cases the nerve passed above the mandibular lingual plate and in one case 
 it ran in the retromolar region accurately on the mandibular surface . in 85.8% of 
 the cases ,
the nerve was in its typical position and in 149 cases ( 23.27% ) it was 
 in direct contact with the lingual plate of the jaw in the alveolar process .
they affirm that there were no difference in the ln position in males and females 
 and no correlation between the ln positions at each side , with both presenting independent 
 topographies .
bataineh   investigated the sensory impairment of the lingual 
 and inferior alveolar nerves after removal of impacted mandibular third molars under 
 local anesthesia and found 2.6% of the patients presenting paresthesia in the ln 
 region , with increased incidence associated with increased lingual flap . fielding and reck   registered a case of permanent bilateral 
 anesthesia of the ln after removal of the third molar and the most probable cause 
 was the anomalous position of the ln .
robinson and smith  
 defend that avoiding lingual retraction reduces the incidence of temporary and permanent 
 damage .
the incidence of damage to the ln was reduced to 0.2% when the lingual flap 
 is avoided and when the lingual plate is preserved .
current 
 protocols in the eua emphasize the increased buccal flap , avoiding involvement of 
 the lingual tissue to reduce the risks of impairment to the ln [ 21 - 23 ] .
this instrument , with a double - ended shaped to fit the lingual contour 
 of the mandible of the third molar region , would be inserted between the lingual 
 periosteum and the lingual plate of the jaw , providing more space for the surgeon 
 to work , better visibility and lingual flap protection .
this technique would be 
 used for procedures of dental sectioning and bone removal in the distal region to 
 the third molar . using this instrument in only 1.6% of the cases presented temporary 
 paresthesia and no case of permanent damage .
many surgeons prefer to use some instruments to perform the nerve protection , 
 as with the molt n 9 instrument .
nevertheless , there are cases of ln injury by 
 compression , because of its sharp edges and because it did not supply sufficient 
 control during insertion in the depth of the molt n 9 . 

chossegros et al .   evaluated the protection of the ln with 
 a periosteum rising ( molt or similar ) .
they concluded that the ln protection , in 
 these cases , is totally unnecessary , which has no advantage for ln protection .
many times it is impossible to accomplish the mandibular third molar removal 
 or other procedures involving this same region without manipulating the lingual 
 mucosa , which already enables injury to the nerve , even temporarily .
this complication 
 must be discussed with the patient to orientate him at the consultation before surgery 
 .
blackburn and bramley   affirmed 
 that the bone must be removed in order to facilitate visualization and the drill 
 must be advanced / directed by the surgeon . in every case
there are cases in 
 the literature of damages to the ln following endotracheal intubation for procedures 
 that do not involve the oral structures [ 4 - 8 ] . in a recent study , 
 the incidence of damage to the ln was higher in mandibular third molar surgeries 
 under general anesthesia ( 18% ) than 3% under local anesthesia . 

the etiology of ln damage associated with general anesthesia is multifactorial : 
 complicated and forced laryngoscope , several attempt of laryngoscope , anterior displacement 
 of the jaw for a long period , compression of the tongue , macroglossia , placing a 
 drain plug in the throat and mandibular retraction .
niemi et al .   affirmed that the deterioration of the function 
 of the ln becomes more difficult with tongue control in anterior - posterior movements . 

this involvement in the voice production might be the result of the motor impairment , 
 suggesting that the damage also results in interference in the proprioceptive answer 
 of the muscular fibres of the tongue .
repairs with or without grafts 
 done immediately after trauma have better results , with 
 progressive worsening when done 3 , 6 , 9 or 12 months after the injury . 

although there have been 
 several attempts , there is not yet an attendance protocol for these cases .
in addition , 
 the long - term outcome of microsurgery is very variable . 

maybe , the difficult access and the constant mobility in the surgery area ( to eat , 
 to swallow and to speak ) can contribute to the low success rate .
this study showed a close relationship of the lingual nerve and the mandibular 
 lingual cortical , presenting a distance of 4.4 mm horizontally and 16.8 mm vertically . 
 as a result ,
unless adequate protection of the lingual nerve is acquired by following 
 an adequate surgical technique , the lingual nerve will always be vulnerable to damage 
 during surgical intervention or manipulation in this region .
 abstractobjectivesthis study evaluated the relationship of the lingual 
 nerve with the adjacent anatomical structures of the mandibular third molar region , 
 influencing the dentist to be aware of the variability of these relationships.material and methodssamples of 24 human corpse half - heads 
 were selected and divided according with the presence or absence of the mandibular 
 third molars . 
 the lingual nerve ( ln ) was explored , showing its run from the oblique 
 line until its crossing with the submandibular gland duct . 
 the measurements along 
 the ln and the adjacent anatomical structures were taken at the retromolar , molar 
 and sublingual region with the use of a digital caliper.resultsthe distance from the ln and the third molar socket , 
 which represents the horizontal distance of the lingual plate to the nerve , on average , 
 was 4.4 mm ( sd 2.4 mm ) . 
 the distance from the ln and the lingual alveolar rim , which 
 represents the vertical relationship between the nerve and the lingual alveolar 
 rim of the third molar socket , on average , was 16.8 mm ( sd 5.7 mm ) . 
 the ln has a 
 varied topography that leaves it very vulnerable during any procedure executed in 
 this region.conclusionsunless adequate protection of the lingual nerve 
 is acquired by following an adequate surgical technique , the lingual nerve will 
 always be vulnerable to damage during surgical intervention or manipulation in this 
 region . 
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS
ACKNOWLEDGMENTS AND DISCLOSURE STATEMENTS