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Anatomic surgery for salivary calculi
Oral SURGERY OralMEDICINE AND&d
VOLUME
25
NUMBER
4
APRIL,
PATHOLOGY
1968
Operative oral surgery
Anatomic surgery for salivary calculi Part III. Calculi
Q. R. Stwal-d, THE
LONDON
in the posterior
part
M.D.X., B.D.X.R.C.S., HOSPITAL
MEDICAL
of the submandibular
duct
X.B., B.8., London, England
COLLEGE
C
alculi which develop in the posterior segment of the extraglandular part of the duct or in the intraglandular part of the duct may reach a large size without the paGent being awa.re of their presence. The internal diameter of the duct in this region is normally of a moderate size, a,nd it becomes dilated to a greater diameter as a result of the partial obstruction caused by the presence of a calm~lns, F:ven with such evidence of partial obstruction, sufEcient saliva may pass around the ralcnlu~ for the patient. to be unawa,rc of the obstruction for many years. Sn obstruction sufficient to cause symptoms can occur in one of two ways: i 1) the stone may increase in size to a point where saliva will only leak around it very slowly or (2.) infection may supervene. Should the saliva in the dilated ducts behind the stone became infected, an acute or subacute sialoadenitis will result. The inflamed duct will swell and tighten about the calculus, and the salivary obstruct.ion will be intensified. Depending on the parts played by 525
OS, O.M. & O.P. April, 1968
infection or obstruction, the patient will complain of an inflammatory swelling of the floor of the mouth and submandibular region or of a swelling of the gland during salivation. In the absence of an acute infection, an attempt should be made to palpate the stone. The index finger of one hand is passed into the mouth and under the lateral margin of the tongue. The mouth should be partly closed to help the patient relax the floor of the mouth, and the pulpal aspect of the finger should be turned downward and slightly laterally. With the fingers of the other hand, the lower pole of the submandibular gland is palpated in the submandibular region and pressed upward toward the examining finger. The upper pole of the gland will be felt moving under the finger, and the stone may be palpated as a hard mass near the gland. The gland itself should also be examined, and its size and consistency should be noted. When an otherwise normal gland or one which has only recently been inflamed is distended with saliva because of an obstruction in the duct, the substance of the gland will still feel elastic. When the gland feels firm and inelastic, it is fibrosed and probably has been chronically infected for many years. The preoperative assessment is mainly concerned with two factors: (1) whether the calculus is accessible from the mouth and the gland is likely to recover from the affects of chronic obstruction and infection and (2) whether the gland is so diseased that recovery is impossible. Assessment of the state of the gland depends upon the history, the physical examination, and the sialogram. Should the patient give a history of intermittent
Fig. 14. A posterior main
duct leaves
oblique occlusal radiograph the gland. (From Seward: British
of a ca.lculus at the point where Dental Journal 115: 266, 1963.)
the
Volume 25 Number 4
Anatomic
surgery
for
salivary
calculi
527
attacks of swelling or acute infection over a period of many years, then it is probable that the gland has suffered irreparable damage. Similarly, a gland that is small and hard on palpation has probably suffered severe damage and is greatly scarred. Should there be fistulas between the duct and the floor of the mouth where previous stones ha.ve ulcerated through and have been discharged sponta.neously, then it is likely that the gland has suffered severely. Assessment of the position of the ca,lculus depends upon the examination, plain radiography, and sialography. A calculus that can be felt clearly from the mouth can be removed via the mouth. If it cannot be palpated, however, then the assessment of its position is dependent upon the radiographic examination. Although in plain radiographs a small percentage of posterior calculi will be shown at the back edge of a central true occlusal film of the floor of the mouth, the majority will be demonstrated only by a posterior oblique occlusal view (Fig. 14). In other words, if the calculus is not projected onto the film by the central true occlusal technique, then it is not amenable to removal by the method used for anterior calculi and must be treated either as a posterior calculus or as a calculus in the gland. An oblique lateral jaw radiograph is valuable for, with experience, a preliminary assessment can be made of the position of a calculus in the posterior part of the duct tree by noting its position in relationship to the mandible. Compared with the other means of assessment, a good sialogram, if one can be obtained, is invaluable in estimating both the position of the stone and the condition of the gland. Provided the duct system has been well filled, there should be litt,le difficulty in locating the stone with considerable accuracy (Fig. 15). Even when the sialographic injection has been incomplete, the films may
Fig. 15 . &4 sialogram $f .~- c-_---u&%&z ‘shdwii ‘in c_ immediately T proximal to the origin of th .e tribntaxy ...I.... ~-111 a...--2 ar, ^L AL.. -^. Such a ealc:UIUS WM LIJIS AVUUI MIC pint where within the borders of the gland. Calculi proximal glandular. (From Seward: British Dental Journal
ying
%ig. 14 demonstrates th .e talc :ulus duct from the upper p(de! of the &cl!and. the duct emerges from tl 1e da nd clr just to this point will undou .bl :edl: * be il xtra115: 266, 1963.)
O.S., O.M. & O.P. April, 1968
still be valuable as long as the main duct as far as the calculus has been completely filled. If, aside from posterior sublingual gland ducts, no tributary ducts are visible anterior to the calculus, then it is probable that the stone lies in the extraglandular pa.& of the duct. Assessment of the condition of the gland itself by sialographic study depends upon filling of the intraglandular ducts, and this is not always easy when there is a calculus in the main duct. If only one calculus is present, it is frequently possible, with patience on the part of both the operator and the patient, to persist with a steady injection until enough contrast medium to outline the intraglandular ducts has passed the obstruction. Inevitably there will be a tendency for the contrast solution to reflux, but if the fusiform “blob” on the cannula is kept firmly against the duct orifice, the amount of reflux can be reduced to a reasonable level. In some instances the examination proves too tedious for the patient and has to be abandoned before the gland has been properly filled. At times, therefore, it can be difficult to distinguish between incomplete filling of the duct tree and destruction of some of the smaller ducts by disease. When there is more than one sizable calculus in the duct, it is unusual to get the fluid past the second calculus and a sialographic assessment of the gland is impossible. For obvious reasons, there are few histologic examinations of glands which have been obstructed by small stones, where symptoms have been of recent onset and where there is a sialographically normal intraglandular duct system. In those instances in which sections from such glands are examined, however, they may show a surprising degree of infiltration with inflammatory cells, including polymorphonuclear leukocytes. Presumably, the inflammatory reaction is reversible, for after such a calculus has been removed the gland appears to function normally and will remain symptomless unless another stone forms. Even if the larger intraglandular ducts are smoothly dilated between their sites of division, so as to give a “string-of-sausages” appearance in a sialogram, there is still a good chance of clinical recovery (Fig. 15). However, where the intraglandular ducts are irregularly and grossly dilated, so as to form cavities rather than tubes, and where in a well-filled gland some of the smaller ducts are not demonstrated, then histologic section will reveal an intense acute and chronic inflammatory infiltration with considerable destruction of acini (Fig. 42). Even if the obstructing calculus is removed, a gland with such changes will remain infected and is best excised. OPERATIVE
PROCEDURE
Because the tongue is an awkward organ to retract, access to the posterior part of the submandibular duct is difficult and the field of operation is small. Furthermore, the lingual nerve lies in close relationship to the duct and can be damaged by blind surgical intervention. An orderly dissection of the area, with the patient under a general anesthetic so that retraction of the tongue is not resisted, offers the best chance of success. The side of the tongue is retracted and the floor of the mouth is infiltrated laterally with a solution containing 1 part Adrenalin in 240,000 parts normal 1. . 1 --- ll”L -- -4 +---**+~~r.n the sublingual reins. The muL(WIIIIUu”:,,,I”*L , LULL ‘L11g ’LUILL.II L” yLL*lLLtiuLu
Volume 25 Number 4
Anatomic
surgery
for
salivary
calculi
529
Fig. 16. A, A view of the incision in the floor of the mouth, made after insertion of a stay suture anteriorly and infiltration of the tissues with vasoconstrictor. B, The duct has been isolated and the blades of a pair of artery forceps passed under it. The forceps grasp a thread which will be used to control the duct during the further dissection.
cous membrane over the duct is incised opposite the premolar teeth, and the wound is deepened with sharp-pointed scissors (Fig. 16, A). The duct is found and mobilized as described for anterior calculi, and the points of a pair of College tweezers or a pair of mosquito artery forceps are passed gently under it (Fig. 16, B) . A length of silk thread is grasped in the tweezers and drawn under the duct to form a stay suture. By following the duct backward, it is possible to identify the lingual nerve at the point where is passes under the duct (Fig. 17). Once the lingual nerve has been seen, the floor of the mouth can be opened more boldly, and the incision can be extended backward with scissors so as to expose both duct and nerve. A pair of fine, curved artery forceps is passed under the nerve opposite the lower second molar (Fig. 17) and, with their aid, a st,rip of narrow tape is drawn through to form a retractor for the nerve. In order to retract the lateral margin of the wound effe&ively, sutures are passed through the lateral flap and through the mucoperiosteum lateral to the upper molars (Figs. 17 and 38). As they are tied, the flap is drawn upward and outward over the lower molar teeth. Special care is taken in the identification and retraction of the lingual nerve hecaus~. of its relationship to the submandibular clurt. During fetal life the lingual nerve 1~~s through the mandibular arch to the lingual swellings, which form the contribution from t,he mandibular arch to the developing tongue. As these swellings enlarge posteriorly to submerge the tuberculum impar, they carry the lingual nerves with them, so that the nerves swing medially across the floor of the mouth to enter the tongue. The submandibular salivary gland and duct develop independently from the epithelium of the floor of the mouth at a later stage, In its development, therefore, the duct passes backward over the lingual nerve where it curves medially into t,he tongue. More posteriorly, the duct lies first on t,he lingual aspect of the nerve and then below it.
OS., ox. & O.P. April, 196s
Fig.
I7
B
Fig.
18
Fig. 17’. The duct has been exposed to a point where the lingual nerve CI‘OSSCS beneath it. The blades of the College tweezers support the lingual nerve lateral to the duct. The arrows point to the nerve medial to the duct. Here it travels over the sublingual veins. The lobulated tissue Iateral to the forceps is the sublingual gland. Pig. 18. a, A tape has been passed under the lingual nerve and the nerve has been drawn laterally. The arrow points to the lingual nerve proximal to the tape. The duct is seen turning down to enter the gland, and the upper pole of the gland is seen immediately medial to the lingual nerve. B. The calculus lies at the point where the duct enters the gland, and in this photograph the duet has been incised, releasing the calculus. Notice how close the lingual nerve is to the calculus.
The lingual nerve enters the operative field from the lingual aspect of the third molar region, where it lies against the mandible beneath the mandibular origin of the superior constrictor and immediately below the lower end of the pterygomandibular ligament. It lies next between the mucosa of the alveolar process and the periosteum and then passes out into the floor of the mouth. At this stage it becomes attached by connective tissue to the upper pole of the submandibular gland, immediately behind the point at which the duct emerges from the gland. For a short distance, therefore, the duet lies below the nerve (Fig. IS). The submandibular duct emerges from the upper and anterior part of the
Volume 25 Number 4
Anatomic
suryery
for
salivary
calculi
531
upper pole of the gland, and the deep part of the gland runs forward below and a little lateral to the duct. In some persons the upper border of the deep part is attached to the duct by a narrow strip of connective tissue; in others, in whom the deep part is large, it bulges up on the lateral side of the duct in line with the posterior sublingual salivary glands. Where the latter state of affairs exists, the lingual nerve comes to lie between the deep part of the gland and the duct for, as it passes forward, the nerve takes up a position on the lateral aspect. of the duct. Farther forward still, and just before it crosses under the duct, the nerve lies between the duct and the posterior sublingual gland (Fig. 1’7). In view of the relationship of the lingual nerve to the alveolar process and the posterior end of the mylohyoid ridge, it is difficult at first to see how it comes to lie above the upper pole of the gland. However, it should be remembered that the mylohyoid ridge protrudes medially and that the superficial part of the submandibular gland lies in a depression in the medial surface of the mandible below the mylohyoid ridge. Although the posterior end of the duct and the deep part of the gland lie above the mylohyoid muscle, they lie below the level of the mylohyoid ridge, since the posterior border of the mylohyoid muscle slopes forward and steeply downward as well as medially on its way to the hyoid bone. At this point, therefore, the lingual nerve is able to pass forward and medially from the lingual aspect of the third molar region to lie above the upper pole of the gland. Thus, it can be seen that, unless the lingual nerve is mobilized and drawn laterally, there is danger that it might be damaged when the duct is incised to release a stone (Fig. 18). At this stage in the operation it helps if an assistant pushes upward against the lower pole of the gland. This raises the upper pole in the wound. To stabilize the tissues further, another silk thread can be passed around the duct close to the gland and, if possible, two additional stay sutures should be inserted-one in the posterior edge of the mylohyoid a.nd another in the upper pole of the gland. As in the case of anterior calculi, the calculus sometimes may be seen or felt through the wall of the duct. If so, the duct is incised over the calculus (Fig. 18, B). Should it not, be seen, the duct should be opened at a likely spot and gently explored. When the calculus is grasped, it is important to take care that it does not slip from the instrument, as it might easily drop over the edge of the mylohyoid and prove difficult, to recover. Leaving it in the tissues would be inviting trouble, as the calculus is likely to be infected. Indeed, another argument in favor of the approach tlescrib4 here is that, there is lrss chance of losing a calrulus in a sizable wound t.han in the wound c*rratecl by the short incision commonly employed. To close the wound, the tape and stay sutures are removed and the incision in the mucous mcmhrane is approximated with just enough black silk sutures to keep it from gaping.
VOLUME
25
NUMBER
4
APRIL,
PATHOLOGY
1968
Operative oral surgery
Anatomic surgery for salivary calculi Part III. Calculi
Q. R. Stwal-d, THE
LONDON
in the posterior
part
M.D.X., B.D.X.R.C.S., HOSPITAL
MEDICAL
of the submandibular
duct
X.B., B.8., London, England
COLLEGE
C
alculi which develop in the posterior segment of the extraglandular part of the duct or in the intraglandular part of the duct may reach a large size without the paGent being awa.re of their presence. The internal diameter of the duct in this region is normally of a moderate size, a,nd it becomes dilated to a greater diameter as a result of the partial obstruction caused by the presence of a calm~lns, F:ven with such evidence of partial obstruction, sufEcient saliva may pass around the ralcnlu~ for the patient. to be unawa,rc of the obstruction for many years. Sn obstruction sufficient to cause symptoms can occur in one of two ways: i 1) the stone may increase in size to a point where saliva will only leak around it very slowly or (2.) infection may supervene. Should the saliva in the dilated ducts behind the stone became infected, an acute or subacute sialoadenitis will result. The inflamed duct will swell and tighten about the calculus, and the salivary obstruct.ion will be intensified. Depending on the parts played by 525
OS, O.M. & O.P. April, 1968
infection or obstruction, the patient will complain of an inflammatory swelling of the floor of the mouth and submandibular region or of a swelling of the gland during salivation. In the absence of an acute infection, an attempt should be made to palpate the stone. The index finger of one hand is passed into the mouth and under the lateral margin of the tongue. The mouth should be partly closed to help the patient relax the floor of the mouth, and the pulpal aspect of the finger should be turned downward and slightly laterally. With the fingers of the other hand, the lower pole of the submandibular gland is palpated in the submandibular region and pressed upward toward the examining finger. The upper pole of the gland will be felt moving under the finger, and the stone may be palpated as a hard mass near the gland. The gland itself should also be examined, and its size and consistency should be noted. When an otherwise normal gland or one which has only recently been inflamed is distended with saliva because of an obstruction in the duct, the substance of the gland will still feel elastic. When the gland feels firm and inelastic, it is fibrosed and probably has been chronically infected for many years. The preoperative assessment is mainly concerned with two factors: (1) whether the calculus is accessible from the mouth and the gland is likely to recover from the affects of chronic obstruction and infection and (2) whether the gland is so diseased that recovery is impossible. Assessment of the state of the gland depends upon the history, the physical examination, and the sialogram. Should the patient give a history of intermittent
Fig. 14. A posterior main
duct leaves
oblique occlusal radiograph the gland. (From Seward: British
of a ca.lculus at the point where Dental Journal 115: 266, 1963.)
the
Volume 25 Number 4
Anatomic
surgery
for
salivary
calculi
527
attacks of swelling or acute infection over a period of many years, then it is probable that the gland has suffered irreparable damage. Similarly, a gland that is small and hard on palpation has probably suffered severe damage and is greatly scarred. Should there be fistulas between the duct and the floor of the mouth where previous stones ha.ve ulcerated through and have been discharged sponta.neously, then it is likely that the gland has suffered severely. Assessment of the position of the ca,lculus depends upon the examination, plain radiography, and sialography. A calculus that can be felt clearly from the mouth can be removed via the mouth. If it cannot be palpated, however, then the assessment of its position is dependent upon the radiographic examination. Although in plain radiographs a small percentage of posterior calculi will be shown at the back edge of a central true occlusal film of the floor of the mouth, the majority will be demonstrated only by a posterior oblique occlusal view (Fig. 14). In other words, if the calculus is not projected onto the film by the central true occlusal technique, then it is not amenable to removal by the method used for anterior calculi and must be treated either as a posterior calculus or as a calculus in the gland. An oblique lateral jaw radiograph is valuable for, with experience, a preliminary assessment can be made of the position of a calculus in the posterior part of the duct tree by noting its position in relationship to the mandible. Compared with the other means of assessment, a good sialogram, if one can be obtained, is invaluable in estimating both the position of the stone and the condition of the gland. Provided the duct system has been well filled, there should be litt,le difficulty in locating the stone with considerable accuracy (Fig. 15). Even when the sialographic injection has been incomplete, the films may
Fig. 15 . &4 sialogram $f .~- c-_---u&%&z ‘shdwii ‘in c_ immediately T proximal to the origin of th .e tribntaxy ...I.... ~-111 a...--2 ar, ^L AL.. -^. Such a ealc:UIUS WM LIJIS AVUUI MIC pint where within the borders of the gland. Calculi proximal glandular. (From Seward: British Dental Journal
ying
%ig. 14 demonstrates th .e talc :ulus duct from the upper p(de! of the &cl!and. the duct emerges from tl 1e da nd clr just to this point will undou .bl :edl: * be il xtra115: 266, 1963.)
O.S., O.M. & O.P. April, 1968
still be valuable as long as the main duct as far as the calculus has been completely filled. If, aside from posterior sublingual gland ducts, no tributary ducts are visible anterior to the calculus, then it is probable that the stone lies in the extraglandular pa.& of the duct. Assessment of the condition of the gland itself by sialographic study depends upon filling of the intraglandular ducts, and this is not always easy when there is a calculus in the main duct. If only one calculus is present, it is frequently possible, with patience on the part of both the operator and the patient, to persist with a steady injection until enough contrast medium to outline the intraglandular ducts has passed the obstruction. Inevitably there will be a tendency for the contrast solution to reflux, but if the fusiform “blob” on the cannula is kept firmly against the duct orifice, the amount of reflux can be reduced to a reasonable level. In some instances the examination proves too tedious for the patient and has to be abandoned before the gland has been properly filled. At times, therefore, it can be difficult to distinguish between incomplete filling of the duct tree and destruction of some of the smaller ducts by disease. When there is more than one sizable calculus in the duct, it is unusual to get the fluid past the second calculus and a sialographic assessment of the gland is impossible. For obvious reasons, there are few histologic examinations of glands which have been obstructed by small stones, where symptoms have been of recent onset and where there is a sialographically normal intraglandular duct system. In those instances in which sections from such glands are examined, however, they may show a surprising degree of infiltration with inflammatory cells, including polymorphonuclear leukocytes. Presumably, the inflammatory reaction is reversible, for after such a calculus has been removed the gland appears to function normally and will remain symptomless unless another stone forms. Even if the larger intraglandular ducts are smoothly dilated between their sites of division, so as to give a “string-of-sausages” appearance in a sialogram, there is still a good chance of clinical recovery (Fig. 15). However, where the intraglandular ducts are irregularly and grossly dilated, so as to form cavities rather than tubes, and where in a well-filled gland some of the smaller ducts are not demonstrated, then histologic section will reveal an intense acute and chronic inflammatory infiltration with considerable destruction of acini (Fig. 42). Even if the obstructing calculus is removed, a gland with such changes will remain infected and is best excised. OPERATIVE
PROCEDURE
Because the tongue is an awkward organ to retract, access to the posterior part of the submandibular duct is difficult and the field of operation is small. Furthermore, the lingual nerve lies in close relationship to the duct and can be damaged by blind surgical intervention. An orderly dissection of the area, with the patient under a general anesthetic so that retraction of the tongue is not resisted, offers the best chance of success. The side of the tongue is retracted and the floor of the mouth is infiltrated laterally with a solution containing 1 part Adrenalin in 240,000 parts normal 1. . 1 --- ll”L -- -4 +---**+~~r.n the sublingual reins. The muL(WIIIIUu”:,,,I”*L , LULL ‘L11g ’LUILL.II L” yLL*lLLtiuLu
Volume 25 Number 4
Anatomic
surgery
for
salivary
calculi
529
Fig. 16. A, A view of the incision in the floor of the mouth, made after insertion of a stay suture anteriorly and infiltration of the tissues with vasoconstrictor. B, The duct has been isolated and the blades of a pair of artery forceps passed under it. The forceps grasp a thread which will be used to control the duct during the further dissection.
cous membrane over the duct is incised opposite the premolar teeth, and the wound is deepened with sharp-pointed scissors (Fig. 16, A). The duct is found and mobilized as described for anterior calculi, and the points of a pair of College tweezers or a pair of mosquito artery forceps are passed gently under it (Fig. 16, B) . A length of silk thread is grasped in the tweezers and drawn under the duct to form a stay suture. By following the duct backward, it is possible to identify the lingual nerve at the point where is passes under the duct (Fig. 17). Once the lingual nerve has been seen, the floor of the mouth can be opened more boldly, and the incision can be extended backward with scissors so as to expose both duct and nerve. A pair of fine, curved artery forceps is passed under the nerve opposite the lower second molar (Fig. 17) and, with their aid, a st,rip of narrow tape is drawn through to form a retractor for the nerve. In order to retract the lateral margin of the wound effe&ively, sutures are passed through the lateral flap and through the mucoperiosteum lateral to the upper molars (Figs. 17 and 38). As they are tied, the flap is drawn upward and outward over the lower molar teeth. Special care is taken in the identification and retraction of the lingual nerve hecaus~. of its relationship to the submandibular clurt. During fetal life the lingual nerve 1~~s through the mandibular arch to the lingual swellings, which form the contribution from t,he mandibular arch to the developing tongue. As these swellings enlarge posteriorly to submerge the tuberculum impar, they carry the lingual nerves with them, so that the nerves swing medially across the floor of the mouth to enter the tongue. The submandibular salivary gland and duct develop independently from the epithelium of the floor of the mouth at a later stage, In its development, therefore, the duct passes backward over the lingual nerve where it curves medially into t,he tongue. More posteriorly, the duct lies first on t,he lingual aspect of the nerve and then below it.
OS., ox. & O.P. April, 196s
Fig.
I7
B
Fig.
18
Fig. 17’. The duct has been exposed to a point where the lingual nerve CI‘OSSCS beneath it. The blades of the College tweezers support the lingual nerve lateral to the duct. The arrows point to the nerve medial to the duct. Here it travels over the sublingual veins. The lobulated tissue Iateral to the forceps is the sublingual gland. Pig. 18. a, A tape has been passed under the lingual nerve and the nerve has been drawn laterally. The arrow points to the lingual nerve proximal to the tape. The duct is seen turning down to enter the gland, and the upper pole of the gland is seen immediately medial to the lingual nerve. B. The calculus lies at the point where the duct enters the gland, and in this photograph the duet has been incised, releasing the calculus. Notice how close the lingual nerve is to the calculus.
The lingual nerve enters the operative field from the lingual aspect of the third molar region, where it lies against the mandible beneath the mandibular origin of the superior constrictor and immediately below the lower end of the pterygomandibular ligament. It lies next between the mucosa of the alveolar process and the periosteum and then passes out into the floor of the mouth. At this stage it becomes attached by connective tissue to the upper pole of the submandibular gland, immediately behind the point at which the duct emerges from the gland. For a short distance, therefore, the duet lies below the nerve (Fig. IS). The submandibular duct emerges from the upper and anterior part of the
Volume 25 Number 4
Anatomic
suryery
for
salivary
calculi
531
upper pole of the gland, and the deep part of the gland runs forward below and a little lateral to the duct. In some persons the upper border of the deep part is attached to the duct by a narrow strip of connective tissue; in others, in whom the deep part is large, it bulges up on the lateral side of the duct in line with the posterior sublingual salivary glands. Where the latter state of affairs exists, the lingual nerve comes to lie between the deep part of the gland and the duct for, as it passes forward, the nerve takes up a position on the lateral aspect. of the duct. Farther forward still, and just before it crosses under the duct, the nerve lies between the duct and the posterior sublingual gland (Fig. 1’7). In view of the relationship of the lingual nerve to the alveolar process and the posterior end of the mylohyoid ridge, it is difficult at first to see how it comes to lie above the upper pole of the gland. However, it should be remembered that the mylohyoid ridge protrudes medially and that the superficial part of the submandibular gland lies in a depression in the medial surface of the mandible below the mylohyoid ridge. Although the posterior end of the duct and the deep part of the gland lie above the mylohyoid muscle, they lie below the level of the mylohyoid ridge, since the posterior border of the mylohyoid muscle slopes forward and steeply downward as well as medially on its way to the hyoid bone. At this point, therefore, the lingual nerve is able to pass forward and medially from the lingual aspect of the third molar region to lie above the upper pole of the gland. Thus, it can be seen that, unless the lingual nerve is mobilized and drawn laterally, there is danger that it might be damaged when the duct is incised to release a stone (Fig. 18). At this stage in the operation it helps if an assistant pushes upward against the lower pole of the gland. This raises the upper pole in the wound. To stabilize the tissues further, another silk thread can be passed around the duct close to the gland and, if possible, two additional stay sutures should be inserted-one in the posterior edge of the mylohyoid a.nd another in the upper pole of the gland. As in the case of anterior calculi, the calculus sometimes may be seen or felt through the wall of the duct. If so, the duct is incised over the calculus (Fig. 18, B). Should it not, be seen, the duct should be opened at a likely spot and gently explored. When the calculus is grasped, it is important to take care that it does not slip from the instrument, as it might easily drop over the edge of the mylohyoid and prove difficult, to recover. Leaving it in the tissues would be inviting trouble, as the calculus is likely to be infected. Indeed, another argument in favor of the approach tlescrib4 here is that, there is lrss chance of losing a calrulus in a sizable wound t.han in the wound c*rratecl by the short incision commonly employed. To close the wound, the tape and stay sutures are removed and the incision in the mucous mcmhrane is approximated with just enough black silk sutures to keep it from gaping.