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Unusual origins of the buccal and mylohyoid nerves
Unusual origins of the buccal and mylohyoid nerves N. G. Jablonski, Hong Kong
A.B., Ph.D.,* C. M. Cheng,** L. C. Cheng,** and H. M. Cheung,**
FACULTY OF MEDICINE. UNIVERSITY
OF HONG KONG
Dissection of the mandibular nerve in a cadaver of southern Chinese origin showed the mylohyoid nerve arising from the lingual nerve and the buccal nerve arising from the inferior alveolar nerve within the mandibular ramus. It is estimated that this variation in the origin of the buccal nerve occurs in 6.1% of the southern Chinese population. (ORAL SURG. ORAL MED. ORAL PATHOL.. 60~487-488,
1985)
V ariations in the branching pattern or topographic relationships of the mandibular nerve frequently account for the failure to obtain adequate local anesthesia in routine oral and dental procedures and for the unexpected injury to branches of the nerve during surgery. This report concerns an unusual case of two relatively rare variations in the branching pattern of the mandibular nerve that were encountered during the dissection of a 54-year-old cadaver of southern Chinese (Hong Kong) origin. In this person the buccal nerve originated from the inferior alveolar nerve within the ramus of the mandible, traversed a narrow, anterosuperiorly oriented retromolar canal, and emerged through a small foramen in the retromolar fossa between the oblique line and the buccinator crest. The nerve then passed forward and sharply upward to penetrate the buccinator muscle. The mylohyoid nerve arose as a small branch from the inferior aspect of the lingual nerve. Both variations were found on the left side only. Origin of the mylohyoid nerve from the lingual nerve has not, to our knowledge, been previously reported. Although the variation in the origin of the buccal nerve has been described by several workers’*4and its significance to local anesthesia has been discussed,*% 5 little is known of the frequency of this variation in major human populations. Inke and Ernst* found retromolar canals in 6.9% of the adult Caucasoid skulls and in 11.9% of the Mongoloid and Negroid skulls they examined. Unfortunately, neither the *Lecturer, Department **Student.
of Anatomy.
sizes of their racial samples nor the frequencies of unilateral and bilateral canals were specified. An unnamed nerve was found in the contents of one of the two retromolar canals they examined histologically. An exceptionally high frequency of retromolar canals in a population of Argentinian mestizos was reported by Schejtman and colleagues.3Retromolar canals were found in thirteen of eighteen heads dissected; in five of these, canals were present bilaterally. Myelinated nerves were found in seven of the eight retromolar canals whose contents they examined. We attempted to determine the frequency of the variation in the origin of the buccal nerve in the local southern (Hong Kong) Chinese population by counting the retromolar foramina found in skulls of local origin. Retromolar foramina similar in size and relative position to that of the original cadaver were found in 14 of the 23 1 skulls examined (6.1%); in one of these, the foramen was present bilaterally. If these foramina were traversed by buccal nerves of aberrant origin, as was indicated in most of the casesdissected by Schejtman and associates,3 this variation is present in a small but significant proportion of the southern Chinese population. This figure is of interest to dental practitioners in Asia and elsewhere, becauseimmigrants from Hong Kong and neighboring regions of southern China constitute large proportions of the “Chinatowns” worldwide. REFERENCES I. Turner W: On some variations in the arrangement of the nerves of the human body. Nat Hist Rev 4: 612-617, 1864. 2. lnke G, Ernst T: Anatomische Variationen als miigliche 487
488 Jablonski et al.
Oral Surg. November. I985
Ursachen fiir Fehlschllge bei lege artis durchgefiihrter Leitungsanasthesie am N. alveolaris inferior, Dtsch Zahn-MundKieferheilkd 39: 298-308, 1963. 3. Schejtman R, Devoto FCH, Arias NH: The origin and distribution of the elements of the human mandibular retromolar canal. Arch Oral Biol 12: 1261-1267, 1967. 4. Singh S: Aberrant buccal nerve encountered at third molar surgery. ORAL SURG ORAL MED ORAL PATHOL 52: 142, 1981. 5. Angelopoulos AP: Anatomical variations in thedistribution of
BOUND
VOLUMES
AVAILABLE
the mandibular nerve and their significance to regional anesthesia. J Okla Dent Assoc 56: 19-29, 1966. Reprint requests to: Dr. N. G. Jablonski Department of Anatomy University of Hong Kong 7/F., Prince Philip Dental Hospital 34 Hospital Rd. Hong Kong
TO SUBSCRIBERS
Bound volumes of ORAL SURGERY, ORAL MEDICINE and ORAL PATHOLOGY are available to subscribers (only) for the 1985 issues from the Publisher, at a cost of $36.75 ($47.75 international) for Vol. 59 (January-June) and Vol. 60 (July-December). Shipping charges are included. Each bound volume contains a subject and author index and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Payment must accompany all orders. Contact The C. V. Mosby Company, Circulation Department, 11830 Westline Industrial Drive, St. Louis, Missouri 63 146, USA; phone (800) 325-4177, ext. 35 I. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular journal subscription.
A.B., Ph.D.,* C. M. Cheng,** L. C. Cheng,** and H. M. Cheung,**
FACULTY OF MEDICINE. UNIVERSITY
OF HONG KONG
Dissection of the mandibular nerve in a cadaver of southern Chinese origin showed the mylohyoid nerve arising from the lingual nerve and the buccal nerve arising from the inferior alveolar nerve within the mandibular ramus. It is estimated that this variation in the origin of the buccal nerve occurs in 6.1% of the southern Chinese population. (ORAL SURG. ORAL MED. ORAL PATHOL.. 60~487-488,
1985)
V ariations in the branching pattern or topographic relationships of the mandibular nerve frequently account for the failure to obtain adequate local anesthesia in routine oral and dental procedures and for the unexpected injury to branches of the nerve during surgery. This report concerns an unusual case of two relatively rare variations in the branching pattern of the mandibular nerve that were encountered during the dissection of a 54-year-old cadaver of southern Chinese (Hong Kong) origin. In this person the buccal nerve originated from the inferior alveolar nerve within the ramus of the mandible, traversed a narrow, anterosuperiorly oriented retromolar canal, and emerged through a small foramen in the retromolar fossa between the oblique line and the buccinator crest. The nerve then passed forward and sharply upward to penetrate the buccinator muscle. The mylohyoid nerve arose as a small branch from the inferior aspect of the lingual nerve. Both variations were found on the left side only. Origin of the mylohyoid nerve from the lingual nerve has not, to our knowledge, been previously reported. Although the variation in the origin of the buccal nerve has been described by several workers’*4and its significance to local anesthesia has been discussed,*% 5 little is known of the frequency of this variation in major human populations. Inke and Ernst* found retromolar canals in 6.9% of the adult Caucasoid skulls and in 11.9% of the Mongoloid and Negroid skulls they examined. Unfortunately, neither the *Lecturer, Department **Student.
of Anatomy.
sizes of their racial samples nor the frequencies of unilateral and bilateral canals were specified. An unnamed nerve was found in the contents of one of the two retromolar canals they examined histologically. An exceptionally high frequency of retromolar canals in a population of Argentinian mestizos was reported by Schejtman and colleagues.3Retromolar canals were found in thirteen of eighteen heads dissected; in five of these, canals were present bilaterally. Myelinated nerves were found in seven of the eight retromolar canals whose contents they examined. We attempted to determine the frequency of the variation in the origin of the buccal nerve in the local southern (Hong Kong) Chinese population by counting the retromolar foramina found in skulls of local origin. Retromolar foramina similar in size and relative position to that of the original cadaver were found in 14 of the 23 1 skulls examined (6.1%); in one of these, the foramen was present bilaterally. If these foramina were traversed by buccal nerves of aberrant origin, as was indicated in most of the casesdissected by Schejtman and associates,3 this variation is present in a small but significant proportion of the southern Chinese population. This figure is of interest to dental practitioners in Asia and elsewhere, becauseimmigrants from Hong Kong and neighboring regions of southern China constitute large proportions of the “Chinatowns” worldwide. REFERENCES I. Turner W: On some variations in the arrangement of the nerves of the human body. Nat Hist Rev 4: 612-617, 1864. 2. lnke G, Ernst T: Anatomische Variationen als miigliche 487
488 Jablonski et al.
Oral Surg. November. I985
Ursachen fiir Fehlschllge bei lege artis durchgefiihrter Leitungsanasthesie am N. alveolaris inferior, Dtsch Zahn-MundKieferheilkd 39: 298-308, 1963. 3. Schejtman R, Devoto FCH, Arias NH: The origin and distribution of the elements of the human mandibular retromolar canal. Arch Oral Biol 12: 1261-1267, 1967. 4. Singh S: Aberrant buccal nerve encountered at third molar surgery. ORAL SURG ORAL MED ORAL PATHOL 52: 142, 1981. 5. Angelopoulos AP: Anatomical variations in thedistribution of
BOUND
VOLUMES
AVAILABLE
the mandibular nerve and their significance to regional anesthesia. J Okla Dent Assoc 56: 19-29, 1966. Reprint requests to: Dr. N. G. Jablonski Department of Anatomy University of Hong Kong 7/F., Prince Philip Dental Hospital 34 Hospital Rd. Hong Kong
TO SUBSCRIBERS
Bound volumes of ORAL SURGERY, ORAL MEDICINE and ORAL PATHOLOGY are available to subscribers (only) for the 1985 issues from the Publisher, at a cost of $36.75 ($47.75 international) for Vol. 59 (January-June) and Vol. 60 (July-December). Shipping charges are included. Each bound volume contains a subject and author index and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Payment must accompany all orders. Contact The C. V. Mosby Company, Circulation Department, 11830 Westline Industrial Drive, St. Louis, Missouri 63 146, USA; phone (800) 325-4177, ext. 35 I. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular journal subscription.