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Accessory Mandibular Foramen During Dental Implant Placement: Case Report and Review of Literature Brooke Pancer, DMD,* Carlos Garaicoa-Pazmiño, DDS,† and Jill D. Bashutski, DDS, MS‡
he interforaminal region is a common area for dental implant placement in the mandible to support fixed partial dentures and overdentures. Although considered a relatively safe surgical area, it is not free of risks and complications. In fact, the incidence of neurosensory disturbance after implant placement in the region of the mental foramen (MF) may be as high as 43%.1–6 Neurosensory impairment may occur at all stages of implant surgery including dental injections, incisions, flap reflection and retraction, osteotomy preparation, implant placement, suturing, and postoperative edema and hematoma. Moreover, damage to anatomical structures remains the major cause of legal action against the dental practitioner.7 As such, proper understanding of vital anatomical structures, surgical principles, implant systems, and treatment planning is the key to reducing neurovascular complications.
T
*Graduate Student, Graduate Periodontics, Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI. †PostDoctoral Student, Graduate Periodontics, Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI. ‡Clinical Assistant Professor, Director of Predoctoral Periodontics, Division of Periodontics, Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI.
Reprint requests and correspondence to: Jill. D. Bashutski, DDS, MS, Division of Periodontics, Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, 1101 North University Avenue, Room 3349, Ann Arbor, MI 481091078, Phone: 734-763-3759, E-mail: jillbash@umich. edu ISSN 1056-6163/14/02302-116 Implant Dentistry Volume 23 Number 2 Copyright © 2014 by Lippincott Williams & Wilkins DOI: 10.1097/ID.0000000000000056
Accurate knowledge of vital anatomical structures, such as the inferior alveolar nerve, mental nerve, and mental foramen, is critical to achieve favorable results during oral surgical procedures and dental implant placement. Although uncommon, variations in mandibular foramina have been reported and if unnoticed and, as a result, injured, may lead to patient morbidity, neurosensory disturbances, and other undesired complications. We present a case report of identification of an accessory mandibular foramen (AMF) encountered during placement of 2 dental implants for a mandibular implant-retained overdenture and demonstrate appropriate
management. In addition, we propose a more reasonable terminology for such accessory foramina so as to facilitate communication through common terminology among health care providers. As conventional radiography (periapical and panoramic films) may not allow for proper identification of such anatomical variations, conebeam computed tomography may be useful in the diagnosis of AMF during treatment planning of dental implants in the mandible. (Implant Dent 2014;23:116–124) Key Words: anatomic variation, cone-beam computed tomography, dental implant
Accurate knowledge of the inferior alveolar nerve, the mental nerve, and MF is critical when performing oral surgical procedures in the interforaminal region. The inferior alveolar nerve is a branch of the mandibular nerve (third division of the trigeminal cranial nerve) that carries both sensory and motor fibers. It enters the mandibular foramen, traverses the mandible anteroinferiorly from lingual to buccal within the mandibular canal where it supplies the molar teeth. It then divides into the dental (incisal) nerve, which continues medially though the incisive canal and the mental bundle, which exits laterally through the MF. In addition to vessels, 3 neural branches emerge from the MF: the mental, labial, and gingival nerves, which collectively innervate the skin
and mucous membranes of the lower lip and chin, and the gingiva from the second premolar to the central incisor.8–10 The MF has been found to be located between the first and second premolars 58% of the time and directly apical to the second premolar 42% of the time.11 Even though the pathway and anatomy of the inferior alveolar nerve and the mental nerve have been well described, anomalies of such structures may take place at any location along their course. A variety of patterns exist regarding number, position, and course, so it should not be assumed that there is simply 1 mandibular canal and 1 MF in the locations described above. One significant anatomical variation regarding the inferior alveolar
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Fig. 1. A, Preoperative panoramic radiograph. B, Preoperative panoramic radiograph with radiographic guide. C, Preoperative cephalometric radiograph with radiographic guide.
nerve is a bifid mandibular canal, which has been reported to have an occurrence of 0.08% to 1%.12–15 In addition, there may be a unilateral absence of the mandibular canal, often associated with unilateral agenesis of teeth and hemifacial microsomia.16–19 There may also be an extension of the inferior alveolar nerve anterior to the MF before exiting the canals, termed the anterior loop. This has been found to occur with a prevalence ranging from 28% to 94% with large variations in length ranging from 0 to 9 mm and a mean of 2 to 4 mm.11,20–25 Regarding the MF, variations may take place in terms of location, with reports of it being found anteriorly by the canine or posteriorly by the first or even second molar.20–22,25–27 In addition, more than 1 MF may be present on each or both sides of the mandible and may take place at any location along the mandibular canal. The nomenclature and categorization of
such foramina is widely variable in the literature.12,14,27–32 Thus, the authors will use the term accessory mandibular foramen (AMF) (in the case of a single additional foramen) or foramina (when multiple additions are noted) to identify these anomalies so as to include all possible locations and sizes of such defects. Radiographic and cadaver studies have reported an occurrence of AMF ranging from 0.88% to 10.66%.28,33 The purpose of this article was to present a case report of the identification of an AMF, discuss appropriate terminology for these anatomical variations, and demonstrate appropriate management with respect to dental implant placement. Radiographic and clinical interpretations of this case are considered and discussed with respect to methods of detecting such anatomical deviations in the goal of preventing complications during dental implant placement. In addition, we will propose a more reasonable terminology for such accessory foramina so as to facilitate communication through common terminology among healthcare providers.
CASE REPORT
Fig. 2. Dissection of the right mental foramen bundle (MF) and the AMF bundle. Note the implant osteotomy side 4 mm mesial to the AMF.
An 84-year-old Caucasian male patient was referred to the Graduate Periodontal clinic at the University of Michigan School of Dentistry for 2 mandibular anterior dental implants for an implant-retained overdenture. The patient’s medical history consisted of asthma, emphysema, history of a myocardial infarction in 1986, benign prostatic hypertrophy, seasonal allergies, slight hearing impairment, hypothyroidism, and osteoarthritis. He was
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taking the following medications: fluticasone/salmeterol, 81 mg aspirin, levothyroxine, fix spacing lisinopril, lovastatin, multivitamins, tiotropium bromide, and tamsulosin. The patient reported a 60 pack-year history of smoking but quit in 1986. Regarding his dental history, he reported extractions of his mandibular and maxillary teeth 4 years ago as a result of extensive periodontal disease. He wore a maxillary complete denture but was unhappy with the mandibular denture because of its poor fit. Thorough informed consent was provided with respect to risk, benefit, and procedure cost. No abnormal findings were noted on clinical and radiographic examination (Fig. 1, A). Radiographic and surgical implant guides were fabricated before surgery based upon periapical, panoramic, and cephalometric conventional radiographs (Fig. 1, B and C). The patient initiated a 10-day course of amoxicillin preoperatively and rinsed with chlorhexidine gluconate 0.12% for 1 minute immediately before surgery. The procedure was done under local dental anesthesia. A midcrestal incision ensuring at least 2 mm keratinized mucosa on either side of the incision line with a midline vertical incision for access were performed followed by full-thickness flap reflection. Elevation of the flap was initiated using an elevator, followed by complete reflection by inserting gauze so as to reflect the tissues without injuring vital structures. Upon reflection, a single MF and bundle were identified on the left hand side, but 2 separate foramina and bundles were noted on the right (Fig. 2). The AMF was positioned approximately 4 mm mesial to the MF and 4 mm from the midline. Because of its proximity to the planned osteotomy site, clinical judgment was used to prepare the implant osteotomy sites such that they were located 4 mm away from the foramina and spaced approximately 12 mm apart so as to maximize the anterior–posterior spread of the restorative unit. Two 4.1 3 13-mm dental implants (Tapered Screw-Vent MTX; Zimmer Dental, Inc., Carlsbad, CA) were placed with primary stability (Fig. 3, A) and covered with healing abutments. The
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Fig. 3. A, Implant positioning. Note sufficient distance (12 mm) between the implants allowing for anterior-posterior spread and the location of the implants with respect to the mandibular midline. B, Panoramic radiograph 2 weeks after dental implant placement revealing adequate distance between implants and from vital structures.
Fig. 4. A, Clinical healing 3 months after implant placement. B, Postoperative panoramic radiograph 3 months after dental implant placement revealing no periimplant bone loss or abnormal findings.
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site was sutured with at the crestal portion and at the releasing incision using a combination of resorbable and nonresorbable sutures. The patient was informed of the risk of paresthesia, analgesics, and an antimicrobial mouth rinse and given thorough postoperative instructions. The patient was advised to abstain from wearing his mandibular denture for 2 weeks. At the 2-week follow-up appointment, the patient did not report any atypical symptoms or signs of paresthesia. Sutures were removed and the mandibular denture was relined with a soft denture reline material (Coe-Soft; GC America Inc., Chicago, IL) so that the patient could resume masticatory function. Healing was within acceptable limits. A panoramic radiograph was taken to confirm appropriate implant position and distance away from vital anatomical structures (Fig. 3, B). The patient was examined at the 4, 6, and 12-week time points. At the 3-month follow-up, a panoramic radiograph was taken to confirm stable marginal and periimplant bone levels and rule out atypical findings (Fig. 4, A). Clinical examination revealed absence of mobility with the reverse torque test, absence of bleeding on probing and exudate; clinically shallow probing depths, and adequate keratinized mucosa around the implants (Fig. 4, B). The implantretained overdenture was delivered at that time.
Table 1. Terminology Considerations for the AMF, True Accessory Mental Foramen, and Nutrient Foramen. Factors Including Continuity From Inferior Alveolar Canal and Nerve, Number, Location, Size, and Contents Are Taken Into Consideration
NSD indicates no significant difference; IAC, inferior alveolar canal; PA, periapical radiograph.
Table 2. Reports of the AMF Based on Sample Size, Incidence, Age, Sex, Population, Location, and Method of Detection Author, Year
Study Design
Age
Byers and Ratcliff, 198348 Serman, 198928
Case report
54
1
Cadaver study
N/A
Zografos and Mutzuri, 198932 Meoli et al, 199349
Cadaver study
Wyatt, 199650
Dario, 200214
Sample Size
Incidence
Sex
Population
Location
Terminology
Caucasian
508
0.88%
N/A
Right, left, African incisive American, Caucasian
Dissection
Ass. w odontogenic keratocyst (third M) 5 unilateral, 2 bilateral
N/A
464
6.68%
230 M, 234 F
Greek
N/A
Dissection
NSD between gender
Case report
41
1
N/A
F
Italian
Left side
CT
Unilateral
Literature review and case report Case report
23
1
N/A
M
African American
Left
Pan
Third M sx
52
1
1% (private practice)
M
Caucasian
Right
Found during tx planning
Bifurcated IAC
N/A
142
7.74%
N/A
Indian
Right, left
CT (not visible w Pan, PA) Dissection
1 bilateral
AMF
62
1
N/A
F
N/A
Left (m root Pan and PA Incidental finding of first M)
N/A
150
10.66%
N/A
Japanese
Right, left (first Mfirst PM area)
CBCT (not visible w Pan)
48
1
N/A
F
Turkish
Right (second PM)
CT (not visible w Pan)
157
7%
48 M, 107 F
Japanese
Right, left
CBCT
Case report
Naitoh et al, 200939
Retrospective
51.5
Bifurcated IAC Mental incisive foramen (ABF) Double mental foramen Double mental foramen Bifurcated IAC
AMF
1.6 3 1.2 mm in size; 1 bilateral, 15 unilateral; most distal and inferior to MF; excluded foramina not connecting to IAC Ass. w odontogenic keratocyst (caninesecond PM). Mesial to MF NSD between gender, diameter, and size; bilateral and unilateral; 1.7 mm2 in size; 1.9 mm diameter; most inferior and distal to MF
AMF
Double mental foramen, AMF by expert AMF
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(continued on next page)
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Balcioglu and Kocaelli, 200947
Pan
Comment
M
Roopa et al, Cadaver 200330 study Case report Cagirankaya and Kansu, 200851 Katakami et al, Retrospective 200833
Right
Detection
N/A
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Table 2. (Continued) Author, Year
Age
Sample Size
De OliveiraRetrospective Santos et al, 201131
N/A
285
Kulkarni et al, 201152 Naitoh et al, 201141
Case report
Thakur et al, 201153
Case report
Imada et al, 201246
Retrospective
Kalender et al, 201240
Retrospective
Sisman et al, 201229
Retrospective 39.7 6 15.9
Retrospective
9.40%
133 M, 152 F
Population Caucasian, Brazilian
Location
Detection
Right, left
CBCT
60, 30, rest N/A
5
40%
1 M, 1 F Japanese
1 Left, 1 bilateral, rest NA
Dissection, CT and CBCT (only 2)
25
1
N/A
M
Indian
Flap
7.70%
130 M, 235 F
Japanese
Right (first M) Right, left
1
N/A
M
Indian
40.9
100
3%
34 M, 66 F
Brazilian
Right (second PM) Right, left
38.6
193
6.50%
92 M, 101 F
Turkish
Right, left
504
10%
307 M, 197 F
Turkish
Right, left
51.7
40
369
Terminology
AMF Only included foramina .1 mm diameter; bilateral and unilateral; single and multiple, 1.95 mm diameter; NSD between gender and population ,1 3 ,1 mm, mesial and ABF distal to MF, contained branches of arteries (facial, buccal, submental) and mental nerve Contained nerve AMF
Excluded nutrient foramina; CBCT, bilateral and unilateral; rotational 1.5 mm2 in size; NSD Pan between location Dissection Distal to MF, chronic pain, tx w mental nerve neurectomy CBCT (not Bilateral and unilateral; 0.93 mm diameter visible w Pan) CBCT Excluded nutrient foramina; NSD between gender, diameter, and location; most inferior to MF; bilateral and unilateral; 1.4 3 1.6 mm in size CT NSD between age, location, and gender; 1.4 mm in diameter; 3 bilateral, 7 unilateral; mesial and distal, superior and inferior to MF
AMF
AMF
AMF
AMF
ABF
ET AL
ABF indicates accessory buccal foramens; MF, mental foramen; N/A, not applicable; NSD, no significant difference; IAC, inferior alveolar canal; PA, perapical radiograph.
Comment
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Cadaver study
Sex
Fuakami et al, 201134
Incidence
ACCESSORY MANDIBULAR FORAMEN DURING DENTAL IMPLANT PLACEMENT
Study Design
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DISCUSSION Several authors described the presence of accessory foramina within the mandible through gross anatomy studies and radiographic images.28–31 The nomenclature and categorization of such foramina are widely variable and confusing. Terms such as multiple mental foramina, mandibular accessory foramina, incisive mental foramina, double mental foramina, retromandibular foramina, accessory mental foramina, accessory buccal foramina, nutrient foramina, interalveolar foramina, additional MF, and incisive foramen have been used to name different anatomical variations of the same structure.28,29,32,34–38 These terms differ based on their location within the mandible, size, and number. AMF should include all additional foramina besides the MF carrying a vital structure. Although some studies claim that they can only be called AMF when there is continuity with the inferior alveolar canal,34,39 advanced imaging may not always be obtained in clinical scenarios, and as such appropriate terminology to obtain a clinical finding must be available. To simplify terminology of these anatomical variations, it is preferred to combine all such defects regardless of number, location, and size and place them under the umbrella of AMF (for a single additional foramen) or foramina (for multiple additions). The sole exceptions include a foramen containing vessels should be termed nutrient foramen and a foramen that has direct continuity to the inferior alveolar canal as demonstrated by cone-beam computed tomography (CBCT) and to the inferior alveolar nerve itself should be termed a true accessory MF. This terminology will serve to facilitate communication among health care providers in both the literature and while discussing clinical cases. An applicable flow chart is depicted in Table 1. The prevalence of AMF has been reported to range from 0.88% to 10.66%.28,33 The formation of these foramina is presumed to be as a result of an early branching of the inferior alveolar nerve before exiting through the MF during the 12th week of gestation.28,39 Additional foramina may also
be associated with bifurcated mandibular canals that carry the inferior alveolar nerve.13 Several studies have evaluated the prevalence, position, and size of AMF and their relationship with ethnicity, sex, and age.33,34 Most studies claim that there is no association between AMF with sex and age.29,31,32,39–41 One study using a considerably larger number and variety of subjects; however, found a higher prevalence in Asian males.42 Although disputed by some,11 others claim that the presence of AMF is higher in certain ethnic groups.27,43 In fact, the prevalence of AMF was 1.4% in American Caucasians, 1.5% in Asian Indians, 5.7% in African Americans, and 9.0% in pre-Columbian Nazca Indians.27 Anatomically, AMF have been described as having smaller diameters as compared with the MF.28,37 Other studies, however, have found no statistical significant difference in this respect.29,31,33,39,40 Such data, however, should be interpreted with caution due to differences in inclusion and exclusion criteria related to nutrient foramina and foramina with a diameter ,1 mm. Numerous tools are available to aid clinicians in understanding their patients’ individual anatomy before surgical intervention. Conventional radiographs including panoramic and periapical images are considered to be the minimum standard of care when treatment planning dental implants as they provide the clinician with valuable information. They do, however, come with limitations including distortion, overlap, and magnification, which may all lead to false interpretation of important anatomical structures.14 CBCT has gain recent popularity in the dental field as it allows for more reliable and accurate 3-dimensional visualization of anatomical structures that may be undetected though traditional radiographic imaging.8,9,44 Moreover, CBCT has been demonstrated to have improved image quality and less magnification and distortion among other tridimensional methods.45 The higher cost and level of radiation associated with CBCTs, however, must also be taken into account. The presence and pathway of the mandibular canal, MF, and AMF in panoramic and periapical radiographic
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images may not be distinct, accurate, or even detectable.46,47 Reasons may include: lack of contrast between the foramen and bone due to the trabecular pattern of bone, thin mandibular bone, thick lingual cortical plate, dark overexposed radiographs, and image distortion.9 The superiority of CBCT in the detection of accessory foramina when compared with traditional radiographs was confirmed in retrospective studies33,41 and is further outlined in Table 2. In fact, Naitoh et al41 found that detection of AMF with panoramic radiographs is ,50% as compared with CBCT images.46,54 Where AMF are identified, special care should be taken to perform safe and successful surgical procedures. Injury to neurovascular bundles contained within these accessory foramina may lead to hemorrhage, paresthesia, dysesthesia, neuropraxia, axonotmesis, neurotmesis, and/or significant patient morbidity.14,55 The identification of accessory foramina and other anatomical variations through tridimensional imagining has proven to be a reliable and accurate tool for presurgical planning. Moreover, it may reduce the rate of unwanted neurovascular complications. Not all anatomical variations may be identified preoperatively. As such, thorough intraoperative examination of vital structures and proper management are needed to ensure the safe placement of dental implants. Foramen may be exposed by using a periosteal elevator to raise a full-thickness mucoperiosteal flap to the mucogingival junction, then using a wet sterile gauze to gently push the mucosa off the bone past the coronal aspect of the foramen so as to protect the nerve from injury. Inserting a blunt curved instrument into the foramen and examining the patency of the distal aspect of the foramen can help to determine the presence of an anterior loop; if patency is not confirmed, then a loop likely exists. A variety of safetyzone recommendations have been made with respect to the minimal distance between the dental implant and nerve, including 2,9 3,3 4,56 and 6 mm.57 So long as reasonable restorative principles can be respected, the dental implant should be placed as far away from the
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nerve as possible. In our clinical case, we were able to place the implant 4 mm anterior to the AMF so as to decrease the risk of a neurosensory complication, while maintaining appropriate interimplant distance and anteroposterior spread of the future overdenture. Complications, however, do arise and as a result proper management is of prime importance. Timely repair of nerve injuries is of critical importance for successful recovery of nerve function. If nerve damage is suspected, a referral to the neurologist, neurosurgeon, or oral maxillofacial surgeon for evaluation and potential surgical correction should be made. If too much time elapses, surgical management may become ineffective and pharmacologic management of chronic pain may be needed. If altered nerve sensation is experienced, a proper diagnosis must be obtained through the use of advanced imaging. It is important to recognize whether the paresthesia, dysesthesia, or dysesthesia is a result of hitting, severing, compressing, or administrating local anesthetic in close proximity to the nerve. If the radiograph demonstrates that the dental implant is encroaching on the nerve, it should be removed or repositioned immediately, and consideration may be given for administering a steroid (locally, through the intravenous line, or orally), antibiotic, and analgesic. If altered sensation results from compression due to swelling or a hemorrhage in close proximity to the nerve, a steroid, antibiotic, and analgesic may also be considered. If the nerve is affected by administration of local anesthesia, the patient may be reassured and followed up over appropriate amount of time to ensure resolution of symptoms. If persistent numbness is still experienced, a steroid, antibiotic, and analgesic may be considered. If symptoms do not resolve with the aforementioned modalities, neurosurgical modalities may need to be implemented and may include external decompression, internal neurolysis, excision of neuroma, neurorrhaphy, nerve graft, nerve sharing, guided nerve regeneration, neurectomy, nerve capping, and nerve redirection.58 If there is insufficient room to place the dental implant, while respecting the
suggested safety zones, the nerve can be repositioned or the ridge can be augmented to create adequate space.10 Nerve lateralization can be performed by raising a mucoperiosteal flap, creating vertical osteotomies distal to the foramen and the second molar along the lateral cortical plate, and then connecting the vertical cuts with a horizontal osteotomy. The cortical window and portion of medullary bone is removed using elevators, the neurovascular bundle is displaced laterally using nerve hooks, the nerve is covered with a dressing or bone wax, and the dental implants may be placed at that time or a later time.59–61 Unlike nerve lateralization, transposition involves the sacrifice of the incisive nerve.61 Although some authors noted no long-term adverse sequelae,60 most authors, however, noted a high rate of transient of permanent sensory dysfunction of up to 54.7% and loss of anterior teeth vitality with nerve transposition postoperatively.2,61,62 The high risks associated with nerve repositioning must be thoroughly considered and as such should not be considered a first-line treatment option.
CONCLUSION Accurate knowledge of the inferior alveolar nerve, mental nerve, and its associated foramen is critical when performing oral surgical procedures and dental implant placement in the mandible. Variations in such anatomical structures, such as AMF, exist so thorough treatment planning is vital to avoid neurosensory complications and potential legal action. The superiority, accuracy, and reliability of CBCT images for the identification of AMF and other anatomical variations over conventional imaging has been well demonstrated and should be considered for presurgical planning. Finally, the surgeon should be aware of, and knowledgeable in, the appropriate management of AMF to achieve safe and favorable results during implant placement.
DISCLOSURE The authors claim to have no financial interest, either directly or
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indirectly, in the products or information listed in the article.
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29. Sisman Y, Sahman H, Sekerci A, et al. Detection and characterization of the mandibular accessory buccal foramen using CT. Dentomaxillofac Radiol. 2012; 41:558–563. 30. Roopa R, Manjunath KY, Balasubramanum V. The direction and location of mental foramen and incidence of accessory mental foramen in south Indian mandibles. Indian J Dent Res. 2003;14:57–58. 31. Oliveira-Santos C, Souza PH, De Azambuja Berti-Couto S, et al. Characterisation of additional mental foramina through cone beam computed tomography. J Oral Rehabil. 2011;38:595–600. 32. Zografos J, Mutzuri A. [Incidence of double mental foramen in a sample of Greek population]. Odontostomatol Proodos. 1989;43:521–523. 33. Katakami K, Mishima A, Shiozaki K, et al. Characteristics of accessory mental foramina observed on limited conebeam computed tomography images. J Endod. 2008;34:1441–1445. 34. Fuakami K, Shiozaki K, Mishima A, et al. Detection of buccal perimandibular neurovascularisation associated with accessory foramina using limited conebeam computed tomography and gross anatomy. Surg Radiol Anat. 2011;33: 141–146. 35. Carter RB, Keen EN. The intramandibular course of the inferior alveolar nerve. J Anat. 1971;108:433–440. 36. Riesenfeld A. Multiple infraorbital, ethmoidal, and mental foramina in the races of man. Am J Phys Anthropol. 1956;14:85–100. 37. Toh H, Kodama J, Yanagisako M, et al. Anatomical study of the accessory mental foramen and the distribution of its nerve. Okajimas Folia Anat Jpn. 1992;69: 85–88. 38. Gahleitner A, Hofschneider U, Tepper G, et al. Lingual vascular canals of the mandible: Evaluation with dental CT. Radiology. 2001;220:186–189. 39. Naitoh M, Hiraiwa Y, Aimiya H, et al. Accessory mental foramen assessment using cone-beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2009;107:289–294. 40. Kalender A, Orhan K, Aksoy U. Evaluation of the mental foramen and accessory mental foramen in Turkish patients using cone-beam computed tomography images reconstructed from a volumetric rendering program. Clin Anat. 2012;25:584–592. 41. Naitoh M, Yoshida K, Nakahara K, et al. Demonstration of the accessory mental foramen using rotational panoramic radiography compared with cone-beam computed tomography. Clin Oral Implants Res. 2011;22:1415–1419.
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42. Hanihara T, Ishida H. Frequency variations of discrete cranial traits in major human populations. IV. Vessel and nerve related variations. J Anat. 2001;199: 273–287. 43. Fishel D, Buchner A, Hershkowith A, et al. Roentgenologic study of the mental foramen. Oral Surg Oral Med Oral Pathol. 1976;41:682–686. 44. Klinge B, Petersson A, Maly P. Location of the mandibular canal: comparison of macroscopic findings, conventional radiography, and computed tomography. Int J Oral Maxillofac Implants. 1989;4: 327–332. 45. Chan HL, Misch K, Wang HL. Dental imaging in implant treatment planning. Implant Dent. 2010;19:288–298. 46. Imada TS, Fernandes LM, Centurion BS, et al. Accessory mental foramina: prevalence, position and diameter assessed by cone-beam computed tomography and digital panoramic radiographs. Clin Oral Implants Res. [Published online ahead of print November 21, 2012]. doi:10.1111/clr.12066. 47. Balcioglu HA, Kocaelli H. Accessory mental foramen. N Am J Med Sci. 2009;1:314–315. 48. Byers SS, Ratcliff JS. Bifurcated mandibular canal. Oral Surg Oral Med Oral Pathol. 1983;56:337. 49. Meoli S, Fucci G, Vaia E. A rare case of double mental foramen. Imaging with computed tomography [in Italian]. Radiol Med. 1993;85:854–857. 50. Wyatt WM. Accessory mandibular canal: Literature review and presentation of an additional variant. Quintessence Int. 1996;27:111–113. 51. Cagirankaya LB, Kansu H. An accessory mental foramen: A case report. J Contemp Dent Pract. 2008;9:98–104. 52. Kulkarni S, Kumar S, Kamath S, et al. Accidental identification of accessory mental nerve and foramen during implant surgery. J Indian Soc Periodontol. 2011; 15:70–73. 53. Thakur G, Thomas S, Thayil SC, et al. Accessory mental foramen: A rare anatomical finding. BMJ Case Rep. 2011;2011. 54. Neves FS, Nascimento MC, Oliveira ML, et al. Comparative analysis of mandibular anatomical variations between panoramic radiography and cone beam computed tomography. Oral Maxillofac Surg. [published online ahead of print August 24th, 2013]. doi:10.1007/s10006013-0428-z. 55. Boronat Lopez A, Penarrocha Diago M. Failure of locoregional anesthesia in dental practice. Review of the literature. Med Oral Patol Oral Cir Bucal. 2006;11: E510–E513. 56. Kuzmanovic DV, Payne AG, Kieser JA, et al. Anterior loop of the mental nerve:
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a morphological and radiographic study. Clin Oral Implants Res. 2003;14:464–471. 57. Solar P, Ulm C, Frey G, et al. A classification of the intraosseous paths of the mental nerve. Int J Oral Maxillofac Implants. 1994;339:344. 58. Bagheri SC, Meyer RA. Management of mandibular nerve injuries from dental implants. Atlas Oral Maxillofac Surg Clin North Am. 2011;19:47–61.
59. Pasqual RJ, Pasqual HN. Surgical repositioning of the mental nerve. Report of a case. Oral Surg Oral Med Oral Pathol. 1967;24:305–306. 60. Smiler DG. Repositioning the inferior alveolar nerve for placement of endosseous implants: Technical note. Int J Oral Maxillofac Implants. 1993;8:145–150. 61. Khajehahmadi S, Rahpeyma A, Bidar M, et al. Vitality of intact teeth anterior
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to the mental foramen after inferior alveolar nerve repositioning: Nerve transpositioning versus nerve lateralization. Int J Oral Maxillofac Surg. 2013;42:1073–1078. 62. Kan JY, Lozada JL, Goodacre CJ, et al. Endosseous implant placement in conjunction with inferior alveolar nerve transposition: An evaluation of neurosensory disturbance. Int J Oral Maxillofac Implants. 1997;12:463–471.
ACCESSORY MANDIBULAR FORAMEN DURING DENTAL IMPLANT PLACEMENT
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Accessory Mandibular Foramen During Dental Implant Placement: Case Report and Review of Literature Brooke Pancer, DMD,* Carlos Garaicoa-Pazmiño, DDS,† and Jill D. Bashutski, DDS, MS‡
he interforaminal region is a common area for dental implant placement in the mandible to support fixed partial dentures and overdentures. Although considered a relatively safe surgical area, it is not free of risks and complications. In fact, the incidence of neurosensory disturbance after implant placement in the region of the mental foramen (MF) may be as high as 43%.1–6 Neurosensory impairment may occur at all stages of implant surgery including dental injections, incisions, flap reflection and retraction, osteotomy preparation, implant placement, suturing, and postoperative edema and hematoma. Moreover, damage to anatomical structures remains the major cause of legal action against the dental practitioner.7 As such, proper understanding of vital anatomical structures, surgical principles, implant systems, and treatment planning is the key to reducing neurovascular complications.
T
*Graduate Student, Graduate Periodontics, Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI. †PostDoctoral Student, Graduate Periodontics, Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI. ‡Clinical Assistant Professor, Director of Predoctoral Periodontics, Division of Periodontics, Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI.
Reprint requests and correspondence to: Jill. D. Bashutski, DDS, MS, Division of Periodontics, Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, 1101 North University Avenue, Room 3349, Ann Arbor, MI 481091078, Phone: 734-763-3759, E-mail: jillbash@umich. edu ISSN 1056-6163/14/02302-116 Implant Dentistry Volume 23 Number 2 Copyright © 2014 by Lippincott Williams & Wilkins DOI: 10.1097/ID.0000000000000056
Accurate knowledge of vital anatomical structures, such as the inferior alveolar nerve, mental nerve, and mental foramen, is critical to achieve favorable results during oral surgical procedures and dental implant placement. Although uncommon, variations in mandibular foramina have been reported and if unnoticed and, as a result, injured, may lead to patient morbidity, neurosensory disturbances, and other undesired complications. We present a case report of identification of an accessory mandibular foramen (AMF) encountered during placement of 2 dental implants for a mandibular implant-retained overdenture and demonstrate appropriate
management. In addition, we propose a more reasonable terminology for such accessory foramina so as to facilitate communication through common terminology among health care providers. As conventional radiography (periapical and panoramic films) may not allow for proper identification of such anatomical variations, conebeam computed tomography may be useful in the diagnosis of AMF during treatment planning of dental implants in the mandible. (Implant Dent 2014;23:116–124) Key Words: anatomic variation, cone-beam computed tomography, dental implant
Accurate knowledge of the inferior alveolar nerve, the mental nerve, and MF is critical when performing oral surgical procedures in the interforaminal region. The inferior alveolar nerve is a branch of the mandibular nerve (third division of the trigeminal cranial nerve) that carries both sensory and motor fibers. It enters the mandibular foramen, traverses the mandible anteroinferiorly from lingual to buccal within the mandibular canal where it supplies the molar teeth. It then divides into the dental (incisal) nerve, which continues medially though the incisive canal and the mental bundle, which exits laterally through the MF. In addition to vessels, 3 neural branches emerge from the MF: the mental, labial, and gingival nerves, which collectively innervate the skin
and mucous membranes of the lower lip and chin, and the gingiva from the second premolar to the central incisor.8–10 The MF has been found to be located between the first and second premolars 58% of the time and directly apical to the second premolar 42% of the time.11 Even though the pathway and anatomy of the inferior alveolar nerve and the mental nerve have been well described, anomalies of such structures may take place at any location along their course. A variety of patterns exist regarding number, position, and course, so it should not be assumed that there is simply 1 mandibular canal and 1 MF in the locations described above. One significant anatomical variation regarding the inferior alveolar
IMPLANT DENTISTRY / VOLUME 23, NUMBER 2 2014
Fig. 1. A, Preoperative panoramic radiograph. B, Preoperative panoramic radiograph with radiographic guide. C, Preoperative cephalometric radiograph with radiographic guide.
nerve is a bifid mandibular canal, which has been reported to have an occurrence of 0.08% to 1%.12–15 In addition, there may be a unilateral absence of the mandibular canal, often associated with unilateral agenesis of teeth and hemifacial microsomia.16–19 There may also be an extension of the inferior alveolar nerve anterior to the MF before exiting the canals, termed the anterior loop. This has been found to occur with a prevalence ranging from 28% to 94% with large variations in length ranging from 0 to 9 mm and a mean of 2 to 4 mm.11,20–25 Regarding the MF, variations may take place in terms of location, with reports of it being found anteriorly by the canine or posteriorly by the first or even second molar.20–22,25–27 In addition, more than 1 MF may be present on each or both sides of the mandible and may take place at any location along the mandibular canal. The nomenclature and categorization of
such foramina is widely variable in the literature.12,14,27–32 Thus, the authors will use the term accessory mandibular foramen (AMF) (in the case of a single additional foramen) or foramina (when multiple additions are noted) to identify these anomalies so as to include all possible locations and sizes of such defects. Radiographic and cadaver studies have reported an occurrence of AMF ranging from 0.88% to 10.66%.28,33 The purpose of this article was to present a case report of the identification of an AMF, discuss appropriate terminology for these anatomical variations, and demonstrate appropriate management with respect to dental implant placement. Radiographic and clinical interpretations of this case are considered and discussed with respect to methods of detecting such anatomical deviations in the goal of preventing complications during dental implant placement. In addition, we will propose a more reasonable terminology for such accessory foramina so as to facilitate communication through common terminology among healthcare providers.
CASE REPORT
Fig. 2. Dissection of the right mental foramen bundle (MF) and the AMF bundle. Note the implant osteotomy side 4 mm mesial to the AMF.
An 84-year-old Caucasian male patient was referred to the Graduate Periodontal clinic at the University of Michigan School of Dentistry for 2 mandibular anterior dental implants for an implant-retained overdenture. The patient’s medical history consisted of asthma, emphysema, history of a myocardial infarction in 1986, benign prostatic hypertrophy, seasonal allergies, slight hearing impairment, hypothyroidism, and osteoarthritis. He was
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taking the following medications: fluticasone/salmeterol, 81 mg aspirin, levothyroxine, fix spacing lisinopril, lovastatin, multivitamins, tiotropium bromide, and tamsulosin. The patient reported a 60 pack-year history of smoking but quit in 1986. Regarding his dental history, he reported extractions of his mandibular and maxillary teeth 4 years ago as a result of extensive periodontal disease. He wore a maxillary complete denture but was unhappy with the mandibular denture because of its poor fit. Thorough informed consent was provided with respect to risk, benefit, and procedure cost. No abnormal findings were noted on clinical and radiographic examination (Fig. 1, A). Radiographic and surgical implant guides were fabricated before surgery based upon periapical, panoramic, and cephalometric conventional radiographs (Fig. 1, B and C). The patient initiated a 10-day course of amoxicillin preoperatively and rinsed with chlorhexidine gluconate 0.12% for 1 minute immediately before surgery. The procedure was done under local dental anesthesia. A midcrestal incision ensuring at least 2 mm keratinized mucosa on either side of the incision line with a midline vertical incision for access were performed followed by full-thickness flap reflection. Elevation of the flap was initiated using an elevator, followed by complete reflection by inserting gauze so as to reflect the tissues without injuring vital structures. Upon reflection, a single MF and bundle were identified on the left hand side, but 2 separate foramina and bundles were noted on the right (Fig. 2). The AMF was positioned approximately 4 mm mesial to the MF and 4 mm from the midline. Because of its proximity to the planned osteotomy site, clinical judgment was used to prepare the implant osteotomy sites such that they were located 4 mm away from the foramina and spaced approximately 12 mm apart so as to maximize the anterior–posterior spread of the restorative unit. Two 4.1 3 13-mm dental implants (Tapered Screw-Vent MTX; Zimmer Dental, Inc., Carlsbad, CA) were placed with primary stability (Fig. 3, A) and covered with healing abutments. The
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ACCESSORY MANDIBULAR FORAMEN DURING DENTAL IMPLANT PLACEMENT
Fig. 3. A, Implant positioning. Note sufficient distance (12 mm) between the implants allowing for anterior-posterior spread and the location of the implants with respect to the mandibular midline. B, Panoramic radiograph 2 weeks after dental implant placement revealing adequate distance between implants and from vital structures.
Fig. 4. A, Clinical healing 3 months after implant placement. B, Postoperative panoramic radiograph 3 months after dental implant placement revealing no periimplant bone loss or abnormal findings.
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site was sutured with at the crestal portion and at the releasing incision using a combination of resorbable and nonresorbable sutures. The patient was informed of the risk of paresthesia, analgesics, and an antimicrobial mouth rinse and given thorough postoperative instructions. The patient was advised to abstain from wearing his mandibular denture for 2 weeks. At the 2-week follow-up appointment, the patient did not report any atypical symptoms or signs of paresthesia. Sutures were removed and the mandibular denture was relined with a soft denture reline material (Coe-Soft; GC America Inc., Chicago, IL) so that the patient could resume masticatory function. Healing was within acceptable limits. A panoramic radiograph was taken to confirm appropriate implant position and distance away from vital anatomical structures (Fig. 3, B). The patient was examined at the 4, 6, and 12-week time points. At the 3-month follow-up, a panoramic radiograph was taken to confirm stable marginal and periimplant bone levels and rule out atypical findings (Fig. 4, A). Clinical examination revealed absence of mobility with the reverse torque test, absence of bleeding on probing and exudate; clinically shallow probing depths, and adequate keratinized mucosa around the implants (Fig. 4, B). The implantretained overdenture was delivered at that time.
Table 1. Terminology Considerations for the AMF, True Accessory Mental Foramen, and Nutrient Foramen. Factors Including Continuity From Inferior Alveolar Canal and Nerve, Number, Location, Size, and Contents Are Taken Into Consideration
NSD indicates no significant difference; IAC, inferior alveolar canal; PA, periapical radiograph.
Table 2. Reports of the AMF Based on Sample Size, Incidence, Age, Sex, Population, Location, and Method of Detection Author, Year
Study Design
Age
Byers and Ratcliff, 198348 Serman, 198928
Case report
54
1
Cadaver study
N/A
Zografos and Mutzuri, 198932 Meoli et al, 199349
Cadaver study
Wyatt, 199650
Dario, 200214
Sample Size
Incidence
Sex
Population
Location
Terminology
Caucasian
508
0.88%
N/A
Right, left, African incisive American, Caucasian
Dissection
Ass. w odontogenic keratocyst (third M) 5 unilateral, 2 bilateral
N/A
464
6.68%
230 M, 234 F
Greek
N/A
Dissection
NSD between gender
Case report
41
1
N/A
F
Italian
Left side
CT
Unilateral
Literature review and case report Case report
23
1
N/A
M
African American
Left
Pan
Third M sx
52
1
1% (private practice)
M
Caucasian
Right
Found during tx planning
Bifurcated IAC
N/A
142
7.74%
N/A
Indian
Right, left
CT (not visible w Pan, PA) Dissection
1 bilateral
AMF
62
1
N/A
F
N/A
Left (m root Pan and PA Incidental finding of first M)
N/A
150
10.66%
N/A
Japanese
Right, left (first Mfirst PM area)
CBCT (not visible w Pan)
48
1
N/A
F
Turkish
Right (second PM)
CT (not visible w Pan)
157
7%
48 M, 107 F
Japanese
Right, left
CBCT
Case report
Naitoh et al, 200939
Retrospective
51.5
Bifurcated IAC Mental incisive foramen (ABF) Double mental foramen Double mental foramen Bifurcated IAC
AMF
1.6 3 1.2 mm in size; 1 bilateral, 15 unilateral; most distal and inferior to MF; excluded foramina not connecting to IAC Ass. w odontogenic keratocyst (caninesecond PM). Mesial to MF NSD between gender, diameter, and size; bilateral and unilateral; 1.7 mm2 in size; 1.9 mm diameter; most inferior and distal to MF
AMF
Double mental foramen, AMF by expert AMF
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(continued on next page)
IMPLANT DENTISTRY / VOLUME 23, NUMBER 2 2014
Balcioglu and Kocaelli, 200947
Pan
Comment
M
Roopa et al, Cadaver 200330 study Case report Cagirankaya and Kansu, 200851 Katakami et al, Retrospective 200833
Right
Detection
N/A
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Table 2. (Continued) Author, Year
Age
Sample Size
De OliveiraRetrospective Santos et al, 201131
N/A
285
Kulkarni et al, 201152 Naitoh et al, 201141
Case report
Thakur et al, 201153
Case report
Imada et al, 201246
Retrospective
Kalender et al, 201240
Retrospective
Sisman et al, 201229
Retrospective 39.7 6 15.9
Retrospective
9.40%
133 M, 152 F
Population Caucasian, Brazilian
Location
Detection
Right, left
CBCT
60, 30, rest N/A
5
40%
1 M, 1 F Japanese
1 Left, 1 bilateral, rest NA
Dissection, CT and CBCT (only 2)
25
1
N/A
M
Indian
Flap
7.70%
130 M, 235 F
Japanese
Right (first M) Right, left
1
N/A
M
Indian
40.9
100
3%
34 M, 66 F
Brazilian
Right (second PM) Right, left
38.6
193
6.50%
92 M, 101 F
Turkish
Right, left
504
10%
307 M, 197 F
Turkish
Right, left
51.7
40
369
Terminology
AMF Only included foramina .1 mm diameter; bilateral and unilateral; single and multiple, 1.95 mm diameter; NSD between gender and population ,1 3 ,1 mm, mesial and ABF distal to MF, contained branches of arteries (facial, buccal, submental) and mental nerve Contained nerve AMF
Excluded nutrient foramina; CBCT, bilateral and unilateral; rotational 1.5 mm2 in size; NSD Pan between location Dissection Distal to MF, chronic pain, tx w mental nerve neurectomy CBCT (not Bilateral and unilateral; 0.93 mm diameter visible w Pan) CBCT Excluded nutrient foramina; NSD between gender, diameter, and location; most inferior to MF; bilateral and unilateral; 1.4 3 1.6 mm in size CT NSD between age, location, and gender; 1.4 mm in diameter; 3 bilateral, 7 unilateral; mesial and distal, superior and inferior to MF
AMF
AMF
AMF
AMF
ABF
ET AL
ABF indicates accessory buccal foramens; MF, mental foramen; N/A, not applicable; NSD, no significant difference; IAC, inferior alveolar canal; PA, perapical radiograph.
Comment
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Cadaver study
Sex
Fuakami et al, 201134
Incidence
ACCESSORY MANDIBULAR FORAMEN DURING DENTAL IMPLANT PLACEMENT
Study Design
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DISCUSSION Several authors described the presence of accessory foramina within the mandible through gross anatomy studies and radiographic images.28–31 The nomenclature and categorization of such foramina are widely variable and confusing. Terms such as multiple mental foramina, mandibular accessory foramina, incisive mental foramina, double mental foramina, retromandibular foramina, accessory mental foramina, accessory buccal foramina, nutrient foramina, interalveolar foramina, additional MF, and incisive foramen have been used to name different anatomical variations of the same structure.28,29,32,34–38 These terms differ based on their location within the mandible, size, and number. AMF should include all additional foramina besides the MF carrying a vital structure. Although some studies claim that they can only be called AMF when there is continuity with the inferior alveolar canal,34,39 advanced imaging may not always be obtained in clinical scenarios, and as such appropriate terminology to obtain a clinical finding must be available. To simplify terminology of these anatomical variations, it is preferred to combine all such defects regardless of number, location, and size and place them under the umbrella of AMF (for a single additional foramen) or foramina (for multiple additions). The sole exceptions include a foramen containing vessels should be termed nutrient foramen and a foramen that has direct continuity to the inferior alveolar canal as demonstrated by cone-beam computed tomography (CBCT) and to the inferior alveolar nerve itself should be termed a true accessory MF. This terminology will serve to facilitate communication among health care providers in both the literature and while discussing clinical cases. An applicable flow chart is depicted in Table 1. The prevalence of AMF has been reported to range from 0.88% to 10.66%.28,33 The formation of these foramina is presumed to be as a result of an early branching of the inferior alveolar nerve before exiting through the MF during the 12th week of gestation.28,39 Additional foramina may also
be associated with bifurcated mandibular canals that carry the inferior alveolar nerve.13 Several studies have evaluated the prevalence, position, and size of AMF and their relationship with ethnicity, sex, and age.33,34 Most studies claim that there is no association between AMF with sex and age.29,31,32,39–41 One study using a considerably larger number and variety of subjects; however, found a higher prevalence in Asian males.42 Although disputed by some,11 others claim that the presence of AMF is higher in certain ethnic groups.27,43 In fact, the prevalence of AMF was 1.4% in American Caucasians, 1.5% in Asian Indians, 5.7% in African Americans, and 9.0% in pre-Columbian Nazca Indians.27 Anatomically, AMF have been described as having smaller diameters as compared with the MF.28,37 Other studies, however, have found no statistical significant difference in this respect.29,31,33,39,40 Such data, however, should be interpreted with caution due to differences in inclusion and exclusion criteria related to nutrient foramina and foramina with a diameter ,1 mm. Numerous tools are available to aid clinicians in understanding their patients’ individual anatomy before surgical intervention. Conventional radiographs including panoramic and periapical images are considered to be the minimum standard of care when treatment planning dental implants as they provide the clinician with valuable information. They do, however, come with limitations including distortion, overlap, and magnification, which may all lead to false interpretation of important anatomical structures.14 CBCT has gain recent popularity in the dental field as it allows for more reliable and accurate 3-dimensional visualization of anatomical structures that may be undetected though traditional radiographic imaging.8,9,44 Moreover, CBCT has been demonstrated to have improved image quality and less magnification and distortion among other tridimensional methods.45 The higher cost and level of radiation associated with CBCTs, however, must also be taken into account. The presence and pathway of the mandibular canal, MF, and AMF in panoramic and periapical radiographic
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images may not be distinct, accurate, or even detectable.46,47 Reasons may include: lack of contrast between the foramen and bone due to the trabecular pattern of bone, thin mandibular bone, thick lingual cortical plate, dark overexposed radiographs, and image distortion.9 The superiority of CBCT in the detection of accessory foramina when compared with traditional radiographs was confirmed in retrospective studies33,41 and is further outlined in Table 2. In fact, Naitoh et al41 found that detection of AMF with panoramic radiographs is ,50% as compared with CBCT images.46,54 Where AMF are identified, special care should be taken to perform safe and successful surgical procedures. Injury to neurovascular bundles contained within these accessory foramina may lead to hemorrhage, paresthesia, dysesthesia, neuropraxia, axonotmesis, neurotmesis, and/or significant patient morbidity.14,55 The identification of accessory foramina and other anatomical variations through tridimensional imagining has proven to be a reliable and accurate tool for presurgical planning. Moreover, it may reduce the rate of unwanted neurovascular complications. Not all anatomical variations may be identified preoperatively. As such, thorough intraoperative examination of vital structures and proper management are needed to ensure the safe placement of dental implants. Foramen may be exposed by using a periosteal elevator to raise a full-thickness mucoperiosteal flap to the mucogingival junction, then using a wet sterile gauze to gently push the mucosa off the bone past the coronal aspect of the foramen so as to protect the nerve from injury. Inserting a blunt curved instrument into the foramen and examining the patency of the distal aspect of the foramen can help to determine the presence of an anterior loop; if patency is not confirmed, then a loop likely exists. A variety of safetyzone recommendations have been made with respect to the minimal distance between the dental implant and nerve, including 2,9 3,3 4,56 and 6 mm.57 So long as reasonable restorative principles can be respected, the dental implant should be placed as far away from the
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nerve as possible. In our clinical case, we were able to place the implant 4 mm anterior to the AMF so as to decrease the risk of a neurosensory complication, while maintaining appropriate interimplant distance and anteroposterior spread of the future overdenture. Complications, however, do arise and as a result proper management is of prime importance. Timely repair of nerve injuries is of critical importance for successful recovery of nerve function. If nerve damage is suspected, a referral to the neurologist, neurosurgeon, or oral maxillofacial surgeon for evaluation and potential surgical correction should be made. If too much time elapses, surgical management may become ineffective and pharmacologic management of chronic pain may be needed. If altered nerve sensation is experienced, a proper diagnosis must be obtained through the use of advanced imaging. It is important to recognize whether the paresthesia, dysesthesia, or dysesthesia is a result of hitting, severing, compressing, or administrating local anesthetic in close proximity to the nerve. If the radiograph demonstrates that the dental implant is encroaching on the nerve, it should be removed or repositioned immediately, and consideration may be given for administering a steroid (locally, through the intravenous line, or orally), antibiotic, and analgesic. If altered sensation results from compression due to swelling or a hemorrhage in close proximity to the nerve, a steroid, antibiotic, and analgesic may also be considered. If the nerve is affected by administration of local anesthesia, the patient may be reassured and followed up over appropriate amount of time to ensure resolution of symptoms. If persistent numbness is still experienced, a steroid, antibiotic, and analgesic may be considered. If symptoms do not resolve with the aforementioned modalities, neurosurgical modalities may need to be implemented and may include external decompression, internal neurolysis, excision of neuroma, neurorrhaphy, nerve graft, nerve sharing, guided nerve regeneration, neurectomy, nerve capping, and nerve redirection.58 If there is insufficient room to place the dental implant, while respecting the
suggested safety zones, the nerve can be repositioned or the ridge can be augmented to create adequate space.10 Nerve lateralization can be performed by raising a mucoperiosteal flap, creating vertical osteotomies distal to the foramen and the second molar along the lateral cortical plate, and then connecting the vertical cuts with a horizontal osteotomy. The cortical window and portion of medullary bone is removed using elevators, the neurovascular bundle is displaced laterally using nerve hooks, the nerve is covered with a dressing or bone wax, and the dental implants may be placed at that time or a later time.59–61 Unlike nerve lateralization, transposition involves the sacrifice of the incisive nerve.61 Although some authors noted no long-term adverse sequelae,60 most authors, however, noted a high rate of transient of permanent sensory dysfunction of up to 54.7% and loss of anterior teeth vitality with nerve transposition postoperatively.2,61,62 The high risks associated with nerve repositioning must be thoroughly considered and as such should not be considered a first-line treatment option.
CONCLUSION Accurate knowledge of the inferior alveolar nerve, mental nerve, and its associated foramen is critical when performing oral surgical procedures and dental implant placement in the mandible. Variations in such anatomical structures, such as AMF, exist so thorough treatment planning is vital to avoid neurosensory complications and potential legal action. The superiority, accuracy, and reliability of CBCT images for the identification of AMF and other anatomical variations over conventional imaging has been well demonstrated and should be considered for presurgical planning. Finally, the surgeon should be aware of, and knowledgeable in, the appropriate management of AMF to achieve safe and favorable results during implant placement.
DISCLOSURE The authors claim to have no financial interest, either directly or
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indirectly, in the products or information listed in the article.
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