J Indian Soc Periodontol. 2011 Jan-Mar; 15(1): 70–73.
doi: 10.4103/0972-124X.82270
Copyright © Journal of Indian Society of Periodontology
PMCID: PMC3134053
Accidental identification of accessory mental nerve and foramen
during implant surgery
Sudhindra Kulkarni, Sampath Kumar, Sujata Kamath, and Srinath Thakur
Department of Periodontics and Implantology, SDM College of Dental Sciences and Hospital, Dharwad,
Karnataka, India
Address for correspondence: Dr. Sudhindra Kulkarni, Department of Periodontics and Implantology, SDM
College of Dental Sciences and Hospital, Dharwad, Karnataka - 580 009, India E-mail:drsudhindrak@gmail.com
Received February 17, 2010; Accepted August 12, 2010.
This is an open-access article distributed under the terms of the Creative Commons AttributionNoncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Abstract
The accessory mental nerve and the corresponding foramen are not a very common
occurrence. In the current case report, we present the notice of an accessory mental
nerve in the mandibular molar area during implant placement. The case was managed
well without any complications.
Keywords: Accessory mental foramen, accessory mental nerve, GBR
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INTRODUCTION
The concept of osseointegration has made implant therapy the most preferred mode for
tooth replacement.[1] The increasing use of implants has along with it brought about
series of reports on potential complications related to implant placement.[2,3] The
availability of adequate bone volume and height is a prerequisite for implant placement;
however, this may not always be possible. Implant placement into compromised sites
needs adjunctive procedures like augmentation of bone either prior to or simultaneously
during the implant placement.[4–7] Simultaneous implant placement and bone grafting
procedure reduces the total duration of the treatment as compared to a staged approach
of grafting and graft integration time of 4-6 monthsfollowed by implant placement and
restorations 3-4 months later. Studies have shown that guided bone regeneration
procedure at the time of implant placement can form and maintain bone formation
around titanium implants.[4,7–12] Although all the clinical and radiographic evaluations
are undertaken prior to implant placement so that the available bone height and
anatomic structures like foramen and bony canals are visualized, some times the finer
structures do get missed out but get identified during the surgical procedure.
The following report is of a case wherein we accidentally identified accessory mental
foramen (AMF) and an accessory mental nerve (AMN) exiting it while carrying out a
guided bone regeneration procedure using a titanium mesh in combination with bovine
anorganic bone for covering a dehiscence defect around an implant in the mandibular
molar area.
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CASE REPORT
A 25-year-old male patient was referred to the Department of Implantology, SDM College
of Dental Sciences and Hospital, Dharwad, India, for replacement of his missing tooth.
On clinical examination it was noted that the patient had a missing mandibular right first
molar (tooth number 46) [Figure 1]. The tooth was extracted due to endodontic failure 8
months back. The alveolar ridge appeared high well rounded. The overlying mucosa
appeared healthy. The orthopantmogram revealed adequate amount of bone available
for implant placement. The available height was 18 mm (1:3 magnifications). It was
decided to place a 5.3 diameter, 13 mm long implant [Figure 2].
Figure 1
Pre-operative
Figure 2
Pre-operative radiograph
The patient was given a 0.2% chlorhexidine rinse for 2 minutes and local anesthesia was
secured on the buccal and lingual sides. A mid-crestal incision extending from the distal
aspect of the 2nd premolar to the mesial aspect of the 2nd molar was made and a full
thickness mucoperiosteal flap was elevated. The alveolar crest was visualized and the
osteotomy was started with a pilot drill for a depth of 13 mm. Sequential drilling was done
to enlarge the osteotomy to facilitate the placement of 5.3 diameter, 13 mm long implant
[Uniti® (Uniti®, Equinox, Holland)]. Implant torqued into the osteotomy site. We noticed
that there was a dehiscence exposing 2–3 mm of the implant on the buccal aspect. It
was decided to cover the dehiscence with graft and titanium mesh. A vertical incision
was placed along the distoincisal line angle of the second premolar, to facilitate the
grafting. While the flap was being reflected we noticed a fine fiber exiting a foramen
located at a distance of approximately 3–4 mm apical to the alveolar crest. The fiber was
carefully dissected from the adjacent tissues and was left undamaged. The foramen and
the fiber were identified as accessory mental foramen and nerve [Figure 3]. The main
trunk and the mental foramen were located in the area between the apices of the two
premolars [Figure 2]. The exposed threads were covered with bovine anorganic bone
[Bio-oss, Geistlich Pharma AG, Wolhusen, Switzerland] and stabilized with a titanium
mesh screen [Synthes, CO, USA], of 1.0-mm sized pores which was contoured to the
defect [Figure 4] During grafting, care was taken so that the nerve fiber was not
traumatized. The flaps were approximated and closed with 4-0 vicryl [Ethicon, Johnson
and Johnson, Aurangabad, India] sutures and primary closure was attained. The patient
was advised not to take any analgesic till the anesthetic effect had worn off, and he was
monitored continuously to check for any signs of nerve injury till 6 hours after the
surgery. A radiograph was made to assess the placement of implant in relation to the
inferior alveolar canal [Figure 5]. Once it was ascertained that no nerve damage had
happened the patient was discharged from the clinic. Three months after the implant
placement the patient was recalled and the 2nd stage procedure was carried out. After 15
days of healing period final impressions were made in vinyl polysiloxane impression
material [Aquasil, Dentsply, De Trey, Konstanz, Germany]. The final restoration was
cemented [Figures [Figures66 and and7]7] and the patient was put on a follow-up care.
The patient is being currently followed up since the past two years. No changes in the
hard and soft tissue levels have been noticed.
Figure 3
Accessory mental nerve and foramen along with the buccal dehiscence on the
implant
Figure 4
Dehiscence covered with titanium mesh and bio-oss
Figure 5
Immediate post implant placement radiograph
Figure 6
Final restoration
Figure 7
Radiograph of the final restoration
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DISCUSSION
The knowledge of the local anatomy plays an important role in the treatment planning
process. Clinical examination and findings from radiographs do not always ensure all the
anatomic structures in a particular area are identified. Accidental identification of
anatomic structures is not new, but the management of cases in these circumstances is
a challenge.[6]
In the present case, AMN and AMF were accidentally detected in the mandibular 1 stmolar
area during implant surgery and were managed successfully.
AMN is a branch of the inferior alveolar nerve, which exits from the main bundle of the
nerve prior to the mental foramen, from an accessory foramen known as accessory
mental foramen. AMN can be detected any location along the course of the mental
nerve.[6] Its occurrence has been reported with an incidence of 3.52% of cases on the
left and 4.22% on the right side of the mandible, in a study done on South Indian
mandibles by Roopa et al.[13] Shankland[14] reported an incidence of 6.62% of
accessory mental foramen in Asian Indians. Injury to any of the nerve during surgical
procedures in this area results in paresthesia of the area supplied by it.[3,6]
In the present case, a 2–3 mm dehiscence was observed on the buccal aspect of the
implant. The dehiscence was covered by GBR procedure, with a combination of bovine
anorganic bone and titanium mesh.GBR technique was chosen because it has been
shown that GBR is the best technique available to cover the dehiscence around
implants. Dahlen et al, have shown that guided bone regeneration can be predictably
carried out around titanium implants.[4,10] Studies by Zitzmann et al, showed that if the
initial defect size is more than 2 mm then GBR is indicated in coverage of the defect
which can be successfully treated by a combination of bovine anorganic bone along with
collagen membrane and the results can be predictability maintained over long
periods.[12] Although the autogenous bone grafts are gold standard for grafting
procedures and are used in combination with bovine bone mineral for
augmentation,[15,16] in the current case as the defect was small (approx 2 mm) bovine
particulate bone mineral was used. Bovine bone mineral when used as an onlay bone
graft has shown bone formation between the particles of the graft.[9,16–18]
Apart from the graft material, the stability of the graft is very important for regeneration.
The titanium mesh not only protects the graft but also maintains the shape around the
defect which attributed to the stiffness of the mesh and can be easily contoured to
achieve a three dimensional adaptation around the ridge.[11] The biocompatibility of the
mesh also makes it suited for long term implantation and also less risk of infection even
after premature exposure as compared to the non-resorbable membranes.[16,19]
In current case, AMN was seen exiting the AMF at a distance of 3–4 mm from the
alveolar crest leading to the thought whether the nerve was traumatized during the
preparation of the osteotomy site or during implant placement. During the grafting
procedure care was taken so that the AMN was not traumatized. The patient was not
medicated with post operative analgesics and till the anesthetic effect waned off. In case
any signs of nerve damage were observed it was decided to remove the implant
immediately. As none of the signs of nerve injury or damage were detected the patient
was discharged.
To summarize the case, it can be said that optimal knowledge of the local anatomy and
radiographic identification of the anatomic structures is important, but there are certain
conditions when these structures are missed out and are identified during surgical
procedure. It is important to manage the aberrant anatomical structures carefully so that
no permanent damage ensues, because any damage to these structures need not
necessarily lead to implant failure but is very commonly associated with legal action
against the practitioner.[3]
To conclude it can be stated that the case wherein an accessory mental nerve exiting an
accessory mental foramen were identified in an area of the mandibular 1stmolar on the
right side was managed without causing any nerve injury. However, imaging techniques
like CT scan that provides a better picture of the operating areas should be carried out
for better planning and avoiding unnecessary complications during implant surgery.
Footnotes
Source of Support: Nil.
Conflict of Interest: None declared.
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