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Year : 2017  |  Volume : 20  |  Issue : 3  |  Page : 274-277

Is 2 mm a safe distance from the inferior alveolar canal to avoid neurosensory complications in implant surgery?

Department of Oral and Maxillofacial Surgery, School of Dentistry, İstanbul Medipol University, Unkapani, Istanbul, Turkey

Date of Acceptance30-Oct-2015
Date of Web Publication3-Mar-2017

Correspondence Address:
Dr. G Gurler
Department of Oral and Maxillofacial Surgery, School of Dentistry, İstanbul Medipol University, Ataturk Bulvari No. 27, Unkapani, Istanbul
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1119-3077.183240

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Aim: The aim of the present study was to compare the neurosensory complications related to implants inserted closer than 2 mm to the inferior alveolar canal (IAC) with those inserted further than 2 mm. Materials and Methods: A total of 474 implants in 314 patients placed posterior to mental foramen area were evaluated retrospectively on panoramic radiographs. Patients were divided into two groups regarding implant proximity to the IAC (Group 1, distance ≤2 mm, Group 2, distance >2 mm). Postoperative neurosensory complications (pain and paresthesia) were recorded. Chi-square test was used for statistical comparison and P ≤ 0.05 was considered significant. Results: One hundred and fifty-three implants (32.2%) were inserted closer than 2 mm to the IAC whereas 321 implants (67.8%) were inserted further than 2 mm. Three implants which had a distance of 0 mm to the IAC (0.63%) caused paresthesia after surgery. Implant distance to IAC did not show a significant difference regarding pain and paresthesia (P = 0.06 and P = 0.08, respectively). Conclusion: When 2 mm is considered as a safety distance, the distance of the implants to the IAC did not yield any statistical difference regarding postoperative neurosensory complications.

Keywords: Dental implants, inferior alveolar nerve injury, neurosensory complication

How to cite this article:
Tufekcioglu S, Delilbasi C, Gurler G, Dilaver E, Ozer N. Is 2 mm a safe distance from the inferior alveolar canal to avoid neurosensory complications in implant surgery?. Niger J Clin Pract 2017;20:274-7

How to cite this URL:
Tufekcioglu S, Delilbasi C, Gurler G, Dilaver E, Ozer N. Is 2 mm a safe distance from the inferior alveolar canal to avoid neurosensory complications in implant surgery?. Niger J Clin Pract [serial online] 2017 [cited 2022 Dec 10];20:274-7. Available from:

   Introduction Top

Implants are used to reconstruct compromised occlusion and to improve patient’s quality of life as well as diet. Implant dentistry has highly predictable results in most cases where there is horizontal and vertical adequate alveolar bone; however, this condition is not met in all cases because of several anatomical challenges.[1],[2] The most important anatomic limitation in the mandible is the inferior alveolar canal (IAC). Positioning of implants close to the IAC and traumatic anesthetic injections may result in damage to the inferior alveolar nerve (IAN), thus loss of sensation in the lower lip can occur.

It has been reported that IAN is the most commonly injured nerve (64.4%), followed by the lingual nerve (28.8%) during oral surgery procedures.[3] The most common factors for IAN injury include third molar surgery, endodontic treatment, local anesthetic injection, and implant surgery.[2] Causes of such injuries include compression, stretch, transection, tearing, laceration, or needle penetration of the nerve.[4],[5],[6] Nerve damage is one of the most unpleasant experiences for the patient, varying from mild paresthesia to complete anesthesia and/or pain. As a result, many daily activities such as speech, kissing, eating, drinking, and shaving are adversely affected.[2],[5]

Preoperative radiological planning can help to determine the location of the IAC and proposed implant sites, and may decrease neural complications during implant surgery. Panoramic radiographs are still the most commonly used radiographs in implant surgery since they are cheaper, widely available, and have less radiation dose than computed tomography (CT).[6],[7]

The aim of the present study was to compare the neurosensory complications of the implants inserted closer than 2 mm and those inserted further than 2 mm to the IAC using panoramic radiographs.

   Materials and Methods Top

Panoramic radiographs of the patients, who underwent dental implant placement in the posterior mandible at istanbul Medipol University, School of Dentistry, Department of Oral and Maxillofacial Surgery between years 2011 and 2014, were retrospectively evaluated. Implant placement was achieved by local infiltration anesthesia (buccal infiltration and lingual mylohyoid anesthesia) in all the patients. The full thickness mucoperiosteal flap was raised from the alveolar crest and the width of bone was assessed. Implant bed was prepared with a physiodispenser device at a speed of 800 rpm and at a torque of 50 n/cm under copious sterile saline irrigation. Drilling sequence was followed concerning surgical kit of the implant company. All root shaped implants with sandblasted and acid-etched surface were inserted at least 6 months following tooth extraction (delayed placement) into D1 or D2 (Misch Classification) alveolar bone. All the patients were prescribed 875 mg amoxicillin +125 mg clavulanic acid combination, 500 mg paracetamol, and 0.2% chlorhexidine mouth rinse postoperatively.

The patients were divided into two groups regarding implants’ proximity to the IAC (Group 1: Distance <2 mm, Group 2: Distance ≥2 mm). Systemic conditions were assessed from the patients’ records. Those who have any neurological disorders, current orofacial sensory disturbance, or any systemic disease that may cause neurosensory disturbance were not included in the study. The panoramic views were obtained using the same machine (Planmeca Romexis®, P255 73KV 12 mA 10.78 s) in natural head position. All measurements were performed by the two authors (ST and ED) and an average of two measurements was accepted as a final distance. Postoperative neurosensory disturbances including pain and paresthesia on the 7th postoperative day were searched from patients’ files. Pain was assessed using a four-point scale where 0: No pain, 1: Mild pain, 2: Moderate pain, and 3: Severe pain. Paresthesia was assessed by two-point discrimination and light touch neurosensory tests.

Vertical linear measurements were taken from the apex of the implant to the superior border of the IAC on panoramic radiographs [Figure 1]. Calibration of the software was adjusted according to the actual implant sizes from the patient records. The study protocol was approved by the Istanbul Medipol University’s Ethical Committee. Postoperative neurosensory complications were recorded. Chi-square test was used for statistical analysis and P ≤ 0.05 was considered significant.
Figure 1: Panoramic radiograph of an implant that caused paresthesia

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   Results Top

Panoramic radiographs of 314 patients (204 male and 110 female, age range, 19-78 years with a mean of 42.8 years) with a total of 474 dental implants were assessed [Table 1] and [Table 2]. Of these, 153 implants had a distance of <2 mm (32.2%) whereas 321 had a distance of ≥2 mm (67.8%) to the IAC. 3 patients (1 male and 2 female), who had an implant distance of 0 mm to the IAC, developed paresthesia after surgery. The implants were backed up and the numbness resolved gradually without any additional medical therapy. Implant distance to IAC did not show a significant difference in occurrence of paresthesia (P = 0.08). There was not a significant difference between the groups regarding pain scores (Group 1: 1 ± 08, Group 2: 1 ± 02, P = 0.06).
Table 1: Distribution of implants regarding tooth number

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Table 2: Distribution of implants regarding distance to IAC

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   Discussion Top

Parallel to increase in the number of practitioners performing implant surgery, problems and complications are expected to increase as well. The damage of the IAN is the most encountered complication related with implant surgery. Over penetration by the drill may result in close insertion of the implant to IAC. This may cause hemorrhage into the canal or contamination of drilling debris, which are major factors for compression and damage of the IAN. It is stated that the incidence of lingual nerve injury has remained stable over the last 30 years, but the incidence of IAN injury has increased due to implant surgery and endodontic treatment.[5],[8] When such injury occurs, a complete healing is difficult if the extent of the injury is not minor. A minor injury only results in temporary numbness, paresthesia, or pain.[1],[6],[8] Interference of IAN may affect patient’s quality of life and psychology. If such complication occurs, the dentist should immediately provide appropriate care and treatment for the patient. In our cases, the penetration through the IAN with either drill or implants did not occur. The paresthesia could possibly result from the heat generated by the drills.

Thermal stimuli can result in bone necrosis and IAN damage. Nerve tissue is more sensitive to thermal changes than the bone; hence, IAN injury is inevitable. The excessive high speed of the drills may increase temperature resulting in necrosis, fibrosis, osteolytic degeneration, and increased osteoclastic activity.[1],[8],[9] Khawaja and Renton[10] emphasized that damage to IAN can arise from cracking of the superior border of the IAC while preparing the implant bed. This may result in hemorrhage into the canal or deposition of debris which causes compression and ischemia of the nerve. Implant itself may also cause nerve injury by direct and indirect trauma. When the implant is intruded through the canal, compression of the nerve may initiate degeneration and ischemia of the neurovascular bundle. Efforts to achieve good primary stability during implant insertion can cause undesired sinking of the implant and nerve damage.[1],[5],[8] In our study, implants were inserted following preoperative evaluation with panoramic radiographs, since cone-beam computed tomography (CBCT) brings extra financial burden for the patient.

One suggested way to prevent IAN injury during implant surgery is to determine safety distance from implant apex to superior border of IAC. Little evidence exists regarding the minimum distance to protect the nerve during bone drilling or implant placement.[1],[5],[6],[8] As a result of a biomechanical study, Sammartino et al.[11] suggested a distance of 1.5 mm to prevent IAN when biomechanical loading is to be considered. Froum et al.[12] reported that if this distance is closer than 6 mm, the risk for IAN may increase during immediate implant placement; on the contrary, Lin et al.[8] stated that even if the distance is closer than 6 mm, the risk for IAN injury did not increase since alveolar housing for implant placement was still available. To determine the exact alveolar bone height, bone density, and length of the proposed implant, thorough radiographic evaluation with CT or CBCT is highly recommended. CBCT provides low radiation dose and high-resolution three-dimensional imaging which enables surgeons to plan implant surgery in critical sites.[6],[7],[13] Basa and Dilek[14] stated that average density and thickness of the bone around the IAC is not resistant enough to withstand drill force. They suggested to assess the bone mass around the canal and to avoid applying excessive force with drills when approaching the canal.

Another suggestion may be the use of local infiltration anesthesia to insert implants in the posterior mandible. Infiltration anesthesia has been shown to be a safe technique to prevent IAN injury and to decrease IAN anesthesia complications as well as to provide sufficient anesthesia in the posterior mandible to insert implants. Repeated IAN anesthesia should be avoided.[15],[16] Surgeon’s experience and skill are other important factors to decrease surgical complications. If IAN injury is diagnosed, the implant should be removed or backed-up as soon as possible. Removal after osseointegration is not effective on resolving nerve damage.[4],[13]

We suggest that, if one can avoid thermal, pressure, and traumatic damage to the IAN, then implants can be placed closer than 2 mm to the IAC.

Anatomical limitations indicated for oral surgical procedures are becoming more tolerated as the studies declare successful results compelling these limitations. There are not conclusive safety distances to avoid damage to anatomical structures during oral surgical procedures. Further clinical and experimental studies are needed to determine consensus on safety limits.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Juodzbalys G, Wang HL, Sabalys G. Injury of the inferior alveolar nerve during implant placement: A literature review. J Oral Maxillofac Res 2011;2:e1.  Back to cited text no. 1
Hillerup S. Iatrogenic injury to the inferior alveolar nerve: Etiology, signs and symptoms, and observations on recovery. Int J Oral Maxillofac Surg 2008;37:704-9.  Back to cited text no. 2
Tay AB, Zuniga JR. Clinical characteristics of trigeminal nerve injury referrals to a university centre. Int J Oral Maxillofac Surg 2007;36:922-7.  Back to cited text no. 3
Shavit I, Juodzbalys G. Inferior alveolar nerve injuries following implant placement-importance of early diagnosis and treatment: A systematic review. J Oral Maxillofac Res 2014;5:e2.  Back to cited text no. 4
Juodzbalys G, Wang HL, Sabalys G, Sidlauskas A. Galindo-Moreno P, Inferior alveolar nerve injury associated with implant surgery. Clin Oral Implants Res 2013;24:183-90.  Back to cited text no. 5
Kütük N, Gönen ZB, Yasar MT, Demirbas AE, Alkan A. Reliability of panoramic radiography in determination of neurosensory disturbances related to dental implant placement in posterior mandible. Implant Dent 2014;23:648-52.  Back to cited text no. 6
Kamrun N, Tetsumura A, Nomura Y, Yamaguchi S, Baba O, Nakamura S, et al. Visualization of the superior and inferior borders of the mandibular canal: A comparative study using digital panoramic radiographs and cross-sectional computed tomography images. Oral Surg Oral Med Oral Pathol Oral Radiol 2013;115:550-7.  Back to cited text no. 7
Lin MH, Mau LP, Cochran DL, Shieh YS, Huang PH, Huang RY. Risk assessment of inferior alveolar nerve injury for immediate implant placement in the posterior mandible: A virtual implant placement study. J Dent 2014;42:263-70.  Back to cited text no. 8
Abarca M, van Steenberghe D, Malevez C, De Ridder J, Jacobs R. Neurosensory disturbances after immediate loading of implants in the anterior mandible: An initial questionnaire approach followed by a psychophysical assessment. Clin Oral Investig 2006;10:269-77.  Back to cited text no. 9
Khawaja N, Renton T. Case studies on implant removal influencing the resolution of inferior alveolar nerve injury. Br Dent J 2009;206:365-70.  Back to cited text no. 10
Sammartino G, Marenzi G, Citarella R, Ciccarelli R, Wang HL. Analysis of the occlusal stress transmitted to the inferior alveolar nerve by an osseointegrated threaded fixture. J Periodontol 2008;79:1735-44.  Back to cited text no. 11
Froum S, Casanova L, Byrne S, Cho SC. Risk assessment before extraction for immediate implant placement in the posterior mandible: A computerized tomographic scan study. J Periodontol 2011;82:395-402.  Back to cited text no. 12
Renton T, Dawood A, Shah A, Searson L, Yilmaz Z. Post-implant neuropathy of the trigeminal nerve. A case series. Br Dent J 2012;212:E17.  Back to cited text no. 13
Basa O, Dilek OC. Assessment of the risk of perforation of the mandibular canal by implant drill using density and thickness parameters. Gerodontology 2011;28:213-20.  Back to cited text no. 14
Altug HA, Sencimen M, Varol A, Kocabiyik N, Dogan N, Gulses A. The efficacy of mylohyoid nerve anesthesia in dental implant placement at the edentulous posterior mandibular ridge. J Oral Implantol 2012;38:141-7.  Back to cited text no. 15
Etoz OA, Er N, Demirbas AE. Is supraperiosteal infiltration anesthesia safe enough to prevent inferior alveolar nerve during posterior mandibular implant surgery?. Med Oral Patol Oral Cir Bucal 2011;16:e386-9.  Back to cited text no. 16


  [Figure 1]

  [Table 1], [Table 2]

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