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 Table of Contents  
Year : 2020  |  Volume : 12  |  Issue : 5  |  Page : 415-418  

Alternative approach to prevent inferior alveolar nerve injury in lower third molar surgery: A pilot study on coronectomy

1 Department of Oral and Maxillofacial Surgery, Thumbay Hospital, Gulf Medical University, Dubai, United Arab Emirates
2 Department of Oral and Maxillofacial Surgery, College of Dentistry, Ajman University, Ajman, United Arab Emirates
3 Department of Orthodontics, Gulf Medical University, Ajman, United Arab Emirates
4 Department of Oral and Maxillofacial Surgery, Raja Muthiah Dental College, Annamalai University, Chidambaram, Tamilnadu, India

Date of Submission04-Feb-2020
Date of Decision07-Feb-2020
Date of Acceptance06-Mar-2020
Date of Web Publication28-Aug-2020

Correspondence Address:
Vannala Venkataramana
Department of Orthodontics, Gulf Medical University, Ajman.
United Arab Emirates
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jpbs.JPBS_123_20

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Context: Injury to inferior alveolar nerve (IAN) in lower third molar (L3M) surgery may lead to unpleasant sensation or anesthesia of lower lip. Considering the quality of life of the patient and the litigations faced by the dentist, alternative treatment approaches to odontectomy have been studied by various researchers. Coronectomy is one such option to prevent the nerve injury. Aims: The aim of this study was to assess the efficacy of coronectomy to reduce nerve injury during L3M surgery in high-risk cases as per radiological signs. Settings and Design: A pilot study was conducted in the oral surgery department of Rajah Muthiah Dental College, Annamalai Nagar, Chidambaram, India to evaluate coronectomy and its usefulness. Materials and Methods: Sixty-five patients who satisfied the inclusion and exclusion criteria for coronectomy were included in the study. The patients were followed up to 1-year period. Statistical Analysis Used: Descriptive statistics was used. Results: None of the patients in the study group had IAN impairment. Conclusions: Coronectomy is a safe alternative for complete odontectomy in high-risk L3M surgery cases. Root migration, infection, and need for second surgery are potential complication. Further studies with more samples and variables need to be performed.

Keywords: Coronectomy, impaction complication, inferior alveolar nerve injury, lip anesthesia, lower third molar surgery

How to cite this article:
Sureshkannan P, Thomas KS, Venkataramana V, Thangavelu A, Thiruneelakandan S. Alternative approach to prevent inferior alveolar nerve injury in lower third molar surgery: A pilot study on coronectomy. J Pharm Bioall Sci 2020;12, Suppl S1:415-8

How to cite this URL:
Sureshkannan P, Thomas KS, Venkataramana V, Thangavelu A, Thiruneelakandan S. Alternative approach to prevent inferior alveolar nerve injury in lower third molar surgery: A pilot study on coronectomy. J Pharm Bioall Sci [serial online] 2020 [cited 2021 Feb 25];12, Suppl S1:415-8. Available from:

   Introduction Top

Surgical removal of impacted tooth is a common procedure. Many years, odontectomy was considered as a gold standard procedure. Inferior alveolar nerve (IAN) injury has been reported by various studies as 0.35%,[1] 6.6%,[2] and 19%[3] following odontectomy.

Radiographic signs such as loss of radiopaque line, diversion of the canal and darkening of the roots in orthopantamogram (OPG),[4],[5] periapical or paradontal (juxta apical area) radiolucency,[3] and roots intersected by mandibular canal in cone beam computed tomography scan[6] warn the surgeon regarding the chances of nerve injury but do not prevent it.[7] Coronectomy is an alternative technique to avoid nerve injury.[8],[9] Many times the fractured root fragments are left inside the jaw bone heals uneventfully.[10] This led the surgeons to remove crown portion of the impacted tooth and leave the roots behind, thereby preventing nerve injury. Ecuyer and Debien[11] developed partial odontectomy in 1984.

The aim of this pilot study was to assess the usefulness of coronectomy to prevent neurosensory deficit in high-risk cases of impacted lower third molar (L3M) surgery.

   Materials and Methods Top

Patients who reported to Raja Muthiah Dental College during the period 2017–2019 for surgical removal of impacted L3M were screened for nerve–root relationship with OPG. Those who had close relationship between the root apex and IAN canal were included for the study. The patients were explained about the surgical procedure and related complications such as nerve injury, root migration and need for second surgery, dry socket, and wound infection. Patients who satisfied the inclusion and exclusion criteria set by Leung and Chen[12] in their randomized control trial were included in the study.

Inclusion criteria

  • (1) Tooth is intimate with IAN based on plain radiograph

    • (a) Interruption of white line of mandibular canal

    • (b) Deviation of mandibular canal

    • (c) Darkening of the roots

    • (d) Abrupt narrowing of the roots

    • (e) Abrupt narrowing of the mandibular canal white line

  • (2) Impacted tooth with pericoronitis and dental caries

  • (3) Impacted tooth predisposing to periodontal pathology in adjacent second molar

Exclusion criteria

  • (1) Impacted tooth not in close contact with mandibular canal as per x-ray panorama

  • (2) Impacted tooth associated with periapical pathology, cyst, and tumor

  • (3) Tooth in the line of fracture or those removed for orthodontic/orthognathic surgery

  • (4) Fibrous dysplasia or radiotherapy to mandible

  • (5) Craniofacial syndromes with preexisting IAN defects

  • (6) Smokers and those who are on oral contraceptives

The study was approved by the institutional review board for human experimentation at Annamalai University, Tamil Nadu. All the participants were given detailed information and written consent was obtained.

A total of 65 patients (40 female and 25 male patients in the age group of 25–45 years) were included in the study and were reviewed for 8-month to 1-year period. The patients were reviewed for presence of neurological deficit, dry socket, postoperative infection, and root migration. Neurosensory deficit was diagnosed if both subjective and objective measurements (light touch test, pain threshold test, and 2-point discrimination test) were different from those on the non-affected side or preoperative baseline. Pre- and postoperative assessment was performed by two different surgeons blinded from each other. Pain if develops after 24h (not the immediate postsurgical pain) of surgery was recorded on a visual analog scale (VAS) ranging from 0 to 10cm, with 0 signifying no pain and 10 signifying the most severe pain that the patient could imagine. Pain was considered as a positive complication if the patient reported 4 or more in the VAS scale based on the study conducted by Giuseppe Monacoet al.[11] Infection was defined as the presence of pus, fever, and pain. Dry socket was defined as the increase in pain intensity 48–72h after surgery, loss of the blood clot in the socket, and wound breakdown with or without foul smell. Patients were reviewed 3 days, 1 week, 3 months, and 1 year after surgery for assessment of neurosensory disturbances in IAN and lingual nerve, dry socket, pain, and root migration. Root migration was evaluated by comparing the position of the roots in relation to the cement-enamel junction of the adjacent second molar immediately after surgery and 1 year after surgery with intraoral periapical x-ray.

Surgical method and care

All the patients were given chlorhexidine mouth wash before starting the surgery. Coronectomy was performed using surgical handpiece and straight fissure bur. The crown was sectioned using 702 fissure bur in the buccolingual direction. Care was taken not to perforate the lingual cortex and the mandibular canal. The sectioning of the crown was performed up to two-thirds of the buccolingual width, and the crown was split using a 7 mm osteotome and mallet. The root portion was kept 3–4 mm sub-crestal and primary closure achieved with 4-0 silk sutures.

Standard postsurgical instructions such as pressure dressing, ice fomentation immediately after surgery, liquid cold diet for 24h, and soft diet for 5 days were given to the patient. Three days’ broad-spectrum antibiotics were prescribed to patients (amoxicillin 500 mg q8h or clindamycin 300 mg q8h if allergic to penicillin).

The sample size for this study was calculated based on the prevalence of IAN injury as 19% based on the study conducted by Renton et al.[3] with 10% chances for error.

Patients were categorized based on the nerve–root relationship, Pederson’s difficulty index, and root form as conical and not conical [Table 1].
Table 1: Categorization of patients

Click here to view

   Results Top

Of 65 patients, 60 had successful coronectomy. Five patients underwent total extraction as the roots were mobilized during the procedure. Two patients developed dry socket and pain. Three patients had root migration less than 2 mm in 1-year period.

   Discussion Top

IAN injury is expected if the roots of the impacted tooth are in close approximation with the nerve. Previously researchers have used x-ray panorama to evaluate the risk of IAN injury.[5],[13],[14] In our study, the risk of nerve injury was assessed with OPG. Interruption of the white line, darkening of the roots, and deviation of the mandibular canal are major risk predictors for IAN injury in OPG.[15],[16] All our patients had the aforementioned radiographic risk factors.

The primary objective in delivering care to patients is to improve the quality of life and not to harm (primum non nocere). Staged surgical removal of impacted third molar,[17] orthodontic-aided extrusion,[18] and pericoronal ostectomy[19] are some of the procedures recommended to prevent IAN injury in high-risk cases, but results are unpredictable and necessitate second surgery. Coronectomy is a predictable and simple procedure. Some studies have reported 0% nerve injury with coronectomy.[10],[20],[21] In our study, none of the patients had IAN injury.

Mobilization of the root fragment (failed coronectomy) occurs if the cut between the root and the crown is incomplete and excess force is given to fracture the crown portion[22] and in case of conical roots.[3] In our study all the five failed coronectomy had conical roots.

Meta-analysis of studies comparing coronectomy and complete odontectomy revealed the reduced risk of dry socket in coronectomy. There is no significant statistical evidence to prove that coronectomy reduces pain and infection rate in comparison to odontectomy.[23] Only 3% of coronectomy group had dry socket. Coronectomy and root retention works better if the roots are left 3–4 mm below alveolar crest, allowing consistent bone formation and reduced root migration.[22],[24] Root migration was minimal and there was no infection and need for second intervention.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Cheung LK, Leung YY, Chow LK, Wong MC, Chan EK, Fok YH Incidence of neurosensory deficits and recovery after lower third molar surgery: a prospective clinical study of 4338 cases. Int J Oral Maxillofac Surg 2010;39:320-6.  Back to cited text no. 1
Hasegawa T, Ri S, Shigeta T, Akashi M, Imai Y, Kakei Y, et al. Risk factors associated with inferior alveolar nerve injury after extraction of the mandibular third molar—a comparative study of preoperative images by panoramic radiography and computed tomography. Int J Oral Maxillofac Surg 2013;42:843-51.  Back to cited text no. 2
Renton T, Hankins M, Sproate C, McGurk M A randomised controlled clinical trial to compare the incidence of injury to the inferior alveolar nerve as a result of coronectomy and removal of mandibular third molars. Br J Oral Maxillofac Surg 2005;43:7-12.  Back to cited text no. 3
Hasegawa T, Ri S, Umeda M, Komori T Multivariate relationships among risk factors and hypoesthesia of the lower lip after extraction of the mandibular third molar. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2011;111:e1-7.  Back to cited text no. 4
Rood JP, Shehab BA The radiological prediction of inferior alveolar nerve injury during third molar surgery. Br J Oral Maxillofac Surg 1990;28:20-5.  Back to cited text no. 5
Xu GZ, Yang C, Fan XD, Yu CQ, Cai XY, Wang Y, et al. Anatomic relationship between impacted third mandibular molar and the mandibular canal as the risk factor of inferior alveolar nerve injury. Br J Oral Maxillofac Surg 2013;51:e215-9.  Back to cited text no. 6
Ghaeminia H, Gerlach NL, Hoppenreijs TJ, Kicken M, Dings JP, Borstlap WA, et al. Clinical relevance of cone beam computed tomography in mandibular third molar removal: A multicentre, randomised, controlled trial. J Craniomaxillofac Surg 2015;43:2158-67.  Back to cited text no. 7
Renton T Update on coronectomy. A safer way to remove high risk mandibular third molars. Dent Update 2013;40:362-8.  Back to cited text no. 8
Pogrel MA, Lee JS, Muff DF Coronectomy: a technique to protect the inferior alveolar nerve. J Oral Maxillofac Surg 2004;62:1447-52.  Back to cited text no. 9
Dachi SF, Howell FV A survey of 3,874 routine full-mouth radiographs. I. A study of retained roots and teeth. Oral Surg Oral Med Oral Pathol 1961;14:916-24.  Back to cited text no. 10
Monaco G, de Santis G, Gatto MR, Corinaldesi G, Marchetti C Coronectomy a surgical option for impacted third molars in close proximity to the inferior alveolar nerve. J Am Dent Assoc 2012;143:363-9.  Back to cited text no. 11
Leung YY, Cheung LK. Safety of coronectomy versus excision of wisdom teeth: a randomized controlled trial. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:821-7.  Back to cited text no. 12
Blaeser BF, August MA, Donoff RB, Kaban LB, Dodson TB Panoramic radiographic risk factors for inferior alveolar nerve injury after third molar extraction. J Oral Maxillofac Surg 2003;61:417-21.  Back to cited text no. 13
Nakagawa Y, Ishii H, Nomura Y, Watanabe NY, Hoshiba D, Kobayashi K, et al. Third molar position: reliability of panoramic radiography. J Oral Maxillofac Surg 2007;65:1303-8.  Back to cited text no. 14
Neves FS, Souza TC, Almeida SM, Haiter-Neto F, Freitas DQ, Bóscolo FN Correlation of panoramic radiography and cone beam CT findings in the assessment of the relationship between impacted mandibular third molars and the mandibular canal. Dentomaxillofac Radiol 2012;41:553-7.  Back to cited text no. 15
Leung YY, Cheung LK Correlation of radiographic signs, inferior dental nerve exposure, and deficit in third molar surgery. J Oral Maxillofac Surg 2011;69:1873-9.  Back to cited text no. 16
Landi L, Manicone PF, Piccinelli S, Raia A, Raia R A novel surgical approach to impacted mandibular third molars to reduce the risk of paresthesia: a case series. J Oral Maxillofac Surg 2010;68:969-74.  Back to cited text no. 17
Alessandri Bonetti G, Bendandi M, Laino L, Checchi V, Checchi L Orthodontic extraction: riskless extraction of impacted lower third molars close to the mandibular canal. J Oral Maxillofac Surg 2007;65:2580-6.  Back to cited text no. 18
Tolstunov L Pericoronal ostectomy as alternative treatment option for extraction of impacted mandibular third molars in proximity to inferior alveolar nerve. J Oral Maxillofac Surg 2010;68:231-2.  Back to cited text no. 19
Mukherjee S, Vikraman B, Sankar D, Veerabahu MS Evaluation of outcome following coronectomy for the management of mandibular third molars in close proximity to inferior alveolar nerve. J Clin Diagn Res 2016;10:57-62.  Back to cited text no. 20
Agbaje JO, Heijsters G, Salem AS, Van Slycke S, Schepers S, Politis C, et al. Coronectomy of deeply impacted lower third molar: incidence of outcomes and complications after one year follow-up. J Oral Maxillofac Res 2015;6:e1.  Back to cited text no. 21
Patel V, Gleeson CF, Kwok J, Sproat C Coronectomy practice. Paper 2: complications and long term management. Br J Oral Maxillofac Surg 2013;51:347-52.  Back to cited text no. 22
Cervera-Espert J, Pérez-Martínez S, Cervera-Ballester J, Peñarrocha-Oltra D, Peñarrocha-Diago M Coronectomy of impacted mandibular third molars: a meta-analysis and systematic review of the literature. Med Oral Patol Oral Cir Bucal 2016;21:e505-13.  Back to cited text no. 23
Leung YY, Cheung LK Coronectomy of the lower third molar is safe within the first 3 years. J Oral Maxillofac Surg 2012;70:1515-22.  Back to cited text no. 24


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