Coronectomy: An Alternative to Complicated Full-Bony Impacted Tooth Removal

In patient cases in which an impacted tooth, typically a third molar, is in close proximity to the inferior alveolar nerve (IAN) canal, the intentional partial odontectomy (coronectomy) procedure has become a surgical treatment option used to avoid nerve injury. The effectiveness of the procedure in reducing the incidence of IAN sensory disturbances has been described frequently in the literature.^1,2

IAN injury is a well-known potential risk and complication of the removal of impacted third molars. The risk of IAN injury has been reported as ranging from 0.5% to 8%, with an incidence of permanent injury reported as less than 1%.^3-7 Preoperative patient evaluations are commonly made using conventional 2-dimensional (2D) periapical and panoramic radiographs. An increased risk of nerve injury is possible in patient cases in which various radiographic signs show a close relationship between mandibular third molars and the IAN canal.⁸ These signs include an IAN canal appearing to cross over the tooth roots, diversion and/or narrowing of the IAN canal, interruption of the "white" superior cortical aspect of the IAN canal, and deflection, darkening, or bifid root apex findings. With today's availability of cone-beam computed tomography (CBCT), it is strongly recommended that for patients who exhibit any of these signs, additional 3-dimensional (3D) radiographic evaluations be carried out prior to surgery.

Case reports describing the use of coronectomy to mitigate potential IAN injury were first published in the early 1990s.^9,10 Publications in the 2000s that outlined successful procedure outcomes have led to its more common use.^1,2

The procedure typically involves removing the entire crown of the tooth, including all the enamel, while intentionally leaving the root portion of the tooth that is close to the IAN canal. A conventional buccal hockey stick incision is made, followed by elevation of a full-thickness mucoperiosteal flap. Using a fissure bur, the crown of the tooth is exposed with conservative bone removal. A fissure bur is then utilized at a 30-degree angle to section the crown from the roots. A round bur is then used to reduce the root portion of the tooth to a point 3 mm to 4 mm below the bone crest in all dimensions, with care taken to remove all enamel. The vital exposed pulp does not require endodontic treatment.

Decayed third molars with possible pulpal exposures are not candidates for coronectomies. If mobility of the root fragment(s) is noted at surgery, it is advisable to remove the mobile root(s) completely. The area is then irrigated with sterile solution and closed primarily in a watertight fashion. Postoperative instructions and medications are given to the patient, similar to those used for the removal of an impacted third molar.

Although occurring less frequently than those encountered with complete impacted third molar removal, common reported postoperative sequelae of a coronectomy include pain, swelling, infection, alveolar osteitis ("dry socket"), and mild neurosensory deficit.^1,11-14 The most common postoperative finding reported is the potential for root migration and exposure. The reported incidence of root migration ranges from 13% to 97%,^15-17 occurring primarily during the first postoperative year.^11,13 While root migration is a common finding radiographically, it rarely requires surgical intervention unless it progresses to intraoral exposure and pain, inflammation, and/or infection. If this occurs, because the root migration is usually in a direction in which the roots move superiorly, away from the IAN canal and toward the ridge crest, their removal is typically a simple surgical procedure. Nerve injury has not been a reported complication of secondary root removal. There is, however, a recent case report of a neurologic deficit occurring 9 months after a coronectomy that was due to root migration of a curved/hooked root intentionally left in place surrounding the IAN canal. The neurologic deficit resolved after secondary root removal.¹⁸ A decrease in root migration has been reported when guided bone regeneration techniques are used with coronectomy surgery.¹⁹

The following case presentations describe coronectomy procedures performed in patients requiring the removal of impacted third molars.

Case 1

A 17-year-old female patient presented with a complaint of pain and pressure in her mandibular third molar areas. The patient's past medical history was negative, she took no medications, and she had no known allergies.

A panoramic radiograph was taken, which revealed full-bony impacted teeth Nos. 1, 16, 17, and 32. Teeth Nos. 17 and 32 appeared to be positioned in close proximity to the IAN canal with a radiographic loss of the IAN canal density and a darkening of the apical aspect of the roots. A CBCT scan then revealed an intimate contact between the roots and the IAN canal. A digital imaging and communications in medicine (DICOM) dataset was created and imported into the implant software (DTX Studio^™, NobelBiocare/Envista Holdings Corp., dtxstudio.com) to create 3D reformation images.

The patient was administered intravenous (IV) sedation and local anesthesia, and teeth Nos. 1 and 16 were removed and coronectomy procedures were performed on teeth Nos. 17 and 32. The patient's postoperative course was uneventful, and no sensory disturbances were reported. (See Figure 1 through Figure 8.)

Case 2

A 20-year-old male patient presented with a complaint of pain, pressure, and swelling in his mandibular third molar areas. His past medical history was negative, he took no medications, and he had no known allergies.

A panoramic radiograph was taken, which revealed full-bony impacted teeth Nos. 1, 16, 17, and 32. Teeth Nos. 17 and 32 appeared to be positioned in close proximity to the IAN canal with a radiographic loss of the IAN canal density and a darkening of the apical aspect of the roots. Additionally, the IAN canal associated with tooth No. 32 appeared to be displaced inferiorly. A CBCT scan was taken, which revealed an intimate contact between the roots and the IAN canal. A DICOM dataset was created and imported into the implant software (DTX Studio) to create 3D reformation images.

With the patient under IV sedation and local anesthesia, teeth Nos. 1 and 16 were removed and coronectomy procedures were performed on teeth Nos. 17 and 32. As in the first case, the patient's postoperative course was uneventful, and no sensory disturbances were reported. (See Figure 9 through Figure 12.)

Case 3

The patient, an 18-year-old woman, presented with a complaint of pain and pressure in her mandibular third molar areas. Her past medical history was negative, she took no medications, and she had no known allergies.

A panoramic radiograph revealed full-bony impacted teeth Nos. 1, 16, 17, and 32. Teeth Nos. 17 and 32 appeared to be positioned in close proximity to the IAN canal with a radiographic loss of the IAN canal density and a darkening of the apical aspect of the roots. Additionally, the IAN canal associated with tooth No. 32 appeared to be displaced inferiorly. A CBCT scan was taken, which revealed an intimate contact between the roots and the IAN canal. A DICOM dataset was created and imported into the implant software (DTX Studio) to create 3D reformation images.

The patient was administered IV sedation and local anesthesia, and teeth Nos. 1 and 16 were removed and coronectomy procedures were performed on teeth Nos. 17 and 32. As in the first two cases, the patient's postoperative course was uneventful, and no sensory disturbances were reported. (See Figure 13 through Figure 16.)

Case 4

A 33-year-old male patient presented with a complaint of pain, pressure, and chronic infection in his mandibular left third molar area. He was evaluated by a local periodontist who took a CBCT scan, which revealed a deeply horizontally impacted tooth No. 17 with a horizontally impacted supernumerary tooth No. 67 superior to and on top of No. 17. Significant bone loss was obvious radiographically, distal and buccal to the apex of tooth No. 18, which was confirmed by periodontal probing. His past medical history was negative, he took no medications, and had no known allergies.

The patient was referred to the authors' office for an evaluation and treatment. In addition to the above radiographic findings, review of the CBCT scan revealed tooth No. 17 positioned in close proximity to the IAN canal with a radiographic loss of the IAN canal density in relation to the roots of the tooth. Under IV sedation and local anesthesia, teeth Nos. 16 and 18 and supernumerary teeth Nos. 66 and 67 were removed, and a coronectomy was performed on deeply impacted tooth No. 17. A mineralized bank bone graft was placed in the region of tooth No. 18 to prepare the site for a future implant placement. The patient's postoperative course was uneventful, and no sensory disturbances were reported. (See Figure 17 through Figure 24.)

In patient cases requiring the removal of an impacted tooth, with 2-dimensional and 3-dimensional evidence of a close relationship between the root(s) of the tooth and the inferior alveolar nerve canal, coronectomy is a well-documented option to successfully mitigate the risk and sequelae of nerve trauma.

Gary Orentlicher, DMD
Section Chief, Oral and Maxillofacial Surgery, White Plains Hospital, White Plains, New York; Private Practice in Oral, Maxillofacial, and Implant Surgery, Scarsdale, New York; Diplomate, American Board of Oral and Maxillofacial Surgery

Andrew Horowitz, DMD, MD
Associate Attending, White Plains Hospital, White Plains, New York; Private Practice in Oral, Maxillofacial, and Implant Surgery, Scarsdale, New York; Fellow, American College of Surgeons