Two-stage extraction by partial grinding of impacted mandibular third molar in close proximity to the inferior alveolar nerve

Abstract

BACKGROUND

Extraction of impacted third molars often leads to severe complications caused by damage to the inferior alveolar nerve (IAN).

AIM

To proposes a method for the partial grinding of an impacted mandibular third molar (IMM3) near the IAN to prevent IAN injury during IMM3 extraction.

METHODS

Between January 1996 and March 2022, 25 patients with IMM3 roots near the IAN were enrolled. The first stage of the operation consisted of grinding a major part of the IMM3 crown with a high-speed turbine dental drill to achieve sufficient space between the mandibular second molar and IMM3. After 6 months, when the root tips were observed to be away from the IAN on X-ray examination, the remaining part of the IMM3 was completely removed.

RESULTS

All IMM3s were extracted easily without symptoms of IAN injury after extraction.

CONCLUSION

Partial IMM3 grinding may be a good alternative treatment option to avoid IAN injury in high-risk cases.

Key Words: Partial grinding, Impacted mandibular third molar, Inferior alveolar nerve, Cone-beam computed tomography

Core Tip: The use of cone-beam computed tomography (CBCT) may prevent damage to the inferior alveolar nerve (IAN), but not reduce the risk of injuries to IAN during impacted mandibular third molar extraction. In our clinic, although the incidence of IAN injury is very low because of adoption of CBCT, we have adopted two-stage extraction in order to avoid injury to IAN to the greatest extent. Compared with other existing methods, our method is safer and better, which is worth promoting.

INTRODUCTION

Impacted mandibular third molar (IMM3) is frequently the most commonly impacted tooth. An impacted third molar often requires extraction. Prolonged retention of IMM3 in the oral cavity can lead to various complications, including gingivitis, infection, caries in adjacent teeth, and bone cysts. IMM3s can be retained only if they are in a favorable position and exhibit good occlusal contact with the opposing teeth[1-4].

The clinical use of cone-beam computed tomography (CBCT) allows three-dimensional examination. CBCT can be helpful in determining the positional relationship of the inferior alveolar nerve (IAN) with an IMM3 by providing coronal and axial views. However, the use of CBCT does not reduce the risk of damage to the IAN during IMM3 extraction[5-8].

Although the incidence of IAN injury is very low, sensory deficits and temporary or permanent lower lip numbness can occur if the IAN is injured[9-11]. These are severe complications of IMM3 extraction that may interfere with daily life activities, such as talking and chewing. In our clinic, we have adopted a two-stage extraction method for cases of IMM3 near the IAN to avoid IAN damage to the greatest extent.

MATERIALS AND METHODS

In all, 25 patients (15 males, 10 females) determined by panoramic X-ray examination to have an IMM3 near the IAN that needed to be removed were included. Each patient was informed about the surgical purpose, surgical protocol, recovery period, possible complications, and potential risks and signed a consent form.

Both stages of all extraction procedures were performed under local anaesthesia with 2% lidocaine (Shanghai Hefeng Pharmaceutical Co., Ltd., Shanghai, China) to anaesthetize the tongue, buccal nerve, and IAN. After flap elevation and bone removal, a major part of the IMM3 crown was ground with a high-speed turbine dental drill. The wound was rinsed with 0.9% saline solution after grinding and then sutured with 4-0 silk; the sutures were removed after 5-7 d. After 6-12 months, when the root tips were observed to be away from the IAN on X-ray examination, the remaining part of the IMM3 was removed. A total of 25 IMM3s that were in close proximity to the IAN were successfully extracted without damage to the IAN.

RESULTS

In our retrospective study of 25 cases, there were no cases of lower lip numbness after the extraction of IMM3s in close proximity to the IAN, based on postoperative chief complaints.

DISCUSSION

Direct IAN-IMM3 contact is considered a risk factor for complications and postoperative sensory impairment following surgical removal of the IMM3 and causes great concern among dentists. However, there have also been studies showing that there is no association between IAN injury and direct IAN-IMM3 contact, whereas there is an association with cortication status. To avoid injuring the IAN, dentists have attempted many methods, such as IMM3 extraction after orthodontic treatment to separate the IAN and IMM3[10,12-17].

For temporary lower lip numbness after IAN exposure, the neurotrophic drug mecobalamin can be administered; moreover, according to our clinical experience, the neurosensory deficits and symptoms of IAN injury can gradually resolve after a certain period. Some surgical interventions can also be used to relieve symptoms of IAN injury[18-20]. However, at present, there is no effective treatment for permanent damage to the IAN.

We adopted a two-stage method for IMM3 extraction. The first stage of the operation consists of grinding a major part of the IMM3 crown to obtain sufficient space for mesial movement of the IMM3. After 6-12 months, when there is distance between the root tips of the remaining part of the IMM3 and the IAN, IMM3 can be completely extracted (Figure 1).

Figure 1 Panoramic views showing changes in relationship between the inferior alveolar nerve and impacted mandibular third molar root position by partial grinding in two cases (arrow indicates the mandibular canal). A: Preoperative panoramic radiograph of Case 1 depicting direct contact between the inferior alveolar nerve (IAN) and the impacted mandibular third molar (IMM3); B: Post-partial grinding panoramic radiograph of Case 1, demonstrating sufficient eruption space between the impacted tooth and adjacent teeth; C: Six-month post-partial grinding view illustrating space between the root of the IMM3 and the superior wall of the IAN canal in Case 1; D: Preoperative panoramic radiograph of Case 2 revealing the IMM3 passing through the IAN; E: Post-partial removal of IMM3 (Phase 1) panoramic radiograph of Case 2, displaying adequate eruption space between the impacted tooth and adjacent teeth; F: Panoramic view after 6 mo of partial grinding indicating that in Case 2, the root of the IMM3 had moved away from the IAN canal following 6 months of partial grinding.

CBCT is expensive and only used in larger dental institutions, and can only clarify the three-dimensional relationship between IMM3 and the IAN. However, if IMM3-IAN is close or IMM3 passes through IAN, routine removal of IMM3 cannot avoid postoperative complications. This approach avoids damage to the IAN. We believe that this method is worth popularizing, especially in grassroots hospitals, which may only have the capability for dental radiography and not CBCT.

CONCLUSION

Partial IMM3 grinding may be a good alternative treatment option to avoid IAN injury in high-risk cases.

ARTICLE HIGHLIGHTS

Research background

The conventional method of extracting impacted mandibular third molars (IMM3) that are closely related to the inferior alveolar nerve (IAN) can easily damage the nerve.

Research motivation

To avoid damaging the IAN during tooth extraction.

Research objectives

To proposes a method for the partial grinding of an IMM3 near the IAN to prevent IAN injury during IMM3 extraction.

Research methods

The first stage was to use a high-speed turbo drill to grind and cut most of the IMM3 dental crowns, leaving the roots in place. After 6-12 months, when the IMM3 root left the nerve canal, complete extraction of the IMM3 root was performed.

Research results

Although it seemed to take longer after two stages, all IMM3s were completely removed, and there were no cases of complications of damaging the IAN.

Research conclusions

Two-stage extraction of IMM3 located closer to the IAN canal can minimize nerve damage to the greatest extent possible.

Research perspectives

Partial IMM3 grinding may be a good alternative treatment option to avoid IAN injury in high-risk cases.