Coronectomy of the mandibular third molar: Respect for the inferior alveolar nerve

Accepted Manuscript Coronectomy for the mandibular third molar: Respect for the inferior alveolar nerve A.J. Kouwenberg, MD, DMD, L.P.P. Stroy, MD, DMD, E.d.Vree – v.d Rijt, MD, DMD, G. Mensink, MD, DMD, PhD, P.J.J. Gooris, MD, DMD, PhD, FEBOMFS PII:

S1010-5182(16)00039-1

DOI:

10.1016/j.jcms.2016.01.025

Reference:

YJCMS 2297

To appear in:

Journal of Cranio-Maxillo-Facial Surgery

Received Date: 17 July 2015 Accepted Date: 27 January 2016

Please cite this article as: Kouwenberg AJ, Stroy LPP, Rijt EdV–vd, Mensink G, Gooris PJJ, Coronectomy for the mandibular third molar: Respect for the inferior alveolar nerve, Journal of CranioMaxillofacial Surgery (2016), doi: 10.1016/j.jcms.2016.01.025. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Coronectomy for the mandibular third molar: Respect for the inferior alveolar nerve

A.J. Kouwenberga MD, DMD; L.P.P. Stroyb MD, DMD; E. d. Vree – v.d. Rijtb MD,

a

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DMD; G. Mensinkc,d MD, DMD, PhD; P.J.J. Goorise,f,g,* MD, DMD, PhD, FEBOMFS

Radboud University Medical Centre, Department of Oral and Maxillofacial Surgery Geert

Grooteplein-Zuid 10, 6525 GA Nijmegen, The Netherlands

University Medical Centre, Department of Oral and Maxillofacial Surgery, Utrecht, the

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b

Netherlands

Amphia Hospital, Department of Oral and Maxillofacial Surgery

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c

Molengracht 21, 4800 RL Breda, The Netherlands d

Leiden

University

Medical

Centre,

Department

of

Oral

and

SurgeryAlbinusdreef 2, 2333 ZA Leiden, The Netherlands e

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Academic Medical Centre, Department of Oral and Maxillofacial Surgery

Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands f

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WA, Seattle, USA

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University of Washington, Department of Oral and Maxillofacial Surgery

*Corresponding author: Peter J.J. Gooris

Amphia Hospital

Molengracht 21, Postbus 90157, 4800 RL Breda, The Netherlands Tel.: +31(076) 595 3111 Fax: +31 076-5953040 E-mail: [email protected]

Maxillofacial

ACCEPTED MANUSCRIPT ACKNOWLEDGEMENTS We thank Serge Steenen for the drawings in Figure 2.

Funding: None

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Conflicts of interest: None

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Coronectomy for the mandibular third molar: Respect for the inferior alveolar

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nerve

SUMMARY

The aim of this study was to evaluate the outcomes of coronectomy as an alternative

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surgical procedure to complete removal of the impacted mandibular third molar in

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patients with a suspected close relationship between the tooth root(s) and the mandibular canal. A total of 151 patients underwent coronectomy and were followed up with clinical examinations and panoramic radiographs for a minimum of 6 months after surgery. None of the patients exhibited inferior alveolar nerve injury. Eruption of the retained root(s) was more frequent in younger patients (18 to 35 years). Thirty-six patients (23.8%)

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exhibited insufficient growth of new bone in the alveolar defect, and 11.3% required a second surgical procedure to remove the root remnant(s). Our results indicate that coronectomy can be a reliable alternative to complete removal of the impacted

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mandibular third molar in patients exhibiting an increased risk of damage to the inferior

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alveolar nerve on panoramic radiographs.

KEYWORDS

coronectomy, inferior alveolar nerve, mandibular canal, decapitation, third molar, wisdom tooth

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INTRODUCTION Removal of the third molars is the most common minor surgical procedure performed by

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oral and maxillofacial surgeons. Damage to the inferior alveolar nerve is considered a serious complication of this surgery (Ramadas and Sealey, 2001; Bouloux et al., 2007). The damage may vary from temporarily altered sensations to permanent injury. The

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estimated risk of inferior alveolar nerve injury varies from 3.9% to 4.1% for temporary sensory disturbances and from 0.4% to 0.9% for permanent injury (Carmichael and

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McGowan, 1992; Bataineh, 2001; Gülicher and Gerlach, 2001; Robert et al., 2005; Jerjes et al., 2006).

Certain signs on panoramic radiographs have been associated with a high risk of nerve injury during removal of the mandibular third molars. Rood et al. (1990) defined an

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increased risk of inferior alveolar nerve injury as the presence of one or more radiographic signs that have been reported to be suggestive of a close relationship between the mandibular canal and the third molar, such as interruption of the white line

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of the mandibular canal wall, darkening around the root(s), diversion of the mandibular canal, narrowing of the mandibular canal, narrowing of the root(s), and deflection of the

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root(s). Estimation of the risk of inferior alveolar nerve injury using preoperative conebeam computed tomography (CBCT) is also possible; however, when compared with panoramic radiography, there is no significant difference in the sensitivity and specificity for predicting inferior alveolar nerve exposure during a removal procedure (Ghaeminia et al., 2009). On the other hand, Ghaeminia et al. (2011) reported a benefit of CBCT in terms of more adequate surgical planning to prevent nerve damage.

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In addition to preoperative imaging, various surgical techniques such as cleavage of the roots in the furcation area can decrease the risk of inferior alveolar nerve damage. Coronectomy is another technique that can decrease nerve morbidity during the surgical

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management of mandibular third molars in high-risk patients (Gleeson et al., 2012; Long et al., 2012; Patel et al., 2013). This procedure involves the deliberate retention of the apical third of the tooth root(s) likely to be in proximity to the inferior dental nerve

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(Gleeson et al., 2012). Appropriate application of the coronectomy technique decreases the risk of damage to the inferior alveolar nerve (Frafjord et al., 2010; Leung et al.,

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2009). While recent studies have shown positive results after coronectomy, the technique is still not widely accepted, probably because of the lack of data on long-term outcomes or the possible requirement of a second procedure to remove the root remnant(s) (Gleeson et al., 2012; Patel et al., 2013).

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From the above perspectives, we conducted this study to analyze the outcomes of coronectomy for the mandibular third molar in patients with an increased risk of inferior alveolar nerve damage on preoperative panoramic radiographs. We hypothesized that the

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incidence of inferior alveolar nerve hypoesthesia during coronectomy is negligible

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compared with that during the complete removal of impacted mandibular third molars.

MATERIALS AND METHODS Study design This prospective study included patients who visited the Department of Oral and

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Maxillofacial Surgery at the Amphia Hospital, Breda, the Netherlands between 2009 and 2013 for removal of the mandibular third molar(s) and were identified as high-risk patients with regard to inferior alveolar nerve injury on preoperative panoramic

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radiographs (Figure 1). Panoramic radiographs were examined for signs of an increased risk of nerve injury, including narrowing or curvature of the mandibular canal, narrowing or curvature of the tooth root(s), overlap, and darkening around the root(s) (Figure 2). To

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prevent unnecessary radiation exposure, we did not perform additional CBCT and

considered the abovementioned signs on panoramic radiographs as risk factors for nerve

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injury. Although the degree of the potential risk can be measured more accurately on CBCT images, we considered patients with any degree of risk on panoramic radiographs as high-risk patients.

All patients were informed of potential complications after complete removal of the

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third molar (i.e., nerve injury) and coronectomy (i.e., possibility of second procedure for remnant removal). After they were adequately informed about the different surgical techniques and the possible outcomes, they decided the procedure they wished to

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undergo. All patients who opted for coronectomy were included in this study and were

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instructed to return for a postoperative follow-up visit at 6 months after surgery. They were informed, once again, of all potential risks and complications, including pain, bleeding, and infection, and were instructed to contact the Department in case of acute problems. This study was performed in accordance with the guidelines of our institution and the tenets of the Declaration of Helsinki on medical protocols and ethics, and it was granted an exemption in writing by the institutional review board. Eventually, 191 patients (76 men and 115 women; age, 12–81 years; mean age,

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30.8 years) were enrolled. The primary outcome variable was postoperative inferior alveolar nerve hypoesthesia. The secondary outcome variable was the requirement of a second procedure for removal of the retained root portions. Independent variables

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included age, sex, impaction depth and direction, and surgeon’s experience. All teeth

were either partially erupted or not erupted (including the depth), and the direction of impaction varied from vertical to horizontal. The signs of a possible close nerve–root

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relationship observed on panoramic radiographs included narrowing of the mandibular canal, curvature of the mandibular canal, narrowing of the root(s), curvature of the

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root(s), overlap, and darkening around the root(s) (Table 1).

Surgical procedure

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All third molars were removed under local anesthesia by senior oral and maxillofacial (OMF) surgeons or OMF surgery (OMFS) residents. Following incision placement and mucoperiosteal flap elevation (Figure 3), bone on the buccal and distal sides of the tooth

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was removed with a round bur, exposing the tooth up to the level of the cementoenamel

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junction. The coronal portion was sectioned from the roots using a fissure bur (Figure 4). The coronectomy cut was carefully placed at an adequate depth on the lingual and mesial sides so that the coronal portion could be elevated without force, thus guaranteeing no movement of the retained root(s). To prevent lingual nerve injury, the cut was not extended lingually into the inner cortex and no lingual flap was raised (Renton et al., 2005). A residual bone height of at least 3 mm was maintained above the root margin. The surface of the root(s) was planed with a round bur (Figure 5). No pulp extirpation

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was performed. After rinsing and irrigation, the wound was primarily closed with simple interrupted sutures. An immediate postoperative panoramic radiograph was obtained to check the position and surface of the retained root portion. No antibiotics or nonsteroidal

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anti-inflammatory drugs were administered before surgery. After surgery, patients were instructed to rinse their oral cavities with chlorhexidine three times daily from 1 day after the procedure until normal dental hygiene was resumed. In case of pain, they were

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prescribed paracetamol or, if not contraindicated, a nonsteroidal anti-inflammatory drug

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in combination with omeprazole.

Data collection

All patients were instructed to return for a postoperative follow-up visit at 6 months after

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surgery or sooner if persisting or recurrent symptoms occurred. Patients who did not show up for the 6-month follow-up visit were excluded from the study.

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The 6-month follow-up examination included evaluations for postoperative hypoesthesia and pocket formation distal to the mandibular second molar. In addition, the

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surgical site was probed to check for exposure of the root remnant(s). Irritation of the inferior alveolar nerve was ruled out by history taking and pinprick and two-point discrimination tests. The pinprick test was performed using a dental probe applied with steadily increasing pressures. The patient was asked to indicate the point at which the sensation changed to sharp from dull. The two-point discrimination test was performed with two dental probes. The probes were drawn a few millimeters across the surface at a constant pressure, and the patient was asked to indicate whether one or two points were

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felt (Loescher et al., 2003). A panoramic radiograph was obtained to check for any movement of the root remnant(s) and the growth of new bone in the apical and coronal defects. Any movement of the root remnant(s) and all postoperative complications were

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recorded.

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Statistical analysis

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To test the correlation between the diverse variables, a Chi quadrate test was used. Probability values of less than 0.05 were considered statistically significant. All statistical analyses were performed using IBM SPSS Statistics software version 20.

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RESULTS

A total of 191 patients underwent coronectomy. Of these, 40 (20.9%) patients who

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underwent coronectomy during the study period were lost to follow-up, even after repeated calls. These patients were subsequently excluded, and the remaining 151 were

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included in the final analysis.

Within this group, there was no damage to either the inferior alveolar nerve or the

lingual nerve. Seventeen (11.3%) patients required a second procedure for removal of the retained root(s), because the remnant(s) erupted coronally to the upper level of the bone, resulting in irritation of the covering gingiva or persistent deep pockets distal to the second molar. However, there were no significant associations between any of the

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clinical parameters analyzed (Table 1). There was a tendency for a correlation between symptom severity (i.e., pain and infection) before treatment and the requirement for a

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second surgery; however, the correlation was not statistically significant (p = 0.088). Furthermore, there was no significant correlation between the surgeon’s experience and the need for a second surgery. Eight and nine patients who required second surgeries

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were treated by a surgeon and a resident, respectively. Table 2 shows the correlation

between variables in terms of p-values. The significant correlations (italics) are further

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elaborated. Sex and symptom severity at the 6-month follow-up (m > f, p = 0.041; Table 3) were significantly correlated, as were age and the amount of root migration at 6 months (Figures 6 and 7). For every 1-year increase in age, the amount of root migration decreased by 0.047 mm (p = 0.000).

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The correlation between symptom severity, particularly pain or gingival sensitivity (i.e., signs of infection) in the treated region, before treatment and that at 6 months was significant, i.e., the greater was the symptom severity before treatment, the greater it was

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at 6 months after treatment (Table 4; p = 0.047). Moreover, the degree of eruption of the third molar before surgery was significantly correlated with migration of the root

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remnant(s) at 6 months after surgery (Table 5). Thus, when 1 and 3 and 2 and 1 were compared, there was no significant correlation (1 vs. 3, p = 0.924; 2 vs. 1, p = 0.117); however, when 2 and 3 were compared, a significant correlation was observed (p = 0.017).

There was no evidence that the retained apical root portion(s) of the most deeply impacted molars exhibited the greatest degree of eruption after coronectomy. However,

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when a third molar is impacted, the root remnants of more superficially impacted teeth

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tend to migrate more coronally.

DISCUSSION

The expected benefit of coronectomy over complete removal of the mandibular third

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molar is the decreased risk of injury to the inferior alveolar nerve (Pogrel, 2009). None of

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the patients exhibited nerve damage in our study, confirming our hypothesis that nerve injury does not occur after coronectomy. Coronectomy decreases the reported risk for temporarily altered sensations and permanent paraesthesia from 3.9%–4.1% and 0.4%– 0.9%, respectively, to 0% (Carmichael et al., 1992; Bataineh et al., 2001; Gülicher et al., 2001; Robert et al., 2005; Jerjes et al., 2006). Other studies have compared complete

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removal of the mandibular third molar with coronectomy. Renton et al. (2005) reported that inferior alveolar nerve damage occurred in 19% patients who underwent complete removal of the impacted third molar and no patient who underwent successful

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coronectomy. In the same report (Renton et al., 2005), 8% patients experienced irritation

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of the inferior alveolar nerve after failed coronectomy, and the incidence of dry socket infection was similar in both the coronectomy and complete removal groups. A potential disadvantage of leaving a root portion behind is the possible risk of

increased postoperative complaints and infection. However, in the present study, retained roots after coronectomy for the mandibular third molars did not result in many complications with regard to infection, pain, and the development of a pathology within the first 6 months after surgery. Although root eruption may occur (Renton et al., 2005;

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Leung et al., 2012), this phenomenon necessitated a second surgical procedure in only 11.3% patients in the present study. The results of the present study are also comparable with those of an earlier, smaller study in a Dutch population (Wijs et al., 2010). In that

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study, none of the patients experienced sensory impairment of the alveolar nerve after coronectomy, while three of 38 patients (7.9%) required removal of problematic root

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remnants.

Frenkel et al. (2014) advised that follow-up for patients who have undergone

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coronectomy should be extended for at least 1 year because of the possibility of root eruption between the first 6 and 12 months. Kohara et al. (2015) showed the progression of eruption even between the first 12 and 24 months, with eruption ceasing only in the third year after the procedure (Kohara et al., 2015).

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Previous studies have also compared the outcomes of coronectomy with and without endodontic treatment. The results of these studies confirmed that endodontic treatment does not affect the rate of success of coronectomy. In the present study, no

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endodontic treatment was involved, which is in accordance with the current literature (Sencimen et al., 2010); furthermore, no periapical lesions developed after coronectomy

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in our patient population.

A disadvantage of coronectomy is the risk of requiring a second procedure. In case

of irritation or complications after coronectomy, the retained root(s) requires removal. Complications include eruption of the root coronally up to the upper level of the bone, which results in irritation of the covering gingiva, persistent deep pockets distal to the second molar, or an infectious process in the area distal to the second molar. Of the 151

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patients included in this study, 17 (11.3%) required a second surgical procedure. We could not identify any clinical parameters that could predict a second procedure. However, preoperative symptom severity showed some tendency for a correlation,

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although it was not significant. In addition, there was no correlation between the

requirement for a second procedure and the surgeon’s experience (senior surgeon or

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resident).

The area just distal to the second molar is the most difficult to view during

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coronectomy, which can result in incomplete sectioning of the crown portion in this area. In such cases, an anteriorly projecting enamel segment of the third molar may be left behind, resulting in postoperative irritation. While this can be recognized on postoperative panoramic radiographs, it was not corrected in some patients (Figure 8). These patients eventually returned to the operating room for additional planing of the

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anterior projecting root segment, in accordance with the current protocol. Frenkel et al. (2015) now recommend that an immediate postoperative panoramic radiograph should be obtained, and if enamel retention is observed, repeat coronectomy should be performed to

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prevent residual root infection.

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CBCT provides the surgeon with three-dimensional information. However, we

considered an overlap of the course of the inferior alveolar canal with the radices of the impacted molar or an aberrant course of the canal or root(s) on panoramic radiographs to be a sufficient indicator of potential nerve irritation. Therefore, we believed that CBCT would not influence our choice of surgery and decided against it. Further studies should include CBCT image acquisition for all patients with suspected root proximity on panoramic radiographs, thus allowing for more accurate identification of high-risk

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patients requiring coronectomy. According to the literature (Long et al., 2012), the rate of root migration after

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coronectomy is high (13.2%–85.3%). However, the migration distance is short (3.06 ± 1.67 mm), and the direction is away from the inferior alveolar nerve. Moreover, the rates of second procedures and root exposure are low (Long et al., 2012). These results are

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consistent with the following outcomes in the present study: migration rate, 84.1% and mean root migration distance, 1.85 mm (standard deviation, 1.34 mm). The migration

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distance was 0–6 mm, which was shorter than that reported in the existing literature. The direction of migration was always away from the inferior alveolar nerve. There is a difference in the degree of eruption and growth of new bone between younger and older patients (Frenkel et al., 2014). For every 1-year increase in age, the amount of

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migration decreases by 0.047 mm. As opposed to our expectations, we found no evidence that the retained apical root portions of the most deeply impacted third molars would exhibit the greatest degree of eruption after coronectomy.

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Furthermore, symptom severity was no greater in the older patient group;

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moreover, age did not influence the amount of new bone growth in the defect, formation of deep pockets distal to the second molar, or the possibility of contacting the root portion(s) with a probe. In older patients, recovery after inferior alveolar nerve damage seems to be slower and more difficult than that in younger patients (Gady et al., 2013). Therefore, one may consider coronectomy as the first choice of treatment for patients with an increased risk of inferior alveolar nerve damage, particularly elderly patients.

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CONCLUSIONS As opposed to complete removal of the impacted third molar, which may cause irritation

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of the inferior alveolar nerve, no paresthesia or anesthesia developed after coronectomy in our study, even in the elderly. However, although no predictors were identified, second surgery may be required in case of persistent postoperative complications. Our results

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suggest that coronectomy is a reliable surgical alternative with a low risk of

complications in patients requiring impacted mandibular third molar removal who exhibit

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a high risk of inferior alveolar nerve injury on preoperative panoramic radiographs.

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Bataineh AB: Sensory nerve impairment following mandibular third molar surgery. J Oral Maxillofac Surg 59:1012 1017, 2001.

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Cilasun U, Yildirim T, Guzeldemir E, Pektas ZO: Coronectomy in patients with high risk of inferior alveolar nerve injury diagnosed by computed tomography. J Oral Maxillofac Surg 69:1557 1661, 2011.

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Frafjord R, Renton T: A review of coronectomy. Oral Surgery 3:1 7, 2010. doi: 10.1111/j.1752-248X.2010.01079.x

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Frenkel B, Givol N, Shoshani Y: Coronectomy of the mandibular third molar: a retrospective study of 185 procedures and the decision to repeat the coronectomy in cases of failure. J Oral Maxillofac Surg 73:587 594, 2015. doi: 10.1016/j.joms.2014.10.011.

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Gady J, Fletcher MC: Coronectomy: indications, outcomes, and description of technique.

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Atlas Oral Maxillofac Surg Clin North Am 21:221 226, 2013. doi: 10.1016/j.cxom.2013.05.008. Epub 2013 Jun 29

Ghaeminia H, Meijer GJ, Soehardi A, Borstlap WA, Mulder J, Bergé SJ: Position of the impacted third molar in relation to the mandibular canal. Diagnostic accuracy of cone

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beam computed tomography compared with panoramic radiography. Int J Oral Maxillofac Surg 38:964 971, 2009. doi: 10.1016/j.ijom.2009.06.007. Epub2009 Jul 28

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Ghaeminia H, Meijer GJ, Soehardi A, Borstlap WA, Mulder J, Vlijmen OJ, Bergé SJ, Maal TJ: The use of cone beam CT for the removal of wisdom teeth changes the surgical

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approach compared with panoramic radiography: a pilot study. Int J Oral Maxillofac Surg 40:834 839, 2011. doi: 10.1016/j.ijom.2011.02.032. Epub 2011Apr 19 Gleeson CF, Patel V, Kwok J, Sproat C: Coronectomy practice. Paper 1. Technique and trouble-shooting. Br J Oral Maxillofac Surg 50:739 744, 2012. doi: 10.1016/j.bjoms.2012.01.001. Epub2012 Jan 28 Gülicher D, Gerlach KL: Sensory impairment of the lingual and inferior alveolar nerves

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following removal of impacted mandibular third molars. Int J Oral Maxillofac Surg 30:306 312, 2001.

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Jerjes W, Swinson B, Moles DR, El-Maaytah M, Banu B, Upile T, Kumar M, Al Khawalde M, Vourvachis M, Hadi H, Kumar S, Hopper C: Permanent sensory nerve

impairment following third molar surgery: a prospective study. Oral Surg Oral Med Oral

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Pathol Oral Radiol Endod 102:e1 e7, 2006.

Kohara K, Kurita K, Kuroiwa Y, Goto S, Umemura E: Usefulness of mandibular third

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molar coronectomy assessed through clinical evaluation over three years of follow-up. Int J Oral Maxillofac Surg 44: 259 266, 2015. doi: 10.1016/j.ijom.2014.10.003. Epub 2014 Nov 8

Leung YY, Cheung LK: Safety of coronectomy versus excision of wisdom teeth: a

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randomized controlled trial. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 108:821 827, 2009. doi: 10.1016/j.tripleo.2009.07.004. Epub 2009 Sep 26

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Leung YY, Cheung LK: Coronectomy of the lower third molar is safe within the first 3 years. J Oral Maxillofac Surg 70:1515 1522, 2012. doi: 10.1016/j.joms.2011.12.029.

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Loescher AR, Smith KG, Robinson PP: Nerve damage and third molar removal. Dent Update 30:375 380, 382, 2003. Long H, Zhou Y, Liao L, Pyakurel U, Wang Y, Lai W: Coronectomy vs. total removal for third molar extraction: a systematic review. J Dent Res 91:659 665, 2012. doi: 10.1177/0022034512449346. Epub 2012 May 23

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Patel V, Gleeson CF, Kwok J, Sproat C: Coronectomy practice. Paper 2: complications and long term management. Br J Oral Maxillofac Surg 51:347 352, 2013. doi:

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10.1016/j.bjoms.2012.06.008. Epub 2012 Jul 12 Pogrel MA: Coronectomy to prevent damage to the inferior alveolar nerve. Alpha Omegan 102:61 67, 2009.

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Robert RC, Bacchetti P, Pogrel MA: Frequency of trigeminal nerve injuries following third molar removal. J Oral Maxillofac Surg 63:732 735, discussion 736, 2005. Rood JP, Shehab BA: The radiological prediction of inferior alveolar nerve injury during

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third molar surgery. Br J Oral Maxillofac Surg 28:20 25, 1990.

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Sencimen M, Ortakoglu K, Aydin C, Aydintug YS, Ozyigit A, Ozen T, Gunaydin Y: Is endodontic treatment necessary during coronectomy procedure? J Oral Maxillofac Surg 68:2385 2390, 2010. doi: 10.1016/j.joms.2010.02.024. Epub2010 Jul 21 Wijs RW, Karssemakers LH, Becking AG: [Coronectomy. An alternative for complete removal of the third molar in the lower jaw] Ned Tijdschr Tandheelkd 117:337 340, 2010 [Article in Dutch].

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TABLES TABLE 1: Patient characteristics Variable Features

Number of patients

Male Female Years Age Partially erupted Eruption of the mandibular third molar Not erupted Vertical Impaction of the mandibular third molar Mesioangular Distoangular Horizontal Level with the occlusal plane of the second Depth of the mandibular third molar molar (measured from highest Below the occlusal plane and above the cervical margin of the second molar point) Below the cervical margin of the second molar Radiographic signs of a Narrowing of the mandibular canal Curvature of the mandibular canal close root–nerve Narrowing of the root(s) relationship (Figure 2) Curvature of the root(s) Overlap Darkening around the root(s)

76 115 12 to 81 109 82 80 83 6 22 25

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Sex

114 52 7 15 7 30 116 16

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Root migration (mm)

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TABLE 2: Correlations between the different parameters measured in this study Second Symptoms Pockets at Bone treatment at 6 months growth in 6 months after defect at 6 after coronectom months after coronectom y y coronectom y Sex .474 .041 .162 .419 Age .957 .962 .950 .960 Symptoms before .088 .047 .185 .786 treatment Mandibular third molar .789 .598 .133 .971 eruption Mandibular third molar .869 .527 .990 .615 impaction Radiographic signs of a .184 .075 .066 .509 close root–nerve relationship The significant correlations are in italics.

.338 .000 .731 .032

.132 .806

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TABLE 3: Correlation between sex and symptom severity at 6 months after coronectomy [observed and expected (n) values] No symptoms at 6 months Symptoms at 6 months Male 51 (54) 8 (5) Female 88 (85) 5 (7)

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TABLE 4: Correlation between symptom severity at the time of coronectomy and that at 6 months after coronectomy [observed and expected (n) values] No symptoms at 6 months Symptoms at 6 months No symptoms at the time of 87 (84) 4 (7) treatment Symptoms at the time of 52 (55) 8 (5) treatment

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TABLE 5: Amount of root migration according to different degrees of impaction at 6 months after coronectomy Mean root migration (mm) 1 Level with the occlusal plane of the mandibular second molar 1.500 2 Below the occlusal plane and above the cervical margin of the 2.064 mandibular second molar 1.463 3 Below the cervical margin of the mandibular second molar

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Figure 3: Incision placement and flap elevation

Figure 5: Root planning.

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Figure 4: Coronal sectioning

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Figure 2: Radiographic signs of a close root–nerve relationship A – Narrowing of the mandibular canal B – Curvature of the mandibular canal C – Narrowing of the root(s) D – Curvature of the root(s) E – Overlap F – Darkening around the root(s)

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CAPTIONS TO ILLUSTRATIONS Figure 1: Suspected relationship between the mandibular canal and the third molar root Note the darkening around the root.

Figure 6: Immediate postoperative panoramic radiograph Note the curvature of the mesial root and some darkening around the distal root. Figure 7: Panoramic radiograph obtained at 6 months after coronectomy The root has migrated coronally.

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Figure 8: Incomplete coronectomy

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