Outcomes of Coronectomy and Total Odontectomy of Impacted Mandibular Third Molars

Abstract

Objective

The aim of this research was to evaluate the surgical complications and neurosensory deficits after coronectomy and the complete removal of mandibular third molars.

Methods

The study sample included patients requiring surgical removal of mandibular third molars. A coronectomy was conducted on 220 teeth showing signs of close proximity to the inferior alveolar canal. A complete extraction was performed on 218 teeth with no risk signs. The patients were evaluated at 1 week and 1, 3, 6, 12, and 24 months after surgery for pain, swelling, neurologic deficit, dry socket, postoperative bleeding, infection, root migration, and eruption.

Results

No significant difference was noted in pain and swelling; however, bleeding and dry socket were significantly higher in the odontectomy group (P = .017). The inferior alveolar nerve deficit was higher in the odontectomy group (3.7%) than the coronectomy group (0.5%) (P = .017). The percentage and distance of root migration of coronectomised teeth at 3, 6, and 12 months were 60% (2.37 ± 0.96 mm), 66% (3.35 ± 0.86 mm), and 74% (3.85 ± 0.93 mm), respectively.

Conclusions

Coronectomy is a safe procedure and should be performed when the roots are closely associated with the mandibular canal. Although root migration is common, the likelihood of root exposure is low and roots rarely need removal.

Introduction

The most frequent surgical procedure in oral surgical practice is the extraction of the mandibular third molar. Many complications could arise both during and after surgery. The most frequent side effects are oedema, trismus, haemorrhage, infection, injury to the alveolar nerve, displacement of the extracted tooth into adjacent spaces, and mandibular angle fracture.^1,2

Although inferior alveolar nerve (IAN) injury is uncommon, serious nerve deficits often result in lawsuits from some patients following the extraction of the mandibular third molars. Serious abnormal effects from an IAN injury include numbness, lower lip paraesthesia, and a reduced quality of life.³ The reported prevalence of IAN injury after mandibular third molar extraction varies from 0.4% to 8%; however, the rate of permanent IAN injury is no more than 1%.^4,5 The percentage can reach 35.64% in high-risk situations.⁶

Rood and Shebab⁷ determined 7 radiologic signs that may indicate a high risk of IAN injury. However, if 3 of the 7 signs are present on panoramic radiographs or there is a suspicion of close relationships between the third molar roots and mandibular canal, cone-beam computed tomography (CBCT) is advised.⁸

Different techniques have been suggested to minimise the risk of IAN injury, including staged removal,⁹ orthodontic extrusion,¹⁰ pericoronal ostectomy,¹¹ and coronectomy.¹² In 1984, Ecuyer and Debien¹³ introduced the coronectomy as an alternative to total extraction for the treatment of third molars that pose a severe risk of injury to the IAN. The method avoids any direct or indirect trauma to the IAN by removing only the crown and leaving the roots in the socket.

The purpose of this study was to assess the consequences of coronectomy and the complete surgical removal of impacted mandibular third molars.

Materials and methods

The sample of this prospective study included patients who presented to a teaching hospital for surgical removal of impacted mandibular third molars between February 2014 and July 2022. The study was conducted in accordance with the Declaration of Helsinki of 1975 and approved by our institutional ethical committee. All patients agreed to participate in the study and signed an informed consent form.

The selected patients were 18 to 60 years old, and the teeth were assigned into 1 of the 2 groups:

Coronectomy group: teeth with high-risk signs of an intimate relation of the inferior alveolar canal (IAC) to the roots on a panoramic radiograph and confirmed by CBCT (Figure).

Fig.

Cone-beam computed tomography (CBCT) showing inferior alveolar canal (IAC) perforating the mesial root.

Odontectomy group: teeth with no risk signs.

Exclusion criteria for coronectomy were nonvital teeth; caries encroaching on the root; periapical infection; immature apex; and absence of adjacent second molars.

The same surgeon performed all surgeries under local anaesthesia. After IAN, lingual, and buccal nerve blocks with lignocaine (2%) and 1:80,000 adrenaline, a standard Ward's flap was reflected. A narrow buccal gutter was made by removing buccal bone with a round or fissure bur down to the cementoenamel. 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 stump was reduced to at least 2 to 3 mm below the bone level. Special attention was given to remove any enamel spikes. Finally, the socket was thoroughly irrigated with saline, and the flap was primarily closed with a 4/0 vicryl suture.

The technique of odontectomy was the same as that prescribed for coronectomy, but the tooth was completely removed with or without tooth sectioning.

The patient was given the usual postoperative instructions, including ice pack application immediately after surgery, a liquid cold diet ion the first day, and a soft diet for the next 5 days. In addition, twice-daily mouthwash with chlorhexidine for 7 days, starting the day after surgery, was prescribed. Patients were given 3 days of broad-spectrum antibiotics (amoxicillin 500 mg every 8 hours or clindamycin 300 mg every 8 hours if a penicillin allergy existed) and paracetamol 500 mg every 6 hours.

Clinical and radiographic (using OPG) evaluations of the patients were performed after 1 week and after 1, 3, 6, 12, and 24 months. Digital panoramic radiographs were obtained with an orthopantomography (Soredex Cranex D Digital Dental X-ray). The radiographic parameters and measurements were acquired digitally. The following variables were recorded.

• 1.Preoperative variables: Demographic data, angulation of the tooth, number and morphology of roots, the distance between the root apex and the IAC, and difficulty of surgery according to the Pernambuco difficulty index¹⁴.
• 2.Intraoperative variables included the duration of surgery and any other complications.
• 3.Postoperative variables: The short-term outcomes included postoperative pain which was evaluated by the patient using a visual analog scale (VAS) of 10 cm, where 0 indicated no pain and 10 indicated the most severe pain. Facial swelling was assessed by the patient as none, mild, moderate, and severe according to the criteria developed by Kamaraj et al.¹⁵ IAN deficits and dry sockets were also documented. The long-term outcomes included delayed healing of the socket, root migration and exposure, infection, and the need for a second surgery.

Results

A coronectomy of impacted third molars was conducted in 243 patients; however, only 212 patients (220 teeth) completed the follow-up visits. The mean age of the patients was 31.7 ± 11.3 years, with 124 females and 88 males.

Complete extraction was performed in 252 patients; however, only 210 patients (218 teeth) completed the follow-up visits. The mean age of the patients was 20.96 ± 10.47 years, with 134 females and 76 males. There was no significant difference in the age and sex distribution between the 2 groups.

There was no significant difference in the depth and direction of impaction, the morphology and number of roots, the Pernambuco surgical difficulty index, or the duration of the operation.

There was no significant difference in the VAS pain score or postoperative facial swelling between the 2 groups (Table 1).

Table 1.

VAS pain score and the degree of facial swelling.

Groups	Variables	Day -1	Day -3	Day- 7
Coronectomy	Pain VAS, mean (± SD)	7.3 (±2.6)	4.8 (±1.6)	1.8 (±1.3)
Odontectomy		6.9 (±3.1)	5.0 (±1.1)	2.0 (±0.9)
Significance	P value*	0.144	0.128	0.062
Coronectomy	Swelling, No.(%)
	None	0 (0.0)	10 (4.5)	179 (81.4)
	Mild	41 (18.6)	73 (33.2)	35 (15.9)
	Moderate	146 (66.4)	120 (54.5)	6 (2.7)
	Severe	33 (15)	17 (7.8)	0 (0.0)
Odontectomy	Swelling, No.(%)
	None	0 (0.0)	4 (1.8)	168 (77.1)
	Mild	32 (14.7)	57 (26.1)	40 (18.3)
	Moderate	137 (62.8)	116 (53.2)	7 (3.2)
	Severe	49 (22.5)	26 (11.9)	3 (1.4)
Significance	P value⁎⁎	0.105	0.121	0.704

^⁎T test.

^⁎⁎Fisher exact test.

VAS, visual analog scale.

The IAN deficit was noted in 3.7% (8/218) of the odontectomy group vs 0.5% (1/220) of the coronectomy group. The difference was significant (P = .017). Postoperative bleeding and dry socket were significantly higher in the odontectomy group than the coronectomy group (P = .017). Only one patient in the odontectomy group had displacement of one root to the submandibular space (Table 2).

Table 2.

Intraoperative and short-term (<1 month) postoperative complications.

Complications	Coronectomy, No. (%)	Odontectomy, No. (%)	P*
Inferior alveolar nerve deficit	1 (0.5)	8 (3.7)	.017
Bleeding	1 (0.5)	8 (3.7)	.017
Dry socket	10 (4.5)	23 (10.5)	.017
Root displacement	0 (0.0)	1 (0.4)	.996

^⁎Fisher exact test.

The long-term outcomes of coronectomy are shown in Table 3. Periapical infections occurred in 6.4% (14/220) of teeth; migration of the roots away from the IAC was seen in 74% (163/220) of teeth; and only one tooth (0.5%) showed root migration toward the canal. A delayed-onset IAN deficit was noted in one tooth (0.5%).

Table 3.

Long-term complications of coronectomy (>1 month).

Complications	No.	%
Periapical infection	14	6.4
Root migration away from IAC	163	74.0
Root migration toward IAC	1	0.5
Delayed onset IAN deficit	1	0.5
Root exposure	18	8.2
Need for removal of root stump	7	3.2

IAC, inferior alveolar canal; IAN, inferior alveolar nerve.

Communication of the roots with the oral cavity was seen in 8.2% (18/220) of teeth, and surgical removal of the remaining roots was done in 3.2% (7/220) of cases.

Sixty percent of teeth showed root migration at 3 months, which increased to 66% at 6 months. The frequency of root migration at 1 year increased to 74%. There was a statistically significant difference in the migration distance amongst 3, 6, and 12 months (Table 4).

Table 4.

Frequency and distance (in mm) of root migration.

Time, mo	Migrating roots, No.(%)	Migration distance (mm) Mean (±SD)	P*
3	134 (60.0)	2.37 (±0.96)	<.0001
6	146 (66.0)	3.35 (± 0.86)	<.0001
12	163 (74.0)	3.85 (± 0.93)	<.0001
24	163 (74.0)	3.89 (±0.95)	>.05

^⁎Analysis of variance followed by Student-Newman-Keuls post hoc test.

Discussion

This study was conducted to compare the outcomes between coronectomy and complete removal of impacted mandibular third molars. The failure rate of coronectomy in this study was 5% (13/255), which is within the reported range of failed coronectomy of 0% in the study of Singh et al¹⁶ and 38.8% in the study of Renton et al.¹⁷

There was no discernible difference in the VAS pain score between the 2 groups. The findings are consistent with those of Singh et al¹⁶ and Renton et al.¹⁷ However, Leung and Cheung¹⁸ found that coronectomy is less painful at 1 week postoperatively. Hatano et al¹⁹ claimed that coronectomy is more painful because of the tight closure and transient pulpitis of the remaining vital pulp.

In this study, there was no discernible difference in facial swelling between the 2 groups. Our results are consistent with those of Singh et al¹⁶ and Kang et al.²⁰ According to other researchers, the oedema following a coronectomy was less severe than that associated with complete tooth removal.^18,20 In addition, Sencimen²¹ claimed that a coronectomy required a wider flap and more bone removal to be completed than a traditional extraction.

In this study, 1 case of IAN deficit followed a coronectomy, and 8 cases followed an odontectomy. The findings of this study are consistent with those of other earlier investigations. Six cases (5%) of IAN deficit were recorded by Hatano et al¹⁹ in the extraction group and 1 patient (1%) in the coronectomy group. Leung and Cheung¹⁸ also reported 1 case (0.5%) of IAN injury after coronectomy and 9 cases (5%) after complete extraction. Although no patients in Kang et al's²⁰ study had an IAN deficit following coronectomy, there were 6 (10.91%) instances in the extraction group. No occurrences of IAN deficit were recorded by Renton et al¹⁷ in the coronectomy group, but 3 cases (3.2%) were documented after a failed coronectomy. Cilasun et al²² reported 2 cases (2%) of IAN injury during extraction, with no case after coronectomy. This difference in the incidence of IAN injury between studies could be explained by variations in the selection criteria for coronectomy, sample size, and surgeon expertise.

In the current study, neither the extraction nor the coronectomy groups experienced infection within the first month after surgery. Without the use of postoperative antibiotics, the reported rate of postoperative infection of the wound following coronectomy was 1.1% (1/102) vs 3.4% (4/188) for the control in the study of Hatano et al,¹⁹ 5.2% (3/58) vs 1% (1/102) for the control in the study of Renton et al,¹⁷ 5.8% in the study of Leung and Cheung,¹⁸ and 10.99% vs 10.20% for the control in the study of Yan et al.²³ Studies with postoperative antibiotic prescription showed an infection rate of 0% for both groups in the studies of Singh et al¹⁶ and Kang et al²⁰ and 1.1% in the coronectomy group vs 0% in the control group in the study of Cilasun et al.²²

In this study, the extraction group experienced considerably more dry sockets (10.5%) than the coronectomy group (4.5%). Our findings are consistent with those of Renton et al,¹⁷ Hatano et al,¹⁹ and Yan et al.²³

At 1 year, 74% of the roots migrated for a distance of 3.85 mm. The results of this study support those of other earlier investigations.16, 17, 18, 19, 20^,24 The highest percentage of root migration was recorded by Hatano et al¹⁹ (85%). According to Leung and Cheung¹⁸ and Kohara et al,²⁵ the roots stop moving after 2 years, probably due to the formation of new bone.

Conclusions

Compared to a routine extraction, a coronectomy is a safe procedure that protects the IAN from injury after third molar surgery. After a coronectomy, bleeding, infection, and dry sockets are less frequently noted than complete tooth removal. Coronectomy also speeds up the bone repair distal to the adjacent second molars. Although root migration is a typical side effect after coronectomy, the likelihood of root exposure and the subsequent requirement for surgical excision is limited.

Conflict of interest

None disclosed.