Journal Pre-proof

Removal of horizontally impacted mandibular third molars with large root bifurcations
using a modified tooth sectioning method

Rui Liao, DDS, PhD, Associate Professor, Xiujing Jiang, DDS, Nurse, Renfei Wang,
DDS, Professor, Xiaofeng Li, DDS, Professor, Qian Zheng, DDS, PhD, Professor,
Hanyao Huang, DDS, PhD, Resident
PII: S0278-2391(20)31508-1
DOI: https://doi.org/10.1016/j.joms.2020.12.011
Reference: YJOMS 59534

To appear in: Journal of Oral and Maxillofacial Surgery

Received Date: 8 October 2020

Revised Date: 1 December 2020
Accepted Date: 5 December 2020

Please cite this article as: Liao R, Jiang X, Wang R, Li X, Zheng Q, Huang H, Removal of horizontally
impacted mandibular third molars with large root bifurcations using a modified tooth sectioning method,
Journal of Oral and Maxillofacial Surgery (2021), doi: https://doi.org/10.1016/j.joms.2020.12.011.

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© 2020 Published by Elsevier Inc on behalf of the American Association of Oral and Maxillofacial
Surgeons
Removal of horizontally impacted
mandibular third molars with large root
bifurcations using a modified tooth
sectioning method
Rui Liao1, DDS, PhD, Associate Professor

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Xiujing Jiang2, DDS, Nurse

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Renfei Wang3, DDS, Professor

Xiaofeng Li3, DDS, Professor

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Qian Zheng4, DDS, PhD, Professor
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Hanyao Huang4, *, DDS, PhD, Resident

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1 Department of Oral Surgery, Hangzhou Dental Hospital, Savaid Medical College,

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University of Chinese Academy of Sciences, Hangzhou, China

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2 Department of Oral Implant, Hangzhou Dental Hospital, Savaid Medical College,

University of Chinese Academy of Sciences, Hangzhou, China

3 Department of General Dentistry, Hangzhou Dental Hospital, Savaid Medical

College, University of Chinese Academy of Sciences, Hangzhou, China

4 State Key Laboratory of Oral Diseases & National Clinical Research Center for
Oral Diseases & Department of Oral Maxillofacial Surgery, West China Hospital of
Stomatology, Sichuan University, Chengdu, China

*Corresponding to: Hanyao Huang, State Key Laboratory of Oral Diseases &
National Clinical Research Center for Oral Diseases & Department of Oral
Maxillofacial Surgery, West China Hospital of Stomatology, Sichuan University, 14
3rd Renmin South Road, Chengdu, China. E-mail: huanghanyao_cn@scu.edu.cn.
Phone: +86-028-85501462.
Acknowledgements: We are grateful to Professor Bing Shi for the support of this study and Dr.
Weiyu Liu for the language editing assistance. This project was supported by the Project of

Medical Technology, Zhejiang, China, granted to R.L. (2018KY144, 2017KY443). The authors

have no conflicts of interest.

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Removal of horizontally impacted
mandibular third molars with large root
bifurcations using a modified tooth
sectioning method

Abstract

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Purpose: To introduce the method and first results of a modified tooth sectioning technique for

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the extraction of horizontally impacted mandibular third molars (M3Ms) with large root

bifurcation.
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Patients and Methods: A total of 300 horizontally impacted M3Ms with large root bifurcation in
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medically healthy patients were included in this prospective study. Patients were divided into two
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groups: the modified method group (test group), in which M3M was sectioned between the distal

root and the remainder of the tooth at the point of root bifurcation; and the conventional method
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group (control group), in which M3M was sectioned between the crown and the root at the
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cementoenamel junction (CEJ). Operation duration, postoperative reactions, complications, and

patient satisfaction were analyzed and compared between two groups.

Results: Each group included 150 M3Ms which were all successfully extracted. Operation

durations in the test and control group were 10.48±3.78 and 15.09±4.24 minutes, respectively

(p<0.05). The test group had significantly better results than the control group with regard to

postoperative reactions and complications (p<0.05). Patients in the test group had higher

satisfaction ratings regarding operation duration and the healing process than those in the control

group (p<0.05).

Conclusions: The modified method of tooth sectioning between the distal root and the remainder

of the tooth can efficiently eliminate resistance from the bone and adjacent M2M and allow for

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just one sectioning of M3M in most cases, which could make the operation straightforward and

safe.

Keywords

Impacted mandibular third molar; operation duration; patient satisfaction; postoperative reaction

and complications; tooth extraction.

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Introduction

Removal of a horizontally impacted mandibular third molar (M3M) is complex. The difficulty

is increased in the case where the tooth has multiple roots with large root bifurcation (Figure

1)1,2. For this type of M3M, after elevation of the mucoperiosteal flap and removal of the bone

covering the crown, the conventional and most commonly used method of tooth sectioning to

eliminate obstruction of the adjacent mandibular second molar (M2M) involves separating the

crown and roots along the cementoenamel junction (CEJ) using a bur3,4. After crown removal,

further sectioning between the multiple roots is necessary at the root bifurcation using a bur or

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chisel5. This conventional method is not easy due to poor visibility and accessibility for the

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surgeon because of the adjacent M2M. Thus, the procedure is time-consuming, usually causes

significant trauma to the adjacent tissue, and may induce serious postoperative

complications6-8.
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In this study, a modified method of tooth sectioning for extraction of horizontally impacted
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M3M with large root bifurcation is designed, and comparisons between our modified method

and the conventional method was performed. This modified method is based on the
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anatomical structure characteristics of this type of tooth, analysis of resistance during removal,
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and substantial clinical experience. Outcomes suggested that our modified method was better

than the conventional extraction approach in cases of horizontally impacted M3M with large
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root bifurcation.

Materials and Methods

Patients and tissue specimens

A total of 300 horizontally impacted M3Ms in medically healthy patients aged 17–66 years

(mean age 29.3 years) were included in this prospective study. The patients did not have any

illnesses and were not taking any medications that could influence the surgical procedure or

postoperative wound healing. The criteria for inclusion and exclusion in this study were

demonstrated in Table 1.

Before the surgical procedure, all patients were informed in detail about the procedure of

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extraction, the time needed for the surgery, and possible intraoperative and postoperative

complications; all signed an informed consent form for inclusion in the study.

An additional preoperative cone-beam computed tomography (CBCT) examination was

performed in cases of deeply impacted M3M in close relationship with the mandibular canal

on panoramic radiographs to obtain detailed information about roots and their relationship

with the inferior alveolar nerve (IAN). The 300 teeth were separated into two groups

randomly with a random number table generated by a computer and extracted using the two

different methods of tooth sectioning.

This study was approved by the Hangzhou Dental Hospital Medical Ethics Committee

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(approval number 2017LL07).

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Surgical procedure
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The teeth were extracted under local anesthesia (4% articaine with 1:100,000 epinephrine). A
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sulcular incision was performed near the mesiobuccal edge of the M2M to its distal portion.

The incision line continued distally about 1.5 cm toward the mandibular ramus. The buccal
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mucoperiosteal flap was reflected, avoiding extensive reflection, especially on the lingual
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aspect, and was retracted carefully.

The bone lying over the crown was removed using a round bur mounted on a high-speed
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surgical handpiece with sufficient physiological saline to cool the operation region, and a
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gutter was formed between the bone and the buccal aspect of the M3M crown when the bur

proceeded along with the M3M buccal crown, the depth of which extended to the prominent

outline of the M3M crown (Figure 2, A and B).

In the test group, the distal cervical part of the crown was firstly removed to ensure the distal

root was separated from the remaining part and about 4 mm room between the distal root and

the crown was created (Figure 2, C and D). The distal root was mobilized with an elevator

and removed mesially and upwardly through the room (Figure 2, E and F); Next, under the

action of a straight elevator inserted at the mesial point of the gutter between the bone and the

M3M crown, the crown with the mesial root as whole was rotated disto-occlusally and

removed due to the elastic characteristic of the bone between roots making no resistance

(Figure 2, G and H; Figure 3A).

In the control group, the tooth was separated with a long straight bur vertically along the CEJ,
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and the crown was separated from the roots under rotation with an elevator (Supplemental

Figure 1A). After the entire crown had been removed, the bottom of the pulp chamber could

be viewed. The tooth was divided between the roots by long straight bur, and the roots were

luxated and separately removed mesially (Supplemental Figure 1B).

After the whole tooth had been removed, the socket was rinsed with physiological saline and

carefully examined for tooth remnants (Figure 3B). The incision was closed with sutures

(Figure 3C). All patients received antibiotics (cefprozil 250 mg twice daily or dirithromycin

500 mg twice daily for those with beta-lactam allergy) and dexamethasone (1.5 mg twice

daily) for 3 days.

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Evaluation

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Clinical evaluations were performed at 2 and 7 days after surgery. All postoperative
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evaluations were conducted by the same dental nurse who was blinded to group assignment.
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The evaluation parameters were: operation duration, primary bleeding on the day of surgery,

pain, edema and trismus level, injury to the IAN at 2 days, pain duration, dry socket, and
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patient satisfaction at 7 days. Patients returned after 7 days to have the sutures removed and
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the satisfaction on the experience during the removal operation, operation duration, and

healing process was rated by the patients, respectively. The definitions and standards were
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listed in the Table 2.

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Statistical analysis

SPSS (version 21.0; IBM Corp. Armonk, NY) was used for statistical analysis. Differences in

numerical data between groups, including operation duration, pain level and duration, edema,

trismus, and patient satisfaction, were analyzed by the t test. Nominal data, including primary

bleeding, dry socket, and injury to the IAN, were analyzed by the chi-square test. In all

analyses, p<0.05 was taken to indicate statistical significance.

Results

No significant differences were observed in patient characteristics between the two groups

(p>0.05) (Table 3). The operation duration differed significantly between the test group and

the control group (10.48±3.78 vs. 15.09±4.24 minutes, respectively; p<0.05). The mean

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values of postoperative pain score, pain duration, edema, and trismus were all significantly

lower in the test group than in the control group (p<0.05). The incidence rates of primary

bleeding, dry socket, and injury to the inferior alveolar nerve (IAN) were all significantly

lower in the test group than in the control group (p<0.05), the injuries to the IAN in the

control group were temporary and recovered within 1-4 months. Patient satisfaction scores

regarding the experience during the removal operation, operation duration, and the healing

process in the test group were 7.62±0.95, 8.03±1.18, and 7.62±0.95, respectively, while those

in the control group were 7.50±1.62 (p>0.05), 6.99±1.51 (p<0.05), and 6.68±1.79 (p<0.05),

respectively (Table 4).

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Discussion
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In the procedure of removing M3M, resistance from roots varies by the root size, shape,
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and position. It is markedly increased in cases with multiple roots and where the distance
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between two root apexes is greater than the width of the cervical trunk, referred to as large

root bifurcation.
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A number of novel methods for M3M extraction have been reported. The two-step

surgical approach9,10 consists of surgical removal of the mesial portion of the anatomical
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crown to create adequate space for mesial M3M migration, and the extraction is performed in
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a second surgical session after migration of the M3M has occurred. The orthodontic

extraction technique11 involves placement of a special bar on the tooth to control the direction

of traction over a period of 6–12 months. However, these methods are not suitable for M3M

with large root bifurcation because of the high degree of resistance from the roots preventing

movement of the tooth. Coronectomy12,13 is another technique which is suitable for

mesioangular and vertical bony impacted M3M, especially for ankylosed tooth. The

disadvantages of coronectomy13,14 include the possible need for a second operation to remove

the root, possible late infection of the retained root, and a high rate of unsatisfactory healing.

This latter method is also unsuitable for M3M horizontally impacted along the course of the

mandibular canal (MC) because sectioning of the tooth could endanger the nerve14.

A straightforward, safe, and efficient method to extract horizontally impacted M3M with

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large root bifurcation is required. The new method described here involves sectioning and

removal of the distal root first, and next removal of the remaining part, rotating occlusally.

The greatest advantage of the new tooth sectioning method is the less complex removal

procedure. First, removing the distal root transforms M3M multiple roots with large root

bifurcation to a single root, which is then more straightforward to remove. Sometimes, the

impaction angulation changes from horizontal to mesioangular if the mesial root lies slightly

upward; this is the least difficult type of M3M angulation to be removed. Second, a single

sectioning procedure is usually sufficient, because after removal of the distal root, the

remainder hinges at the mesial root apex when elevated and the center is shifted deeper, thus

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clearing the distal surface of the M2M successfully. Furthermore, the elastic characteristic of

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the bone between roots made no resistance, as a result the remaining part can be elevated

without further sectioning in most cases. -p

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Another advantage of the new method is that it makes surgery safer. Surgeons should be

able to visualize all procedures intraoperatively to ensure precision and avoid injury to
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adjacent structures15. In the new method, sectioning of the distal root is not as deep as in the
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conventional technique, and it is at a greater distance from the adjacent tooth crown. This

prevents the M2M crown from blocking the light and the surgeon’s view, thus aiding in
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visibility and making the surgery safer and more convenient. Meanwhile, this new method
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can help avoid uncertain and excessive bone removal, like the bone closed to IAN or between

roots.

Operation duration is a factor for the evaluation of operation difficulty16. The operation

duration of M3M removal depends on the depth of impaction, complexity of the procedure,

difficulty of the surgery, operator experience, patient compliance, etc. In this study, operation

duration was shorter in the test group than in the control group, without difference in depth of

impaction, indicating the possible effect of the new sectioning on simplifying the procedure as

well as providing better visibility and accessibility for the surgeon.

Postoperative reactions indicate the degree of inflammation around the operation site.

They are influenced by factors such as age, relative depth of the impaction, postoperative

management, and trauma to the adjacent structures during the removal surgery. In this study,

we excluded the possible bias in patient subjective opinions regarding the post-operative
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reactions through randomization in the large sample, at the same time, we took the same

post-operative management in the two groups. Results showed the new method was

associated with reduced post-operative reactions. This finding may be explained as the more

straightforward method and shorter operation duration17,18, and reduced surgical trauma in the

test group. The etiology of dry socket is not clear, but several risk factors were reported,

including smoking, oral contraceptive use, surgical trauma, gender, and age19-21. Whether the

new method could reduce the dry socket rate was not clear, and further study is needed. In the

control group, six M3Ms (4%) were associated with primary bleeding and temporary

hypoesthesia of the lip and chin on the operation side, but the test group had no such cases.

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Retrospective analysis of CBCT scan data showed relative depth of the six M3Ms was C type,

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and the teeth were all closely related to the MC. The degree of surgical difficulty increases
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with increasing depth of the impacted tooth22. The bleeding and temporary hypoesthesia may
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be resulted from the possible excessive sectioning to breach the upper wall of MC and injury

to the mandibular vein lying superiorly in the MC5 when the M3Ms were very complicated to
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be removed in the control group.

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Higher satisfaction scores regarding the operation duration and healing process in the

test group, indicating that patients preferred the new method to the conventional method, were
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consistent with the results for operation duration and postoperative reactions and
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complications in the two groups. However, the two groups did not differ significantly in terms

of satisfaction regarding the experience during the removal operation, indicating that the new

method did not improve the experience of surgery.

Two points regarding the procedure should be clarified. First, the surgeon must be aware

the bone removal is aimed to expose the crown and root bifurcation. Usually, the precise and

finite bone removal will not result in severe post-operative reactions, but excessive bone

removal is not suitable and will possibly aggravate the post-operative reactions. Second, if the

crown of the M3M is closely attached to the root of the M2M, additional buccolingual

sectioning with a bur on the crown is needed to clear the distal surface of the M2M. This can

sometimes be predicted on analysis of panoramic radiographs.

We emphasize the need for caution when performing the modified tooth sectioning

method. The following situations can potentially cause injury to the lingual nerve during
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operation: (a) when separating the tooth and penetrating the lingual plate, the lingual nerve

can be directly damaged; (b) bone fractures of the lingual plate caused by forceful removal of

root can injure the lingual nerve; (c) repeated punctures of the mandibular nerve block during

anesthesia can damage the lingual nerve. To protect the lingual nerve in these situations, a

lingual retractor can be used12. Other complications, such as dry socket, postoperative pain

and bleeding, and root displacement, should also be considered during operation.

This study is not without its limitations. Specifically, the proposed method was only

performed by one surgeon. Future study should include evaluations of this modified method

by more surgeons. A more comprehensive study of this modified method’s complications

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should also be conducted. In our follow-up study, we have more systematically analyzed this

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new method and its complications.
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In conclusion, compared with the conventional method of tooth sectioning, the new method of

sectioning between the distal root and the remainder of the tooth at the point of root
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bifurcation is more straightforward and safer. Therefore, it is of clinical value and may be an
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alternative for oral-maxillofacial surgeons in the removal of horizontally impacted M3M with

a large root bifurcation.

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Tables
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Table 1. The criteria for inclusion and exclusion

Criteria
Inclusion 1. M3M horizontally impacted on panoramic radiographs
2. M3M had multiple roots with large root bifurcation.(The
distance between two root apexes was greater than the width
of the cervical trunk)
Exclusion 1. Patients with severe uncontrolled systemic diseases, such as
leukemia, lymphoma, hemophilia, cardiac diseases, cardiac
dysrhythmia, hypertension, diabetes, hyperthyroidism, renal
disease, etc.
2. American Society of Anesthesiologists (ASA) III or above;
3. Patients with a coagulation disorder;
4. Female patients who were pregnant or menstruating;
5. Patients taking systemic corticosteroids, immunosuppressive
agents, bisphosphonates, or cancer chemotherapeutic agents;

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 6. Patients with a history of therapeutic radiation to the head and
neck region;
7. Patients with limitation of mouth opening and could not place
three fingers between the upper and lower central incisors
when opening the mouth;
8. Severe pericoronitis, ulcer, or other inflammation in the area of
the M3M;
9. Patients who did not agree to return to the hospital for
follow-up at the request of the trial.

Table 2. The definitions and standards for evaluation

Variable Definitions and standards

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Operation duration The time from the beginning of incision to the end of the suture
Pain The level assessed using a 10-cm visual analogue scale (VAS)

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Pain duration Patients were asked how many days postoperative pain had
persisted after 7 days.
Edema
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The degree ranked from 0 to 3 [0: no edema; 1: light edema (just
visible); 2: moderate edema (local); 3: severe edema (extended)]
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Trismus The degree ranked on a scale from 0 to 3 [0: no trismus; 1: light
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trismus (when opening the mouth, the patient could insert two
fingers vertically together); 2: moderate trismus (the patient could
insert one finger into the mouth); 3: severe trismus (the patient
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could not stretch to insert one finger into the mouth)]

Primary bleeding Bleeding continued after the patient had bitten on sterile gauze
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sponges, and packing hemostasis with absorbable gauze was

required
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Dry socket Continuous throbbing and excruciating pain referring to other

areas; alveolar socket covered with grayish necrotic tissue; denuded
alveolar bone; and halitosis.
Injury to the IAN* Patient had lower lip numbness on the same side; this was assessed
by measuring the function of the IAN with light touch stimulation.
Satisfaction Rated by patients through drawing a vertical line on a 10-cm
visual analogue scale (VAS) with the end points “dissatisfied” and
“completely satisfied.” on the experience during the removal
operation, operation duration, and healing process respectively.
* IAN, inferior alveolar nerve

Table 3. Patient Characteristics.

Test group (n=150) Control group (n=150) P value
Gender (Male/Female) 84/66 79/71 0.562
Age (yr) 28.99±9.96 29.39±10.62 0.809
ASA Class (I/II) 128/22 132/18 0.497
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Relative Depth(A/B/C) 12/107/31 16/105/29 0.720
Values are numbers or means±SD.
Relative Depth of the Third Molar in Bone: Position A: The highest portion of the tooth on a
level with or above the occlusal line; Position B: The highest portion of the tooth below the
occlusal line, but above the cervical line of the second molar; Position C: The highest portion
of the tooth on a level with or below the cervical line of the second molar.

Table 4. Operation duration, postoperative reactions, complications and patient

satisfaction in two groups
Variable Test group Control group (n=150) t value P
(n=150)
I. Operation duration and postoperative reactions
Operation duration 10.48±3.78 15.09±4.24 9.959 <0.001*

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Pain 1.97±0.60 5.59±1.58 26.280 <0.001*
Pain duration 1.51±0.70 2.91±0.79 16.255 <0.001*

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Edema 1.27±0.47 1.89±0.56 10.531 <0.001*
Trismus 0.83±0.51 1.47±0.68 9.104 <0.001*
II. Complications
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Primary bleeding 0(0%) 6(4%) - 0.030*
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Dry socket 1(0.7%) 8(5.3%) - 0.036*
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Injury to the IAN 0(0%) 6(4%) - 0.030*

III. Patient satisfaction
The experience during 7.62±0.95 7.50±1.62 0.78 0.434
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removal operation
Operation duration 8.03±1.18 6.99±1.51 6.68 <0.001*
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The healing process 7.62±0.95 6.68±1.79 5.69 <0.001*

Data are means ± SD (Numerical) or number (%) (Nominal)
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Statistically significant difference (P<0.05) was observed between groups (*).

Figures legends

Figure 1. Horizontally impacted M3Ms with large root bifurcation.

(A) Schematic diagram of horizontally impacted M3M with large root bifurcation. (B)

Representative horizontally impacted M3M with large root bifurcation. (C) Representative

radiography of horizontally impacted M3Ms with large root bifurcation. Black arrow showed

the M3M.

Figure 2. The modified tooth sectioning method for extraction of horizontally impacted

M3Ms with large root bifurcation.

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(A and B) The bone lying over the crown was removed, and a gutter shape of bone at the

buccal side of the M3M crown to prominent outline of crown was also removed. (C and D)

The tooth was first separated between the distal root and the remainder of the tooth at the

point of root bifurcation. (E and F) The distal root was luxated with an elevator and removed

upward and mesially. (G and H) The crown with the mesial root as a whole was rotated

distocclusally and removed around the mesial root apex as the center with a radius of the

distance between the mesial cusp and the mesial root apex, clearing the distal surface of the

M2M, and then raised and removed occlusally, due to the elastic characteristic of the bone

between roots, making no resistance.

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Figure 3. The representative extracted M3M and the management of extraction sockets
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(A) The representative extracted M3M with the modified tooth sectioning method. (B) After
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the whole tooth had been removed, the socket was rinsed with physiological saline and

carefully examined for tooth remnants. (C) The incision was closed with sutures.
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Supplemental Materials
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Supplemental Figure 1. The conventional tooth sectioning method for extraction of

horizontally impacted mandibular third molars (M3Ms) with large root bifurcation.
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The first step as bone removal was as the same as the modified method. (A) After bone

removal, the tooth was separated vertically along the cervical line and the crown was removed

upward. (B) The remainder of the tooth was divided longitudinally between the roots and the

roots were luxated mesially and removed separately.

14
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