Removal of horizontally impacted mandibular thrid molar with large root

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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
https://doi.org/10.1016/j.joms.2020.12.011
https://doi.org/10.1016/j.joms.2020.12.011
Removal of horizontally impacted 
mandibular third molars with large root 
bifurcations using a modified tooth 
sectioning method 
Rui Liao1, DDS, PhD, Associate Professor 
Xiujing Jiang2, DDS, Nurse 
Renfei Wang3, DDS, Professor 
Xiaofeng Li3, DDS, Professor 
Qian Zheng4, DDS, PhD, Professor 
Hanyao Huang4, *, DDS, PhD, Resident 
1 Department of Oral Surgery, Hangzhou Dental Hospital, Savaid Medical College, 
University of Chinese Academy of Sciences, Hangzhou, China 
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 
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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 
Purpose: To introduce the method and first results of a modified tooth sectioning technique for 
the extraction of horizontally impacted mandibular third molars (M3Ms) with large root 
bifurcation. 
Patients and Methods: A total of 300 horizontally impacted M3Ms with large root bifurcation in 
medically healthy patients were included in this prospective study. Patients were divided into two 
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 
group (control group), in which M3M was sectioned between the crown and the root at the 
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 
chisel5. This conventional method is not easy due to poor visibility and accessibility for the 
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. 
In this study, a modified method of tooth sectioning for extraction of horizontally impacted 
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 
anatomical structure characteristics of this type of tooth, analysis of resistance during removal, 
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 
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 intotwo 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 
(approval number 2017LL07). 
Surgical procedure 
The teeth were extracted under local anesthesia (4% articaine with 1:100,000 epinephrine). A 
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 
mucoperiosteal flap was reflected, avoiding extensive reflection, especially on the lingual 
aspect, and was retracted carefully. 
The bone lying over the crown was removed using a round bur mounted on a high-speed 
surgical handpiece with sufficient physiological saline to cool the operation region, and a 
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. 
Evaluation 
Clinical evaluations were performed at 2 and 7 days after surgery. All postoperative 
evaluations were conducted by the same dental nurse who was blinded to group assignment. 
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 
patient satisfaction at 7 days. Patients returned after 7 days to have the sutures removed and 
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 
listed in the Table 2. 
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). 
Discussion 
In the procedure of removing M3M, resistance from roots varies by the root size, shape, 
and position. It is markedly increased in cases with multiple roots and where the distance 
between two root apexes is greater than the width of the cervical trunk, referred to as large 
root bifurcation. 
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 
crown to create adequate space for mesial M3M migration, and the extraction is performed in 
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 
clearing the distal surface of the M2M successfully. Furthermore, the elastic characteristic of 
the bone between roots made no resistance, as a result the remaining part can be elevated 
without further sectioning in most cases. 
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 
adjacent structures15. In the new method, sectioning of the distal root is not as deep as in the 
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 
visibility and making the surgery safer and more convenient. Meanwhile, this new method 
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. 
Retrospective analysis of CBCT scan data showed relative depth of the six M3Ms was C type, 
and the teeth were all closely related to the MC. The degree of surgical difficulty increases 
with increasing depth of the impacted tooth22. The bleeding and temporary hypoesthesia may 
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 
be removed in the control group. 
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 
consistent with the results for operation duration and postoperative reactions and 
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 
should also be conducted. In our follow-up study, we have more systematically analyzed this 
new method and its complications. 
 
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 
bifurcation is more straightforward and safer. Therefore, it is of clinical value and may be an 
alternative for oral-maxillofacial surgeons in the removal of horizontally impacted M3M with 
a large root bifurcation.
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Tables 
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 
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) 
Pain duration Patients were asked how many days postoperative pain had 
persisted after 7 days. 
Edema The degree ranked from 0 to 3 [0: no edema; 1: light edema (just 
visible); 2: moderate edema (local); 3: severe edema (extended)] 
Trismus The degree ranked on a scale from 0 to 3 [0: no trismus; 1: light 
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 
could not stretch to insert one finger into the mouth)] 
Primary bleeding Bleeding continued after the patient had bitten on sterile gauze 
sponges, and packing hemostasis with absorbable gauze was 
required 
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 
(n=150) 
Control group (n=150) t value P 
I. Operation duration and postoperative reactions 
Operation duration 10.48±3.78 15.09±4.24 9.959 <0.001* 
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* 
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 
Primary bleeding 0(0%) 6(4%) - 0.030* 
Dry socket 1(0.7%) 8(5.3%) - 0.036* 
Injury to the IAN 0(0%) 6(4%) - 0.030* 
III. Patient satisfaction 
The experience during 
removal operation 
7.62±0.95 7.50±1.62 0.78 0.434 
Operation duration 8.03±1.18 6.99±1.51 6.68 <0.001* 
The healing process 7.62±0.95 6.68±1.79 5.69 <0.001* 
Data are means ± SD (Numerical) or number (%) (Nominal) 
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 crownwith 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. 
 
Figure 3. The representative extracted M3M and the management of extraction sockets 
(A) The representative extracted M3M with the modified tooth sectioning method. (B) After 
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. 
Supplemental Materials 
Supplemental Figure 1. The conventional tooth sectioning method for extraction of 
horizontally impacted mandibular third molars (M3Ms) with large root bifurcation. 
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. 
 
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