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British Journal of Oral and Maxillofacial Surgery xxx (2015) xxx–xxx
Efficacy of the technique of piezoelectric corticotomy for orthodontic traction of impacted mandibular third molars夽 Zhigui Ma, Guangzhou Xu ∗ , Chi Yang ∗∗ , Qianyang Xie, Yuqing Shen, Shanyong Zhang Department of Oral Surgery, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University, School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, PR China Accepted 2 January 2015
Abstract Our aim was to assess the efficacy of piezoelectric corticotomy for orthodontic traction of mandibular third molars close to the inferior alveolar nerve. Thirty patients with impacted third molars close to the nerve were included in the study, 15 of whom were treated with conventional orthodontic traction and 15 with piezoelectric corticotomy. We recorded duration of treatment including exposure and orthodontic traction, and time to the final extraction. Postoperative complications including trismus, swelling, and pain were also noted. Alveolar bone levels mesial and distal to the second molars were evaluated on cone-beam computed tomographic (CT) images. Student’s t test was used to assess the significance of differences between the groups. After orthodontic treatments all impacted third molars were successfully removed from the inferior alveolar nerve without neurological damage. The mean (SD) duration of surgical exposure in the piezoelectric corticotomy group was significantly longer than that in the conventional group (p = 0.01). The mean (SD) duration of traction was 4 (2.3) months after piezoelectric corticotomy, much shorter than the 7.5 (1.3) months in the conventional group (p = 0.03). There were no significant differences in postoperative complications between the groups. There was a significant increase in the distal alveolar height of second molars after treatment in both groups (p < 0.01). We conclude that the use of piezoelectric corticotomy allows more efficient and faster traction of third molars with a close relation between the root and the inferior alveolar nerve, although it took longer than the traditional technique. © 2015 Published by Elsevier Ltd. on behalf of The British Association of Oral and Maxillofacial Surgeons.
Keywords: Piezoelectric corticotomy; Orthodontic traction; Cone-beam CT; Impacted third molar; Bone formation
Introduction 夽
This project was supported by Shanghai Municipal Education Commission Research Fund for Young College and University Teachers (jdy11027), Research Fund of Shanghai Municipal Health Bureau (20134Y061) and College Scientific Research Fund (2012-12). ∗ Corresponding author at: Department of Oral and Maxillofacial Surgery, Ninth People’s Hospital, Collage of Stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai Research Institute of Stomatology, 639, Zhi Zao Ju Rd, 200011 Shanghai, People’s Republic of China. ∗∗ Co-corresponding author. E-mail addresses: [email protected] (G. Xu), [email protected] (C. Yang).
Neurological changes that result from damage to the inferior alveolar nerve are the most serious complication of the extraction of mandibular third molars, and the incidence of associated paraesthesia has been reported to be 1.1%.1 The main factor is the proximity of the roots of the tooth to the nerve.2 The application of orthodontic traction can successfully displace the roots away from the nerve, which reduces the risk of damage.3–5 However, the duration of treatment is often long, the mean (SD) in our previous report being 6.6 (SD = 2.1).6 Mesially inclined and horizontal teeth often require longer treatment (6–12 months).4
http://dx.doi.org/10.1016/j.bjoms.2015.01.002 0266-4356/© 2015 Published by Elsevier Ltd. on behalf of The British Association of Oral and Maxillofacial Surgeons.
Please cite this article in press as: Ma Z, et al. Efficacy of the technique of piezoelectric corticotomy for orthodontic traction of impacted mandibular third molars. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.01.002
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Corticotomy of the alveolar bone, which has recently been introduced into orthodontics, enables the orthodontist to facilitate the movement of teeth.7 With the technique one tooth can be moved 2–3 times further in a third or a quarter of the time required for traditional orthodontics.8 This is a remarkable advance in the case of regional orthodontic treatment using simple orthodontic devices. Piezoelectric surgery® is efficient for osteotomy because it is a selective, micrometrical cut that produces a limited area of bleeding.9 We have used piezoelectric corticotomy of the alveolar bone to facilitate orthodontic movement of teeth and compared it with conventional orthodontic traction for impacted third molars. The aim of the study was to find out which of these two techniques was better for orthodontic traction of mandibular third molars close to the inferior alveolar nerve.
Patients and methods Between August 2010 and August 2013, 30 patients were recruited from the Department of Oral Surgery, Shanghai Ninth People’s Hospital affiliated with Shanghai Jiao Tong University, School of Medicine (Shanghai, China). The protocol was approved by the local ethics committee (201048) and patients gave informed consent. All the operations were completed by the same surgeon, and orthodontic treatments by the same orthodontist. The selection criteria included patients who were judged to be at high risk of injury to the inferior alveolar nerve based on radiographic features in routine preoperative dental pantomographs and cone-beam computed tomography (CT, J. Morita Mfg Corp, Kyoto, Japan), and whose mandibular third molars were impacted and in need of exposure (we included third molars with horizontal, mesioangular, and vertical impaction according to the classification of Tay et al.10 ). Participants had no periradicular conditions or active periodontal disease, no tooth loss, no systemic diseases, and they did not smoke. The treatment methods were randomly assigned using a computer-generated randomisation list. Fifteen patients (6 men and 9 women, mean (SD) age 27 (5.6) years) were treated by traditional orthodontic traction, and the other 15 patients (5 men and 10 women, mean (SD) age 24 (4.8) years) were operated on with surgically assisted orthodontic traction with piezocorticotomy. Surgical and orthodontic technique After block anesthesia with local infiltration of the buccal nerve had been given, a full-thickness intrasulcular flap was fashioned from the mesial to the distal margins of the second molar with a distal releasing incision. The mucoperiosteal flap was reflected to expose the third molar and the cortical bone. In the conventional traction group the bone on the occlusal and buccal surfaces of the tooth was removed by low-speed drilling with copious irrigation for cooling. In the piezocorticotomy group the bone was removed with a
Fig. 1. Two vertical cuts were made mesially and distally around the third molar. The horizontal osteotomy connected with vertical osteotomies was also made by piezosurgery® .
piezoelectric device (Piezosurgery® , Silfragent, Italy). The amplitude of the microvibrations was from 80 to 100 m with a frequency of 28 to 32 kHz, corresponding to a handpiece power rating of 45 W. Vertical corticotomy cuts were made around the root of the third molar, and stopped just short of the alveolar crest (about 2 mm). These cuts were connected near the apices of the teeth with a horizontal cut. Cuts were made just beneath the buccal cortical plate (Fig. 1). The orthodontic appliance was inserted and bonded to the buccal surface of the impacted tooth. As described in our previous paper, two steps were used for mesially and horizontally inclined third molars and one step for vertically impacted teeth.6 A hook was bonded with a light-cured composite on the exposed surface of the impacted tooth, and a 3-loop spring (0.016 in. stainless steel) was welded to the adjacent second molar band with the end in contact the hook, to distalize the mesially or horizontally impacted molar first. A cantilever 0.017 in. × 0.025 in. was then used to push the third molar upright and extrude it (Fig. 2). The patients were monitored every month for the movement of the impacted teeth. Cone-beam CT was used to evaluate the relation between the roots and the inferior alveolar nerve before extraction. Once the impacted root apex had been separated from the nerve the third molar could be removed. An antibiotic (amoxicillin; 50 mg/kg in 2 daily doses for 3 days) and an analgesic (paracetamol; 750 mg every 6 h) were prescribed as necessary. Rinsing with 0.12% chlorhexidine gluconate was also recommended. The wound was sutured, and the sutures removed one week later. Clinical assessments The duration of treatment was the primary outcome variable, including the exposure, orthodontic traction, and final dental extraction after the root had separated from the nerve. Duration of anaesthesia, flaps, and sutures were not recorded. All subjects had a follow-up visit after 48 h for evaluation of trismus, swelling, and pain. Trismus was evaluated by a measurement of the difference of maximal interincisal
Please cite this article in press as: Ma Z, et al. Efficacy of the technique of piezoelectric corticotomy for orthodontic traction of impacted mandibular third molars. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.01.002
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Fig. 2. Diagram of orthodontic extraction. A 3-loop spring was used to move the impacted third molar distally, with the end contacting the hook. A cantilever was then hooked on to the main arch wire to extrude the third molar further.
opening before and after exposure. Postoperative swelling was the difference in the distance from the region of the distal trigone to the skin measured before and after exposure, as described by Sortino et al.9 Pain was scored by the patients on a visual analogue scale (VAS) that ranged from 0 (no pain) to 100 (the most severe pain). Neurological injuries were evaluated from any postoperative changes in the sensitivity of the tissues innervated by the inferior alveolar nerve (evaluated both subjectively and objectively, using light touch and a needle). Radiological measurements The largest sagittal slice of the second molar was selected on cone-beam CT images. The alveolar height was the distance from the alveolar crest to the apical line, which was tangential to the long axis of the second molar. The long axis of the second molar was a line that passed through the central groove to the middle of the apices of the root. Mesial and distal alveolar bone levels were measured (Fig. 3). When the distal bone level is lower than the mesial level, distal bone resorbs. Linear measurements for bone level were obtained with MB-Ruler measuring software (accurate to 0.01 mm) (Markus Bader, Berlin, Germany). Statistical analysis All measurements from the cone-beam CT scans were made twice by the same operator and the mean value was used in the final evaluation. Analyses were made with the help of the program SPSS for Windows (version 16.0; SPSS Inc, Chicago, IL, USA) and Student’s t test was used to compare the significance of differences between clinical and radiological variables in the two groups. Probabilities of less than 0.05 were accepted as significant.
Results The groups were comparable. In the conventional traction group, 3 third molars were horizontally impacted, 6 mesioangularly, and 6 vertically. In the piezocorticotomy
Fig. 3. Measurement of the level of alveolar bone. A baseline was drawn tangentially to the long axis of the second molar through the apex of the root. The levels of mesial and distal bone were the distances from the alveolar crest to the apical line. The anatomical proximity of the inferior alveolar nerve to the root of the third molar and the loss of osteoperiodontal tissue at the distal second molar were noted before treatment in a case of mesial impaction.
group, 2 were horizontally, 6 mesioangularly, and 7 vertically impacted. All third molars in both groups were totally and successfully separated from the inferior alveolar nerve after treatment, with no neurological injuries (Figs. 3 and 4). The mean (SD) duration of surgical exposure was 8.4 (3.1) min in the conventional traction group and 15.1 (4.7) min in the piezocorticotomy group. The mean (SD) time to completion of the orthodontic traction was 7.5 (1.3) months in the conventional group, but 4 (2.3) months in the piezocorticotomy group, both differences being significant (p = 0.01 and p = 0.03, respectively). There was no significant difference in the time that it took to complete the final extraction (p = 0.14) between the two groups, and no significant differences in the amount of trismus (p = 0.31), postoperative swelling (p = 0.11), or pain (p = 0.41) 48 h after exposure of impacted third molars (Table 1).
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Table 1 Mean (SD) duration of treatment, trismus, swelling, and pain in the two groups (n = 15 in each). Variable
Conventional traction
Duration of exposure (min) Duration of orthodontic traction (months) Extraction time (min) Complications (mm) Trismus Swelling VAS for pain
Piezo corticotomy
p value
8.43 (3.1) 7.53 (1.3) 5.20 (1.4)
15.13 (4.7) 4.00 (2.3) 5.53 (1.7)
0.01 0.03 0.14
15.32 (2.9) 9.54 (1.4) 45.43 (10.8)
16.35 (2.6) 8.71 (1.4) 48.72 (10.8)
0.31 0.11 0.41
VAS = visual analogue scale. Table 2 The mean (SD) distal alveolar level of second molars (mm) before and after treatment in the two groups (n = 15 in each). Level of second molar
Mesial Distal Mesiodistal
Conventional traction
p value
Before
After
10.21 (3.1) 6.75 (2.7) 3.46 (1.7)
9.77 (3.6) 9.66 (3.6) 0.11 (2.0)
Alveolar bone height of second molars Table 2 shows that the distal bone height of the second molars was significantly lower than that of the mesial height before treatment, but there was a significant increase in the distal measurement after treatment in both groups (p = 0.01). There were no significant differences between the mesial and distal alveolar levels in either group after treatment.
Discussion Traction of mandibular third molars has been one of the most difficult problems in traditional orthodontics, particularly in
Fig. 4. The separation of the impacted third molar from the inferior alveolar nerve and a good level of alveolar bone distal to the second molar could be seen after the piezocorticotomy-facilitated orthodontic traction in the same case as Fig. 3.
0.23 0.01 0.01
Piezo corticotomy
p value
Before
After
10.75 (2.7) 7.19 (2.3) 3.56 (2.1)
10.49 (1.9) 10.31 (1.4) 0.18 (2.5)
0.51 0.01 0.01
adults, because of the duration of the treatment period. However, with the assistance of decortication, it has now become possible to separate third molars rapidly from the inferior alveolar nerve, and to the best of our knowledge we are the first to report this method. Piezosurgery® is a suitable instrument thanks to its ease of use and selectivity of bone cutting. We used piezoelectric corticotomy to cut the alveolus around the third molars without entering the cancellous bone, and so avoided the risk of damage to underlying structures such as the inferior alveolar nerve. The mean time for alveolar cutting was considerably increased using ultrasound piezosurgery compared with the usual device, which confirms the results of Sortino et al.9 and Bartuli et al.11 who also found that more time was needed compared with the rotatory osteotomy used in the extraction of impacted third molars. However, this was minor when compared with the reduction in the total duration and might be attributed to the longer time it took us to finish the piezoelectric corticotomy. Although piezosurgery® was less effective in corticotomy, it can provide clean and precise osteotomies with smooth walls and better visualisation of the surgical field.12 The complications were similar, and there was no neurological damage after either technique. Periodontal defects at the distal aspect of second molars have been common after the removal of impacted third molars. Rosa et al.13 reported that the periodontal condition of distal second molars worsened from 3 to 6 months, and Kugelberg14 reported infraosseous loss measured up to 4 mm in 32% of 215 patients two years after extraction of an impacted third molar. Extraction of impacted third molars may also lead to partial exposure of the root, which increases the sensitivity of the dentine and the susceptibility to caries.15 The use of this corticotomy-facilitated traction could improve the periodontal status of the second molar, as well as help to move the root from the inferior alveolar nerve. However, our study did not confirm the results of Kwon et al., 16 who
Please cite this article in press as: Ma Z, et al. Efficacy of the technique of piezoelectric corticotomy for orthodontic traction of impacted mandibular third molars. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.01.002
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reported findings of slightly decreased osseous support adjacent to the osteotomy sites and periodontal defects in some cases with short interdental distances. We found that the alveolar bone height distal to second molars increased after treatment in both groups, and was similar after the two techniques. A good osteoperiodontal level at the distal aspect of the second molar was found after treatment in all types of impaction. However, the mean (SD) duration was 7.5 (1.3) months in patients treated by traditional orthodontic traction and 4 (2.3) months in patients treated by piezoelectric corticotomy. These results indicate that this technique may be highly effective at the periodontal level, particularly in cases of severe impaction that result in an infrabony periodontal defect distal to the adjacent second molar, and provide one way to avoid bone replacement grafts and prevent extractionrelated periodontal defects after removal of impacted third molars. However, long-term stability of this newly formed bone requires further study. In corticotomy-facilitated traction, it was assumed that the main resistance to movement of the tooth was from the cortical plates of bone, and by disrupting its continuity the orthodontic intervention could be completed in much less time than normally expected.17 The possible biomechanical explanation for rapid tooth movement described by Frost is called “regional acceleratory phenomenon”.18 Another study reported that when cortical bone was injured by corticotomy, this phenomenon accelerated the normal regional healing processes by transient bursts of remodeling of bony tissue.19 Vercellotti et al.20 showed in dogs that osseous repair and remodelling was quicker at an early stage after piezosurgery® . The most remarkable new bone formation occurred between 2 and 3 weeks, whereas piezoelectric surgery showed a tendency towards faster remodelling.21 Tooth movement should be finished within 3–4 months, after which the bone blocks would start to fuse together.22 We took full advantage of the limited time to accelerate the movement of the teeth. Our findings supported and confirmed fast, undisturbed bony healing of the piezo-osteotomy-facilitated orthodontics. Compared with traditional traction, our corticotomy technique moves teeth more rapidly, and results in quicker treatment time with less discomfort. We have shown that corticotomy-facilitated orthodontics results in shorter treatment and more formation of new bone distal to second molars, although exposure takes longer than with the traditional technique. This approach may be an effective alternative in the removal of impacted third molars that are close to the inferior alveolar nerve in selected cases, and causes no neurological injuries.
Conflict of interest We have no conflict of interest.
5
Ethics statement/confirmation of patients’ permission The protocol was approved by the local ethics committee (201048) and patients gave their informed consent.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.bjoms. 2015.01.002.
References 1. Queral-Godoy E, Valmaseda-Castellón E, Berini-Aytés L, et al. Incidence and evolution of inferior alveolar nerve lesions following lower third molar extraction. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:259–64. 2. Bui CH, Seldin EB, Dodson TB. Types, frequencies, and risk factors for complications after third molar extraction. J Oral Maxillofac Surg 2003;61:1379–89. 3. Bonetti GA, Parenti SI, Checchi L. Orthodontic extraction of mandibular third molar to avoid nerve injury and promote periodontal healing. J Clin Periodontol 2008;35:719–23. 4. Alessandri Bonetti G, Bendandi M, Laino L, et al. Orthodontic extraction: riskless extraction of impacted lower third molars close to the mandibular canal. J Oral Maxillofac Surg 2007;65:2580–6. 5. Wang Y, He D, Yang C, et al. An easy way to apply orthodontic extraction for impacted lower third molar compressing to the inferior alveolar nerve. J Craniomaxillofac Surg 2012;40:234–7. 6. Ma ZG, Xie QY, Yang C, et al. An orthodontic technique for minimally invasive extraction of impacted lower third molar. J Oral Maxillofac Surg 2013;71:1309–17. 7. Germec¸ D, Giray B, Kocadereli I, et al. Lower incisor retraction with a modified corticotomy. Angle Orthod 2006;76:882–90. 8. Wilcko WM, Wilcko MT, Bouquo JE, et al. Rapid orthodontics with alveolar reshaping: two case reports of decrowding. Int J Periodontics Restor Dent 2001;21:9–19. 9. Sortino F, Pedullà E, Masoli V. The piezoelectric and rotatory osteotomy technique in impacted third molar surgery: comparison of postoperative recovery. J Oral Maxillofac Surg 2008;66:2444–8. 10. Tay AB, Go WS. Effect of exposed inferior alveolar neurovascular bundle during surgical removal of impacted lower third molars. J Oral Maxillofac Surg 2004;62:592–600. 11. Bartuli FN, Luciani F, Caddeo F, et al. Piezosurgery vs High Speed Rotary Handpiece: a comparison between the two techniques in the impacted third molar surgery. Oral Implantol (Rome) 2013;6:5–10. 12. Vercellotti T. Technological characteristics and clinical indications of piezoelectric bone surgery. Minerva Stomatol 2004;53: 207–14. 13. Rosa AL, Carneiro MG, Lavrador MA, et al. Influence of flap design on periodontal healing of second molars after extraction of impacted mandibular third molars. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;93:404–7. 14. Kugelberg CF. Impacted lower third molars and periodontal health, An epidemiological, methodological, retrospective and prospective clinical, study. Swed Dent J Suppl 1990;68:1–52. 15. Derton N, Perini A, Giordanetto J, et al. Orthodontic partial disimpaction of mandibular third molars prior to surgical extraction. Int Orthod 2009;7:181–92 [in French]. 16. Kwon HJ, Pihlstrom B, Waite DE. Effects on the periodontium of vertical bone cutting for segmental osteotomy. J Oral Maxillofac Surg 1985;43:952–5.
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17. Kole H. Surgical operations on the alveolar ridge to correct occlusal abnormalities. Oral Surg Oral Med Oral Pathol 1959;12: 515–29. 18. Frost HM. The regional acceleratory phenomenon: a review. Henry Ford Hosp Med J 1983;31:3–9. 19. Shih MS, Norrdin RW. Regional acceleration of remodeling during healing of bone defects in beagles of various ages. Bone 1985;6: 377–9.
20. Vercellotti T, Nevins ML, Kim DM, et al. Osseous response following resective therapy with piezosurgery. Int J Periodontics Restor Dent 2005;25:543–9. 21. Ma L, Stübinger S, Liu XL, et al. Healing of osteotomy sites applying either piezosurgery or two conventional saw blades: a pilot study in rabbits. Int Orthop 2013;37:1597–603. 22. Alghamdi AS. Corticotomy facilitated orthodontics: review of a technique. Saudi Dent J 2010;22:1–5.
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ARTICLE IN PRESS Available online at www.sciencedirect.com
British Journal of Oral and Maxillofacial Surgery xxx (2015) xxx–xxx
Efficacy of the technique of piezoelectric corticotomy for orthodontic traction of impacted mandibular third molars夽 Zhigui Ma, Guangzhou Xu ∗ , Chi Yang ∗∗ , Qianyang Xie, Yuqing Shen, Shanyong Zhang Department of Oral Surgery, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University, School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, PR China Accepted 2 January 2015
Abstract Our aim was to assess the efficacy of piezoelectric corticotomy for orthodontic traction of mandibular third molars close to the inferior alveolar nerve. Thirty patients with impacted third molars close to the nerve were included in the study, 15 of whom were treated with conventional orthodontic traction and 15 with piezoelectric corticotomy. We recorded duration of treatment including exposure and orthodontic traction, and time to the final extraction. Postoperative complications including trismus, swelling, and pain were also noted. Alveolar bone levels mesial and distal to the second molars were evaluated on cone-beam computed tomographic (CT) images. Student’s t test was used to assess the significance of differences between the groups. After orthodontic treatments all impacted third molars were successfully removed from the inferior alveolar nerve without neurological damage. The mean (SD) duration of surgical exposure in the piezoelectric corticotomy group was significantly longer than that in the conventional group (p = 0.01). The mean (SD) duration of traction was 4 (2.3) months after piezoelectric corticotomy, much shorter than the 7.5 (1.3) months in the conventional group (p = 0.03). There were no significant differences in postoperative complications between the groups. There was a significant increase in the distal alveolar height of second molars after treatment in both groups (p < 0.01). We conclude that the use of piezoelectric corticotomy allows more efficient and faster traction of third molars with a close relation between the root and the inferior alveolar nerve, although it took longer than the traditional technique. © 2015 Published by Elsevier Ltd. on behalf of The British Association of Oral and Maxillofacial Surgeons.
Keywords: Piezoelectric corticotomy; Orthodontic traction; Cone-beam CT; Impacted third molar; Bone formation
Introduction 夽
This project was supported by Shanghai Municipal Education Commission Research Fund for Young College and University Teachers (jdy11027), Research Fund of Shanghai Municipal Health Bureau (20134Y061) and College Scientific Research Fund (2012-12). ∗ Corresponding author at: Department of Oral and Maxillofacial Surgery, Ninth People’s Hospital, Collage of Stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai Research Institute of Stomatology, 639, Zhi Zao Ju Rd, 200011 Shanghai, People’s Republic of China. ∗∗ Co-corresponding author. E-mail addresses: [email protected] (G. Xu), [email protected] (C. Yang).
Neurological changes that result from damage to the inferior alveolar nerve are the most serious complication of the extraction of mandibular third molars, and the incidence of associated paraesthesia has been reported to be 1.1%.1 The main factor is the proximity of the roots of the tooth to the nerve.2 The application of orthodontic traction can successfully displace the roots away from the nerve, which reduces the risk of damage.3–5 However, the duration of treatment is often long, the mean (SD) in our previous report being 6.6 (SD = 2.1).6 Mesially inclined and horizontal teeth often require longer treatment (6–12 months).4
http://dx.doi.org/10.1016/j.bjoms.2015.01.002 0266-4356/© 2015 Published by Elsevier Ltd. on behalf of The British Association of Oral and Maxillofacial Surgeons.
Please cite this article in press as: Ma Z, et al. Efficacy of the technique of piezoelectric corticotomy for orthodontic traction of impacted mandibular third molars. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.01.002
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Corticotomy of the alveolar bone, which has recently been introduced into orthodontics, enables the orthodontist to facilitate the movement of teeth.7 With the technique one tooth can be moved 2–3 times further in a third or a quarter of the time required for traditional orthodontics.8 This is a remarkable advance in the case of regional orthodontic treatment using simple orthodontic devices. Piezoelectric surgery® is efficient for osteotomy because it is a selective, micrometrical cut that produces a limited area of bleeding.9 We have used piezoelectric corticotomy of the alveolar bone to facilitate orthodontic movement of teeth and compared it with conventional orthodontic traction for impacted third molars. The aim of the study was to find out which of these two techniques was better for orthodontic traction of mandibular third molars close to the inferior alveolar nerve.
Patients and methods Between August 2010 and August 2013, 30 patients were recruited from the Department of Oral Surgery, Shanghai Ninth People’s Hospital affiliated with Shanghai Jiao Tong University, School of Medicine (Shanghai, China). The protocol was approved by the local ethics committee (201048) and patients gave informed consent. All the operations were completed by the same surgeon, and orthodontic treatments by the same orthodontist. The selection criteria included patients who were judged to be at high risk of injury to the inferior alveolar nerve based on radiographic features in routine preoperative dental pantomographs and cone-beam computed tomography (CT, J. Morita Mfg Corp, Kyoto, Japan), and whose mandibular third molars were impacted and in need of exposure (we included third molars with horizontal, mesioangular, and vertical impaction according to the classification of Tay et al.10 ). Participants had no periradicular conditions or active periodontal disease, no tooth loss, no systemic diseases, and they did not smoke. The treatment methods were randomly assigned using a computer-generated randomisation list. Fifteen patients (6 men and 9 women, mean (SD) age 27 (5.6) years) were treated by traditional orthodontic traction, and the other 15 patients (5 men and 10 women, mean (SD) age 24 (4.8) years) were operated on with surgically assisted orthodontic traction with piezocorticotomy. Surgical and orthodontic technique After block anesthesia with local infiltration of the buccal nerve had been given, a full-thickness intrasulcular flap was fashioned from the mesial to the distal margins of the second molar with a distal releasing incision. The mucoperiosteal flap was reflected to expose the third molar and the cortical bone. In the conventional traction group the bone on the occlusal and buccal surfaces of the tooth was removed by low-speed drilling with copious irrigation for cooling. In the piezocorticotomy group the bone was removed with a
Fig. 1. Two vertical cuts were made mesially and distally around the third molar. The horizontal osteotomy connected with vertical osteotomies was also made by piezosurgery® .
piezoelectric device (Piezosurgery® , Silfragent, Italy). The amplitude of the microvibrations was from 80 to 100 m with a frequency of 28 to 32 kHz, corresponding to a handpiece power rating of 45 W. Vertical corticotomy cuts were made around the root of the third molar, and stopped just short of the alveolar crest (about 2 mm). These cuts were connected near the apices of the teeth with a horizontal cut. Cuts were made just beneath the buccal cortical plate (Fig. 1). The orthodontic appliance was inserted and bonded to the buccal surface of the impacted tooth. As described in our previous paper, two steps were used for mesially and horizontally inclined third molars and one step for vertically impacted teeth.6 A hook was bonded with a light-cured composite on the exposed surface of the impacted tooth, and a 3-loop spring (0.016 in. stainless steel) was welded to the adjacent second molar band with the end in contact the hook, to distalize the mesially or horizontally impacted molar first. A cantilever 0.017 in. × 0.025 in. was then used to push the third molar upright and extrude it (Fig. 2). The patients were monitored every month for the movement of the impacted teeth. Cone-beam CT was used to evaluate the relation between the roots and the inferior alveolar nerve before extraction. Once the impacted root apex had been separated from the nerve the third molar could be removed. An antibiotic (amoxicillin; 50 mg/kg in 2 daily doses for 3 days) and an analgesic (paracetamol; 750 mg every 6 h) were prescribed as necessary. Rinsing with 0.12% chlorhexidine gluconate was also recommended. The wound was sutured, and the sutures removed one week later. Clinical assessments The duration of treatment was the primary outcome variable, including the exposure, orthodontic traction, and final dental extraction after the root had separated from the nerve. Duration of anaesthesia, flaps, and sutures were not recorded. All subjects had a follow-up visit after 48 h for evaluation of trismus, swelling, and pain. Trismus was evaluated by a measurement of the difference of maximal interincisal
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Fig. 2. Diagram of orthodontic extraction. A 3-loop spring was used to move the impacted third molar distally, with the end contacting the hook. A cantilever was then hooked on to the main arch wire to extrude the third molar further.
opening before and after exposure. Postoperative swelling was the difference in the distance from the region of the distal trigone to the skin measured before and after exposure, as described by Sortino et al.9 Pain was scored by the patients on a visual analogue scale (VAS) that ranged from 0 (no pain) to 100 (the most severe pain). Neurological injuries were evaluated from any postoperative changes in the sensitivity of the tissues innervated by the inferior alveolar nerve (evaluated both subjectively and objectively, using light touch and a needle). Radiological measurements The largest sagittal slice of the second molar was selected on cone-beam CT images. The alveolar height was the distance from the alveolar crest to the apical line, which was tangential to the long axis of the second molar. The long axis of the second molar was a line that passed through the central groove to the middle of the apices of the root. Mesial and distal alveolar bone levels were measured (Fig. 3). When the distal bone level is lower than the mesial level, distal bone resorbs. Linear measurements for bone level were obtained with MB-Ruler measuring software (accurate to 0.01 mm) (Markus Bader, Berlin, Germany). Statistical analysis All measurements from the cone-beam CT scans were made twice by the same operator and the mean value was used in the final evaluation. Analyses were made with the help of the program SPSS for Windows (version 16.0; SPSS Inc, Chicago, IL, USA) and Student’s t test was used to compare the significance of differences between clinical and radiological variables in the two groups. Probabilities of less than 0.05 were accepted as significant.
Results The groups were comparable. In the conventional traction group, 3 third molars were horizontally impacted, 6 mesioangularly, and 6 vertically. In the piezocorticotomy
Fig. 3. Measurement of the level of alveolar bone. A baseline was drawn tangentially to the long axis of the second molar through the apex of the root. The levels of mesial and distal bone were the distances from the alveolar crest to the apical line. The anatomical proximity of the inferior alveolar nerve to the root of the third molar and the loss of osteoperiodontal tissue at the distal second molar were noted before treatment in a case of mesial impaction.
group, 2 were horizontally, 6 mesioangularly, and 7 vertically impacted. All third molars in both groups were totally and successfully separated from the inferior alveolar nerve after treatment, with no neurological injuries (Figs. 3 and 4). The mean (SD) duration of surgical exposure was 8.4 (3.1) min in the conventional traction group and 15.1 (4.7) min in the piezocorticotomy group. The mean (SD) time to completion of the orthodontic traction was 7.5 (1.3) months in the conventional group, but 4 (2.3) months in the piezocorticotomy group, both differences being significant (p = 0.01 and p = 0.03, respectively). There was no significant difference in the time that it took to complete the final extraction (p = 0.14) between the two groups, and no significant differences in the amount of trismus (p = 0.31), postoperative swelling (p = 0.11), or pain (p = 0.41) 48 h after exposure of impacted third molars (Table 1).
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Table 1 Mean (SD) duration of treatment, trismus, swelling, and pain in the two groups (n = 15 in each). Variable
Conventional traction
Duration of exposure (min) Duration of orthodontic traction (months) Extraction time (min) Complications (mm) Trismus Swelling VAS for pain
Piezo corticotomy
p value
8.43 (3.1) 7.53 (1.3) 5.20 (1.4)
15.13 (4.7) 4.00 (2.3) 5.53 (1.7)
0.01 0.03 0.14
15.32 (2.9) 9.54 (1.4) 45.43 (10.8)
16.35 (2.6) 8.71 (1.4) 48.72 (10.8)
0.31 0.11 0.41
VAS = visual analogue scale. Table 2 The mean (SD) distal alveolar level of second molars (mm) before and after treatment in the two groups (n = 15 in each). Level of second molar
Mesial Distal Mesiodistal
Conventional traction
p value
Before
After
10.21 (3.1) 6.75 (2.7) 3.46 (1.7)
9.77 (3.6) 9.66 (3.6) 0.11 (2.0)
Alveolar bone height of second molars Table 2 shows that the distal bone height of the second molars was significantly lower than that of the mesial height before treatment, but there was a significant increase in the distal measurement after treatment in both groups (p = 0.01). There were no significant differences between the mesial and distal alveolar levels in either group after treatment.
Discussion Traction of mandibular third molars has been one of the most difficult problems in traditional orthodontics, particularly in
Fig. 4. The separation of the impacted third molar from the inferior alveolar nerve and a good level of alveolar bone distal to the second molar could be seen after the piezocorticotomy-facilitated orthodontic traction in the same case as Fig. 3.
0.23 0.01 0.01
Piezo corticotomy
p value
Before
After
10.75 (2.7) 7.19 (2.3) 3.56 (2.1)
10.49 (1.9) 10.31 (1.4) 0.18 (2.5)
0.51 0.01 0.01
adults, because of the duration of the treatment period. However, with the assistance of decortication, it has now become possible to separate third molars rapidly from the inferior alveolar nerve, and to the best of our knowledge we are the first to report this method. Piezosurgery® is a suitable instrument thanks to its ease of use and selectivity of bone cutting. We used piezoelectric corticotomy to cut the alveolus around the third molars without entering the cancellous bone, and so avoided the risk of damage to underlying structures such as the inferior alveolar nerve. The mean time for alveolar cutting was considerably increased using ultrasound piezosurgery compared with the usual device, which confirms the results of Sortino et al.9 and Bartuli et al.11 who also found that more time was needed compared with the rotatory osteotomy used in the extraction of impacted third molars. However, this was minor when compared with the reduction in the total duration and might be attributed to the longer time it took us to finish the piezoelectric corticotomy. Although piezosurgery® was less effective in corticotomy, it can provide clean and precise osteotomies with smooth walls and better visualisation of the surgical field.12 The complications were similar, and there was no neurological damage after either technique. Periodontal defects at the distal aspect of second molars have been common after the removal of impacted third molars. Rosa et al.13 reported that the periodontal condition of distal second molars worsened from 3 to 6 months, and Kugelberg14 reported infraosseous loss measured up to 4 mm in 32% of 215 patients two years after extraction of an impacted third molar. Extraction of impacted third molars may also lead to partial exposure of the root, which increases the sensitivity of the dentine and the susceptibility to caries.15 The use of this corticotomy-facilitated traction could improve the periodontal status of the second molar, as well as help to move the root from the inferior alveolar nerve. However, our study did not confirm the results of Kwon et al., 16 who
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reported findings of slightly decreased osseous support adjacent to the osteotomy sites and periodontal defects in some cases with short interdental distances. We found that the alveolar bone height distal to second molars increased after treatment in both groups, and was similar after the two techniques. A good osteoperiodontal level at the distal aspect of the second molar was found after treatment in all types of impaction. However, the mean (SD) duration was 7.5 (1.3) months in patients treated by traditional orthodontic traction and 4 (2.3) months in patients treated by piezoelectric corticotomy. These results indicate that this technique may be highly effective at the periodontal level, particularly in cases of severe impaction that result in an infrabony periodontal defect distal to the adjacent second molar, and provide one way to avoid bone replacement grafts and prevent extractionrelated periodontal defects after removal of impacted third molars. However, long-term stability of this newly formed bone requires further study. In corticotomy-facilitated traction, it was assumed that the main resistance to movement of the tooth was from the cortical plates of bone, and by disrupting its continuity the orthodontic intervention could be completed in much less time than normally expected.17 The possible biomechanical explanation for rapid tooth movement described by Frost is called “regional acceleratory phenomenon”.18 Another study reported that when cortical bone was injured by corticotomy, this phenomenon accelerated the normal regional healing processes by transient bursts of remodeling of bony tissue.19 Vercellotti et al.20 showed in dogs that osseous repair and remodelling was quicker at an early stage after piezosurgery® . The most remarkable new bone formation occurred between 2 and 3 weeks, whereas piezoelectric surgery showed a tendency towards faster remodelling.21 Tooth movement should be finished within 3–4 months, after which the bone blocks would start to fuse together.22 We took full advantage of the limited time to accelerate the movement of the teeth. Our findings supported and confirmed fast, undisturbed bony healing of the piezo-osteotomy-facilitated orthodontics. Compared with traditional traction, our corticotomy technique moves teeth more rapidly, and results in quicker treatment time with less discomfort. We have shown that corticotomy-facilitated orthodontics results in shorter treatment and more formation of new bone distal to second molars, although exposure takes longer than with the traditional technique. This approach may be an effective alternative in the removal of impacted third molars that are close to the inferior alveolar nerve in selected cases, and causes no neurological injuries.
Conflict of interest We have no conflict of interest.
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Ethics statement/confirmation of patients’ permission The protocol was approved by the local ethics committee (201048) and patients gave their informed consent.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.bjoms. 2015.01.002.
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