|Year : 2014 | Volume
| Issue : 6 | Page : 748-754
|Corticotomy-assisted retraction: An outcome assessment
S Vijayashri Sakthi1, B Vikraman2, VR Shobana1, S Kavitha Iyer1, NR Krishnaswamy1
1 Department of Orthodontics, Ragas Dental College and Hospital, Chennai, Tamil Nadu, India
2 Department of Oral and Maxillofacial Surgery, Ragas Dental College and Hospital, Chennai, Tamil Nadu, India
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|Date of Submission||02-Oct-2014|
|Date of Decision||24-Oct-2014|
|Date of Acceptance||27-Jan-2015|
|Date of Web Publication||02-Mar-2015|
| Abstract|| |
Background: To assess the efficiency and treatment outcome of patients treated with corticotomy-assisted en-masse orthodontic retraction as compared with the en-masse retraction without corticotomy.
Materials and Methods: Forty adult patients with bimaxillary protrusion requiring correction of bidental proclination constituted the sample. The study group consisted of 22 patients (male 11, female 11) willing to undergo surgery to reduce the duration of their orthodontic treatment and 18 patients (male 9, female 9) desirous of undergoing conventional orthodontic treatment without surgical intervention constituted the control group. Comparison of rate of retraction and anchor loss between the study and the control group was assessed.
Results: Average rate of space closure of 1.8 mm/month in the maxilla and 1.57 mm/month in the mandible was observed in the study group compared to 1.02 mm/month in the maxilla and 0.87 mm/month in the mandible in the control group. The rate of retraction accelerated during the first 2 months of retraction. Molar anchor loss of approximately 0.6 mm occurred in the study group, and 1.8 mm occurred in the control group during the 4 months.
Conclusion: The rate of retraction with study group was twice as faster when compared to the control group, accelerating during the first 2 months of retraction. There was better anchorage control with the undecorticated molar segment during the retraction period but was found to increase as time advanced.
Keywords: Adult orthodontics, corticotomy, orthodontic retraction, regional acceleratory phenomenon
|How to cite this article:|
Sakthi S V, Vikraman B, Shobana V R, Iyer S K, Krishnaswamy N R. Corticotomy-assisted retraction: An outcome assessment. Indian J Dent Res 2014;25:748-54
Patients with bimaxillary protrusion seek orthodontic treatment to decrease the procumbency of the lips.  Extracting the first four premolars and retracting the anterior segments with maximum anchorage is the most common way to straighten the profile.
|How to cite this URL:|
Sakthi S V, Vikraman B, Shobana V R, Iyer S K, Krishnaswamy N R. Corticotomy-assisted retraction: An outcome assessment. Indian J Dent Res [serial online] 2014 [cited 2019 Nov 15];25:748-54. Available from: http://www.ijdr.in/text.asp?2014/25/6/748/152191
The anatomic limits set by the cortical plates of the alveolus at the level of the incisor apices act as barriers to incisor retraction. Orthodontic treatment requiring closure of the extraction space, has side effects such as bone loss, ,, root resorption, , gingival recession,  root dehiscence,  and fenestration. 
Adult patients who seek orthodontic treatment often desire that their treatment be completed in as short a period as possible.  In 1959, Köle  introduced a technique called selective alveolar decortications to enable movement of the bone segment. In 2001, Wilcko et al.  developed a new method of combining corticotomy, alveolar augmentation, and orthodontic treatment. They have observed that orthodontic tooth movement is accelerated by the increase of bone turnover and decrease of bone density because osteoclasts and osteoblasts are increased due to a regional acceleratory phenomenon (RAP). ,
One possible method for completing treatment in a shorter period is through orthodontic treatment combined with corticotomy. ,, This period of accelerated tooth movement usually lasts for 4-6 months. ,
Due to the limited studies of corticotomy facilitated orthodontics in bimax cases, the aim of the present study was to assess the efficiency of treatment outcome of patients treated with corticotomy-assisted en-masse orthodontic retraction with a modified protocol as compared with the en-masse retraction without corticotomy.
| Materials and methods|| |
Twenty-two patients (male 11, female 11), willing to undergo surgery to reduce the duration of their orthodontic treatment were selected as sample for the study and 18 patients (male 9, female 9), reluctant to undergo any surgical interventions desirous of undergoing conventional orthodontic treatment constituted the control group. The group allocation was not blinded. It was based on the willingness of the patient to opt for an additional minor surgical procedure that may influence the duration of orthodontic treatment
Cases with bimaxillary protrusion, angles class I malocclusion, interincisal angle <125°, crowding ≤3 mm. Requiring first premolar extraction in all the four quadrants. Adult patients between the age of 18-25 years. Patients with satisfactory periodontal health and good oral hygiene. Not under any systemic medication.
Patients with severe skeletal dysplasia in all three dimensions. Nonconsenting adults. Severe crowding. Symptoms of temperomandibular disorders. Patients on medication for systemic disorders, pregnancy or steroid therapy.
All patients included in the study required extraction of all first premolars and were treated with 0.022' slot Roth appliance. In the study group, leveling and aligning were carried out until 0.019" × 0.025" stainless steel archwire could be fully engaged in the bracket slot, the first premolars were not extracted till the time of retraction stage. Whereas in the control group, the first premolars were extracted prior to aligning stage of treatment (as traditional). The surgery was carried out under local anesthesia (Lignox 2%A). Surgical procedure was handled by the same maxillofacial surgeon. Lower arch procedure preceded 2 weeks ahead of the upper arch. First premolars were extracted at the time of the surgery and a stainless steel 0.019" × 0.025" archwire with soldered brass hooks was placed before flap elevation in the study group. Sulcular incisions from the distal aspect of one canine to the contralateral canine were placed, and full thickness flap was elevated, 3 mm above the apical region of the tooth. 701 fissure bur and number 2 size round bur mounted on a micromotor handpiece under copious irrigation was used for decortications (only cortical surface scoring and not through and through penetration). If there was a good amount of inter-root distance between two adjacent teeth vertical interdental cortical surface scoring was done otherwise only surface punch hole were placed in the area, stopping 2 mm short of the alveolar crest, occlusally. Horizontal decortications connected the vertical 2 mm beyond root apex. Selective alveolar decortication from the mesial aspect of one canine to the mesial surface of the contralateral canine involving the anteriors was performed. Similarly, a palatal flap incision was raised immediately for decortications of the superficial surface of the palatal bone for RAP to occur.
The graft was placed only in cases with Evidence of bone loss (dehiscence and fenestration) on flap elevation with demineralized freeze-dried allograft (demineralized freeze-dried bone allograft - Rocky Mountain Tissue Bank) wetted with sterile saline and maintained in the desired position by the full thickness flap, sutured with an interrupted loop, nonresorbable 4-0 black silk suture material, left in place for 1-2 weeks. Initiation of orthodontic force was done within 5-7 days after the surgery with the help of closed NiTi coil spring which was engaged from the first molar tube to the soldered hook on the archwire delivering a force of 250 g for en-masse retraction using sliding mechanics, similarly in the control group.
A case treated with corticotomy-assisted retraction is depicted from [Figure 1] [Figure 2] [Figure 3] [Figure 4] [Figure 5] [Figure 6].
|Figure 1: (a) Pretreatment extraoral photographs (b) Posttreatment extraoral photograph|
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|Figure 2: (a) Pretreatment intraoral photograph (b) Posttreatment intraoral photograph|
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|Figure 5: (a) Pretreatment lateral cephalogram (b) Posttreatment lateral cephalogram|
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|Figure 6: (a) Pretreatment orthopantamogram (b) Posttreatment orthopantamogram|
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Study models at monthly intervals and the lateral cephalometric radiographic records every 2 months were taken for assessment.
Methodology for evaluation of extraction space closure in the dental cast
Following extractions, space closure was measured using a digital vernier caliper at the maximum contour of the mesial point of second premolar and the distal maximum contour of the canine on the study model and was repeated every month.
Methodology for evaluation of retraction and anchor loss
Maxilla and Mandible: Using lateral cephalograms
Linear measurements were taken from pterygoid vertical along the Frankfort horizontal plane, horizontal distance from pterygoid vertical to the jig on the molar [Figure 3]a and b] and incisor bracket was used in the maxilla. Whereas, linear measurements were taken from sella vertical along the SN plane, horizontal distance from the sella vertical to the jig on the molar [Figure 3]a and b], and incisor bracket to assess anchor loss and retraction, respectively [Figure 9].
Comparison with the conventional group for the en-masse retraction
The space closure was compared in both the groups before the start of retraction. The time taken for space closure in the corticotomy group was compared with the space closure in the conventional group.
All statistical analyses were performed using SPSS software package (SPSS for Windows XP, version 17.0, Chicago, IL, USA). For each variable measured on the lateral cephalogram, the mean and the standard deviation were calculated.
Paired t-test was used to determine statistical significance of the difference between left and right side variables within maxilla and mandible.
Independent t-test was used to determine statistical significance of the difference between the rate of retraction, molar anchor loss before retraction (T1) and after retraction (T2) between the study group and the control group.
One-way ANOVA followed by Tukey's HSD test was done to evaluate and compare the rate of space closure and anchor loss between the studied monthly time intervals.
P < 0.05 was considered statistically significant. Power of the sample is 0.95.
| Results|| |
Rate of retraction in the maxilla and mandible compared during monthly intervals in study and control group [Table 1].
|Table 1: Rate of retraction in the maxilla and mandible compared during monthly intervals in study and control group|
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Duration and rate of retraction
There was no significant difference in the quantum of extraction spaces in the maxilla and the mandible between the study group and the control group [Figure 8]a].
- Extraction space closure of 92.8% in the study group and 54.5% in the control group was achieved during the 4-month period
- Average rate of space closure of 1.8 mm/month and 1.02 mm/month was achieved in the in the study group and control group, respectively, during the 4-month period.
Comparison of rate of space closure in the maxilla and mandible at monthly intervals
- Extraction space closure of 91.6% in the study group and 51.5% in the control group was achieved during the 4-month period
- Average rate of space closure of 1.57 mm/month in the study group and 0.87 mm/month was achieved in the control group during the 4-month period.
- Acceleration of rate of space closure was statistically significant during the first 2 months of retraction in the study group
- No significant rate of acceleration and rate of space closure were found in the maxilla and/or the mandible during the monthly intervals in the control group.
Molar anchor loss in the maxilla and mandible compared between the study and the control group (mm) [Table 2].
|Table 2: Molar anchor loss in the maxilla and mandible compared between the study and the control group (mm)|
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In the 4-month period during which the space closure was assessed, the following changes were observed [Figure 8]b].
- Molar anchor loss of approximately 0.86 mm occurred in the study group, and 1.8 mm occurred in the control group.
- Molar anchor loss of approximately 0.51 mm occurred in the study group, and 1.6 mm occurred in the control group.
Comparison of anchor loss
- Statistically significant difference was present between the study group and the control group
- The amount of anchor loss increased as time advanced in the study group.
| Discussion|| |
In the treatment of bimaxillary protrusion, two important factors for consideration are: Esthetic improvement of the dentofacial area and the establishment of a stable dental relationship. Because of the protrusive dentition and lips many patients with bimaxillary protrusion seek orthodontic care to decrease this procumbency.  The treatment approach usually consists of extracting the four first premolars and retracting the anterior teeth with maximum anchorage. Time is an important factor during the course of orthodontic treatment. 
Mavreas  in a systematic review indicated that the duration of treatment for four premolar extraction cases was approximately 18.6 months (retraction of anteriors alone took 8 months). Long  evaluated the effectiveness of interventions on accelerating orthodontic tooth movement found, corticotomy to be effective and safe procedure to accelerate orthodontic tooth movement. Therefore, the procedure employed in the current study can be considered to be an effective and mode of intervention.
There is sufficient evidence in the literature by Wilcko et al.,  Spena et al.,  Fischer,  Moon et al.,  Yaffe et al.,  Mostafa et al.,  Generson et al.,  Chung et al., , Hassan et al.,  Ahn et al.,  Newman  and many others suggesting that corticotomy is a viable option for accelerating orthodontic treatment. The RAP exists probably for about 4 months. , Anecdotal evidence shows that when the teeth are extracted just before commencing space closure, then space closure tends to be faster, owing to the reduced bony resistance offered by freshly healed extraction site to tooth movement. 
Thus to take advantage of the maximum RAP response which exists for 4 months, delayed extraction of the first bicuspid would be advantageous in accelerating tooth movement. Further, the undecorticated molar segment acts as an anchorage module during the period of retraction. This protocol has been used effectively to enhance the en-masse retraction of the anterior segment compared with the conventional en-masse retraction in bimaxillary protrusion patients.
The teeth were stabilized with stainless steel wire (0.019" × 0.025") to minimize torque loss and to bring about bodily/controlled tipping movements during retraction. The posterior segment (second premolar, first and second molar) was not decorticated to enable them to serve as an anchorage module.
In Wilcko's et al. protocol,  corticotomy was performed prior to aligning and an additional procedure viz.; ostectomy (surgical removal of cortical plate) in the extraction space was recommended, which would be a cumbersome and expensive method. Thus rather than removing a large amount of cortical bone around the first bicuspid, delayed extraction of the first bicuspid without removal of the cortical bone was carried out further cases selected had very minimal crowding and delaying extraction did not prolong the treatment. Nevertheless, minor inconvenience as a result of transient inflammation was seen following the procedure. 
In our study, 701 tapering fissure bur for interdental scoring and number 2 round bur for punch hole perforation were used which is an acceptable method for decortications. ,
A few case reports Germeη et al.,  Kim et al.,  Aboul-Ela et al.,  Lino et al.,  suggest corticotomy can be beneficial in bimaxillary protrusion cases. Most of these studies employ either an implant or involves independent canine retraction.
The technique for alveolar decortication is based upon cortical bone thickness than upon any particular preconceived pattern of bone injury with a surgical bur, such as cuts or dots or a combination of cuts and dots. The surgical scarring barely penetrates the cortical bone into the medullary space on both the labial and lingual surfaces. 
Molar anchor loss has not been documented convincingly in the literature for corticotomy assisted retraction. Therefore, our study aimed to evaluate the rate of retraction and the amount of molar anchor loss that occurred during the retraction period compared to the control group for the same period.
Anchor loss was assessed with the help of lateral cephalogram similar to the method proposed by Badri Thiruvengadachari  with modified jigs placed on the upper and lower, right and left first molar [Figure 3]a and b] to differentiate the right from the left molar [Figure 9]. Anchor loss was correlated with the space closure and effective retraction in the Study group was assessed and compared with the control group (approximately 4-5 months). Case report superimposition refers [Figure 7].
|Figure 8: (a) Graph of amount of incisor retraction in mm (b) Graph of amount of anchor loss in mm|
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In our study, there was no significant difference in the extraction space in the study and the control group which accounted to be on an average of 7.63 mm in the maxilla and 6.77 mm in the mandible in spite of early extraction in the control group when compared with the study group which could be due to the fact that the cases selected for the study had minimal crowding. Thus, the study and the control group can be effectively compared.
About 92.8% (7.05 mm) of extraction space closure in the study group and 54.5% (4.15 mm) of extraction space closure in the control group were achieved by the end of 4 th month in the maxilla. 91.6% (6.3 mm) of extraction space closure in the study group (corticotomy group) and 51.7% (3.5 mm) of extraction space closure was achieved in the control group for the same period of time in the mandible.
The average rate of space closure was 1.8 mm/month in the maxilla and 1.6 mm/month in the mandible of the study group. This correlates with the studies of Aboul-Ela et al.,  who reported the mean rate of individual maxillary canine retraction, was on an average about 1.42 mm/month.
There was a peak increase in the rate of retraction during the first 2 months of retraction in the maxilla (2.01 mm/month) and in the mandible (1.89 mm/month) which started to decline by the end of 4 th month. This finding is in concurrence with that of Aboul-Ela et al.  who reported that the rate of space closure peaked during the end of 1 st and 2 nd month and reduced by the end of the 4 th month. This could be biologically co-related with the transient RAP phenomenon as mentioned by Frost  which remains active for 4 months. Thus, the time period of assessment of retraction for the first 4-month period after corticotomy can be substantiated.
An average anchor loss of 0.6 mm occurred in maxilla and mandible for a period of 4-6 months. There is no pertinent literature to substantiate molar anchor loss in corticotomy-assisted retraction as most of the study used temporary anchorage devices to bolster anchorage. To the best of our knowledge, this study would probably be the first to correlate pure anchor loss and the efficiency of the undecorticated posterior segment to act as an efficient anchorage source. Similarly, in a previous study on a conventional en-masse retraction by Wook Heo, approximately 4 mm of retraction of upper incisal edge resulted in 1 mm of anchor loss in the upper molar. Since the complete space closure in the control group was not assessed in the current study, there could be further anchor loss at the end of the retraction.
| Summary and conclusion|| |
Based on the outcome of this study, it is reasonable to conclude that corticotomy-assisted retraction drastically reduces the overall duration of orthodontic treatment. It is particularly useful in maximum anchorage cases by using selective decortications the anchorage segment can be made virtually stationary, thereby eliminating the need for other anchorage boosters.
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N R Krishnaswamy
Department of Orthodontics, Ragas Dental College and Hospital, Chennai, Tamil Nadu
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]
[Table 1], [Table 2]
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