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Table of Contents   
ORIGINAL RESEARCH  
Year : 2015  |  Volume : 26  |  Issue : 3  |  Page : 237-243
Assessment of stability of orthodontic mini-implants under orthodontic loading: A computed tomography study


1 Department of Orthodontics and Dentofacial Orthopedics, Pacific Dental College and Hospital, Debari, Udaipur, Rajasthan, India
2 Department of Prosthodontics, Pacific Dental College and Hospital, Debari, Udaipur, Rajasthan, India

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Date of Submission26-Dec-2014
Date of Decision02-Apr-2015
Date of Acceptance15-Jun-2015
Date of Web Publication14-Aug-2015
 

   Abstract 

Objectives: Miniscrews have been used in recent years for anchorage in orthodontic treatment. However, it is not clear whether the miniscrews are absolutely stationary or move when force is applied. This prospective clinical study was undertaken to evaluate the mobility of orthodontic miniscrews under orthodontic loading using computed tomography. Materials and Methods: Ten adult patients (7 females and 3 males with mean age of 19 years, 7 mm overjet) who required en masse retraction of upper and lower anterior teeth infirst premolar extraction spaces were included in this study. After initial alignment of anterior teeth, the 0.019" ×0.025" stainless steel archwire were placed in preadjusted edgewise appliance. The miniscrews (diameter - 1.3 mm, length - 7 mm) were inserted in between second premolar and thefirst molar in the maxilla (zygomatic buttress) and in mandible on the buccal side as direct anchorage. Immediately after placement of miniscrews without waiting period, NiTi coil springs (force of 150 g in the maxilla and 100 g in the mandible) were placed for the retraction. Denta Scans were taken immediately before force application (T1) and 6 months later (T2). The mean changes obtained at T1 and T2 in Denta Scans (axial plane, coronal plane, paraxial plane) were evaluated to determine any movement of different parts of miniscrews using one-way ANOVA test and Student's unpaired t-test. Results: On average, miniscrews were extruded and tipped forward significantly, by 1 mm at the screw head in the axial plane (Group III) and 0.728 mm in the coronal plane (Group IV). Tail of miniscrews showed average tipping of 0.567 mm in the axial plane (Group I) and 0.486 mm in the paraxial plane (Group V). Least average mobility was shown by screw body of 0.349 mm in the axial plane (Group II). Clinically, no significant mobility was observed. Conclusion: Miniscrews are a stable anchorage for orthodontic tooth movement but do not remain absolutely stationary like an endosseous implant throughout orthodontic loading although miniscrews might move according to placement site, orthodontic loading, and inflammation of peri-implant tissue. Waiting period between miniscrews placement and orthodontic loading does not significantly affect the miniscrew mobility so immediate loading can be recommended. To prevent hitting any vital organs because of miniscrew mobility, it is recommended that they can be placed in a nontooth-bearing area that has no foramen, major nerves, or blood vessel pathway, or in a tooth-bearing area allowing a 1.5 mm safety clearance between the miniscrew and dental root.

Keywords: Axial plane, coronal plane, miniscrews, paraxial plane

How to cite this article:
Garg KK, Gupta M. Assessment of stability of orthodontic mini-implants under orthodontic loading: A computed tomography study. Indian J Dent Res 2015;26:237-43

How to cite this URL:
Garg KK, Gupta M. Assessment of stability of orthodontic mini-implants under orthodontic loading: A computed tomography study. Indian J Dent Res [serial online] 2015 [cited 2020 Feb 18];26:237-43. Available from: http://www.ijdr.in/text.asp?2015/26/3/237/162874
Successful orthodontic treatment has always relied on intraoral anchorage with a high resistance to displacement.[1] The growing demand for orthodontic treatment methods that require minimal compliance and provide maximal anchorage control, particularly for adults, has led to the expansion of implant technology in orthodontics.[2] Endosseous implants and onplants have been used as direct or indirect orthodontic anchorage for different clinical purposes. They have been used in maxillary posterior region for retraction of anterior teeth, mandibular retromolar area as direct anchorage for molar protraction and uprighting,[3][4][5] and in the palate as an indirect anchorage for canine or anterior teeth retraction or molar distalization.[6][7][8] Endosseous implants and palatal onplants are thought to provide absolute or rigid anchorage.[3],[4],[6] They integrate with the surrounding bone and thus remain absolutely stationary under orthodontic loading.[5],[9] For the miniscrews, it is suggested that a waiting period for bone healing and osseointegration before loading is unnecessary because the primary stability (mechanical retention) of the miniscrews is sufficient to sustain a regular orthodontic loading.[10][11][12] However, the behavior of the miniscrews under orthodontic loading is not clear clinically; do they remain absolutely stationary like endosseous implants or move according to the orthodontic loading? The answer could affect their use as orthodontic anchorage.[2] The purpose of this clinical computed tomography (CT) study was to answer this question and report the behavior of miniscrews under orthodontic loading.


   Materials and Methods Top


The present study was prospective in nature. It involved a sample size of 10 patients, undergoing orthodontic treatment in the Department of Orthodontics and Dentofacial Orthopaedics, S.D.M. College of Dental Sciences and Hospital, Dharwad, Karnataka.

Inclusion criteria





  • Comprehensive medical and dental history ruling out any systemic illness
  • Routine blood investigations were done to rule out any blood dyscrasias
  • Patients who had increased overjet (7 mm) and required maximum retraction of upper and lower anterior teeth
  • Adequate alveolar bone support between the second premolar andfirst molar region (zygomatic buttress) in maxilla and in mandible, healthy periodontium and no root pathology.


Ten patients (seven females, three males, overjet - 7 mm) who had miniscrews as anchorage for the en masse retraction of anterior teeth were included. Their ages ranged from 15 to 23 years (average - 19 years) old. All patients gave informed consent for miniscrews placement method, possibilities of failure, irritation, or local inflammation during orthodontic treatment, and for Denta CT Scan. The absoanchor miniscrew was 1.3 mm in diameter and 7 mm in length (Dentos Inc., South Korea) [Figure 1]. The miniscrew placement site was between the second premolar andfirst molar (zygomatic buttress) in maxilla and mandible. The zygomatic buttress of the maxilla is a pillar of cortical bone running along the zygomatic process of the maxilla and the zygoma. It is usually located above the maxillaryfirst molar in an adult or between the maxillary second premolar and thefirst molar in a younger patient. After topical application of 15% lignocaine, self-drilled miniscrews were placed between the second premolar andfirst molar in maxilla and mandible on buccal side by a single operator followed by loading immediately with no waiting period for healing. Orthodontic forces of 150 g and 100 g were applied in maxilla and mandible, respectively, by NiTi closed coil spring between the miniscrew and hooks made on 0.019″ × 0.025″ stainless steel wire between the lateral incisor and canine in preadjusted edgewise appliance (0.022″ MBT) for retraction of anterior teeth afterfirst premolars extractions. The forces applied were measured using Dontrix gauge (ODG-503 INVECTA™ 16 OZ. 01-39, Invecta, Ortodental, USA). The patients were seen at the 1-month interval for 6 months to deliver the required force.
Figure 1: Mini-implant and screwdriver

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Denta Scan was performed in all the patients who underwent immediate postimplant placement (T1) followed by a follow-up Denta Scan at 6 months interval (T2) at 130 KVp and 45 mA. The Denta Scan (CT) was performed on Siemens Somatom Emotion Duo Dual-Slice CT Scanner Machine [Figure 2] and [Figure 3]. The study protocols included:
Figure 2: Siemens Somatom Emotion Duo Dual-Slice Scanner Machine

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Figure 3: Computed tomography console

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  • 1 mm sagittal localized slices
  • Spiral 1 mm axial slices covering both the maxilla and mandible at zero degree Gantry angle (GT), with patient in supine position
  • The axial principal images were loaded into Denta Scan Software (GE Healthcare, USA) and reformatted axial images were considered parallel to the maxillary palatal plane and mandibular alveolus, respectively, for corresponding implant location. The curvilinear plane is doted to reformate 1 mm paraxial and panoramic (cross-sectional) images
  • 2 mm direct coronal slices perpendicular to the hard palate with the patient in prone position. These 2 mm coronal slices were reformatted in 1 mm coronal slices.


The above study provided multiplanar evaluation technique in three different planes namely axial, coronal, and cross-sectional (paraxial).

Reference planes

Maxilla





  • Line connecting the anterior nasal spine and posterior nasal spine (mid palatine suture) in axial plane [Figure 4]
  • A horizontal line drawn tangentially along the roof of hard palate in coronal plane [Figure 5]
  • Drawn tangential to corresponding alveolus in the paraxial plane [Figure 6].
Figure 4: Line connecting anterior nasal spine and posterior nasal spine (mid palatine suture) in axial plane

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Figure 5: Line tangent to hard palate in coronal plane

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Figure 6: Line tangent to corresponding alveolus in paraxial plane

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Mandible





  • Line connecting corresponding spinous process offirst cervical vertebra and mid-point between central incisors in axial plane [Figure 7]
  • Tangential line along the lingual portion of the mandible in coronal plane [Figure 8]
  • Line drawn tangential to corresponding alveolus in the paraxial plane [Figure 9].
Figure 7: Line connecting corresponding spinous process offirst cervical vertebra and mid-point between central incisors in axial plane

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Figure 8: A tangential line drawn along the lingual portion of the mandible in coronal plane

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Figure 9: Line tangent to corresponding alveolus in paraxial plane

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Structural configuration of mini-implant

Structural configuration of each mini-implant is divided into three parts:





  • Tail: Midpoint between the pointed tip of mini-implant
  • Body: Midpoint between tail and head of mini-implant
  • Head: Midpoint between the blunt ends that fits on to the screwdriver.


Average changes in the mobility of the different parts of mini-implants in all patients at T1 and T2 were divided into five groups in different planes of Denta Scan (axial, coronal and paraxial planes).





  • Group I: Average changes in the mobility of tail of mini-implants in axial plane in 10 patients on right and left sides
  • Group II: Average changes in the mobility of body of mini-implants in axial plane in 10 patients on right and left sides
  • Group III: Average changes in the mobility of head of mini-implants in axial plane in 10 patients on right and left sides
  • Group IV: Average changes in the mobility of head of mini-implants in coronal plane in 10 patients on right and left sides
  • Group V: Average changes in the mobility of tail of mini-implants in the paraxial plane in 10 patients on right and left sides.



   Results Top


The obtained values were subjected to statistical analysis. The mean, standard error, and standard deviation were tabulated. The unpaired Student's t-test and one-way ANOVA test were used to determine the level of significance. On average, the miniscrews were tipped forward significantly at screw head by 1 mm in the axial plane and 0.728 mm in the coronal plane. The tipping and extrusion at the screw tail and the screw body were not significant. On average, miniscrews tail were tipped by 0.567 mm in the axial plane and by 0.486 mm in paraxial plane whereas, miniscrews were tipped forward by 0.349 mm at screw body in the axial plane.

[Table 1] shows the highest value of mean difference of mobility score is by Group III followed by Groups I and II on the right, left side, and total in the axial plane.
Table 1: Mean difference and SD at T1 and T2 in all groups in the term of mobility scores (cm) on right, left, and total in axial, coronal and paraxial plane in all patients

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[Table 2] compares the three groups (I, II, III) at T1 and T2 with respect to mobility scores on the right side in the axial plane. On comparison, the mean difference of mobility scores at T1 and T2 in Groups I and II in the axial plane shows statistically significant difference with P = 0.0003. It shows more mobility in Group I compared to Group II. Comparison of the mean difference of mobility score shows more mobility in Group III than Group I with P < 0.0001. Comparison of the mean difference of mobility score shows more mobility in Group III than Group II with P < 0.0000.
Table 2: Comparison of three groups (I, II, III) at T1 and T2 with respect to mobility scores by one-.way ANOVA test on right side (cm) in axial plane in all patients

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[Table 3] shows pairwise comparison of three groups (I, II, III) at T1 and T2 with mobility scores in the sequence of Group III > Group I > Group II on right side in axial plane.
Table 3: Pairwise comparison of three groups (I, II, III) with respect to mobility scores at T1 and T2 on right side (cm) in axial plane in all patients

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[Table 4] compares the three groups (I, II, III) at T1 and T2 with respect to mobility scores on the left side in the axial plane. On comparison, the mean difference of mobility scores at T1 and T2 in Groups I and II in the axial plane shows statistically significant difference with P < 0.0033. It shows more mobility in Group I compared to Group II. Comparison of the mean difference of mobility score shows more mobility in Group III than Group I with the P < 0.0004. Comparison of the mean difference of mobility score shows more mobility in Group III than Group II with the P < 0.0000.
Table 4: Comparison of three groups (I, II, III) at T1 and T2 with respect to mobility scores by one-.way ANOVA test on left side (cm) in axial plane in all patients

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[Table 5] shows pairwise comparison of three groups (I, II, III) at T1 and T2 with mobility scores in the sequence of Group III > Group I > Group II on left side in axial plane.
Table 5: Pairwise comparison of three groups (I, II, III) at T1 and T2 with respect to mobility scores on left side (cm) in axial plane in all patients

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[Table 6] compares the three groups (I, II, III) at T1 and T2 with respect to total (right and left side) mobility scores in the axial plane. It shows more mobility in Group I compared to Group II with P < 0.0000. Comparison shows more mobility in Group III than Group I with P < 0.0000. Comparison shows more mobility in Group III than Group II with P < 0.0000.
Table 6: Comparison of three groups (I, II, III) at T1 and T2 with respect to mobility scores by one-.way ANOVA test of total (right + left ) (cm) in axial plane in all patients

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[Table 7] shows pairwise comparison of three groups (I, II, III) at T1 and T2 with mobility scores as total in the sequence of Group III > Group I > Group II in the axial plane.
Table 7: Pairwise comparison of three groups (I, II, III) at T1 and T2 with respect to mobility scores by student's unpaired t-.test total (right+left ) (cm) in axial plane

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[Table 8] shows statistically nonsignificant difference of mobility scores at T1 and T2 in Groups I and V on right side (P > 0.1622), left side (P > 0.1549), and in total (P > 0.0601).
Table 8: Comparison of Groups I and V at T1 and T2 with respect to mobility scores by student's unpaired t-.test on right, left, and total (cm) in all patients nonsignificant (P>0.05)

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[Table 9] shows statistically significant difference of mobility scores at T1 and T2 in Groups III and IV on right side (P < 0.0091), left side (P < 0.0247), and in total (P < 0.0072).
Table 9: Comparison of Groups III and IV at T1 and T2 with respect to mobility scores by student's unpaired t-.test on right, left, and total (cm) in all patients

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   Discussion Top


Anchorage, defined as a resistance to unwanted tooth movement is a prerequisite for the orthodontic treatment of dental and skeletal malocclusions.[13] Controlling anchorage helps to avoid undesirable tooth movements. However, even a small reactive force can cause undesirable movements, so it is important to have absolute anchorage (miniscrews) to avoid them.[14] However, the behavior of miniscrews under orthodontic loading is not clear clinically.[2] Few studies have been done to assess the stability of mini-implants under orthodontic loading using lateral cephalograms. We have used CT to evaluate the mobility of different parts of orthodontic miniscrews under orthodontic loading. This study shows that miniscrews are stable anchorage for orthodontic tooth movement although the screw head was tipped forward significantly 1 mm and 0.728 mm on average in axial and coronal plane, respectively, followed by tipping of 0.567 mm at screw tail and 0.349 mm at screw body in axial plane. Displacement of miniscrews was clinically insignificant thus the miniscrews remained clinically stable but not absolutely stationary under orthodontic loading.[2] The mobility of mini-implants during orthodontic loading possibly occur due to inflammation of peri-implant tissue.[15] Inflammation of peri-implant tissue was observed in most of our cases after orthodontic loading, which could possibly explain the miniscrews mobility in our study. Therefore, we believe that prevention of inflammation is important to prevent the mobility of miniscrews.

It has been suggested that a waiting period is not necessary before loading miniscrews because their primary stability (mechanical retention) is sufficient to sustain normal orthodontic loading, and this would not compromise the clinical stability of miniscrews.[10][11][12] In fact, recent reports recommended immediate loading to the implant anchor.[16] In our study, miniscrews were loaded (150 g force in the maxilla and 100 g force in mandible for anterior teeth retraction) immediately without any waiting period between miniscrews placement and orthodontic loading.

It has been shown histologically, that when the orthodontic load was placed prematurely a layer of fibrous tissue would interpose at the bone-implant contacts.[17] Although there was no histologic evidence in this study, we hypothesize that the miniscrews were not osteo-integrated and that a layer of fibrous tissue was interposed between the miniscrews and the surrounding bone. This layer of fibrous tissue allowed the miniscrews to be extruded and tipped in the direction of orthodontic loading, just like a tooth against the periodontal ligament. This hypothesis explains why miniscrews in our study showed some mobility.

The miniscrews placed left side for anterior teeth retraction shows less mobility compared to those placed right side in our study. The reason could be unilateral chewing habit of the patients (right side) and better oral hygiene on the left side of the dental arch by the right-handed patients who are most of the population.[16] It has been suggested that miniscrews placed at the attached gingiva betweenfirst and second premolar show higher success rate than those placed at the attached gingiva between the second premolar andfirst molar.[18] In this study, miniscrews were placed at the attached gingival between the second premolar andfirst molar, which might be the cause of mobility, which was clinically insignificant. Stability of miniscrews under orthodontic loading is also affected by close approximation of miniscrews to the dental roots. Failure rate of the miniscrews that invaded the roots was 79.2%.[19] In this study, most of the miniscrews were placed away from the root of teeth but some miniscrews showed close contact to the root surface which might be the cause of miniscrews mobility.

The question to be answered is this: Does it really matter whether miniscrews move when loaded? Miniscrews are used as temporary fixtures for orthodontic tooth movement and will be removed at the end of treatment. It seems that miniscrews, as temporary fixtures, do not have to remain absolutely stationary under orthodontic loading, as long as the treatment effects are achieved. Nevertheless, the displacement of miniscrews would be a serious matter when the displacement harms adjacent vital organs, such as dental roots, nerves, and blood vessels. This is very important, yet overlooked possibility. Therefore, miniscrews should not be placed at a site adjacent to any vital organ. A suitable implant site for miniscrews could be in a non-tooth-bearing area that has no foramen or pathway for any major nerves and blood vessels. When miniscrews are placed in a tooth-bearing area, a clearance of 1.5 mm between the miniscrew and the dental root is recommended for safety, based on the finding of this study that mobility was ranging from 0.349 to 1.


   Conclusions Top


Miniscrew head shows highest mobility (0.728–1 mm) followed by the tail (0.567–0.486 mm) and body (0.349 mm). Clinically, no significant mobility was observed. Thus, miniscrews are a stable anchorage for orthodontic tooth movement but do not remain absolutely stationary like an endosseous implant throughout orthodontic loading although miniscrews might move according to placement site (more mobility on right side than left side, more mobility when placed between second premolar andfirst molar than those placed betweenfirst premolar and second premolar), orthodontic loading (150 g in maxilla and 100 g in mandible for anterior teeth retraction is appropriate), inflammation of peri-implant tissue. Waiting period between miniscrews placement and orthodontic loading does not significantly affect the miniscrew mobility so immediate loading can be recommended. To prevent hitting any vital organs because of miniscrew mobility, it is recommended that miniscrews be placed in a non-tooth-bearing area that has no foramen, major nerves, or blood vessel pathway, or in a tooth-bearing area allowing a 1.5 mm safety clearance between the miniscrew and dental root.







 
   References Top

1.
Kyung HM, Park HS, Bae SM, Sung JH, Kim IB. Development of orthodontic micro-implants for intraoral anchorage. J Clin Orthod 2003;37:321-8.  Back to cited text no. 1
    
2.
Liou EJ, Pai BC, Lin JC. Do miniscrews remain stationary under orthodontic forces? Am J Orthod Dentofacial Orthop 2004;126:42-7.  Back to cited text no. 2
    
3.
Roberts WE, Marshall KJ, Mozsary PG. Rigid endosseous implant utilized as anchorage to protract molars and close an atrophic extraction site. Angle Orthod 1990;60:135-52.  Back to cited text no. 3
    
4.
Roberts WE, Nelson CL, Goodacre CJ. Rigid implant anchorage to close a mandibularfirst molar extraction site. J Clin Orthod 1994;28:693-704.  Back to cited text no. 4
    
5.
Chen J, Esterle M, Roberts WE. Mechanical response to functional loading around the threads of retromolar endosseous implants utilized for orthodontic anchorage: Coordinated histomorphometric and finite element analysis. Int J Oral Maxillofac Implants 1999;14:282-9.  Back to cited text no. 5
    
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Block MS, Hoffman DR. A new device for absolute anchorage for orthodontics. Am J Orthod Dentofacial Orthop 1995;107:251-8.  Back to cited text no. 6
    
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Wehrbein H, Feifel H, Diedrich P. Palatal implant anchorage reinforcement of posterior teeth: A prospective study. Am J Orthod Dentofacial Orthop 1999;116:678-86.  Back to cited text no. 7
    
8.
Byloff FK, Kärcher H, Clar E, Stoff F. An implant to eliminate anchorage loss during molar distalization: A case report involving the Graz implant-supported pendulum. Int J Adult Orthodon Orthognath Surg 2000;15:129-37.  Back to cited text no. 8
    
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Saito S, Sugimoto N, Morohashi T, Ozeki M, Kurabayashi H, Shimizu H, et al.Endosseous titanium implants as anchors for mesiodistal tooth movement in the beagle dog. Am J Orthod Dentofacial Orthop 2000;118:601-7.  Back to cited text no. 9
    
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Costa A, Raffainl M, Melsen B. Miniscrews as orthodontic anchorage: A preliminary report. Int J Adult Orthodon Orthognath Surg 1998;13:201-9.  Back to cited text no. 10
    
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Melsen B, Verna C. A rational approach to orthodontic anchorage. Prog Orthod 1999;1:10-22.  Back to cited text no. 11
    
12.
Costa A, Dalstra M, Melsen B. Aarthus anchorage system. Ortognatodonzia Ital 2000;9:487-96.  Back to cited text no. 12
    
13.
Graber TM. Orthodontics: Principles and Practice. Philadelphia: WB Saunders; 1998.  Back to cited text no. 13
    
14.
Papadopoulos MA, Tarawneh F. The use of miniscrew implants for temporary skeletal anchorage in orthodontics: A comprehensive review. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;103:e6-15.  Back to cited text no. 14
    
15.
Miyawaki S, Koyama I, Inoue M, Mishima K, Sugahara T, Takano-Yamamoto T. Factors associated with the stability of titanium screws placed in the posterior region for orthodontic anchorage. Am J Orthod Dentofacial Orthop 2003;124:373-8.  Back to cited text no. 15
    
16.
Park HS, Jeong SH, Kwon OW. Factors affecting the clinical success of screw implants used as orthodontic anchorage. Am J Orthod Dentofacial Orthop 2006;130:18-25.  Back to cited text no. 16
    
17.
Majzoub Z, Finotti M, Miotti F, Giardino R, Aldini NN, Cordioli G. Bone response to orthodontic loading of endosseous implants in the rabbit calvaria: Early continuous distalizing forces. Eur J Orthod 1999;21:223-30.  Back to cited text no. 17
    
18.
Moon CH, Lee DG, Lee HS, Im JS, Baek SH. Factors associated with the success rate of orthodontic miniscrews placed in the upper and lower posterior buccal region. Angle Orthod 2008;78:101-6.  Back to cited text no. 18
    
19.
Kang YG, Kim JY, Lee YJ, Chung KR, Park YG. Stability of mini-screws invading the dental roots and their impact on the paradental tissues in beagles. Angle Orthod 2009;79:248-55.  Back to cited text no. 19
    

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Correspondence Address:
Kamlesh Kumar Garg
Department of Orthodontics and Dentofacial Orthopedics, Pacific Dental College and Hospital, Debari, Udaipur, Rajasthan
India
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Source of Support: Nil, Conflict of Interest: None


DOI: 10.4103/0970-9290.162874

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    Figures

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