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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 53  |  Issue : 1  |  Page : 27-37

Evaluation of tooth surface characteristics after application of intrusive orthodontic forces using scanning electron microscope: An In vivo study


1 Private Practice, Sant Baba Rangi Ram Ji Charitable Hospital (Regd), V.P.O. Jaja, Hoshiarpur, Punjab, India
2 Prof. and Head of Department, Department of Orthodontics, SGT Dental College and Research Institute, Gurgaon, Haryana, India
3 Prof., Department of Orthodontics, SGT Dental College and Research Institute, Gurgaon, Haryana, India
4 Senior Lecturer, Department of Orthodontics, SGT Dental College and Research Institute, Gurgaon, Haryana, India

Date of Submission17-Apr-2018
Date of Acceptance13-Sep-2019
Date of Web Publication04-Feb-2019

Correspondence Address:
Dr. Seema Grover
Department of Orthodontics, SGT Dental College and Research Institute, Gurgaon, Haryana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jios.jios_55_18

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  Abstract 


Introduction: Orthodontic forces when applied to tooth structure leads to some amount of resorption depending upon force duration and magnitude applied. Study aimed to evaluate tooth surface changes after application of intrusive orthodontic forces using scanning electron microscope. Materials and Methods: 20 patients were selected requiring first premolar extraction for treatment of malocclusion with fixed mechanotherapy and were divided into four groups. Group I and III consisted application of 50 gm of light force on right side and left side respectively for 4 weeks intervals. Group II and IV consisted application of 150 gm of heavy force on right side and left side respectively for 8 weeks intervals. A cantilever spring was attached from buccal tube of molar band to bracket bonded on first premolar. After 4 and 8 weeks respectively; first premolars were extracted and surface chareacteristics were evaluated using SEM. Each tooth sample was divided into middle and apical third and further into buccal, lingual, mesial and distal surfaces on each tooth. Results: Statistical significant (P < 0.001) changes were observed in middle third area using both light and heavy forces. Conclusions: Heavy forces during intrusion should be used cautiously in orthodontic biomechanics, if such procedures are to be carried out over a long period of time.

Keywords: Force duration, intrusion, scanning electron microscopy, tooth movement


How to cite this article:
Kaur G, Sidhu MS, Grover S, Dabas A, Dogra N. Evaluation of tooth surface characteristics after application of intrusive orthodontic forces using scanning electron microscope: An In vivo study. J Indian Orthod Soc 2019;53:27-37

How to cite this URL:
Kaur G, Sidhu MS, Grover S, Dabas A, Dogra N. Evaluation of tooth surface characteristics after application of intrusive orthodontic forces using scanning electron microscope: An In vivo study. J Indian Orthod Soc [serial online] 2019 [cited 2019 Jun 16];53:27-37. Available from: http://www.jios.in/text.asp?2019/53/1/27/251554




  Introduction Top


Orthodontic tooth movement is a biomechanical process which evokes plethora of reactions in paradental tissues at both cellular and molecular levels. Orthodontic forces affect extracellular matrix and cells of periodontal ligament, alveolar bone, gingiva, and dental pulp. Oppenheim[1] refers to an orthodontic force as the physiologic force, stating that “the vitality of periosteum suffers no injury during the application of ‘physiological forces’. Hence, tooth movements induced can be classified as physiological tooth movements provided force evolved is of such a nature to result in tissue reactions that are normal vital manifestations of cells of tissues environmental tooth.[2] Schwarz[3] advocated optimal force level for tooth movement between 7 and 26 g/cm,[2] and also stated that orthodontic forces should not exceed capillary pressure of 20 mmHg since strangulation of vessels could ensue with subsequent necrosis. Excessive force on tooth results in hyalinization due to anatomic and mechanical factors.[4],[5],[6]

Intrusion refers to the apical movement of geometric center of root in respect to the plane based on the long axis of tooth. Light force of 15–25 g per maxillary incisor was recommended for clinical intrusion, although higher force can be utilized with anterior high-pull headgear. A force of 15–25 g per tooth has been recommended for intrusion of nontraumatized maxillary incisors.[7] According to Strang,[8] “too powerful force might shut off the arterial blood supply and this causes a devitalization of various elements in pulp.”[9],[10]

Chan and Darendeliler[11] found that 50 g of constant and continuous force could produce an ideal amount of tooth movement, but exceeding this force might cause periodontal ischemia, leading to root resorption. Owman-Moll et al.[12] reported that tooth movements and the severity of root resorption are not affected by doubling the force magnitude from 50 to 100 cN (1 N = 100c N). The root resorption increases after 7 weeks with 50 cN force compared with 100 cN. Reitan[13] proposed the use of light forces during orthodontic treatment to increase the cellular activity in the surrounding tissues and reduce the risk of root resorption.

In the past, the extent of root resorption has been examined with radiographs, light microscopy, and scanning electron microscopy (SEM).[14] It has been reported that SEM provides enhanced visual and perspective assessment of root surfaces and when recorded in stereo pairs, provides resolution, and detail not attainable with histologic models reconstructed from serial sections.[15] Hence, the present study was conducted to evaluate pulp vitality after the application of intrusive orthodontic forces with help of an electric pulp tester, and surface characteristic changes of extracted teeth were visualized under SEM.


  Materials and Methods Top


The present study was started as a split-mouth clinical study with the age group of 13–25 years patients, who reported to the department for their routine fixed mechanotherapy treatment. An Ethical Clearance was obtained for the study from the Institutional Committee (SGTU/FDS/24/1465). The patients requiring bilateral maxillary first premolar extractions as part of their fixed orthodontic treatment were randomly selected for the study irrespective of age and gender. Patients with a history of major systemic disease, active use of medication, severe crowding, and previous orthodontic treatment were excluded from the study.

Keeping power of the study as per our objective set at 80% for a clinical significant difference for the effect size of 0.6; the sample size was calculated to be 18. Hence, considering attrition of sample of two patients, 20 patients were selected for this study.

Basic records of patients, including lateral cephalogram, orthopantomogram, models, and photographs, were taken to meet the strict selection criteria. The present study was conducted on 40 maxillary first premolars collected from 20 prospective orthodontic patients and was divided into four groups based on the amount and duration of intrusive force on premolars to be extracted as follows:

  • Group I: 20 right upper premolars with application of light intrusive forces (50 g) for 4 weeks (T1)
  • Group II: 20 left upper premolars with application of heavy intrusive force (150 g) for 4 weeks (T1)
  • Group III: 20 right upper premolars with application of light intrusive forces (50 g) for 8 weeks (T2)
  • Group IV: 20 left upper premolars with application of heavy intrusive forces (150 g) for 8 weeks (T2).


Fixed mechanotherapy treatment was started for all patients with MBT 0.022” slot (Ortho Organizers, Carlsbad, CA, USA) specification in lower arch and 0.016” SS wire was placed as initial wire. For the upper arch, only premolars and molars were bonded and banded, respectively, to evaluate intrusion force effects following light and heavy forces. This study was undertaken to evaluate changes taking place on different surfaces of premolars root after the application of orthodontic intrusive forces using SEM. Furthermore, electric pulp testing was done in all patients to see the response of periodontium to light and heavy, intrusive forces.

A cantilever spring device was designed to exert intrusive force selectively on premolars of selected sample [Figure 1]. The spring was made from 0.019” × 0.025” stainless steel straight archwire. It incorporated a helix near the first molar extending anteriorly to first premolar tooth where wire was bent to form a hook and inserted in the first molar tube posteriorly. Cantilever spring was positioned 3 mm above slot of bracket of the first premolar in passive state. Force magnitude required for intrusion of premolars of both sides of arch was measured with dontrix gauze (ORJ Force Gauze) [Figure 2] in all patients. Hence, in consideration of root surface area of first premolar, 50 g of light force on the right side premolar of upper arch and 150 g of heavy force on the left side upper premolar were applied. All patients were regularly followed up at 1-week interval for 4 weeks (Groups I and II) and for 8 weeks (Groups III and IV) consecutively [Table 1].
Figure 1: Cantilever spring device inserting intrusive force on premolars

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Figure 2: Dontrix force measuring gauze

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Table 1: Division of sample of 40 premolars based on duration and force amount

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Electric pulp testing was used to acquire information about pulp vitality based on the stimulation of sensory nerves. It relies on subjective assessments and comments from the patient. All four groups were evaluated for pulp testing at the initial day of force application, at baseline, at 4th week, and at 8th week consecutively.

After 8 weeks, 20 patients of Groups III and IV had undergone a pulp vitality test followed by the first premolar extractions. Cantilever springs were removed, and intraoral photographic records of patients were taken using the scale in Groups I and II [Figure 3] and [Figure 4]. Marked intrusion was noticed clinically after heavy, intrusive force application for Group IV at 8-week intervals [Figure 5] and [Figure 6]. Extractions were done keeping in consideration that teeth were subjected to minimal trauma to facilitate optimal evaluation of surface changes.
Figure 3: Four weeks after application of intrusive forces on the right side (light force)

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Figure 4: Four weeks after application of intrusive forces on the left side (heavy force)

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Figure 5: Eight weeks after application of intrusive forces on the right side (light force)

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Figure 6: Eight weeks after application of intrusive forces on the left side (heavy force)

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Scanning electron microscopic evaluation

Dried samples were taken for Scanning Electron Microscopy (SEM) at Advanced Instrumentation Research Facility Center at Jawaharlal Nehru University, New Delhi [Figure 7]. Samples were kept for pure gold coating in sputter coater (Polaron SC7640 NK) [Figure 8]. Coated samples were mounted on metal stubs using double-sided carbon tape and were placed inside SEM (Carl ZeissEVO 40, Germany) [Figure 9] and [Figure 10]. Each sample was divided into middle and apical one-third which were further divided into buccal, lingual, mesial, and distal surfaces, respectively. At first, the image of the whole tooth root was captured at low magnification ranging between ×23 and ×28 to visualize total number of irregular areas on each surface [Figure 11]. Afterward, each area was individually scanned at 500× magnification [Figure 12] and [Figure 13]. In this study, scanning electron microscopic images were subjected to AutoCAD software (Autodesk; Version 2013) to quantify affected area of each sample [Figure 14].
Figure 7: Scanning electron microscope

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Figure 8: Sputter coater for sample coating

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Figure 9: Pure gold-coated samples

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Figure 10: Samples fixed on metal stubs on double-sided carbon tape

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Figure 11: Scanned image of whole sample at the lowest magnification

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Figure 12: Scanning electron microscopy image of sample with light intrusive force (×500)

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Figure 13: Scanning electron microscopy image of sample with heavy intrusive force (×500)

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Figure 14: Affected surface area value after irregular object was selected

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  Results Top


The study was done to evaluate surface changes after light and heavy force application in a sample of 40 maxillary first premolars collected from 20 prospective orthodontic patients. All readings were recorded using AutoCAD software and subjected for statistical analysis. Software used for statistical analysis was Statistical Package for Social Sciences.

[Table 2] shows the effects of light force application in Groups I and III on middle, apical, and total affected surface area at 4-and 8-week intervals; and statistically significant changes were found with 8-week duration force on intragroup comparison. [Table 3] depicts heavy force application effects in Group II at 4-week interval and Group IV at 8-week interval. Highly significant (P ≤ 0.001) changes were observed at middle, apical, and total affected surface area in Group II.
Table 2: Intergroup comparison of light force application of Group I and Group III in middle, apical, and total affected surface area (106 μm2) at 4 (T1) and 8 weeks' (T2) intervals

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Table 3: Intergroup comparisons of heavy force application of Group II and Group IV in middle, apical, and total affected surface area (106 μm2) at 4 (T1) and 8 weeks' (T2) intervals

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When Group I and Group III were compared for light and heavy force application, respectively, at 4-week intervals; significant changes were observed in Group III at middle, apical, and total affected surface area [Table 4]. Intergroup comparison of Group I (light force) at 4-week intervals and Group IV (Heavy force) at 8-week intervals showed highly significant changes at middle, apical, and total affected surface area [Table 5].
Table 4: Intergroup comparisons of light force (Group I) and heavy force (Group II) application in middle, apical, and total affected area at 4-week (T1) intervals

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Table 5: Intergroup comparison of light force (Group I) application at 4-week (T1) interval and heavy force (Group IV) at 8-week (T2) interva

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Analysis of variance (ANOVA) test was used in the present study which splits total variation into two parts; one between groups and other within groups. On comparing, middle, apical, and total affected surface area in both Group I (Light) and Group II (Heavy) force groups at 4 weeks (T1) and Group III (Light) and Group IV (Heavy) at 8-week (T2) interval using the one-way ANOVA; “F” value was found to highly significant between both groups [Table 6].
Table 6: Comparison of middle, apical, and total affected surface area in both light (Groups I and III) and heavy (Groups II and IV) force groups at 4 (T1) and 8 weeks' (T2) intervals using the one-way analysis of variance

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[Table 7] depicts the comparison of buccal, lingual, and mesial and distal affected area with light force application in Group I at 4 weeks and in Group III at 8-week intervals; and statistically significant (P ≤ 0.001) changes were found on intergroup comparison at all levels. [Table 8] shows an intragroup comparison in Group II at 4 weeks and Group IV at 8-week intervals with heavy force application. Highly significant (P ≤ 0.001) changes were observed at buccal, lingual, and mesial and distal affected surface area.
Table 7: Intergroup comparison of buccal, lingual, mesial, and distal surfaces after light force (Group I) application at 4 weeks (T1) and Group III at 8-week (T2) intervals

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Table 8: Intergroup comparison of buccal, lingual, mesial, and distal surfaces in heavy force (Group II) at 4 weeks (T1) and Group IV at 8-week (T2) intervals

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Intergroup comparison between Group I and Group II at weeks, 4-week intervals showed significant changes at buccal, lingual, and mesial and distal affected area [Table 9]. When Groups I and IV were compared for light and heavy force application at 4 and 8 weeks intervals, highly significant changes were seen observed at buccal, lingual, and mesial and distal affected surface area [Table 10]. ANOVA test indicated highly significant changes between and within groups at buccal, lingual, and mesial and distal affected surface area [Table 11].
Table 9: Intergroup comparison of buccal, lingual, mesial, and distal surfaces in light force (Group I ) and heavy force (Group II) at 4-week (T1) interval

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Table 10: Intergroup comparison of buccal, lingual, mesial, and distal surfaces in light force (Group I) at 4-week (T1) interval and heavy force (Group IV) at 8-week (T2) interval

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Table 11: Comparison between buccal, lingual, mesial, and distal surfaces in light (Group I) and heavy (Group II) force groups at 4 weeks (T1) and in Group III and Group IV at 8-week (T2) intervals using the one-way analysis of variance

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[Table 12] shows electropulp testing values done in Groups I and III and Groups II and IV at baseline (T0), 4 weeks (T1), and 8 weeks' (T2) intervals. There was a subsequent increase in values with increase of force and duration in both groups.
Table 12: Mean values (μA) of electric pulp testing in light force (Group I and III) at baseline (T0) and at 4-week (T1) interval and heavy force (Group II and IV) at baseline (T0), 4 weeks (T1), and 8-week (T2) intervals

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  Discussion Top


Keeping in consideration the importance of orthodontic tooth movement and its relation to tooth structure, the present study was conducted to evaluate surface changes taking place in tooth after light and heavy forces application and then checking the vitality of tooth using electric pulp tester. In literature, very few studies have been done on human premolars to know surface changes produced after external forces application to periodontium.[16],[17],[18]

The light force of 50 gm was continuously applied for 4 weeks, after which teeth were evaluated for surfaces changes using SEM. It was viewed that root resorption craters were seen on all surfaces of root which were small in size and number, even though resorptive areas were unevenly spread on the root; middle third of root was highly affected as compared to all other areas. According to the literature, when light and for short-duration force is applied, the root resorption occurring can be reversible due to continued deposition of bone. Resorption craters after such light force does not exceed to dentin and pulp but remain until cementum.[19],[20] This can be reason that, in the current study, less resorption craters were appreciated after light force application. This is supported by the findings of Jimenez-Pellegrin et al.[21] where they investigated presence, location, and severity of root resorption after orthodontic force of 50 g using SEM.

Furthermore, when duration of light force of 50 gm was increased to 8 weeks, a significant increase in the amount of root resorption was observed in middle third of root surface, and resorption craters increased both in size and number. This might be due to increased osteoclastic activity for 8 weeks of force application. Another reason can be an acute inflammatory response taking place during the early phase of orthodontic tooth movement. Wu et al.[22] investigated the amount of root resorption volumetrically after application of controlled light forces of 25 gm for 6–8 weeks. They found significant differences in the extent of root resorption with substantially longer force duration groups with a mean value of 0.44 –0.74 mm3 from 4 weeks to 8 weeks. Montenegro et al.[23] observed similar findings and suggested that duration of force application appears to be an important factor in determining root resorption even when force is kept constant.

Heavy force (150 gm) application for 4 weeks produced large size craters on almost all the surfaces of the tooth. When duration was 4 weeks, craters were shallow and scalloped, but when duration was exceeded, craters present were such as concave depressions. It was due to the reason that when force is increased; undermining resorption takes place which cannot be reversed especially when it reaches dentin.[24],[25] Chan et al.[26] analyzed root resorption craters after application of light and heavy orthodontic forces and clearly demonstrated that heavy force group had significantly greater volumetric resorption as compared to light force group.

The apical third was least affected when compared to middle one-third with both light and heavy forces. Even, when duration was increased to 8 weeks, resorption was seen in the apical region which was more as compared to 4 weeks but less as compared to the middle third of root surface which was affected the most in the present study. However, on comparing different areas, middle third area of root was highly affected, and apical third was less affected than middle third at 4-and 8-week intervals. This is in correlation with studies done by Jimenez-Pellegrin et al.[21] who concluded that resorptive areas were mainly localized at the middle third of root surface with the presence of dense and deep concavities. Furthermore, in a study done by Wu et al.,[22] it was clearly demonstrated that significant differences in light force group occurred only at the middle third of root surface which is in agreement with the present study. Whereas Barbagallo et al.[27] found that apical third of root surface was more prone to resorptive lesions when heavy forces were applied for longer duration which is in contrast with the present study findings. Among mesial and distal surfaces, light forces affected mesial surface at 4-and 8-week intervals whereas heavy forces affected both mesial and distal surfaces in this study. This correlates with the findings of Harris et al.[28] who used 200 gm of intrusive force in their study.

Aras et al.[29] conducted a study in which they chose continuous and intermittent orthodontic forces to evaluate root surface changes after weekly reactivation. It was 12 weeks' experimental study in which 150 gm of force was applied on maxillary premolars, showing differences in both continuous and intermittent force groups with the mean values of 4.91 mm3 in continuous force group and 3.13 mm3 in the intermittent force group corresponding to the middle surface root area to be more affected which is consistent with the present study findings. With an increase in the magnitude of force, the phase of tooth movement at certain threshold becomes constant, further leading to resorption only which is irreversible as it reaches dentin. In a study done by Barbagallo et al.,[27] heavy forces were applied for longer duration, and the apical third of root surface was more prone to resorptive lesions which are in contrast with the present study findings and when root resorption is severe, it is called as irreversible undermining root resorption.

When the electric pulp tester exceeded from baseline to 4 weeks and 8 weeks with light and heavy forces, and reaction of patients to stimulus was delayed. This would have been due to cellular changes that took place in tooth after forces were applied. Furthermore, electric pulp testing is based on the stimulation of sensory nerves and relies on assessments and responses from patients.[10] Han et al.[30] and Sadhasivam et al.[31] reported a significant reduction in the pulpal blood flow when force duration was increased to few days.

It is important to measure the force to move teeth in orthodontic manner. Factors to be considered are movement type, size of given force, and patient's age in relation to dental periapical condition.[32] It is advisable to give force not more than capillary pressure of 20 mmHg to prevent disruption of blood circulation into pulp which can be followed by a pulp tissue necrosis. Even though force magnitude and orthodontic biomechanics are not sole factors leading to surface resorption, heavy forces during intrusion should be used cautiously especially if such procedures are to be carried out over a long period.


  Conclusions Top


  1. There was a statistically highly significant increase in area of root resorption craters from 4 to 8 weeks' interval of force application either with light or heavy orthodontic intrusive forces
  2. Middle third of tooth root was highly affected with resorption craters in both 4 and 8 weeks' interval with both light and heavy, intrusive forces concluding that effect of orthodontic forces on tooth surface depends on both magnitude and duration of force application
  3. Depending on the amount of compressive stresses produced by intrusive force; In light force group, the mesial surface of tooth root was significantly affected whereas in the heavy force group both mesial and distal surfaces were affected to maximum at 4 and 8 weeks' intervals
  4. On the basis of electric pulp testing, after intrusion with different forces, pulp still had vitality as after every stimulation patient responded positively. Hence, with orthodontic forces within limits, teeth had not undergone any necrosis or pulpal inflammation.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Strang RH. Factors of influence in producing a stable result in treatment of malocclusions. Am J Orthod 1946;32:313-32.  Back to cited text no. 8
    
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Chan E, Darendeliler MA. Physical properties of root cementum: Part 5. Volumetric analysis of root resorption craters after application of light and heavy orthodontic forces. Am J Orthod Dentofacial Orthop 2005;127:186-95.  Back to cited text no. 11
    
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Owman-Moll P, Kurol J, Lundgren D. Effects of a doubled orthodontic force magnitude on tooth movement and root resorptions. An inter-individual study in adolescents. Eur J Orthod 1996;18:141-50.  Back to cited text no. 12
    
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Reiten K. Effect of force magnitude and direction of tooth movement on different alveolar bone types. Angle Orthod 1964;34:244-55.  Back to cited text no. 13
    
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Reitan K. Initial tissue behavior during apical root resorption. Angle Orthod 1974;44:68-82.  Back to cited text no. 14
    
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Kvam E. SEM of tissue changes on the pressure surface of human premolars following tooth movement. Scand J Dent Res 1972;80:357-68.  Back to cited text no. 15
    
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Proffit W, Fields H, Sarver D. The biologic basis of orthodontic therapy. In: Contemporary Orthodontics. 4th ed. St. Louis: C.V. Mosby; 2006. p. 331-58.  Back to cited text no. 16
    
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Malek S, Darendeliler MA, Swain MV. Physical properties of root cementum: Part I. A new method for 3-dimensional evaluation. Am J Orthod Dentofacial Orthop 2001;120:198-208.  Back to cited text no. 17
    
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Malek S, Darendeliler MA, Rex T, Kharbanda OP, Srivicharnkul P, Swain MV, et al. Physical properties of root cementum: Part 2. Effect of different storage methods. Am J Orthod Dentofacial Orthop 2003;124:561-70.  Back to cited text no. 18
    
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Kurol J, Franke P, Lundgren D, Owman-Moll P. Force magnitude applied by orthodontists. An inter- and intra-individual study. Eur J Orthod 1996;18:69-75.  Back to cited text no. 19
    
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Chan E, Darendeliler MA. Physical properties of root cementum: Part 7. Extent of root resorption under areas of compression and tension. Am J Orthod Dentofacial Orthop 2006;129:504-10.  Back to cited text no. 20
    
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Jimenez-Pellegrin C, Arana-Chavez VE. Root resorption in human mandibular first premolars after rotation as detected by scanning electron microscopy. Am J Orthod Dentofacial Orthop 2004;126:178-84.  Back to cited text no. 21
    
22.
Wu AT, Turk T, Colak C, Elekdağ-Turk S, Jones AS, Petocz P, et al. Physical properties of root cementum: Part 18. The extent of root resorption after the application of light and heavy controlled rotational orthodontic forces for 4 weeks: A microcomputed tomography study. Am J Orthod Dentofacial Orthop 2011;139:e495-503.  Back to cited text no. 22
    
23.
Montenegro VC, Jones A, Petocz P, Gonzales C, Darendeliler MA. Physical properties of root cementum: Part 22. Root resorption after the application of light and heavy extrusive orthodontic forces: A microcomputed tomography study. Am J Orthod Dentofacial Orthop 2012;141:e1-9.  Back to cited text no. 23
    
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Reitan K. Some factors determining the evaluation of force in orthodontics. Am J Orthod 1957;43:32-45.  Back to cited text no. 24
    
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Paetyangkul A, Turk T, Elekdag-Turk S, Jones AS, Petocz P, Cheng LL, et al. Physical properties of root cementum: Part 16. Comparisons of root resorption and resorption craters after the application of light and heavy continuous and controlled orthodontic forces for 4, 8, and 12 weeks. Am J Orthod Dentofacial Orthop 2011;139:e279-84.  Back to cited text no. 25
    
26.
Chan EK, Darendeliler MA, Petocz P, Jones AS. A new method for volumetric measurement of orthodontically induced root resorption craters. Eur J Oral Sci 2004;112:134-9.  Back to cited text no. 26
    
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Barbagallo LJ, Jones AS, Petocz P, Darendeliler MA. Physical properties of root cementum: Part 10. Comparison of the effects of invisible removable thermoplastic appliances with light and heavy orthodontic forces on premolar cementum. A microcomputed-tomography study. Am J Orthod Dentofacial Orthop 2008;133:218-27.  Back to cited text no. 27
    
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Harris DA, Jones AS, Darendeliler MA. Physical properties of root cementum: Part 8. Volumetric analysis of root resorption craters after application of controlled intrusive light and heavy orthodontic forces: A microcomputed tomography scan study. Am J Orthod Dentofacial Orthop 2006;130:639-47.  Back to cited text no. 28
    
29.
Aras B, Cheng LL, Turk T, Elekdag-Turk S, Jones AS, Darendeliler MA, et al. Physical properties of root cementum: Part 23. Effects of 2 or 3 weekly reactivated continuous or intermittent orthodontic forces on root resorption and tooth movement: A microcomputed tomography study. Am J Orthod Dentofacial Orthop 2012;141:e29-37.  Back to cited text no. 29
    
30.
Han G, Hu M, Zhang Y, Jiang H. Pulp vitality and histologic changes in human dental pulp after the application of moderate and severe intrusive orthodontic forces. Am J Orthod Dentofacial Orthop 2013;144:518-22.  Back to cited text no. 30
    
31.
Sadhasivam N, Premkumar S, Muthuswamy L. Effective human pulpal blood flow changes during brief intrusive force application and continuous orthodontic force application using laser Doppler flowmetry. J Indian Orthod Soc 2010;44:55-61.  Back to cited text no. 31
  [Full text]  
32.
Hamersky PA, Weimer AD, Taintor JF. The effect of orthodontic force application on the pulpal tissue respiration rate in the human premolar. Am J Orthod 1980;77:368-78.  Back to cited text no. 32
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12]



 

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