Open Access

Root resorption during orthodontic treatment with Invisalign®: a radiometric study

Progress in Orthodontics201718:12

https://doi.org/10.1186/s40510-017-0166-0

Received: 3 February 2017

Accepted: 18 April 2017

Published: 15 May 2017

Abstract

Background

Root resorption (RR) is described as a permanent loss of tooth structure from the root apex. Many reports in the literature indicate that orthodontically treated patients are more likely to have severe apical root shortening, interesting mostly maxillary, followed by mandibular incisors. The aim of the study was to investigate the incidence and severity of RR in adult patients treated with aligners. The study group consisted of 71 class I adult healthy patients (mean age 32.8 ± 12.7) treated with aligners (Invisalign®, Align Technologies, Santa Clara, CA, USA). All incisors, canines, upper first premolars, and first molars were assessed. Root and crown lengths of 1083 teeth were measured in panoramic radiographs at the beginning (T0) and at the end (T1) of clear aligner therapy. Individual root-crown ratio (RCR) of each tooth and therefore the relative changes of RCR (rRCR) were determined. A decrease of rRCR was assessed as a reduction of the root length during treatment.

Results

All patients had a minimum of one teeth affected with a reduction of root length, on average 6.38 ± 2.28 teeth per patient. Forty one, 81% of the 1083, measured teeth presented a reduction of the pre-treatment root length. A reduction in percentage of >0% up to 10% was found in 25.94% (n = 281), a distinct reduction of >10% up to 20% in 12.18% (n = 132) of the sample. 3.69% (n = 40) of the teeth were affected with a considerable reduction (>20%).

Conclusions

Orthodontic treatment with Invisalign® aligners could lead to RR. However, its incidence resulted to be very similar to that described for orthodontic light forces, with an average percentage of RR < 10% of the original root length.

Keywords

Adult patients Aligners Root resorption

Background

Root resorption (RR) is a permanent loss of tooth structure from the root apex [1]. Its clinical outcomes in orthodontic patients are highly variable and depend on genetic predisposition, individual biologic variability, and mechanical factors [2]. Several authors demonstrated that RR occurs even without orthodontic treatment [36], but patients who underwent orthodontic treatment are more likely to show severe apical root shortening [7].

In histological studies, orthodontically moved teeth show an occurrence of RR greater than 90% [810]. Lower percentages are reported for diagnostic radiographic techniques. The average amount of tissue loss is less than 2.5 mm [1114] or varies from 6 to 13% for different teeth [15] in radiographic studies.

RR is usually classified as minor or moderate in most orthodontic patients. Severe resorption, if exceeding 4 mm or one-third of the original root length, is seen in 1–5% of teeth7 [1618].

Root resorption has two phases: during the first phase, the damage of the external surface of the root causes the exposition of denuded mineralized tissue, while in the second one, multinucleated cells are stimulated to colonize the denuded mineralized tissue, getting to a resorption process [19]. Without any further stimulation, cementum-like material will spontaneously repair the damage within 2–3 weeks. With persistent inflammatory process, deeper root dentin will be involved and RR radiographically detected [20]. When forces at the root apex exceed the resistance and reparative ability of the periapical tissues, RR occurs [21]. It begins approximately 2–5 weeks into treatment, but radiographical appearance requires 3–4 months.

Furthermore, the association between RR and the amount of orthodontic tooth movement21 [2224] has been demonstrated. Since the amount of tooth movement depends on the severity of the malocclusion, a severe malocclusion represents a risk factor for RR. Class I patients with normal overjet show less RR than class II or III patients [25].

Several studies [2628] suggest that light continuous forces are perceived as intermittent ones and allow the healing of the resorbed cementum, preventing further resorption. The Invisalign® treatment technique belongs to removable appliances, so intermittent forces are applied to the teeth. The aim of the present study was to investigate the incidence and severity of RR in adult patients treated with aligners.

Methods

In the present study, we evaluated 71 (25 males and 46 females) adult healthy patients treated with aligners (Invisalign®, Align Technologies, Santa Clara, CA, USA). The mean age was 32.8 ± 12.7 (age range 18–71). We did not differentiate data by gender or age since previous studies pointed out that sex and age of patients could not be considered as potential confounding factors [29, 30]. In this prospective study, patients were recruited from December 2014 to December 2015 among the private practice patients in xxx, xxx. The panoramic radiographs were taken at the beginning (T0) and at the end (T1) of orthodontic treatment with the same device. The average treatment duration was 14 months.

Inclusion criteria for all the patients were adult patients (>18yo), normodivergent, and class I malocclusion with crowding (arch length discrepancy <6 mm).

Exclusion criteria were evidence of root resorption on pre-treatment panoramic radiographs, severely dilacerated roots, endodontically treated teeth, patients requiring other orthodontic systems, extraction therapy or any surgical treatment, and patients presenting tooth wear with dentin exposure at the initial examination.

The anterior crowding was resolved by IPR (interproximal enamel reduction) and/or protrusion of anterior teeth, determined by the orthodontist, depending on the initial overjet (protrusion) or crown’s shape (IPR). The mean IPR was 0.33 mm (min. 0 mm, max. 0.5 mm).

All incisors and canines, upper first premolars, and first molars were assessed. A total of 1083 teeth were evaluated.

The measurement of the dental panoramic radiographs was performed by using Orisceph® (Orisceph Rx®, Elite Computer Italia, Vimodrone, MI, Italia).

On the basis of Krieger et al. [31], Fritz et al. [32], and Linge and Linge11, all root and crown measurements were assessed by one examiner blinded about the study, in a stochastic sequence. The crown length was represented by the distance between incisal edge and cemento-enamel junction (on the long axis). The root length was represented by the distance between cemento-enamel junction and apex (Fig. 1).
Fig. 1

Measurement of the panoramic radiographs: root and crown lengths (CEJ = cemento-enamel junction). Individual root-crown-ratio (RCR) was determined considering pre- and post-treatment root and crown length

As stated by Krieger et al. [31] and Fritz et al. [32], individual root-crown ratio (RCR) and therefore the relative changes of RCR (rRCR) were determined considering pre- and post-treatment root and crown length. An rRCR of 100% indicates no change of the pre-treatment root length relative to the post-treatment root length. A decrease of rRCR indicates a reduction of the root length during treatment.

Data analysis and collection were performed using the SPSS® software program (Statistical Package for Social Science) for Windows Version 23.0 (Inc., Chicago, II, USA).

The averages of the two measurements were used to calculate RCR and the changes in RCR. Absolute and relative frequencies of RCR were calculated for every tooth. Quantitative measurements are described by mean and standard deviation.

Results

The mean rRCR for every tooth is shown in Table 1.
Table 1

Number of measured elements, mean, and standard deviation of RCR for every tooth

 

1.6

1.4

1.3

1.2

1.1

2.1

2.2

2.3

2.4

2.6

No. of teeth

69

66

67

65

70

69

64

69

65

58

Mean rRCR (%)

100

103

104

104

102

103

100

104

102

101

Standard deviation

13.09

12.47

14.93

11.82

14.15

13.58

15.38

14.55

14.66

13.42

  

4.3

4.2

4.1

3.1

3.2

3.3

  

No. of teeth

  

71

71

70

70

68

71

  

Mean rRCR (%)

  

107

102

100

106

104

105

  

Standard deviation

  

13.78

16.5

13.28

13.48

12.27

13.48

  
All patients had a minimum of one teeth affected with a reduction of the root length (rRCR < 100%), on average 6.38 ± 2.28 teeth per patient (Fig. 2).
Fig. 2

Distribution of the amount of affected teeth per patient

Forty one percent (n = 29) of all patients had a minimum of one tooth with a 20% root length reduction.

In this study, 41.81% of the 1083 teeth (n = 453) showed a reduction of post-treatment root length (rRCR < 100%). A reduction up to 10% was found in 25.94% (n = 281), a distinct reduction from 10% up to 20% in 12.18% (n = 132) of the sample. 3.69% (n = 40) of the teeth were affected with a considerable reduction (>20%) (Table 2).
Table 2

Number and percentage of teeth presenting rRCR ≥ 100% (no RR), rRCR between 90 and 100 (slight RR), rRCR between 80 and 90 (moderate RR), rRCR ≤80 (severe RR)

rRCR (%)

No. of teeth

Percent

≥100

630

58.12

90 ≤ X < 100

281

25.94

80 ≤ X < 90

132

12.18

<80

40

3.69

TOT

1083

100

The values of the individual teeth are shown in Tables 3 and 4.
Table 3

Number and percentage of the upper teeth presenting rRCR = 100% (no RR), rRCR between 90 and 100 (slight RR), rRCR between 80 and 90 (moderate RR), and rRCR = 80 (severe RR)

RCR %

1.6

1.4

1.3

1.2

1.1

2.1

2.2

2.3

2.4

2.6

No. of teeth

36

39

41

46

39

39

31

41

36

27

≥100

52.17%

59.09%

61.19%

70.77%

55.71%

56.52%

48.44%

59.42%

55.38%

46.55%

No. of teeth

15

17

15

14

16

20

19

18

20

22

90 ≤ x < 100

21.74%

25.75%

22.39%

21.54%

28.86%

28.98%

29.69%

26.08%

30.77%

37.93%

No. of teeth

16

9

9

4

13

7

9

8

3

7

80 ≤ x < 90

23.19%

13.63%

13.43%

6.15%

18.57%

10.14%

14.06%

11.59%

4.61%

12.07%

No. of teeth

2

1

2

1

2

3

5

2

6

2

<80

2.9%

1.51%

2.98%

1.54%

2.86%

4.35%

7.81%

2.9%

9.23%

3.45%

TOT no. of teeth

69

66

67

65

70

69

64

69

65

58

%

100%

100%

100%

100%

100%

100%

100%

100%

100%

100%

Table 4

Number and percentage of the lower teeth presenting rRCR = 100% (no RR), rRCR between 90 and 100 (slight RR), rRCR between 80 and 90 (moderate RR), and rRCR = 80 (severe RR)

RCR %

4.3

4.2

4.1

3.1

3.2

3.3

No. of teeth

50

38

39

46

37

45

≥100

70.42%

53.52%

55.71%

65.71%

54.41%

63.38%

No. of teeth

15

17

12

17

25

19

90 ≤ x < 100

21.13%

23.94%

17.14%

24.28%

36.76%

26.76%

No. of teeth

6

10

13

7

5

6

80 ≤ x < 90

8.45%

14.08%

18.57%

10.00%

7.35%

8.45%

No. of teeth

0

6

6

0

1

1

<80

0.00%

8.45%

8.57%

0.00%

1.47%

1.41%

TOT no. of teeth

71

71

70

70

68

71

%

100%

100%

100%

100%

100%

100%

The percentage of teeth with rRCR < 100% are shown in the Fig. 3.
Fig. 3

Percentage of teeth affected by RR (rRCR < 100%)

A severe RR was observed only in 3.69% of teeth. As shown in Fig. 4, severe RR occurs mostly in the upper left premolars, upper left lateral incisors, lower right lateral, and central incisors.
Fig. 4

Percentage of teeth affected by severe RR (rRCR ≤ 80%)

Discussion

A previous review from Rossini et al. [33] demonstrated that Invisalign® is effective for simple malocclusions treatment. Starting from this consideration, the present study investigated the incidence of RR in a sample of adult patients with class I malocclusions, showing a very limited incidence of significant severe RR.

As shown in Table 3, 41.81% of the 1083 analyzed teeth (n = 453) were affected by post-treatment reduction of the root length. Even if in the present study we did not investigate the direct comparison of aligner treatment outcomes with fixed conventional appliances ones, data reported by other studies recently investigating RR both with aligners and multibracket appliances [29] seem to be consistent. Lund et al. [34] reported an incidence of 91%, but crowding was resolved by multibraket appliances and first premolars extraction, with a resultant more complex treatment. Iglesias-Linares et al. [30] recently demonstrated that treatments with increased discrepancy index, due to sagittal apical displacement increase, were more likely associated with a higher incidence in RR. However, there were no statistically significant differences whether removable aligners or fixed appliances were used, when genetic predisposition is excluded.

When considering RR severity in our study, the incidence of minimal RR (<10%) was 26%, mild RR (10–20%) was 12%, and severe RR (>20%) was only 3.69%. These values are consistent with those reported by Krieger et al. [31] with a minimal RR ranged from 25 to 32%, mild RR from 11 to 18%, and severe RR from 1 to 14% for mandibular incisors.

In other studies [2224, 32, 3541], maxillary incisors showed a consistent average apical RR, more than any other analyzed tooth, followed by mandibular incisors and mandibular first molars.

Tieu et al. [42] in their systematic review evaluated RR in maxillary and mandibular incisors during non-surgical orthodontic treatment of class II division I malocclusions; as a result, the majority of teeth experienced mild to moderate resorption following treatment, and the prevalence of incisor root resorption ranged between 65.6 and 98.1%.

According to several authors (Weltman [1] Eisel [43] Elhaddaoui [44]) RR, measured on panoramic or periapical radiographs, is usually less than 2.5 mm, with a <20% percentage of severe resorption (>4 mm or >1/3 original root length) affecting mostly maxillary lateral incisors.

In the present study, the prevalence of severe RR in maxillary incisors ranged from 1.54% (12) to 7.81% (22) and in mandibular incisors from 0 (31) to 8.57% (41). These results are significantly lower than those described by the previous authors.

The higher incidence of RR in maxillary and mandibular incisors may be explained with the greater extending of movement of these teeth than the rest of dentition, and the root structure of the incisors, its relationship to bone and the periodontal membrane, which transfers most of the forces to the apex [30].

Schwartz et al. [45] suggested that an orthodontic force heavier than the partial pressure of the periodontal capillaries (26 g/cm2) lead to periodontal ischemia and consequently to RR. In their prospective study, Barbagallo et al. [46] quantify premolar cementum resorption generated by treatment with ClearSmile® (ClearSmile, Woollongong, Australia) aligners using x-ray microtomography. Comparing the obtained values with those of a fixed appliance generating heavy or light orthodontic forces, the results showed that the aligner group had a similar RR to the light-force group and approximately six times greater than the untreated control group. These findings could be explained by the finite element analysis conducted by Cattaneo et al. in 2009 [47] on the PDL performance under light force loading: light continuous forces are perceived as intermittent by the periodontium because of the viscoelastic nature of PDL and the application of vertical forces during function and parafunction.

Orthodontic treatment with Invisalign® aligners could lead to RR as any other orthodontic treatment. The incidence of RR resulted consistent to the one described for orthodontic light forces (RR < 10% of original root length). Further studies on more complex malocclusions treated with aligners are guaranteed in order to analyze RR incidence with respect to comprehensive orthodontic treatments.

Conclusions

The present study investigated the incidence and severity of RR in adult patients treated with aligners during class I treatments. Every patient showed a minimum of one tooth with root length reduction. On average, 6.39 teeth per patient were affected. Overall, 41.81% of the measured 1083 teeth showed signs of apical root resorption, but only 3.69% a reduction of over 20% of the pre-treatment root length. Severe RR affected mostly the upper lateral incisors and lower lateral and central incisors.

Abbreviations

IPR: 

Interproximal enamel reduction

RCR: 

Root-crown ratio

RR: 

Root resorption

rRCR: 

Relative changes of RCR

Declarations

Authors’ contributions

GG has made substantial contributions in acquisition and interpretation of data and has been involved in drafting the manuscript and revising it critically for important intellectual content. SR has made substantial contributions in acquisition and interpretation of data and has been involved in drafting the manuscript and revising it critically for important intellectual content. TC has made substantial contributions to conception and design of the study and has been involved in drafting the manuscript and revising it critically for important intellectual content. FG has made substantial contributions to conception and design of the study and has been involved in drafting the manuscript and revising it critically for important intellectual content. GR has made substantial contributions in interpretation of data. SP has made substantial contributions in interpretation of data. GC carried out the statistical analysis and interpretation of data. AD has been involved in supervision during the draft of the manuscript, revising it critically for important intellectual content, and has given final approval of the version to be published. All authors read and approved the final manuscript.

Competing interests

Dr. Castroflorio and Dr. Garino have held lectures and conferences for Align Technology in the past 5 years. The presented study was conducted without any support (financial or technical) by Align Technology.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors’ Affiliations

(1)
Department of Surgical Sciences, University of Torino
(2)
Department of Statistics and Quantitative Methods, University of Milano-Bicocca

References

  1. Weltman B, Vig K, Fields H, Shanker S, Kaizar E. Root resorption associated with orthodontic tooth movement: a systematic review. Am J Orthod Dentofacial Orthop. 2010;137:462–76.View ArticlePubMedGoogle Scholar
  2. Al-Qawasmi RA, Hartsfield Jr JK, Everett ET, et al. Genetic predisposition to external apical root resorption. Am J Orthod Dentofacial Orthop. 2003;123:242–52.View ArticlePubMedGoogle Scholar
  3. Al-Nazhan S. External root resorption after bleaching: a case report. Oral Surg Oral Med Oral Pathol. 1991;72:607–9.View ArticlePubMedGoogle Scholar
  4. Counts AL, Widlak RA. Generalized idiopathic external root resorption. J Clin Orthod. 1993;27:511–3.PubMedGoogle Scholar
  5. Rivera EM, Walton RE. Extensive idiopathic apical root resorption. A case report. Oral Surg Oral Med Oral Pathol. 1994;78:673–7.View ArticlePubMedGoogle Scholar
  6. Snelgrove RA. Generalized idiopathic apical root resorption as an incidental finding in an adolescent: a case history. Dent Update. 1995;22:276–8.PubMedGoogle Scholar
  7. Killiany DM. Root resorption caused by orthodontic treatment: an evidence-based review of literature. Semin Orthod. 1999;5:128–33.View ArticlePubMedGoogle Scholar
  8. McLaughlin KD. Quantitative determination of root resorption during orthodontic treatment. Am J Orthod. 1964;50:143.View ArticleGoogle Scholar
  9. Stevnik A, Mjor IA. Pulp and dentine reactions to experimental tooth intrusion. A histological study of the initial changes. Am J Orthod. 1970;57:370–85.View ArticleGoogle Scholar
  10. Harry MR, Sims MR. Root resorption in bicuspid intrusion. A scanning electron microscope study. Angle Orthod. 1982;52:235–58.PubMedGoogle Scholar
  11. Linge BO, Linge L. Root length of upper canines and orthodontic therapy. Fortschr Kieferorthop. 1983;44:392–407.View ArticlePubMedGoogle Scholar
  12. Linge L, Linge BO. Patient characteristics and treatment variables associated with apical root resorption during orthodontic treatment. Am J Orthod. 1991;99:35–43.View ArticleGoogle Scholar
  13. Mirabella AD, Artun J. Risk factors for apical root resorption of maxillary anterior teeth in adult orthodontic patients. Am J Orthod. 1995;108:48–55.View ArticleGoogle Scholar
  14. Mavragani M, Boe OE, Wisth PJ, Selvig KA. Changes in root length during orthodontic treatment: advantages for immature teeth. Eur J Orthod. 2002;24:91–7.View ArticlePubMedGoogle Scholar
  15. Blake M, Woodside DG, Pharoah MJ. A radiographic comparison of apical root resorption after orthodontic treatment with the edgewise and speed appliances. Am J Orthod. 1995;108:76–84.View ArticleGoogle Scholar
  16. Lupi JE, Handelman CS, Sadowsky C. Prevalence and severity of apical root resorption and alveolar bone loss in orthodontically treated adults. Am J Orthod Dentofacial Orthop. 1996;109(1):28–37.View ArticlePubMedGoogle Scholar
  17. Levander E, Malmgren O. Evaluation of the risk of root resorption during orthodontic treatment: a study of upper incisors. Eur J Orthod. 1998;10:30–8.View ArticleGoogle Scholar
  18. Levander E, Malmgren O, Stenback K. Apical root resorption during orthodontic treatment of patients with multiple aplasia: a study of maxillary incisors. Eur J Orthod. 1998;20:427–34.View ArticlePubMedGoogle Scholar
  19. Trope M. Root resorption of dental traumatic origin: classification based on etiology. Pract Periodontics Aesthet Dent. 1998;10:515–22.PubMedGoogle Scholar
  20. Fuss Z, Tsesis I, Lin S. Root resorption-diagnosis, classification and treatment choices based on stimulation factors. Dent Traumatol. 2003;19:175–82.View ArticlePubMedGoogle Scholar
  21. Parker RJ, Harris EF. Directions of orthodontic tooth movements associated with external apical root resorption of the maxillary central incisor. Am J Orthod Dentofacial Orthop. 1998;114:677–83.View ArticlePubMedGoogle Scholar
  22. Fox N. Longer orthodontic treatment may result in greater external apical root resorption. Evid Based Dent. 2005;6:21.View ArticlePubMedGoogle Scholar
  23. Newman WG. Possible etiologic factors in external root resorption. Am J Orthod. 1975;67:522–39.View ArticlePubMedGoogle Scholar
  24. Kook YA, Park S, Sameshima GT. Peg-shaped and small lateral incisors not at higher risk for root resorption. Am J Orthod Dentofacial Orthop. 2003;123:253–8.View ArticlePubMedGoogle Scholar
  25. Kaley J, Phillips C. Factors related to root resorption in edgewise practice. Angle Orthod. 1991;61:125–32.PubMedGoogle Scholar
  26. Acar A, Canyurek U, Kocaaga M, Erverdi N. Continuous vs. discontinuous force application and root resorption. Angle Orthod. 1999;69:159–63. discussion 163–164.PubMedGoogle Scholar
  27. Reitan K. Effects of force magnitude and direction of tooth movement on different alveolar bone types. Angle Orthod. 1964;34:244–55.Google Scholar
  28. Dougherty HL. The effects of mechanical forces upon the mandibular buccal segments during orthodontic treatment. Part II. Am J Orthod. 1968;54:83–103.View ArticlePubMedGoogle Scholar
  29. Castro IO, Alencar AH, Valladares-Neto J, Estrela C. Apical root resorption due to orthodontic treatment detected by cone beam computed tomography. Angle Orthod. 2013;83:196–203.View ArticlePubMedGoogle Scholar
  30. Iglesias-Linares A, Sonnenberg B, Solano B, et al. Orthodontically induced external apical root resorption in patients treated with fixed appliances vs removable aligners. Angle Orthod. 2016;87(1):3–10.View ArticlePubMedGoogle Scholar
  31. Krieger E, Drechsler T, Schmidtmann I, Jacobs C, Haag S, Wehrbein H. Apical root resorption during orthodontic treatment with aligners? A retrospective radiometric study. Head Face Med. 2013;9:21.View ArticlePubMedPubMed CentralGoogle Scholar
  32. Fritz U, Diedrich P, Wiechmann D. Apical root resorption after lingual orthodontic therapy. J Orofac Orthop. 2003;64:434–42.View ArticlePubMedGoogle Scholar
  33. Rossini G, Parrini S, Castroflorio T, Deregibus A, Debernardi CL. Efficacy of clear aligners in controlling orthodontic tooth movement: a systematic review. Angle Orthod. 2015;85:881–9.View ArticlePubMedGoogle Scholar
  34. Lund H, Gröndahl K, Hansen K, Gröndahl HG. Apical root resorption during orthodontic treatment. A prospective study using cone beam CT. Angle Orthod. 2012;82:480–7.View ArticlePubMedGoogle Scholar
  35. Goldson L, Henrikson CO. Root resorption during Begg treatment: a longitudinal roentgenologic study. Am J Orthod. 1975;68:55–66.View ArticlePubMedGoogle Scholar
  36. Malmgren O, Goldson L, Hill C, Orwin A, Petrini L, Lundberg M. Root resorption after orthodontic treatment of traumatized teeth. Am J Orthod. 1982;82:487–91.View ArticlePubMedGoogle Scholar
  37. Kennedy DB, Joondeph DR, Osterberg SK, Little RM. The effect of extraction and orthodontic treatment on dentoalveolar support. Am J Orthod. 1983;84:183–90.Google Scholar
  38. Harris EF, Kineret SE, Tolley EA. A heritable component for external apical root resorption in patients treated orthodontically. Am J Orthod Dentofacial Orthop. 1997;111:301–9.View ArticlePubMedGoogle Scholar
  39. Janson GR, De Luca CG, Martins DR, Henriques JF, De Freitas MR. A radiographic comparison of apical root resorption after orthodontic treatment with 3 different fixed appliance techniques. Am J Orthod Dentofacial Orthop. 2000;118:262–73.View ArticlePubMedGoogle Scholar
  40. Sameshima GT, Sinclair PM. Predicting and preventing root resorption: part I. Diagnostic factors. Am J Orthod Dentofacial Orthop. 2001;119:505–10.View ArticlePubMedGoogle Scholar
  41. Brin I, Tulloch JF, Koroluk L, Philips C. External apical root resorption in Class II malocclusion: a retrospective review of 1-versus 2-phase treatment. Am J Orthod Dentofacial Orthop. 2003;124:151–6.View ArticlePubMedGoogle Scholar
  42. Tieu LD, Saltaji H, Normando D, Flores-Mir C. Radiologically determined orthodontically induced external apical root resorption in incisors after non-surgical orthodontic treatment of class II division 1 malocclusion: a systematic review. Prog Orthod. 2014;15:48.View ArticlePubMedPubMed CentralGoogle Scholar
  43. Eisel A, Katsaros C, Berg R. The course and results of the orthodontic treatment of 44 consecutively treated Class-II cases. Fortschr Kieferorthop. 1994;55:1–8.View ArticlePubMedGoogle Scholar
  44. Elhaddaoui R, Benyahia H, Azeroual MF, Zaoui F, Razine R, Bahije L. Resorption of maxillary incisors after orthodontic treatment—clinical study of risk factors. Int Orthod. 2016;14:48–64.PubMedGoogle Scholar
  45. Schwartz AM. Tissue changes incidental to tooth movement. Int J Orthod. 1932;18:331–52.Google Scholar
  46. 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.View ArticlePubMedGoogle Scholar
  47. Cattaneo PM, Dalstra M, Melsen B. Strains in periodontal ligament and alveolar bone associated with orthodontic tooth movement analyzed by finite element. Orthod Craniofac Res. 2009;12:120–8.View ArticlePubMedGoogle Scholar

Copyright

© The Author(s). 2017

Advertisement