- Email: [email protected]
Predicting and preventing root resorption: Part II. Treatment factors
ORIGINAL ARTICLE
Predicting and preventing root resorption: Part II. Treatment factors Glenn T. Sameshima, DDS, PhD,a and Peter M. Sinclair, DDS, MSDb Los Angeles, Calif The main objective of this study was to determine which treatment factors are most clearly identified with external apical root resorption that is detectable on periapical radiographs at the end of orthodontic treatment. The records of 868 patients who completed fixed, edgewise treatment from experienced clinicians in private practice were examined. The horizontal and vertical displacement of the root apex of the maxillary central incisor was measured on cephalometric radiographs. Patients who underwent first premolar extraction therapy had more resorption than those patients who had no extractions or had only maxillary first premolars removed. Duration of treatment and the horizontal (but not vertical) displacement of the incisor apices were significantly associated with root resorption. No differences were found for slot size, archwire type, use of elastics, and types of expansion. However, there was considerable variation among the 6 offices that were surveyed; 1 office averaged nearly a full millimeter more of resorption per anterior tooth than the office with the least amount of root resorption. We conclude that the clinician should exercise caution with those patients in whom extraction therapy is planned for overjet correction that requires above average treatment time. Finally, each clinician should be aware that the root resorption seen in one practice may be different from the root resorption found in another practice. (Am J Orthod Dentofacial Orthop 2001;119:511-5)
very clinical orthodontist has observed apical root resorption at the end of treatment and wanted to know what caused it. In most studies of root resorption, treatment factors top the list of “usual suspects.” When Wolff’s law of bone transformation (pressure causing resorption) was still considered a law, force magnitude and direction were thought to be the primary agents and although we now know this law was a gross oversimplification, mechanical factors continue to be investigated in great detail.1-9 Finite element models have been constructed to aid in our understanding of these force systems.10-12 From these models, it is evident that the greatest amount of force is applied at the root-alveolar crest junction rather than at the root apex. Thus, treatment factors that must be evaluated have come to include more clinical factors (such as type of appliance [slot size], use of rigid archwires, use of large rectangular archwires, extraction pattern, surgical procedures, expansion, use of functional appliances, dura-
E
tion of treatment, amount of torque applied, displacement distance of the apex, removable vs fixed).13-16 The first part of this study examined a host of diagnostic factors and found that the most resorbed teeth were the anterior teeth. Among these, the maxillary incisors were the most resorbed, with a mean resorption of 1.43 mm. Adult patients were found to have more resorption of lower anterior teeth, and teeth with an abnormal root shape also had greater root resorption. Asian patients were found to have less root resorption than white patients, who experienced less root resorption as a group than Hispanic patients. Very weak correlations were established for initial root length and overjet, but not overbite. This article will examine a number of treatment variables that are the most likely to be associated with root resorption, as culled from the literature, as well as previously unreported factors. In particular, this study will show that interoffice differences must be considered in any investigation of root resorption.
From the Department of Orthodontics, University of Southern California, Los Angeles, Calif. aAssistant Professor. bProfessor & Chair. Reprint requests to: Glenn T. Sameshima, DDS, PhD, Department of Orthodontics, DEN 312D School of Dentistry, University of Southern California, Los Angeles, CA 90089-0641; e-mail, [email protected]. Submitted, May 2000; revised and accepted, September 2000. Copyright © 2001 by the American Association of Orthodontists. 0889-5406/2001/$35.00 + 0 8/1/113410 doi:10.1067/mod.2001.113410
MATERIAL AND METHODS
Eight hundred sixty-eight patients with pre- and posttreatment periapical films that showed the root apices of all teeth from first molar to first molar in both arches were studied. All cases were treated with fixed edgewise appliances, and exclusionary and inclusionary criteria were set forth in the protocol. Six private practices supplied the necessary records. 511
512 Sameshima and Sinclair
American Journal of Orthodontics and Dentofacial Orthopedics May 2001
Table I. Root apex displacement: mean root resorption of
maxillary central incisors grouped by horizontal distance apex displaced (n = 637) Group
Apical displacement (mm)
Root resorption (mm)
0-1.5 1.5-3.0 3.0-4.5 >4.5
1.04 1.46* 1.67* 1.57*
Table II. Root apex displacement: mean root resorption of maxillary incisors grouped by extrusion or intrusion (n = 637) Root resorption (mm) Tooth
1 2 3 4
*Significantly different from group 1 (<1.5-mm retraction) by ANOVA (P < .05).
All films were scanned, and the images were displayed on a large computer monitor at approximately double magnification. Commercial software was used to measure the root apex, the midpoint of the cementoenamel junction, and the midpoint of the incisal edge or cusp tip. Pre- and posttreatment films were compared side-by-side to minimize identification error. (For further details on methods, see Part I.) Pre- and posttreatment lateral headfilms were used to determine the vertical and horizontal displacement of the maxillary incisors. Tracings of maxillary structures (hard palate, key ridge, and pterygomaxillary fissure) and the maxillary incisor were made on matte acetate tracing media from the pretreatment cephalogram. A best-fit regional superimposition was performed on the basis of these structures on the posttreatment film. 17 The maxillary incisor was then traced in its final position. The tracings were digitized and analyzed with custom software written by the author specifically for this purpose. The algorithms were based largely on methods previously established by other investigators.18 Displacement of the apex in horizontal and vertical directions was computed. The pretreatment average length of the maxillary central incisors from the periapical films was used in the computations. Method error was computed by retracing pairs (preand posttreatment) of cephalometric films 2 weeks after initial scanning and tracing on 20 randomly chosen cases. Dahlberg’s tests for replicates were found to be well within the accepted ranges for these types of data. Preliminary data analysis consisted of visual inspection of data with graphs and exploratory statistics. Data were summarized with descriptive statistics. Univariate analyses were calculated for categoric and continuous variables after assumptions were tested with graphs (generally scatter plots) and subtests. Significance was established at alpha = 0.05. Data that failed normality and equal variance tests were either transformed or subject to nonparametric equiva-
Right lateral incisor Right central incisor Left central incisor Left lateral incisor
Extrusion 1.65 1.37 1.32 1.56
Intrusion 1.57 1.31 1.23 1.46
P value NS NS NS NS
lents (eg, Kruskal-Wallis for analysis of variance [ANOVA]). All tests of individual group means for ANOVA were post-hoc (unplanned). Student-NeumanKeuls or Tukey’s HSD were generally used, unless the data conformed to more stringent requirements for cell count equality and group balance. RESULTS
In an analysis of horizontal root displacement, mean root resorption for the paired maxillary central incisors only was used to stratify the data into 4 categories (Tables I and II). Horizontal displacement greater than 1.5 mm resulted in significantly greater root resorption by 0.5 mm or more. The greatest amount of resorption (1.67 mm) was found in incisors displaced between 3.0 and 4.5 mm horizontally. Vertically, the data were partitioned into extrusion and intrusion groups for each maxillary incisor. There were no significant differences found between the 2 groups. Patients were categorized according to the treatment variable extraction (Table III). Four classifications were used: none (no extractions), 4 first premolars, maxillary first premolars only, and other extractions (such as 4 second premolars, a lower incisor extraction). First premolar extraction cases had significantly more resorption (1.43 mm vs 1.09 mm) than nonextraction cases for maxillary central incisors. There were no significant differences among the classifications for the maxillary lateral incisor, although first premolar extraction cases had the greatest amount of root resorption (1.58 mm). For maxillary canines, mandibular incisors, and mandibular canines, the first premolar and other extraction cases had greater resorption than the nonextraction and upper premolar cases. Comparisons were made among the 6 participating offices (Table IV). For baseline demographic information, no statistical comparisons were computed; however, the variation among the offices is notable. For example, extraction percentage ranged from a high of
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Table III. Root
resorption by extraction pattern Maxillary (mm)
Nonextraction (n = 424) Four first premolars (n = 290) Maxillary first premolars (n = 122) Other (eg, second premolars [n = 31])
Mandibular (mm)
Central
Lateral
Canine
Central
Lateral
Canine
1.09 ± 1.21 1.43 ± 1.38† 0.88 ± 0.89 1.31 ± 1.09
1.37 ± 1.29 1.58 ± 1.37 1.23 ± 1.03 1.56 ± 1.39
0.67 ± 1.21* 1.57 ± 1.43 1.06 ± 0.99 1.55 ± 1.45
0.45 ± 0.82* 0.84 ± 0.84 0.58 ± 1.07 1.01 ± 0.90
0.48 ± 1.01* 1.05 ± 1.24 0.65 ± 0.91 1.27 ± 1.15
0.45 ± 1.11* 1.41 ± 1.49 0.34 ± 1.04 1.17 ± 1.36
*Nonextraction †First
group significantly less root resorption than the 4 first premolar and “other” groups (both P < .001). premolar group significantly greater root resorption than nonextraction group (P < .01) and maxillary first premolar group.
Table IV. Baseline
characteristics of the 6 offices Ethnicity (%)
Office 1 2 3 4 5 6
n 154 123 183 138 106 164
Start age (y) 13.1 ± 6.2 17.6 ± 8.7 14.2 ± 5.9 17.8 ± 8.1 12.7 ± 5.8 13.8 ± 1.9
Duration (mo)
Percent extraction (%)
Asian
White
Hispanic
32.9 ± 9.4 26.2 ± 6.4 42.4 ± 13.1 25.5 ± 6.7 36.4 ± 3.2 25.0 ± 5.9
23 55 32 78 55 70
5 3 2 95 36 5
87 93 93 1 46 35
8 3 4 4 17 54
78% to a low of 23%. Ethnicity was also highly variable among offices: Four offices saw predominantly white patients; 1 office had 95% Asian patients, and another office saw a majority of Hispanic patients. Differences in root resorption among offices was striking (Table V). Office 6 had the most root resorption overall, followed closely by office 2. The greatest amount, recorded in office 6, was for a maxillary lateral incisor (1.91 mm). The least amount of resorption was found for office 4 in the maxilla and office 5 in the mandible. The maxillary lateral incisor was the most resorbed tooth for all 6 offices. Statistically, office 2 had significantly greater root resorption than the other groups (except office 6) for all anterior teeth except the maxillary canine. Office 6 also had significantly more resorption than all groups (except office 2) for all teeth except the mandibular canine. The disparity between the offices with the greatest and least amounts of root resorption was nearly 1 mm. There was a significant correlation (P < .05) between the duration of treatment and the amount of apical root resorption for maxillary central incisors. There were no significant differences for transverse treatments (rapid palatal expansion/slow expansion/none). There were also no differences for the variables of Class II elastics, finishing elastics, slot size (0.018 mm vs 0.022 mm) and predominant wire use (steel vs nickel-titanium) for all 6 pairs of anterior teeth.
DISCUSSION
Treatment variables clearly play an important role in the occurrence of external apical root resorption as the result of orthodontic tooth movement. This article once again illustrates the importance of the examination of dentition by location. The response of maxillary and mandibular teeth to these parameters was notably different. Displacement of the root apex was found to be significant, but only in the horizontal direction. Our results are generally in agreement with previous reports, although some reports have determined displacement in other terms, such as torquing.15,19-24 The significance of this finding, together with the positive correlation found with overjet, strongly suggests that there is some component of the root apex that has a lower threshold for irreversible change than other parts of the root. The same mechanism that is involved in irreversible shortening of the apex in abnormally shaped apices is probably involved in the vulnerability of the apex to distal retraction. Extraction pattern was also found to be a significant factor in root resorption. Patients who underwent 4 first premolar extraction therapy had greater resorption than those patients who were treated with nonextraction. Patients with the classification of other type of extractions (ie, 4 second premolars, 2 maxillary premolars, a mandibular incisor, asymmetric extractions) also demon-
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American Journal of Orthodontics and Dentofacial Orthopedics May 2001
Table V. Interoffice
variation: mean root resorption for 6 anterior teeth by office Office Resorption Maxilla (mm) Central Lateral Canine Mandible (mm) Central Lateral Canine *Significantly †Significantly
1
2
3
4
5
6
1.42 1.63 1.03
1.45* 1.78* 1.07
1.14 1.28 0.99
0.73† 0.91† 0.95
1.04 1.14 0.90
1.60* 1.91* 1.77*
0.50 0.55 0.69
0.92* 1.12* 1.23*
0.55 0.55 0.80
0.55 0.68 0.85
0.45 0.56 0.39
0.99* 1.19* 1.01
higher. lower.
strated increased resorption. Interestingly, patients with only upper premolar extractions did not have more resorption than the nonextraction cases, which seems to contradict our other findings that overjet and horizontal distance of apical displacement were significant. The few other studies that examined this factor did not find it to be significant.19,22,25 Longer treatment time was found to be significantly associated with increased root resorption for maxillary central incisors. Harris and Baker26 suggest that there is a threshold time at which the dynamic process is overwhelmed and significant resorption takes place. Previous studies generally support the significance of extended treatment time,15,19,26-30 although a few studies have not.19,26 One study of 31 variables found that duration of treatment was the factor most highly correlated with root resorption in maxillary incisors.20 The reason for extended treatment may itself shed some light on this association. Perhaps a heroic nonsurgical treatment plan was carried out; perhaps an uncooperative patient was allowed to continue treatment, or perhaps a clinician spent a much longer period on finishing and fine detailing. These are a few of the reasons that treatment times may extend the treatment beyond the norm. The mechanical treatment variables in our study were not significantly associated with apical resorption. Slot size and archwire type were not found to be important. Use of elastics was also not associated with increased resorption. This last variable is very hard to measure; the cynic would argue that so few patients wear Class II and finishing elastics properly that it is not surprising no effect was found (although other studies have found a moderate correlation).7,20 Perhaps of greatest interest in this study was our finding of significant interoffice variation. This goes a long way in explaining the reason that so many different studies over the years have found such different
results. It is possible that experienced clinicians achieve a comfort level with the amount of resorption they see in their patients. It is also equally possible that they alter their treatment plans either at the beginning of treatment or along the way. This is particularly logical in cases in which previous trauma has been reported or is visible on clinical inspection. The amount of root resorption among the 4 offices was significantly different, with 2 offices showing much higher amounts than the other 4 offices. It would be informative to see whether factors found to be significantly associated with resorption could explain interoffice differences. There were no differences among the offices in the amount of apical displacement. There were insufficient numbers of patients in different ethnic groups within individual practices for us to make a valid analysis. We did, however, look specifically within 1 office that had a reasonable sampling of 3 ethnic groups. There was no significant difference within this office for ethnicity in a comparison of the means for all 6 anterior teeth. It must be emphasized that, although this article and others have found clinical factors that are highly associated with root resorption, causation has not been proved. Severe resorption is rare, so it is difficult to design an appropriate, testable hypothesis. We agree with current clinical recommendations to use caution in moving abnormally shaped teeth a long distance for a long time, especially if severe resorption happens often in your practice. We also highly recommend taking progress periapicals a few months after active tooth movement for patients at risk. If root resorption is found, the literature supports an inactive phase of 4 to 6 months before the resumption of treatment. In extreme cases, treatment must be halted; appliances must be removed, and a surgical or prosthetic treatment plan must be adopted. The orthodontist should always review the final periapicals before sending the patient back to the general dentist for a regular dental visit. Appropriate counseling and follow-up are necessary should severe resorption be encountered. Root resorption rarely results in significant morbidity after orthodontic therapy, and the resorptive process ceases with the removal of active forces.32-34 In essence, the case is handled no differently (by the periodontist or general dentist) from one in which vertical bone loss has compromised the crown-root ratio.35 CONCLUSIONS
The findings of these 2 articles (Parts I and II) clearly show that root resorption is a multifactorial phenomenon. Caution should be exercised in patients in whom the clinician plans to displace the maxillary incisors distally, in patients with abnormally shaped
American Journal of Orthodontics and Dentofacial Orthopedics Volume 119, Number 5
roots, in extraction cases, in patients who have been in treatment for a longer than usual period of time, and in adult patients. In this study, Asian patients had less root resorption than white or Hispanic patients. Finally, interoffice variation is a significant factor; the clinician who treats a high number of patients who experience severe root resorption would be well advised to collect good data on these patients and compare them with the offices in this study. We thank Drs Young-Ho Kim, Young-Kyu Lim, William Redmond, Mark Wong, Warren Schacter, Gordon Kilmer, and Young-Jin Kim for their contributions to this project and John Morrison for statistical advice. REFERENCES 1. Alexander SA. Levels of root resorption associated with continuous arch and sectional arch mechanics. Am J Orthod Dentofacial Orthop 1996;110:321-4. 2. Beck BW, Harris EF. Apical root resorption in orthodontically treated subjects: analysis of edgewise and light wire mechanics. Am J Orthod Dentofacial Orthop 1994;105:350-61. 3. 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 Dentofacial Orthop 1995;108:76-84. 4. Goldin B. Labial root torque: effect on the maxilla and incisor root apex. Am J Orthod Dentofacial Orthop 1989;95:208-19. 5. Goldson L, Henrikson CO. Root resorption during Begg treatment: a longitudinal roentgenographic study. Am J Orthod 1975;68:55-66. 6. Kurol J, Owman-Moll P, Lundgren D. Time-related root resorption after application of a controlled continuous orthodontic force. Am J Orthod Dentofacial Orthop 1996;110:303-10. 7. Linge L, Linge BO. Patient characteristics and treatment variables associated with apical root resorption during orthodontic treatment. Am J Orthod Dentofacial Orthop 1991;99:35-43. 8. Owman-Moll P, Kurol J, Lundgren D. The effects of a four-fold increased orthodontic force magnitude on tooth movement and root resorptions: in intra-individual study in adolescents. Eur J Orthod 1996;3:287-94. 9. Owman-Moll P, Kurol J, Lundgren D. Continuous versus interrupted orthodontic force related to early tooth movement and root resorption. Angle Orthod 1995;65:395-402. 10. McGuinness N, Wilson AN, Jones M, Middleton J, Robertson NR. Stresses induced by edgewise appliances in the periodontal ligament: a finite element study. Angle Orthod 1992;62:15-22. 11. McGuinness N, Wilson AN, Jones M, Middleton J, Robertson NR. A stress analysis of the periodontal ligament under various orthodontic lodgings. Eur J Orthod 1991;13:231-42. 12. Jeon PD, Turley PK, Moon HB, Ting K. Analysis of stress in the periodontium of the maxillary first molar with a three-dimensional finite element model. Am J Orthod Dentofacial Orthop 1999;115:267-74. 13. Brezniak N, Wasserstein A. Root resorption after orthodontic treatment: Part 1. Literature review. Am J Orthod 1993; 103:62-6.
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14. Brezniak N, Wasserstein A. Root resorption after orthodontic treatment: Part 2. Literature review. Am J Orthod 1993;103:138-46. 15. Vlaskalic V, Boyd RL, Baumrind S. Etiology and sequelae of root resorption. Semin Orthod 1998;4:124-31. 16. Killiany D. Root resorption caused by orthodontic treatment: an evidence-based review of literature. Semin Orthod 1999;5:128-33. 17. Bjork A, Skeiller V. Growth of the maxilla in three dimensions as revealed radiographically by the implant method. Br J Orthod 1977;4:53-65. 18. Mirabella AD, Artun J. Prevalence and severity of root resorption in adults during orthodontic treatment with multibonded appliances. Eur J Orthod 1995;17:93-9. 19. Baumrind S, Korn EL, Boyd RL. Apical root resorption in orthodontically treated adults. Am J Orthod Dentofacial Orthop 1996;110:311-323. 20. Taithongchai R, Sookkorn K, Killiany DM. Facial and dentoalveolar structure and the prediction of apical root shortening. Am J Orthod Dentofacial Orthop 1996;110:296-302. 21. Dermaut LR, De Munk A. Apical root resorption of upper incisors caused by intrusive tooth movement: a radiographic study. Am J Orthod Dentofacial Orthop 1986;90:321-6. 22. Kaley J, Phillips C. Factors related to root resorption in edgewise practice. Angle Orthod 1991;61:125-32. 23. 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. 24. Mirabella AD, Artun J. Risk factors for apical root resorption of maxillary anterior teeth in adult orthodontic patients. Am J Orthod Dentofacial Orthop 1995;108:48-55. 25. McFadden WM, Engstrom C, Engstrom H, Anholm JM. A study of the relationship between incisor intrusion and root shortening. Am J Orthod Dentofacial Orthop 1989;96:390-6. 26. Harris EF, Baker WC. Loss of root length and crestal bone height before and during treatment in adolescent and adult orthodontic patients. Am J Orthod Dentofacial Orthop 1990;98:463-9. 27. Levander E, Malmgren O. Evaluation of the risk of root resorption during orthodontic treatment: a study of the upper incisors. Eur J Orthod 1988;10:30-8. 28. Odenrick L. Nailbiting: frequency and association with root resorption. Br J Orthod 1985;12:78-81. 29. Sharpe W, Reed B, Subtelny JD, Poison A. Orthodontic relapse, apical root resorption, and crestal alveolar bone levels. Am J Orthod Dentofacial Orthop 1987;91:252-7. 30. Hendrix I, Carels C, Kuijgers-Jagtman AM, Van T Hof M. A radiographic study of posterior apical root resorption in orthodontic patients. Am J Orthod Dentofacial Orthop 1994;105:345-9. 31. Linge BO, Linge L. Apical root resorption in upper anterior teeth. Eur J Orthod 1983;5:173-83. 32. Copeland S, Green LJ. Root resorption in maxillary central incisors following active orthodontic treatment. Am J Orthod Dentofacial Orthop 1986;89:51-5. 33. Remington DN, Joondeph DR, Artun J, Riedel RA, Chapko MK. Long-term evaluation of root resorption occurring during orthodontic treatment. Am J Orthod Dentofacial Orthop 1989;96:43-6. 34. Parker WS. Root resorption: long-term outcome. Am J Orthod Dentofacial Orthop 1997;112:119-23. 35. Levander E, Malmgren O. Long-term follow-up of maxillary incisors with severe apical root resorption. Eur J Orthod 2000; 22:85-92.
Predicting and preventing root resorption: Part II. Treatment factors Glenn T. Sameshima, DDS, PhD,a and Peter M. Sinclair, DDS, MSDb Los Angeles, Calif The main objective of this study was to determine which treatment factors are most clearly identified with external apical root resorption that is detectable on periapical radiographs at the end of orthodontic treatment. The records of 868 patients who completed fixed, edgewise treatment from experienced clinicians in private practice were examined. The horizontal and vertical displacement of the root apex of the maxillary central incisor was measured on cephalometric radiographs. Patients who underwent first premolar extraction therapy had more resorption than those patients who had no extractions or had only maxillary first premolars removed. Duration of treatment and the horizontal (but not vertical) displacement of the incisor apices were significantly associated with root resorption. No differences were found for slot size, archwire type, use of elastics, and types of expansion. However, there was considerable variation among the 6 offices that were surveyed; 1 office averaged nearly a full millimeter more of resorption per anterior tooth than the office with the least amount of root resorption. We conclude that the clinician should exercise caution with those patients in whom extraction therapy is planned for overjet correction that requires above average treatment time. Finally, each clinician should be aware that the root resorption seen in one practice may be different from the root resorption found in another practice. (Am J Orthod Dentofacial Orthop 2001;119:511-5)
very clinical orthodontist has observed apical root resorption at the end of treatment and wanted to know what caused it. In most studies of root resorption, treatment factors top the list of “usual suspects.” When Wolff’s law of bone transformation (pressure causing resorption) was still considered a law, force magnitude and direction were thought to be the primary agents and although we now know this law was a gross oversimplification, mechanical factors continue to be investigated in great detail.1-9 Finite element models have been constructed to aid in our understanding of these force systems.10-12 From these models, it is evident that the greatest amount of force is applied at the root-alveolar crest junction rather than at the root apex. Thus, treatment factors that must be evaluated have come to include more clinical factors (such as type of appliance [slot size], use of rigid archwires, use of large rectangular archwires, extraction pattern, surgical procedures, expansion, use of functional appliances, dura-
E
tion of treatment, amount of torque applied, displacement distance of the apex, removable vs fixed).13-16 The first part of this study examined a host of diagnostic factors and found that the most resorbed teeth were the anterior teeth. Among these, the maxillary incisors were the most resorbed, with a mean resorption of 1.43 mm. Adult patients were found to have more resorption of lower anterior teeth, and teeth with an abnormal root shape also had greater root resorption. Asian patients were found to have less root resorption than white patients, who experienced less root resorption as a group than Hispanic patients. Very weak correlations were established for initial root length and overjet, but not overbite. This article will examine a number of treatment variables that are the most likely to be associated with root resorption, as culled from the literature, as well as previously unreported factors. In particular, this study will show that interoffice differences must be considered in any investigation of root resorption.
From the Department of Orthodontics, University of Southern California, Los Angeles, Calif. aAssistant Professor. bProfessor & Chair. Reprint requests to: Glenn T. Sameshima, DDS, PhD, Department of Orthodontics, DEN 312D School of Dentistry, University of Southern California, Los Angeles, CA 90089-0641; e-mail, [email protected]. Submitted, May 2000; revised and accepted, September 2000. Copyright © 2001 by the American Association of Orthodontists. 0889-5406/2001/$35.00 + 0 8/1/113410 doi:10.1067/mod.2001.113410
MATERIAL AND METHODS
Eight hundred sixty-eight patients with pre- and posttreatment periapical films that showed the root apices of all teeth from first molar to first molar in both arches were studied. All cases were treated with fixed edgewise appliances, and exclusionary and inclusionary criteria were set forth in the protocol. Six private practices supplied the necessary records. 511
512 Sameshima and Sinclair
American Journal of Orthodontics and Dentofacial Orthopedics May 2001
Table I. Root apex displacement: mean root resorption of
maxillary central incisors grouped by horizontal distance apex displaced (n = 637) Group
Apical displacement (mm)
Root resorption (mm)
0-1.5 1.5-3.0 3.0-4.5 >4.5
1.04 1.46* 1.67* 1.57*
Table II. Root apex displacement: mean root resorption of maxillary incisors grouped by extrusion or intrusion (n = 637) Root resorption (mm) Tooth
1 2 3 4
*Significantly different from group 1 (<1.5-mm retraction) by ANOVA (P < .05).
All films were scanned, and the images were displayed on a large computer monitor at approximately double magnification. Commercial software was used to measure the root apex, the midpoint of the cementoenamel junction, and the midpoint of the incisal edge or cusp tip. Pre- and posttreatment films were compared side-by-side to minimize identification error. (For further details on methods, see Part I.) Pre- and posttreatment lateral headfilms were used to determine the vertical and horizontal displacement of the maxillary incisors. Tracings of maxillary structures (hard palate, key ridge, and pterygomaxillary fissure) and the maxillary incisor were made on matte acetate tracing media from the pretreatment cephalogram. A best-fit regional superimposition was performed on the basis of these structures on the posttreatment film. 17 The maxillary incisor was then traced in its final position. The tracings were digitized and analyzed with custom software written by the author specifically for this purpose. The algorithms were based largely on methods previously established by other investigators.18 Displacement of the apex in horizontal and vertical directions was computed. The pretreatment average length of the maxillary central incisors from the periapical films was used in the computations. Method error was computed by retracing pairs (preand posttreatment) of cephalometric films 2 weeks after initial scanning and tracing on 20 randomly chosen cases. Dahlberg’s tests for replicates were found to be well within the accepted ranges for these types of data. Preliminary data analysis consisted of visual inspection of data with graphs and exploratory statistics. Data were summarized with descriptive statistics. Univariate analyses were calculated for categoric and continuous variables after assumptions were tested with graphs (generally scatter plots) and subtests. Significance was established at alpha = 0.05. Data that failed normality and equal variance tests were either transformed or subject to nonparametric equiva-
Right lateral incisor Right central incisor Left central incisor Left lateral incisor
Extrusion 1.65 1.37 1.32 1.56
Intrusion 1.57 1.31 1.23 1.46
P value NS NS NS NS
lents (eg, Kruskal-Wallis for analysis of variance [ANOVA]). All tests of individual group means for ANOVA were post-hoc (unplanned). Student-NeumanKeuls or Tukey’s HSD were generally used, unless the data conformed to more stringent requirements for cell count equality and group balance. RESULTS
In an analysis of horizontal root displacement, mean root resorption for the paired maxillary central incisors only was used to stratify the data into 4 categories (Tables I and II). Horizontal displacement greater than 1.5 mm resulted in significantly greater root resorption by 0.5 mm or more. The greatest amount of resorption (1.67 mm) was found in incisors displaced between 3.0 and 4.5 mm horizontally. Vertically, the data were partitioned into extrusion and intrusion groups for each maxillary incisor. There were no significant differences found between the 2 groups. Patients were categorized according to the treatment variable extraction (Table III). Four classifications were used: none (no extractions), 4 first premolars, maxillary first premolars only, and other extractions (such as 4 second premolars, a lower incisor extraction). First premolar extraction cases had significantly more resorption (1.43 mm vs 1.09 mm) than nonextraction cases for maxillary central incisors. There were no significant differences among the classifications for the maxillary lateral incisor, although first premolar extraction cases had the greatest amount of root resorption (1.58 mm). For maxillary canines, mandibular incisors, and mandibular canines, the first premolar and other extraction cases had greater resorption than the nonextraction and upper premolar cases. Comparisons were made among the 6 participating offices (Table IV). For baseline demographic information, no statistical comparisons were computed; however, the variation among the offices is notable. For example, extraction percentage ranged from a high of
Sameshima and Sinclair 513
American Journal of Orthodontics and Dentofacial Orthopedics Volume 119, Number 5
Table III. Root
resorption by extraction pattern Maxillary (mm)
Nonextraction (n = 424) Four first premolars (n = 290) Maxillary first premolars (n = 122) Other (eg, second premolars [n = 31])
Mandibular (mm)
Central
Lateral
Canine
Central
Lateral
Canine
1.09 ± 1.21 1.43 ± 1.38† 0.88 ± 0.89 1.31 ± 1.09
1.37 ± 1.29 1.58 ± 1.37 1.23 ± 1.03 1.56 ± 1.39
0.67 ± 1.21* 1.57 ± 1.43 1.06 ± 0.99 1.55 ± 1.45
0.45 ± 0.82* 0.84 ± 0.84 0.58 ± 1.07 1.01 ± 0.90
0.48 ± 1.01* 1.05 ± 1.24 0.65 ± 0.91 1.27 ± 1.15
0.45 ± 1.11* 1.41 ± 1.49 0.34 ± 1.04 1.17 ± 1.36
*Nonextraction †First
group significantly less root resorption than the 4 first premolar and “other” groups (both P < .001). premolar group significantly greater root resorption than nonextraction group (P < .01) and maxillary first premolar group.
Table IV. Baseline
characteristics of the 6 offices Ethnicity (%)
Office 1 2 3 4 5 6
n 154 123 183 138 106 164
Start age (y) 13.1 ± 6.2 17.6 ± 8.7 14.2 ± 5.9 17.8 ± 8.1 12.7 ± 5.8 13.8 ± 1.9
Duration (mo)
Percent extraction (%)
Asian
White
Hispanic
32.9 ± 9.4 26.2 ± 6.4 42.4 ± 13.1 25.5 ± 6.7 36.4 ± 3.2 25.0 ± 5.9
23 55 32 78 55 70
5 3 2 95 36 5
87 93 93 1 46 35
8 3 4 4 17 54
78% to a low of 23%. Ethnicity was also highly variable among offices: Four offices saw predominantly white patients; 1 office had 95% Asian patients, and another office saw a majority of Hispanic patients. Differences in root resorption among offices was striking (Table V). Office 6 had the most root resorption overall, followed closely by office 2. The greatest amount, recorded in office 6, was for a maxillary lateral incisor (1.91 mm). The least amount of resorption was found for office 4 in the maxilla and office 5 in the mandible. The maxillary lateral incisor was the most resorbed tooth for all 6 offices. Statistically, office 2 had significantly greater root resorption than the other groups (except office 6) for all anterior teeth except the maxillary canine. Office 6 also had significantly more resorption than all groups (except office 2) for all teeth except the mandibular canine. The disparity between the offices with the greatest and least amounts of root resorption was nearly 1 mm. There was a significant correlation (P < .05) between the duration of treatment and the amount of apical root resorption for maxillary central incisors. There were no significant differences for transverse treatments (rapid palatal expansion/slow expansion/none). There were also no differences for the variables of Class II elastics, finishing elastics, slot size (0.018 mm vs 0.022 mm) and predominant wire use (steel vs nickel-titanium) for all 6 pairs of anterior teeth.
DISCUSSION
Treatment variables clearly play an important role in the occurrence of external apical root resorption as the result of orthodontic tooth movement. This article once again illustrates the importance of the examination of dentition by location. The response of maxillary and mandibular teeth to these parameters was notably different. Displacement of the root apex was found to be significant, but only in the horizontal direction. Our results are generally in agreement with previous reports, although some reports have determined displacement in other terms, such as torquing.15,19-24 The significance of this finding, together with the positive correlation found with overjet, strongly suggests that there is some component of the root apex that has a lower threshold for irreversible change than other parts of the root. The same mechanism that is involved in irreversible shortening of the apex in abnormally shaped apices is probably involved in the vulnerability of the apex to distal retraction. Extraction pattern was also found to be a significant factor in root resorption. Patients who underwent 4 first premolar extraction therapy had greater resorption than those patients who were treated with nonextraction. Patients with the classification of other type of extractions (ie, 4 second premolars, 2 maxillary premolars, a mandibular incisor, asymmetric extractions) also demon-
514 Sameshima and Sinclair
American Journal of Orthodontics and Dentofacial Orthopedics May 2001
Table V. Interoffice
variation: mean root resorption for 6 anterior teeth by office Office Resorption Maxilla (mm) Central Lateral Canine Mandible (mm) Central Lateral Canine *Significantly †Significantly
1
2
3
4
5
6
1.42 1.63 1.03
1.45* 1.78* 1.07
1.14 1.28 0.99
0.73† 0.91† 0.95
1.04 1.14 0.90
1.60* 1.91* 1.77*
0.50 0.55 0.69
0.92* 1.12* 1.23*
0.55 0.55 0.80
0.55 0.68 0.85
0.45 0.56 0.39
0.99* 1.19* 1.01
higher. lower.
strated increased resorption. Interestingly, patients with only upper premolar extractions did not have more resorption than the nonextraction cases, which seems to contradict our other findings that overjet and horizontal distance of apical displacement were significant. The few other studies that examined this factor did not find it to be significant.19,22,25 Longer treatment time was found to be significantly associated with increased root resorption for maxillary central incisors. Harris and Baker26 suggest that there is a threshold time at which the dynamic process is overwhelmed and significant resorption takes place. Previous studies generally support the significance of extended treatment time,15,19,26-30 although a few studies have not.19,26 One study of 31 variables found that duration of treatment was the factor most highly correlated with root resorption in maxillary incisors.20 The reason for extended treatment may itself shed some light on this association. Perhaps a heroic nonsurgical treatment plan was carried out; perhaps an uncooperative patient was allowed to continue treatment, or perhaps a clinician spent a much longer period on finishing and fine detailing. These are a few of the reasons that treatment times may extend the treatment beyond the norm. The mechanical treatment variables in our study were not significantly associated with apical resorption. Slot size and archwire type were not found to be important. Use of elastics was also not associated with increased resorption. This last variable is very hard to measure; the cynic would argue that so few patients wear Class II and finishing elastics properly that it is not surprising no effect was found (although other studies have found a moderate correlation).7,20 Perhaps of greatest interest in this study was our finding of significant interoffice variation. This goes a long way in explaining the reason that so many different studies over the years have found such different
results. It is possible that experienced clinicians achieve a comfort level with the amount of resorption they see in their patients. It is also equally possible that they alter their treatment plans either at the beginning of treatment or along the way. This is particularly logical in cases in which previous trauma has been reported or is visible on clinical inspection. The amount of root resorption among the 4 offices was significantly different, with 2 offices showing much higher amounts than the other 4 offices. It would be informative to see whether factors found to be significantly associated with resorption could explain interoffice differences. There were no differences among the offices in the amount of apical displacement. There were insufficient numbers of patients in different ethnic groups within individual practices for us to make a valid analysis. We did, however, look specifically within 1 office that had a reasonable sampling of 3 ethnic groups. There was no significant difference within this office for ethnicity in a comparison of the means for all 6 anterior teeth. It must be emphasized that, although this article and others have found clinical factors that are highly associated with root resorption, causation has not been proved. Severe resorption is rare, so it is difficult to design an appropriate, testable hypothesis. We agree with current clinical recommendations to use caution in moving abnormally shaped teeth a long distance for a long time, especially if severe resorption happens often in your practice. We also highly recommend taking progress periapicals a few months after active tooth movement for patients at risk. If root resorption is found, the literature supports an inactive phase of 4 to 6 months before the resumption of treatment. In extreme cases, treatment must be halted; appliances must be removed, and a surgical or prosthetic treatment plan must be adopted. The orthodontist should always review the final periapicals before sending the patient back to the general dentist for a regular dental visit. Appropriate counseling and follow-up are necessary should severe resorption be encountered. Root resorption rarely results in significant morbidity after orthodontic therapy, and the resorptive process ceases with the removal of active forces.32-34 In essence, the case is handled no differently (by the periodontist or general dentist) from one in which vertical bone loss has compromised the crown-root ratio.35 CONCLUSIONS
The findings of these 2 articles (Parts I and II) clearly show that root resorption is a multifactorial phenomenon. Caution should be exercised in patients in whom the clinician plans to displace the maxillary incisors distally, in patients with abnormally shaped
American Journal of Orthodontics and Dentofacial Orthopedics Volume 119, Number 5
roots, in extraction cases, in patients who have been in treatment for a longer than usual period of time, and in adult patients. In this study, Asian patients had less root resorption than white or Hispanic patients. Finally, interoffice variation is a significant factor; the clinician who treats a high number of patients who experience severe root resorption would be well advised to collect good data on these patients and compare them with the offices in this study. We thank Drs Young-Ho Kim, Young-Kyu Lim, William Redmond, Mark Wong, Warren Schacter, Gordon Kilmer, and Young-Jin Kim for their contributions to this project and John Morrison for statistical advice. REFERENCES 1. Alexander SA. Levels of root resorption associated with continuous arch and sectional arch mechanics. Am J Orthod Dentofacial Orthop 1996;110:321-4. 2. Beck BW, Harris EF. Apical root resorption in orthodontically treated subjects: analysis of edgewise and light wire mechanics. Am J Orthod Dentofacial Orthop 1994;105:350-61. 3. 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 Dentofacial Orthop 1995;108:76-84. 4. Goldin B. Labial root torque: effect on the maxilla and incisor root apex. Am J Orthod Dentofacial Orthop 1989;95:208-19. 5. Goldson L, Henrikson CO. Root resorption during Begg treatment: a longitudinal roentgenographic study. Am J Orthod 1975;68:55-66. 6. Kurol J, Owman-Moll P, Lundgren D. Time-related root resorption after application of a controlled continuous orthodontic force. Am J Orthod Dentofacial Orthop 1996;110:303-10. 7. Linge L, Linge BO. Patient characteristics and treatment variables associated with apical root resorption during orthodontic treatment. Am J Orthod Dentofacial Orthop 1991;99:35-43. 8. Owman-Moll P, Kurol J, Lundgren D. The effects of a four-fold increased orthodontic force magnitude on tooth movement and root resorptions: in intra-individual study in adolescents. Eur J Orthod 1996;3:287-94. 9. Owman-Moll P, Kurol J, Lundgren D. Continuous versus interrupted orthodontic force related to early tooth movement and root resorption. Angle Orthod 1995;65:395-402. 10. McGuinness N, Wilson AN, Jones M, Middleton J, Robertson NR. Stresses induced by edgewise appliances in the periodontal ligament: a finite element study. Angle Orthod 1992;62:15-22. 11. McGuinness N, Wilson AN, Jones M, Middleton J, Robertson NR. A stress analysis of the periodontal ligament under various orthodontic lodgings. Eur J Orthod 1991;13:231-42. 12. Jeon PD, Turley PK, Moon HB, Ting K. Analysis of stress in the periodontium of the maxillary first molar with a three-dimensional finite element model. Am J Orthod Dentofacial Orthop 1999;115:267-74. 13. Brezniak N, Wasserstein A. Root resorption after orthodontic treatment: Part 1. Literature review. Am J Orthod 1993; 103:62-6.
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