Volumetric Evaluation of Root Resorption During ...

©2014 JCO, Inc. May not be distributed without permission. www.jco-online.com

Volumetric Evaluation of Root Resorption During Orthodontic Treatment SHREYA AJMERA, BDS SHIVANAND VENKATESH, BDS, MDS, MOrth RCS SANJAY V. GANESHKAR, BDS, MDS, MDO RCPS

R

oot resorption is an idiopathic and unpredict able adverse effect of orthodontic treatment that may occur either apically or along the root surfaces in and around pressure zones.1-6 A number of predisposing factors have been proposed, including individual susceptibility,7,8 genetics,9 systemic factors,10 gender,9,11,12 age,11,13 amount of force applied,14 type of tooth movement,15,16 anatomical variation,11,13,17 type of orthodontic appliance and mechanics used,18-20 and treatment duration.3 Susceptibility to root resorption varies considerably, but even teeth with no radiographic signs of resorption have been reported to develop extensive areas of resorption.18 Although root resorption may seem to compromise the results of orthodontic treatment, the root loss does not affect the longevity or the functional capacity of involved teeth.1,6 Treatment mechanics largely determine the location of root resorption, since the pressure side will vary depending on the tooth movement. In palatal expansion, resorption develops mainly in

Dr. Ajmera

buccal areas, where it may remain undiagnosed unless it is extensive.21 Root resorption can begin early in the leveling and alignment stage of orthodontic treatment; because the stress distribution along the roots during bodily movement is less than the stress concentration at the apex caused by tipping, early resorption is usually associated with tipping movements.22 Several studies have also associated root resorption with intrusion.15,16,23-25 Root resorption has traditionally been detected through such means as periapical radiographs,22,26 panoramic radiographs,27 subtraction radiography, and scanning electron microscopy (SEM),14 but these methods are subject to magnification errors and unreliable reproducibility.28 Moreover, root resorption is a three-dimensional phenomenon, and conventional radiographs provide only two-dimensional representations.29 Histological studies have been found accurate but cannot be used for routine clinical evaluation. More promising is the recent development of 3D imaging and analysis, which offers the ability to

Dr. Shivanand Venkatesh

Dr. Ganeshkar

Dr. Ajmera is a postgraduate resident and Dr. Ganeshkar is Professor and Head, Department of Orthodontics and Dentofacial Orthopedics, SDM College of Dental Sciences, Sattur, Dharwad, Karnataka, India. Dr. Shivanand Venkatesh is an Assistant Professor, Department of Orthodontics and Dentofacial Orthopedics, M.S. Ramaiah Dental College and Hospital, Bangalore, Karnataka 560054, India; e-mail: [email protected].

VOLUME XLVIII NUMBER 2

© 2014 JCO, Inc.

113

Volumetric Evaluation of Root Resorption During Orthodontic Treatment

view dental structures at any angle, providing accurate measurements without superimpositions and with no more radiation exposure than from standard x-rays.30-34 The present study used cone-beam computed tomography (CBCT) to measure the volumes of external apical resorption and surface root resorption during simultaneous en masse intrusion and retraction of anterior teeth. Materials and Methods After approval by the institutional review board and ethical committee, patients age 12-16 reporting to the Department of Orthodontics and Dentofacial Orthopaedics were recruited for this prospective study, and informed consent was obtained. Patients with prior orthodontic treatment, traumatic injuries, restorations, or root-canal treatment were excluded. Each patient displayed either proclination of the upper anterior teeth or mild-to-moderate crowding associated with excessive overbite, requiring extraction of the first premolars and 2-4mm of orthodontic correction. A total of 48 patients (21 males, 27 females, mean age 13.6 years) were treated with .022" preadjusted MBT* edgewise brackets. In each case, after leveling and alignment, mini-implants (Absoanchor,** 2mm × 7mm) were placed in the infrazygomatic crest of the maxilla between the second premolar and first molar for anchorage of vertical forces to intrude the anterior teeth (Fig. 1). A force of 200g was applied from the implants for simultaneous en masse intrusion and retraction on an .019" × .025" stainless steel archwire. Pilot Study A pilot study was first performed to evaluate the accuracy and reproducibility of results from a Kodak CS 9000*** CBCT with small field of view. The volume obtained by physical measurement of an extracted tooth using a water-displacement technique (Fig. 2A) was compared with the volume measured by the machine. Upper right anterior teeth were removed from a freshly macerated human skull, and defects mimicking root resorption were created with a carbide bur (Fig. 2B) for com-

114

parison with a control group of upper left anterior teeth with intact roots. The 3D images obtained from the CS 9000 before and immediately after preparation of the teeth were compared to images from the commonly used iCAT† CBCT machine, using DICOM files imported into Mimics‡ 3D software for calculation of soft- and hard-tissue volumes. Differences between the values obtained from the water-displacement technique, the CS 9000, and the iCAT were not statistically significant (initial p = .8; post-defects p = .9). Data Collection Three-dimensional images of the 48 patients’ maxillary anterior teeth were taken just before treatment and after the completion of space closure following simultaneous en masse intrusion and *Trademark of 3M Unitek, Monrovia, CA; www.3Munitek.com. **Dentos, Daegu, Korea. Distributed by Great Lakes Orthodontics, Ltd., Tonawanda, NY; www.greatlakesortho.com. ***Carestream Health, Inc., Rochester, NY; www.carestream. com. †Registered trademark of Imaging Sciences International, LLC, Hatfield, PA; www.i-cat.com. ‡Registered trademark of Materialise, Leuven, Belgium, www. materialise.com.

A

B Fig. 1 A. Simultaneous intrusion and retraction on .019" × .025" stainless steel archwire, with anchorage from mini-implants placed in infrazygomatic crest of maxilla between second premolars and first molars. B. Overbite significantly improved at end of space-closure phase.

JCO/FEBRUARY 2014

Ajmera, Shivanand Venkatesh, and Ganeshkar

retraction (Fig. 3). The CS 9000 CBCT machine was set with an x-ray source potential of 70kVp, 10mA, at an exposure time of 10.8 seconds. To reduce potential radiation exposure, only the anterior teeth were scanned. The DICOM files were imported into Mimics volume- and surface-rendering software, and the volumetric image was manipulated to display the root surfaces from various orientations. Threshold values were set individually for each patient. Since no manual measurements were taken, operator error was not evaluated. Volumetric Analysis Manual segmentation of the tissues was performed so that the same number of Hounsfield units would be used for each patient’s before-andafter records. The six anterior teeth were care-

A

A

B Fig. 2 A. Physical volume of extracted tooth measured using water-displacement technique. B. Irregularities created with carbide bur on extracted upper right central incisor, lateral incisor, and canine to mimic root-resorption defects.


B Fig. 3 Cone-beam computed tomography images of anterior teeth before treatment (A) and after space closure (B).

115


A

B

C

D

E

F

Fig. 4 A. Segmentation of six anterior teeth using Mimics software. B. Segmentation of crown and root on plane passing through cementoenamel junction. C. Root imported into 3-matic software module. D. Center of gravity identified and root oriented in two planes. E. Roots segmented into four parts before treatment and after space closure and superimposed on orientation planes. F. Volume of each section calculated and compared. (Images reproduced by permission of International Journal of Engineering Research and Development, India; www.ijerd.com.)

116

JCO/FEBRUARY 2014


fully segmented from one another in the 3D images and adjusted for 3D orientations (Fig. 4A). The root was separated from the crown on a plane parallel to the cementoenamel junction, passing through the maximum contour of the CEJ on the labial side (Fig. 4B). Each root was isolated and color-coded, and its volume was calculated.7 The center of gravity of each root was identified using the software’s 3-matic‡ module (Fig. 4C) and oriented along two perpendicular planes, so that the center of gravity coincided with the intersection of the two planes (Fig. 4D). This allowed the root to be segmented into four parts— mesial, distal, palatal, and labial (Fig. 4E)—for tabulation of individual volumes (Fig. 4F). Statistical Analysis Pretreatment and post-space-closure mean root volumes were calculated for each tooth and its four segments. Analyses of changes in these volumes were conducted by means of nonparametric tests. The Kruskal-Wallis test was used to compare the differences between pretreatment and post-space-closure volumes. Results Differences between the pretreatment and

post-space-closure volumetric measurements were statistically significant (Table 1). The overall loss of root volume was greatest for the lateral incisors and least for the canines. The lateral and central incisors showed more volumetric loss in the palatal and mesial segments, while the canines showed more volumetric loss in the distal sections. Differences in volumetric losses among the four segments were statistically significant, but there was no significant difference between the right and left sides. Discussion Root resorption remains a common iatrogenic problem in orthodontics. Radiographs, histological sections, and SEM provide only 2D evaluations of the mesial and distal aspects of the root35 and, except for radiographs, can be used only on extracted teeth. Chan and colleagues found histological sections to be laborious and technique sensitive.28,35 CBCT does allow 3D imaging and analysis, but factors such as voxel size, scatter radiation, grayscale bit depth, and artifacts caused by metallic objects have an important influence on the visualization of subtle anatomic structures. The smaller the voxel size, the higher the spatial resolution; the smaller the field of view, the less

TABLE 1 COMPARISON OF PRETREATMENT AND POST-SPACE-CLOSURE ROOT VOLUMES USING KRUSKAL-WALLIS TEST (MEAN RANKING*) Overall Mesial Buccal Distal Palatal Segment Segment Segment Segment Right canine Right lateral incisor Right central incisor Left central incisor Left lateral incisor Left canine Chi-square P

27.74 26.80 78.00 47.30 58.82 38.10 46.31 39.80 73.94 48.50 20.91 27.25 55.134 34.713 0.001 0.032

13.20 33.90 23.90 35.00 26.90 58.70 29.00 25.20 43.65 28.00 24.90 41.50 34.50 22.20 56.00 11.30 34.90 22.85 48.135 52.758 48.348 0.025 0.001 0.012

*The differences in root resorption volumes were ranked and all ranks were added for derivation of mean rankings. Within each mean ranking, “H” is calculated and treated as chi-square; those values are then compared, based on degrees of freedom, to determine the “p” value. Mean volumetric measurements and standard deviations are published in the online version of this article at www.jco-online.com.


117


noise from scatter radiation. These considerations led us to use CBCT with a small field of view (also known as digital volumetric tomography) to study volumetric changes. The Kodak CS 9000 unit, with a voxel size of 100 microns × 100 microns × 100 microns and a field of view of 55mm, was validated in the pilot study, as corroborated by Michetti and colleagues in an evaluation of rootcanal anatomy.36 To our knowledge, this is the first study to measure the amount of root resorption on all four surfaces of the subject teeth. Mimics software with its 3-matics tool was used to separate the tissues according to their density in Hounsfield units. Each tooth was segmented into its crown and root portions to avoid the effects of artifacts from the metal brackets in the post-space-closure scans. The center of gravity of each root was determined, and the coordinates were applied to the same root in the post-space-closure image to eliminate any discrepancies. Separating the teeth from the other tissues and locating the center of the root minimized any errors that might have been caused by manual segmentation. Baysal and colleagues followed a similar method in evaluating root resorption during rapid maxillary expansion,37 but they measured only the overall changes in pre- and post-treatment root volume, rather than the differences for each segment of each individual tooth. Furthermore, the present study is the first in which 3D measurements were used to assess rootvolume loss after intrusion and retraction. Root resorption was evaluated in maximum-anchorage cases with mild-to-moderate maxillary crowding or severe proclination associated with deep overbite. Root volume decreased in every tooth, in agreement with studies by Levander and Malmgren38 and Smale and colleagues.22 The rootvolume loss of the lateral incisors was significantly more than for the central incisors and canines (Table 1), probably because the lateral incisor root is smaller and more conical in shape, so that it experiences heavier forces compared to the other teeth.13,18,39,40 When individual tooth surfaces were compared, the root-volume loss increased from palatal to mesial to buccal to distal for the central and

118

lateral incisors, but from distal to mesial to palatal to buccal for the canines. With simultaneous en masse intrusion and retraction, the stress concentration would be higher on the apex of the palatal side, which could explain the higher amount of resorption on the palatal surfaces of the central and lateral incisors. The canine’s distal surface would experience greater force and thus more resorption. The distally directed forces of space closure would also cause mesial tipping of the roots and thereby increase stress concentration, especially on the apical third of the roots, accounting for the greater resorption on all mesial surfaces. Because the mini-implants conserved anchorage and made more extraction space available for retraction of the anterior teeth, orthodontic treatment time was lengthened. Increased tooth movement and duration of treatment are well-known factors contributing to root resorption.3,40-45 Conclusion Since resorption on the buccal and palatal root surfaces can be evaluated only on tomographic images, we used a new CBCT-based method to measure the resorption of individual root segments, making it difficult to compare our results with those of previous studies. The factors disposing a patient to root resorption from tooth movement are more biological than diagnostic, however, and further research is required to form definitive conclusions. REFERENCES 1. Ketcham, A.H.: A preliminary report of an investigation of apical root resorption of permanent teeth, Int. J. Orthod. 13:97-127, 1927. 2. Ketcham, A.H.: A progress report of an investigation of apical root resorption of vital permanent teeth, Int. J. Orthod. 15:310328, 1929. 3. Ramanathan, C. and Hofman, Z.: Root resorption during orthodontic tooth movements, Eur. J. Orthod. 31:578-583, 2009. 4. Brezniak, N. and Wasserstein, A.: Root resorption after orthodontic treatment: Part 1. Literature review, Am. J. Orthod. 103:62-66, 1993. 5. Reitan, K.: Initial tissue behaviour during apical root resorption, Angle Orthod. 44:68-82, 1978. 6. Brezniak, N. and Wasserstein, A.: Root resorption after ortho-

JCO/FEBRUARY 2014


dontic treatment: Part 2. Literature review, Am. J. Orthod. 103:138-146, 1993. 7. Owman-Moll, P.; Kurol, J.; and Lundgren, D.: Continuous versus interrupted continuous orthodontic force related to early tooth movement and root resorption, Angle Orthod. 65:395-401, 1995. 8. Kurol, J.; Owman-Moll, P.; and Lundgren, D.: Time-related root resorption after application of a controlled continuous orthodontic force, Am. J. Orthod. 110:303-310, 1996. 9. Harris, E.F.; Kineret, S.E.; and Tolley, E.A.: A heritable component for external apical root resorption in patients treated orthodontically, Am. J. Orthod. 111:301-309, 1997. 10. McNab, S.; Battistutta, D.; Taverne, A.; and Symons, A.L.: External apical root resorption of posterior teeth in asthmatics after orthodontic treatment, Am. J. Orthod. 116:545-551, 1999. 11. Sameshima, G.T. and Sinclair, P.M.: Predicting and preventing root resorption: Part 1. Diagnostic factors, Am. J. Orthod. 119:505-510, 2001. 12. Hendrix, I.; Carels, C.; Kuijpers-Jagtman, A.M.; and Van’t Hof, M.: A radiographic study of posterior apical root resorption in orthodontic patients, Am. J. Orthod. 105:345-349, 1994. 13. Mirabella, A.D. and Artun, J.: Prevalence and severity of apical root resorption of maxillary anterior teeth in adult orthodontic patients, Eur. J. Orthod. 17:93-99, 1995. 14. Chan, E. and Darendeliler, M.A.: Physical properties of root cementum: Part 5. Volumetric analysis of root resorption craters after application of light and heavy orthodontic forces, Am. J. Orthod. 127:186-195, 2005. 15. Parker, R.J. and Harris, E.F.: Directions of orthodontic tooth movements associated with external apical root resorption of the maxillary incisor, Am. J. Orthod. 114:677-683, 1998. 16. Harry, M.R. and Sims, M.R.: Root resorptions in bicuspid intrusion: A scanning electron microscope study, Angle Orthod. 52:235-258, 1982. 17. Linge, L. and Linge, B.O.: Patient characteristics and treatment variables associated with apical root resorption during orthodontic treatment, Am. J. Orthod. 99:35-43, 1991. 18. Linge, B.O. and Linge, L.: Apical root resorption in upper anterior teeth, Eur. J. Orthod. 5:173-183, 1983. 19. Kinsella, P.: Some aspects of root resorption in orthodontics, N.Z. Orthod. J. 1:21-25, 1971. 20. Stuteville, O.H.: Injuries of the teeth and supporting structures caused by various orthodontic appliances, and methods of preventing these injuries, J. Am. Dent. Assoc. 14:1494-1507, 1937. 21. Barber, A.F. and Sims, M.R.: Rapid maxillary expansion and external root resorption in man: A scanning electron microscope study, Am. J. Orthod. 79:630-652, 1981. 22. Smale, I.; Artun, J.; Behbehani, F.; Doppel, D.; Van’t Hof, M.; and Kuijpers-Jagtman, A.M.: Apical root resorption 6 months after initiation of fixed orthodontic appliance therapy, Am. J. Orthod. 128:57-67, 2005. 23. Costopoulos, G. and Nanda, R.: An evaluation of root resorption incident to orthodontic intrusion, Am. J. Orthod. 109:543548, 1996. 24. Demaut, L.R. and De Munck, A.: Apical root resorption of upper incisors caused by intrusive tooth movement: A radiographic study, Am. J. Orthod. 90:321-326, 1986. 25. Harris, D.A.; Jones, A.S.; and Darendeliler, M.A.: Physical properties of root cementum: Part 8. Volumetric analysis of root resorption craters after application of light and heavy orthodontic forces: A microcomputed tomographic scan study, Am. J. Orthod. 130:639-647, 2006. 26. Artun, J.; Van’t Hullenaar, R.; Doppel, D.; and KuijpersJagtman, A.M.: Identification of orthodontic patients at risk of


severe apical root resorption, Am. J. Orthod. 135:448-455, 2009. 27. Rosenberg, H.N.: An evaluation of the incidence and amount of apical root resorption and dilaceration occurring in orthodontically treated teeth, having incompletely formed roots at the beginning of Begg treatment, Am. J. Orthod. 61:524-525, 1972. 28. Chan, E.K. and Darendeliler, M.A.: Exploring the third dimension in root resorption, Orthod. Craniofac. Res. 7:64-70, 2004. 29. Dudic, A.; Giannopoulou, C.; Leuzinger, M.; and Kiliaridis, S.: Detection of apical root resorption after orthodontic treatment by using panoramic radiography and cone-beam computed tomography of super-high resolution, Am. J. Orthod. 135:434-437, 2009. 30. Hajeer, M.Y.; Ayoub, A.F.; Millett, D.T.; Bock, M.; and Siebert, J.P.: Three-dimensional imaging in orthognathic surgery: The clinical application of a new method, Int. J. Adult Orthod. Orthog. Surg. 17:318-330, 2002. 31. Aboudara, C.; Hatcher, D.; Nielsen, I.; and Miller, A.: A threedimensional evaluation of the upper airway in adolescents, Orthod. Craniofac. Res. 6:173-175, 2003. 32. Mah, J. and Sachdeva, R.: Computer-assisted orthodontic treatment: The SureSmile process, Am. J. Orthod. 120:85-87, 2001. 33. Harrel, W.E.: Three-dimensional diagnosis & treatment planning: The use of 3D facial imaging and 3D cone beam CT in orthodontics and dentistry, Australas. Dent. Pract., July/ August 2007, pp. 107-113. 34. Larson, B.E.: Cone-beam computed tomography is the imaging technique of choice for comprehensive orthodontic assessment, Am. J. Orthod. 141:402-407, 2012. 35. Chan, E.K.; Darendeliler, M.A.; Petocz, P.; and Jones, A.S.: A new method for volumetric measurement of orthodontically induced root resorption craters, Eur. J. Oral Sci. 112:134-139, 2004. 36. Michetti, J.; Maret, D.; Mallet, J.P.; and Diemer, F.: Validation of cone beam computed tomography as a tool to explore root canal anatomy, J. Endod. 36:1187-1190, 2010. 37. Baysal, A.; Karadede, I.; Hekimoglu, S.; Ucar, F.; Ozer, T.; Veli, I.; and Uysal, T.: Evaluation of root resorption following rapid maxillary expansion using cone-beam computed tomography, Angle Orthod. 82:488-494, 2012. 38. Levander, E. and Malmgren, O.: Evaluation of the risk of root resorption during orthodontic treatment: A study of upper incisors, Eur. J. Orthod. 10:30-38, 1988. 39. Reitan, K.: Effects of force magnitude and direction of tooth movement on different alveolar bone types, Angle Orthod. 34:244-255, 1964. 40. McFadden, W.M.; Engstrom, C.; Engstrom, H.; and Anholm, J.M.: A study of the relationship between incisor intrusion and root shortening, Am. J. Orthod. 96:390-396, 1989. 41. Massler, M. and Malone, A.J.: Root resorption in human permanent teeth, Am. J. Orthod. 40:619-633, 1954. 42. Goldie, R.S. and King, G.J.: Root resorption and tooth movement in orthodontically treated, calcium-deficient, and lactating rats, Am. J. Orthod. 85:424-430, 1984. 43. Hall, A.: Upper incisor root resorption during stage II of the Begg technique, Br. J. Orthod. 5:47-50, 1978. 44. Engstrom, C.; Granstom, G.; and Thilander, B.: Effect of orthodontic force on periodontal tissue metabolism, Am. J. Orthod. 93:486-495, 1988. 45. Remington, D.N.; Joondeph, D.R.; Artun, J.; Riedel, R.A.; and Chapko, M.K.: Long-term evaluation of root resorption occurring during orthodontic treatment, Am. J. Orthod. 96:43-46, 1989.

119