ORIGINAL ARTICLE
A radiographic comparison of apical root resorption after
orthodontic treatment with 3 different fixed appliance techniques
Guilherme R. P. Janson, DDS, MSc, PhD, MRCDC,a Graziela de Luca Canto, DDS, MSc,b
Décio Rodrigues Martins, DDS, MSc, PhD,c José Fernando Castanha Henriques,c DDS, MSc, PhD,
and Marcos Roberto de Freitas, DDS, MSc, PhDd
São Paulo, Bauru, Brazil
Apical root resorption is an undesirable, but frequent side effect of orthodontic treatment, and therefore improvements
in orthodontic techniques and materials are in constant development to decrease it. One of the most
recently developed orthodontic techniques is the Bioefficient Therapy that uses contemporary orthodontic materials.
Therefore, the primary objective of this study was to compare the amount of root resorption after orthodontic
treatment between the simplified standard edgewise technique (group 1), the edgewise straight wire system
(group 2), and the Bioefficient Therapy (group 3). It was also the purpose of this investigation to evaluate
the amount of root resorption in the whole sample studied and the prevalence of root resorption in the upper and
lower incisors. Thus, periapical radiographs were obtained with the long cone paralleling technique for the upper
and lower incisors from 30 patients for each group. Root resorption was ranked by scores by 2 examiners who
had an excellent intra and interexaminer calibration by Kendall concordance coefficient. Results of the Kruskal-
Wallis test demonstrated that group 3 (Bioefficient Therapy) presented less root resorption than the others. It
was speculated that the factors responsible for the lesser resorption in this technique were the use of heat-activated
and superelastic wires with the bracket design in this technique as well as the use of a smaller rectangular
stainless steel wire (0.018 × 0.025 inch) in a 0.022 × 0.028 inch slot during incisor retraction and the finishing
stages, as compared to the other techniques. Considering the whole sample, there was no root resorption
in 2.25% of the analyzed teeth. There was only a slight resorption in 42.56%, a moderate resorption in 53.37%,
an accentuated resorption in 1.40% and an extreme root resorption in only 0.42% of the teeth. The prevalence
of resorption for each incisor indicated, in decreasing order, a greater resorption for the upper centrals, followed
by the upper laterals, lower centrals, and lastly the lower lateral incisors. (Am J Orthod Dentofacial Orthop
1999;118:262-73)
This article is based on research submitted by Dr. Graziela de Luca Canto in partial fulfillment of the requirements for the degree of Master of Science in Orthodontics, University of São Paulo at Bauru Dental School.
From the Department of Orthodontics. Bauru Dental School. University of São Paulo.
aAssociate Professor.
bOrthodontic Graduate Student.
cFull Professor.
dAssociate Professor and Head.
Reprint requests to: Dr Guilherme R. P. Janson, Department of Orthodontics, Bauru Dental School, University of São Paulo, Alameda Otavio Pinheiro
Brisolla 9-75, Bauru – SP – 17043-101, Brazil; e-mail, jansong@travelnet.com.br
Submitted October 1998, and accepted March 1999.
Copyright © 2000 by the American Association of Orthodontists.
0889-5406/2000/$12.00 + 0 8/1/99136
doi:10.1067/mod.2000.99136
Practical Procedures & AESTHETIC DENTISTRY
Unable to eliminate the patient’s intrinsic factors that may predispose to root resorption, the orthodontists are constantly improving materials and techniques to minimize this undesirable treatment side effect. In 1963 the first nickel-titanium alloy was developed1 and was first used in Orthodontics in
1971.2 Twenty-two years later the new superelastic nickel-titanium wires that deliver light and continuous forces with large amounts of activation and
for long periods of time were developed in China3 and Japan.4
Concurrently with wire evolution the brackets were also improved to take advantage of the quality of these new materials, in reducing the force magnitude applied to the teeth. In 1995, Viazis5,6 introduced triangular brackets, with an increased interslot distance to decrease even more the forces delivered by the new generation of nickel-titanium wires and consequently to provide a more biologic orthodontic intervention with less discomfort to the patient. The use of this bracket system with the heat-activated, superelastic, nickel-titanium rectangular (or square) wires (Bioforce Ionguard, GAC International, Inc, New York) was called bioefficient therapy.5,6 Nevertheless, there is no investigation concerning the resorption potential of these new materials and techniques. Therefore, the primary objective of this study was to compare the amount of root resorption after orthodontic treatment
between the Simplified Standard Edgewise Technique (group 1), the Edgewise Straight Wire System (group 2), and the Bioefficient Therapy5,6 (group 3). It was also the purpose of this investigation to compare the amount of root resorption in the whole sample studied, and the prevalence of root resorption in the upper and lower incisors.
MATERIAL AND METHODS
Material
Ninety patients were used in this study, with an age range between 10 years 1 month and 26 years 10 months, regardless of race, sex, and type of malocclusion. Patients that presented apical root resorption or endodontic treatment at the pretreatment stage were excluded from the sample, as well as patients whose orthodontic records were incomplete. Poor quality radiographs were also eliminated. None of the patients were retreatment cases.
Group 1 consisted of 30 patients treated with the Simplified Edgewise Technique at the orthodontic clinic at Bauru Dental School, University of São Paulo.
Eleven were female and 19 were male, with a mean age of 13.92 years (age range, 10.08 to 26.83 years) at the beginning of treatment. The malocclusion types consisted of 12 Class I, 16 Class II Division 1, 1 Class II Division 2, and 1 Class III. Eleven cases were treated with 4 extractions, 3 with extraction of 3 teeth, 1 with extraction of only 2 teeth, and 15 without extractions. The mean treatment time was 29.13 months. The Simplified Standard Edgewise Technique is characterized by the use of 0.022 × 0.028 inch conventional brackets (Morelli, Sorocaba, Brazil) associated with an extraoral headgear and a lip bumper to reinforce anchorage for the upper and lower teeth, respectively, when necessary. There is no anchorage preparation. The usual wire sequence begins with a 0.015 inch twist-flex or 0.016 nitinol wire, followed by 0.016, 0.018, 0.020, and finally a 0.021 × 0.025 inch stainless steel wire
(Unitek, Monrovia, Calif). In extraction cases, the canines are initially retracted only a small amount to allow space for leveling and aligning of the anterior
teeth. The anterior teeth are retracted en masse with the rectangular wire, after leveling and aligning. To accomplish this, the dimensions of the rectangular wire are electrolytically reduced in the posterior segments to reduce the friction forces with the brackets and tubes. The retraction of the canines and of the anterior teeth are performed with elastic chains. Deep overbites are usually corrected by reversing and accentuating the curve of Spee of the stainless steel arch wires from the beginning, until an overcorrection is obtained. This overcorrection is maintained by accentuating and
reversing the curve of Spee in the rectangular wire as well. The mean amount of overjet, overbite, and the anteroposterior position of the upper and lower incisors of the 3 groups, at the beginning and at the end of treatment are illustrated in Table I. Group 2 consisted of 30 patients treated with the
Roth (Lancer Orthodontics Inc, San Marcos, Calif) Edgewise Straight Wire System at the orthodontic clinic at Baura Dental School, University of São Paulo. Fifteen were female and 15 were male, with a mean age of 14.18 years (age range from 10.91 to 26 years) at the beginning of treatment. Seven cases were Class I, 19 Class II Division 1, 2 Class II Division 2, and 2 Class III malocclusion types. Thirteen cases were treated with 4 extractions, five with extraction of only 2 teeth, and 12 without extractions. The mean treatment time was 19.26 months. The brackets had 0.022 × 0.028 inch slots and the wire sequence and mechanics are similar to the Simplified Standard Edgewise Technique, beginning with a 0.015 inch twist-flex or 0.016 nitinol wire,
followed by 0.016, 0.018, 0.020, and finally a 0.021 × 0.025 inch stainless steel wire (Unitek). To reinforce anchorage, an extraoral headgear and a lip bumper are used for the upper and lower teeth, respectively, when necessary. Group 3 consisted of 30 patients treated with the Bioefficient Therapy (GAC International). Nineteen were treated at the orthodontic clinic at Baura Dental School, University of São Paulo, and 11 were treated in a private practice. The malocclusion types consisted of 13 Class I, 10 Class II Division 1, 6 Class II Division 2, and 1 Class III. Fourteen were female and 16 were male, with a mean age of 14.29 years (age range, 10.41 to 23.66 years) at the beginning of treatment. Fifteen cases were treated with 4 extractions, 6 with extraction of 2 teeth, 1 with only 1 extraction, and 8 without extractions. The mean treatment time was 18.93 months. The brackets had 0.022 × 0.028 inch slots and the wire sequence begins with a 0.020 × 0.020 inch Bioforce Ionguard (GAC International) followed by a 0.018 × 0.025 inch stainless steel arch wire (Unitek). In extraction cases, the canines are completely retracted into the extraction spaces with superelastic retraction springs on the 0.020 × 0.020 inch Bioforce Ionguard arch wire. After leveling and aligning and retraction of the canines, the 0.018 × 0.025 inch stainless steel arch wire is inserted and the incisors are retracted on this wire with superelastic retraction springs. Extraoral headgear and lip bumper can also be used to reinforce anchorage for the upper and lower teeth, respectively. The use of these anchorage reinforcement devices can be reduced when the second molars are
included in the mechanics. Deep overbites are corrected with the stainless steel rectangular arch wire with reverse and accentuated curve of Spee, until an overcorrection is obtained.
To quantify resorption, periapical posttreatment radiographs of the upper and lower incisors, totaling 712 teeth, were examined. The decision to work with only the incisors was reached because they are the teeth subjected to greater movement during treatment, primarily in extraction cases and because most authors7-15 agree that they are more frequently and intensely resorbed during treatment. The other records were used to determine patient’s sex and age at the beginning of therapy, the type of treatment undertaken (with or without extractions) and the orthodontic technique that was used.
Fig 1. Score system of Levander and Malmgren (redrawn from Levander and Malmgren16) grade 0,
absence of root resorption; grade 1, mild resorption, root with its normal length and only an irregular
contour; grade 2, moderate resorption, small area of root loss with the apex exhibiting an almost
straight contour; grade 3, accentuated resorption, loss of almost one third of root length; grade 4,
extreme resorption, loss of more than one third of the root length.
Methods
The posttreatment periapical radiographs of the patients treated at the University were obtained by a single operator with the DABI 70 Spectro 1070X x-ray machine, set up for 70 kV, 10 mA, and an exposure time of 1 second, with the long cone paralleling technique. Kodak Ektaspeed EP 21 films were used, and the angles were obtained by an intraoral XCP (Rinn- Dentisply) positioner. The radiographs of the private practice patients were obtained by 2 different operators with the same type of positioner mentioned above, with a Yoshida X 70F x-ray machine, set up for 70KVP and 15 mA, using the same technique. Kodak DF 58 films were used and exposed for 0.9 second. All radiographs were processed automatically. Standardization of the radiographs taken by different operators was not a concern because resorption was evaluated by the score system of Levander and Malmgren16 that classifies it into 5 grades (Fig 1). The radiographic analysis was blind and was performed by 2 examiners with a magnifying glass. The resorption grade of each tooth was recorded on each patient’s chart. Other information, such as age, sex, technique used and whether the treatment was conducted with or without extractions, was recorded on the chart later.
Error study
• Intraexaminer error. Thirty teeth were randomly selected (10 from each group) and remeasured by the same examiner (examiner A). The repeated measurements were tested by the Kendall coefficient of concordance that demonstrated an excellent level of intraexaminer agreement (Table II).
• Interexaminer error. The 180 radiographs were evaluated by 2 examiners and the level of agreement between examiners A and B was tested by Kendall’s
coefficient of concordance. Results were similar to the intraexaminer calibration, showing a statistically high level of agreement between the examiners as shown on Table III. Therefore it was not necessary to use the measurements of examiner B. They were only used to test the precision of examiner A’s measurements.
Statistical Analysis
The amount of root resorption between the three orthodontic techniques was compared by means of the Kruskal-Wallis nonparametric test. Because some patients in group 3 were treated in a private practice, it was decided to evaluate whether there was a difference in the amount of resorption between patients treated in the University and those treated in the private practice, within group 3, with the Mann-Whitney test. Because of the inherent difficulties in standardizing the groups with respect to the type of malocclusion, at the beginning of treatment the amount of extractions in each group was compared to assist in interpreting the results. This comparison was performed by the analysis of variance (F test).
Descriptive statistics were used to evaluate the percentage of root resorption in the whole sample and the prevalence of resorption in each incisor was evaluated by the Kruskal-Wallis test.
RESULTS
Comparisons Between the Groups
Amount of resorption.
The comparison of the amount of root resorption observed in the 3 groups demonstrated that group 3 presented, on average, less resorption than
groups 1 and 2 and that the amount of resorption among these last two were similar (Table IV, Fig 2). Results of the amount of resorption analysis within
group 3 among patients treated in the University or in a private practice indicated that the subgroup treated in private practice presented less resorption than those treated in the University (Table V, Fig 3). Because there was a difference between the two subgroups, it was decided to compare the other two groups (groups 1 and 2) with the subgroup treated in the University, by means of the Kruskal-Wallis test. Results of this comparison showed that the first 2 groups presented more resorption than the subgroup treated in the University (Table VI, Fig 4).
Amount of extractions (complementary evaluation). The amount of extractions, evaluated through the analysis of variance, was not statistically different
between the groups (Tables VII and VIII). Group 1 had, on average, 1.79 teeth extracted; group 2, 2.06, and group 3, 2.43 (Fig 5). It should be noticed that
group 3 had the largest amount of extractions, although this difference was not statistically significant.
Amount of Root Resorption Consequent to Orthodontic Treatment
From the 90 cases of the sample, 712 teeth were analyzed: 355 in the maxilla and 357 in the mandible. Of the total, 16 (2.25%) did not present any root
resorption (grade 0), 303 (42.56%) presented only a mild resorption (grade 1), 380 (53.37%) presented moderate resorption (grade 2), 10 (1.40%) had accentuated resorption (grade 3), and only 3 (0.42%) presented extreme resorption (grade 4) (Fig 6).
Prevalence of Resorption in the Incisors (Kruskal-Wallis test)
Generally, it could be observed that the most resorbed teeth were the upper central incisors, followed by the upper laterals, lower central incisors, and
lastly the lower lateral incisors (Fig 7).
Fig 3. Comparison of the resorption amount within group 3: patients treated in the University or in a private practice.
DISCUSSION
Sample Selection And Method
In samples consisting of patients treated by different professionals several variables should be considered. It is very difficult to obtain groups large enough and treated by a single operator with three different techniques. The Bioefficient Therapy was only recently introduced,5,6 and therefore it would be practically impossible that a single professional would have 30 cases concluded with this technique and two other groups of 30 cases treated with
the Simplified Standard Edgewise Technique and the Edgewise Straight Wire System at the time this project was being conducted. As Krogman17 stated: “In research perfection may be the goal, but adequacy is the most useful standard.” Furthermore, there are other works14,15,18- 20 in the literature that were conducted with samples from different sources that stated that this factor should not interfere with the results.
The method of periapical radiographs is the best for clinical studies of apical root resorption and therefore is used by the great majority of authors.11,13,14,16,20-30 Periapical radiographs are much superior to the panoramic, occlusal, and the lateral cephalometric radiographs for studying root structures, primarily when obtained with the long cone paralleling technique.31 This technique provides less radiation to the patient when radiographing the upper and lower incisors, causes less image distortion; the superimposition errors are also smaller when compared with the panoramic and cephalometric radiographs. The reduction in radiation to the patient is particularly important for children, adolescents, and young adults, who are more radiosensitive than adults, because of the fast-growing organs, position of the thyroid, and the longer time for the radiation effects to become apparent.31 The automatic film processing enabled a standardization of the radiographs regarding density and contrast, with a consequent similar
brightness.
Subjective methods, such as the presently used method of Levander and Malmgren,16 are predominantly used in root resorption studies* following tooth
movement, in contrast to other methods that quantified resorption by comparing measurements obtained in radiographs before and after treatment,9,18,22,25,26,30 and therefore they seem to be very reliable. Their primary advantage is that they are not dependent on standardization
of the initial radiographs. In the present study, the intraexaminer and interexaminer errors demonstrated an excellent concordance level between
the examiners, attesting to the precision of the evaluation (Tables II and III).
Amount of Resorption
Comparison between the groups. The most important result was that root resorption was not greater in the group treated with the Bioefficient Therapy when compared with the other groups. One could think that the introduction of a rectangular wire in the initial treatment stages, such as recommended in this technique, would lead to an increased root resorption. However, it was shown that the smaller resorption amount in the group treated with the Bioefficient Therapy could be due to the biocompatibility of the new orthodontic wires and brackets. When the types of malocclusions in the groups are
compared, it can be seen that there is some similarity. The amount of Class I in the Standard Edgewise Technique group is similar to that in the Bioefficient Therapy group and the number of Class III cases is also similar among all three groups. Group 3 had only a smaller amount of Class II Division 1 cases than the other 2 groups, but on the other hand, it had more Class II Division 2 cases. Regarding the resorption potential, Class II Division 2 cases present higher risks because of the intrusion mechanics necessary to correct the anterior overbite characteristic of these cases, as previously reported,22,23,32,34 and also the labial torque to correct the incisors’ palatal inclination. Therefore an even greater resorption would be expected in this group.
Table I shows the mean amount of overjet and overbite of the groups. It can be seen that the overjet in group 3 is a little bit more than 1 mm less than the other two groups in the beginning and that the amount of change is approximately 1 mm less as well. Therefore it could be speculated that the difference in resorption level between group 3 and the others could be based on the difference in the amount of correction of the over-jet, as it has been shown to be associated with a greater risk of resorption.32 However, the amount of overbite in the 3 groups is very similar, as well as the changes that occurred with treatment that would therefore lead to a similar resorption amount in the groups. It is interesting to mention that the mechanics used for the overbite correction in the 3 groups was very similar, accentuating and reversing the curve of Spee in the upper and lower arch wires, respectively.
The cephalometric measurements regarding upper and lower incisors mean retraction of the groups is also presented in Table I. Although the use of 1-NA and 1- NB is not ideal to evaluate the retraction of these teeth, it gives an idea of the amount of movement experienced by them. It can be seen that the upper and lower incisors of group 3 experienced more retraction than the other groups. Therefore, if resorption is associated with the amount of tooth movement as has been suggested in some studies,32,35 then this would be a factor contributing to a larger resorption in this group as compared to
the others. The lower incisor anteroposterior positions of group I before and after treatment show that there was a small mean proclination of these teeth instead of retraction. The reason for this might be that there were many nonextraction cases in this group that may have experienced some labial movement of the incisors. Therefore, when the mean anteroposterior movement was calculated, the amount of retraction of the extraction cases was not greater then the proclination of the incisors experienced by the nonextraction cases. Retrospectively, the balanced effects of the malocclusion
types, amount of overjet, overbite, and retraction of the incisors in the groups would tend to lead to more resorption in group 3 and therefore could not
explain the obtained results.
Another factor worth considering for the resorption level is the treatment time. In this regard, it may be speculated that the longer treatment time in group 1 might have contributed to the greater resorption found in this group, as it has been shown to be an aggravating factor for root resorption.34,36,37 However, resorption was very similar between groups 1 and 2 (Table IV), suggesting that other factors might have influenced the difference with group 3.
Fig 4. Comparison of resorption amount between groups 1, 2, and the University subgroup of group 3.
Fig 5. Comparison of amount of extractions in 3 groups.
Although there are few studies comparing techniques that use superelastic wires, some remarks are worth mentioning in regard to the lesser resorption level found in group 3. In 1993, Miura38 stated that the discovery of the “super-elastic” properties of NiTi alloy wires and its use in osteoclast recruitment, is a significant scientific breakthrough for the orthodontic specialty, establishing a new standard of biologic treatment in clinical orthodontics.
The superelastic wires produce a more biologic action, with less discomfort to the patient.5,6 Shape memory, heat activation, superelasticity, differential
force, and coating with nitrogen ions of these wires combined with the bracket design of the Bioefficient Therapy makes orthodontic treatment very comfortable for the patient even when a rectangular wire is inserted in the initial treatment phases. In the Simplified Standard Edgewise Technique and in the Edgewise Straight Wire System, the stainless steel round and rectangular wires tend to apply heavier forces to the teeth, in addition to presenting greater friction with the brackets.39 In order to overcome this friction, larger retraction forces are necessary39 that can increase the resorption risk and discomfort to the patient.5 These techniques also use a 0.021 × 0.025 inch rectangular stainless steel wire for retraction of the anterior teeth, that is larger than the 0.018 × 0.025 inch stainless steel wire used in the Bioefficient Therapy. Because the brackets of the 3 systems present 0.022 × 0.028 inch slots, the forces delivered in the first 2 systems are greater than in the Bioefficient Therapy. This factor could also account for the greater resorption in groups 1 and 2. In addition, because the majority of the edgewise techniques use a continuous arch wire, teeth leveling is performed in an indiscriminate
manner so that the lateral incisor receives the same force that the canine does. The heat-activated, superelastic Bioforce Ionguard wires present differential forces, with 80g in the anterior and 320g in the posterior segment, to move teeth without overloading them.5,6 To increase the wire length between the brackets and consequently reduce even further the force applied by the arch wire, it is necessary to have a large interslot distance. Therefore it is evident that a single bracket would be more efficient than a twin bracket. The Bioefficient Therapy triangular bracket is single and provides
an increase in the interslot distance that consequently allows an increase in the interslot arch wire length and a greater flexibility, whereas its design still ensures an efficient tooth movement with good control of tip and rotation. In 1955, Quintanilla et al40 compared the friction of these brackets5,6 with others commercially available (Roth, Shoulder, Synergy, Standard twin, Lang single) and found that they needed a lesser force to produce the initial tooth movement. In some cases (Viazis versus Lang single), the friction was up to 10 times less. In 1996, LaFerla41 confirmed that these brackets present less friction compared with others such also claimed that the design of the brackets facilitated the sliding mechanics because of the ligation method:
the bracket elbows keep the elastic ligatures away from the arch wire, decreasing the resistance to sliding. The is different from the conventional brackets in which the ligatures are tightly tied, increasing friction and hindering tooth movement. The action of the triangular brackets, associated with the heat activated superelastic wires and the use of 0.018 × 0.025 inch rectangular stainless steel wires in accessories with 0.022 × 0.028 inch slots
seem to have been at least partially responsible for the lesser root resorption after orthodontic treatment, observed in group 3 (Bioefficient Therapy).
Other accessories may have also contributed to the reduced resorption found in the group treated with the Bioefficient Therapy. The superelastic retraction springs apply a constant force of 150g as opposed to the elastic chains that present a decreasing force with time.5 This light and continuous force might have contributed to the lesser resorption found in this group as well. When the resorption level of patients within group 3 who had been treated in a private practice (subgroup PP) were compared with those who had been treated in the University (subgroup UNI) the results demonstrated
that the former presented less root resorption than the latter (Table V, Fig 3). The possible cause of this difference could be the greater clinical experience of the private clinician, compared with the clinical skills of graduate orthodontic students in the University. It should also be considered that the University patients were treated by 9 students. It is evident that a neophyte is more prone to introduce collateral effects in the orthodontic mechanics than an experienced professional. These collateral effects may then induce more resorption as was observed. In view of these results, one could speculate that the fact that some of the patients in group 3 had been treated in a private practice might have accounted for the smaller resorption amount when compared with groups 1 and 2 for the same reason already mentioned. Therefore, to discard this possibility, the University subgroup of group 3 was then compared to groups 1 and 2, although the number of patients in the University subgroup was only 19 subjects and not ideal for
statistical purposes. However, it was considered valuable as a complementary evaluation. The results of this evaluation showed that the University subgroup also presented less resorption than the other groups, suggesting that the smaller resorption level of group 3, in comparison with the others, could be the result of differences in the orthodontic technique used and not differences in professional skills (Table VI, Fig 4).
Fig 6. Percentage of resorption in the examined teeth (n = 712).
Amount of Extractions in the Groups
Selecting compatible groups according to the type of malocclusion presented earlier for treatment, the type of orthodontic treatment, and the amount of extractions to be performed is very difficult. With respect to the types of malocclusion and treatment performed, the subjects were randomly selected and yet yielded quite similar amounts of malocclusion types in each group, as already mentioned. Considering that extraction cases usually imply larger tooth movements to correct the malocclusions and that this could implicate in a greater resorption potential,32,35 the amount of extractions in the groups was compared. The results in Tables VII and VIII and Fig 5 show that the amount of extractions was statistically similar among the groups, and consequently, the differences in resorption levels cannot be explained by dissimilarities in the amount of tooth movement between the groups on the basis of the amount of extractions. Although there were no statistically significant differences in the amount of extractions among the groups, it can be observed that there was a tendency toward an increase, from group 1 to group 3 (Table VIII). When Tables I and VIII are compared, it can be observed that
the amount of retrusion of the incisors is proportional to the amount of extractions in each group. Therefore analyzing the amount of tooth movement based on the amount of extractions is compatible to the analysis in relation to the anteroposterior movement of the incisors. Because no statistical comparison of the amount of retrusion of the incisors among the groups was conducted, the numbers only show a tendency for a greater
retraction of these teeth in group 3.
Amount of Root Resorption Consequent to Orthodontic
Treatment
From the total sample of teeth (n = 712), only 2.25% showed no root involvement (grade 0), 42.56% presented only an apical blunting (grade 1), and 53.37% presented moderate resorption (grade 2) (Fig 6). It was also evident that resorption consequent to treatment is rarely accentuated (grade 3) or extreme (grade 4) as only 1.82% of the teeth presented this amount of resorption. These results are similar to those of Beck and Harris32 who observed resorption in 62% of the incisors and considered “resorbed teeth” to be only those presenting with grades 2, 3, or 4, which in this work would add up
to 55.90%. Maybe this difference of almost 6% is associated with the orthodontic techniques used, as Beck and Harris32 used edgewise and Begg. The results are also similar to those of Remington,19 Kaley and Phillips,12 and Desields33 and present small differences from those of Levander and Malmgren16 who found accentuated resorption in 17% of the teeth. However, these numbers might have been aggravated because their sample consisted only of upper incisors that are the most resorbed teeth during treatment.7-15 Nevertheless, the results of the present study that apical root
resorption during orthodontic treatment is rarely extreme agree with most of the authors.12,19,24,33
Prevalence of Resorption in the Incisors
The prevalence of resorption in the incisors was similar to that reported in the literature,7,8,11,12,14,29,32 that is, in a decreasing order, a larger resorption of the upper central incisors, followed by the upper lateral incisors, lower central incisors, and lastly the lower lateral incisors. This helps to substantiate the precision of the method used in the present investigation (Fig. 7).
Fig 7. Mean resorption scores for each incisor in 3 groups (ICI, upper central incisor; ULI, upper lateral incisor; LCI,
lower central incisor; LLI, lower lateral incisor).
CLINICAL CONSIDERATIONS
The most important consequence of these results is that orthodontic mechanics can be simplified with the new orthodontic materials, by obtaining 3-dimensional control of tooth movement with a superelastic, heatactivated rectangular wire from the beginning of treatment, and that this will not cause more resorption than usual. Therefore this will require less chair time for the practitioner and provide more comfort for the patient. However, other studies have to be done in order to confirm this tendency as well as to better elucidate any advantages of this new technology. Histologic studies
of tissue changes consequent to tooth movement with these appliances are necessary.
CONCLUSIONS
1. Treatment with the Bioefficient Therapy did not produce an increase in the amount of root resorption. In fact, group 3 (Bioefficient Therapy) presented
even less root resorption than group 1 (Simplified Standard Edgewise Technique) and group 2 (Edgewise Straight Wire System). It was speculated
that the factors responsible for the smaller resorption in this technique were the use of heat activated and superelastic wires with the bracket design in
this technique as well as the use of a smaller rectangular stainless steel wire (0.018 × 0.025 inch) in a 0.022 × 0.028 inch slot during incisor retraction and
the finishing stages, as compared to the other techniques.
2. From all the teeth examined, 2.25% did not have root involvement; 42.56% had only a mild resorption; 53.37% had moderate resorption; 1.40% had
accentuated resorption; and only 0.42% had extreme resorption.
3. The teeth that presented more root resorption were, in decreasing order, the upper central incisors, the upper lateral incisors, the lower central incisors, and lastly, the lower lateral incisors. We would like to acknowledge Dr Luis Carlos de Mesquita Cabral for his kindness in permitting the use
of his patients’ data and CNPQ (Brazilian National Research Foundation) for its support.
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