Abstract
INTRODUCTION:
The purpose of this study was to evaluate and compare the incidence of orthodontically induced inflammatory root resorption (OIIRR) after en masse maxillary incisors intrusion and retraction with controlled tipping versus bodily movement using cone beam computed tomography (CBCT).
MATERIAL AND METHODS:
This study is a retrospective study performed on CBCT scans of 36 adult females who had their maxillary first premolars extracted followed by en masse anterior retraction and intrusion using labial biocreative therapy type II. Subjects were divided into two groups of 18 subjects each based on the type of tooth movement required during en masse retraction: Group I; the controlled tipping group, and Group II; the bodily movement group. The amount of intrusion, crown and root retraction, change in incisor inclination, and difference in tooth length was measured from the CBCT scans. Independent t tests were used to compare the measurements between the two groups. Pearson rank correlation analysis was applied to identify the relationship between the mean dental changes and the mean changes in tooth length for all four upper incisors.
RESULTS:
OIIRR was found in all four maxillary incisors in both groups. No significant differences were found between the two groups. OIIRR was positively correlated to the amount of root apex retraction and negatively correlated to the change in incisor inclination.
CONCLUSIONS:
Anterior retraction and intrusion lead to obvious root resorption affecting all maxillary incisors. No significant differences were found between the two groups. Careful clinical monitoring is needed for patients requiring anterior retraction with intrusion with maximum anchorage.
Keywords: Anterior intrusion, anterior retraction, biocreative therapy, CBCT, root resorption
Introduction
Orthodontically induced inflammatory root resorption (OIIRR) is an unpleasant iatrogenic effect encountered following orthodontic tooth movement. It is defined as a sterile inflammatory process that is complex and multifactorial and characterized by permanent shortening of the tooth root.[1] OIIRR is believed to occur following destruction of the protective cell layer covering the tooth root as a result of the application of heavy orthodontic forces.[2] Almost 90% of orthodontic patients will experience OIIRR with the maxillary incisors being the most commonly affected teeth.[1,3] In most cases, OIIRR is mild and insignificant with a mean shortening of about 1.5 mm.[3] However, in about 5% of adults and 2% of adolescents, more than 5 mm shortening of the roots can be seen.[4] Many factors were reported to predispose the patient to OIIRR including abnormal root shape,[5] previously traumatized teeth,[6] excessive orthodontic forces,[7] prolonged duration of orthodontic treatment,[8] and contact of root apex with the cortical plates of bone.[9]
Anterior retraction following premolar extraction is a common treatment modality to treat dentoalveolar protrusion. This requires careful consideration of the applied biomechanical system to achieve torque control and the required type of tooth movement during retraction (whether by controlled tipping or bodily movement).[10] The amount of incisor retraction, the required torque control, and the often-required simultaneous intrusion predispose the patient to OIIRR.[11,12] Handelman described the palatal cortical plates as orthodontic walls[13] and failure to pay attention to the available alveolar housing during retraction carries the risk of excessive apex lingual movement and eventually contact with the cortical plate, which again can predispose the patient to OIIRR.[9]
Biocreative therapy is a treatment approach that allows targeted tooth movement with control of torque and anchorage during retraction.[14] The use of an overlay intrusive arch allows simultaneous retraction and intrusion. Simultaneous anterior retraction and intrusion were reported to cause the greatest root resorption among all dental movements.[15] Liou et al.[16] investigated apical root resorption of maxillary incisors after en masse retraction and intrusion using skeletal anchorage. They concluded that the use of mini-screws allow for more anterior retraction but also prolongs the orthodontic treatment duration and can predispose the patients to more apical root resorption. Similarly, Martins et al.[17] evaluated the influence of intrusion mechanics combined with anterior retraction on OIIRR of maxillary incisors. They found significantly more apical root resorption occurring in the group where simultaneous anterior retraction and intrusion were carried out compared with retraction alone.
However, to our knowledge, no study has reported on the incidence of OIIRR following anterior retraction and intrusion using the biocreative therapy technique. Furthermore, in a systematic review, Weltman et al.[3] provided evidence that the use of heavy forces in comprehensive orthodontic treatment can increase the risk of OIIRR. However, none of the included studies compared between the controlled tipping versus bodily movement in anterior retraction in extraction cases. Costopoulos et al.[15] reported the most influential forces causing OIIRR to be the application of intrusive forces together with palatal root torque, and thus biocreative technique for anterior retraction can pose a risk of OIIRR.
The purpose of this retrospective study was to evaluate and compare the incidence of OIIRR after maxillary incisors intrusion and retraction with controlled tipping versus bodily movement using the biocreative therapy technique.
Material and Methods
This study was approved by the Ethical Committee of the Faculty of Dentistry, Ain Shams University (Approval No.: FDASU-RecIR102211). Sample size was calculated based on the study by de Freitas et al.[18] For detection of a mean difference of 0.5 between the groups, at a significance level of 5% and power of 80%, a sample size of minimum of 12 subjects in each group would be required. Accordingly, the records for 36 adult females who had their maxillary first premolars extracted followed by anterior retraction and intrusion using labial biocreative therapy were selected from the University database. All subjects had maxillary dentoalveolar protrusion, minimal crowding in the upper arch (<4 mm) and had cone beam computed tomography (CBCT) scans available before retraction (T0) and 3 months after retraction (T1). The mean age of the patients was 24.4 + 1.8 years. Subjects were divided into two groups of 18 subjects each based on the type of tooth movement required during retraction: Group I; controlled tipping, and Group II; bodily movement.
Labial biocreative therapy type II was used for anterior retraction and intrusion following first premolar extraction.[14] Maximum anchorage was obtained by using mini-implants (AbsoAnchor, 8 mm length. 1.6 mm diameter) placed inter-radicularly between the second premolar and first molar [Figure 1]. Retraction time was calculated for both groups. All subjects had CBCT scans immediately before and 3 months after retraction with the parameters set to 120 kVp at 5 mA for a total scan time of 8.9 s. Using InVivo5 software (Anatomage, San Jose, CA, USA), the following measurements were blindly performed:
Figure 1.
Final set up for anterior retraction and intrusion. (a and b) 7 mm hook was used for controlled tipping movement; (c and d) 10 mm hook was used for bodily retraction
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Measurements of anterior retraction and intrusion
A customized CBCT analysis was used to calculate the amount of crown retraction and root apex lingual movement, amount of vertical movement (intrusion), and the change in labiolingual inclination of the incisors [Table 1].
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Measurements of apical root resorption
A fully reconstructed three-dimensional image with sagittal, coronal, and axial slices was generated. The volume was oriented so that the axial slice is perpendicular to the long axis of the incisor, and the coronal and sagittal slices were rotated so that measurements of tooth length can be made parallel to the long axis of the incisor for accurate and consistent measurement [Figure 2a].
Table 1.
Reference lines and measurements used in the CBCT analysis of anterior retraction and intrusion
| Reference line/measurement | Definition |
|---|---|
| Long axis of the incisor | Line connecting incisal edge and root apex |
| Frankfort horizontal plane | Plane defined by 3 landmarks: right orbitale, right porion and left porion. |
| Midsagittal plane | Plane defined by 3 landmarks: nasion, anterior nasal spine, and basion. |
| S-vertical plane | Plane through Sella and perpendicular to the Frankfort horizontal plane and midsagittal planes. |
| Palatal plane | Plane defined by two landmarks: ANS and PNS points and perpendicular on the midsagittal plane. |
| Coronal retraction | Linear perpendicular distance from incisal edge to to S-vertical plane. |
| Root retraction | Linear perpendicular distance from root apex to S-vertical plane. |
| Amount of intrusion | Linear perpendicular distance from incisal edge to palatal plane |
| Labio-lingual inclination | The angle formed between the long axis of the incisor and the palatal plane. |
Figure 2.
(a) Orienting the volume so that the axial slice is perpendicular to the long axis of the incisor, and the coronal and sagittal slices were rotated so that measurements of tooth length can be made parallel to the long axis of the incisor for accurate and consistent measurement; The tooth length was measured as the linear distance between the incisal edge and root apex, measured parallel to the long axis of the tooth on the sagittal slice (b) and was confirmed on the coronal slice (c)
Tooth length was measured as the linear distance between the incisal edge and root apex, parallel to the long axis of the tooth on the sagittal slice, and was confirmed on the coronal slice [Figure 2b and c]. Apical root resorption was calculated as the difference in tooth length (T1-T0), [Figures 3 and 4]. Percentage of apical root shortening was calculated as the difference in tooth length (T1-T0) divided by the original root length (T0).
Figure 3.
Measurement of tooth length in controlled tipping group. (a) before retraction; (b) after retraction
Figure 4.
Measurement of tooth length in bodily retraction group. (a) before retraction; (b) after retraction
Severity of apical root resorption was calculated by ranking it into 5 degrees, according to the method of Malmgren et al.[6] Every maxillary incisor was given a score, with a total of 144 scores (72/group).
Error measurement
All CBCT measurements were performed by one trained orthodontist. To assess measurement error and reliability, 15 patients were randomly selected, and measurements were repeated after 4 weeks. Method error was assessed using the Dahlberg formula.[19] The reliability of the data was evaluated by calculating the intraclass correlation coefficient. Dahlberg's error was less than 0.5 mm for each parameter. The intraclass correlation coefficients for all measurements were higher than 0.90.
Statistical analysis
The Shapiro–Wilk test was used to test for normality and demonstrated that the variables were normally distributed. Paired t tests were used to compare the measurements of anterior retraction and intrusion within each group and between the two groups. Differences in tooth length measurements within each group were compared using paired t tests. Independent samples t tests were used to compare the difference in dental and tooth length measurements between the two groups. Pearson rank correlation analysis was applied to identify the relationship between the mean dental changes and the mean changes in tooth length for all four upper incisors.
Results
Measurements of anterior retraction
The mean amount of crown and root apex retraction, amount of intrusion, as well as the change in faciolingual inclination within each group are shown in Table 2. In both groups, the crownas well as the root apex were significantly moved in a lingual direction, with significantly more root apex retraction in the bodily movement group. In group 1, the incisors were retracted with a controlled tipping movement with a significant change in incisor inclination (10.26˚ + 4.7˚ for the central incisors, 10.49˚ +5.16˚ for the lateral incisors), whereas in group 2, the incisors were retracted with mostly translational movement with less than 5˚ change in faciolingual inclination after retraction (3.41˚ +2.33˚ for the central incisors, 4.15˚ +2.28˚ for the lateral incisors). In both groups, significant amount of intrusion occurred during retraction, with significantly more intrusion in the controlled tipping group [Table 2].
Table 2.
Pre- (T0) and post- (T1) retraction dental measurements and comparison of changes after retraction in each group and between the two groups
| Incisor | Variable | Group | T0 | T1 | P a | Change | Diff | P b |
|---|---|---|---|---|---|---|---|---|
| Central incisors | Crown retraction | Group I | 86.30 (4.09) | 79.29 (4.36) | 0.00000* | −7.01 (1.19) | 1.35 (0.55) | 0.02873* |
| Group II | 83.50 (8.21) | 77.85 (7.92) | 0.00000* | −5.65 (1.02) | ||||
| Root apex retraction | Group I | 73.37 (3.77) | 71.04 (4.07) | 0.00025* | −2.33 (0.97) | 2.72 (0.85) | 0.04432* | |
| Group II | 71.70 (6.71) | 66.65 (5.30) | 0.00001* | −5.05 (1.79) | ||||
| Intrusion | Group I | 27.61 (3.42) | 26.16 (3.47) | 0.00510* | −1.45 (1.02) | -0.59 (0.21) | 0.04176* | |
| Group II | 28.23 (4.32) | 27.07 (4.26) | 0.00012* | −1.16 (0.54) | ||||
| Faciolingual Inclination | Group I | 120.88 (6.11) | 110.62 (6.69) | 0.00046* | −10.26 (4.70) | 6.85 (1.85) | 0.00703* | |
| Group II | 118.21 (3.58) | 114.8 (4.09) | 0.00105* | −3.41 (2.33) | ||||
| Lateral incisors | Crown retraction | Group I | 81.45 (3.70) | 74.64 (4.26) | 0.00000* | −6.81 (1.36) | 0.95 (0.59) | 0.12691 |
| Group II | 80.15 (7.92) | 74.29 (7.6) | 0.00000* | −5.86 (0.94) | ||||
| Root apex retraction | Group I | 71.03 (4.48) | 68.76 (4.50) | 0.00012* | −2.27 (0.84) | 2.94 (0.75) | 0.041713* | |
| Group II | 68.71 (6.23) | 63.5 (6.54) | 0.00042* | −5.21 (1.30) | ||||
| Intrusion | Group I | 27.05 (2.75) | 25.13 (2.47) | 0.00025* | −1.92 (0.80) | 0.92 (0.35) | 0.01940* | |
| Group II | 27.27 (4.09) | 26.26 (3.94) | 0.00172* | −1.01 (0.58) | ||||
| Faciolingual Inclination | Group I | 117.90 (8.96) | 107.41 (7.25) | 0.00070* | −10.49 (5.16) | 6.34 (2.16) | 0.04453* | |
| Group II | 121.45 (3.66) | 117.29 (5.64) | 0.00111* | −4.15 (2.28) |
Values are presented as mean (standard deviation). Group I, controlled tipping group; Group II, bodily movement group; Diff, the difference between the two groups; a: Comparison of pretreatment and posttreatment measurements within groups; and b, comparison between groups; significance level was *P < 0.05.
Measurements of apical root resorption
A statistically significant decrease in tooth length was found in both groups (P < 0.05, Table 3) indicating apical root resorption in all four maxillary incisors. The mean amount of apical root resorption ranged from 0.73 to 1.76 mm, with an average reduction in tooth length ranging from 7.02% to 16.92%. However, no significant difference was found between the two groups.
Table 3.
Pre- (T0) and post- (T1) retraction measurements of tooth length and comparison of changes after retraction within each group and between the two groups
| Group | Group I |
Group II |
Mean Diff bet the groups | 95% Confidence interval of the Difference |
P-value | |||
|---|---|---|---|---|---|---|---|---|
| Tooth | Mean difference (T1-T0) | P-value | Mean difference (T1-T0) | P-value | Lower | Upper | ||
| Right central | 8.94+2.79 (%) | 0.00964* | 7.02+1.25 (%) | 0.04381* | 0.20 | -0.74 | 1.14 | 0.65177 |
| -0.93+0.29 (mm) | -0.73+0.13 (mm) | |||||||
| Left central | 8.37+0.87 (%) | 0.03259* | 8.55+2.5 (%) | 0.03562* | 0.18 | -0.93 | 1.28 | 0.73489 |
| -0.87+0.09 (mm) | -0.89+0.26 (mm) | |||||||
| Right lateral | 7.88+1.25 (%) | 0.02508* | 9.61+0.19 (%) | 0.04343* | -0.18 | -1.25 | 0.90 | 0.73080 |
| -0.82+0.13 (mm) | -1.00+0.02 (mm) | |||||||
| Left lateral | 12.40+3.65 (%) | 0.01127* | 16.92+5.19 (%) | 0.01230* | -0.47 | -1.81 | 0.87 | 0.46502 |
| -1.29+0.38 (mm) | -1.76+0.54 (mm) | |||||||
*Significant at P<0.05. Group I, controlled tipping group; Group II, bodily movement group
Pearson rank correlation analysis showed that apical root resorption was not correlated to the amount of crown retraction or the amount of intrusion [Table 4]. However, it was positively correlated to the amount of root apex retraction (for the central incisors, r = 0.39; and for the lateral incisors, r = 0.43) and negatively correlated to the change in incisor inclination (for the central incisors, r = −0.251; and for the lateral incisors, r = −0.314).
Table 4.
Correlation between apical root resorption and possible predisposing factors in groups I and II combined
| Apical root resorption |
||
|---|---|---|
| Central incisors | Lateral incisors | |
| Retraction at incisor tip | ||
| r | –0.09 | 0.015 |
| P | 0.461 | 0.95598 |
| Retraction at root apex | ||
| r | 0.39 | 0.43 |
| P | 0.013* | 0.043* |
| Intrusion | ||
| r | 0.17 | 0.352 |
| P | 0.172 | 0.642 |
| Change of incisor inclination | ||
| r | –0.251 | –0.314 |
| P | 0.046* | 0.015* |
*Significant at P<0.05. Group I, controlled tipping group; Group II, bodily movement group
The distribution of the severity of apical root resorption, scored according to the method described by Malmgren et al.[6] showed that group I, controlled tipping group, had 11.11% of the teeth with score 1, 63.89% of the teeth with score 2, whereas the remaining 25% were classified with score 3. Group II, the bodily movement group, had 9.72% of the teeth with score 1, 61.11% of the teeth with score 2, and 29.17% with score 3. None of the teeth in either group were given the score 0 or 4 [Table 5].
Table 5.
Distribution of teeth with apical root resorption according to the scoring system of Malmgren et al. (1982)
| Score | Group I (n=72) |
Group II (n=72) |
Total (n=144) | ||
|---|---|---|---|---|---|
| n | % | n | % | ||
| 0 | 0 | 0.00 | 0 | 0.00 | 0 |
| 1 | 8 | 11.11 | 7 | 9.72 | 15 |
| 2 | 46 | 63.89 | 44 | 61.11 | 90 |
| 3 | 18 | 25.0 | 21 | 29.17 | 39 |
| 4 | 0 | 0.00 | 0 | 0.00 | 0 |
Group I, controlled tipping group; Group II, bodily movement group
Measurement of the duration of anterior retraction
The average duration of retraction was 12.5 + 2.24 months for Group I and 12.85 + 3.12 months for Group II [Table 6]. No statistically significant differences were noted between the two groups.
Table 6.
Comparison of the duration of retraction between the two groups
| Measurement | Group | Mean±SD | Mean Diff | P |
|---|---|---|---|---|
| Duration of retraction (months) | I | 12.5+2.24 | 0.3 | 0.80312 |
| II | 12.85+3.12 |
Group I, controlled tipping group; Group II, bodily movement group; SD, Standard deviation; Mean Diff, mean difference
Discussion
The use of biocreative therapy offers many advantages regarding the biomechanical considerations needed for anterior retraction and intrusion.[14] Skeletal anchorage offers maximum anchorage, which is often needed in dentoalveolar protrusion cases. In addition, the applied force system enables accurate vertical and torque control to achieve targeted tooth movement. However, biological considerations merit special attention. Torque control together with the intrusion movement has been previously reported to be a risk factor for OIIRR.[16] The purpose of this study was to evaluate and compare the extent and severity of OIIRR following en-masse anterior intrusion and retraction with controlled tipping versus bodily movement, using mini-implants for anchorage in bimaxillary protrusion patients.
Both metric evaluation as well as the structural method described by Malmgren[6] were used in this study to thoroughly investigate OIIRR after en-masse anterior intrusion and retraction. CBCT scans were used which was reported to be an accurate tool for evaluation of OIIRR, with a discrepancy of 0.3 mm compared with the intraoral periapical radiograph, which was shown to underestimate root resorption by 2.6 mm on the average.[20] Tooth length was calculated from the incisal edge to root apex rather than calculating the root length from the cemento-enamel junction (CEJ) to root apex. This was done to avoid errors due to difficulty in accurately estimating the CEJ due to partial volume averaging in the CBCT, and also because of possible error that may be introduced because of different levels of CEJ between the labial and palatal side.
In our study, the mean root resorption ranged from 0.73 mm to 0.93 mm for the central incisor and 0.82 mm to 1.76 for the lateral incisors. This is close to the findings of Gupta et al.,[21] who reported root resorption of 1.79 + 0.71 mm for the lateral incisor, and 1.57 + 0.88 mm for the central incisor. Similarly, Artun et al.[22] found root shortening of 1.17 + 1.15 mm in lateral incisor and 1.01 + 1.05 mm in central incisor following anterior retraction. Barros et al.[23] found no significant difference between the severity of OIIRR when the incisors were retracted with or without skeletal anchorage. Liou and Chang[16] found significant difference in apical root resorption with a mean difference of 0.4 mm between incisors retracted with and without mini-implants. This mild root resorption may not be clinically significant.
The distribution of OIIRR shows that none of the patients in either group had a score 0 or 4 for any incisor. This confirms that a certain degree of root resorption appears to occur with orthodontic treatment. On the other hand, it also shows that extreme root resorption is an uncommon occurrence following orthodontic treatment.
Comparison between the two types of tooth movement revealed no significant differences between the two groups. Pearson rank correlation analysis showed that apical root resorption was not correlated to the amount of crown retraction or the amount of intrusion [Table 4]. However, it was positively correlated to the amount of root apex retraction (for the central incisors, r = 0.39; and for the lateral incisors, r = 0.43) and negatively correlated to the change in incisor inclination (for the central incisors, r = -0.251; and for the lateral incisors, r = -0.314). According to Mukaka,[24] this can be interpreted as a weak correlation between OIIRR and the change in incisor inclination, and a moderate correlation between OIIRR and the amount of root apex retraction.
From a clinical perspective, it seems prudent that for bimaxillary protrusion cases requiring simultaneous anterior retraction and intrusion with maximum anchorage from mini-implants, particular attention should be paid to avoid the risk of excessive root resorption discovered at the end of the orthodontic treatment. Progress periapical radiographs need to be taken 6 months after the start of the retraction phase. The best available evidence suggests that orthodontic mechanics should be discontinued for at least 6 months in the event that root resorption was evident mid-treatment.[25] This allows a period of rest which may encourage root repair. Further retraction can be then done with light force, allowing longer intervals between activations and preferably avoiding intrusion movement. The current study suggests that the type of tooth movement during anterior retraction, whether by controlled tipping or bodily movement, didn't have a significant effect on the incidence of OIIRR. However, the dimensions of the bony alveolus merits special attention to avoid contact of the root apex with the palatal cortical plate of bone, which can further increase the risk of OIIRR.[9]
Conclusions
En-masse anterior retraction and intrusion leads to obvious root resorption affecting all maxillary incisors.
The null hypothesis was not rejected. There were no significant differences in root resorption when anterior retraction was performed with controlled tipping or bodily movement. However, retraction with bodily movement resulted in greater horizontal displacement of the incisor apex.
None of the teeth in either group had a score 0 or 4 for any incisor.
OIIRR was positively correlated to the amount of horizontal root retraction and negatively correlated to the change in incisor inclination. However, it was not correlated to the amount of crown retraction or intrusion.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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