Introduction
The objective of this study was to investigate the effects of dehiscence and fenestration on external apical root resorption (EARR) in maxillary incisors.
Methods
Seventy-eight patients were selected for this study. We set dehiscence, fenestration, sex, extraction, or nonextraction, tooth position, initial age, and duration of treatment as independent variables and EARR as the dependent variable. General statistical descriptions for these variables were made by mean, standard deviation and occurrence rates, etc. To make the data visualization and find more information, 2 heat maps were made. Generalized estimation equation analysis was performed to determine associations between EARR and independent variables.
Results
The occurrence rates of dehiscence and fenestration in maxillary incisors were 14.77% and 10.74%, respectively. The average value of EARR was 1.09 ± 0.87 mm in this study. Dehiscence, tooth position, extraction, initial age, and duration had significant correlations with EARR. The ratio of exponent B was 1:1.643 for dehiscence and nondehiscence, whereas fenestration and sex had no significant association with EARR.
Conclusions
The amount of EARR at maxillary incisors in patients with dehiscence before orthodontic treatment might be less than that in patients without it, and different incisors might have different contributions to it. However, the low value of exponent B for dehiscence meant that there might be other unknown factors that were involved in this study.
Highlights
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Dehiscence before treatment is associated with external apical root resorption (EARR).
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Tooth position, extraction, initial age, and duration also correlated with EARR.
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Fenestration and sex had no significant association with EARR.
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Other factors such as density or hardness might be involved.
Orthodontic tooth movement is a biologic remodeling process involving teeth roots, alveolar bones, and periodontal ligaments ; external apical root resorption (EARR) often occurs during orthodontic tooth movement. Most patients with mild EARR have no clinical symptoms throughout their lifetime; however, the roots shorten >4 mm in some patients with severe EARR, and this shortening can affect the life of the teeth.
EARR frequently occurs in maxillary incisors during orthodontic tooth movement. , At the same time, alveolar bones around these roots are remodeled (resorbed and regenerated) along with the directions of the tooth movements. Therefore, if there are defects in these alveolar bones before treatment, both resorption and regeneration processes might be affected. Our understanding of differences in the amount of EARR between patients with and without alveolar bone defects is uncertain.
One kind of alveolar bone defect results from diseases such as periodontitis, cyst, and tumor. The other kind of alveolar bone defects occurs under a healthy alveolar bone condition like dehiscence and fenestration, which are common and easy to be overlooked before orthodontic treatment. The lack of facial or lingual cortical plates, which results in exposing the cervical root surface and affecting the marginal bone, represents an alveolar bone defect called dehiscence. When there is still some bone in the cervical region, the defect is termed fenestration. Dehiscence and fenestration are weak structures of alveolar bone, and it is unclear that to what extent dehiscence or fenestration can shorten the lifetime of the teeth.
Dehiscence and fenestration cannot be found by conventional 2-dimensional (2D) x-ray films, such as periapical films, panoramic radiographs, and cephalographs. In recent years, cone-beam computed tomography (CBCT) has been widely used in dental clinical practice, which can detect dehiscence and fenestration with relative lower dose radiation and better image resolution. , , The amount of EARR was usually measured by periapical films before; recently, it was confirmed that the measurement of EARR by CBCT was more accurate and reliable than 2D x-ray films. Therefore, CBCT is a suitable examination tool to uncover the association between EARR and dehiscence or fenestration.
It was reported that several risk factors such as age, sex, extraction or nonextraction, duration of treatment, and classification of malocclusion might play a role in EARR alone or combination. In the present study, we hypothesized that dehiscence and fenestration had no correlations with EARR. To balance the factors between and within-subjects, a generalized estimation equation (GEE), a useful statistical method, was used to analyze them.
Material and methods
This retrospective study was approved by the Medical Ethics Committee of the School of Stomatology, China Medical University. All patients and their parents signed informed consent.
The specific reasons for which CBCTs were taken were as follows: intent to use orthodontic miniscrews, extraction of the third molars, alveolar bone defects, temporomandibular disorder, or suspected temporomandibular disorder and narrow airway and snore, etc. All patients and their parents signed informed consent.
The inclusion criteria were (1) patients treated with labial fixed orthodontic appliances, (2) patients with well-developed roots in maxillary incisors, (3) complete patients’ data and CBCT data before and after treatment (Digital Imaging and Communications in Medicine format). The exclusion criteria were (1) patients with impacted maxillary incisors before or during orthodontic treatment, (2) patients treated with functional appliance, (3) obvious root resorption of maxillary incisors before treatment, (4) patients with periodontitis before treatment.
The sample size was calculated according to an alpha significance level of 5% and a beta of 20% to achieve 80% power by G∗Power (version 3.1.9.2; Franz Faul University, Kiel, Germany) with the effect size set by 0.35. The minimum sample size was 46 patients.
Our initial sample comprised 78 patients (19 males, 59 females) with an average initial age of 14.80 ± 4.05 from 2015 to 2019 ( Table I ). The sagittal skeletal pattern was classified: Class I malocclusion (1° < ANB < 5°), Class II malocclusion (ANB ≥5°), and Class III malocclusion (ANB ≤1°). Thirty-three patients (42.31%) were classified with Class I malocclusion, 30 patients (38.46%) were classified with Class II malocclusion, and 15 patients (19.23%) were classified with Class III malocclusion before treatment, respectively.
| Variables | N | Mean ± standard deviation |
|---|---|---|
| Initial age, y | 78 | 14.80 ± 4.05 |
| Duration of treatment, mo | 78 | 30.46 ± 5.78 |
To measure the length of the EARR, the Digital Imaging and Communications in Medicine files from CBCT (NewTom VG; Aperio Services, Verona, Italy) data were imported into Proplan (version 1.5; Materialise, Leuven, Belgium). CBCT data were acquired with an exposure time of 3.6 seconds at 3.80 mA and 110 kV, with a slice thickness of 0.25 mm and a field of view of 140 × 140 mm. CBCT images were resliced along the plane perpendicular to the long axis of the measured incisor root and adjusted in the reorganized multiplanar reformation view so that each of the orthogonal planes (transverse, coronal, and sagittal) was perpendicular to the long axis of the incisor. To obtain an even more precise measurement, we reconstructed the measured incisor to check if each of these 3 planes was precisely perpendicular to the long axis of the incisor in 3-dimensions. The root lengths of maxillary incisors were blindly measured on the reorganized sagittal plane before and after orthodontic treatment ( Fig 1 ). The values of EARR were calculated by the values of root lengths before treatment subtracting those after treatment.
We identified whether the incisors had dehiscence or fenestration by CBCT before treatment. The criterion of dehiscence is that distance between the cementoenamel junction and the alveolar bone level >2 mm occurs at 3 consecutive interfaces in CBCT ( Fig 2 ). The fenestration is that bone defect does not include an alveolar crest ( Fig 3 ). We obtained the binary data of dehiscence and fenestration as observed independent variables, respectively.
We collected tooth position, initial age, sex, extraction or nonextraction, and duration of treatment as another 5 independent variables in this study ( Tables I and II ).
| Variables | Subjects | N | % |
|---|---|---|---|
| Sex | Male | 19 | 24.36 |
| Female | 59 | 75.64 | |
| Extraction | Yes | 58 | 74.36 |
| No | 20 | 25.64 | |
| Dehiscence | Yes | 26 | 33.33 |
| No | 52 | 66.67 | |
| Fenestration | Yes | 18 | 23.08 |
| No | 60 | 76.92 |
Statistical analysis
Thirty-nine patients from all included patients were selected randomly and remeasured with an interval of 2 weeks. For dehiscence and fenestration, 2 orthodontists (C.C. and Y.X.) evaluated them twice, respectively. No difference was found in the presence of dehiscence and fenestration. Interobserver and intraobserver errors were assessed by kappa test, with the perfect agreement (1.0). For a continuous variable, 1 orthodontist (C.C.) performed all measurements twice. The intraobserver error was evaluated with the intraclass correlation coefficient (ICC) ( Table III ). In addition, system errors were calculated with t tests, and random errors were calculated with the method of moments estimator formula ( Table IV ).
| Parameter | ICC |
|---|---|
| Pretreatment root length | 0.991 |
| Posttreatment root length | 0.988 |
| EARR | 0.976 |
| Variable | First measurement, mean ± SD | Second measurement, mean ± SD | MME | P value |
|---|---|---|---|---|
| EARR (mm) | 1.00 ± 0.74 | 1.02 ± 0.73 | 0.11 | 0.25 |
General statistical descriptions for this sample were made by mean, standard deviation and occurrence rates, etc. To make the data visualization and find more information, 2 heat maps were made by HemI (version 1.0.3.7; http://hemi.biocuckoo.org/ ).
GEE analysis was performed to determine associations between EARR and dehiscence, fenestration, tooth position, initial age, sex, extraction or nonextraction, and duration of treatment. Statistical significance was set at P <0.05. The data were processed with SPSS software (version 20.0; IBM, Armonk, NY).
Results
There were 14 maxillary incisors excluded in this study, the 6 were missing before patients’ first visits to our office, and the other 8 were treated with root canal therapy. Therefore, 298 teeth were included in this study.
There were clinical characteristics of included patients for numerical variables (initial age [years] and duration of treatment [months]), binary variables (sex, extraction, dehiscence, and fenestration) ( Tables I and II ).
Intraobserver agreement was reliable according to ICC. The ICCs between the first and second measurements for EARR were >0.9 ( Table III ). No statistically significant systematic error was detected, and the random error was within an acceptable level ( Table IV ).
The mean lengths of EARR were 0.98 ± 0.87 mm, 1.01 ± 0.78 mm and 0.99 ± 0.82 mm in maxillary left, right, and all central incisors, and 1.16 ± 1.00 mm, 1.22 ± 0.82 mm, and 1.19 ± 0.91 mm in maxillary left, right, and all lateral incisors, respectively ( Table V ).
| Maxillary incisor | n | Amount of EARR (mm), mean ± standard deviation | Total (mm), mean ± standard deviation |
|---|---|---|---|
| Left central | 74 | 0.98 ± 0.87 | 0.99 ± 0.82 |
| Right central | 75 | 1.01 ± 0.78 | |
| Left lateral | 74 | 1.16 ± 1.00 | 1.19 ± 0.91 |
| Right lateral | 75 | 1.22 ± 0.82 | |
| Total | 298 | 1.09 ± 0.87 | |
The occurrence rates of dehiscence and fenestration in maxillary incisors before orthodontic treatment were 14.77% and 10.74%, respectively. Both occurrence rates were more in lateral incisors than those in central incisors. The occurrence rates of dehiscence and fenestration were 6.04% and 2.01% in central incisors, respectively, and 23.49% and 19.46% in lateral incisors, respectively ( Table VI ).
| Maxillary incisor | n | Dehiscence, % (n) | Total dehiscence, % (n) | Fenestration, % (n) | Total fenestration, % (n) |
|---|---|---|---|---|---|
| Left central | 74 | 6.76 (5) | 6.04 (9) | 1.35 (1) | 2.01 (3) |
| Right central | 75 | 5.33 (4) | 2.67 (2) | ||
| Left lateral | 74 | 24.32 (18) | 23.49 (35) | 17.57 (13) | 19.46 (29) |
| Right lateral | 75 | 22.67 (17) | 21.33 (16) | ||
| Total | 298 | 14.77 (44) | 10.74 (32) | ||
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