External Apical Root Resorption in Patients Treated with Passive Self-Ligating System

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External Apical Root Resorption in Patients
Treated with Passive Self-Ligating System
Masaru Yamaguchi1 and Yasuhiro Tanimoto2
1Department of Orthodontics,
2Dental Biomaterials,
Nihon University School of Dentistry at Matsudo
Japan
1. Introduction
External apical root resorption (EARR) is an unavoidable pathologic consequence of
orthodontic tooth movement. It can be defined as an iatrogenic disorder that unpredictably
occurs after orthodontic treatment, whereby the resorbed apical root portion is replaced
with normal bone. EARR is a sterile inflammatory process that is extremely complex and
involves various disparate components, including mechanical forces, tooth roots, bone, cells,
surrounding matrix, and certain known biologic messengers (Krishnan & Davidovitch, 2006;
Meikle, 2006). In the relationship between EARR and inflammatory cytokines, Zhang et al.
(2003) indicated that interleukin (IL)-1 and tumour necrosis factor (TNF)-alpha are
important for the induction and the further processing of mechanically-induced root
resorption in the rat. Receptor activator of nuclear factor κB ligand (RANKL) is a cytokine
that belongs to the TNF family and is essential for the induction of osteoclastogenesis.
Osteoblasts and bone marrow stromal cells produce this cytokine, and its signals are
transduced by the specific receptor RANK, which is localized on the cell surface of
osteoclast progenitors. The RANKL/RANK system has been suggested to play an integral
role in osteoclast activation during orthodontic tooth movement. Shiotani et al. (2001)
observed RANKL in osteoblasts, osteocytes, fibroblasts, and osteoclasts during the
application of orthodontic forces. The RANKL/RANK system may regulate the natural
process of root resorption in deciduous primary teeth (Lossdörfer et al., 2002). Therefore,
these inflammatory cytokines contribute to alveolar bone remodeling and to resorption
during orthodontic tooth movement and EARR.
The wire friction influences the forces acting in a continuous arch system. Damon (2006a)
suggested that the nearly friction-free system, using the self-ligation brackets and high-tech
wires, may not cause periodontal problems, including alveolar bone loss. Other studies
reported that static friction measured in vitro is much less with a passive self-ligating
system than with any other type of fixed appliance (Berger, 1990; Sims et al., 1993). The
friction force disturb orthodontic tooth movement, thus, it is expected that influence for the
periodontal tissue is different from the self-ligating brackets in the conventional appliances.
We reported that GCF levels of substance P (SP), one of neuropeptides which cause the local
inflammation, SP for the passive self-ligating system sites were significantly lower than for
the teeth with conventional brackets at 24 hours (Yamaguchi et al., 2009). Thus, the passive

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self-ligating system is useful to reduce the inflammation and pain resulting from
orthodontic forces.
The purposes of this study were to measure EARR and the levels of RANKL in GCF in
patients undergoing with self-ligating brackets compared with conventional appliances, and
to compare them.
2. Materials and methods
2.1 Subject selection
Forty subjects were selected from patients seeking treatment in the Department of
Orthodontics at the Nihon University School of Dentistry at Matsudo. Forty orthodontic
patients (9 males, 31 females, mean age of 18.5 ± 4.6 years) were enrolled in the study, after
meeting the following criteria: (1) good general health; (2) lack of antibiotic therapy during
the previous 6 months; (3) absence of anti-inflammatory drug administration in the month
preceding the study; (4) healthy periodontal tissues with generalized probing depths ≦3
mm and no radiographic evidence of periodontal bone loss. Informed consent from the
subjects was obtained after an explanation of the study protocol, which was reviewed by the
ethic committee of Nihon University School of Dentistry at Matsudo (#10-019).
Two groups were set up, one ‘conventional bracket’ (CB) and another ‘self-ligation bracket’
(SL) groups. Twenty patients (4 males, 16 females) were treated with self-ligating brackets
(Damon 3; Ormco, Japan, Tokyo, Japan). A matched control group of 20 patients (5 males, 15
females) was selected from the same registry and treated with the conventional brackets
(.022-inch slot; Ormco. These controls were matched with the group for age, sex, and ANB,
overjet, and overbite values before orthodontic treatment (T1).
The selection criteria for the subjects were the following.
1.
Class I crowded malocclusion.
2.
Four premolar extractions.
3.
Excellent quality records.
4.
Only patients with no history or evidence of tooth injury or wear, as shown on the
charts and diagnostic records, were included.
2.2 Measurement of EARR and tooth position
To record the above parameters, the following measurements and evaluations were
executed.
Tooth length: Tooth length of the maxillary central incisor at T1 and T2 was measured on
the cephalogras from the incisal edge to the apex. When a difference in the length of the 2
adjacent maxillary central incisors was evident, the shorter root length was recorded.
Baseline measurements of ANB angle, overjet (along the occlusal line), and overbite
(perpendicular to the occlusal line) at T1 were made on the cephalograms.
Measurement of root length (EARR) and tooth position were performed according to the
method of Brin and Bollen (2011).
Change in root length (EARR) of the maxillary central incisor was record as the difference
between tooth lengths from T1 to T2.
Maxillary incisor movements were measured as the following. (1) The axial inclination of
the maxillary central incisor to SN (1/SN) between T1 and T2. (2) The vertical and
horizontal distances that the maxillary central incisor root was moved during orthodontic
treatment (Table 1).

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Table 1. Descriptive parameters of the 2 groups at T1 (± SD)
2.3 GCF collection
GCF was collected from the mesial and distal sides of the upper central and lateral incisors.
GCF sampling was performed using the method of Yamaguchi et al. (2006a), and collected
at before (T1) and after (T2) orthodontic treatment. The tooth was gently washed with water,
and then the sites under study were isolated with cotton rolls (to minimize saliva
contamination) and gently dried with an air syringe. Paper strips (Periopaper, Harco,
Tustin, CA, USA) were carefully inserted 1 mm into the gingival crevice and allowed to
remain there for 1 minute, after which a second strip was placed at the same site. Care was
taken to avoid mechanical injury. The contents were eluted out into 1x phosphate buffer
saline (PBS) containing 0.1mM phenylmethylsulphonyfluoride and stored at –80°C until
further processing (Fig. 1).


Fig. 1. GCF was collected from the mesial and distal sides of the upper central and lateral
incisors.

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2.4 Enzyme immunoassay
The s of RANKL and OPG level were measured in duplicate using a commercial ELISA kit
(Quantikine, R&D Systems, Inc., Minneapolis, MN, USA), with the results expressed as
pg/µg of total protein in the GCF.
2.5 Statistical methods
Statistical analysis among the groups was performed using one-way ANOVA and Scheffe
test to evaluate the statistical difference between each pair of groups.
3. Results
3.1 Measurement of EARR and tooth position
The 2 groups were matched for sex (P = 0.505) and chronologic age at T1 (P = 0.643). Good
agreement was also found for the ANB angle (P = 0.544), overjet (P = 0.478) and overbite (P
= 0.377) at T1. The tooth lengths at T1 in both groups were similar: 26.8 ±1.6 in the CB group
and 27.0 ±1.7 in the SL group (P = 0.6312) (Table 1).
Table 2 showed that the duration of treatment was not significant between the CB group
and the SL group (P = 0.891).In both groups, the lengths were reduced at T2 (Table 2): 24.6
mm ± 2.0 in the CB group and 26.2 mm ±1.5 in the SL group. Tooth lengths in the 2 groups
were statistically different at T2 (P = 0.05).


Table 2. Comparison of changes (± SD) during mechanotherapy (T1-T2) in EARR and tooth
position in the Conventional bracket and Self-ligation bracket groups (absolute values in
parentheses)
The mean amount of root resorption of the maxillary central incisor measured on the lateral
cephalogram was significantly greater in the CB group than the SL group at T2. This mean
difference in EARR between the groups did reach statistical significance.

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In Table 2, the axial movements of the central incisor—vertical and horizontal apical
movements—are presented.
The 1/SN change between T1 and T2 indicated an increase in the axial inclination in the CB
and SL groups (about 6°). Change in the axial inclination of the maxillary central incisor
(1/SN) was not significant difference between the CB group and the SL group (P = 0.901).
The amounts of vertical movement of the apex were also not significant difference in both
groups (P = 0.883). For the horizontal movements of the apex, similar (P = 0.750) amounts of
distal palatal root movement were observed in both groups (Table 2).
3.2 GCF study
GCF volume has been correlated with inflammatory state, however, there was no
statistically significant difference in the mean as for the volume of GCF between CB group
and SL group at T1 (CB: 0.41 ± 0.06 μl, SL: 0.39 ± 0.09 μl ) and T2 (CB:0.40 ± 0.07 μl, SL: 0.42 ±
0.05 μl ), respectively. In all of the patients, probing depths remained less than 2 mm and
gingival health was excellent, with no gingival bleeding.
At T1, there were no significant differences in the mean RANKL value between the CB and
the SL. However, the mean RANKL value in the CB was significantly higher in the SL at T2
(p<0.05). While, the mean OPG values for the CB and SL were not significantly difference
between T1 and T2. (Fig. 2)


Fig. 2. Changes in RANKL and OPG concentrations in the GCF samples from the
conventional brackets (CB) and self-ligating bracket (SL). Significant differences in
concentrations between T1 and T2 are indicated with an * (p < 0.05) , and between CB and
SL with an †(p < 0.05), correspondingly.
4. Discussion
In this study, the mean amount of root resorption of the maxillary central incisor measured
on the lateral cephalogram was significantly greater in the CB group than the SL group at T2
(Table 2).
Considering to risk factor of EARR, according to Weltman et al. (2010) it are divided into the
treatment-related and patient-related factors. Orthodontic treatment-related risk factors