Miniscrews for orthodontic anchorage

Prévia do material em texto

ORIGINAL ARTICLE
Miniscrews for orthodontic anchorage:
analysis of risk factors correlated with the
progressive susceptibility to failure
Yilin Xin,a Yeke Wu,b Chenjou Chen,a Chen Wang,a and Lixing Zhaoa
Chengdu, China
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Introduction: The phenomenon of orthodontic anchorage miniscrews loosening after being implanted several
times happens in daily clinical practice, and the reasons need to be traced. This study aimed to investigate the
underlying risk factors influencing the progressive susceptibility of orthodontic miniscrews to failure. Methods:
Overall, 889 miniscrews were successively inserted into 347 patients because some loosened or fell off once,
twice, or more before achieving their purposes. The number of miniscrew failures (ie, once, twice, or more) was
defined as progressive susceptibility to failure. The clinical indicators were assessed via univariate analysis, mul-
ticollinearity diagnosis, and Poisson log-linear regression model with stepwise calculation to screen out.
Results: The progressive susceptibility of miniscrews to failure was proved to be affected by the age of patients,
the onset of force application, site of placement, and appliance type. Age and onset of force application pre-
sented a negative relationship with susceptibility. Miniscrews inserted in the palatal region appeared to be
more stable than the forepart of the arch. In contrast, the retromaxillary and retromandibular areas obtained
the lowest stability. The patients with fixed appliances were more unlikely to suffer progressive failure than
removable appliances. In addition, the larger number of screws inserted in each patient, the greater probability
of failure. Conclusions: Younger people with removable appliances that miniscrews inserted in the retromax-
illary or retromandibular regions and earlier onsets of loading had a higher progressive susceptibility to loos-
ening. Meanwhile, the failure rate was elevated with the increasing number of screws per patient received.
(Am J Orthod Dentofacial Orthop 2022;-:e1-e11)
There is no doubt that anchorage control is thebedrock of successful orthodontic treatment.Orthodontists have always preferred and pursued
absolute anchorage because of its superior ability to
stay stationary when tooth movement happens. Because
Gainsforth and Higley1 used an absolute anchorage
device in dogs as pioneers for traction in 1945, plenty
of intraoral and extraoral appliances have been
Key Laboratory of Oral Diseases, and National Clinical Research Center for
iseases, and Department of Orthodontics, West China Hospital of Stoma-
y, Sichuan University, Chengdu, China.
rtment of Stomatology, Hospital of Chengdu University of Traditional Chi-
edicine, Chengdu, China.
thors have completed and submitted the ICMJE Form for Disclosure of Po-
l Conflicts of Interest, and none were reported.
ork was supported by grants from the National Nature Science Foundation
ina (Nos. 31670992 and 81973684).
ss correspondence to: Lixing Zhao, State Key Laboratory of Oral Diseases,
ational Clinical Research Center for Oral Diseases, and Department of Or-
ntics, West China Hospital of Stomatology, Sichuan University, No. 14,
Section, Renminnan Rd, Chengdu 610041, China; e-mail, zhaolixing@
u.cn.
itted, February 2022; revised and accepted, July 2022.
5406/$36.00
2 by the American Association of Orthodontists. All rights reserved.
//doi.org/10.1016/j.ajodo.2022.07.013
fabricated, which requires the patient’s compliance.
The anchorage control paradigm has shifted toward
temporary anchorage devices, including miniscrews
and miniplates.2 Although the success rates of minis-
crews are inferior to miniplates, they are still popular
with orthodontists owing to the advantages such as
easier implantation and removal on account of tiny vol-
ume, minimized tissue invasion from surgery, and the
fewest constraints of the optional placement locations
in the alveolar bone.3 In recent decades, extensive clin-
ical studies and systematic reviews have reported the
wide application of orthodontic miniscrews.
Unfortunately, the most undesirable weakness for
miniscrews is a lack of stability and the possibility of loos-
eningbefore accomplishing the clinical purpose. Although
it was reported that the success rate of miniscrews ex-
ceeded 90.00%, loosenings of miniscrews frequently
happened in daily clinical practice because of the enor-
mous amount of patients.4 When miniscrews are loose
or fall off, the alternative solutions are to change the treat-
ment plan or reinsert them, but they might repeatedly fail
with secondary or third reimplantation. Indeed, the risk
factors contributing to the instability of primarily inserted
e1
Delta:1_given name
Delta:1_surname
Delta:1_given name
Delta:1_surname
Delta:1_given name
mailto:zhaolixing@scu.edu.cn
mailto:zhaolixing@scu.edu.cn
https://doi.org/10.1016/j.ajodo.2022.07.013
Fig 1. Structure of 2 types of miniscrews from 2 brands.
VectorTAS (6.0 3 1.4 mm and 8.0 3 1.4 mm [gold] and
10.0 3 2.0 mm [blue]) and Microimplant Anchorage (rep-
resents all size miniscrews in this study [gray]).
e2 Xin et al
miniscrews were reported by previous research. Neverthe-
less, only a few studies focused on the second or third
insertion of miniscrews, and the conclusion of these
studies remains elusive because of contradictory find-
ings.5-8 Primary or secondary failure of miniscrews
might be attributed to incidental factors such as variable
bone quality of the insertion sites, improper surgical
procedures operated by inexperienced clinicians, and
periimplantitis caused by poor oral hygiene.9 In contrast,
for those repetitively occurring failures, theremight bepo-
tential intractable influential factors that could be traced.
However, it is still a vacancy in the research field regarding
the progressive susceptibility of consecutively failed
miniscrews to loosening or falling off.
Therefore, this study was designed to investigate the
underlying indicators affecting the outcomes of
miniscrews, including success and number of failures
(ie, once, twice, or more), which indicated the progres-
sive susceptibility to instability.
MATERIAL AND METHODS
The study design and ethical considerations were
approved by West China Hospital of Stomatology, Si-
chuan University (No. WCHSIRB-D-2021-502). The
medical history of subjects was obtained to analyze
retrospectively in this study. Subjects comprised in this
study belonged to 2 different experienced orthodontists
(L.Z. et al). Both of them had received professional and
strict training in the department of orthodontics, and
the operation was homogeneous. Written informed con-
sent was obtained from each patient or their parents
before surgery. Patients were enrolled in this study
with titanium alloy miniscrews (VectorTAS; Ormco,
Glendora, Calif; and Microimplant Anchorage; Dentos,
Daegu, South Korea) (Fig 1) of different sizes (6.0 3
1.4 mm, 8.0 3 1.4 mm, 10.0 3 2.0 mm; expressed as
length 3 diameter) inserted as orthodontic anchorage
from January 2017 to December 2020. The sample
who records with pathologic bone loss, history of any le-
sions or bone disorders affecting bone density, medica-
tions affecting bone density, or underlying cysts were
identified and excluded from this study.
Subjects belonged to 2 different experienced ortho-
dontists and were thus divided into 2 clinical groups to
record and compare the data. Before the surgery, cone-
beam computed tomography (CBCT) images were ob-
tained to analyze the anatomic features (root proximity,
cortical bone thickness [CBT], maxillary sinus, etc) and
determine the appropriate location for the miniscrews
insertion. The diameter and length of miniscrews were
selected to avoid injuring roots and minimize damage
to the surrounding tissues. After anesthetic infiltration,
all miniscrews were inserted by flapless surgery with the
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self-drilling procedure (Fig 2).After surgery, an antibiotic
(amoxicillin) was prescribed for 3 days with a dose of 1.0
g/d that should not exceed 4.0 g/d only comprised sub-
jects in group 1. In addition, 0.12% chlorhexidine
mouthwash was prescribed for a week for all subjects.
No indications of mobility on placement were detected.
All procedures in each group were performed by the
same orthodontist with an assistant. The force used for
the anchorage procedure would range from 50-200 g
of force. In addition, miniscrews were removed once sta-
bility was not achieved, and a novel miniscrew with the
same or a different size (with a change in diameter and
length) would be reinserted into the original position (be-
tween the same pair of teeth as the first insertion with the
mesial or distal position, height and insertion angle
slightly changed) or a different site after various periods.
In most patients, it tended to be reinserted consecutively
2-3 or even 4 times, except for some subjects changed to
other anchorages, such as face-bow or Nance holding
arch. Clinical success was defined as no clinically detect-
able mobility until they accomplished their clinical pur-
pose, and the miniscrews that did not meet these
criteria were considered failures.
To investigate the potential risk factors correlated
with the outcomes of the consecutively inserted
miniscrews, 21 indicators were included and divided
into 3 categories: host factors, miniscrew factors, and
management factors (Table I). Meanwhile, the total
number of miniscrews insertion per person and overall
failure rate (divide the total number of failed miniscrews
by the total number of inserted miniscrews for each
Journal of Orthodontics and Dentofacial Orthopedics
Fig 2. Miniscrew inserted into the retromaxillary area with the self-drilling procedure in a patient treated
with a removable appliance.
Xin et al e3
patient) were also gathered. It is worth noting that, in the
classification of indicators, the sagittal skeletal facial
pattern was expressed as ANB, representing the angle
of skeletal points A, B, and nasion. Meanwhile, the ver-
tical skeletal facial pattern was determined according to
SN-MP, defined as the angle of the mandibular plane to
the sella-nasion plane. Additional factors have been
listed in Table I and will not be discussed specifically
here. Radiographic data were assessed by cortical and
cancellous bone density, CBT, bone quantity, and dis-
tance between inserted site teeth roots via RadiAnt DI-
COM viewer (Medixant, Poznan, Poland) software.
After multiplanar reconstruction by RadiAnt DICOM
viewer and transverse plane were used to determine
the most suitable slice after alignment with reference
planes passing through the incisive foramen and poste-
rior nasal spine (Fig 3). In the maxilla, use the interradic-
ular site from the second premolar and first molar as an
example (located 6.0mm from the cementoenamel junc-
tion) to assess imaging data (Fig 4). In addition, use the
mandible located 5.0 mm from the cementoenamel
junction (Fig 5) to measure the variables we need (Figs
6 and 7).
Pearson’s c2 or Fisher exact test was selected to
calculate the underlying independent categorical vari-
ables. One-way analysis of variance or the Kruskal-
Wallis test was conducted for continuous variables.
Moreover, carrying out the normality test was indispens-
able to confirm the most appropriate statistical test
model. To eliminate the interference caused by multicol-
linearity among the 21 independent variables, as the
American Journal of Orthodontics and Dentofacial Orthoped
host factor was taken into account, we performed a mul-
ticollinearity diagnosis using Spearman correlation anal-
ysis. Parameters indicated to be significant by univariate
analysis were put into Poisson log-linear regression
model in a generalized estimating equation and calcu-
lated stepwise with the robust estimate. The dependent
variable in Poisson log-linear regression was the number
of miniscrew failures, including never failed (y 5 0),
failed once (y 5 1), and failed twice or more (y 5 2).
The incidence rate ratio (IRR) and 95% confidence inter-
val were calculated for the significant variables from the
final generalized estimating equation model. A P value
of #0.05 was considered statistically significant as
determined with SPSS (version 25.0; IBM Corp, Armonk,
NY).
RESULTS
Three hundred forty-seven patients (55 male, 292 fe-
male; aged 25.62 6 7.43 years) with a total of 889
miniscrews inserted as orthodontic anchorage were
included in this retrospective study lasting for 5 years.
Because children and teenagers were enrolled, we did
not incorporate smoking and systemic conditions into
the clinical variables. Overall, 77.62% (690 out of 889)
of the miniscrews did not become loose. In contrast,
17.10% (152 out of 889) of miniscrews failed once,
and 5.29% (47 out of 889) failed twice or more during
reimplantation. Because the normality test proved that
age and onset of force application data were not nor-
mally distributed, data were analyzed with the Kruskal-
Wallis test. One-way analysis of variance was used for
ics - 2022 � Vol - � Issue -
Table I. The list of 21 independent variables
Category Variable classification
Host factors
Gender Male, female
Age 10-59 y
Sagittal skeletal relationships (ANB) Class III (\2�), Class I (2�-4�), Class II (.4�)
Vertical skeletal pattern (SN-MP) Low angle (\29�), average angle (29�-40�), high angle (.40�)
Bone mineral density of cancellous bone, Hu 36.51-1184.74
Bone mineral density of cortical bone, Hu 268.40-1995.41
CBT, mm 0.48-6.02 mm
Bone quantity, mm 2.71-18.93 mm
Distance between inserted teeth roots, mm 0.74-8.25 mm
Oral hygiene Good, fair, poor
Miniscrew factors
Diameter, mm 1.4, 2.0
Length, mm 6.0, 8.0, 10.0
Different brands of miniscrews VectorTAS and Microimplant Anchorage
Management factors
The onset of force application, d 0-361
Clinical purpose Anterioposterior direction (retraction and molar distalization), vertical direction(intrusion
and protraction), combination (uprighting and combination among others)
Clinician groups 1 and 2
Site of placement Retromaxillary/retromandibular area, forepart area, palatal area,
Maxillary and mandibular arch of placement Maxilla and mandible
Left and right sides of the arch Left and right
Placement: soft-tissue type Attached gingiva and movable mucosa
Appliances type Fixed and removable
CBT, cortical bone thickness.
e4 Xin et al
continuous data with a normal distribution like the bone
mineral density of cancellous bone, the bone mineral
density of cortical bone, CBT, bone quantity, and dis-
tance between inserted teeth roots. The outcomes of
the univariate analysis are shown in Table II. A P value
of \0.05 was identified for the following variables:
age and oral hygiene of patients, brands of miniscrews,
the onset of force application, clinical groups, site of
placement, and appliance type. Eliminating the interfer-
ence among variables via the multicollinearity diagnosis
was analyzed by Spearman correlation analyses, and the
outcomes are shown in Figure 8.
Then variables were put into Poisson log-linear
regression model, suggesting that the age (IRR, 0.977;
P 5 0.021), the onset of force application (IRR, 0.995;
P 5 0.001), site of placement (IRR, 0.498; P 5 0.010),
and appliance type (IRR, 1.664; P5 0.005) were associ-
ated with incidence rate (Table III, Fig 9). According to
the Poisson log-linear regression model results, younger
patients were more vulnerable to loosening than older
patients. The later onset of force application for minis-
crews achieved relatively higher stability. Miniscrews in-
serted in the retromaxillary or retromandibular area were
more susceptible to mobility than the forepart area,
whereas the palatal area was the most favorable district
with the lowest failure rate. Patients with fixed
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orthodontic appliances are more unlikely to suffer
from progressive susceptibility of orthodontic minis-
crews to failure than removable appliances(Invisalign;
Align Technology, Santa Clara, Calif). In addition, the to-
tal number of miniscrews each subject received was posi-
tively correlated (correlation coefficient 5 0.549;
P \0.001) with the overall failure rate according to
the Spearman correlation analysis.
DISCUSSION
Based on our previous research, this study was inno-
vative in further exploring the correlations from the
potential clinical indicators, including host, miniscrews,
and management factors, to the progressive susceptibil-
ity of miniscrews to loosening for zero, once, and twice
or more.10-13 It demonstrated factors including age, site
of placement, the onset of force application, and
orthodontic appliance type correlated with the
progressive susceptibility for miniscrews to failure. In
contrast to other studies that focused only on the
success rate of primarily inserted miniscrews, we
classified the ending into 3 sequential grades: succeed,
failed once, and failed twice or more. The clinical
indicators significantly affected the outcome of
miniscrews, which allowed failure times to be traced.
The unstable and subjective parameters, such as
Journal of Orthodontics and Dentofacial Orthopedics
Fig 3. Reference planes via multiplanar reconstruction.
Fig 4. Located at 6.0 mm from the cementoenamel junction (CEJ) in the maxilla.
Fig 5. Located at 5.0 mm from the cementoenamel junction (CEJ) in the mandible.
Xin et al e5
American Journal of Orthodontics and Dentofacial Orthopedics - 2022 � Vol - � Issue -
Fig 6. Cortical and cancellous bone mineral density measurement in round area.
Fig 7. Cortical bone thickness (CBT), bone quantity, and distance between inserted site teeth roots
assessment.
e6 Xin et al
management factors that vary with operators, were
accounted for by statistical analysis.
For host-related factors, the continuous character of
data was retained to preserve the authentic information
because the artificial classification of age might alter
the feature of original data leading to a biased conclusion.
Age was negatively correlated with the progressive
susceptibility of miniscrews for loosening (ie, screws in-
serted in older patients tended to be more stable than
those in younger patients). This coincided with the study
declaring that the success rate of mini-implants was
higher in subjects aged .35 years.4 In addition, in a
meta-analysis by Hong et al,14 significant differences in
the success rate of miniscrews between people aged
$20 years and \20 years existed only if the sample
size surpassed 200, and the authors suggested an alterna-
tive for removable or extraoral appliances in adolescents.
Alharbi et al15 indicated that the failure rate was 8.60%
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for miniscrews placed in young patients (aged#18 years),
whereas it was 11.20% for adults (aged .18 years). In
summary, the outcome for studies with classification
criteria of 18, 20, or 35 years was consistent with our find-
ings, indicative of higher miniscrews stability in older sub-
jects. Some researchers suggested that higher bone
quality, bone quantity, and CBT in older subjects might
explain this phenomenon3,16; although, in this study,
the influence of these variables was not significant. In
this study, the age range was not large enough, and the
majority of subjects were younger. In addition, the sample
size for CBCT data included in this study was partly insuf-
ficient because of loss or poor quality of data. Further-
more, contradictory findings have shown miniscrews
were more unstable in older patients,17,18 which might
be due to a higher proportion of adolescent vs adult sub-
jects in the sample.15 As such, the age range of the sub-
jects should be greater in future studies. Additional
Journal of Orthodontics and Dentofacial Orthopedics
Table II. The result of univariate analysis with demographic information
Indicators
Y 5 0 (miniscrews
never failed)
Y 5 1 (miniscrews
failed once)
Y 5 2 (miniscrews
failed twice or more) P value
Gender 0.831
Male 108/889 (12.15) 25/889 (2.81) 6/889 (0.67)
Female 582/889 (65.47) 127/889 (14.29) 41/889 (4.61)
Age (26 y [21, 30])z 690/889 (77.62) 152/889 (17.10) 47/889 (5.29)
Sagittal skeletal relationships (ANB) 0.183
Class III 130/889 (14.62) 28/889 (3.15) 9/889 (1.01)
Class I 140/889 (15.75) 43/889 (4.84) 7/889 (0.79)
Class II 420/889 (47.24) 81/889 (9.11) 31/889 (3.49)
Vertical skeletal pattern (SN-MP) 0.244
Low angle 112/889 (12.60) 20/889 (2.25) 4/889 (0.45)
Average angle 352/889 (39.60) 90/889 (10.12) 25/889 (2.81)
High angle 226/889 (25.42) 42/889 (4.72) 18/889 (2.02)
Bone mineral density of cancellous bone
(417.33 6 174.51 Hu)y
412/544 (75.74) 97/544 (17.83) 35/544 (6.07)
Bone mineral density of cortical bone
(831.71 6 265.37 Hu)y
415/544 (76.29) 96/544 (17.65) 33/544 (6.07)
CBT (1.84 6 0.86 mm)y 415/544 (76.29) 96/544 (17.65) 33/544 (6.07)
Bone quantity (12.62 6 2.62 mm)y 416/544 (76.47) 95/544 (17.46) 33/544 (6.07)
Distance between inserted teeth roots
(3.14 6 1.41 mm)y
412/544 (75.74) 95/544 (17.46) 33/544 (6.07)
Oral hygiene 0.008*
Good 29/889 (3.26) 14/889 (1.57) 5/889 (0.56)
Fair 425/889 (47.81) 76/889 (8.55) 29/889 (3.26)
Poor 236/889 (26.55) 62/889 (6.97) 13/889 (1.46)
Miniscrew length, mm 0.728
6.0 11/889 (1.24) 4/889 (0.45) 0/889 (0.00)
8.0 657/889 (73.90) 143/889 (16.09) 47/889 (5.29)
10.0 22/889 (2.47) 5/889 (0.56) 0/889 (0.00)
Miniscrew diameter, mm 0.690
1.4 668/889 (75.14) 147/889 (16.53) 47/889 (5.29)
2.0 22/889 (2.47) 5/889 (0.56) 0/889 (0.00)
Different brands of miniscrews 0.035*
VectorTAS 384/889 (43.19) 102/889 (11.47) 27/889 (3.04)
Microimplant Anchorage 306/889 (34.42) 50/889 (5.62) 20/889 (2.25)
The onset of force application§ (43 d [22, 107])z 689/889 (77.50) 121/889 (13.61) 20/889 (2.25)
Clinical purpose 0.733
Anterioposterior direction (retraction and molar
distalization)
630/889 (70.87) 134/889 (15.07) 44/889 (4.95)
Vertical direction (intrusion and protraction) 37/889 (4.16) 12/889 (1.35) 2/889 (0.22)
Combination (uprighting and combination
among others)
23/889 (2.59) 6/889 (0.67) 1/889 (0.11)
Clinician groups 0.031*
1 334/889 (37.57) 91/889 (10.24) 26/889 (2.92)
2 356/889 (40.04) 61/889 (6.86) 21/889 (2.36)
Site of placement 0.049*
Retromaxillary/retromandibular area 626/889 (70.42) 135/889 (15.19) 43/889 (4.84)
Forepart area 57/889 (6.41) 11/889 (1.24) 2/889 (0.22)
Palatal area 7/889 (0.79) 6/889 (0.67) 2/889 (0.22)
Maxillary and mandibular arch of placement 0.103
Maxilla 523/889 (58.83) 117/889 (13.16) 42/889 (4.72)
Mandible 167/889 (18.79) 35/889 (3.94) 5/889 (0.56)
Left and right sides of the arch 0.221
Left 352/889 (39.60) 66/889 (7.42) 22/889 (2.47)
Right 338/889 (38.02) 86/889 (9.67) 25/889 (2.81)
Placement: soft-tissue type 0.638
Attached gingiva 627/889 (70.63) 138/889 (15.52) 45/889 (5.06)
Movable mucosa 63/889 (7.09) 14/889 (1.57) 2/889 (0.22)
Xin et al e7
American Journal of Orthodontics and Dentofacial Orthopedics - 2022 � Vol - � Issue -
Table II. Continued
Indicators
Y 5 0 (miniscrews
never failed)
Y 5 1 (miniscrews
failed once)
Y 5 2 (miniscrews
failed twice or more) P value
Appliances type 0.037*
Fixed 593/889 (66.70) 118/889 (13.27) 40/889 (4.50)
Removable 97/889 (10.91) 34/889 (3.82) 7/889 (0.79)
Note. Presented values are n/total n (%). Normally distributed continuous variables are shown as mean6 standard deviation, whereas nonnormally
distributed variables are shown as median (interquartile range).
CBT, cortical bone thickness.
*Statistically significant (P\0.05); yNormally distributed continuous variables are shown as mean6 standard deviation; zNonnormally distributed
variables are shown as median (interquartile range); §Fifty-nine miniscrews loosed before the onset of force application.
Fig 8. Correlation coefficient (cc) about significant results of Spearman correlation analysis. cc .0,
positive correlation; cc\0, negative correlation; |cc| 5 0.0-0.2, very weak correlation; |cc| 5 0.2-0.4,
weak correlation; |cc| 5 0.4-0.6, moderate correlation; |cc| 5 0.6-0.8, strong correlation;|cc| 5 0.8-
1.0, very strong correlation.
Table III. The outcomes of the Poisson log-linear
regression model for significant factors
Indicators Exp(b),95% confidence interval P value
Age 0.977 (0.958-0.997) 0.021
Onset of force application 0.995 (0.992-0.998) 0.001
Appliances type 1.664 (1.166-2.318) 0.005
Site of placement 0.498 (0.284-0.84) 0.010
e8 Xin et al
factors, including smoking, periodontal conditions, and
systematic diseases, should also be considered.
For the site of placement, this study presented the
palatal region as the most appropriate site for stable
insertion and superior to the forepart area of the arch,
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whereas the retromaxillary and retromandibular zone
was the least stable. Mohammed et al19 indicated the
success rate was 90.80% in the area from the second pre-
molar to the first molar in the maxilla and 90.30% for the
area between the lateral incisor and the canine; however,
each of these sites lagged behind the palatal district. Ue-
sugi et al6 revealed secondary insertion in the midpalatal
suture area obtained higher stability than the maxillary
buccal area (MB) for those who failed in the primary
installation of MB. As such, they proposed to change
the secondary insertion site to the midpalatal suture
area for the thinner soft tissue, thicker cortical bone,
and more favorable oral hygiene than MB.6 Notably,
oral hygiene has been proved to be an important
Journal of Orthodontics and Dentofacial Orthopedics
Fig 9. Forest plot about incidence rate ratio (IRR) of the Poisson log-linear regression model for sig-
nificant factors.
Xin et al e9
predictor of the success of miniscrews—especially in-
serted in the palatal area—although no strong correla-
tion was found in this study between it and the
progressive susceptibility to failure.20 To some extent,
the biased conclusion might be derived from grading
oral hygiene status based on the entire oral cavity rather
than delicate regional divisions, such as the buccal or
palatal area. Overall, the median and paramedian regions
of the anterior palate are considered to be ideal place-
ment sites for miniscrews because of the lower possibility
of contacting the tooth roots.21 The paramedian area
seemed preferable as it demands a shorter force arm
and possesses the greatest palatal CBT between the
canine and first premolar.21 In addition, a study showed
the miniscrews with a greater distance to the alveolar
crest had a higher success rate.22
This study demonstrated no significant difference in
the success rate of miniscrews inserted on the left or
right side. In contrast, a higher failure rate was reported
on the right side in Park et al.23 This might be attributed
to the overwhelming superiority of right-handed sub-
jects in quantity, leading to easier access to the left for
better hygiene.23
The optimal onset of force application has long been
a disputed issue as to whether a period of healing is
necessary for miniscrews stability. Previous research
demonstrated immediate loading might destabilize
implants and result in more failures.24-26 Chen et al27
proposed that inflammation control and delayed loading
was still necessary for temporary anchorage devices to
American Journal of Orthodontics and Dentofacial Orthoped
achieve sufficient primary stability even after 3 weeks
of healing, although osseointegration was not required
at this stage. However, Nkenke et al28 found no obvious
differences in daily bone apposition, bone-implant con-
tact, and bone density in the presence or absence of early
loading. It was also reported that none of the loaded im-
plants failed after merely 3 weeks of healing, indicating a
shorter latency period required for stabilization.29 In
summary, screws can resist the loadings with adequate
bone support following the healing period. In this study,
approximately 27.60% of miniscrews initiated loading
time ranging from immediately to 1 month, whereas
66.70% postponed loading until 3 months. The suscep-
tibility to failure was found to reduce along with the
postponed onset of loading.
With regard to the orthodontic appliance type, fixed
appliances were shown to be more unlikely to suffer
from progressive susceptibility to failure in this study.
However, studies comparing microbiological and peri-
odontal changes in teenagers demonstrated better
compliance with oral hygiene, less plaque, and fewer
gingival inflammatory reactions with removable vs fixed
appliances.30 Although patients treated with removable
appliances possess better oral hygiene, they had a
greater tendency for failure in this study. This may be
attributed to patients with removable appliances being
more unlikely to postpone the onset of force application
because they are always being asked to load in elastic cir-
cles themselves until 2 (clinical group 2) or 3 (clinical
group 1) weeks after inserting miniscrews by the
ics - 2022 � Vol - � Issue -
e10 Xin et al
orthodontist. In contrast, patients with fixed appliances
tend to use elastic chains or coil springs by the ortho-
dontist, which could not be replaced themselves. Longer
loading latency periods were shown to reduce the sus-
ceptibility to loosening or falling off in this study. In
addition, patients with removable alliances possess
longer intervals of an orthodontic appointment. Thus,
conditions such as miniscrews covered by mucosa or
inflammation of soft tissues might not be treated
promptly.
This study showed that the overall failure rate of
miniscrews was positively correlated with the number
of screws inserted in each subject. Specifically, the
more miniscrews received the greater probability of
instability. This may be attributed to greater difficulty
in maintaining good oral cavity hygiene, especially the
soft tissue around the neck of miniscrews, and vulnera-
bility to inflammation. In addition, Topouzelis et al31
demonstrated that for each additional miniscrew a
patient received, their success rate decreased by
67.00%; thus, indicating more intensive oral hygiene
education and observation should be provided.
Apart from these factors, host factors (ie, gender,
sagittal and vertical skeletal facial patterns, and distance
between inserted site teeth roots), miniscrew factors (ie,
length and diameter of miniscrew and different brands
of miniscrews), and management factors (ie, soft-
tissue type placement site, clinical purpose, and
maxillary and mandibular arch of placement) were also
investigated in this study. Although some of these
variables have positive outcomes based on univariate
analysis (ie, multicollinearity diagnosis and Poisson
log-linear regression model), confounding factors or
false positive conditions were filtered out. No significant
associations were between these factors and eventual
progressive susceptibility to failure.
Themajor limitation of this researchwas its retrospec-
tive design. Thus, some items could not be traced accu-
rately, such as the precise placement angle and loading
force, insertion torque, and the proximity of the
miniscrew to an adjacent tooth root (lacking CBCT after
insertedminiscrews). In contrast, some inserted sites such
as infrazygomatic crest or mandibular ramus could be
classified further to distinguish the progressive suscepti-
bility of orthodontic miniscrew to failure. Therefore, a
randomized controlled trial would allow subjects to be
followed over time. Finally, the power test analysis for
Poisson log-linear regression was not performed before
the start of the study because of the baseline rate for
progressive susceptibility of orthodontic miniscrews to
failure in the population was lacking. Therefore, the
sample size might be insufficient within 5 years. This
- 2022 � Vol - � Issue - American
could be addressed with greater subject enrollment or
conducting a multicenter randomized controlled trial
as a follow-up to compensate for the shortage.
The progressive susceptibility of miniscrews to failure
in patients has been associated with age, the onset of
force application, theplacement site of screws, and the
appliance type. Theolder patientswith delayed orthodon-
tic loadings treated with fixed appliances were more
insusceptible to miniscrews mobility. Clinicians should
use the least amount of miniscrews possible for
anchorage control and preferentially select the palatal re-
gion or forepart area of the arch, following the original
clinical purpose and treatment plan to the greatest extent.
CONCLUSIONS
1. The progressive susceptibility of orthodontic
miniscrew anchorage to failure was associated with
the age of patients, the onset of force application,
the site of placement, and orthodontic appliance type.
2. Older people and longer latency periods of loading
could reduce the susceptibility to loosening or fall-
ing off.
3. The palatal area tended to be the most suitable site
for stable implantation, whereas the retromaxillary
and retromandibular district was the worst.
4. Patients treated with removable appliances tend to
have higher progressive susceptibility to loosening
than patients treated with fixed appliances.
5. The more screws each patient receives, the greater
probability of failure.
AUTHOR CREDIT STATEMENT
Yilin Xin contributed to conceptualization, method-
ology, software, data curation, original draft prepara-
tion, and manuscript review and editing; Yeke Wu
contributed to manuscript review and editing; Chenjou
Chen contributed to data curation; Chen Wang contrib-
uted to data curation; and Lixing Zhao contributed to
supervision and funding acquisition.
ACKNOWLEDGMENTS
The study design and data proofreading were also
approved by a statistician (Guanjian Liu, Chinese
Evidence-Based Medicine Center, West China Hospital,
Sichuan University, Chengdu, China).
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	Miniscrews for orthodontic anchorage: analysis of risk factors correlated with the progressive susceptibility to failure
	Material and methods
	Results
	Discussion
	Conclusions
	Author credit statement
	Acknowledgments
	References