R E S E A R C H Open Access
Incidence of pulp sensibility loss of anterior
teeth after paramedian insertion of
orthodontic mini-implants in the anterior
, Dirk Bister
, Jörg A. Lisson
and Björn Ludwig
Background: The aim of this retrospective investigation was to evaluate the incidence of loss to pulp sensibility
testing (PST) of maxillary front teeth after paramedian (3 to 5 mm away from the suture) orthodontic mini-implant
(OMI) insertion in the anterior palate.
Methods: A total of 284 patients (102 males, 182 females; mean age was 14.4 years (±8.8) years at time of OMI-
Insertion) with a total of 568 OMIs (1.7 mm diameter, length 8 mm) were retrospectively investigated. A binomial
regression analysis was performed to explore covariates, such as age, gender, inclination of upper central incisors,
dentition status and insertion position of OMIs that could have contributed to loss of sensibility. Statistical
significance was set at p< 0.05.
Results: Loss of response to PST was encountered during retention in 3 out of 284 patients and the respective
OMIs had been placed at height of the second rugae (R-2). Affected teeth were a right canine, a left lateral and a
left central incisor. Subsequent root canal treatment was successful. Results of the binomial regression analysis
revealed that the covariate insertion position (R-2) of OMIs (p= 0.008) had statistically significant influence on loss
of response to PST.
Conclusions: (1) Although there was no radiographic evidence for direct root injury, the proximity of the implants
to the anterior teeth was nevertheless statistically related to loss of PST. (2) In all cases of PST loss OMIs were
inserted at the second rugae. Therefore OMIs should be placed either more posteriorly, at the third rugae or in the
median plane. (3). Loss of PST was not increased for patients with palatal OMI (0.18%) compared to samples
without OMI (0.25%).
Keywords: Orthodontic mini-implant, Paramedian insertion, Maxilla, Pulp sensibility loss, Anterior teeth
Sensibility is defined as the ability to respond to a stimu-
lus and testing of the dental pulp, which can be per-
formed using different techniques. In clinical practice
commercially available refrigerant sprays (cold - tests)
are often used for pulp sensibility testing (PST)  and
the response is recorded as positive or negative. Various
factors such as previous trauma , patient age , peri-
odontal attachment loss  or medications (sedatives,
tranquilizers, analgesics)  are known to have an influ-
ence on the response. It is known that orthodontic tooth
movement can affect PST response temporarily , but
sensibility is thought to return to normal after completion
of treatment. The authors state that there is no agreement
in the literature regarding potential long-term sequelae:
reported pulpal responses after orthodontics included cir-
culatory vascular stasis and necrosis . Cases of pulpal
necrosis following orthodontic therapy have been occa-
sionally reported [8, 9], but this is unusual.
* Correspondence: email@example.com
Department of Orthodontics, University of Saarland, Homburg/Saar,
Private Practice, Am Bahnhof 54, 56841 Traben-Trarbach, Germany
Full list of author information is available at the end of the article
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Hourfar et al. Head & Face Medicine (2017) 13:1
Adjunctive procedures such as extensive enamel strip-
ping  and subtractive Odontoplasty [11, 12] may lead
to a critical rise in intrapulpal temperature  with
subsequent pulp necrosis . Clinicians performing
PSTs use the qualitative sensory manifestations to ex-
trapolate the state of the pulp to assess the “vitality”of
the tooth [1, 14]. “Sensibility”and “vitality”are hence
often used interchangeably [1, 5], although it is well
known that PST can produce false positive and false
negative results for vitality.
Orthodontic mini-implants (OMIs) have changed
orthodontic paradigms by broadening the spectrum of
dental movements . Numerous risks and complica-
tions associated with the use of OMIs have been de-
scribed before and specific complications such as
unintentional root damage [16, 17], if severe enough can
lead to loss of sensibility and vitality.
The anterior palate is most suitable  as inser-
tion site for OMIs because of high success rates 
and ideal anatomical conditions. Palatal bone quality
and quantity for safe insertion of OMIs has been well
documented [20–22]. Despite these findings, uninten-
tional root damage of a lateral incisor after parame-
dian OMI-Insertion in the anterior palatal vault has
been reported .
The aim of this retrospective investigation was to
evaluate incidence of response loss to PST of maxillary
front teeth after paramedian OMI insertion in the anter-
Patients and treatment protocol
Patients with no history of previous orthodontic treatment
and need for OMI supported orthodontic biomechanics
were included. All patients received treatment by a single
orthodontist (B. L.) in a specialist orthodontic practice
(Traben-Trarbach, Germany), including fixed orthodontic
appliances with OMI placement. As previously described
[24–26], two OMIs were inserted symmetrically parasagit-
tal (3 to 5 mm away from the suture)  into the anterior
palate for appliance attachment. OMIs were loaded two
weeks after insertion, because of manufacture of the appli-
ances attached to them.
Unrestored maxillary permanent front teeth without
history of trauma and previous dental treatment
–chemo and/or radiotherapy during tooth
–history of previous surgery requiring endotracheal
–severe crowding of the upper front teeth
–history of previous orthodontic treatment
–tooth agenesis (except for third molars) or tooth loss
–enamel stripping or occlusal adjustments to the
upper front teeth
–medications such as sedatives, tranquilizer,
Only one type of mini-implant (1.7 mm diameter, length 8
mm) was used (OrthoEasy®, Forestadent, Pforzheim,
Germany). This implant system has an anodized surface
and features a self-tapping and cutting design and is made
from Titanium-alloy (Ti-6Al-4 V). Following patient con-
sultation and consent, 0.2 ml to 0.5 ml of local infiltration
anaesthesia (Ultracain® D-S, Sanofi-Aventis Deutschland
GmbH, Frankfurt, Germany) was used. The OMIs were
inserted without soft tissue incision or pre-drilling, per-
pendicular to the bone surface, using a motorised dental
handpiece at an insertion speed of 60 RPM. Torque limi-
tation was 30 Ncm. All OMIs were removed at debond.
Bonding and debonding of the fixed appliance
Bonding and removal of the fixed appliances followed a
standardized protocol. Self- ligating steel Brackets (Quick®,
Forestadent, Pforzheim, Germany) were indirectly bonded
applying a light cure bonding material (Transbond® Su-
preme LV, 3 M Unitek, Monrovia, Calif., USA). A halogen
light was used for curing composite material according to
Bracket removing pliers were used for debonding. The
residual adhesive on each tooth was removed with fluted
tungsten carbide burs and the surface finished using sili-
cone carbide polishers. All clean-up procedures included
Pulp sensibility testing
Thermal PST (cold test) of the maxillary front teeth was
performed just prior to OMI-insertion, at debond of the
fixed appliance/OMI-removal and 24 month post debond.
Endo-Ice® (Coltène/Whaledent Inc., Cuyahoga Falls, Ohio,
USA), producing a temperature of −50 °C was used. The
product was applied to the teeth using a cotton wool pad.
Response was recorded as either positive or negative.
Records included full documentation for the entire
treatment including appropriate radiographs.
Diagnosis of radiographic material
All radiographs were taken with an Orthophos® XG 3
(Sirona, Bensheim, Germany).
Hourfar et al. Head & Face Medicine (2017) 13:1 Page 2 of 7
Panoramic x-rays (OPGs)
OPGs were available pre-treatment (initial diagnostics)
and were used for the diagnosis of bony and dental
anomalies/pathologies prior to OMI-insertion.
Using the pre-treatment cephalograms (initial diagnostics)
the inclination of upper central incisors (U1/ANS-PNS)
prior to OMI-insertion was measured (Fig. 1), and 108° ±
5°  was regarded as a standard mean value.
Assessment of OMIs’insertion positions
Position of the OMIs were assessed using the plaster
working models for the appliances.
Because palatal rugae have been previously described
as stable, clinically visible structures , the insertion
positions of the OMIs were classified in relation to the
medial ends of palatal rugae:
1. at second rugae (R-2)
2. between second and third rugae (R-2/3)
3. at third rugae (R-3)
Data collection and statistical analysis
Data was collated using Microsoft Excel® 2007, (Microsoft
Corp., Redmond, Wash., USA). All cephalometric angular
measurements and the assessment of the implant position
were re-measured after three months by the same oper-
ator. Average intra-examiner reliability calculated by the
coefficient of variation (COV) was 0.01 for the former and
using the intraclass correlation coefficient (ICC) was 1.0
for the latter.
A binomial logistic regression analysis was performed
to explore covariates, such as age, gender, Inclination of
upper centrals, dentition status and insertion position of
OMIs that could possibly have contributed to loss of
sensibility. Statistical analysis was performed using SPSS®
for Windows®, version 22.0 (IBM Corp., Armonk, New
York, USA). Statistical significance was set at p< 0.05.
A total of 284 patients (102 males, 182 females) with a
total of 568 OMIs met the inclusion criteria. All patients
were of Caucasian origin. At the time of OMI-insertion
the mean age was 14.4 years ± 8.8 years. 169 patients
were in mixed dentition, and 109 patients were in per-
manent dentition. Average inclination of upper incisors
(U1/ANS-PNS) was 109.81° ± 8.37°; they were hence
slightly proclined. Most OMIs were inserted at the third
rugae (Table 1). In none of the patients root injuries
were diagnosed on the available radiographs.
Loss of response to pulp sensibility testing (PST)
Loss of response to PST was encountered in 3 (1.06%)
out of 284 patients or 0.53% per OMI. The percentage
was 0.18% (n= 3) for the 1704 maxillary incisors and ca-
nines and 0.18% (n= 2) for the 1136 maxillary incisors
respectively. PST was found negative in the three af-
fected patients in the second half of two year retention
phase following debond of the fixed appliances. Affected
maxillary teeth were: A right canine, a left lateral and a
left central incisor. Details are in Table 2.
The three affected patients initially presented with
painful teeth and were hence referred to an endodontic
specialist for further clinical and radiographic diagnosis.
All affected teeth received root canal treatment. After
successful treatment the symptoms resolved. Interest-
ingly, no root injury was diagnosed on the intraoral films
during endodontic treatment.
Results of the binomial logistic regression analysis re-
vealed that covariates gender (p=0.996),ageatOMI-
Insertion (p= 0.456), Inclination of upper incisors (U1/
ANS-PNS) (p= 0.289) and dentition status (p=0.587)had
no statistically significant influence on loss of response to
Fig. 1 Inclination of upper central incisors. Measurement of the Inclination of upper central incisor (U1/ANS-PNS) between the palatal plane (ANS-
PNS) and the long axis of U1 (Is-Isa)
Hourfar et al. Head & Face Medicine (2017) 13:1 Page 3 of 7
PST, whereas the insertion position of OMIs (p=0.008)
Loss of response to PST and vitality respectively was en-
countered in 3 out of 284 patients of our sample. The
percentage was 0.18% for the 1704 maxillary incisors
and canines and 0.18% for the 1136 maxillary incisors
respectively. Interestingly, these results are very similar
to those of an investigation by Bauss et al. . They
also found a small percentage of 0.25% (n= 2) for 800
healthy non-traumatized permanent incisors in 200 ran-
domly selected patients who underwent fixed treatment
without OMI placement.
In all affected patients of our sample, symptoms that
led to referral to an endodontic specialist were encoun-
tered during retention. Occurrence of symptoms was
late, considering loss of vitality was only detected long
after OMI removal and debond. However, considerable
variation has been described in the literature [23, 31–33]
and loss of vitality can occur up to 2 years after OMI
placement  because root injury can remain symp-
tomless over a long period of time. Er et al.  reported
a periradicular lesion caused by unintentional root dam-
age after paramedian placement of two OMIs (1.5 mm
diameter, length 10 mm) in the anterior palate for a dis-
talizing appliance in a 22-year-old female, thus requiring
endodontic treatment. Two months after OMI-insertion,
the patient complained of pain and the right maxillary
lateral incisor was endodontically treated.
Root perforations after buccal interradicular insertion
of OMIs have also been reported: two cases of maxillary
first molars [32, 33] and a mandibular right lateral inci-
sior . In the latter additional periapical surgery was
performed for retrograde root canal treatment.
After loss of response to PST, patients were referred to
an endodontic specialist who diagnosed pulp necrosis
and undertook endodontic treatment. Because no root
injury could be diagnosed on the available plain film ra-
diographs and all patients were free of symptoms after
treatment, no additional cone beam computed tomog-
raphy (CBCT) was performed, although this would have
been the modality of choice to diagnose the exact loca-
tion of the possible root injury site . Therefore, we
cannot completely exclude root perforations due to OMI
insertion and this has to be kept in mind when consider-
ing the results of this investigation.
It was well known that OMIs did not remain station-
ary during orthodontics  and primary (direct) and
secondary (migration) displacement has been observed.
Primary displacement is due to the elastic characteristics
of the bone whereas the latter occurs under orthodontic
loading over time, caused by remodeling processes of
the bone. In a systematic review by Nienkemper et al.
 secondary displacement of OMIs was found 0.23 to
1.08 mm for the head, 0.1 to 0.5 mm for the body and
0.1 to 0.83 mm for the tip. Maximum values ranged
from 1.0 to 4.1 mm for the head, 1.0 to 1.5 mm for the
body and 1.0 to 1.92 mm for the tip. Tipping angles ran-
ging from 1.0 to 2.65° were noted. The mean extrusion
of OMIs ranged from 0.1 to 0.8 mm and intrusion of up
to 0.5 mm was also observed. In our study OMIs were
removed at the time of debond and the tip of displaced
OMIs might have interfered with the tissues supplying
surrounding teeth with innervation and vascularity.
Besides possible complications with the use of OMIs
[16, 17] affecting PST response and pulp vitality, numer-
ous relationships between orthodontics and adjunctive
procedures respectively and the state of the dental pulp
were also described [37–39]. Patients requiring adjunctive
procedures to orthodontics on maxillary front teeth such
as approximal enamel reduction  and occlusal adjust-
ments [11, 12] were not included, because pulpal
temperature may have risen critically during the proced-
It has been reported that orthodontic tooth move-
ments like intrusion might also influence PST response
[7, 40]. Radiographic examination, albeit limited to two-
dimensional plain film radiographs, did not reveal any
close proximity between the OMIs and the roots of the
teeth. It is therefore unlikely that direct Injury led to loss
However loss of response to PST and vitality might
have been caused by orthodontics itself. This may be
relevant for the canine that required root canal treat-
ment, as direct injury of this tooth during OMI-
Insertion in the anterior palate was unlikely to have
caused this issue and has never before been reported in
literature. Moreover the patient was an adult (37 years)
Table 2 Details of affected patients
Gender Patient 1 Patient 2 Patient 3
female female female
Age (years) 37 11 12
Inclination U1 (degrees) 99.20 98.50 110.50
OMIs insertion positions R-2 R-2 R-2
Affected tooth (FDI-Notation) 13 22 21
R-2, OMI’s insertion position at second rugae
Table 1 Distribution of OMIs insertion positions’in relation to
Insertion position Number Percent
second rugae (R-2) 76 13.4
between second and third rugae (R-2/3) 24 4.2
third rugae (R-3) 468 82.4
Hourfar et al. Head & Face Medicine (2017) 13:1 Page 4 of 7
and older than the other patients affected (11 and 12
years). Hamersky et al. suggested  that orthodontic
forces cause biochemical and biologic pulpal tissue changes
and that orthodontic forces may be less safe as the age of
the patient increases. Open apices allow vessels to enter the
pulp and the increased amount of loose connective tissue
in this apical area may help to maintaining pulpal blood
flow during orthodontic force application; this argument
has also been made by other authors [42, 43]. Remarkably
Ingle et al.  found that the maxillary canine, which is
generally not affected by dental trauma, appears to be the
tooth most susceptible to pulp hemorrhage and necrosis
when exposed to orthodontic force application, suggesting
ischemic infarction as most likely cause.
The possibility of dental trauma before, during and
subsequent to orthodontic treatment plays an import-
ant role when interpreting the results of our study.
Incidence of dental trauma is subject to continuous
investigation [45–47] and data from the United States
revealed that 25% of the population from 6 to 50 years of
age may have suffered dental trauma to the anterior teeth
. Surprisingly, some patients are unaware of this and
many choose not to seek dental treatment [45, 48] and
taking a past dental history is likely to be unreliable. Most
dental injuries occur during the first two decades of life;
the most accident-prone time was found from the age 8 to
12 years [46, 48]. Dental trauma is more frequent in boys
than girls however there is considerable variation .
Maxillary central incisors, followed by the lateral incisors
are most frequently involved . One investigation eval-
uated pulp vitality in teeth suffering trauma during ortho-
dontic therapy; prevalence of pulp necrosis was 18.6% 
and this was much higher than our findings.
We excluded patients who had a past history of gen-
eral anaesthesia; dental trauma during endotracheal in-
tubation anaesthesia is one of the most common
encountered adverse events of general anaesthesia .
Maxillary central incisors are affected most frequently
. Incidence of dental trauma reporting was found to
be smaller than 0.2%  when assessed by anaesthesiol-
ogists compared to 12.1%  when assessed by dentists.
It was suggested that examinations should hence be con-
ducted by dental surgeons .
Alomari et al.  examined PST response using elec-
tric pulp testing (EPT) during and after orthodontic
treatment. The threshold of response to PST using EPT
was found to vary during but returned to pre-treatment
values towards the end of the retention phase. The au-
thors suggested that responses to electrical pulp testing,
should be interpreted with caution during orthodontics
and that a negative PST response does not always indi-
cate pulpal necrosis.
In daily clinical practice a refrigerant spray (RS) is
often used for practical reasons  and in our study
we also used a RS producing a local temperature of -50
°C. There is little evidence which cold delivery method
is most accurate in determining pulp responsiveness.
Jones et al.  compared carbon dioxide dry ice sticks
(CO2) with RS and concluded that RS and CO2 were
equivalent in determining pulpal responsiveness, but
To distinguish between “sensibility”and “vitality”ad-
vanced techniques such as Laser-Doppler techniques
(Laser Doppler Flowmetry - LDF) to measure intrapulpal
blood flow can be used [1, 5]. LDF was found to be a re-
liable method. However, it is technique-sensitive 
and extra-pulpal blood flow, mainly from the periodon-
tal ligament, may contaminate the signal . Moreover
LDF is time-consuming [57, 59] and hence not always
practical for routine clinical use.
Regression analysis showed that only the insertion
position of the OMIs was a statistically significant covar-
iate (p= 0.008) for loss of vitality. In the three patients
affected by a negative response to cold testing the OMIs
were inserted at the second rugae (R-2), and we must as-
sume that a more posterior insertion directed to the
third rugae (R-3) is more likely to preserve vitality. This
is in agreement with a recent investigation by Hourfar
et al.  which examined bone availability for OMI in-
sertion in relation to the palatal rugae. Most bone was
found in the vertical dimension at the first and second
rugae for 8 mm long OMIs. Yet they stated that it was
challenging to access the area of the second rugae clinic-
ally: OMIs would have to be inserted vertically to avoid
damage to the incisor roots and perpendicular insertion
to the bone surface might not be suitable for this area.
The inclination of upper incisors (U1/ANS-PNS) was
not a statistically significant covariate (p= 0.289) al-
though a slight tendency towards proclination was noted
within in the sample.
To our knowledge, this study is the first retrospective
study that investigates the relationship between OMI po-
sitioning and loss of PST response and pulp vitality.
Time delay of endodontic complications was accounted
months after debond. We propose further research using
prospective designs to verify the outcome of our
Although there was no radiographic evidence of
OMI induced trauma to the teeth that lost vitality,
the proximity of the implants to the anterior teeth
was positively and related to loss of PST (p= 0.008).
In all cases of PST loss OMIs were inserted at the
second rugae (R-2) and we therefore we recommend
Hourfar et al. Head & Face Medicine (2017) 13:1 Page 5 of 7
that OMIs should be placed either more posteriorly,
at the third rugae (R-3), or in the median plane.
This will decrease risk of trauma to the roots of the
PST/vitality loss post OMI-insertion in the anterior
palate was only 0.18%. We conclude that the risk of
palatal OMIs leading to loss of PST/vitality of the
upper front teeth is small.
The authors express their thanks to Mr. J. Hammer for participating in the
collection of data.
Availability of data and materials
For confidentiality issues, the data will only be shared in aggregate form as
presented in the tables.
JH conceived the project, gathered and processed the data, created the
material presented (tables, electronic images, references, et cetera) and
drafted the manuscript. DB translated and critically revised the manuscript.
JAL critically revised the manuscript. BL reviewed the process and critically
revised the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Consent for publication
Ethical approval and consent to participate
Ethical approval for this study and for the use of existing radiographic
material respectively was granted (No 224/13, Ärztekammer des Saarlandes,
Department of Orthodontics, University of Heidelberg, Heidelberg, Germany.
Department of Orthodontics, Guy’s and St Thomas’NHS Foundation Trust
and King’s College Dental Institute, London, UK.
Orthodontics, University of Saarland, Homburg/Saar, Germany.
Practice, Am Bahnhof 54, 56841 Traben-Trarbach, Germany.
Received: 6 September 2016 Accepted: 21 December 2016
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