ntroduction size calculation was carried out using

ntroduction

Mini-screw implants or temporary anchorage devices
(TADs) are now a popular means of conserving
orthodontic anchorage. Kanomi1 originally introduced
the titanium mini-implant with a diameter and length
specifically designed for orthodontic purposes. A
number of case reports2–7 and clinical studies8–11 have
investigated the effectiveness of TADs for acting as
stable anchor units; however, in many of these cases the
TADs have been inserted after completion of the
levelling and alignment phase. In situations where
conservation of anchorage is considered critical, the
orthodontist is often required to introduce measures
immediately after placement of the appliance to

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Address for correspondence: Mohit Sharma, Armed Forces
Medical College, Pune, Maharastra, India.
Email: [email protected]
# 2012 British Orthodontic Society

reinforce anchorage, before there has been any sig-
nificant amount of mesial movement of the upper
molars.

The aim of this study was to investigate anchorage loss
when using a conventional transpalatal arch (TPA) in
comparison to a mini-screw implant placed at the start of
levelling and aligning. Anchorage loss was represented by
a measurement of mesial upper first molar movement
during maxillary canine retraction.

Materials and methods

This study included subjects attending the outpatient
Department of Orthodontics and Dentofacial Orthopedics

DOI 10.1179/14653121226878

JO June 2012 Scientific Section Mini-implants v TPA for absolute anchorage: RCT 103

at the Armed Forces Medical College, Pune, India.
Approval for the study was obtained from the local ethical
committee of the Armed Forces Medical College (Reference
number: DR10518/AFMC/Dental/Ortho/RCT/7). Informed
written consent was obtained from the patient and/or parent
before commencement of the study.

A sample size calculation was carried out using a
standard formula12 considering that a mean difference
of 25% (d) in post-procedure change between two
techniques would be clinically significant with a pooled
error of 20% (s) at 95% confidence and 80% power. This
suggested a sample size of 11 subjects in each experi-
mental group; however, in order to enhance the effect
size and allow for any sample loss, 15 subjects per group
was proposed. Sample size calculation was carried out
using the Power and Sample Size Calculator developed
by the Vanderbilt University (available online).

The following inclusion criteria were applied:

N Minimum age at the beginning of treatment of
14 years

N In the permanent dentition
N Absence of gross caries in any of the maxillary dental

units
N ANB angle ,4u
N Need for extraction of the maxillary first premolars to

be carried out as confirmed by a diagnostic workup
N Bimaxillary proclination with class I molars and
crowding of ,5 mm in the maxillary arch (assessed

using Little’s Irregularity Index13)
N Absence of any systemic illness.

The following exclusion criteria were applied:

N History of previous orthodontic treatment
N Angle’s class III malocclusion
N Congenital absence of permanent teeth
N Cases not requiring the extraction of the maxillary

first premolars
N Cases with poor periodontal support
N Cases with cleft lip and or palate, craniofacial

syndromes or requiring surgical intervention for
correction of the malocclusion.

After screening of subjects, those who fulfilled the inclusion
criteria and agreed to take part were randomly allocated to
either Group A – the mini-screw implant group or Group B
– the TPA group. Each subject was assigned a computer-
generated random number. When a total of 30 had been
recruited they were arranged in ascending order according
to their assigned random number. The first patient of the
arranged number list was assigned to group A, the next to
group B. This was carried out alternatively until all the
patients were assigned to one of the two groups (Appendix-
CONSORT). The random numbers were generated using

EPI Info 6 software (Centers for Disease Control and
Prevention CDC Atlanta, GA, USA) by a faculty member
independent from the study.

Prior to starting treatment all subjects underwent
thorough oral prophylaxis and pre-orthodontic restorative
procedures where required. Extractions of the premolars
were carried out as required by the treatment plan before
the placement of the mini-screws or TPA. The following
orthodontic treatment procedures were undertaken:

Group A – Mini-screw implant: all mini-screw implants
were inserted by a single operator (MS) using a standard
technique. Prior to insertion an intra-oral periapical
radiograph was taken of the interdental space between
the maxillary second premolar and maxillary first molar
using a paralleling technique to assess root angulations
and the amount of inter-radicular bone present between
the roots of the adjacent teeth. The micro-implant was
placed in an area which afforded a clear margin of at least
2.5 mm between the roots of the teeth. The selected
implant site was thoroughly cleaned with a mixture of 2%
BetadineTM (Intas Pharmaceuticals Ltd, India) and
saline. Topical anaesthetic (15% Lidocaine) was sprayed
on the attached gingiva, between the roots of the second
premolar and first molar, 15 min prior to insertion. The
distance between the planned site of insertion and the
mesial/distal marginal ridges of the maxillary first molar
and the maxillary second premolar was measured with a
William’s periodontal probe. Care was taken that the
mini-screw implant was not inserted into the mobile
alveolar mucosa. A 1 mm round tungsten carbide bur
rotating at a speed of 1500 rpm was used to make a 1 mm
deep purchase point in the buccal cortex through the
alveolar mucosa. Constant irrigation was provided using
a mixture of Betadine and saline to help flush out debris
generated during the drilling process and also to dissipate
the heat generated. Titanium mini-screw implants of
1.2 mm diameter and 8 mm length, with a self-tapping
design (Denticon OMI) were placed initially at an angle
of 90u to the buccal mucosa, then after the first 3–4 thread
turns, the angulation of the screw driver was changed to
30–40u. Threading was stopped once the collar of the
mini-screw touched the alveolar mucosa. Stability and
mobility of the inserted mini-screw implants was checked
with the help of cotton tweezers by holding the head of
the mini-screw and gently applying lateral force. A post-
insertion periapical radiograph was taken for each case to
confirm the position of the implant. All patients were
recalled 3 days after insertion for loading. The mini-screw
implant was checked for mobility, swelling or acute
inflammation with discharge. Subjective symptoms of
pain were also assessed. The mini-screw implant was
engaged with the bracket of the maxillary second
premolar using a 0.010-inch stainless steel (SS) ligature

104 Sharma et al. Scientific Section

JO June 2012

Figure 1 Maxillary 2nd premolar engaged with mini-screw
implant using 0.010- inch SS ligature wire

wire (Fig. 1), which was passed through the hole in
the head of the implant. Following the completion of
levelling and alignment, nitinol closed coil springs (Leone
International, Italy) of length 9 mm were engaged from
the mini-screw implant head to the canine hook to
provide a continuous force of 150 g for the purpose of
canine retraction (Fig. 2).14

Group B – TPA: Correctly sized maxillary first molar
bands were placed on the upper first molars. An alginate
impression was taken with the bands in situ and sent to a
laboratory for casting and manufacture of a TPA made
with 0.9 mm SS wire soldered to the palatal surface of the
bands. The TPA was cemented into place using glass
ionomer cement. Levelling and alignment of the dental
arches was carried out until 0.01960.025-inch SS
archwires were placed. Canine retraction was undertaken
using 9 mm nitinol closed coil springs of length 9 mm,
which were engaged from the molar tube hooks to the
canine power arms (Figure 3a,b) to provide a continuous
force of 150 g.

For subjects in both groups, routine procedures for
banding and bonding were carried out by a single
operator (MS) immediately after placement of the mini-
implant or TPA. The fixed appliances were managed by
two other orthodontists (VS) and (BK) in addition to
(MS) and a strict protocol was followed by all the
operators. A 0.02260.028-inch SS pre-adjusted edgewise
appliance (MBT prescription, 3M UNITEK) was used
for all subjects. Alignment and levelling of the arch was
carried out using a 0.014-inch and 0.016-inch nickel
titanium archwires followed by 0.018-inch SS round,
0.01760.025-inch SS and finally a 0.01960.025-inch SS
rectangular for the purpose of canine retraction. The
maxillary canines were retracted until they were in
contact with the second premolars following which, the
mini-screw implant or TPA was removed to avoid
observer bias and a post-canine retraction cephalometric
radiograph was taken.

All pre-treatment and post-retraction cephalometric
lateral skull radiographs were taken by a single
investigator (MS) using the Orthostage Auto III
NCM machine (Ashi Roentegen Industries, Japan). A

Figure 2

Nitinol closed coil spring engaged

standard magnification factor (10%) was maintained for
all radiographs.

Cephalometric analysis

All pre- and post-treatment cephalometric radiographs
were hand traced by one investigator (DC) who was
masked as to the details of the study. To determine the
amount of horizontal movement of the maxillary first
molar, the pterygoid vertical plane (PTV)15 was used as
a reference (Figure 4). The PTV is constructed as a
vertical line extending inferiorly from a point (SE)
located by the intersection of the shadows of the greater
wings of the sphenoid and passing through the inferior
point of PTM. The distance between the PTV and the
centroid point on the upper first molar (defined as the
mid-point on a horizontal line between the greatest
mesial and distal convexity of the crowns) was used to
determine the position of the maxillary first molar. The
difference between the pre-treatment and post-canine
retraction position was used to determine mesial molar
movement. The position of the right and left maxillary
first molars were averaged. When a double image was
present, the midpoint between the two points was
traced. All measurements were undertaken using a
digital calliper calibrated in millimetres to two decimal
places. All cephalometric radiographs were retraced for
pre- and post-treatment readings after 3 weeks by the
same investigator.