A report on mini-screw research articles

1. A Combined Report of 7 Articles
Related to Miniscrews
By – Vikram Sachan
128/04/2020

2. Outline
1. Comparison of success rates of orthodontic miniscrews by the insertion method.
2. Miniscrew design and bone characteristics: An experimental study of primary stability.
3. Peak Torque Values at Fracture of Orthodontic Miniscrews.
4. Evaluation of insertion, removal and fracture torques of different orthodontic mini-implants in
bovine tibia cortex.
5. Insertion Torque of Orthodontic Miniscrews According to Changes in Shape, Diameter and
Length.
6. Fracture Resistance of orthodontic mini implants a biomechanical in vitro study.
7. The effect of insertion angle on orthodontic mini-screw torque.
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3. Comparison of success rates of
orthodontic miniscrews by the
insertion method
Jung Suk Kima, Seong Hwan Choib, Sang Kwon Chaa, Jang Han Kima, Hwa Jin Leea, Sang Seon
Yeoma, Chung Ju Hwangb
Goun Miso Dental Clinic, Seongnam, Korea
Department of Orthodontics, College of Dentistry and Institute of Craniofacial Deformity, Yonsei
University, Seoul, Korea
Published - 2012
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4. Goal – Compare Motor Hand Piece and Manual Screw Driver success rate.
4
Advantages Disadvantages
Maintains constant rotational speed throughout
surgery.
Expensive.
Provides adequate Torque and power. Require pre-setting of the motor before the
insertion procedure.
Can stabilize the orientation or angle of the
drilling, decrease the risk of mini-screw fracture at
the apex by preventing excessive pressure during
self-drilling, and maintain a constant drilling
speed.
Inexperienced orthodontist may cause the mini-
screws to wobble or wiggle out of place, and
stability can be compromised.
Reduced risk of NiTi file breakage.
By implementing auto stop mechanism, becomes
safer against fracture.
Useful for stabilizing the orientation of insertion
the palate or most posterior area of the mouth.
Table 1. Advantages and Disadvantages of using Motor hand piece
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6. Conclusions
1. Hand drivers provides better tactile sensation and awareness with respect to insertion angle
and force for beginners.
2. The overall success rate was higher when the engine driver was used, which gives higher
success rates with 8-mm-long mini-screws.
3. Regarding gender, success rates were significantly higher in men when the engine driver was
used. In women no statistically significant difference, with respect to insertion method, was
found.
4. Regarding insertion sites, higher success rates were observed in the maxilla than in the
mandible.
5. The engine driver improved the success rate of miniscrew placement in both the maxilla and
the mandible, the amount of improvement in success rates by using the engine driver was
significantly higher in the mandible.
6. The engine driver is one of the helpful tool for improving the initial stability and success rate of
orthodontic miniscrews.
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7. Miniscrew design and bone characteristics:
An experimental study of primary stability
Marco Migliorati, Stefano Benedicenti, Alessio Signori, Sara Drago,
Fabrizio Barberis, Henry Tournier,f and Armando Silvestrini-Biavatig
Genoa, Italy
Published - 2011
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8. Goal - To evaluate the correlations between Bone characteristics, Orthodontic miniscrew designs,
and Primary stability.
Methodology –
1. 4 different miniscrews were placed in pig ribs.
2. Scanning Electron Microscope is used to obtain measurable images of the threads.
3. The maximum insertion torque of the screws and the maximum load value in the pullout force
tests were measured.
4. Bone specimen characteristics were analyzed by using Cone-Beam Computed Tomography.
5. The insertion site cortical thickness as well as both cortical and marrow bone density were
evaluated.
6. The nonparametric Kendall rank correlation (tau) was used to evaluate the strength of the
associations among the characteristics measured.
7. No predrilling pilot hole is used during insertion of miniimplants.
8. In a pull-out test a universal testing machine with a 10-kN load cell was used; sensibility of the
load cell was 0.1 N.
9. A crosshead speed of 2 mm/min was applied in a controlled environment at 27 deg. C and 70%
humidity. The maximum load and screw displacement at peak load were measured.
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10. Conclusions
1. For pull-out force, maximum insertion torque, and
cortical bone thickness, no differences were
observed among the groups.
2. Temporary skeletal anchorage devices placed into
thick cortical bone sites had better stability than
those inserted into thin cortical bone sites.
3. Higher bone density does not particularly affect the
resistance of insertion of the screws but might
result in better stability when tested with a pull-out
test.
4. Cortical thickness was not found to be correlated
with maximum insertion torque but was positively
associated with pull-out force. Thus, it is mainly the
thickness (quantity) and not the density (quality) of
the cortical bone that guarantees the stability of
miniscrews.
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11. 5. Measured insertion torque by self-drilling (14.5 Ncm) and predrilling (9.2 Ncm).
6. 8-10 Ncm insertion torque value was recommended to increase the success rate of predrilling
screws.
7. A lower insertion torque value could indicate weaker clinical primary stability of the screws, and
a higher insertion torque value might produce tighter bone contact.
8. Cortical thickness and marrow bone density play key roles in the mechanical interlock between
the threads of the screws and the bone structure.
9. Differences in cortical bone thickness were more relevant for initial stability of the miniscrews
than cortical bone quality.28/04/2020 11

12. Peak Torque Values at Fracture
of Orthodontic Miniscrews
TYLER H. JOLLEY, DMD
CHUN-HSI CHUNG, DMD, MS
Published - 2007
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13. Goal – To evaluate Peak Torque Values at the Fracture point.
Methodology –
1. Twenty miniscrews each from five different manufacturers were tested:
a) Orlus Orthodontic Mini-Implant, 1.6mm in diameter (1.2mm core diameter), 7mm long.
b) Dual-Top Anchor System, 1.6mm in diameter (1mm core diameter), 6mm long.
c) LOMAS Quattro, 1.5mm in diameter (1mm core diameter), 7mm long.
d) Temporary Orthodontic Micro Anchorage System (TOMAS), 1.6mm in diameter (1.2mm
core diameter), 8mm long.
e) Ortho Implant, 1.8mm in diameter (1.5mm core diameter), 6mm long.
2. A selfdrilling miniscrew was inserted directly through the gingival or oral mucosa into bone.
3. A non-selfdrilling miniscrew was inserted through a pilot hole that has been drilled into the
bone with a bur with a depth of 3mm and a diameter of 1.3mm.
4. Polycarbonate (PC 1000) rods of 1" in diameter, were cut into 100:1"-long sections.
5. If the miniscrew did not fracture, its peak torque value was recorded when it had been screwed
completely into the rod, with the screw head at the rod surface.
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14. 6. A Screwdriver was inserted into the Jacobs chuck of an Imada torque wrench which was driven
into the pilot hole by turning the screwdriver clockwise at 6 rpm.
7. A Student t-test was used to determine the statistical significance of the differences in mean
torque values among the miniscrew types.
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15. Conclusions –
1. The largest-diameter screw (Ortho Implant) emerging as the strongest and the smallest-
diameter screw (LOMAS Quattro) as the weakest bond between bone and screw.
2. All the miniscrews were inserted through 1.3 mm pilot holes, the smaller-diameter miniscrews
might have required less insertion force than usual, thus increasing their apparent torque
strengths.
3. Miniscrew strength could also be affected by the thread design and the material composition -
in particular, whether the alloy contains hard or soft titanium.
4. For successful anchorage of miniscrew, the mechanical lock (torque) of the screw in the bone
must withstand the applied force.
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16. Evaluation of insertion, removal and
fracture torques of different orthodontic
mini-implants in bovine tibia cortex
Maria Fernanda Prates da Nova, Fernanda Ribeiro Carvalho, Carlos
Nelson Elias, Flavia Artese
Published - 2008
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17. Goal - To Evaluate mini-implants of different sizes for the following factors: (a) insertion torque, (b) removal
torque, (c) fracture torque, (d) shear tension, (e) normal tension and (f) type of fracture.
Methodology-
1. 20 self-drilling mini-implants were used, 10 manufactured by SIN and 10 by Neodent, measuring 8 and 7
mm in length, respectively and all with 1.6 mm in diameter.
2. 10 mini-implants, for each brand, 5 did not have a neck and the other 5 had a 2 mm neck, and were
separated into 4 groups: SIN without neck (S), SIN with neck (SN), Neodent without neck (N) and Neodent
with neck (NN).
3. All mini-implants were inserted into bone cortex and removed with a low speed handpiece connected to
a digital torque meter.
4. The mini-implants were also submitted to a fracture test.
5. The Insertion, Removal and Fracture torques, as well as the calculated Shear and Normal Tensions were
compared between all groups using ANOVA.
6. The type of fracture was assessed by a Scanning Electron Microscope.
Conclusion -
1. The greater the diameter, the greater is the insertion torque, since it is proportional to the contact area
between mini-implant and bone.
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19. Table 1 – Experimental results of Max. Insertion, Removal, Mean fracture torque and Shear tension .
S SN N NN
MIT (N-Cm) 25.2 ± 1.9 23.2 ± 4.9 26.0 ± 2.4 30.6 ± 1.8
MRT (N-Cm) 17.2 ± 4.9 17.6 ± 7.6 16.6 ± 7.5 25.0 ± 5.5
MFT (N-Cm) 35.1 ± 4.9 35.1 ± 2.7 27.4 ± 1.1 30.6 ± 1.8
ST (MPa) 1123.1 ± 168.3 1041.9 ± 154.8 1124.8 ± 123.0 1088.7 ± 128.728/04/2020 19

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21. 2. Absence of the neck seems not to affect insertion or removal torques.
3. Recommended limiting insertion torque should be 20 Ncm in order to avoid fractures.
4. An increase in the cross-section diameter of the mini-implant was followed by an increase in
fracture torque.
5. The smaller core diameter and the greater insertion torques can explain the smaller resistance
to fractures of the mini-implants
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22. Insertion Torque of Orthodontic
Miniscrews According to Changes in
Shape, Diameter and Length
Seon-A Lima; Jung-Yul Chab; Chung-Ju Hwang
Published - 2007
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23.  Methodology –
1. The maximum insertion torque (MIT) was measured using a
torque tester at a constant speed of 3 rpm.
2. Cylindrical and taper type of miniscrews (Biomaterials Korea Inc,
Seoul, Korea) with different lengths, diameters, and pitches were
tested.
3. Rotational axis of the torque tester was rotated clockwise at a
speed of 3 rpm, and the torque values were recorded every 0.1
second using a computer program.
4. A weight of 470 g was attached to the rotational axis of the
torque tester and a dial indicator depth gauge with 1/100 mm of
accuracy was used.
5. A Kruskal-Wallis significance test was performed at α = 0.05 level
of significance to determine the changes in MIT according to the
length and width of the miniscrew.
 Goal - To determine the variation in the insertion torque of orthodontic miniscrews according to the
screw Length, Diameter, and Shape.
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27. Conclusions –
1. In the 1.5-mm thick cortical bone, the MIT value increase with increasing in screw length for
both the cylindrical and taper type screws.
2. The MIT of the implant increased with increasing screw length in the cylindrical type, there was
a significant difference in MIT according to the change in length.
3. The cylindrical type required a longer period of time to penetrate the bone than the tapered
type screw.
4. The torque of the screw implant increased rapidly in the last part of the incomplete thread
region of the cylindrical type and the sloped region for the tapered type because the outside
diameter remains constant in the cylindrical type, while the upper portion of the incomplete
part (0.5–1 pitch) of the thread widens.
5. The change in diameter, length and cortical bone thickness caused the change in torque and
greatest change in stress.
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28. Fracture Resistance of
orthodontic mini implants a
biomechanical in vitro study
Benedict Wilmes, Agamemnon Panayotidis and Dieter Drescher
Department of Orthodontics, University of Düsseldorf, Germany
Published - 2011
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29. Goal – To determine the Fracture Resistance and
cause of mini screws.
Methodology –
1. 41 different mini-implants with diameters ranging
from 1.3 to 2.0 mm were inserted in acrylic glass
by a robot system.
2. Predrilling was performed using a bench drilling
machine at 915 rpm.
3. 10 mini-implants of each type were manually
inserted using the handheld screwdriver of the
respective mini-implant system
4. The insertion torque was measured and the
maximum torque at the time of mini-implant
fracture was evaluated.
5. Significance of the mean value differences was
evaluated by Kruskal–Wallis tests.
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31. Results
1. Three different fracture types were identified depending on the mini-implant type and the
driver shaft employed:
2. Most of the mini-implants fractured at the level of the acrylic block (Figure 7a), which clinically
represents the surface of the cortical bone.
3. The self-tapping type of the Tomas pin fractured between the head and the thread of the mini-
implant (Figure 7b).
4. The Dual Top Screw (G2) fractured at the interface to the driver (Figure 7c).
Figure 7 Mini-implant fracture at (a) the level of the acrylic block (Dual Top 2 × 10 mm) (b) between the head and the thread
of the mini-implant (self-tapping type Tomas pin), and (c) at the interface to the driver [employing the cross driver shaft, Dual
Top Screw (G2)].
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32. Conclusions
1. The diameter of the mini-implant had a major impact on
fracture torque values.
2. Predrilling is a good approach to reduce fractures and
failures. However, lengthy process than self-drilling
screws.
3. Using a torque-controlled driver can reduce the risk of
fracture and failure. A more reliable alternative is a dental
surgical unit with electronic torque control.
4. It is recommended to adjust the insertion torque limit to a
value lower than the lowest fracture value.
5. If mini-implants are inserted at a site with high bone
quality, pre-drilling is important even for self-drilling mini-
implants to minimize the risk of mini-implant fracture.
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33. The effect of insertion angle on
orthodontic mini-screw torque
Seyed Hamid Raji, Saeed Noorollahian, Seyed Mohsen Niknam
University of Medical Sciences, Isfahan, Iran
Published – 2013
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34.  Methodology –
1. 72 mini-screws (Dual Top Anchor System, Jeil, 1.6 mm diameter, 8
mm length) were used.
2. All were randomly divided into 4 equal groups and inserted in poly
carbonate plates with 3 mm thickness.
3. The maximum insertion torque (MIT) and maximum removal
torque (MRT) were recorded using a digital torque
tester/screwdriver.
4. Each group had a different insertion angle (90, 75, 60 and 45
degree ).
5. The data were analyzed by SPSS software (version 18) using one-
way ANOVA and post-hoc Tukey’s tests. The level of significance
was set at 0.05.
 Goal – To determine the Effect of Insertion Angle on orthodontic mini-screw torque.
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35. Conclusions –
1. Changing the insertion angle from 90o to 75o resulted in MIT decrease (P < 0.001), but the
change from 75o to 60o increased the MIT (P < 0.001).
2. Decreasing the insertion angle from 60o to 45o also resulted in the increase of MIT (P = 0.428).
3. Decreasing the insertion angle increased MRT values.
4. When applying forces on the screw heads, generates larger moment and induces higher stress
on the bone-screw interface.
5. The oblique placement of mini-screws increases their contact with the cortical bone, but
placing mini-screws in less than 90 degree in the alveolar bone has no anchorage advantage.
6. The cortical bone thickness in 30 degree is 1.5 times thicker than in 90 degree. If a screw is
placed perpendicular to the tooth long axis, it enters the inter-radicular area faster than when
placed with angle. Therefore, placing mini-screws with a 30o - 40o angle allows using longer
mini-screws and decreases the risk of root injury.
7. Mini-screws placed with an oblique angle, induced higher stresses on the bone and produced
micro-fractures; therefore, mini-screws should be placed perpendicular as long as root damage
can be avoided.
8. Pre-drilling was done to prevent the screw tip slippage on the poly-carbonate plates and reduce
insertion torque.
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36. Pitch and Longitudinal Fluting
Effects on the Primary Stability
of Miniscrew Implants
Christine L. Brinley; Rolf Behrents; Ki Beom Kim; Sridhar Condoor; Hee-
Moon Kyung; Peter H. Buschang
Published - 2009
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37. Goal - To test the hypotheses that pitch and fluting have no effect on the primary stability of miniscrew
implants (MSIs).
Methodology –
 Control Design – Surgical grade
Titanium, 6 mm long, major and minor
diameters 1.8 mm and 1.6 mm, thread
was a 90-degree asymmetrical buttress
design with a 1.0 mm pitch. The apical 3
mm of the MSI was tapered; it was self-
drilling and self-tapping without flute.
 Experimental Design – To evaluate the
effect of pitch, Control MSIs with 1 mm
pitch were compared with 0.75 mm and
1.25 mm MSIs. The depth of each flute
extended through the threads to the
core; each flute was 0.225 mm wide.
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38.  Testing Methods - Both synthetic and cadaver bone models were used to evaluate the effects of
pitch and fluting.
Mechanical testing –
 Placement Torque - All miniscrews were hand-placed with intermittent rotation into specimens
secured in a custom-made device. The screwdriver was braced and maintained in the same
position throughout insertion.
 Pull-out Strength - A vertical force of 10 mm/min, oriented parallel to the long axis, was applied
until failure occurred.
 Statistical Analysis – Pitch was evaluated first with the use of the Kruskal-Wallis test followed by
pairwise comparison with a Mann-Whitney test. The effect of fluting was evaluated with a Mann-
Whitney test. The relationship between insertion torque and pull-out strength was assessed by
means of Spearman rank order correlation.
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40. Conclusions –
1. Longer screws exhibit greater pull-out strength than shorter screws, and screws with greater
diameter provide greater resistance to pull-out.
2. Screw-type implants with greater thread depth have greater purchase strength in porous
materials and thus higher primary stability.
3. An asymmetrical thread design, with a 45-degree leading and a 90-degree trailing angle,
facilitates insertion while making removal more difficult.
4. Decreasing the surface area of an MSI by increasing the pitch or adding flutes, theoretically,
decrease friction and placement torque.
5. Pitch is negatively related to pull-out strength.
6. Decreased placement torque and cortical damage occur as the number and length of flutes are
increased, due to increased clearance of bone chips, which tend to accumulate around the
threads and provide resistance.
7. The presence of decrease and increase pull-out strength. However, it has less holding power
than fully threaded screws.
8. Pull-out strength significantly increases as pitch decreases from 1.0 mm to 0.75 mm.
9. MSIs with flutes have significantly higher placement torque and pull-out strength than MSIs
without flutes.28/04/2020 40

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Any Questions

42. 4228/04/2020