Research Article :
Stability
of miniscrews or Temporary Anchorage Devices (TADs) is an essential factor for
successful application in orthodontics. Miniscrews removal torque can be used
as an indicator of miniscrews stability. The objective of this work was to
compare removal torque between self-drilling tapered mini-screws and
cylindrical miniscrews. Materials and Methods: Two groups of TADs were inserted in the maxillae
of orthodontic patients to provide stationary anchorage for front teeth
retraction. Group 1: 20 tapered
self-drilling miniscrews, Group 2:
20 cylindrical self-drilling miniscrew. Split mouth technique was used. All of
the TADs were inserted parallel to the occlusal plane, between roots of the 2nd
maxillary premolar and 1st maxillary molar. The TADs were
immediately loaded with constant and continuous load using 8 mm long heavy
short Nickel Titanium coil spring. The coil spring was stretched between the
heads of the two types of TADs and crimpable hooks that fixed on arch wire just
distal to the anterior six maxillary teeth. After complete retraction of the
anterior maxillary teeth, TADs were removed using torque adjustable
screw-removal. At the moment of movement of the TAD the torque was recorded in Newton
Centimeter (Ncm). Results: Mann Whitney U Test resulted in a significant
difference between the two groups, indicating that cylindrical TADs had
significantly higher removal torque than tapered TADs (means were 3.20 Ncm ± 0.20
and 2.70 Ncm ± 0.10 respectively). Conclusion:
Physical properties have a considerable influence on the stability of the TADs.
Cylindrical TADs are showed more mechanical interlock into the bone. Contemporary
orthodontics skeletal anchorage such as TADs (miniscrews),
palatal
implants or mini-plates has led to a paradigm
shift in the field, particularly the stationary anchorage concept [1,2]. It has
been advocated that miniscrews can provide orthodontists with the stationary
anchorage latterly without any complications of loss of anchorage [3]. TADs,
nowadays, has glory in the field of orthodontic
practice and research because they possess
several noticeable advantages including: ease of use, relatively low coast, no
need for dental or extra-oral anchorage and possibility of immediate loading
[4-7]. Introduction of these devices has broadened the spectrum of the
orthodontics increasing the efficiency and decreasing pitfalls [3]. Nevertheless, the successful rate
of miniscrews
depends largely on their stability into the bone [2,8-11]. It has been
advocated that the primary stability of mini-implants
or miniscrews is the mechanical stability achieved immediately after insertion,
which shows how much the screw is engaged or locked into the bone. This primary
stability is manifested as a stable anchorage for the various clinical
applications [12]. According to several authors primary stability and
consequently success rates of TADs are influenced by quality and quantity of
the host bone, surgical technique, and screw geometry. Immediate loading and
anchorage demands mandate stationary miniscrews (TADs), in other words,
stability of the TADs is an issue that must be considered [2,13,14]. The
stability of mini-implants has been attributed to physical factors (device
design and dimensions) and biological factors including the nature of the bone
around the miniscrew, particularly bone density [15]. This study was done to
compare the stability of tapered self-drilling TADs and cylindrical
self-drilling TADs using removal torque resisting
force as an indicator. The
Materials: The sample consisted of two groups. Group 1: 20 tapered self-drilling
miniscrews *(1.4 mm neck diameter and 1.3 mm diameter near the apex)
(Figure1a), Group 2: 20 cylindrical self-drilling miniscrews *(1.4 mm
neck diameter, 1.4 mm diameter near the apex) (Figure 1b). Figure
1a: Photograph showing tapered miniscrew. Subjects:
20 adults, 18-25years old, healthy patients (13 females, 7 males), were
randomly selected from the Outpatient
Department (OPD) section of the department of
orthodontics, university of Benghazi. All the subjects were upper first
premolar extraction cases. Each subject received two TADs, one from each group,
that one maxillary buccal side received a TAD of group 1 and the other side
received another TAD of group 2. Allocation of which side would receive which
type of TAD was a random process. Figure
1b: Photograph showing cylindrical miniscrew. Procedures:
After swabbing the area with Alcohol for disinfection, and application of
infiltration local anesthesia, drill-free TADs were one-step inserted in the
designated sites. The insertion was made between roots of upper first premolar
and upper first molar. Insertion was done using palm and thumb grip until the
penetration of bone, then pen grasp grip was used to rotate the miniscrew till
it was completely inserted, with only its head exposed in the oral cavity.
Immediate, constant and continuous load was applied using 8 mm long, heavy short
Nickel
Titanium coil spring*.
It was stretched between the heads of the two of TADs (on the right and the
left of the patient maxilla), and two hooks that cramped on the heavy arch wire
(Figure 2). The load lasted for
18-24 weeks period, and then TADs were removed by using adjustable-torque
screwdriver*. *SH
1413-10, Dentos, Daegu, Korea Figure
2: Split mouth, one buccal maxillary side received
cylindrical TAD while the other side received tapered TAD. After the extraction spaces were
closed by anterior teeth retraction, the miniscrews were removed in a
counterclockwise direction using a torque screwdriver. This screwdriver has
adjustable resisting torque force ranging from 0 Ncm to 5 Ncm. The amount of removal
torque was indicated by the edge of the
rotating handle on numeric scale. Starting with 0.5 Ncm resisting torque force
TAD was unscrewed, if this amount of force was not enough to unscrew the TAD
(this was noticed by a click sound from the clutches of the screwdriver, and
the screwdriver rotates without movement of the screw), the force was incrementally
increased by about 0.25 Kg/Cm till the TAD get unscrewed. This torque force was
considered as the removal torque force for the TAD. Statistical
Analysis Statistical analysis was carried
out using IBM SPSS statistics 22®. Mann
Whitney U test was run also to compare the removal
torque measurements for each TADs type. The results revealed significant
difference (p<0.01) between the mean removal torque of the tapered TADs,
which was 02.70 Ncm ± 0.10 and the mean removal torque of the cylindrical TADs,
which was 3.20 Ncm ± 0.20 (Table 1). Table
1: The descriptive analysis data of the removal torque
of both miniscrew types. Stability of micro-implants
(TADs) is affected by several factors such as the surrounding bone density, and
amount of mechanical interlock between the screw and the hosting bone. There
are several other factors that influence the stability of the TADs in the bone
including topographical features of the TAD itself, type of bone, site of
insertion etc. Many studies have investigated the various factors affecting the
success rate of TADs, conflicting results have made the identification of
critical factors difficult. For instance, while some studies did not identify
any significant differences between the success rates of TADs inserted in the
mandible and those inserted in the maxilla other researcher advocated that
insertion of TADs the maxilla are more successful that those inserted in the mandible,
similarly, conflicting results have been reported with respect to sex, age, TADs
length and TADs diameter [16-28]. On the other hand there is a
universal conscience that mechanical interlock/primary stability is a reliable
indicator of TADs stability [15,20,27,29]. The scope of this research is to
evaluate the effect of topographical feature of Tapered and Cylindrical TADs on
the stability using torque removal as an indicator [29-32]. Kim et al. have
revealed possible osseointegration between TADs and bone! However, they
conclude that yet the mechanical interlocking plays a major rule stability of
miniscrews [33]. Stability of TADs is crucial for successful orthodontic
use of miniscrews, since miniscrews are solely
used for stationary anchorage. Stationary anchorage, in essence is that one
when only wonted tooth movement is involved in the orthodontic treatment [34].
For this reason, mechanical interlocking of the TADs into the bone must be
insured, and in turn the mechanical interlocking is largely influenced by the topographical
features of TADs [35]. The higher removal torques the more mechanical
engagement between the TAD and the bone and vice versa. Hong et al. emphasized
that site of insertion and physical properties of the TADs plays a major role
in the success rate orthodontic treatment using TADs, while gender makes no
difference [29,31]. Mann Whitney U Test resulted in a
significant difference between the two groups. The cylindrical design TADs had
higher removal torque (mean=3.20 Ncm ± 0.20) compared to the tapered TADs
(mean=2.70 Ncm ± 0.10), this owed to difference in the topographical differences
between the two types of TADs [36]. While Kim et al. concluded that no
difference between the two types of TADs in regards with removal torque values,
nevertheless Kim and his colleagues had used short TADs [37]. In this study the
cylindrical
miniscrew resisted removal all over the entire
length of its shaft and threads, however in tapered miniscrews, the resistance
to removal was only at first and at the coronal part of the shaft of
miniscrews, and quickly declines, this finding also revealed by Drago and Del
Castillo, and Cha et al. [26,28]. However the high removal torque
of cylindrical miniscrew compared to tapered
miniscrew as in the present study was mostly
evident in long length miniscrews (10 mm) rather than short length screws (6, 7
mm), and this might be due to the resistance of bone to screw removal that was
evident in small surface areas as reported by Chen et al. [29]. On the other
hand Kim et al. found Maximum
Removal Torque (MRT) in the conical group miniscrews
compared to cylindrical ones. This was not the case of the present study where
living bone was used and not saw bones, which lack remodeling with the
interface of miniscrews by time. Kim et al. concluded that physical properties
considerably effects the stability of TADs into the bone, where tapered TADs
showed lower removal torque [30,38]. Stability of miniscrews or Temporary
Anchorage Devices must be ensured in advance for a
successful orthodontic
treatment plane. Physical properties such as
taper of the TADs significantly affect the removal torque. The removal torque
of TADs is a reliable indicator of stability. Cylindrical TADs are more stable
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908-914. https://doi.org/10.2319/071808-374.1 Mahfud F Mohamed, Assistant Professor, Department of
Orthodontics, Faculty of Dentistry, University of Benghazi, Libya, Tel: 00281927633852,
E-mail: mafud.alaty@uob.edu.ly
Mohamed FM. Removal torque
analyses of two self-drilling orthodontic Temporary Anchorage Devices (TADs) (2019)
Dental Res Manag 3: 64-67. Miniscrews,Temporary anchorage devices, Anterior maxillary teeth, Torque removal.Removal Torque Analyses of Two Self-drilling Orthodontic Temporary Anchorage Devices (TADs)
Abstract
Full-Text
Introduction
Materials
and Methods
*SH
14-10, Dentos, Daegu, Korea
Removal Torque
Measurement
Results
Discussion
Conclusions
References
*Corresponding author
Citation
Keywords
