Evaluation of the Rate of Anterior Segment Retraction Using Friction Versus Frictionless Mechanics: A Randomized Clinical Trial
Phase: NA
Conditions: Bimaxillary Protrusion
Sponsor: Future University in Egypt

Evaluation of the rate of anterior segment retraction 
using friction versus frictionless mechanics: A  
randomized clinical trial. 
 
 
 
Protocol submitted for the partial fulfillment of Masters’ degree in 
Orthodontics  
Faculty of Oral and Dental Medicine, Future University 
  
 
Submitted by 
Monica Guirguis Youssif Tawfik 
B.D.S. 2013 
 
 
 
  (January 3rd, 2019) 
 
 

 
 
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Title of research: 
Evaluation of the rate of anterior segment retraction using friction versus frictionless 
mechanics. 
Funding: 
No sources of funding to be declared. 
Roles and responsibilities: 
Principle investigator: 
Monica G. Tawfik, BDS, masters’ student and will be the main operator in carrying 
out all the procedures for patients and is responsible for sample recruitment, clinical 
procedures, data collection, writing of thesis and result interpretation and analysis. 
Main supervisor:  
Yehia Mostafa, BDS, MSc, PhD –  Principle investigator and Chairman of the 
Department of Orthodontics and Dento-facial Orthopedics, Future University in 
Egypt. Has created the idea of the research and will aid in the data analysis and 
the deduction of conclusions.  
Co-supervisor:  
Fouad El- Sharaby, BDS, MSc, PhD – Associate Professor- Department of 
Orthodontics and Dento-Facial Orthopedics- Cairo University. Has aided in 
mapping out the study design, will also contribute to the follow-up visits, 
execution of the random allocation of the sample, analysis generation, result 
elucidation and withdrawal of conclusions.  
 

 
 
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Committees: 
• Orthodontics Department Council. 
• College Board Committee. 
• Ethics Committee. 
 
 

 
 
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Introduction 
       In this day and age, facial and dental aesthetics play key roles in promoting a 
healthier self-esteem, perceived attractiveness and gaining better career opportunities. 
This has, in turn, motivated patients to seek orthodontic treatment. Thus far, there has 
been a continuous pursuit by researchers for methods that provide the best possible 
aesthetics and function, in the shortest duration, with the least amount of drawbacks. 
     Despite, the various advantages of orthodontic treatment, its main disadvantage is 
the prolonged duration [1,2].  
     In many cases presented to the orthodontic clinic, four first premolar extractions 
are required. In bimaxillary dentoalveolar protrusion, four premolar extractions will 
provide space in both arches to align and/or retract anterior teeth.  
     Individuals having bimaxillary dentoalveolar protrusion are characterized by 
proclined upper and lower incisors and increased procumbency of the lips thus 
suffering from poor facial esthetics [3]. 
     Extraction space closure may be done by two different methods; the en masse 
retraction method which involves retraction of all six anterior teeth in one step. While 
the two-step retraction method involves the full retraction of the canine followed by 
the four incisors. 
     The two-step technique is considered more advantageous over en masse retraction 
in the sense that retraction of the canine and then the retraction of the four incisors 
will induce less load on the anchorage units and ensure full retraction on the anterior 
teeth. This will be achieved via increasing the number of teeth in the anchorage unit 
via including the canine while retracting the four incisors [4]. Although the two-step 
technique may seem to be more time consuming than en masse retraction, it is 

 
 
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thought to be well worth the wait to decrease the amount of anchorage loss and to 
maximize the amount of anterior segment retraction.  
     Various methods of anterior segment retraction have been implemented, the major 
two methods are friction and frictionless mechanics. Friction mechanics; which is 
also termed as “sliding mechanics”; involves the sliding of the teeth along the arch 
wire. While frictionless mechanics also termed as “segmental mechanics” involves 
the movement of the teeth due to the action of the loop or spring. Frictionless 
mechanics doesn’t involve the sliding of the teeth along the arch wire i.e. there isn’t 
any friction between the wire and the bracket during tooth movement.[4]    
    Friction “sliding” mechanics involves the use of elastomeric power chains and coil 
springs and space closure occurs by the sliding of the brackets on the wire [5]. It is 
more convenient and more frequently used for its simplicity for the patient and 
clinician. However, it provides compromised results due the unaccounted loss of 
force due to friction.[6]   Friction is mainly the result of; bracket slot width, bracket 
composition, wire dimensions and composition, ligation method used, interbracket 
distance and the interface between the bracket and archwire[7]. 
     On the other hand, in frictionless “segmental” mechanics, there is no guiding wire; 
hence there is no loss of applied force due to friction. This is due to the fact that the 
spring provides both the force and the moment. Therefore, this renders frictionless 
mechanics with a properly shaped loop more predictable and versatile than sliding 
mechanics [7]. Therefore, in frictionless mechanics a meticulously designed appliance 
has a greater activation range and a more constant force level and moment to force 
ratio.  
  Thus far, there has been a void in the literature regarding the optimum method to be 
utilized for anterior segment retraction in patients with bimaxillary protrusion. Hence, 

 
 
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there is a need for a randomized clinical trial to gain some evidence as to which 
method should be implemented in the day-to-day clinical practice.   
  
 
 

 
 
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Literature Review. 
       In every orthodontic treatment involving space closure following extractions of 
the first premolars, the question of the optimum method of retraction comes to mind. 
The two methods frequently employed are either friction or frictionless mechanics. 
Consequently, the time taken for anterior segment retraction has been under constant 
assessment by various researchers. Moreover, achievement of superior aesthetics, 
determined by optimum tip, torque and vertical position, must be accomplished. 
Nevertheless, side effects like anchorage loss, root resorption and pain must be 
evaluated and minimized. Previous studies and/or reviews that were conducted in 
relation to this study are discussed under the following titles:   
1) Frictionless mechanics for anterior segment retraction. 
2) Friction mechanics for anterior segment retraction. 
3) Comparison of the rate of retraction in Friction vs. Frictionless mechanics. 
4) Anchorage Requirements and Efficiency of Mini-screws 
5) Pain and Satisfaction associated with Orthodontic Therapy. 
6) 3D model scanning and its reliability. 
 
 

 
 
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1) Frictionless mechanics for Anterior Segment Retraction. 
    Kuhlberg and Burstone, (1997)[8] assessed the outcome of off-center positioning 
on the force system produced by segmented 0.017 x 0.025-inch TMA T-loops. The 
spring was placed in seven positions, centered, 1mm, 2mm and 3mm toward the 
anterior attachment, and 1mm, 2mm and 3mm toward the posterior attachments. The 
horizontal and vertical forces were measured as well as the alpha and beta moments 
were measured over 6mm of spring activation. The results portrayed that alpha/beta 
moment ratio was dependent only on the spring position and independent of spring 
activation. Eccentric positioning of the T-loop springs effectively produces a 
consistent moment differential through the range of spring activation. 
    Chen at al, (2000)[9] evaluated the moments and forces generated by various 
orthodontic T-loop spring designs. The impact of dimensional changes (within 
clinically used ranges) and the addition of gable bends with the heat treatment were 
measured. Increasing the vertical or horizontal dimension reduced the spring’s load 
deflection rate and its moment/force ratio.  
    Thiesen et al, (2005)[10] performed a study to necessitate the incorporation of 
helices in the design of the T-loops. Evaluating the mechanical characteristics of the 
beta-titanium T-loops with and without helices, with 0- and 180-degree gable bends, 
constructed from 0.017x0.025" and 0.019x0.025" wire using forty beta-titanium T-
loops that were centrally positioned in a universal testing machine. The horizontal 
force and the moment/force ratios during activation were recorded at 1mm intervals, 
up to 7mm maximum. The study demonstrated that the transverse section of the wire 
had the greatest effect on the horizontal force produced by the loops. It was found 
that loops made with the smaller 0.017x0.025 wire produced significantly lower 
levels of horizontal force. Lower moment/force ratios were obtained with loops with 
gable bends. As a rule of thumb, T- loops with helices produced lower magnitudes of 

 
 
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horizontal force and moment/force ratios than plain T-loops but the plain T-loops 
with 180-degree gable bends yielded more adequate force systems.  
   Keng et al, (2011)[11] conducted a randomized controlled trial on Twelve patients 
(six males and six females) aged between 13 and 20 years who had upper premolar 
extractions were included, and each acted as their own control, with a NiTi T-loop 
allocated to one quadrant and TMA to the other using a split mouth block 
randomization design. The loops were activated 3 mm at each visit to deliver a load 
of approximately 150g to the upper canine teeth. They found that the mean rate of 
canine retraction using preactivated NiTi and TMA T-loops was 0.91 mm/month 
(±0.46) and 0.87 mm/month (±0.34), respectively. The canine tipping rates were 0.71 
degrees/month (±2.34) for NiTi and 1.15 degrees/month (±2.86) for TMA. Both the 
rate of space closure and the tipping were not significantly different between the two 
wire types. In conclusion they found that there was no difference in the rate of space 
closure or tooth angulation between preactivated TMA or NiTi T-loops when used to 
retract upper canines.  
    Almeida et al, (2016) [12] compared between thirty compound T-loop springs that 
were divided into three groups according to the dimensions of the nickel-titanium 
wire used for its design: 0.016” × 0.022”, 0.017” × 0.025”, and 0.018” × 0.025”. 
The loops were tested on the Orthodontic Force Tester machine at an interbracket 
distance of 23 mm and activated 9 mm. Conclusively, the larger wires tested 
produced higher forces with slight increase on the moments, but the Moment to Force 
Ratio (M/F) produced by the 0.016” × 0.022” wire was the highest found. 
 
 
 
 

 
 
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2) Friction mechanics for anterior segment retraction. 
   Bokas and Woods, (2006) [13] compared the rates of maxillary canine retraction 
and molar anchorage loss when using either NiTi springs or elastomeric chains 
delivering a known force with sliding edgewise mechanics. Twelve patients who 
required maxillary canine retraction into first premolar extraction sites as part of 
their orthodontic treatment were selected. In a split-mouth design, these patients 
received pre-calibrated NiTi springs (112 quadrants) and pre-measured 
elastomeric chains (12 quadrants), all delivering disinitial forces of 
approximately 200 g and being reactivated at 28 day intervals. The results found 
indicated that the rates of space closure and molar anchorage loss using either 
NiTi springs or elastomeric chains, if reactivated every 28 days, are likely to be 
similar. 
   Halimi et al, (2012) [14] they searched an electronic database for the records 
taken between 1970 and 2011 and a few manual reviews for relevant 
publications. They conveyed that rapid force decay of elastomeric chains 
occurred after some time and therefore affects its clinical and mechanical 
properties.  
  Furthermore, Barlow and Kula, (2008)[15], also conducted a systematic review 
to evaluate the strength of literature on the various factors that affect the 
efficiency i.e. the rate of tooth movements using sliding mechanics for extraction 
space closure. They deduced that arch wire properties, type, size, diameter as 
well as bracket design, material and force delivery systems affected the amount 
of friction generated and hence, affected tooth movement. But it was found that 
the arch wire size, controlled tipping better but had no effect on the rate of 
closure. On the other hand, they concluded that elastomeric chains produced 
similar retraction rate when compared to 150g and 200g nickel-titanium springs. 
This was further backed by Chaudhari and Tarvade, (2015) [16], as they 
compared nickel titanium closed coil springs and elastomeric chains in terms of 

 
 
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rate of en-masse retraction and anchorage loss. Clinically and radiographically, 
they found that elastomeric chains produced faster rate of retraction but higher 
anchorage loss.  
3) Comparison of the rate of retraction in Friction vs. Frictionless 
mechanics.  
   In his article, Burstone, 1962[17] introduced the segmented arch technique also 
called the frictionless approach for closure of extraction spaces. He claimed that the 
frictionless technique possessed superior mechanics and greater tooth control in 
contrast to sliding mechanics also called friction mechanics. He based this on the 
concept of delivering constant light forces that would provide more desirable tooth 
movements. Moreover, he added that the frictionless technique provided the operator 
with the ability to add a heavy cross-sectional wire for control of the anchor units and 
low deflection wire for force delivery on the active units.  
   Ziegler and Ingervall, (1989)[18] performed a clinical study of maxillary canine 
retraction with a retraction spring and with sliding mechanics. The efficiency of 
maxillary canine retraction by means of sliding mechanics along an 0.018-inch labial 
arch and an Alastik chain was compared with that using the canine retraction spring 
designed by Gjessing. The rate of canine retraction and degree of tipping, and 
rotation of the canines were studied in 21 subjects by one of these two methods on 
either side of the dental arch. Measurements were made in the mouth and on 
photographs of dental casts. It was found that the canine was retracted faster and with 
less distal tipping with the spring than with the sliding mechanics. The canine 
retraction spring was not superior to the sliding mechanics in controlling canine 
rotation during the retraction. 
    Dinçer et al, (2000) [19] conducted this study aiming to evaluate the effect on 
the dentoalveolar structures of the application of Poul Gjessing (PG) springs 
(Frictionless mechanics) for retraction of upper incisors and to compare the 

 
 
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outcome with the effect of a closed coil spring (Friction mechanics) retraction 
system. Thirty-six subjects with Angle Class I or Class II malocclusions were 
selected for the study, the PG group with 17 subjects and the closed coil group 
with 19 patients. In the frictionless group the rate of retraction was higher by 
1.07mm/ 3 weeks than the friction mechanics. In both groups the incisor 
retraction was accompanied by mesial movement of the buccal segments. Distal 
movement of the root apex of the incisors was observed in both groups, although 
more pronounced in the PG group (P < 0.01). A significant incisor intrusion 
resulting in a decrease in overbite was found in the PG group, whereas the deep 
bite increased significantly in the coil spring group. The PG spring produced a 
three-dimensional control in the movement of the upper incisors, so that 
application of additional intrusive mechanics after completion of the incisor 
retraction became unnecessary. 
     Ren et al (2003) [20] carried out a systematic review to find the optimum force 
magnitude for orthodontic tooth movement. Search was carried out on Medline 
and manually from the main orthodontic and dental journals, 400 articles were 
found. Mainly, animal studies were found evaluating different force magnitudes 
on different kinds of animals. Although, the relation between force magnitude 
and rate of tooth movements was not evaluated. Hence, this study found that 
there is a void in literature regarding the relation of optimum force magnitudes 
and the rate of tooth movement.  
     Makhlouf et al, (2018) [21], compared canine retraction techniques by NiTi 
closed coil spring delivering friction mechanics and T-loop delivering frictionless 
mechanics using a Cone Beam Computed Tomography (CBCT). They evaluated 
the amount of tooth movement as well as root resorption on ten patients in a split 
mouth study design. The right maxillary canines were retracted using T-loops 
made on 0.017 x 0.025 TMA wires and the left maxillary canine using NiTi coil 
springs with a retraction force of 150g. The NiTi coil spring side showed a higher 

 
 
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distal movement than the T-loop side, however, both methods did not cause root 
resorption with controlled retraction force.  
4) Anchorage Requirements and Efficiency of Miniscrews.  
   Upadhyay et al, (2008)[22], conducted a study to determine the efficiency of 
mini-implants as intraoral anchorage units for en-masse retraction compared with 
conventional methods of anchorage reinforcement. It was found that mini-
implants were efficient for intraoral anchorage reinforcement for en-masse 
retraction and intrusion of maxillary anterior teeth. No anchorage loss was seen 
in either the horizontal or the vertical direction in the miniscrew group when 
compared with the conventional method.  
   Moreover, skeletal anchorage by mini-implants produced greater anterior tooth 
retraction (8.17mm vs 6.73 mm) and less maxillary molar mesialization (0.88mm 
vs 2.07 mm), with a shorter treatment duration (29.81 vs 32.29 months) 
compared to extraoral headgear anchorage in patients with maxillary 
dentoalveolar protrusion as reported by Yao et al, (2008)[23]. 
   Chaimanee et al, (2011),[24] investigated the safe zones for mini-screw implant 
placement. Periapical radiographs of 60 subjects with skeletal Class I, II or III 
patterns were examined. For each interradicular site, the areas and distances at 3, 
5, 7, 9 and 11 mm for the alveolar crest were measured. The study’s conclusion 
was that for all skeletal patterns, the safest zones were the spaces between the 
second premolars and between the first and second molars in the mandible. 
   Pithon et al, (2012) [25] investigated whether orthodontic mini implants provide 
absolute anchorage during the retraction of maxillary anterior teeth after the pre-
molar extractions via a systematic review. 550 articles were initially listed, four 
were found to be potentially eligible, ending with three being selected after 
applying the inclusion and exclusion criteria. Two of these articles showed 
absolute anchorage provided by mini-implants and the other demonstrated slight 

 
 
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loss of anchorage. There was strong scientific evidence that orthodontic mini-
implants provide absolute anchorage during the retraction of maxillary teeth. 
  Sandler et al, (2014)[26] performed a 3- arm parallel randomized clinical trial to 
compare the effectiveness of temporary anchorage devices (TADs), Nance button 
palatal arches, and headgear for anchorage supplementation in cases requiring 
maximum anchorage. The study comprised of 78 patients with mean age of 14.2 
years requiring maximum anchorage and fulfilling all inclusion criteria. Mesial 
molar movement, duration of anchorage reinforcement, number of treatment 
visits, number of casual and failed appointments, total treatment time, dento-
occlusal change and patients’ perceptions of the method of anchorage support 
was detected. There were more problems with the headgear and Nance buttons 
than with the TADs. The quality of treatment was better with TADs. As a result, 
TADs might be the preferred method for reinforcing orthodontic anchorage in 
patients who need maximum anchorage. 
   Wahabuddin et al (2015)[27] studied the clinical efficiency of mini-screws in 
anchorage reinforcement during en-masse retraction of anterior teeth. They 
concluded that mini-screws were able to resist traction forces up to 200-250g. 
They also recommended that mini-screws stability required precise surgical 
technique as well as proper patient cooperation and oral hygiene measures.  
  Antoszewska-Smith et al (2017)[28] by conducting a systematic review and 
meta-analysis they compared the efficacy of mini-screws and conventional 
methods for anchorage reinforcement. They found that the use of mini-screws 
was more superior in anchorage preservation and, to some extent, enables the 
reduction of treatment time.  
    Moreover, Chopra et al (2017)[29] also evaluated amount of anchorage loss 
between mini-implants and conventional anchorage methods (Nance button and 
lingual arch). They conducted the study on 50 patients with bimaxillary 

 
 
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dentoalveolar protrusion who require four first premolar extractions. They found 
that anchorage loss was significantly lower using mini-screws (0.2mm in 
maxillar arch and 0.20mm in the mandibular arch). While, when using 
conventional methods anchorage loss was (2.0mm in the maxillary arch and 
2.1mm in the mandibular arch). They concluded that mini-screws along with 
proper patient and mini-screw selection, were a viable and better alternative to 
conventional anchorage reinforcement methods.  
    Becker et al (2018)[30] conducted a systematic review to find the efficacy of 
orthodontic mini-implants for en-masse retraction in the maxilla. They reported 
that mini-implants were associated with significantly lower anchorage loss in the 
first upper molars compared to conventional anchorage methods for en-masse 
retraction. 
5) Pain associated with Orthodontic Therapy. 
     Rosier et al, (2002)[31] studied the difference between the Visual Analog Scale 
(VAS) and the Verbal Descriptor Scale (VDS) in context of the reproducibility of 
pain measurement and pain perception. Each patient was asked to recall the worst 
physical pain of their life and rate its intensity and unpleasantness at the beginning of 
each session. The rating of pain intensity reported via the VAS had significantly 
smaller session-to-session variation than the VDS. While measuring perceived pain 
intensity and pain unpleasantness, VAS was significantly more sensitive to small 
differences and did not portray some of the ordering effects that were present with the 
VDS. 
     Caraceni et al, (2002)[32] evaluated pain measurement tools (PMTs) in palliative 
care research performed in a multi- lingual multicentre setting. They concluded that 
Visual analogue scales, numerical rating scales, and verbal rating scales are 
considered valid to evaluate pain intensity in clinical trials and in other types of 

 
 
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studies. The McGill Pain Questionnaire and Brief Pain Inventory are valid in many 
multilingual versions.  
    Luppanapornlarp et al, (2010)[33] compared different magnitudes of 
continuous orthodontic force in order to determine the optimum orthodontic 
force. They measured Interleukin IL-1b levels in human gingival crevicular fluid 
(GCF), pain intensity, and the amount of tooth movement. This was carried out in 
the duration of canine retraction in 16 patients with Class I bimaxillary 
protrusion. Retraction of maxillary canines was performed using nickel–titanium 
coil springs on segmented arch-wires with continuous forces of 50g in one group 
and 150 g in the other group, while the lower canines were used as a control. It 
was found that IL-1b concentration in the 150 g group displayed the highest level 
at 24 hours and 2 months with significant differences compared with the control 
group. At 24 hours, the mean VAS score of pain intensity from the 150 g force 
was significantly greater than from the 50 g force. 
      Campos et al, (2013) [34] conducted a study on twenty males to evaluate the 
relationship between the patient’s motivation and the level of informed pain in 
the two stages of treatment. The questionnaire was divided into five categories 
including motivation towards treatment. Pain intensity was evaluated daily for 
fourteen days using a visual analog scale (VAS). The VAS was considered to 
have good reliability in recording motivation and pain intensity experienced by 
the patient.  
6)3D model scanning and its reliability. 
        Santoro et al (2003)[35] compared the reliability of measurements carried out 
on digital models and plaster models. Two independent examiners measured 
tooth size, overbite and overjet on both models belong to randomly selected 
pretreatment records of 76 patients. They concluded that, there was a significant 
difference in measurements tooth size and overbite readings with the 

 
 
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measurements on digital casts being smaller. On the other hand, there was no 
difference in the overjet measurements.  
    Asquith et al (2007)[36] evaluated the accuracy and reproducibility of 
measurements made on digital models. They scanned ten study models using 
Arius3D Foundation System to produce 3D images. To measure reliability and 
reproducibility, two examiners measured eleven parameters, twice, on both 
digital models and study models. They concluded that digital models were a 
reliable mode of measurement and there was no longer a need to produce study 
models.  
      Leifert et al, (2009)[37] compared space analysis using digital models and 
plaster models. 25 impressions were made into plaster models and another 25 
impressions were made into 3D digital models using OrthoCAD software. Two 
examiners measured tooth width and arch lengths on models of patients with 
Class I crowded permanent dentition. They concluded that the accuracy of the 
software for space analysis evaluation is clinically acceptable and reproducible 
when compared to manual measurements on plaster models.   
       Thiruvenkatachari et al, 2009[38] measured 3D tooth movement with a 3D 
surface laser scanner aiming to  develop a method of measuring 3-dimensional (3D) 
tooth movement using a 3D surface laser scanner. This study also tested the accuracy 
of this method, and to compare the measurements with those from cephalometric 
radiographs. They superimposed pre-treatment and posttreatment models on the 
palatal rugae then the accuracy and reliability of the laser scanner were evaluated on 
the experimental model. The results showed the laser scanner was accurate to 0.0235 
mm for anteroposterior measurements and 0.0071 mm for buccolingual movements 
for every 0.5 mm of movement. They concluded that accurate and reliable 
measurements of tooth displacement were achieved via the 3D laser scanner and it 
can be considered an alternative to cephalometric radiographs. 

 
 
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     Kau et al, (2010) [39] endeavored to determine if measurements obtained from 
digital models from cone beam computed tomography (CBCT) images were 
comparable to the traditional method of digital study models by impressions. Digital 
models of 30 subjects were used. InVivoDental (Anatomage, San Jose, Calif) 
software was used to analyze CBCT scans taken by a Galileos cone beam scanner 
(Sirona, Charlotte, NC) and OrthoCAD (Cadent, Fairview, NJ) software was used to 
analyze impression scans of patients at different stages of orthodontic treatment. 
Impressions were taken using alginate and were mailed to OrthoCAD for digital 
conversion. The scans were then electronically returned in digital format for analysis. 
Finally, they deduced that CBCT digital models were as accurate as OrthoCAD 
digital models in making linear measurements for overjet, overbite, and crowding 
measurements.  
  Sousa et al, (2012)[40] assessed the reliability of measurements made on 3D digital 
models that were scanned using a laser scanner (D-250, 3Shape). Using Geomagic 
Study 5 software, twenty digital models were analyzed. Eleven linear measurements 
were done including measurements of arch length and width. Measurements were 
carried out manually on plaster models as well as using the software on digital 
models. They found that there was so statistical difference between measurements 
made on digital models and plaster models. Hence, digital models were, both 
reproducible and reliable, modes of linear measurements.  
   Kim and Lagravére, (2016) [41] aimed to compare the accuracy of Bolton 
analysis obtained from digital models scanned with the Ortho Insight three-
dimensional (3D) laser scanner system to those obtained from cone-beam 
computed tomography (CBCT) images and traditional plaster models. CBCT 
scans and plaster models were obtained from 50 patients. Plaster models were 
scanned using the Ortho Insight 3D laser scanner; Bolton ratios were calculated 
with its software. CBCT scans were imported and analyzed using AVIZO 
software. Plaster models were measured with a digital caliper.  

 
 
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Data were analyzed with descriptive statistics and the intraclass correlation 
coefficient (ICC). They finally found that laser scanned digital models are highly 
accurate compared to physical models and CBCT scans for assessing the spatial 
relationships of dental arches for orthodontic diagnosis. 
     Rossini et al, (2016)[42] conducted a systematic review to evaluate the 
accuracy and sensitivity of measurements carried out on digital models compared 
to plaster models. Thirty-five relevant articles were selected from the years 
between January 2000 to November 2014 by using a grading system developed 
by the Swedish Council on Technology Assessment in Health Care and the 
Cochrane tool for risk of bias assessment to rate the methodologic quality. They 
found that there was no significant difference in all measured parameters, in 
majority of studies. Therefore, they concluded that digital models possessed high 
levels of accuracy, reliability and reproducibility when compared with 
conventional study models.  
    Furthermore, Abdi et al, (2017)[43] carried out a study in order to evaluate the 
validity of maxillary models by the weighted rugae superimposition method. 
They randomly selected 24 maxillary plaster models of 12-year-old patients as 
well as their models at 14 years old. They scanned the models two times using a 
bench top structured light 3D scanner. Once using the weighted rugae and the 
other using the unweighted rugae superimposition methods.  They concluded that 
the un-weighted superimposition made no significant differences in terms of total 
displacements of registration landmarks, while the weighted method recognized 
the medial points of the 3rd rugae as the most stable landmark. Hence, the 
weighted rugae superimposition method was found to be a stable method for 
analysis of tooth movements.  
 

 
 
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   Most recently, Pazera and Gkantidis, (2020)[44] carried out a retrospective 
study using twenty- four pre- and post- treatment cephalometric radiographs as 
well as their 3D digital models. They aimed to investigate the anteroposterior and 
vertical changes of the median rugae which is often used as a reference for 
superimposition of dental models in reference to the underlying skeletal 
structures. The incisive papilla and the three rugae points were placed on dental 
models and then registered on the cephalometric radiographs. The vertical and 
horizontal movements of the papilla and the rugae points, as well as a central 
incisor were measured (Viewbox 4 Software). They concluded that, both the 
second and the third rugae can be used as references for superimposition for 
assessment of tooth movement. While the use of the incisive papilla and first 
rugae was not recommended as they were affected by tooth movement.  
 
 
 

 
 
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Aim of the Study 
The aim of the current study was to assess the rate of anterior segment retraction 
using friction or frictionless mechanics. As well as evaluate the tip, torque, 
vertical position, and root resorption of the incisors. Moreover, anchorage loss 
and pain experienced was assessed.  
A-PICO Question: 
Patient/Population: 
 
Female orthodontic patients with bimaxillary protrusion requiring first 
premolars extractions followed by anterior segment retraction. 
Intervention: 
Anterior segment retraction using T- loops (Frictionless mechanics) with 
mini-screws used as anchorage. 
Comparator: 
Anterior segment retraction using sliding mechanics (Friction mechanics) 
with mini-screws used as anchorage. 
Outcomes: 
• Primary Outcome: measuring the rate of anterior segment retraction for 
space closure when frictionless and friction mechanics were used. 
Secondary Outcomes: measuring the changes in incisal position with regards to 
tip, torque and vertical position following 
 

 
 
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Outcome measure: 
Outcome measure 
Measure tool 
Measure unit 
1ry 
Outcome 
Assess the rate of anterior 
segment retraction  
Digital 
scanned 
dental models. 
 
 mm  
2ry 
Outcomes  
1) Assess amount of 
anchorage loss. 
Digital 
scanned 
dental models. 
 
mm 
 
2) Pain 
Pain scoring sheets 
given to patients. 
VAS scoring from 
1-10 
 
B-Research question: 
In orthodontic adolescent patients in need of 1st premolar extractions followed by 
anterior segment retraction, is there a difference, in terms of rate of anterior 
segment retraction, between friction and frictionless mechanics? 
Objectives of the study 
Research hypothesis: 
The null hypothesis of this research is that there is no difference in rate of 
anterior segment retraction between friction and frictionless mechanics. 
 
 

 
 
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Primary objective: 
Measuring the rate of anterior segment retraction using frictionless versus friction 
mechanics. 
Secondary objectives: 
Assess amount of anchorage loss and pain experienced.   
Study design: 
This is a randomized clinical trial with two arms parallel group and 1:1 
allocation ratio. In one group, frictionless mechanics will be applied 
during anterior segment retraction while the other will receive friction 
mechanics during retraction to compare the results for differences in rate.   
 
 
 
 
 
 
 
 
 

 
 
23 
 
Materials and Methods 
I)participants, interventions, and outcomes 
A] Study Setting: 
The study will be performed in the clinic of the Orthodontic Department at the 
Faculty of Oral and Dental Medicine, Future University. The recruited sample 
would be from the Egyptian urban and rural population. 
B] Eligibility criteria: 
➢ Inclusion criteria: for the participants include the following: 
1. Adolescent patients (females only). 
2. Patients requiring 1st premolars extraction followed by anterior segment 
retraction. 
3. Patients with fully erupted permanent teeth (not necessarily including 
the 3rd molar). 
4. Cases requiring maximum anchorage during anterior segment 
retraction.  
➢ Exclusion Criteria: for the involved subjects included: 
1. Patients suffering from any systemic diseases interfering with tooth 
movement. 
2. Patients with extracted or missing permanent teeth. (except for third 
molars). 
3. Patients with badly decayed teeth.  
4. Patients with any parafunctional habits.  
 
 

 
 
24 
 
C] Interventions: 
➢ Medical History Questionnaire: 
For every patient to exclude the presence of any systemic condition 
interfering with orthodontic treatment.  
➢ Clinical Examination: 
Oral structures will be examined to identify caries, fracture or 
missing teeth.  Gingival tissues will be carefully examined for any 
gingivitis, periodontitis, recession or lesions. 
➢ Diagnosis 
Check the potential patient to fulfill the previously mentioned 
inclusion criteria. Every participant will be asked to sign an 
informed consent about the study. Full set of records (study models, 
lateral cephalometric radiographs, photos) will be taken for every 
patient as part of the routine procedure for treatment of patients in 
the clinic of the Orthodontic Department, Future University. 
 
➢ Clinical Procedure: 
After taking pre-treatment records, every patient will undergo: 
• 
Bonding of all teeth except for first premolars, banding/bonding the 
first and second molars will be done using bidimensional brackets 
Roth prescription (0.022 slot prescription brackets) 
• 
Levelling and alignment for the bonded and banded teeth will be 
initiated which will be done by following the wire sequence: 0.014 
NiTi , 0.016×0.022 NiTi and  0.017×0.025 StSt.  
• 
Then miniscrews will be placed in upper arch between 2nd premolar 
and 1st molar. 
• 
The patient will be referred for extraction of 1st premolars then canine 
retraction will take place on a 0.017×0.025 StSt arch wire. 

 
 
25 
 
• 
Once canine retraction stage is completed, the patient will be referred 
for the taking of pre-intervention records. 
➢ Acquisition of pre-intervention records: 
• 
Impressions will be taken followed by digital scanning for the 
produced stone models which are the T0 record. 
➢ Beginning of Retraction: 
 
Frictionless group:  
• 
A ligature wire extending between the canines and mini-screws will be 
used for proper anchorage control. 
• 
Closing retraction T-loops will be fabricated using 0.017 x 0.025 TMA 
wire. The loop will be positioned in half the remaining extraction space 
after canine retraction. [15], [16]. 
• 
A gable angle of 45˚ will be added. 
• 
Distal activation of 4 mm will be done that will produce around 160 g 
per side of retraction force[17], with cinch back the wire distal to 2nd  
molars bilaterally. 
 
Friction group:  
• 
Crimpable hooks added to the arch wire (0.017”x0.025” Stainless steel) 
distal to the lateral incisor passing through the center of resistance of the 
anterior segment. 
• 
A ligature wire extending between the canines and mini-screws will be 
used for proper anchorage control. 

 
 
26 
 
• 
Retraction will start on a 0.017”x0.025” Stainless steel wire with an 
elastomeric power chain (force applied will be 160 g)  extending 
between the crimpable hooks and the mini-screws. 
• 
The force will be measured by a force gauge and reactivated each visit 
to maintain force of retraction constant all over the retraction phase. 
 
 
➢ 
Follow up visits 
 
Patients will be asked to attend for follow up sessions every 4 weeks for: 
• 
Evaluation of the mini implants stability. 
• 
Replacement of the power chain to maintain a force of 160g. 
• 
Reactivation of the T-loop by further distal activation and cinch back. 
 
➢ Criteria for discontinuing or modifying the allocated intervention: 
  
In cases of prolonged swelling or pain related to the miniscrew the patient 
will be given strict oral hygiene measures and may wait for three weeks 
before the beginning of retraction. 
In cases of loose or broken miniscrews, the screw will be removed and 
replace the miniscrew after total resolution of the inflammation. 
 
➢ Post-retraction Questionnaire: 
The patients of both groups will be asked to fill in questionnaires 
regarding their experience with both techniques. 
 

 
 
27 
 
➢ Retraction records 
The scanned dental models will assess the rate of retraction and molar 
anchorage loss achieved throughout the study.  
➢ Material Used 
• American Orthodontics Brackets, Roth prescription, Bidimensional slot 
size. 
• American Orthodontics Elastomeric power chains 
• American Orthodontics Elastomeric O-ties  
• American Orthodontics Ligature wire. 
• Jeil, Mini Screws, 8 mm length.  
• American Orthodontics Arch wires.  
• American Orthodontics Molar bands/tubes.  
D] Outcomes 
Primary outcome: is to monitor the rate of anterior segment retraction 
using both frictionless and friction methods. 
Secondary outcomes is to monitor anchorage loss and pain, in association 
with each technique after retraction during anterior segment retraction,. All 
outcomes will be assessed as the difference between T0 at the start of 
anterior segment retraction after full canine retraction and Tfinal after 
complete space closure. 
 
E] Participant timeline:  
1. The principle investigator will screen the potential patients through careful 
clinical examination of patients at the orthodontic department, Faculty of 
Oral and Dental Medicine, Future University.  

 
 
28 
 
2. All recruited patients should fulfil the previously mentioned inclusion and 
exclusion criteria.  
3. Every participant will be asked to sign an informed consent before the 
beginning of the study.  
4. After patient's enrolment, each participant will be asked for pre-
intervention records to ensure proper diagnosis.  
5. The supervisor will randomly allocate the patients to one of the 
intervention groups.  
6. Active intervention will begin after proper leveling and alignment of the 
upper and lower arches and canine retraction.  
7. The principle investigator will take pre-retraction records for every 
participant. (T0) 
8. In Friction mechanics group, Power chain is used for anterior segment 
retraction while in Frictionless group, T-loop is used for retraction.  
9. Each patient will come every 4weeks for follow up visit, for appliance 
activation and uptake of impression for interim records.  
10. After complete space closure, the principle investigator will take post-
retraction records for each participant. (Tfinal) 
11. Every patient will fill up a questionnaire regarding his experience during 
treatment.  
12. The principle investigator will continue the normal treatment and achieve 
proper finishing for every patient after the end of the study. 
 

 
 
29 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Screening of patients seeking 
orthodontic treatment at the 
orthodontic department outpatient
Patient enrollment 
Pre-intervention records 
Concealed Allocation 
Leveling and alignment, mini-screws, 
Extraction, canine retraction.  
Friction group 
Frictionless group 
Activation of PC and T-loop 
Acquisition of post-retraction 
Patient questionnaire 
Data collection and management 
Recruitment 
Preparatory 
phase 
Interventions 
Follow up 
End of study 
Eligibility criteria and 
informed consent  
Average 9 months 
After complete 
retraction 
Dropouts and missed 
data recorded 
Monthly follow up visits 
for activation 
Pre-retraction record 
Missed appointment 
records 
CONSORT flow chart of the flow of participants in the study. 

 
 
30 
 
E] Sample size calculation:  
Our sample size calculation is based on a previous study comparing the effect of 
friction and frictionless mechanics. [14] 
F] Recruitment strategy:  
The principal investigator will recruit the patients from the clinic of Orthodontic 
department, Faculty of Oral and Dental Medicine- Future University.  
Screening of patients will continue until the total number of participants for the 
study is collected.  
 
II) Assignment of interventions:  
A] Sequence generation:  
The supervisor of the study will apply Computer generated random numbers to 
randomly assign patients to Group A (Friction) or B (Frictionless) using 
Microsoft Office Excel 2007 sheet. and will write the patient numbers in the first 
column, and will select function RAND()to generate the randomization number 
in the second column. These numbers will be sorted according to the 
randomization number so the first column numbers will be randomly distributed.  
 
B] Allocation concealment mechanism:  
The supervisor of the study will write the randomization numbers of the patients 
in opaque white papers folded three times to form sealed envelopes and store it 
inside a box. Then will keep the Codes for randomization at the secretary office.  
 
C] Implementation:  
At time of intervention, the main operator will send the patient to the secretary 
office. Then, the assigned employee will open the box and ask the patient to 
select one envelope. the main operator will assign each participant for the 

 
 
31 
 
corresponding intervention either (friction or frictionless group) according to the 
list of codes of randomization.  
Assignment to either intervention will occur before leveling and alignment stage.  
 
D] Blinding:  
Blinding of the operators: Blinding will not be possible for the operators during 
the application interventions and during the follow up visits. The principal 
operator is responsible for assigning subjects to interventions according to the 
concealed allocation, appliance activation at follow up visits, dental impressions 
and acquisition of dental casts.  
 
Blinding of the outcome assessors: It is a single blinded study, the outcome 
assessors only will be blind. The patients name will be sealed from pre and post 
study models. Then two assessors will carry on, blindly and independently, the 
measurements and analysis of the study. 
 
III) Data collection, management and analysis: 
A] Data collection methods:  
 
Primary outcome:  
 
1. Retraction rate: to assess the antero-posterior movement of anterior teeth and 
first molars, the principle investigator will take study models for every 
participant monthly during the follow up visits. Then will digitize the models and 
identify the landmarks, reference lines and planes on the pre, interim and post-
retraction digital dental models for measurements reading.  
 
 

 
 
32 
 
Secondary outcomes: 
1.  Anchorage loss: will be accessed by the principal investigator via scanned 
study models before and after the completion of retraction by identifying the 
landmarks, reference lines and planes, then will interpret the measurements in 
degrees and millimeters. 
 
2. Pain: Each patient will fill a questionnaire regarding his treatment experience 
in a VAS scoring from 1-10. The questionnaire will include several questions 
related to oral hygiene, pain and discomfort experienced throughout the trial. 
 
B] Data management:  
A colleague outside the research team will enter the data and organize it in excel 
sheets in the computer of the orthodontic department.  
Data will include all photographs, models, radiographs and filled questionnaire.  
 
C] Statistical Analysis:  
• The principle investigator will be responsible for the extraction of the required 
data from the study models taken at every follow up visit. The data will be sent to 
a specialized statistician.  
• The specialized statistician will be responsible for the statistical analysis of the 
study by:  
1. Presenting the data as mean, standard deviation (SD) and Standard error (SE) 
values.  
2. Using Paired t-test to compare between the friction and the frictionless group 
of retraction as well as to compare between the pre-and post -treatment data for 
each group.  
3. Using Kolmogorov Smirnov and Shapiro Wilk tests to determine the rate of 
anterior segment retraction.  

 
 
33 
 
4. Statistically evaluate the patient acceptance for both techniques.  
• For this study, the specialized statistician will use IBM11 SPSS12 Statistics 
Version 20 for Windows to perform the required statistics.  
• The significance level will be P ≤ 0.05. Highly significant variables are detected 
when P value is less than 0.01.  
 

 
 
34 
 
Assessors Reliability:  
• To achieve high reliability for measurements, the supervisor will choose a well-
experienced inter-examiner during the study.  
• A training session will be provided for the examiners to ensure standard 
measurements techniques.  
• Each examiner will complete the measurements on a model and will repeat the 
procedure after one week to assess the intra- and inter-examiner reliability.  
• The supervisor will compare the measurements of the two assessors for 
disagreement with a difference of more than one millimeter.  
• The supervisor will evaluate the amount of variation in measurements among 
and between examiners to test the performance of each assessor.  
• The examiner with less reliability will receive additional training but will be 
replaced during the study.  
• The specialized statistician will calibrate the intra and inter-examiner reliability 
for the measurements of the study by Inter-observer and intra-observer reliability 
was assessed using P ≤ 0.05. 
 
IV) Method Monitoring:  
A] Data Monitoring: An independent Data Monitoring Committee (DMC) will 
monitor the results of the study. The Committee will include the trial’s 
supervisors, who will periodically review the trial data and identify the need for 
any adjustments or modifications during the study.  
 
B] Interim Analysis: no interim analysis will be performed during the study.  
 
C] Harm: The main operator will document and report any harms or unwanted 
effects during the study intervention to the trial supervisors. Also any unpleasant 

 
 
35 
 
experience will be reported by the patient in the final questionnaire at the end of 
the retraction. The main operator will be responsible for the management of any 
adverse effects or unfavorable side effects resulting from the appliance. 
  
D] Auditing: The supervisor will follow up and review the different 
interventions and resulting data. And he will periodically follow up the trial 
progress including recruitment of patients, allocation of participants to study 
groups; adherence to interventions and reporting of harms. A meeting with the 
senior supervisor will be set every 3 months to monitor the progress of the study 
and the need for any adjustments. 
 
V) Ethics and dissemination:  
A] Research Ethics Approval:  
The Ethical committee in Future University, Egypt will review the protocol 
before they approve it. The research Ethics committee will evaluate the different 
interventions of the study to ensure its ethical validity and the potential benefits 
to the participants. 
  
B] Protocol amendments:  
The main investigator will be responsible to complete a formal amendment in 
case of any modifications or adjustments to protocol that may affect the conduct 
of the study, as changes in the study design or intervention procedures. The 
Orthodontics department, Faculty of Oral and Dental Medicine, Future 
University and the Ethics Committee will approve such amendment before 
proceeding in the study .  
 
 
 
 

 
 
36 
 
C] Consent:  
The main investigator will be in charge for detailed explanation and elaboration 
of the different steps of the study interventions for each patient. Then will ask 
every participant to sign a written consent before they begin treatment. The 
consent will be written in Arabic.  
 
D] Confidentiality:  
The main investigator will store any personal information about the participants 
collected during the study separately from study records in locked files in areas 
with only access to the supervisors responsible for auditing and analysis. Also, 
will keep the files in the Department Of Orthodontics, Faculty of Oral and Dental 
Medicine, Future University and will identify all the reports, data and 
administrative forms by a coded ID number to maintain participant 
confidentiality. Participant information won't be used outside the study except 
with written permission of the participant.  
 
E] Declaration of interests:  
No financial interests are to be declared by the supervisors and the principle 
operator. This study is a part of a Masters’ degree in Orthodontics, Faculty of 
Oral and Dental Medicine, Future University and it is self-funded by the 
principal investigator.  
 
 
F] Access to data:  
The supervisors and the principal investigator will only have access to the data of 
the study. All the data will be secured by a password to maintain confidentiality. 
No other parties are allowed to assess the results until the study is terminated and 
the conclusions are revealed.  
 

 
 
37 
 
G] Ancillary and post-trial care:  
Any complication associated with the intervention will be managed by the 
principal operator. Then the two group of patients will continue their regular 
orthodontic treatment according to the treatment plan described for each case. 
 
H] Dissemination Policy:  
The trial results will be available to the participants, health care professionals and 
the public by publication of the study in high quality national and international 
journals. The principal investigator will present a copy of the thesis at the Faculty 
of Oral and Dental Medicine, Future University library and will distribute 
additional copies among the main universities in Egypt. 
 
 
 
 
 
 
 
 
 
 
 

 
 
38 
 
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