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Aim: Torque control in lingual orthodontics is essential to obtain optimal aesthetic results, nevertheless three dimensional control of anterior teeth depends on many factors and the role of ligatures in establishing the engagement of the wire into the slot is considered as a key point. The aim of this in vitro experimental study was to evaluate how different ligatures exposed to usage degradation perform in maintaining torque control in a customized lingual bracket appliance using two differently sized wires. Materials and methods: A typodont with eight extracted human teeth was created and a set of customized lingual brackets was obtained. Lingual ligatures and ordinary ligatures were tested on the 0.016x0.022 NiTi and the 0.016x0.024 SS wires using a compression/traction machine to calculate the efficiency in torque control. For each wire and type of ligature, the typodont was stored in physiological saline Sodium- Chloride 0.9%, pH 5.5 to simulate the oral environment for one month and then the mechanical test was repeated. A statistical analysis was performed. Annali di Stomatologia 2018;VIII (2):59-64 59 Results: No significant differences were found in angle values between ligatures or timepoints when the complete set of data was tested (p&gt;0.01). Conclusions: The ligature type and stretching by use did not affect torque efficiency during the first month.



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Annali di stomatologia
efficiency
Torque expression of a customized lingual appliance according to different elastomeric ligatures over time: an in vitro study
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Original Article
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2022-08-09
2018-06-01
2023-12-04
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Ann Stomatol (Roma)
A. Silvestrini-Biavati
2018
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Torque expression of a customized lingual appliance according to different elastomeric ligatures over time: an in vitro study
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                                                                                                Original article



    Torque expression of a customized lingual
    appliance according to different elastomeric
    ligatures over time: an in vitro study




                                                                                              li
                                                                                            na
    Marco Migliorati1 DDS, MS, PhD                         Results: No significant differences were found in
    Daniela Poggio1 DDS                                    angle values between ligatures or timepoints
    Sara Drago1 MSc, DDS                                   when the complete set of data was tested
    Alberto Lagazzo2 MEng, PhD                             (p>0.01).




                                                                                          io
    Roberto Stradi3 DDS, MS                                Conclusions: The ligature type and stretching by
    Fabrizio Barberis2 MEng                                use did not affect torque efficiency during the
    Armando Silvestrini-Biavati1 MD, DDS                   first month.




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                                                           Key words: orthodontics, torque, efficiency.
    1 Orthodontics Department, School of Dentistry,
    University of Genova, Genova, Italy
                                                           Introduction




                                                                   rn
    2 Section of Materials Engineering, Department of

    Civil, Chemical and Environmental Engineering
    (DICCA), University of Genova, Genova, Italy           The demand for an aesthetic orthodontic treatment
    3 School of Orthodontics and Temporomandibular         has increased and more attention has been payed to




                                                      te
    disorders, University of Naples, Naples, Italy         “invisible” orthodontic techniques, such as clear align-
                                                           ers and lingual orthodontics. Lingual orthodontics is a
                                                           reliable option for clinicians who want to fully accom-
                                                    In
    Corresponding author:                                  plish therapeutic targets, because of the possibility of
    Sara Drago                                             treating every malocclusion the same as the labial
    Orthodontics Department, School of Dentistry,          approach, from extraction cases to orthognathic pa-
    University of Genova                                   tients, and other nonextraction treatments (1, 2).
    Largo Rosanna Benzi 10                                 The functionality and the aesthetics of the outcome
                               ni

    16132 Genova, Italy                                    are achieved by three-dimensional control of teeth
    E-mail: dr.sara.drago@gmail.com                        during all the phases of the therapy; this control is
                                                           particularly important for upper anterior teeth and it is
                             io


                                                           obtained by using biomechanics that are different
    Summary                                                from the labial technique. In fact, in lingual orthodon-
                                                           tics biomechanical changes are due to a different ap-
                           iz



    Aim: Torque control in lingual orthodontics is es-     plication point of the force, which affects the vertical
    sential to obtain optimal aesthetic results, never-    position of teeth. Particularly, in all extraction cases,
    theless three dimensional control of anterior teeth    the space closure can determine considerable prob-
            Ed




    depends on many factors and the role of ligatures      lems in incisors inclination.
    in establishing the engagement of the wire into        Torque expression is affected by many factors, in-
    the slot is considered as a key point. The aim of      cluding the bracket position, the size of the wire, the
    this in vitro experimental study was to evaluate       alloy of the wire, the friction between the wire and the
    how different ligatures exposed to usage degra-        brackets, the tensile properties of + different elas-
    dation perform in maintaining torque control in a      tomeric ligatures and the procedures adopted to man-
 IC




    customized lingual bracket appliance using two         age third order movements (3-6). The effect of force
    differently sized wires.                               decay on elastomeric ligatures is important as well,
    Materials and methods: A typodont with eight ex-       because the engagement of the wire into the slot de-
    tracted human teeth was created and a set of cus-      termines the force which is transmitted to the tooth
C




    tomized lingual brackets was obtained. Lingual         and the degradation of ligatures could make this en-
    ligatures and ordinary ligatures were tested on        gagement sub-optimal at some stage.
    the 0.016x0.022 NiTi and the 0.016x0.024 SS wires      Force decay of elastics and ligatures is not an un-
    using a compression/traction machine to calcu-         known effect in orthodontic practice: patients are rec-
©




    late the efficiency in torque control. For each wire   ommended to daily change orthodontic elastics and
    and type of ligature, the typodont was stored in       doctors are invited to establish an initial force with
    physiological saline Sodium- Chloride 0.9%, pH         about 8 to 14% of compensation above the force for
    5.5 to simulate the oral environment for one           the desired movement, because of the significant
    month and then the mechanical test was repeat-         force degradation presented during the first twelve
    ed. A statistical analysis was performed.              hours by most products (7). The force delivered by

    Annali di Stomatologia 2018;IX (2):59-64                                                                     59
    M. Migliorati et al.


    elastomeric chains decays rapidly over time as well,         dried for 20 seconds. Customized lingual 0.022 x 0.022
    with consequences on their mechanical properties             brackets (Incognito®,3M Unitek, Monrovia, Calif) in
    and clinical efficacy (8-10).                                their indirect bonding tray were then bonded with an
    However, a limitation of many in vitro studies on this       orthodontic composite (RelyX™ Unicem 2 Automix; 3M
    subject is that they are based on measurements of            Unitek, Monrovia, Calif). After the composite was
    the force and of the extension of ligatures which are        cured, all samples were extracted from the resin block
    stretched until rupture (11, 12), whereas a better clini-    and tied to a 0.018x0.025 SS archwire (Incognito®, 3M




                                                                                                     li
    cal simulation may be obtained by focusing on how            Unitek, Monrovia, Calif) one by one. Then the teeth




                                                                                                   na
    the ligature influences the behavior of the entire slot-     crowns were included in a block of soft wax to stay
    wire system. The measure of torque moment is a fea-          integral with each other. Once more, the lateral surface
    sible laboratory observation and represents an out-          of the resin block was dug over with a denture bur in a
    come which is strongly related to the appliance per-         straight handpiece, and the teeth roots were put along
    formance.                                                    a straight line in the pit and encased in fluid transparent




                                                                                                 io
    The aim of the present study was to evaluate how dif-        resin (metil-metacrylate). The resin was cured and the
    ferent ligatures exposed to usage degradation per-           wax was removed from the crowns. The obtained teeth
    form in maintaining torque control in a customized lin-      position in the typodont allowed slots to be passively




                                                                           az
    gual bracket appliance, using two different wire sizes.      engaged by the archwire (Fig. 1).

                                                                 Wires
    Methods                                                      The tested archwires were: 0.016x0.022 NiTi, and




                                                                         rn
                                                                 0.016x0.024 SS. (Incognito®, 3M Unitek, Monrovia,
    Typodont                                                     Calif). Both wires were first measured with a digital
    Eight extracted human teeth were collected: a central        caliper to verify if the nominal dimension corresponded
    upper right incisor, two upper lateral incisors (right and   to the real one.




                                                          te
    left), two upper canines (right and left), two upper first
    bicuspids (right and left) and one upper second              Ligatures
    bicuspid (left). All teeth were carefully cleaned with       Easy-to-tie (L1) and lingual ligatures (L2) were tested
                                                        In
    ultrasonic and manual instruments, disinfected with          (Alastik, 3M Unitek, Monrovia, Calif).
    hydrogen peroxide and stored in physiological saline
    Sodium-Chloride 0.9%, pH 5.5 in order to avoid               Testing machine
    dehydration, elasticity loss, and to prevent the risk of     The bracket matching the missing incisor was tied to
    fractures.                                                   the wire as the “testing” bracket on which the
                               ni

    Transparent metil-metacrylate components (Orthojet,          measurements were performed. An extension was
    Lang. Wheeling, IL 60090 USA) were carefully mixed           laser-welded to the bracket in order to apply the
    not to produce air bubbles and then poured into a 100        necessary force to study it. The extension was a round
                             io


    mm X 35 mm X 25 wax box (Tenatex Red, Kemdent.               steel wire large 1.5 mm in diameter. At the distance of
    Purton, Swindon Wiltshire, UK) to create a resin base        10 mm a bottleneck was created on the wire, to
    where the teeth could be accommodated. The resin             recognize and keep the same force application point
                           iz



    was cured in a curing water machine (30°C, 6 atm).           trough all tests. The extension was laser welded to the
    Then the lateral surface of the resin block was dug over     back of the bracket.
    with a denture bur in a straight handpiece, and once         The Zwick/Roell Z0.5 machine (sensibility: <1%,
           Ed




    enough space had been created, the teeth roots were          displacement sensibility 1μm, full scale range 500N)
    put along a straight line in the pit and encased in fluid    was used to apply forces to the system, using forces
    transparent resin (metil-metacrylate). The teeth were        from 0N to 0.6N. The typodont was fixed to the
    not positioned along the natural shape of the arch, but      ZwickLine® machine by bolts and screws that engaged
    in a straight line, in order to study the mechanical         with the grooves on the plate, so that the model was
    properties of the system. The crowns emerged from the        solidly fixed to the machine, in order to create a system
 IC




    resin and presented a contact point with each adjacent       suitable to the application of forces.
    tooth; one empty space was left for the missing tooth        The model was positioned by placing the side with the
    (upper left incisor). The block was cured again to obtain    largest area on the plate, so that the lingual side of the
    teeth stability.                                             teeth was above, the vestibular side below, the coronal
C




    A silicone biphasic impression of the obtained typodont      portion of the teeth on the right and the roots housed in
    was taken (Hydrorise, Zhermack. Badia Polesine (RO),         the resin on the left.
    Italy) and sent to the Incognito® lab. A set of              The traction system was hooked to the bottleneck
    customized brackets, an indirect bonding tray and            extension of the testing bracket via a rigid metallic
©




    straight sectional wires of different materials and          perforated screw. The extension of the testing bracket
    dimensions were obtained.                                    was placed in the drilling of the screw (Fig. 1).
    All teeth were sanded with aluminium oxyde (50µ), then       A connection -like an enarthrosis joint- was used
    they were etched for 30 seconds with 32%                     between the screw and the machine to prevent the
    orthophosphoric acid (Scotchbond™, 3M Unitek,                decomposition of the force in the horizontal
    Monrovia, Calif), rinsed with water for 30 seconds and       components and to maintain a constant vertical

    60                                                                                Annali di Stomatologia 2018;IX (2):59-64
    Torque expression of a customized lingual appliance according to different elastomeric ligatures over time:
    an in vitro study




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                                                          te
    Figure 1. Experimental setting (the homemade typodont and the testing machine).
                                                        In
    traction. The torque moment [Nmm] was calculated by            interquartile ranges. Data were tested for normality
    multiplying the applied force through the arm, that is         using the Shapiro-Wilk test.
    the distance between the axis of rotation and the point        To evaluate differences between ligatures for time-
                               ni

    of application of the force which was fixed to 10 mm           points, a non-parametric analysis of variance was
    through the whole experiment. The torque angle [°] was         performed. Differences with a p-value less than 0.01
    algebraically calculated: the ZwickLine® machine is            were selected as significant and data were acquired and
                             io


    able to measure also the displacement performed by             analysed using R v3.4.4 software environment (13).
    the extension, thus knowing the displacement (δ) and
    the arm (b) we can derive the sine of:
                                                                   Results
                           iz



    sin θ=δ/b
                                                                   Descriptive statistics are reported in Table 1 and Figure
            Ed




    The value of the torque angle (θ) was then derived by          2. Continuous variables are given as median with
    the arcsine function. When the angle between the               range, whereas categorical variables as numbers. The
    extension and the machine changes, the arm of the              non-parametric analysis is reported in Table 2.
    force changes as well, thus the error was corrected            No significant differences were found in angle values
    after data collection.                                         between ligatures or timepoints when the complete
    The mechanical testing was repeated for each wire and          set of data was tested (p-value=0.7090 and p-value=
 IC




    for each type of ligature. For each wire and type of           0.6832).
    ligature, the typodont was stored in physiological saline
    Sodium- Chloride 0.9%, pH 5.5 to simulate the oral
    environment for one month and then the mechanical              Discussion
C




    test was repeated.
                                                                   Experimental setting
    Software                                                       Since the introduction of lingual customized appli-
    The TestXpert® II Zwick-Roell software was used to             ances the problem of torque control in the anterior
©




    collect data and to represent the torque moment -on            area has been a very important issue, addressed by
    the ordinate-, with the torque angle -on the abscissa- in      different Authors (14-17).
    a Cartesian graph.                                             Previous studies on torque control with buccal brack-
                                                                   ets had focused mostly on the play between wire size
    Statistical analysis                                           and slot dimensions. In a study comparing the torque
    Descriptive statistics are expressed as median and             play (degrees) of several lingual brackets with wires

    Annali di Stomatologia 2018;IX (2):59-64                                                                             61
    M. Migliorati et al.


    Table 1. Descriptive statistics. Medians and interquartile ranges of angle values in each wire reading group for all types of
    ligatures and timepoints. Ligatures: L1: AlastiK™ Easy-to-tie, L2: AlastiK™ lingual ligature.

                                                          Wires
                               016x022 NiTi                           016x024 ss
    L1        T0               9.74 [3.84, 13.21]                     2.44 [1.39, 3.88]




                                                                                                            li
              T1               10.01 [4.37, 13.34]                    2.66 [1.20, 4.24]




                                                                                                          na
    L2        T0               8.44 [3.36, 12.71]                     2.66 [1.56, 4.07]
              T1               8.77 [3.47, 12.71]                     2.60 [1.51, 4.44]




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    Figure 2. Medians and interquartile ranges graph of angle values: a) according to the type of ligatures: Ligature 1, AlastiK™
    Easy-to-tie; Ligature 2, AlastiK™ Lingual ligatures; b) according to the status: status 1=fresh ligatures, status 2=stretched
    ligatures.
                               iz



    Table 2. Summary of non-parametric analysis. Results are          slot. Hence, in these systems the effect of the ligature
    expressed as coefficient of regression (Coeff.) with 95%          type on three dimensional control of anterior teeth be-
              Ed




    confidence interval (95%).                                        comes essential, and from a clinical point of view,
                                                                      emphasis is given to particular ligature methods to
    Variable               Coeff.              95% CI
                                                                      obtain a better control.
    (Intercept)            100.23              64.89; 135.57          Sifakakis et al. compared different lingual brackets
    Status
                                                                      using a traditional o-ring configuration to compare the
                                                                      torque variation (18). They concluded that cus-
 IC




         1                 0                   -                      tomized brackets produced the highest moments, but
         2                 3.36                -12.85; 19.58          they assumed that the moment is dependent by the
                                                                      ligation mode.
    Ligature                                                          The present study was focused on two ligatures: a
C




         L1                0                   -                      traditional one (AlastiK™ Easy-to-tie) and a type of
                                                                      ligature (AlastiK™ Lingual ligature) specifically devel-
         L2                -3.18               -22.14; 15.78
                                                                      oped to sit better the wire into the slot for a better tip
                                                                      and torque control in lingual brackets. The experi-
©




                                                                      mental setup was inspired by the lingual torque
    of various sizes it was found that customized brack-              analysis performed by Lossdörfer et al. (19) who
    ets were the most precise system (17). In fact, in lin-           used a customized lingual appliance bonded on a ty-
    gual orthodontics with customized brackets the final              podont. Data collection was improved in the present
    arch wire is fully engaged into the slot, with less               study by a continuous data acquisition, which was ob-
    space for movements or rotation of the wire into the              tained through a mathematical elaboration of the

    62                                                                                       Annali di Stomatologia 2018;IX (2):59-64
    Torque expression of a customized lingual appliance according to different elastomeric ligatures over time:
    an in vitro study

    movement analysis. The typodont was made of ex-                Conclusions
    tracted human teeth, so that the bonding procedure
    was the one which is ordinarily applied in the clinical        In this in vitro study a torque expression record using
    practice. Moreover, it was decided to put the teeth on         two different ligatures and two wires was obtained for
    a straight line, and to use wires in a straight shape, in      a customized lingual appliance at two different time-
    order to eliminate any kind of distortion due to the           points:
    wire configuration and to avoid any kind of interfer-          - the ligature type did not affect the torque efficiency




                                                                                                             li
    ence on the wire-bracket-ligature system.                      - there were no differences in torque performance




                                                                                                           na
    The simulation was completed by applying forces in a               between fresh and stretched ligatures.
    range between 0N and 0.6N: by multiplying the ap-
    plied force through the 10 mm long arm, we obtained
    torque values beyond the 6 Nmm threshold. This was             References
    in accordance with the literature, which indicates val-




                                                                                                         io
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                                                                               az
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                                                           te
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                                                                   5.    Morina E, Eliades T, Pandis N, Jäger A, Bourauel C.
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                                                                         El Haje O. Comparative analysis of force degradation of la-
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                                                                         tex orthodontic elastics of 5/16’’diameter: an in vitro study.
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                           iz



                                                                   8.    Halimi A, Benyahia H, Doukkali A, Azeroual MF, Zaoui F. A
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©




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    Annali di Stomatologia 2018;IX (2):59-64                                                                                          63
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        tomized lingual bracket appliance. Am J Orthod Dentofacial         19. Lossdörfer S, Bieber C, Schwestka-Polly R, Wiechmann D.
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                                                                                                                 na
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                                                                                                               io
        2013;35:375-380.                                                       thod Dentofac Orthop. 2011;139:e31-44.




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    64                                                                                             Annali di Stomatologia 2018;IX (2):59-64
