cherry loop - a new loop to move mandibular molar mesialy

7/31/2019 Cherry Loop - A New Loop to Move Mandibular Molar Mesialy

1/6

R Peretta

M Segu

Authors affiliations:

R. Peretta, Orthodontic Department, University

of Padua, Padua, Italy

M. Segu, TMD Department, University of

Pavia, Pavia, Italy

Correspondence to:

Peretta Redento, MD, DDS, MScContra S. Marco 13

36100 Vicenza

Italy

Tel: +39 444325967

E-mail: [email protected]

To cite this article:

Prog. Orthod. 2, 2001; 2429

Peretta R, Se gu M:

Cherry loop: a new loop to move the mandibular

molar mesially

Copyright Munksgaard 2001

ISSN 1399-7513

Cherry loop: a new loop to

move the mandibular molar

mesially

Abstract: The aim of this study was to test the clinical

efficacy of a new loop named cherry loop in correcting the

Class II relationship by the mesial movement of the first lower

molars in the TweedMerrifield technique. We compared the

amount of molar mesial movement in two groups of patients

treated with upper first bicuspid and lower second bicuspid

extractions. The study was conducted using two X-rays, one

before treatment and one after the molars had moved.

Mandibular molars and incisors were traced and their positionsanalyzed along a Cartesian coordinate system. Movements

were related to stable structures: lower borders of the

mandible and the symphysis. The cherry loop performance

was compared to that of the shoehorn loop. Cherry loop

averaged 5.25 mm of average mesial movement, whereas the

shoehorn loop yielded only 3.28 mm. The vertical control of

molars was better with the new loop; we had only 1.24 mm of

extrusion compared to 3.24 mm with the usual loop. The

anteroposterior stability of the incisors was better too; we had

1.54 mm of distal movement of the crowns compared to 2.24

mm with the shoehorn loop. A serendipitous finding was that

the occlusal plane could be controlled by the cherry loop. It

can be oriented to best fit the growth pattern. In turn, in the

growing patient, a favorable skeletal response can be

expected.

Key words: Class II malocclusion; loop; mesial molar

movement

Introduction

Probably the extraction of lower second premolar fol-

lowed by mesial movement of the first molar is the

treatment strategy preferred by most orthodontists forClass II correction (1). The obvious advantage of this

choice for the clinician is the potential to restore a normal

inter-arch relationship when the mandibular sagittal

growth is not substantial or is completely absent, as in

adult patients. Unfortunately, efforts to move a molar

mesially are often troubled by a variety of problems. The

first and most important is the retroclination of mandibu-

lar incisors. Segment of the dental arch anterior to the

premolars is commonly utilized as the anchorage area

24


2/6

Peretta and Segu. Cherry loop

when mesially directed forces are applied to the molar.

These forces can come from closing loops, intra-arch

elastics, or some others. The reactive forces generated by

these systems are responsible for the lingual movement of

anterior teeth.

Class II elastics can be a problem; while they can move

the molars mesially, they can also cause them to tip and to

extrude (2). In this scenario, extrusion of the first molar is

the most important problem to solve. These teeth rou-

tinely extrude when subjected to mesially directed trac-tion forces. This problem is attributable to an erroneous

shaping of the tip-back bends, commonly used to control

the tooth axis. In fact, bodily movement of the molar is

achieved by adding a pair of counterclockwise forces

generated by a tip-back (second-order) bend, which is

necessary to thrust the roots forward. The combination of

these with the protraction forces moves the molar tooth

in a controlled manner. Most commonly, a tip-back bend

is placed mesial to the molar, but unfortunately this is a

serious technical error. The second-order bend that does

not fall directly into the center of the interbracket space

produces imbalanced moments as it creates vertical forcesthat are extrusive for the tooth nearest the bend (3). The

greater the difference of the moments, the greater the

extrusive tendency. The vertical force vector can be re-

duced to a negligible magnitude if the equilibrium of the

moments is thoroughly controlled. Ideally, the second-or-

der bend should be placed exactly at the center of the

interbracket space. This problem occupies a decidedly

lengthy period of treatment time, almost a year in my

experience, to obtain a very modest, but real, movement

of the tooth. The aim of this study is to verify the clinical

effects of a new loop designed to move the lower molar

mesially. The authors named this new loop cherry loop

because it resembles the fruit.A loop designed to move a molar mesially can be

thought clinically useful when it can close the extraction

or agenesis site better than it can occur spontaneously (4)

and when the dental extrusion that occurs as a side effect

does not exceed the physiological eruption of the teeth

(5). The design of the loop reported here is based on three

distinct considerations. First, it had to address the prob-

lem of moving the lower first molars without taxing the

incisors. This was achieved by sequencing the movements:

first the mesial movement of the root and, subsequently,

the crown. Secondly, the design adheres to the principal

that the lesser the mechanical stress imposed on the tooth,the greater the movement. The third consideration con-

cerns the fact that cuspal interference from the antagonist

teeth on the extruded molar impedes the mesial

movement.

We report here the performance of the cherry loop. Its

efficiency was tested by comparing it to the classic shoe-

horn (TweedMerrifield) technique. These patients were

treated by second premolar extractions and the control

group was left untreated.

Materials and methods

The cherry loop is made of resilient 0.170.25 stainless-

steel wire. This wire is sufficiently elastic and slides

smoothly inside a 0.220.28 molar tube. Using a pair of

Rouland pliers, a large-diameter round loop is bent; it has

the following characteristics: height, 8 9 mm; width, 8

mm; open 34 mm at the occlusal end in an effort to

avoid bite stress and to minimize the deformation of the

wire (Fig. 1a). The position of the loop must be rigorouslykept at one-half the distance separating the bracket of the

lower first bicuspid from the molar tube of the first molar

(Fig. 1b). As the molar is protracted, the loop must be

brought to one-half the distance. This can be achieved by

shortening, at the proper time, the wire with a V bend

placed distal to the canine tooth. The activation of the

loop occurs in two phases.

First phase

After measuring the readout (6), i.e., the inclination of the

molar tube with respect to the plane of occlusion, the

distal part of the wire is bent 15 to form an active

tip-back. Hence, the severity of the tip bend on the wire

depends on the initial inclination of the molar. A metal tie

is extended between the internal part of the loop and the

hook of the molar tube. The action will be a pure rotation

of the root, without movement of the crown. The reac-

tion to this movement is a clockwise pivoting of the front

portion of the arch. Of course, this is an acceptable

movement if it is part of the treatment plan. Otherwise,

this effect can be prevented by the use of anterior vertical

elastics. It is interesting to observe that the reaction tomesial movement of the root (Fig. 1c) is expressed in a

vertical direction in the anterior area and that this effect is

easily compensated by the use of vertical elastics. In order

that the reaction occurs in the described manner, it is

necessary that the position of the loop is exactly at the

center of the extraction space. A distally positioned bend

would cause a severe extrusion of the molar during the

uprighting and this must be avoided absolutely. An exag-

gerated mesial position and therefore of the tip-back

bend would not be efficient to obtain the straightening

of the molar axis.

Second phase

When the root shifts mesially, the inclination of the

molar tube becomes positive with respect to the plane of

occlusion by ca. 5 (Fig. 1d). This occurs over a period of

24 months in relation to the initial readout of the tooth.

At this point, the crown can be moved mesially.

Prog Orthod 2, 2001/24292 25


3/6


The tip back bend is eliminated and the arch is brought

into plane (Fig. 1e). A metallic tie is applied to the cherry

loop and bound to the molar tube, causing a ca. 1.5-mm

opening of the loop. The loop closure develops a force

couple in a clockwise direction, which forces a clockwise

rotation of the tooth around its center of resistance. This

force system moves the crown mesially. The vector of

reaction is in a distal direction. However, since the real

force developed is quite modest, the lingual movement of

the front teeth is minimal as well. Usually, the movement

of the molar crown is very fast, and after 15 days, the

loop can be reactivated at the tip-back bend for further

mesial displacement of the root (Fig. 1f). The two-phase

activation proceeds until the entire space is closed.

This protocol to move the molar mesially was tested on

a sample group of 20 Class II patients chosen who sa-

tisfied the following clinical criteria:

Normal or slightly hyper-divergent skeletal pattern. In

low-angle cases extraction of the second premolars is

contraindicated.

Correct or slight labial position of the lower incisors.

Protruded upper incisor with somewhat weak chin.

Following the extraction of 14, 24, 35, and 45 in this

experimental group of patients, the maxillary incisors and

canines were moved distally and the mandibular molars

mesially.This group compared to a matched malocclusion group,

consisting of 20 cases treated by the authors together with

the team of instructors from the EPGET (European Post-

graduate in Edgewise Technique) Italy (Drs Sandro Segu,

Emilio Contini, and Alberto Casali).

Treatments were monitored by cephalometric tracing

data. The recordings were the mandibular contour, sym-

physis, first molar, and the pre-treatment incisor posi-

Fig. 1. (a) Loop features: 8 mm high and wide, 4 mm occlusally open; 0.170.22 SS archwire. (b) Activation of the distal tip. The loop position

is exactly in the center of the extraction space. (c) Root mesial movement. The balance of the moments avoids the molar extrusion. (d) The root

mesial movement continues until a value of +510 of readout is obtained. (e) The distal tip is eliminated and the loop is activated opening 1.52

mm. (f) After crown protraction, it is possible to start again with a new mesialization of the root.

2Prog Orthod 2, 2001/242926


4/6


Fig. 2. Points and planes used in this research.

whereas negative values indicate intrusive and distal direc-

tions. The cant of the occlusal plane was denoted by a

positive value to show clockwise rotation, and the nega-

tive value signals counterclockwise rotation.

Discussion

As seen in Table 1, the average mesial molar crown

movement (DCoM-AP) obtained in patients treated with a

cherry loop was 5.25 mm, against the 3.28 mm of the

shoehorn loop. The average root movement (DRaM-AP)

was greater in the cherry loop as well; 7.75 mm versus

6.28 mm yielded by the shoehorn method. It is apparent

from these figures that the cherry loop is highly capable of

translating the molar crown mesially. Both the crown and

the roots came forward far more efficiently with the

cherry loop than with the classical Tweed Merrifield

mechanics. It is important to note that this result is not

reached at the expense of the incisor positions. In fact, the

average retraction at the incisor crown (DCoI-AP) in the

cherry loop group was 1.54 mm, against the 2.41mm of the shoehorn group. This difference demonstrates

that the theoretical biomechanical model of the cherry

loop function is clinically reproducible during the course

of the treatment. Clearly, the cherry loop is among the

practical armamentarium of the clinician.

The vertical reaction to the mesial movement of the

molar root can be easily compensated by the use of

anterior box elastics. It should be noted, however, that

the vertical position of the crown and the radicular apex

were seen to be very stable, with a value of the DCoI-V of

tions. Tracings were done before and after mandibular

space closures. A reference system of Cartesian coordi-

nates was constructed, with the initial occlusal plane as

axis X and a straight line orthogonal to the initial occlusal

plane and passing through the rearmost point of the

symphysis as axis Y (Fig. 2). The following points were

projected onto these planes: CoI, incisor coronale; CoM

molar coronale; RaI, incisor radicular; RaM, molar radic-ular. In the first tracing, the point coordinates defined the

sagittal and vertical positions of the teeth with respect to

the reference planes. The first tracing was then superim-

posed on the second tracing. The Cartesian coordinates

were registered on the posterior border of the symphysis

as this area is reported to be the most stable during growth

(7) and treatment. Differences in the coordinate measure-

ments were then computed. A positive delta sign (D)

convention was used for the extrusion and protraction of

teeth, while the negative D was used for retraction and

intrusion. Since the vertical variations of the teeth influ-

ence the inclination of the mandibular occlusal plane, testswere made on the stability or the variation by measuring

the variation of angle A included between the line orthog-

onal to the mandibular plane passing through the ret-

rosymphyseal point and the initial occlusal plane. A

positive value was conventionally given to the clockwise

rotation of the occlusal plane and a negative value to the

counterclockwise rotation.

These two sample groups were also compared to an

untreated control group of 20 patients (12 females and 8

males). The measurements in this group were made first at

the mean age of 12 years and then again at age 14. These

values were similar to those reported earlier by others (4,

8).

Results

The results obtained are shown in Table 1. The difference

between pre-treatment values and post-molar movement

data are expressed by the delta (D) symbol. Positive values

denote extrusion or forward movement directions,

Table 1. Average movements at the following landmarks:

incisor coronale, CoI; molar coronale, CoM; incisor radic-

ular, RaI; and molar radicular, RaM

Cherry ControlD (in mm) Shoehorn

loop loop

Anteroposterior 0.755.25CoM 3.28

3.74CoM 1.24 2.05Vertical

7.75 6.28 0.41Anteroposterior RaM

0.75 3.53RaM 1.05Vertical

0.35CoI 2.411.54Anteroposterior2.510.41CoIVertical 1.55

0.53RaI 0.58 0.14Anteroposterior

1.13Vertical RaI 0.25 1.56

AOcclusal plane 0.37 +3.71

The positive sign indicates occlusal or mesial movements; negative values indicatemovements in the gingival or distal directions. Concerning the occlusal plane, apositive value shows clockwise rotation and a negative value shows counterclock-wise rotation

Prog Orthod 2, 2001/24292 27


5/6


Fig. 3. Improvement of the profile for the mandibular response.

Fig. 4. (a) Pre-treatment X-ray. (b) Post-treatment X-ray.

0.41 mm and a value of the DRaI-V of 0.25 mm. Also, the

activation of the cherry loop in an anteroposterior direc-

tion for a short time and a low intensity of force does

not show a significant influence on the anteroposterior

position of the incisor crown, DCoI-AP 1.54 mm and

of the radicular apex DRaI-AP, measuring 0.58 mm.

Probably, the most interesting aspect of the effects of

the cherry loop is in the improvement of the verticalcontrol of the dentition. In fact, the lower first molar

crown of the experimental group DCoM-V shows an

extrusion of 1.24 mm, against the 3.74 mm of the second

group. The lower incisor of the second group also ex-

truded, but since the actual amount of tooth movement is

less than that of the molars, the overall effect consists in

a clockwise rotation of the mandibular occlusal plane.

This effect was not seen in the cherry loop group

where, to the contrary, the occlusal plane has demon-

strated a substantial stability with only a little tendency to

rotate counterclockwise. The clinical importance of this

fact can well be understood considering that the clockwiserotation of the occlusal plane induces a clockwise rotation

of the entire mandible (9, 10). Presumably, as a result, the

horizontal component of the mandibular growth is de-

creased. This phenomenon limits the corrective effect of

treatment on the characteristics of patients Class II

profile (11). The judicious equilibrium of the moments

generated by the progressive activation of the loop is the

most convincing explanation of the clinical success of a

vertical control of the dentition. The smallest counter-

clockwise rotation of the occlusal plane orients the

mandibular growth mesially and the subsequent advanced

chin improves the profile (Figs. 35).

Conclusions

This clinical experiment with the cherry loop to move the

mandibular molars mesially following second premolar

extraction provided us with the evidence. The positions of

these teeth can be improved substantially by a significant

mesial movement. The anteroposterior position of the

lower incisors is also seen to be more stable with respect

to the sample groups treated with the shoehorn loop,

presenting minimum withdrawal and substantial vertical

stability. Certainly, the best effect was the vertical control

of the molars. Our ability to control the single tooth

movements has led to a consequent improvement: the

control of the mandibular occlusal plane. The stability of

the occlusal plane or only a slight closure thereof make it

possible to orient the mandibular growth in a sagittal

direction. This maneuver reduces the treatment time and

yields a more satisfying clinical and esthetic result. We

therefore recommend this new loop for routine use. It can

be incorporated into the Tweed Merrifield technique suc-

Fig. 5. Superimposition.

2Prog Orthod 2, 2001/242928


6/6


cessfully, as well as other orthodontic techniques. We

need to asses the stability of the corrected tooth positions

(molars and incisors) in a future study.

Riassunto

Lobiettivo di questo studio e la sperimenzione dellefficacia clinica di

una nuova ansa, chiamata Cherry loop, per la correzione dei rapporti

di classe due mediante la mesializzazione dei primi molari mandibolari

in tecnica Tweed Merrifield. E stata comparata la quantita di mesial-

izzazione molare mandibolare ottenuta in due campioni di pazienti di

seconda classe trattati con estrazione dei primi premolari superiori e

secondi premolari inferiori. Il confronto e stato eseguito su due lastre

prese prima del trattamento e dopo mesializzazione dei molari. Sono

stati fatti due tracciati della mandibola, dei molari e degli incisivi. La

posizione dei denti prima e dopo mesializzazione molare e stata rile-

vata con misure millimetriche rispetto a due assi cartesiani costruiti

sulle strutture stabili della base mandibolare e della sinfisi. Nel primo

gruppo la mesializzazione e stata ottenuta con lansa di mesializzazione

shoehorn, mentre il secondo gruppo e stato trattato con la nuova ansa

cherry loop. La quantita media di mesializzazione ottenuta con cherry

loop e stata di 5,25 mm a fronte dei 3,28 mm ottenuti con shoehorn.

Anche il controllo verticale dei molari e stato migliore con la nuovaansa con solo 1,24 mm di estrusione rispetto ai 3,74 dellansa

tradizionale. Anche la sta bilita anteroposteriore degli incisivi e stata

migliore con la nuova ansa con solo 1,54 mm di distalizzazione coro-

nale contro i 2,24 mm ottenuti con la shoehorn. Un dato interessante

fornito da questo studio riguarda inoltre il controllo del piano oc-

clusale ottenuto dalla nuova ansa che consente di orientare sagittal-

mente la crescita mandibolare ottenendo una risposta scheletrica

favorevole.

References

1. Klontz HA. Diagnosis and force systems utilized in treating the

maxillary first bicuspid and mandibular second bicuspid extraction

case. J CH Tweed Found 1987;15:1958.

2. Schumacher HA, Bourauel C, Drescher D. Analysis of forces

and moments in arch guided molar protraction using Class I and

Class II elastics. An in-vitro study. J Orofac Orthop 1996;57(1):4

14.

3. Ronay F, Kleinert W, Melsen B, Burstone CJ. Force system devel-

oped by V bends in an elastic orthodontic wire. Am J Orthod

Dentofac Orthop 1989;96:295301.

4. Mamopoulou A, Hag U, Schrodeer U, Hansen K. Agenesis of

mandibular second premolars. Spontaneous space closure after ex-

traction therapy: a 4-year follow-up. Eur J Orthod 1996;18(6):589

600.

5. Watanabe E, Demirjian A, Buschang P. Longitudinal post-eruptive

mandibular tooth movements of males and females. Eur J Orthod

1996;21(5):45968.

6. Klontz HA. Readout. J CH Tweed Found 1985;13:536.

7. Bjork A. Variation in the growth pattern of the human mandible.

Longitudinal radiographic study by the implant method. J Dent

Res 1963;42:40011.

8. Riolo M, Moyers R, McNamara J, Hunter S. An Atlas of Cranio -

facial Growth, Monograph No. 2, Craniofacial Growth Series. AnnArbor, MI: Center for Human Growth and Development, Univer-

sity of Michigan; 1974.

9. Schudy FF. Cant of the occlusal plane and axial inclination of

teeth. Angle Ortho 1963;33:6982.

10. Merrifield LL. Analysis concepts and values. Part II. J CH

Tweed Inter Found 1989;17:4964.

11. Gebeck TR. Analysis concepts and values. Part I. J CH Tweed

Inter Found 1989;17:1948.

Prog Orthod 2, 2001/24292 29

cherry loop - a new loop to move mandibular molar mesialy

Documents