Dimensional Changes in Dental Arches After Treatment with a Prefabricated Functional ApplianceDimensional Changes in Dental Arches After Treatment with a
Prefabricated Functional Appliance
Ramirez-Yañez G* / Sidlauskas A** / Junior E*** / Fluter J****
The purpose of this study was to determine the effect of the T4K, a prefabricated functional appliance, on thetransverse and anterior-height dimensions of the maxillary and mandibular dental arches. Dimensions before andafter treatment were measured on the sample, then, natural growth was subtracted from the treatment effects andcompared with twice the error of the method. A clinically significant increase of both dimensions was observedin the maxilla and mandible when Class II malocclusion patients were treated with the T4K. Therefore, this retrospective study demonstrates that T4K is a valid treatment choice at an early age when transverse expansion ispart of the treatment goal.
Key words: Dentofacial orthopedics, transverse expansion, functional appliance
J Clin Pediatr Dent 31(4):279-283, 2007

INTRODUCTION
unctional appliances have been reported since early in thepast century to produce skeletal and dentoalveolar changes.1-5 Furthermore, treatment of children with increased
overjet using functional appliances reduces the probability ofneeding orthognathic surgery later.6 The skeletal effect of theseappliances appears to result from various phenomena: remodeling and relocation of the glenoid fossa7,8, accelerated and enhanced condylar growth9,10 and neuromuscular adaptation.11-13
Thus, functional appliances have been proposed to treat skeletal
deficiencies, such as reduced mandibular growth and transverse
development.9,14 However, their efficiency in this respect is still
controversial.15
One of the criticisms of studies involving functional appliances
is how much of the treatment result is a direct effect of the functional appliance and how much is due to natural growth. Evaluating how much growth or development is directly produced by
an appliance can be done by comparison with a control group.
However, this is a very complicated task, because it is difficult
to randomly allocate patients to control and treatment groups insuch a way that both groups are comparable. Furthermore, doinga prospective study might raise the ethical question of not providing treatment when needed or worse, the consequences of notreatment.16 An alternative is retrospective studies. However, in
those studies data have to be compared with a control group built

F*German Ramirez-Yañez, DDS, MDSc, PhD* Assistant Professor, 		Marquette University, School of Dentistry, Milwaukee, WI**Anatanas Sidlauskas, DDS, PhD, MOrth, CSEd Professor, Faculty of
Odontology, Kaunas University of Medicine, Lithuania*** Eider Junior, DDS, MOrth Associate Professor, Center for Muscular
Dysfunction of the Face, University of ABO, Victoria, Brazil****John Fluter, BDS Private Practice, Brisbane, QLD, Australia
Send all correspondence to: Dr. German O Ramirez-Yañez, School of Dentistry,
Marquette University, 1801 West Wisconsin Avenue, Milwaukee, WI 53233

from published normative data precisely matching with the treatment group for age, sex and treatment time.17,18 Another difficultywith orthodontic appliance studies is that not all statistically significant treatment outcomes really equate to clinically significant
changes. To solve the latter problem, the net effect of treatment
can be contrasted with twice the method error so treatment effectcan be considered clinically significant when it is at least twice
the method error.17,19
The trainer for kids (T4K™, Myofunctional Research Co, Australia) is a polyurethane prefabricated functional appliance (Figure 1), which is claimed to correct malocclusions at an early age
by acting on muscular dysfunction and repositioning the mandible.20 It is composed of various elements designed to stimulate thefacial and masticatory muscles and muscles of the tongue. A previous report has demonstrated that it relocates the mandible in amore forward position in Class II division 1 patients.21 Therefore,
this prefabricated functional appliance appears to produce a sagittal effect similar to that reported for other functional appliancessuch as the bionator 2,3, twin block4, Fränkel regulator1,22, Harvold
activator1 and Herbst.7,22 On the other hand, an increase of approximately 1.5 mm in maxillary and of 2.9 mm in mandibularinterpremolar distances has been reported with other functional
appliances such as the Frankel regulator23. Some patients treatedwith the T4K have also shown an increase in dental arch width,
but the effect of this appliance on the transverse dimension has
not yet been evaluated. Therefore, the purpose of this retrospective study was to determine the effect of the T4K on the transverse
and anterior-height dimensions of the maxillary and mandibular
dental arches. To determine the clinical significance of the results
when comparing the dimensions before and after treatment, thetreated group was compared with a control group created fromnormative data and contrasted with twice the method error.
MATERIAL AND METHODS
Pre- and posttreatment casts from 60 patients treated only with

E-mail: german.ramirez@marquette.edu

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Dimensional Changes in Dental Arches After Treatment with a Prefabricated Functional Appliance
the T4K (Figure 1) over 1.3 ± 0.5 years were measured. The
study involved preadolescent children (8.3 ± 1.0 years old at the
beginning of treatment) of both sexes (32 girls and 28 boys) from
3 different countries, Australia (10 patients), Brazil (26 patients)and Lithuania (24 patients). All patients had Class II, Division
1 malocclusions with crowded teeth. This sample composed thetreated group.

Figure 1: The T4K showing the various parts composing
the prefabricated functional appliance: (1) dental channels
with predetermined bite position; (2) facial bowls to separate buccinators and orbicularis oris muscles from dental
arches; (3) lingual bowls to help guide mandibular repositioning; (4) lingual tag to stimulate tongue repositioning; (5)device to reduce activity of the menton musculature.
A control group composed of 32 girls and 28 boys was built
from data published by Moorees.24 Briefly, data from clinical histories of the patients in the treated group were used to determine
age at the beginning and at the end of treatment, as well as theduration of treatment. Thus, each patient in the treated group had
a matched control from normative data with respect to age, sex
and observation period.
Distances measured
Four measurements were made on maxillary and mandibular
casts of each patient in both treated and control groups: intercanine (IC) distance, interpremolar (IP) distance, intermolar (IM)distance and height of anterior arch (AAH). IC was determinedas the distance between the tips of the canines. IP in the maxillaryarch was the distance between the mesial fossae of the deciduous
first molars or the first premolars, and in the mandibular arch, thedistance between the tips of the mesial cusps of the deciduous
first molars or the first premolars. IM was the distance between
the central fossae of the permanent first molars in the maxillaryarch, and the distance between the central cusp tips of the lower
permanent first molars of the mandibular arch (Figure 2).
In the maxillary arch, AAH was determined by the distance between the middle point of a line drawn between the fossae of thedeciduous first molars or first premolars, and the incisal border ofthe central incisors at the midline. In the mandibular arch, AAH
was similarly measured, but the line was drawn between the mesial cusps of the deciduous first molars or first premolars (Figure2). If any of the central incisors was positioned more labially thanthe other, AAH was measured to the incisor more labially posiThe Journal of Pediatric Dentistry

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Figure 2: Diagram showing various measurements performed on casts in this study.
tioned.
Inclusion criteria for the treated group were those patientstreated only with the T4K and having measurement reference
points present at the beginning and end of treatment. Therefore,
when the primary first molars were exfoliated during the treatment period, the first premolars must have been erupted by theend of the observation period to measure the IP distance.
Data analysis
Statistical analysis was performed following the methods
described by Trenouth17 and Valant.18 Data obtained from eachmeasurement (pre- and posttreatment) within and between both
treatment and control groups were analyzed using Mann Whitneytest. This nonparametric statistical test was chosen because thedata was nonhomogeneous and might not have been normally
distributed. The statistical test was performed using Prism 4(GraphPad Software Inc, San Diego, Calif). A P-value lower than
.05 was considered significant.
Error of the method was determined by the formula:where d is the difference between measurement pairs
and n is the number of pairs.

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Dimensional Changes in Dental Arches After Treatment with a Prefabricated Functional Appliance
Table 1: Changes in Transverse Dimension. Treatment (T) and Control (C)Groups Before (1) and After (2) Observation Period in mm.

Table 2: Clinical Significance of Net Treatment Effect* Caused by the T4K.

increase was also observed in the maxillaryarch for IC distance, but not in the mandibular (Table 1). No significant differences were
found within the treated group in the maxillary
and mandibular AAHs at the end of the observation period when compared with the initial
measurement. The control group showed asignificantly increased IC, IP and IM in the
maxillary arch during a growth period similar
to that of the treatment group, whereas IP wasthe only transverse distance significantly increased in the mandibular arch over the observation period (Table 1). No significant change
was observed in the AAH distances either inthe maxillary or mandibular dental arch over
the observation period for the control group.
Although it was not the purpose of this study,
improved tooth alignment was observed inmost of the treated cases.
To differentiate the effect of treatment with
T4K over natural growth, the clinical significance was determined as explained above by
subtracting the value of natural growth fromthe value of the treatment effect, then compared with twice the method error. These
results are shown in Table 2. Clinical significance for T4K treatment was observed in the
IP and IM distances for both maxillary andmandibular arches. The IC distance showedno clinical significance in either the maxillary
or mandibular arches, although in the maxillary arch the increase in IC distance for thetreatment group was twice that occurring in
the control group (Table 2). T4K caused aclinically significant increase in AAH in the
maxillary arch, but not in the mandibular.

DISCUSSION
Functional appliances have been extensively reported in the literature as a valid alternative for treating malocclusions, as they
may stimulate jaw growth and developmentin preadolescent patients.1-3,5,7-12,22,25 However,
evaluating which portion of the result is produced directly by the appliance and which by natural growth isdifficult.16 In this retrospective study, the clinical effect producedby the prefabricated functional appliance used to stimulate development of the dental arches in preadolescent patients was determined, first, by building a control group from normative data;second, by subtracting the treatment effect from natural growth;and third, by contrasting the difference with twice the method
error.17-19 Thus, it was observed that patients treated with the T4K
had significantly increased transverse dimensions at the first premolars and first molars having statistical significance. Therefore,
T4K can be recommended as a useful tool for stimulating transverse development in young patients.
An increase in IP and IM distances has been reported to be
associated with an increase in arch perimeter.26,27 Current results*Determined by subtracting natural growth occurring in control group over theobservational period from the effect produced by the T4K on dental archdimensions (T net effect) and comparing with twice the method error (2ME).
T = T2 – T1; T net effect = T – C.

Clinical significance of treatment with the T4K on maxillary
and mandibular arch dimensions was determined by subtracting
natural growth from the treatment change, then, the differencecompared with twice the method error.18 A difference higher thanthe value of twice the method error was considered a clinicallysignificant effect produced by the functional appliance.
RESULTS
Changes in transverse dimensions and AAH for both maxillary
and mandibular arches within and between both treatment andcontrol groups were statistically analyzed and results are shownin Table 1. Patients treated with the T4K showed a significant
increase in IP and IM distances at the end of the observation period in both maxillary and mandibular dental arches. Significant
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Dimensional Changes in Dental Arches After Treatment with a Prefabricated Functional Appliance
have demonstrated that both maxillary and mandibular IP and
IM distances are significantly increased by the T4K, thus, theperimeter of the arches may have increased, providing moreroom for tooth alignment, which was frequently noticed in thetreated group at the end of the observation period. Furthermore,
the highest effect is produced at the first premolars, and a lower
but still significant effect at the first molars. It thus appears the
prefabricated functional appliance stimulates further transverse
development overlapping that produced by natural growth, which
may be an asset when treating patients with crowding caused bydecreased maxillary or mandibular transverse development.
This study has demonstrated that T4K stimulates transverse
development, but it also appears that it tends to round the maxillary dental arch. This is inferred because there was an increasein IP and IM distances associated with a clinically significant
reduction in maxillary AAH, which may be due to an effect on
the inclination of the maxillary incisors reported in a previous
study.21 This dentoalveolar effect appears not to occur in the mandibular arch as there was no clinically significant effect in thatgroup treated with the T4K. Although the current study did notinclude x-ray measurement, these results seem to agree partlywith those reported by Usumez and coworkers.21 They reported
that the T4K has a dentoalveolar effect, in that it significantly reduces the inclination of the maxillary incisors while significantly
increasing the inclination of the mandibular incisors. The current
study showed no significant effect on the mandibular AAH, suggesting that there were no significant variations in mandibular
incisors inclination. Further studies may be required to clarify
how this functional appliance affects the position and inclinationof the mandibular incisors. In short, the T4K stimulates dimensional development of the maxillary arch, tending to round it,
whereas on the mandibular arch it stimulates transverse development without significantly affecting the anterior arch.
The significant transverse development observed in the current study appears to be produced mainly by the buccal shieldsof the prefabricated functional appliance used for treatment inthis study. The facial bowls included in the structure of T4K may
stimulate transverse development in a way similar to Fränkel
regulators28,29, in separating the buccinator and orbicularis oris
muscles from the teeth and reducing the forces produced by thosemuscles on the buccal aspects of the teeth. These forces are reported to normally be 2.7 g on the maxillary dental arch and 2
g on the mandibular dental arch in normal occlusion30, but they
may increase up to 21 g in the molar region and up to 80 g in
the canine region in thumb-sucking patients.30,31 Through the facial bowls, the T4K releases the teeth from those forces appliedby the facial muscles directly on the tooth crowns30,32, but at thesame time, tensional forces are delivered to the alveolar and basal
bone at the insertion sites of the buccinators and orbicularis oris
muscles.33 These tensional forces stimulate bone formation on
the external surfaces of the maxilla and mandible33, and thereby
may produce that clinically significant increase in transverse dimensions observed in this study. We postulate that the increasein transverse dimensions reported in this study occurs in a way
similar to that observed in the Fränkel Regulator23, wherein there
is bodily movement of the dentoalveolar unit and not tipping of
the teeth. However, radiographic studies are required to evaluate
those changes in the basal and the alveolar bone, as well as in the
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long axes of the teeth.
It has been reported that most arch dimensions are establishedat 7 years of age.34,35 Therefore, the results of this study, added tothose from a previous study concluding that T4K relocates themandible to a more forward position in Class II Division 1 patients21, confirm that this prefabricated functional appliance canbe recommended for treating Class II Division 1 malocclusionsin preadolescent patients. Furthermore, this appliance might beused to treat malocclusions wherein a lack of transverse development is causing tooth crowding. However, further studies are
required to demonstrate the effect of the T4K on other malocclusions.
CONCLUSIONSThis retrospective study has shown that the T4K, a prefabricated functional appliance, is a valid alternative to treat malocclusions at an early age, as it clinically significantly stimulates
transverse development of the dental arches. Therefore, this appliance is a valuable tool in improving dental arch development
when a lack of transverse development is diagnosed at an earlyage.
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