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Application of functional orthodontic appliances to treatment of mandibular retrusion syndrome - Effective use of the TRAINER System

Akira KANAO; Masanori MASHIKO; Kosho KANAO

This paper introduced the mechanics of the the TRAINER System™ and clinical cases treated with the T4K™, demonstrating the effectiveness of the appliance in guiding the mandible forward and expanding the upperand lower arches in maxillary protrusion cases with “mandibular retrusion syndrome” often seen among Japanese. When we first saw the appliance, we wondered if such a simple appliance would have any effect. However, many “mandibular retrusion syndrome” cases have been treated successfully with the T4K™ in our clinic. We would like to further increase our clinical experience with the TRAINER System™ and collect objective and scientific data to validate the theory behind and the treatment effect of the system. We also hope to gain a better, more accurate understanding of growth peak, which is the key to the success of Phase I treatment to produce a greater effect in a shorter period of time.


Introduction
 

There have recently been an increasingnumber of parents complaining of their chil-dren’s health-related problems other thancaries, such as decline in exercise ability,open-mouth posture, slow eating, allergy andmisaligned teeth. Indeed, studies have shownincreases in the number of children with diffi-culty masticating hard chewy food or inabilityto swallow correctly1,2). The decline in oralfunction is attributed to dietary changesamong children in the modern Japanese soci-ety including the eating of soft foods at homeand elsewhere3,4). It has also been shown thatthe perioral muscles in growing children influ-ence body posture, respiration, mastication,deglutition, speech and morphology of thejaws and teeth5,6).

When it is difficult to breathe through thenose due to, for example, tonsillitis or allergicrhinitis, habitual mouth-breathing is inevitable.Mouth breathing has been shown to adverselyaffect the morphology of the dental arch andjaw bones7). It causes dryness of oral and pha-ryngeal mucosa. Dry mucosa is more sensitiveand susceptible to inflammation. Inflamedmucosa is more vulnerable to bacterial infec-tion, which in turn aggravates the inflammato-ry condition. The pharynx gets swollen when inflamed, making the airway narrower. Airwayconstriction increases breathing difficulty,which induces mouth breathing further. Pha-ryngeal inflammation caused by mouth breath-ing spreads to the tonsils. The tonsils have animmunoprotective function, but become asource of infection once infected8). Infectedtonsils cause further narrowing of the upperand lower airways. Mouth breathing habit thushas negative impact, particularly on the mor-phology of the jaws and dental arches ingrowing children. The morphology of the jawsand dental arches then begins to control func-tion, perpetuating a downward or negativespiral of vicious circle.

Pediatric dentists are in a better position todiscover this downward spiral through thedental health checkup system they haveestablished and promoted, which will givethem a chance not only to help children withdental problems but to collaborate withotorhinolaryngologists, pediatricians and otherspecialists.

 
Maxillary protrusion
 

In our previous paper, we reported on“mandibular retrusion syndrome” in mandibu-lar protrusion cases9). Maxillary protrusion canbe classified into three main skeletal types; 1)overdeveloped maxilla, 2) underdevelopedmandible, 3) combination of the two.

Nezu, et al.10,11)showed in their studiesassessing anteroposterior relationship of themaxilla and mandible relative to Nasion-per-pendicular (McNamara Line) that a greatmajority or 73% of Japanese Class II maloc-clusions were associated with manidbularretrusion while true maxillary protrusion(overdeveloped maxilla) accounted for only7%. In our view, etiologies of maxillary protru-sion due to mandibular retrusion includemyofunctional habits during infancy and earlychildhood, e.g., thumb/finger sucking, pacifieruse and the way babies are breast-fed.

 
Fig. 1 Maxillary protrusion aggravated by myofunctional habits
 
This case in the primary dentition had alarge overjet causing lip incompetence (Fig.1). Without good lip seal, he had to build neg-ative intraoral pressure for swallowing by curl-ing the lower lip under the upper anteriorteeth. Lip incompetence leads to further deformation of the jaws and dental arches,making lip closure even more difficult. He alsoexhibited marked mentalis and buccinatorsstrain during swallowing. The inward forceexerted by the buccinators causes constric-tion of the upper and lower dental arches intoa V shape and pressure from the strainedmentalis muscle pushes the mandible downand back. This clockwise rotation of themandible can be a cause of airway constric-tion, giving rise to the above-mentioned nega-tive spiral.
 

Fig. 2 Before Phase I treatment with Bionator (age 10Y8M)
 

Fig. 3 After Phase I treatment with 1 year and 1 month of Bionator (age 11Y9M)
     
Fig. 4 Before Phase I
(age 10Y8M)
Fig. 5 End of Phase I treatment
(age 11Y9M)
Fig. 6 Changes after 1 year and
1 month of treatment
 

In our clinic, we have been using appliances that are optimal for Phase I treatment of maxillary protrusion, such as bite plane, Bionator and Twin Bock, and found these appliances very effective. Fig. 2 to 8 shows a case treated with Bionator.

This patient had an overjet of +6mm and overbite of +6mm with ANB of 10.3º and FMA of 21.9º. He was diagnosed as having a Class I division 1 malocclusion with a normal maxilla and a retrusive mandible. Bionator was used to stimulate forward mandibular growth in Phase I. The patient’s good complianceallowed for full effect of the appliance. There was adequate improvement in anterior coupling to an overjet of +2mm and overbite of +2mm at the end of Phase I treatment. Cephalometric analysis demonstrated a tendency
for improvement in ANB (9.4º) and FMA (25.7º).

 
Fig. 7 Maxillary and mandibular changes Fig. 8 Cephalometric changes
 
Fig. 9 Bionator used
 

Bionator is a functional appliance developed by Balter12) in the 1950’s. It is a mono-block appliance with the upper and lower parts integrated into one unit, comprising resin, wires and an expansion screw. It is mainly used for treatment of maxillary protrusion. A construction bite is taken with the mandible brought forward to an edge-to-edge position. The appliance has the effects of increasing the intraoral volume and facilitating lip seal.

In our clinic, Bionators were previously used in children at Hellman’s dental age IIC to IIIB. The appliance had to be frequently adjusted by grinding or adding resin due to such problems as mobility of exfoliating primary teeth and ectopic eruption of successive permanent teeth. This increased chairtime and the appliance adjustment was sometimes very difficult to make. In our search for optimal appliances by trial and error, we were introduced to the TRAINER System™ in 2000. The TRAINER System™ lineup includes the T4K™ (TRAINER for Kids), T4A™ (TRAINER for Alignment), T4B ™ (TRAINER for Braces) and T4CII™ (TRAINER for Class II). The T4K™ is further divided into two types, soft and harder. Although we were initially puzzled by the wide range of appliances available in the product lineup, appliance selection is simple and straightforward. The T4K™ is the appliance of choice when the second molars are still unerupted. The T4A™ or T4CII™ is selected thereafter. The T4B™, which is designed to be used with braces, tends to increase patient susceptibility to stomatitis. The T4B™ can be used as a retainer to maintain mandibular position after insufficient Phase I treatment.

When we first incorporated the TRAINER System™ into our practice, we used it for bite opening prior to multi-bracket appliance therapy. We later observed added benefits of the system in eliminating minor crowding and improving Class II relationship in many cases. Some parents were satisfied with the improvements obtained with the TRAINER System™ and declined further treatment, giving us mixed feelings. In fact, the number of patients treated with multi-bracket appliances in our clinic decreased after the introduction of the TRAINER System™. The next section will describe the effectiveness of the T4K™ in Phase I treatment.

 
Features and objectives
of the TRAINER System™
 

The TRAINER System™ appliances were designed and developed as a functional appliance system through repeated refinements over a period of 10 years to arrive at the current stable design. These appliances were devised to improve muscle function. They were approved as orthodontic appliances by the Japanese regulatory authority in 2008 (Fig. 10).

The TRAINER System™ appliances look similar to a positioner. The latter is fabricated on setup models and allows some tooth movement. The positioner is more like a bite block made of elastic resin and designed to settle teeth and occlusion to predetermined, setup positions. In contrast, the TRAINER System™ appliances are designed not only to improve form but to harmonize form and function.

 
Fig. 10 Soft type made of silicone (left), harder
type made of polyurethane (right)
 
Structure of the TRAINER
System™ appliance
 

The TRAINER System™ appliance is a flexible appliance made of non-thermoplastic silicone (soft) or polyurethane (harder) (Fig. 11). It is used to improve oral function. Treatment is initiated with the soft type, followed by the harder type. The appliance has two main effects, one to guide hard tissues, i.e. jaws and dental arches, and the other to guide soft tissues, i.e. perioral muscles.

 
The TRAINER System™ appliance brings the mandible forward using the upper anterior teeth as an anchorage source. It also has an arch-expansion effect on a constricted arch, creating room for tooth alignment. Thus, mild crowding may be eliminated with proper use of the appliance.
 

Fig. 11 Structure of T4KTM
 
Patients with maxillary protrusion and mandibular retrusion often show mentalis strain. The TRAINER System™ appliance positions the mandible forward as a hard-tissue guidance system, facilitating lip seal and nasal breathing. This effect is unique to mono-block appliances. The appliance also promotes proper functioning of the perioral muscles that are involved in abnormal swallowing with the lower lip caught behind the upper anterior teeth or tongue-thrust swallowing. This helps to widen the lower airway.
 
Target ages and uses
of the TRAINER System™
 

The objective of orthodontic treatment is to achieve maximum effect with minimum necessary treatment. Functional appliances including the TRAINER System™ should be used during active growth. There are large gender and individual variations in the timing of growth peak. Scammon’s growth curves indicate that maxillary growth is similar to neural growth and mandibular growth to general growth. This means that treatment timing varies greatly depending on the type of malocclusion (Fig. 12).

The instruction manual of the TRAINER System™ recommends the age ranges in which each appliance can be used effectively; 2 to 5 years for INFANT TRAINER™, 6 to 12 years for the T4K™ and over 12 years for the T4A™. Because of individual variations in growth, age limits vary from one patient to another. Our patients are instructed to wear the TRAINER appliance for around 2 hours during the day and at night during sleep depending on the child’s age.

In our office, the use of the T4K™ is initiated when the child is at Hellman’s dental age IIC or older rather than at a given calendar age. Therapy with the T4K™ should be started with 30 minutes to 1 hour of daytime wear of the soft type. When the patient is accustomed to the soft-type appliance after one month of use, wear time is increased from 1 hour to 1.5 and then to 2 hours. Nighttime wear is finally added. Patient information is gathered before treatment using the assessment chart introduced in our previous article. At every monthly visit, the patient is asked how much time he wore it during the previous one month.

 
Fig. 12 Optimal timing for Phase I treatment
 
Case presentation
< Case 1 S.N. > (Fig. 13-20)
Diagnosis: An 8-year-old girl presented with protruded anterior teeth. Facial photographs showed a retrusive mandible, a protrusive maxilla, an everted lower lip and mentalis strain. Intraorally, E/E terminal plane was of distal step type bilaterally. The upper anterior teeth were protrusive with an overjet of +6mm and overbite of +3mm. Cephalometric analysis showed retrusion of B-point, ANB of 6.8º and FMA of 31.0º. Based on these initial records, she was diagnosed as having a Class II division 1 malocclusion.
—End of Phase I treatment: 2 years and 10 months of treatment time
At the end of Phase I treatment with the T4K™, both the patient and parents felt that the face no longer looked protrusive. Her post-treatment facial photographs show improvements in mandibular retrusion, upper lip protrusion, lower lip curl and metalis strain. Intraorally, the molar relationship remained Class I on the left side and Class II on the right side. Both overjet and overbite were reduced to +2mm. Cephalometrically, ANB was improved to 5.1º with a slightly increased but favorable FMA of 33.2º. Comparison of pre- and post-treatment models showed an increase of 3mm in upper interpremolar width.
 
Fig. 13 Before Phase I treatment with T4KTM (age 8Y0M)
 
Fig. 14 After Phase I treatment with 2 years and 10 months of T4KTM (age 10Y10M)

 

Fig. 15 Before Phase I
(age 8Y0M)
Fig. 16 After Phase I
(age 10Y10M)
Fig. 17 Changes after 2 years and 10 months of treatment Fig. 20 Changes in upper and lower dental arches Fig. 18
   
Fig. 18 Maxillary and mandibular changes Fig. 19 Cephalometric changes
 
Fig. 20 Changes in upper and lower dental arches
 
(Fig. 21-28)
Diagnosis: The patient was a half-Japanese half-Caucasian girl aged 7 years 8 months with chief complaints of deep bite and lack of lower incisor display. Facially, a low-angle tendency was noted. Molar relationship was Class II on both sides. The upper anterior teeth were protrusive with an overbite of +6mm and overbite of +5mm. Cephalometric analysis showed retruded B-point, ANB of 6.2º and FRMA of 22.5º. Thus, the case was diagnosed as Class II division 1.
—End of Phase I treatment: 1 year and 1 month of treatment time

At the end of Phase I treatment with the T4K™, the patient and parents were happy with good tooth alignment. Retrognathic appearance was improved as the upper lip protrusion, lower lip curl and mentalis strain were eliminated. Molar relationship was corrected to Class I. The overjet and overbite were reduced to +1.5mm and +2mm, respectively. ANB and FMA were improved to 4.3º and 19.9º, respectively. There was an increase of 3mm in upper inter-premolar width when pre- and post-treatment models were compared.

 
Fig. 21 Before Phase I treatment with T4KTM (age 7Y8M)
 
Fig. 22 After Phase I treatment with 1 year and 1 month of T4KTM (age 8Y9M)
 
Fig. 23 Before Phase I
(age 7Y8M)
Fig. 24 After Phase I
(age 8Y9M)
Fig. 25 Changes after 1 year
and 1 month of treatment
   
Fig. 26 Maxillary and mandibular
changes
Fig. 27 Cephalometric changes
 
Fig. 28 Changes in upper and lower dental arches
 
<Case 3 W.K.> (Fig. 29-36)

Diagnosis: A 9-year-9-month girl came in with protruded anterior teeth. Facially,mandibular retrusion, upper lip protrusion, lower lip curl and mentalis strain were noted. Intraorally, molar relationship was Class II on both sides. The upper anterior teeth appeared protrusive with an overjet of +6mm and overbite of +4mm. Frenum surgery was necessary to release tongue-tie. Cephalometric analysis showed retruded B-point, ANB of 5.6º and FMA of 20.1º. The patient was diagnosed as having a Class II division 1 malocclusion.

—End of Phase I: 1 year and 5 months of treatment time
After Phase I treatment with the T4K™, the patient and parents no longer felt that the teeth were protruded. Favorable facial changes were observed with improvement of mandibular retrusion and elimination of upper lip protrusion, lower lip curl and mentalis strain. Molar relationship was corrected to Class I on both sides. Both overjet and overbite were reduced to +1.0mm. Lingual frenectomy was successfully performed 6 months into treatment. There were favorable changes in ANB and FMA to 4.4º and 21.3º, respectively. The lower inter-premolar width increased 4mm as measured on models.
 

Fig. 29 Before Phase I treatment with T4KTM (age 9Y9M)
 

Fig. 30 After Phase I treatment with 1 year and 5 months of T4KTM (age 11Y2M)
 
Fig. 31 Before Phase I
(age 9Y9M)
Fig. 32 After Phase I
(age 11Y2M)
Fig. 33 Changes after 1 year and
5 months of treatment
   
Fig. 34 Maxillary and mandibular changes Fig. 35 Cephalometric changes
 

Fig. 36 Changes in upper and lower dental arches

 
<Case 4 W.E. > (Fig. 37-44)
Diagnosis: A 7-year-10-month-old girl presented with a deep bite. Facial examination showed a retruded mandible, a protrusive upper lip, an everted lower lip and mentalis strain. Molar relationship was Class I on the left and Class II on the right. The upper anterior teeth were protrusive with an overjet of +5mm and overbite of +4mm. Surgical revision of a high upper labial frenum was needed. Cephalometrically, ANB was 5.2º with retruded B point. FMA was 35.0º. These data led to the diagnosis of a Class II division 1 malocclusion.
—End of Phase I: 1 year and 5 months of treatment time
The patient and parents felt that the teeth became nice and straight at the end of treatment with the T4K™. Facially, upper lip protrusion, lower lip curl and mentalis strain were eliminated with a reduction in retrusive appearance of the mandible. The molar relationship was still Class I on the left and Class II on the right. Both overjet and overbite were decreased to +1.0mm. The frenum attachment was released and repositioned 6 months into treatment and remains in good condition. ANB was reduced to 4.7º and FMA to 33.8º. Model analysis showed an increase of 4mm in upper inter-premolar width.
 

Fig. 37 Before Phase I treatment with T4KTM (age 7Y10M)
 

Fig. 38 After Phase I treatment with 1 year and 5 months of T4KTM (age 9Y3M)
 
Fig. 39 Before Phase I
(age 7Y10M)
Fig. 40 After Phase I
(age 9Y3M)
Fig. 41 Changes after 1 year
and 5 months of treatment
   
Fig. 42 Maxillary and mandibular
changes
Fig. 43 Cephalometric changes
 
Fig. 44 Changes in upper and lower dental arches
 
Discussion
 

We were able to experience the effectiveness of the T4K™ through the cases we treated. The T4K™ is a prefabricated, single-sized appliance. Its most prominent feature is the ability to encourage proper use of the perioral muscles. The T4K™ helps to establish a natural occlusal relationship for each individual child and to form an unstrained pattern of chewing. Morphologically, it creates an environment conducive to proper perioral soft tissue movement and natural posture of the perioral muscles.

Our experience suggests that the T4K™ is as effective as Bionator or Twin Block, though it may not be as easy to wear. Hellman Dental age 3B, a period closer to mandibular growth peak, may be the most desirable time for functional appliance therapy. The T4K™ can be used effectively in Hellman Dental age 3B as well, for it enables eruption guidance of ectopic canines and premolars into the dental arch. This is difficult to accomplish with Bionator or Twin Block.

The T4K™ has an arch-expansion effect without an expansion screw. All cases presented in this paper showed arch width increases in the upper posterior area. The T4K™ applies expansive force to a narrower dental arch because of a difference in width between the appliance and the dental arch. In our experience, the T4K™ is also effective in developing the lower dental arch. For patients with severe arch deformities, prior treatment such as orthodontic alignment of anterior teeth and arch expansion with an expander may be needed before the use of the T4K™, as is the case for Bionator and Twin Block.

In the treatment of “mandibular retrusion syndrome”, the T4K™ works by guiding the mandible forward using the upper anterior teeth for anchorage. The upper tooth channel of the appliance is configured in such as way as to torque the crowns palatally, decreasing the labial inclination of the upper incisors. Proclination of the lower incisors may occur with the use of the appliance, though not observed in the present cases.

The mechanism of action of the T4K™ on the soft tissues is to encourage normal swallowing by bringing the anterior teeth into an edge-to-edge position and thereby facilitating lip seal. This action is common to other functional appliances. In our view, proper oral function simply consists of light tooth contact, lip seal, stable tongue posture and nasal breathing (Fig. 45), yet there aren’t many children equipped with all these elements. We even see many adults walking with the mouth open.

The posture of the perioral muscles is acquired and becomes a habit through repeated swallowing and breathing in infancy and early childhood13). The optimal timing for myofuncitonal intervention is a period of active growth and development with high adaptive capacity 14). If the timing is missed, the child would acquire compensatory habits, which would require considerable efforts to correct later in life.

We regard morphological correction or normalization as a key to the establishment of normal function when mouth breathing and other myofunctional habits persist. As we continue to observe our growing patients, it is our hope to promote healthier growth through Phase I treatment with this objective in mind and by paying close attention to form and function.

 
Summary
 
This paper introduced the mechanics of the the TRAINER System™ and clinical cases treated with the T4K™, demonstrating the effectiveness of the appliance in guiding the mandible forward and expanding the upperand lower arches in maxillary protrusion cases with “mandibular retrusion syndrome” often seen among Japanese. When we first saw the appliance, we wondered if such a simple appliance would have any effect. However, many “mandibular retrusion syndrome” cases have been treated successfully with the T4K™ in our clinic. We would like to further increase our clinical experience with the TRAINER System™ and collect objective and scientific data to validate the theory behind and the treatment effect of the system. We also hope to gain a better, more accurate understanding of growth peak, which is the key to the success of Phase I treatment to produce a greater effect in a shorter period of time.
 
References
 
1) Maeda T, Imai R, Higuchi N, et al.: A study on eating function and behavior of children —Occlusal force and chewing force. J Jap Soc Pediatr Dent. 27; 1002-1009, 1989.
2) Okazaki M: Significance of chewing training in young children. Pediatrics of Japan 41: 2167-2175, 2000
3) Funakoshi M: Patho-oral physiology. Tokyo, Gakken Shoin, 112-132, 1990.
4) Nishida Y: Reevaluation of chewing function of the first molar. J. Gifu Dent College 16: 1-15, 1989.
5) Kerr J, McWilliam JS, Linder-Aronson S.: Mandibular form and position related to changed mode of breathing — a five-year longitudinal study. Angle Orthod. Summer; 59(2): 91-96, 1987
6) Schievano D, Rontani RMP, Berzin F.: Influence of myofunctional therapy on the perioral muscles. Clinical and electromyographic evaluations. J. Oral rehab. 26: 564-569, 1999.
7) Harvold EP, Tomer BS, Vargervik K, Chierici G.: Primate experiments on oral respiration. Am J Orthod. Apr; 79(4): 359-372, 1981.
8) Kataura A: An organ with two faces — Tonsil and its diseases. Nanzando. 97-99, 2005.
9) Kanao A: Application of T4K TRAINER to “mandibular retrusion syndrome”. J Clin Pediatr Dent. 12(9): 45-58, 2007.
10) Nezu H, et al.: Morphological classification of Class II malocclusions in Japanese in relation to Nasionperpendicular (McNamara line). J Jap Orthod Soc 44: 749, 1985
11) Nezu H: Kyouseishikagaku Bioprogressive Shindangaku. Rocky Mountain Morita, 74, 2004.
12) Balters, W.: Ergebnis der gesteurten Selbstheilung von kieferorthpadishen Anomlien, Dtsch Zahnaerzil 15: 241-248, 1960.
13) Inoue N, Sakashita R: Dental health from infancy for the mouth and future of children. Medi- Science, 126-129, 1992.
14) Kin T: Easy child-care, finishing weaning at age 1 year. Gendaishorin, 57-69, 2004.
15) Myofunctional Research Co.: TRAINER SYSTEM™ DVD, 2008.
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