MYO RESEARCH DOCUMENT


Early Treatment Class II Malocclusion

By Dr Kevin J.Bourk

Most orthopaedic and orthodontic problems which come to fruition in the mixed dentition, then to maturity in adolescence, have their genesis in very early childhood. 1

Recent work (N.P. Martinez et al 2 Southern Illinois Uni. School of Medicine) on 3 - 5 year old children showed 16% of children had digital habits, 33% T.M.J. clicks, 67% wear facets and 30% teeth grinding habits - physiological and physical factors all impacting on genetic development.

On previous occasions when addressing early developing problems I have spoken about treatment for early Class III (5%), crossbites (17.5%) and openbites (15%). On this occasion I would like to relate to the Class II malocclusion, which is the bread and butter of orthopaedic treatment, and with which we have much success today using Clark, Mew and Bionator appliances in older children.

There is little doubt that genetic structure plays a very important role in the relationship of the developing mandible to the skull base. We can know this by observation and inquiry. However, it has taken research workers such as Potter (Uni. North Caroline) and others such as McNamara, Frankel and Pancherz to scientifically demonstrate that, in the face, genetic development is overwhelmed by the environment.

We know how readily the thumb sucking habit will distort an infant's appearance, showing that the early bone development is very susceptible to pressure. Observing this, I find it a little puzzling to understand why treatment is ever delayed.

J. Verada (Uni. Turku Finland) 3 has shown that the sagittal relationship in the primary dentition (age 3 years) varies significantly between those who finally developed a Class II or Class I relationship. He found that the terminal plane in the normal Class I group of infants at age 3 years was mesial 1.3mm, and in the children who developed a Class II relationship was 1.3 mm distally, and that the differential became greater as age progressed. His results showed that the transverse dimension in the primary dental arch is impaired in the maxilla, but not in the mandible in Class II cases.

He concluded that the lower arch grows normally, but assumes a more distal position to occlude with the narrow upper arch. All this makes sense to the clinician who invariably sees mandibular posterior teeth tipped lingually in Class II cases, and explains the improved vertical dimension in infants who exercise their stomatognathic systems with daily "myo" chewing (expanding the developing maxilla and promoting nose breathing, so essential to normal growth.

Research work by 4 K. Maki (Showa Uni. Tokyo) and R. Tanaka (Uni. Nagaski) shows that mechanical stress (chewing) produces changes in the density and morphology of the bone, and that cancellous bone adapts to occlusion induced stress.

Chewing, of course, is of ultimate importance to the proper functioning of the parotid gland, whose secretions play such an important role in the overall health of the oral cavity. A striking example of this is in South Africa where the workers on the sugar plantations in spite of their frequent and high consumption of sucrose are caries-free. Their chewing produces a salivary milieu protecting the oral cavity.

Numerous studies continue to emerge from international dental research institutions highlighting the interdependence of skeletal anatomy. For instance S. Kapila (Uni. Cal. S.F.) 5 has shown that a medio lateral deviation of the mandible in the rest position induces asymmetries both in the internal structure of the bone, and in the cranio-skeletal morphology of a rapidly growing mammal. And again, H. Joy and D. Carlson (Uni. Michigan) 6 have shown how early septal deviation which produces respiratory impairment can cause a reduction in mid facial growth and malocclusion in rats. So it is not surprising that a retruded human mandible produces inadequacies both in the physiology and morphology of the upper skeletal components (cervical spine), and subsequently in the lumbar area.

Clinically we notice this interconnection in the treatment of T.M.J. Dysfunction.

Petrovic, McNamara and Woodside have all shown that when you unload the condyle with an anterior repositioning device in a young child, you cause stimulation to growth in the fossa and in the condyle. These studies support Osaka dental Uni. research which shows that in the young the direction of growth correlated with the direction of strain.

And again Y. Sim and D. Carlson (Uni. Michigan 1994) 7 demonstrated that bite splints used in Rhesus monkeys which increase the vertical dimension of the mid face also caused 62% increase in the chrondroblastic layer and marked thickening of the pre-chrondroblastic layer.

M. Spady (Uni. Baylor) A. Demirjian (Uni. Montreal) 8 in 1991 have shown that rotational and remodeling changes are significantly greater during childhood than adolescence, and that children in the primary dentition show the greatest amount of remodeling change. 9

Two examples will suffice to show the importance of function. The Clarke Appliance owes much of its success to being a truly functional appliance. The muscles, bone and joints function in a forward position when eating, and the central comparator does the remodeling. Secondly K. Yamada and D. Kimmel 10 (School of Med. Crighton) showed that when experimental animals (rats) 4 weeks old chewed hard food (rather than just swallowing soft food) mineral deposition was markedly increased in the mandible, and condylar cartilage development proceeded more rapidly - as the following table shows:

Age
Mineral
Mineral
Deposit of
4 wks Deposit Deposit Condylar
  Inferior Ramus Cartilage
  Mandible Surface  
     
Soft Food 1.7 4.8 54
     
Hard Food 2.7 6.2 76

 

It is important to understand that in the infant the Glenoid Fossa is in the process of formation. It is in its most rapid state of change in morphology at age 2-5 years. 11

Unlike forward repositioning in the adolescent, where vertical growth in the posterior alveolus is necessary for final stability, the infant's mandible will, over a 12 month period, remodel to accept the more forward position without producing the posterior open-bite. (See Fig 1 - 4).

All scientific indicators point in the direction of early treatment of Class II malocclusion. The research has been done and the evidence is clear. It remains for this knowledge to be transferred into general clinical practice.




SOME CASES:


Fig. 1 Developing Class II Malocclusion in a child aged 3 years 6 months.


Fig. 2 Repositioning of mandible after 1 year of treatment (MYO Munchee and a MEW III device)

This child's problem was a closed bite with a trapped mandible. He was also, as evidenced by the wearing down of his teeth, a nocturnal grinder.
These photos demonstrate that such problems can be rectified easily at an early age.



B.T.'s Class II Malocclusion was fairly typical. When treatment commenced, BT was 3 years and 10 months old.

 

Fig. 3  Developing Class II Malocclusion.
As indicated by the red line, the deciduous molar position is 1.3 mm distal to the terminal plane.
 

Fig. 4  The problem is fully corrected by 12 months' MYO Munchee therapy.

Impressions were taken, and a bite recorded; the anteriors were in an edge to edge relationship, but 1.3mm apart.

An anterior repositioning appliance was constructed, in this case a Mew III. Composite was added to the buccal of the upper E's to provide positive retention for the clasps. The child was examined monthly. Bone and joint changes take place slowly. The child should exercise with the myo (which is set in a Class I relationship) for 10 minutes daily. This gives stimulation to all bones, joints and muscles of the Stomagnathic System and facilitates morphological change. Young children manage the appliance much the same way as their older siblings. After about 12 months the child will tend to close into a Class I position. To consolidate this relationship composite is added to the deciduous canines to proprioceptively encourage the mandible to permanently assume the desired Class I relationship. It will be noted that there is no space between the upper and lower 2nd deciduous molars. (Fig 4).

Other simple methods may be used to relieve a genetic predisposition to faulty development. The mandible may be genetically short, and if the maxilla is also influenced by environmental factors such as frequent head colds, then what is likely is a potentially serious developing Class II malocclusion.




 
Fig. 5  A severe case of Class II Malocclusion.   Fig. 6  Improvement after 13 months of MYO Munchee treatment

Treatment in this case was as follows:

1. To free the entrapped mandible with an upper Sagittal.

2. To institute good function with daily Myo chewing.

3. Use a ramp (even while eating) to encourage forward positioning of the mandible after the anterior teeth have been moved forward with the sagittal appliance. This patient had no problem functioning with the ramp.

4. Composite was added to the canines to proprioceptively reposition the mandible.


The 'treat late' mindset is under serious challenge, with work such as this demonstrating excellent results from very early correction. Unlike later treatment, early intervention with the use of MYO devices improves musculature and bony structures. There is a general improvement in appearance.

This is shown clearly in the pictures below, which really are "the last word" in this debate.

 

Fig. 7  At 3 years 6 months this child is exhibiting the gross facial disfiguration associated with Class II Malocclusion.
 
Fig. 8  At age 7 MYO Munchee and orthopaedic therapy are complete





Bibliography

L. King - J. Dent Res. 1990 Abstr. 1814 "A Sibling Analysis Of Malocclusions".

N.P. Martinez, K. Rubinich, D. Tylka, J. Dent. 1994 Abstr. 2136A. "Assessment Of Bruxism In Pre School Children".

R.H. Potter, J. Dent Res. 1990 Abstr. 1836. "A Twin Half-Sib Model For Occlusal Traits".

J. Verada, J. Dent Res. Abstr. 2098, 1993 "Skeletal Development of CII Malocclusion In Early Childhood".

K. Maki, Y. Shibaski, T. Fuklihara J.D.R. 1991 "Relationship Between Bone Density And Stress In The Growing Mandible".

R. Tanaka, H. Murakami, T. Kitahara, H. Suzuki. J.D.R. 1991 Abstr. P.797 "Relationship Between Stress And Trabecular Pattern In Mandible While Occluding".

G. Cimasoni - "Monographs In Oral Science" Vol.3.

S. Kapila, A. Miller, D. Curtis, D. Hatcher J.D.R. 1990 Abs. 1844 "Effect Of Lateral Deviation Of Mandibular Growth On Cranio Mandibular Function".

H. Joy, D. Carlson, J. Dent Res. 1990 Abstr. 1399 - "Nasal Septal Deviation And Mid Facial Growth In Rats."

J. Huggare, E. Harkness, J.D. Res. Abstr. 1214 Special Issue 1993 - "Association Between Head Posture And Dental Occlusion".

S. Steigman, Y. Michaeli, M. Terespolsky. J.D.R. 1990 Abstr. 1397 - "The Effect Of Combined Occlusal And Mechanical Forces On PDL Of Rat Incisor".

K. Yamada, D. Kimmel, J. Dent Res. 1990 Abstr. 1816 - "Soft Diet Effects On Mandibular Growth In Young Rats".

Personal Correspondence - Uni. Manitoba Winnipeg.




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