::for.education

The Effects of Orthopedic Forces on Growing Children During Orthodontic Treatment

by Dr. R.G. "Wick" Alexander

One of the most intriguing subjects in orthodontics is growth and development. During 40 years in orthodontics, the knowledge and understanding of this subject has changed tremendously. What is known today about this intriguing subject? Can particular forces affect or control growth of the maxillofacial complex? The answer is that under certain circumstances, excellent changes can occur. In orthodontic treatment the affected areas include the maxilla, mandible and the dentoalveorlar complex. This knowledge was first discovered in graduate school when studying the effects on tooth position and maxillofacial growth during scoliosis treatment with the Milwaukee brace. For the first time in orthodontic literature, the conclusions stated that forces applied to the mandible (Milwaukee Brace) “demonstrates a directional change of growth in the lower face of a growing child.” The occlusal forces created by the brace extruded the incisors and depressed the molars. These forces also depressed the total anterior face height. The good news from this study is that the maxillofacial growth can be altered. Clinically, however, it impossible to create the same force levels worn almost 24 hours a day as those achieved by the Milwaukee Brace patient.

Before orthopedic forces have an opportunity to control or change growth, the patient must have growth potential. In general, a good rule to follow is that females grow earlier and males grow later. Therefore, “early treatment” in the mixed dentition is usually more successful with females. If possible, delaying treatment in males is preferred. Several methods to determine growth potential have been used … hand and wrist x-rays and cervical vertebrae x-rays are useful but tend not to be too reliable in the borderline stages when it is not known if the patient has any growth left., The old fashioned way of observing the parents and siblings sizes and talking with the parents about the growth potential are usually as good indicators as other approaches.

Growth takes place in three planes of space: transverse, vertical and sagital.

Transverse Dimension

Of these three directions, the transverse dimension is the most predictable. A narrow maxilla in a growing child can almost always be expanded with rapid palatal expansion and have predictable and stable results. This is considered an orthopedic correction. A narrow mandibular arch can then be expanded with controlled stability, usually with a lip bumper. This should be termed dentoalveolar expansion.

In nongrowing patients, non-surgical palatal expansion is also possible, although more guarded.

Sagital Dimension

When discussing the sagital dimensional control orthopedically, it has been found that the maxilla is a very malleable bone. The forward growth of the maxilla can be controlled effectively by the use of orthopedic appliances such as headgear or functional appliances. As shown by many studies, the maxilla is actually inhibited from growing while the mandible reaches its genetic potential.

Also, in a class III patient, the maxilla can be advanced slightly by the use of a face mask.

In addressing the orthopedic correction or control of the mandible, the fact is that there are few if any appliances that can be used to control mandibular growth. A claim that certain appliances can “grow” mandibles has been found to be lacking in long term evidence.

The debate among orthodontists is whether or not it is possible to “stimulate “ the growth of the mandible, as claimed by advocates of certain functional appliances. The reality, based on many studies and clinical experience, is that no type of orthopedic force can stimulate mandibular growth. The mandible has certain potential genetic growth that will express itself if given the “opportunity.” This opportunity is accomplished by unlocking the mandible when growth has been inhibited as a result of the malocclusion. To be able to “grow the mandible” beyond its genetic potential is just wishful thinking. Maybe someday genetic research will allow the stimulation of growth of the mandible, but it will take a different approach from the “orthopedic’ appliances used today.

Vertical Dimension

The vertical dimension is readily the most difficult pattern to affect In reflecting upon the Milwaukee Brace study, it IS possible to permanently decrease the mandibular angle if the force is severe enough. The reality is that such a force and time required (24 hours per day) is not realistic for a patient to wear.

If the patient has a vertical skeletal pattern, it is extremely difficult to do anything more than control this pattern, keeping from making it worse.

Treatment of high angle cases is accomplished by the use of a high pull headgear, extractions in some cases and “squeezing” exercises. If followed consciencually, controlling the high angle pattern can be achieved.

Diagnosis & Treatment Planning

The orthodontist can assemble certain facts to address the orthopedic problems by studying the cephalometric tracing to determine the skeletal pattern and measuring the intermolar width and occlusion in the study models. Depending upon the findings, specific “orthopedic” appliances can be used to correct the skeletal discrepancies.

In orthodontic treatment of growing children, however, it must be realized that the patient is a “moving target.” The amount of growth that takes place during treatment will play an important role in the success of the treatment. Evaluating the amount of growth potential the patient has is an erratic science at best. The orthopedic forces used on Class II skeletal patterns that have produced the best and most consistent results have been produced by the facebow headgear. This appliance can be utilized as a cervical pull, combination pull or high pull which give specific force vectors to the maxilla. The active force of the headgear is placed on maxillary first molars whose archwires are tied-back. The great advantage of the headgear is that the “opposite” force to the teeth is on the back of the neck, rather than the lower anterior teeth as is necessary with functional appliances. Therefore, no side reaction on this orthopedic force occurs.

Of equal importance to the success of the treatment is the patient’s ability to follow instructions. Any orthodontist is only as good as his patient. The patient must be educated to believe in the treatment and motivated to follow the instructions given by the orthodontist.

Summary

In most growing children, influencing the maxillofacial skeletal pattern in a positive way can be accomplished in a consistent manner.

The maxilla has the most potential for change. It can be expanded, moved forward, and inhibited from moving forward. The maxillary dentoalveolar complex can be extruded, inhibited and even intruded.

Conversely, the mandible has many more limitations. Without surgery, the most positive effect on the mandible is to create an “atmosphere” to allow the mandible grow and reach its genetic potential. The mandibular dentoalveolar complex can be changed within certain limitations.