A myriad of force values have been applied during the evolution of orthodontics. It was once thought that heavier forces moved teeth more quickly—making large, bulky, high-force appliances in vogue. High intermittent forces also were employed at times to overcome the friction caused by restrictive brackets.
Dr. P.R. Begg clearly demonstrated that a minimal force (2 oz.) was not only sufficient, but an optimum application for dental malocclusions and skeletal mal-alignments.
Light Force Orthodontics and its ultimate goals are defined by three principles:
1. Ultra light forces: The rapid movement of teeth through bone to their final destination using very light forces (2 oz.).
2. Overcorrection: The exaggeration of movement, both skeletal and dental. A Class II to a strong Class I, deep bite to a slightly open bite, and overcorrection of rotated teeth to a mirror image of their original positions are among examples.
3. Exaggerated finish: Finish to an edge-to-edge position to permit a favorable soft landing to the desired finish. This helped popularize the Tooth Positioner, which in conjunction with the envelope of forces, massaged the teeth into a position over apical base for long-term stability.
How it works
The effectiveness of light forces is perhaps best demonstrated in extreme cases that involve tooth movement as well as a skeletal component. The Class II malocclusion always has been a dramatic complaint and an ongoing challenge for correction.
Light Force Orthodontics takes a simple approach. Rapid bite opening unlocks the interferences and allows the mandible to be receptive to Class II mechanics while the teeth move simultaneously in a near frictionless environment. It is an unrestricted journey to their natural position over their apical bases.
The Class II case
A 12-year-old male presented with an extreme Class II malocclusion (Figs. 1-2). He had a 100% overbite and a 22-mm overjet. The molar and cuspid relationships were both full step C lass II positions.
The patient’s Cephalometric values pre treatment:
Wits: +13 mm
FMA: 24°
I to SNa: 126°
I to APo: -6 mm
When evaluating a severe case of this kind, it is important to understand the problems very clearly before designing a treatment plan. This means ignoring the impulse to extract and realizing surgical intervention may be necessary.
The problems we see in this case are:
• A 100% overbite
• A full step Class II relationship of first molars and cuspids
• Extreme flaring of the maxillary anteriors
• A severe retrognathic skeletal pattern (Figs. 3-5)
The low FMA challenges bite opening and the high Wits +13 mm means that the mandible needs to be translated—a whole lot.
Dr. Donald Enlow once told me that “the mandible will translate to the greatest extent of its genetic blueprint.” This gives hope to all cases, but we sometimes fall short for the same reason.
Our decision not to extract was based on the advantages of Light Force Orthodontics. We opted to look for early bite opening and used whatever spaces we had.
Treatment
The treatment started with banding the first molars and bracketing the upper and lower six anteriors (Figs. 6-8). Coralex, a zero/zero Tip-Edge© bracket, was selected, and anchor bands were placed in a .016 Australian archwire. Class II elastics (2 oz.) were applied. The maxillary anteriors were retracted while the mandible translated at a rather remarkable rate. The appointments were six weeks apart, and virtually no changes were made during treatment.
We achieved overcorrections in all respects as the anterior teeth came edge to edge (Figs. 9-11). At that time, the remaining bicuspids were bracketed to achieve final torquing and paralleling of all teeth.
The patient finished treatment with a Class I occlusion accompanied by a perfectly functioning anterior guidance system and great improvement in the facial profile (Figs. 12-13 and 14-16).
Cephalometric values post treatment:
Wits: +2 mm
FMA: 24°
I to SNa: 106°
I to APo: + 2 mm
The benefits
Using heavy intermittent forces is the least efficient way to move teeth through bone.
There are many reasons, including patient comfort, to use light continuous forces. Under the best circumstances, when used with active light resilient archwires, the results are dramatic. It is important to have a near frictionless environment for this to occur. The Coralex bracket was selected because of the freedom it affords the bracket/wire dynamic and the subsequent easy movement of the teeth involved.
Conclusions
Human tissue responds to stimuli, not muscle. As teeth move through bone, a special balance occurs. Osteoclastic activity on one side is compensated by Osteoblastic activity on the other. This becomes a smooth transition, if stimulated by ultra light continuous forces. Heavy intermittent forces cause an excessive inflammatory response, resulting in an obstruction to movement. The skeletal pattern underwent a large anterior/posterior correction for the same reasons. The light elastic forces did not override the bite opening bends. The bite opened quickly to allow the mandible to express itself to a class I skeletal pattern.
Dr. Conlin is an orthodontic specialist who has taught for 27 years. He began practicing orthodontics in 1959 and has provided orthodontic education for 22 years. He delivers several workshops each year, is a noted speaker at national and international meetings, and lectures to the graduate departments of several universities. Dr. Conlin is Director, Orthodontics for Non-Orthodontists at the Scottsdale Center
for Dentistry.
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