With the advance of treatment, space created within the rear arches increases. The skull slowly returns to the correct position, changing its inclination with respect to the jaw.
With the advance of treatment muscles chains (blue lines) stretch in an isometric fashion, with eccentric contraction. These muscle chains are subjected to a continuous stretching very tiring to the body.
The arrow Fm represents the direction of the force exerted by the muscles of the stomatognathic system.
The arrow Fr represents the direction of the force exerted by the shortened muscle chains, plus the force of gravity.
When the fulcrum is located in the canine-incisor area Fm is less than Fr. In this case the lever is not able to keep the skull in an ideal position. Conversely, when the fulcrum is in the premolar and molar area, Fr is greater than Fm as the lever is perfectly capable of maintaining the skull upright.
We can also say that when the fulcrum is in the canine-incisor area, the lever is disadvantageous, when it is in the premolar and molar area it is advantageous.
