MOLAR
DEROTATING SPRING
Molar Rotations
Molar rotations may be bilateral or unilateral. When maxillary molars are found rotated along an axis lingual to their central fossae, the mesiobuccal cusps will be mesially positioned.
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Palatal Arch
For optimum correction of maxillary molar rotations a palatal arch may be used. For this, the horizontal tabs of the palatal arch are bent on the right and/or left sides. The palatal arch can be inserted actively or passively into the mouth. With passive insertion, the palatal arch is activated intraorally. There are many problems associated with using palatal arches. The fabrication of a palatal arch is difficult, activation and insertion increases chair-side time, the palatal arch limits the movements of tongue, and it can be uncomfortable for the patient. The palatal arch can not be used in cases that mandibular molar rotations are present. In addition, the two ends of the palatal arch do not function independently.
Molar Derotating
Spring
Many of the problems associated with using a palatal arch can be solved by using this spring technique. In full banded and bonded cases with double slot tubes and lingual sheaths attached on molars, an expanded heavy arch wire is inserted from the distal of one second premolar to other and then a single rectangular wire acting as the spring (0.016x0.022 Stainless Steel or BetaTitanium) is inserted in the molar auxiliary tube. According to molar rotations, the spring can be inserted palatally, mesiobuccally or distobuccally. In the palatal approach, the wire is inserted in the lingual sheath and tied with wire ligatures or elastomeric rings to the main arch wire in the premolar area (figure 3)
In the mesiobuccal approach, the wire is bent as in (figure 4A) and inserted into the tube from the mesial. The wire is then tied buccally in the area of the premolars (figure 5).
When the approach is distobuccal, the wire is bent as in (figure 4B) and inserted into the tube from the distal, then wire is tied to buccally to the premolars at the level of the arch wire activating the spring. (figure 6).
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After inserting
the wire into the molar tube, the free arm will be extremely displaced at
the premolars and when tied to the buccal side of the premolars exerts a force
of movement on the molar causing it to derotate (figure 7A, B, C).
Advantage
This spring is
fabricated easily and requires little chair-side time. The derotating spring
does not limit the tongue’s movement and is comfortable for the patient. This
spring is also separate and independent from the opposite side. In addition,
in cases that mandibular molar rotations are present it can still be used
easily. The side effect of this spring is to constrict the arch and cause
palatal movement of the premolars making it necessary to expand the main arch
wire.
Dr . Hossain Dabagh Asadollahi