Unequal outer and inner bow configurations: comparing 2 asymmetric headgear systems.
BACKGROUND
Asymmetric headgear is used when different molar distalization forces (MDF) are needed on the right and left sides of the jaw to correct a Class II molar relationship.


METHODS
We investigated 2 asymmetric headgear configurations, the outer-bow and the inner-bow, on cervical-pull headgear. In the first configuration, 5 hooks were soldered on 1 side of the outer bow at 10-mm intervals, making this side shorter; in the other, 4 stops (1.5 mm) were added to 1 side of the inner bow, making this side longer. The right and left MDF and the extraoral force (EF) were measured simultaneously with 2 fork transducers and a testing machine, respectively.


RESULTS
A 40-mm difference between the long and short outer bows resulted in a 2.17-fold greater MDF on the long-side molar (7:3 ratio). The 3-4 stop configuration provided the optimal inner-bow arrangement, with stop/no-stop MDF ratios of 7:3 and 10:0, respectively, at 10 N EF. At low-to-medium EF levels, a unilateral MDF developed on the stop side with zero MDF on the no-stop side. The sum of the right and left MDF nearly equaled the EF in the outer-bow asymmetry and was 60% in the inner-bow setting; this suggests strong lateral forces in the latter.


CONCLUSIONS
Clinically, for a bilateral unequal Class II relationship, the system of choice is outer-bow asymmetric headgear. For a unilateral Class II relationship with 1 side in a Class I molar relationship (Class II subdivision), inner-bow asymmetric headgear is recommended.
Brosh
Tamar
T
Maurice and Gabriela Goldschleger School of Dental Medicine, Tel Aviv University, Israel. tbrosh@post.tau.ac.il
Portal
Schay
S
Sarne
Ofer
O
Vardimon
Alexander D
AD
D003799:Dental Stress Analysis / Q000295:instrumentation; D005115:Extraoral Traction Appliances; D006801:Humans; D008963:Molar; D016382:Orthodontic Appliance Design; D013314:Stress, Mechanical; D013499:Surface Properties; D014087:Tooth Movement Techniques / Q000295:instrumentation; D014159:Transducers