6Sandler PJ, Atkinson R, Murray AM. For four sixes. Am J Orthod Dentofacial Orthop,2000, 117:4]8-434.
7Daugaard-Jensen I.Extraction of first molars in discrepancy cases.Am J Orthos,1973,64:115-136.
8Hom BM. Turley PK. The effects of space closure of the mandibular first molar area in adults. Am J Orthod,1984,85:457-469.
9Williams R,Hosila FJ.The effect of different extraction sites upon incisor retaction.Am J Orthod,1976,69:388-410.
10Abu Aihaija ES,McSheny PF,Richardson A.A cephalometric study of the effect of extraction of lower first permanent molars.J Clin Pediatr Dent,2000,24:195-198.