FIBRE ORTHODONTIC RETAINER PROPERTIES 695 3 of FIBRE ORTHODONTIC

Riedel (1960) recognized that after orthodontic treatment , the teeth tend to return to their original positions because the periodontal tissues have not had suf cient time to reorganize themselves. During this reorganization period , the teeth must be maintained in the position achieved orthodontically, by means of removable or  xed retention systems. When relapse is expected, a splint is often used on completion of orthodontic treatment to resist the dislocating forces acting on the teeth. These forces ( Littlewood et al. , 2006 ; Edman Tynelius et al., 2010 ) are mainly occlusal, those exerted by the masticatory muscles or tongue, and elastic rebound forces are exerted by the periodontal tissues. The resultant force is transmitted to the teeth and then to the splint, principally as  exural forces. Retention is consequently important and must continue until periodontal reorganization has been fully achieved. Stainless steel (SS) orthodontic sectional archwires are often used in the anterior lingual segment as  xed retention. These , however, have some drawbacks due to the excessive stiffness of the In vitro determination of the mechanical and chemical properties