1. Treatment of irregularities of the permanent or adult teeth;Angell;Dent Cosmos,1860
2. Retention – the stepchild of orthodontia;Hahn;Angle Orthod,1944
3. Retention;Littlewood,2013
4. Biological basis for orthodontic relapse;Thilander;Sem Orthod,2000
5. Responsibilities and retention;Littlewood;APOS Trends Orthod,2017