Takahashi CM, Cunha RS, De Martin AS, Fontana CE, Silveira CFM, da Silveira Bueno CE. In Vitro Evaluation of the Effectiveness of ProTaper Universal Rotary Retreatment System for Gutta-Percha Removal with or without a Solvent. Journal of Endodontics. 2009 Nov;35(11):1580–3. doi: 10.1016/j.joen.2009.07.015.