1. American Association of Endodontists 2015 Case difficulty assessment form and guidelines http://www.aae.org/uploadedFiles/Dental_Professionals/Endodontic_Case_Assessment/2006CaseDifficultyAssessmentFormB_Edited2010.pdf
2. Canadian Academy of Endodontics 2015 Case classification according to the degrees of difficulty and risk http://www.caendo.ca/newcae/wp-content/uploads/2014/10/degrees_english.pdf
3. A three-dimensional study of canal curvatures in the mesial roots of mandibular molars;Cunningham;Journal of Endodontics,1992
4. Endodontic case difficulty assessment: the team approach;Curtis;General Dentistry,1999
5. Accumulated hard tissue debris produced during reciprocating and rotary nickel-titanium canal preparation;De-Deus;Journal of Endodontics,2015