d e n t a l m a t e r i a l s 2 9 ( 2 0 1 3 ) 1280–1286 Available online at www.sciencedirect.com ScienceDirect jo ur nal ho me pag e: www.intl.elsevierhealth.com/journals/dema The influence of substance loss and ferrule height on the fracture resistance of endodontically treated premolars. An in vitro study Abdulaziz Samran a,b,c,* , Shadi El Bahra a,d , Matthias Kern a a Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts University at Kiel, Kiel, Germany b Department of Fixed Prosthodontics, School of Dentistry, Ibb University, Ibb, Yemen c Al-Farabi Dental College, Riyadh, Saudi Arabia d Department of Removable Prosthodontics, School of Dentistry, Damascus University, Damascus, Syria a r t i c l e i n f o Article history: Received 3 February 2013 Received in revised form 14 August 2013 Accepted 7 October 2013 Keywords: Residual coronal wall Ferrule height Glass fiber post Resin cement a b s t r a c t Objective. This study evaluated the effect of different ferrule heights and varying degrees of substance loss on the fracture resistance of endodontically treated premolars. Methods. Eighty extracted and endodontically treated lower premolars were used and divided into 5 test groups (n = 16) depending on the ferrule height: A (0.0 mm), B (0.5 mm), C (1.0 mm), D (1.5 mm) and E (2.0 mm) respectively. Teeth in subgroups were either with 1 or 2 residual coronal dentin walls which were 3 mm in height and 1 mm in thickness. Teeth were restored with glass fiber posts and cast crowns. All specimens were then subjected to dynamic load- ing in a masticatory simulator for 1,200,000 loading cycles with a nominal load of 5 kg at 1.2 Hz combined with thermal cycling (5–55 ◦ C, dwell time 30 s). Then specimens were quasi- statically loaded at 30 ◦ in a universal testing machine until fractured. Data were analyzed with 2-way ANOVA, followed by multiple comparisons using Tukey HSD test (˛ = .05). Results. Mean (SD) failure loads for groups ranged from 679.5 ± 164.9 N to 1084.5 ± 269.9 N. Two-way ANOVA revealed that both the ferrule height and the number of residual coronal walls had a significant influence on the fracture resistance (P < .001 and P = .006, respectively). Significant increases were produced in the final fracture resistance, when the ferrule height was increased, which was reduced to approximately 37% when teeth with 2 mm ferrule height were compared with teeth without a ferrule. Significance. Under the conditions of this in vitro study, increasing the number of resid- ual coronal walls and ferrule height had a significant effect on the fracture resistance of endodontically treated premolars restored with prefabricated posts. © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. 1. Introduction Endodontically treated teeth (ETT) have been problematic because of coronal destruction from dental caries, fractures, ∗ Corresponding author at: Department of Prosthodontics, Propaedeutics and Dental Materials School of Dentistry, Christian-Albrechts University at Kiel, Arnold-Heller Strasse 16, 24105 Kiel, Germany. Tel.: +49 431 5972877; fax: +49 431 597 2860. E-mail addresses: asamran@proth.uni-kiel.de, aasamran@gmail.com (A. Samran). previous restoration, and endodontic therapy. This results in an increase of the likelihood of fracture of the treated tooth during function [1]. The prognosis of ETT is influenced by different parameters such as amount of hard tissue loss [2], presence of a minimum of 1.5–2.0 mm ferrule height 0109-5641/$ – see front matter © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.dental.2013.10.003