The influence of substance loss and ferrule height on the fracture resistance of endodontically treated premolars. An in vitro study

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 loading 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 degrees C, dwell time 30 s). Then specimens were quasi-statically loaded at 30 degrees in a universal testing machine until fractured. Data were analyzed with 2-way ANOVA, followed by multiple comparisons using Tukey HSD test (alpha = .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 residual coronal walls and ferrule height had a significant effect on the fracture resistance of endodontically treated premolars restored with prefabricated posts. (C) 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.