To evaluate the effect of the length of fiber-posts adhesively cemented on (1) the fracture strength of endodontically treated teeth, and (2) the push-out bond strength after cyclic loading.
Sixty extracted single-rooted teeth were sectioned at the CEJ and endodontically treated. After 24 hours of water storage at 37°C, RelyX Posts (3M-ESPE) were cemented with Panavia F 2.0 (Kuraray). A standardized composite core was built. Specimens were divided in three groups depending on the root-crown ratio: A) 2:1; B) 3:2; C) 1:1, and submitted to 1,250,000 cycles using a chewing simulator (Willytech). Immediately afterwards, 10 specimens per group were fractured using a universal loading device (Microtester-Instron). From the remaining 10 specimens, 2 sections of 2 mm thickness (coronal-apical) were prepared and submitted to the push-out test.
Regarding fracture strength, specimens restored with shorter posts (group C) performed significantly better than group A (p=0.02). Regarding push-out bond strength, overall the apical level scored significantly lower than the coronal one (p<0.05). Particularly, significant differences were observed between coronal and apical sections in groups B (p=0.047) and C (p=0.016).
Although the unfavourable stress distribution under cyclic loading appeared to affect the bond strength of shorter posts into the root canal, a shorter length of posts preserves more tooth structure, increasing the root-fracture resistance, and may thus reduce the occurrence of catastrophic failures.