Introduction:

Tooth pieces, after endodontic treatment, increase their susceptibility to fracture, a phenomenon mainly associated with loss of tooth structure.

Objective:

To evaluate, in vitro, the resistance to fracture of upper premolars with endodontic treatment by traditional, conservative and conservative ninja access, with temporary and final restoration.

Methods:

A prospective study of longitudinal experimental design was carried out with 42 donated upper premolars, separated into three groups, according to the type of endodontic access to be applied; in turn, each was then divided into two subgroups, according to the type of restoration, and a control group, not performed endodontic treatment. After treatment and restoration, fracture resistance was evaluated using oblique compressive loading (45°) in a universal loading machine. The loads required for fracture were recorded in newtons and statistically compared.

Results:

The parts treated by conservative ninja access with provisional and final restoration required an average fracture load of 513.45 N and 638.13 N, respectively; this forces were significantly higher than the resistance values offered by the other treatments, with p < 0.05. Likewise, there were no significant differences in the resistance values obtained between the cases of conservative access and traditional access, nor when comparing the types of applied restoration, with P<0.05.

Conclusions:

In in vitro endodontics, the design of the access to the cavity of conservative ninja type significantly affected the resistance to fracture of the upper premolars, acquiring a biomechanical behavior similar to that of the control pieces.