Abstract: Objective To evaluate the effect of different designs of marginal preparation on stress distribution in the mandibular
premolar restored with endocrown using three-dimensional finite element method. Methods Four models with different
designs of marginal preparation, including the flat margin, 90° shoulder, 135° shoulder and chamfer shoulder, were
established to imitate mandibular first premolar restored with endocrown. A load of 100 N was applied to the intersection of
the long axis and the occlusal surface, either parallel or with an angle of 45° to the long axis of the tooth. The maximum values
of Von Mises stress and the stress distribution around the cervical region of the abutment and the endocrown with different
designs of marginal preparation were analyzed. Results The load parallel to the long axis of the tooth caused obvious stress
concentration in the lingual portions of both the cervical region of the tooth tissue and the restoration. The stress distribution
characteristics on the cervical region of the models with a flat margin and a 90° shoulder were more uniform than those in the
models with a 135° shoulder and chamfer shoulder. Loading at 45° to the long axis caused stress concentration mainly on the
buccal portion of the cervical region, and the model with a flat margin showed the most favorable stress distribution patterns
with a greater maximum Von Mises stress under this circumstance than that with a parallel loading. Irrespective of the loading
direction, the stress value was the lowest in the flat margin model, where the stress value in the cervical region of the
endocrown was greater than that in the counterpart of the tooth tissue. The stress level on the enamel was higher than that on
the dentin nearby in the flat margin model. Conclusion From the stress distribution point of view, endocrowns with flat
margin followed by a 90° shoulder are recommended.