The influence of ferrule effect and length of cast and FRC posts on the stresses in anterior teeth

Objectives

The purpose was to assess the influence of ferrule effect and length of cast post and cores, and FRC posts on the strength of anterior teeth.

Materials and methods

The investigations were conducted by means of finite element analysis with the application of contact elements. Thirteen 3D models of maxillary first incisors were generated: model 1 was an intact tooth; 2A – a tooth with all-ceramic crown with ferrule effect, 2B–D a teeth restored with, ferrule and FRC posts of various lengths 13 mm, 8 mm, 4 mm, 3A – a tooth with ceramic crown without, ferrule effect, 3B and C teeth without ferrule and 10 mm, 5 mm length FRC posts, 4B–D teeth with ferrule, restored by cast posts and cores of 13 mm, 8 mm, 4 mm lengths and 5B and C teeth without ferrule, restored with cast posts and cores of 10 mm, 5 mm lengths. Each model was subject to a load with a total force of 100 N uniformly distributed under the lingual cingulum, at an angle of 130°. To evaluate, the strength of tooth tissues, ceramics and composites, the modified von Mises failure criterion was used, for FRC the Tsai-Wu criterion and for cast NiCr alloy the von Mises criterion. Contact stresses were calculated at the luting cement–tissue interface.

Results

Ferrule effect in teeth reduces mvM stresses in dentin, in posts and in luting cement. The contact tensile stresses around posts in teeth with ferrule effect were 1.7–3.0 times smaller than in, teeth without ferrule. Lower mvM stresses occurred in teeth with cast posts in comparison with FRC posts. The mvM stresses in teeth with posts of various lengths were similar, irrespective of post material.

Significance

Ferrule effect in teeth with posts and cores has a critical influence on stress reduction. Using posts and cores made of rigid materials leads to stress reduction in teeth. Post length has a small, effect on stress values in tooth structures.