Introduction:
Labially inclined anterior teeth are an aesthetic and biomechanical problem. Will the prosthetic restoration of a damaged incisor whose root is inclined labially withstand chewing forces?

Aim of the study:
To estimate the influence of anterior teeth inclination on the strength of incisors reinforced with post and cores.

Material and methods:
The experiment was conducted by using FEA with contact elements. 3-D models of maxillary central incisors were created: model A – tooth, model B - tooth with a post and core. The axes of A and B models were positioned as follows: 1 - retroclined, 2 - normally inclined, 3 - labially inclined at 10%, 30% and 50% angle of inclination, respectively. Each model was subjected to a force of 100N. The modified von Mises failure criterion (mvM) was used to evaluate the strength of the tooth structures and cement. Contact stresses at the cement-tissue interface adjacent to prosthetic restorations were calculated.

Results:
The lowest reduced stresses were recorded for the palatally inclined incisors (model A1). In the dentine of the labially inclined incisor (model A3), the mvM stresses were up to 80% higher in comparison with the normally inclined incisor (A2). In the proclined anterior tooth with a post and core restoration (B3), the value of equivalent contact stresses increased by more than a half in relation to the properly positioned model B2. The concentration of stresses occurred on the palatal side of the tooth cervix. In the post and core, Von Mises stresses of 100 MPa were noted.

Conclusions:
The equivalent stresses in the structures of incisors increase with the proclination of the tooth axis. In inclined anterior teeth restored with post and cores there occurred significantly higher and unfavourably distributed stresses than in normally positioned teeth. Post and core build-up of proclined incisors have a higher predisposition to debonding of the restoration, bending of the post, or even fracture of the root.