Effect of finish line level of all ceramic crown on stress distribution within dentin of maxillary central incisor with an abfraction lesion

Purpose: to evaluate by means of three dimensional finite element analysis, the effect of finish line location on stress distribution on dentin of maxillary central incisor affected by abfraction lesion and covered with IPS e. max (Lithium di silicate) crown.
Statement of the problem: In some cases of abfraction, the tooth need to be covered with full coverage crown, but, location of finish line may affect dentin integrity.
Materials and Methods: 3D finite element model of unprepared maxillary central incisor was made. By deleting method, IPS e.max crown was designed and geometric dimensions of prepared tooth were introduced as the following guidelines, 2 mm incisal reduction, 1.5 mm reduction of labial surface and 1 mm circumferential shoulder finish line. The position of labial finish line was designed in three different levels apical to the upper margin of the abfraction lesion (0.5. 1.0 and 1.5 mm) forming three models to be tested (A, B and C) respectively in addition to unprepared control model.
Results: For all tested four models, the calculated stresses with 125° applied load were higher than that with 60° with statistical significant differences. The calculated stresses at the control model in both directions of applied load were lower than that in other tested models (A, B and C) with statistical significant differences. For control model at 125° applied load, Von Mises equivalent stress value was (40.27 MPa), whereas, in case of 60° applied load, was (26.33 MPa). For model (A) where the finish line of IPS e.max crown is established 0.5 mm apical to the upper edge of the abfraction lesion, Von Mises equivalent stress values were (22.14 & 39.68 MPa) respectively.
Conclusion: In all tested models, maximum stresses increased with increasing the angle of applied load, and model (B and C) provided more favorable stress distribution than that in model (A).