[The influence of ferrule effect on post-restored restoration using extended finite element method]

To investigate the stress distributions and cracks initiation and propagation within the cementation of post and core restored teeth with various ferrule heights.

Three-dimensional finite element (FE) models of post and core restored teeth with different ferrule heights (0, 1, 2, 3 mm) were created by using the data of a three-dimensional non-contact digital scanning.Vertical oblique forces of 350 N (45° to the long axis of the root) were applied on the lingual surface of the teeth (4 mm below the incisal edge). Both linear analysis and extended finite element methods (XFEM) were used to investigate stress distributions, especially those in the adhesive interfaces.

Linear analysis results showed that the stress distributions within the root were quite similar among the groups. However, obvious stress concentrations were detected on palatal glass ionomer cement layer in the groups with 0 mm and 1 mm ferrule. According to the XFEM results, cracks were firstly initiated within the glass ionomer cement layer, and then propagated towards the adhesive resin cement layer. The ultimate loads that induced the damage within glass ionomer cement layer and adhesive resin cement layer in 0 mm ferrule group (50.4 and 94.7 N) were less than those in 3 mm ferrule group (65.9 and 228.2 N).

Adhesive interface was the susceptible structure of post and core restored teeth.Increasing ferrule height can significantly reduced the stress concentration within the palatal adhesive interface.