Fracture strengths of endocrown restorations fabricated with different preparation depths and CAD/CAM materials

Abstract

The objectives of this study were to compare the fracture strength of endocrown restorations fabricated with different preparation depth and various CAD/CAM ceramics, and to assess the fracture types. Endodontically treated 100 extracted human permanent maxillary centrals were divided into two preparation depth groups as short (S: 3-mm-deep) and long (L: 6-mm-deep), then five ceramic subgroups, namely: feldspathic-ceramic (Vita Mark II-VM2), lithium-disilicate glass-ceramic (IPS e.max CAD-E.max), resin-ceramic (LAVA Ultimate-LU), polymer infiltrated ceramic (Vita Enamic-VE) and monoblock zirconia (inCoris TZI-TZI) (n=10/subgroup). The endocrowns were fabricated by CAD/CAM and were cemented with resin cement (RelyX U200). The teeth were thermally cycled (5,000cycles) and fracture tests were performed at 45º angle to the teeth. The data were statistically analyzed (Kruskal-Wallis, Mann Whitney U), failure modes were evaluated with stereomicroscopy. Zirconia group provided the statistically highest fracture strength, but also exhibited non-repairable failures. Preparation depth has an effect on the fracture strength only for feldspathic ceramic.

Fracture resistance and failure modes of endocrowns manufactured with different CAD/CAM materials under axial and lateral loading

“…12 Moreover, the lateral forces increase the irreparable fracture ratio, because the stresses are accumulated in the cervical area and do not spread along the long axis. 22 The effect of loading, or group (conventional crown and endocrowns) on the failure modes (repairable vs irreparable) was not statistically significant. The multivariable analysis was applied to evaluate the effect of group and loading simultaneously on the failure modes, it showed statistically significant effect in selective comparisons only, may be because of the limitation in the number of specimens (n = 10).…”

“…But LDS is more rigid and has a high modulus of elasticity (95 GPa), which concentrates strain in weak area and results in irreparable fractures . Moreover, the lateral forces increase the irreparable fracture ratio, because the stresses are accumulated in the cervical area and do not spread along the long axis …”

“…In comparison with the traditional treatment, all ceramic endocrowns have the advantages of good mechanical properties, high biocompatibility, good esthetics, preservation of the remaining tooth structure, and saving time . The available literature has reported that molars restored with endocrowns had good clinical performance and they showed higher fracture resistance than molars restored with fiber post and conventional crowns .…”

“…19 In comparison with the traditional treatment, all ceramic endocrowns have the advantages of good mechanical properties, high biocompatibility, good esthetics, preservation of the remaining tooth structure, and saving time. 10,[20][21][22] The available literature has reported that molars restored with endocrowns had good clinical performance [23][24][25][26][27][28] and they showed higher fracture resistance than molars restored with fiber post and conventional crowns. 14,29,30 Some studies discussed the effect of different preparation shapes on the success of endocrown restorations like ferrule height 25,31 or pulp chamber extension.…”

Fracture resistance, failure mode and stress concentration in a modified endocrown design

“…Deeper extension into the pulp chamber increases bonding surfaces and load to failure values, however transmits all the forces to the root dentin [28]. And the lateral loading concentrates strain in the cervical area and does not distribute it toward the long axis running to non-restorable fractures [38].…”