PeerJ
Fracture resistance of mandibular molar endocrown with different preparation designs: an in vitro study
By Awang Iskanderdzulkarnein PMB, Raja Mohd N, Ahmad Ubaidillah AH and 3 others.
Abstract
Background
Endocrowns have gained popularity as a conservative option for restoring endodontically treated molars because their success rates are comparable to those of conventional crowns. However, there is limited evidence on the effectiveness of different endocrown marginal designs, particularly concerning their fracture resistance and failure modes under axial and oblique loading. This in vitro study aimed to evaluate the fracture resistance and failure modes of three different endocrown marginal designs on mandibular molars and compare them with endocrowns under axial and oblique loading.
Methods
Sixty-four extracted mandibular molars were root-treated and lined with flowable composite (1.5 mm thickness) before being embedded in epoxy resin blocks. The samples were divided into four groups (n = 16): three endocrown groups with different preparation designs (butt-joint, 0.8 mm chamfer, and 1.0 mm shoulder) and one group with conventional crowns. Crown preparations were performed with a high-speed handpiece mounted on a modified milling device, targeting a 2.0 mm anatomical occlusal reduction for conventional crowns and a 4.0 mm central chamber depth with a 2.0 mm axial wall height (ferrule) for endocrowns (except the butt-joint design, which had no ferrule preparation). Restorations were fabricated using the Chairside Economical Restoration of Esthetic Ceramics (CEREC) Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) system with lithium disilicate (IPS e.max CAD; minimum occlusal thickness: 1.5 mm) as the restorative material and cemented with the RelyX Ultimate dual-cure resin adhesive. After 1,500 thermocycling cycles, the samples were divided into two subgroups (n = 8) for axial and oblique loading tests. The fracture resistance was tested using a universal testing machine at a crosshead speed of 0.5 mm/min, applying a load of up to 5,000 N until fracture. Failure modes were examined using a stereomicroscope at 5x magnification and categorized as catastrophic or non-catastrophic. The mean fracture resistance was compared using one-way Analysis of Variance (ANOVA) with Bonferroni post-hoc tests, and Fisher's exact test was used to assess the association between preparation designs and failure modes (p < 0.05).