Biomechanical considerations for endocrowns in restoring endodontically treated teeth

Background: Endodontically treated teeth have an increased risk of biomechanical failure because of significant loss of tooth structure. The ideal restorative technique and material for such teeth is always a challenge for the clinician. Aims: The aim of this project was to evaluate the effect of using different dental CAD/CAM materials on the biomechanical behaviour of endodontically treated teeth restored with a new technique named endocrown. Methodology: In this study, a thorough comparison of endocrown restorations fabricated from new types of all-ceramic, resin based composite and zirconia dental restorative materials through a series of systematic tests on human permanent premolars was performed. An extensive thermal and mechanical cyclic testing, static mechanical loading, micro-computed tomography analysis, scanning electron microscopy, optical profilometry, and finite element analysis evaluated the efficiency of endocrowns in terms of their mechanical properties and behaviour, fitting accuracy and stress distribution pattern. Results: The current study reported significant effects for material selection along with restoration design and remaining sound tooth structure on the restoration efficiency of endodontically treated teeth. A significant interaction between restoration design and material type was observed, in which resin-based composite resulted in highest fracture strength among endocrowns, however all materials tested were able to survive dynamic thermo-mechanical fatigue testing simulating 2.5 years of clinical service. Monolithic translucent zirconia resulted in the highest number of catastrophic failures in restored teeth. The stress distribution pattern in the studied models revealed that the use of glass ceramics with endocrowns could enhance their long term bonding efficiency and retention, while resin composite endocrowns present a lower risk of catastrophic failure. Glass ceramics showed superior fitting accuracy and exhibited the smoothest and most homogenous fitting surface’s roughness profile. Conclusions: The mechanical behaviour, stress distribution and adaptation of resin based composite and glass ceramic endocrowns were clinically acceptable providing sufficient amount of sound tooth structure is preserved. Zirconia endocrowns should be avoided with premolar teeth owing to the low fracture resistance and high risk of catastrophic failures. Endocrowns are not recommended in cases with no remaining buccal and lingual coronal walls.