Objectives: To evaluate the biomechanical influence of reconnecting the buccal and lingual walls of endodontically treated lower molar with a large MOD cavity. Methods: 3D models were created from a micro-CT scan of an extracted intact lower human molar. Finite element analysis was then used to compare the stress distribution and displacement of the structures between different models: Unrestored MOD on ETT (Unrest), MOD on ETT restored with composite resin (Norm), MOD on ETT reinforced with a non-invasive ring (Ring) and intact tooth as the control (Int). Results: This study showed that the Unrest model presented the highest stress values at the cervical level. The non-invasive Ring model showed the lowest stress values at the cervical level, and the lowest deflection of the cusps. Conclusions: Mechanically reconnecting the remaining tooth structures has a direct positive effect on stress distribution and deformation of the remaining structures. Clinical relevance: Reinforcing ETT in a non-invasive direct approach is efficient in terms of preserving sound tooth structures, reducing the time of treatment and eliminating the laboratory steps required to create the restorations.