Objective To establish three-dimensional finite element model of two-piece post crown to the mandibularfirst molar residual roots, and analyze the stress distribution characteristic to the residual roots with differentadhesives, so as to get the best combination under different conditions.Methods The complete mandibular first molarin vitro was selected, the crown was removed along the cemento-enamel junction, then the residual roots were scannedby CT. CT images were imported into a reverse engineering software, and the three-dimensional finite element modelof the mandibular first molar residual roots was reconstructed. Titanium two-piece post crown of the mandibular firstmolar residual roots was produced, then was scanned by CT. The model was reconstructed and assembled by MIMICS.The stress distribution of the root canal and root section under the vertical load and lateral load with different bondingsystems were analyzed.ResultsThree-dimensional finite element model of two-piece post crown to the mandibularfirst molar residual roots was established. With the increasing of elastic modulus of the adhesives, the maximumstress within the root canal was also increasing. Elastic modulus of zinc phosphate was the biggest, so the stresswithin the root canal was the biggest; elastic modulus of Superbond C&B was the smallest, so the stress within theroot canal was the smallest. Lateral loading stress was much larger than the vertical load. Under vertical load, theload on the root section was even with different bonding systems. Under lateral load, the maximum stress was muchlarger than the vertical load. The stress on the root section was minimum using zinc phosphate binder, and the stresson the root section was maximum using Superbond C&B.Conclusion In two-piece post crown restorations, there issignificant difference between different adhesives on tooth protection. When the tooth structure of the root canalorifices is weak, in order to avoid the occurrence ofsplitting, the larger elastic modulus bonding system isthe first choice, such as zinc phosphate binder. Whenthe resistance form of the root canal orifices is goodenough but the root is too weak, it is suggested that the smaller elastic modulus bonding system is the first choice,such as Superbond C&B.
