Dowel material and crown ferrule on the biomechanical of tooth

Objective: The aim of this study was to evaluate the mechanical behavior of a maxillary central incisor restored with three types of dowels placed on remaining dental crown with three different heights (0, 1 or 2 mm) simulating the “ferrule effect”.

Method: Based on computed microtomography, nine models of a maxillary central incisor restored with a complete ceramic crown were obtained. 3 different dentin heights (ferrule = 0, 1 or 2 mm) and 3 types of dowels (glass fiber = GFD; nickel-chromium = NiCr; gold alloy = Au) were used, as follow: GFD0 – restored with GFD with absence of ferrule (= 0mm); GFD1 – similar, with 1mm of ferrule; GFD2 – similar, with 2-mm of ferrule. The models based on NiCr and Au alloys followed the same description and numerical identification. The Ansys Workbench 12.0 was used to determine the stress fields after loading the palatine surface of the crown with 180N at 45o to the tooth long axis. The external surface of the periodontal ligament was fixed in the three axis (x=y=z=0). 

Result: The maximum principal stress (σ_max) (MPa) in the crown dentin were: GFP0=117, NiCr0=30, Au0=64; GP1=113, NiCr1=102, Au1=84; GFP2=102, NiCr2=260, Au2=266. The σ_max (MPa) in the root dentin were: GFP0=159, NiCr0=151, Au0=158, GFP1=92; NiCr1=60, Au1=67; GFP2=97, NiCr2=87, Au2=97. 

Conclusion: The influence of different posts was more evident in the remaining dentin crown, mainly for the ferrule of 2mm. In the root dentin, the results were more similar, independently of the post and dentin heights. NiCr and Au dowels raised the stress in the remaining dentin crown up to 3 times in the ferrule of 2mm, in comparison with fiber post.