Objectives : The aim of this study was to evaluate, using finite element analysis, the risk of debonding at the post/resin cement interface and root fracture in teeth restored with a metallic cast post (MCP) or glass fiber post (GFP). The hypothesis was that GFP would present a lower risk of debonding and/or of root fracture.

Materials and methods : 3D finite element models of premolars with oval root canals restored with MCP or GFP were created. Two post/cement interface conditions were simulated: bonded (B) and non-bonded (nB). The risk of fracture indexes (RFI) for the dentin, post and core were calculated by dividing the top 5% maximum principal stress registered in each material ( σ _5% ) by its tensile strength (TS) reported in the literature. The RFI calculated for the intact tooth ( I ) was considered the control. The risk of debonding was analyzed only for models with bonded interface. Tensile (maximum principal) and shear stresses in the post/resin cement interface were analyzed to determine the risk of debonding. The two post types had different cross-sections and resin cement thicknesses. In order to isolate the effect of the elastic modulus of the posts on the risk of debonding, metallic cast posts with a circular cross sectional area (bonded circular metallic posts: CMP-B) and glass fiber posts in the anatomic shape (bonded anatomic glass fiber post: AFP-B) were also simulated.

Results : Metallic posts induced higher tensile and shear stresses along the interface compared to the glass fiber posts, regardless of the shape. The RFI values are listed in the table.

Models	Dentin			Core			Post
	σ 5%	TS	RFI	σ 5%	TS	RFI	σ 5%	TS	RFI
MCP-B	36.2	104	0.35	16.2	821	0.02	127.9	821	0.16
MCP-nB	37.6	104	0.36	75.6	821	0.09	321.5	821	0.39
GFP-B	40.8	104	0.39	4.6	55	0.08	8.2	99	0.08
GFP-nB	56.5	104	0.54	84.1	55	1.53	378.7	99	3.83
I	39.0	104	0.38

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