[Influence of base materials on stress distribution in endodontically treated maxillary premolars restored with endocrowns].

ABSTRACT

OBJECTIVE: To evaluate the influence of base materials on stress distribution in endodontically treated maxillary premolars restored with endocrowns using three-dimensional finite element analysis. METHODS: A maxillary second premolar was scanned by Micro-CT and a three-dimensional finite element model of ceramic endocrown with 1 mm thickness of base was established. A model without base was also established as a negative control. Four kinds of conventional base materials with different elastic modulus were adopted light cure glass ionomer(3M Vitrebond, 3 657 MPa), flowable composite resin(3M Filtek Z350XT Flowable Restorative, 7 300 MPa), high strength glass ionomer(GC Fuji Ⅸ, 13 130 MPa), and posterior composite resin(3M Filtek P60, 19 700 MPa). With a 200 N force loaded vertically and obliquely, the distribution and magnitude of stress in the tooth tissue and adhesive layer were investigated by three-dimensional finite element analysis. RESULTS: The maximum von Mises stress values(vertical/oblique) in dentin and adhesive layer were measured as follows (1) no base material: 19.39/70.49 MPa in dentin and 6.97/17.97 MPa in adhesive layer; (2) light cure glass ionomer 19.00/69.75 MPa in dentin and 6.87/16.30 MPa in adhesive layer; (3) flowable composite resin 18.78/69.33 MPa in dentin and 6.79/16.17 MPa in adhesive layer; (4) high strength glass ionomer 18.71/69.20 MPa in dentin and 6.74/16.07 MPa in adhesive layer; (5) posterior composite resin 18.61/69.03 MPa in dentin and 6.70/16.01 MPa in adhesive layer. Under the same loading condition, models with different elastic moduli of base materials had similar stress distribution patterns. The von Mises stress of tooth tissue was mainly concentrated in the tooth cervix. Under oblique load, the regions where von Mises stress concentrated in were similar to those under a vertical load, but the values increased. The stress concentration in the tooth cervix was alleviated in models with base materials compared with the model without base material. The maximum von Mises stress in the tooth tissue and adhesive layer decreased when the elastic modulus of base materials increased and got close to that of dentin. CONCLUSION: The posterior composite resin of which the elastic moduli is high and close to that of dentin is recommended as base material for premolar endocrowns to alleviate the concentration of stress in tooth cervix and adhesive layer.