An in vitro investigation of cast post and partial core design.

OBJECTIVES: Following endodontic therapy, the provision of a cast post and core restoration may be indicated. Many authors advocate retaining sound coronal dentine where possible, improving the resistance to fracture of the endodontically treated tooth. However, there is little conclusive experimental evidence to support this recommendation. This laboratory study was designed to investigate the effect of retained sound coronal dentine on the strength of a tooth restored with a cemented post and partial core restoration under direct loading.
METHODS: Specimens with retained coronal dentine buccally, lingually, or buccally and lingually were restored with cast post and partial cores and tested to failure using an Instron Universal Testing Machine, Model 1195. Control post and full core restorations were also tested. The mode of failure for all specimens was recorded photographically.
RESULTS: Teeth with retained buccal coronal dentine and post and partial cores were significantly less resistant to failure than controls with post and full cores (P < 0.01), failure occurring through crack initiation and propagation at the junction of the cast partial core and dentine core. There was no statistically significant difference in the strength of teeth with retained lingual coronal dentine or buccal and lingual dentine when compared to the control.
CONCLUSIONS: In conclusion, this in vitro model demonstrates that retained coronal dentine will not strengthen a tooth restored with a cast post and partial core. The clinical benefit of retaining buccal coronal dentine is brought into question when set against the increased technical effort and difficulty of producing the restoration in the dental technical laboratory and the possible overriding benefit of ferruling the crown margin onto a sound root structure.