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Ali AO, Kelly JR et al. J Prosthodont 2012; 21: 614–621

Convergence angles of preparations for tradition castings should be between 10°-20° in order to maximise resistance to dislodgement and to facilitate seating of the restoration. Yet when it comes to zirconia copings, others investigators found that the marginal and internal adaptation significantly improved as convergence increased from 6° to 20°. This in vitro study examined the retentive values for sand-blasted zirconia copings luted with different resin cements. There were no differences in these values achieved with Panavia F 2.0, Rely X Unicem and Clearfil SA. When failure was observed with Panevia F 2.0, generally the cement remained on the abutment tooth in contrast to the mode of failure for the other two materials when cement was located on the coping. In addition, zirconia copings cemented on teeth with 15° convergence had significantly higher retention than if the preparation had 30° convergence.