Evaluation of the fracture resistance of posterior monolithic CAD/CAM crowns restoring custom-made implant abutments after artificial aging

This study was carried out to investigate the effect of using different commercially available CAD/CAM materials for fabrication of molar crowns on the fracture strength of custom-made abutments after dynamic loading and thermal cycling.
A total of 88 identical custom-made CAD/CAM abutments milled out of titanium, zirconia, lithium disilicate and ceramic-reinforced polyetheretherketone were divided into 11 test groups (n=8) and restored with CAD/CAM crowns milled out of zirconia, lithium disilicate, and ceramic-reinforced polyetheretherketone. Lithium disilicate abutments were restored only with lithium disilicate and ceramic-reinforced polyetheretherketone crowns. Specimens were artificially aged in a chewing simulator for 1.2 million cycles of dynamic loading with simultaneous thermal cycling. The surviving specimens were loaded to fracture in the universal testing machine. The data were tested for normality using the Shapiro-Wilk test and for homogeneity of variance using the Levene test revealing heterogeneity and deviation from the normal distribution. Statistical significance was tested for using Welch’s Analysis of variance with post-hoc Games-Howell test (95% confidence interval).
In total, 81 specimens survived the artificial aging process simulating five years of clinical service. The fracture modes and means of the fracture strength varied between the groups, zirconia abutments restored with zirconia crowns had the highest mean with 5529.5 N and lithium disilicate abutments restored with ceramic-reinforced polyetheretherketone crowns had the lowest mean with 1582.5 N.
Although the tested combinations showed different fracture values and modes, all the groups that survived the artificial aging and fractured above 900 N are considered safe from a mechanical point of view for restoring single implants in the posterior region within normal loading conditions.

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