Effect of build orientation, sintering schedule, and resin cement on the bond strength of additively manufactured zirconia to dentin.

Statement Of Problem Whether the manufacturing protocol (build orientation and sintering schedule) of additively manufactured (AM) zirconia impacts the bond strength compared with subtractively manufactured (SM) zirconia remains unclear.Purpose The purpose of this in vitro study was to evaluate the effect of build orientation (45 degrees and vertical), sintering schedule (1-step and 2-step), and resin cement on the shear bond strength (SBS) and failure mode of AM zirconia bonded to dentin compared with that of SM zirconia.Material And Methods One hundred fifty 3Y-TZP zirconia cylinders (Ø2×4 mm) were produced by AM (INNI Cera BCM-W1000) or SM (IPS e.max ZirCAD MT). AM specimens were printed vertically at 90 degrees or at 45 degrees and subjected to 1-step or 2-step sintering; SM specimens were milled and sintered. The specimens were divided into 3 subgroups to be luted to human dentin (n=10) with 3 dual-polymerizing resin cements (SpeedCEM Plus; Ivoclar AG, RelyX Ultimate; 3M Dental, Panavia V5; Kuraray Noritake Dental). Dentin and zirconia surfaces were pretreated per cement and manufacturer protocols. After 24 hours, SBS was measured, and failure modes evaluated. The data were analyzed using 2-way ANOVA to assess the effects of manufacturing technique (AM or SM) and resin cement and using 3-way ANOVA exclusively within the AM group to evaluate the effects of build orientation, sintering schedule, and resin cement, followed by Tukey post hoc tests (α=.05).Results According to the 2-way ANOVA, zirconia manufacturing technique (AM or SM) did not significantly influence SBS, whereas resin cement had a significant effect (P<.001). Within the AM groups, the 3-way ANOVA revealed that resin cement was also the only factor significantly affecting SBS (P<.001), with no significant effects of build orientation or sintering schedule (P>.05). SpeedCEM Plus (8.9 ±3.7 MPa) showed the significantly lowest SBS and RelyX Ultimate (15.1 ±5.3 MPa), and Panavia V5 (15.7 ±4.9 MPa) yielded similar SBS. No significant difference was found in failure mode between AM and SM zirconia (P=.647), but differences existed between cements (P<.001). Almost all failures (98%) in SpeedCEM Plus groups were adhesive at the dentin-cement interface. The RelyX Ultimate and Panavia V5 groups had approximately 20% adhesive and approximately 50% cohesive failures within dentin.Conclusions No significant differences in SBS or failure mode were found between AM and SM zirconia. Build orientation and sintering schedule of AM zirconia had no influence on the bond strength of zirconia to dentin, whereas resin cement had a significant effect. In general, SpeedCEM Plus resulted in the significantly lower bond strength of AM and SM zirconia to dentin than did RelyX Ultimate or Panavia V5.