Purpose: Aftermarket computer-aided design/computer-assisted manufacture (CAD/CAM) milled zirconia (Zr) abutments were recently introduced with minimal independent research regarding their fracture resistance. Thirdparty manufacturers often alter the original equipment manufacturers' (OEM) design with unknown effects on fracture resistance. These alterations include elimination of the titanium insert with subsequent introduction of Zr into the implant, changes to connection designs and shapes, and/or alterations to prosthetic screw design. This in vitro study compares the static load fracture resistance and mode of failure of alternatively engineered Zr abutments with those of prefabricated (OEM) Zr abutments with internal, external, and conical connections. Materials and Methods: Twenty Zr stock abutments (five per group) from OEMs were selected to demonstrate fracture resistance of external hex, internal connection, and conical connection implant designs (control groups). Atlantis abutments (Dentsply) (test group) were manufactured by means of CAD/CAM to match the OEM abutments (control groups). All samples had full-coverage all-ceramic crowns luted to the abutments. Static load fracture resistance was evaluated with an Instron test device. Modes of abutment failure were evaluated using both light and scanning electron microscopy. Results: A Welch two-sample t test evaluated the OEM control groups vs the Atlantis test groups. Static load to failure (N) for each representative control group vs test group revealed (1) conical design OEM (387 N) vs Atlantis (211 N) (P .011), (2) external-hex OEM (408 N) vs Atlantis (218 N) (P .035), (3) trilobe internal connection OEM (430 N) vs Atlantis (260 N) (P .014), and (4) internal connection OEM (448 N) vs Atlantis (244 N) (P .02). Conclusion: Atlantis CAD/CAM Zr abutments demonstrated static fracture loads lower than those of their OEM counterparts. Failure modes were Zr fractures in the conical and external hex groups. The internal connection groups demonstrated a mixed mode of failure, with screw head fracture 100% of the failures in the internal Zr connection group. The trilobe internal connection group exhibited screw-head fracture in two of five samples and Zr fracture in the remaining three samples. Clinicians should consider avoiding the alternatively engineered Atlantis Zr abutment for restoration of posterior single teeth in cases in which occlusal forces may exceed 350 to 400 N. Schlagwörter: CAD/CAM abutment, implant-abutment fracture, zirconia abutment