Evaluation of fracture strength and failure mode of zirconia molar implant abutments manufactured with additive and subtractive manufacturing technologies.

STATEMENT OF PROBLEM: Studies comparing and evaluating the additive and subtractive manufacturing of zirconia implant abutments are limited.

PURPOSE: The aim of this study was to compare the fracture resistance of additively and subtractively manufactured 2-piece zirconia abutments.

MATERIAL AND

METHODS

The specimens were divided into 3 subgroups: control group (prefabricated titanium abutment: PZ), subtractive manufacturing group (SZ), and additive manufacturing group (AZ) according to the abutment manufacturing technique (n=10). Abutments and crowns designed to replicate a mandibular molar tooth morphology were fabricated from 3Y-TZP and 4Y-TZP zirconia disks for each group. In the SZ group, the zirconia abutment was fabricated using subtractive manufacturing, whereas in the AZ group the zirconia abutment was fabricated using additive manufacturing. Except for the PZ group, zirconia abutments were cemented onto titanium base abutments using a hybrid abutment resin cement, and all abutments were subsequently screw-retained to the implants (Ø4.4×12 mm, internal connection, Trias Implants; Servo-Dental GmbH & Co KG) with a torque of 25 Ncm. Prior to crown cementation, the intaglio surfaces of all crowns were airborne-particle abraded using 110-µm Al₂O₃ particles and treated with a primer. The crowns were cemented to the abutments under a constant load in all groups using a dual-polymerizing resin cement. The artificial aging process was conducted within a mastication simulator subjected to 1 200 000 cycles, followed by fracture resistance testing performed using a universal testing machine. Failure modes were examined under a stereomicroscope, and fracture lines were analyzed by scanning electron microscopy (SEM) under ×35 magnification (EVO 40; Carl Zeiss AG). Data were evaluated using the Welch ANOVA with Tamhane T2 post hoc tests (α=.05)

RESULTS

A significant difference was found among the groups in fracture resistance (P=.011). The AZ group showed higher values than the PZ group (P=.041), while no significant differences were observed between AZ and SZ (P=.080) or PZ and SZ (P=.999). SEM analysis showed crack and fracture lines. PZ specimens exhibited plastic deformation, whereas SZ and AZ groups exhibited different failure types.

CONCLUSIONS

Additively manufactured zirconia abutments demonstrated fracture strength comparable with that of subtractively manufactured zirconia abutments and higher than that of prefabricated titanium abutments, with screw loosening being the predominant failure mode.