Micromechanical properties of Yttria-doped zirconia ceramics manufactured by direct ink writing

The physical-mechanical properties of 3D-printed versus conventional milled zirconia for dental clinical applications: A systematic review with meta-analysis

AIM OF STUDY

This systematic review aimed to compare the physical-mechanical properties of 3D-printed (additively manufactured (AM)) zirconia compared to conventionally milled (subtractive manufactured: SM) zirconia specimens.

MATERIALS AND METHODS

A thorough search of Internet databases was conducted up to September 2023. The search retrieved studies that evaluated AM zirconia specimens and restorations regarding the physical-mechanical properties and mechanical behavior of zirconia. The main topic focused on 3Y-TZP. However, records of 4YSZ and 5YSZ were also included to gather more comprehensive evidence on additively manufactured zirconia ceramic. The quality of studies was assessed using the ROB2 tool, Newcastle Ottawa scale, and the Modified Consort Statement. Of 1736 records, 57 were assessed for eligibility, and 38 records were included in this review, only two clinical trials meet the inclusion criteria and 36 records were laboratory studies. There were no signs of mechanical complications and wear to antagonists with short-term clinical observation. SM thin specimens ≤1.5 mm showed statistically significant higher flexural strength than AM zirconia (p ≤ 0.01), while thicker specimens showed comparable outcomes (p > 0.5). The fracture resistance of dental restorations was dependent on the aging protocol, restoration type, and thickness. The bond strength of veneering ceramic to zirconia core was comparable.

CONCLUSIONS

The results pooled from two short-term clinical trials showed no signs of mechanical or biological complications of additively manufactured 3Y-TZP zirconia crowns. The flexural strength might depend on the specimens' thickness, but it showed promising results to be used in clinical applications, taking into account the printing technique and orientation, material composition (yttria content), solid loading, and sintering parameters. 3D-printed restorations fracture resistance improved when adhered to human teeth. The veneering ceramic bond was comparable to milled zirconia specimens. Long-term RCTs are recommended to confirm the mechanical behavior of 3D-printed restorations.

3D-printed versus conventionally milled zirconia for dental clinical applications: Trueness, precision, accuracy, biological and esthetic aspects

OBJECTIVES

This systematic review aimed to compare the clinical outcome, internal gap, trueness, precision, and biocompatibility of 3D-printed (AM) compared to milled (SM) zirconia restorations.

DATA SOURCE

A thorough search of Internet databases was conducted up to September 2023. The search retrieved studies compared AM zirconia to SM zirconia restorations regarding clinical outcome, fit, trueness, precision, and biocompatibility.

STUDY SELECTION

Of 1736 records, only 59 were screened for eligibility, and 22 records were included in this review. The quality of studies was assessed using the revised Cochrane risk-of-bias tool (ROB2), and the Modified Consort Statement. One clinical study exhibited a low risk of bias. All laboratory studies revealed some bias concerns. Short-term observation showed 100 % survival with no signs of periodontal complications. 3D-printed zirconia crowns showed statistically significant lower ΔE and a better match to adjacent teeth (p ≤ 0.5). The fit, trueness, and precision vary with the printing technique and the tooth surface.

CONCLUSIONS

3D-printed zirconia crowns provide better aesthetic color and contour match to adjacent natural teeth than milled crowns. Both 3D printing and milling result in crowns within the clinically acceptable internal and marginal fit. Except for nanoparticle jetting, the marginal gap of SM crowns was smaller than AM crowns, however, both were clinically acceptable. Laminate veneers might be more accurately produced by 3D printing. 3D-printed axial surface trueness was better than milled axial surfaces. Long-term RCTs are recommended to confirm the clinical applicability of 3D-printed restorations.

CLINICAL SIGNIFICANCE

Internal fit and gap, precision, and trueness are fundamental requirements for successful dental restorations. Both techniques produce restorations with clinically acceptable marginal and internal fit. Axial surfaces and narrow or constricted areas favored 3D-printed than conventionally milled zirconia.