The Flexural Strength and Flexural Modulus of Stereolithography Additively Manufactured Zirconia with Different Porosities

Abstract

Purpose: Additive manufacturing (AM) technologies are capable of fabricating complex geometries with different porosities. However, the effect of such porosities on mechanical properties of stereolithography (SLA) AM zirconia with different porosities is unclear. The purpose of this in vitro study was to investigate the mechanical properties namely flexural strength, and flexural modulus of AM zirconia with different porosities. Materials and Methods: A bar (25 × 4 × 3 mm) for flexural strength test (ISO standard 6872/2015) was designed by CAD software program and standard tessellation language (STL) file was obtained. The STL file was used to fabricate a total of 80 bars in four groups. Three experimental groups each containing 20 samples were manufactured using an SLA ceramic printer (CeraMaker 900; 3DCeram Co) and zirconia material (3DMix ZrO 2 paste; 3DCeram Co) with different sintering post processing to achieve different porosities including 0%-porosity (AMZ0), 20%-porosity (AMZ20), and 40%-porosity (AMZ40). The same STL file was used for subtractive manufacturing or milling of 20 zirconia bars as control group (CNCZ) with the same dimensions using a commercial zirconia. Three-point bending tests were performed for all groups following ISO standard 6872/2015 specification using a universal testing machine. Outcomes measured included load at fracture, mean flexural strength, and flexural modulus and they were compared across the experimental groups using a one-way ANOVA. Post hoc pair wise comparison between each pair of the groups were performed using Tukey test. Results: There was a significant difference between the four groups, in terms of fracture load, flexural strength and flexural modulus using one-way ANOVA. AM zirconia with 0% porosity (AMZ0) showed the highest value for fracture load (1132.7 ± 220.6 N), flexural strength (755.1 ± 147.1 MPa) and flexural modulus (41,273 ± 2193 MPa) and AM zirconia with 40% porosity (AMZ40) showed the lowest fracture load (72.13 ± 13.42 N), flexural strength (48.09 ± 8.95 MPa) and flexural modulus (7177 ± 506 MPa). Tukey's pairwise comparisons detected a significant difference between all the possible pairs for all variables except flexural modulus between AMZ0 and CNCZ. The Weibull moduli presented the lowest value for AMZ20 (4.4) followed by AMZ40 (6.1), AMZ0 (6.1), and the highest value was for CNCZ (8.1). Conclusion: AM zirconia with 0% porosity showed significantly higher flexural strength and flexural modulus when compared to milled and AM zirconia with 20% and 40% porosities.

Additive Manufacturing of Dental Ceramics: A Systematic Review and Meta‐Analysis

“…However, 3 studies reported higher flexural strength for AM ceramics, which was contrary to the meta‐analysis in this systematic review, with 2 of these studies using zirconia, 60,43 and one using alumina 42 . For the studies on zirconia, this could be attributed to the use of high translucency and low strength SM zirconia as a control in one study 60 . The other study reported far higher flexural strength than what is reported in similar literature.…”

“…A total of 16 in vitro studies were included in the qualitative analysis 35,42‐45,47,58‐67 43,45,58–61,66,67 alumina (3 studies)], 35,42,62 hardness [zirconia (2 studies), 58,64 alumina (2 studies)], 35,62 fracture toughness [zirconia (1 study), 64 alumina (2 studies)], 35,62 morphology [zirconia (2 studies), 58,64 alumina (1 study)], 62 roughness [zirconia, (2 studies)], 58,64 Weibull distribution [zirconia (2 studies), 59,61 alumina (2 studies)], 62,42 density [zirconia (2 studies)], 61,64 sintering shrinkage [zirconia (2 studies)], 61,42 structure [zirconia (4 studies)], 44,61,64,67 fracture resistance [zirconia (2 studies)], 47,65 load bearing capacity [zirconia (1 study)], 63 wettability [zirconia (1 study)], 64 biocompatibility [zirconia (1 study)], 64 elastic modulus [zirconia (1 study)], 44 and chemical composition [zirconia (2 studies)] 61,43 (Table 2).…”

“…Meta‐analysis was performed for the flexural strength parameter with 7 out of the 11 studies that reported on flexural strength 42,43,45,58‐60,67 . Three studies were excluded because they had no control group, 61,62,66 and 1 study used a different testing method (biaxial flexural strength) 35 .…”

“…A total of 28 studies were eventually included for the qualitative and quantitative assessments (Fig 1). 7,21,22,30,35,[41][42][43][44][45][46][47][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] The included studies were classified into 3 domains: accuracy, esthetics and color, and physical and mechanical properties. A summary of the characteristics and data of the included studies is presented in Table 2.…”

“…A total of 16 in vitro studies were included in the qualitative analysis. 35,[42][43][44][45]47,[58][59][60][61][62][63][64][65][66][67] Different parameters were reported; these include flexural strength [zirconia (8 studies), 43,45,[58][59][60][61]66,67 alumina (3 studies)], 35,42,62 hardness [zirconia (2 studies), 58,64 alumina (2 studies)], 35,62 fracture toughness [zirconia (1 study), 64 alumina (2 studies)], 35,62 morphology [zirconia (2 studies), 58,64 alumina (1 study)], 62 roughness [zirconia, (2 studies)], 58,64 Weibull distribution [zirconia (2 studies), 59,61 alumina (2 studies)], 62,42 density [zirconia (2 studies)], 61,64 sintering shrinkage [zirconia (2 studies)], 61,…”