Effect of Different Additive Manufacturing Technologies on the Fracture Load of 3-Unit Monolithic Zirconia Fixed Partial Dentures: In Vitro Mechanical Evaluation and Energy-Dispersive Spectroscopy Analysis

Abstract

Statement of problem. Studies examining the influence of different fabrication techniques on the fracture load (FL) of monolithic zirconia restorations are sparse. Purpose. The purpose of this in vitro study was to compare the FL of monolithic zirconia restorations manufactured with different technologies. Material and methods. A typodont model with a missing left first molar was used and laboratory scanned (inEos X5; Dentsply Sirona). Data were transferred to a computer-aided design software program (InLab 16.1; Dentsply Sirona). The cement space for the 3-unit fixed partial dentures was set at 50 mu m, and the connector area was specified as 9 +/- 0.2 mm(2). The subtractive technique was designated as the control group (GC Initial Zirconia HT; GC Corp), while 3 experimental groups were created by using different additive techniques (Gr(SLA) [3DMix Zirconia 3Y; 3D Ceram], Gr(DLP) [Inni Cera; Aon], and Gr(LCM) [LithaCon 3Y 210; Lithoz]) (n=8). In all groups, 3 mol% yttria-stabilized tetragonal zirconia polycrystalline was used. The FL test was conducted on models fabricated from glass-filled resin-based methacrylate and postpolymerized. After thermal cycling (5000 cycles, 5-55 degrees C), all specimens were loaded with a stainless-steel ball at a crosshead speed of 1 mm/minute until fracture in a precision universal testing device. The maximum loads at fracture were recorded in N. Weibull analysis was used to determine the characteristic strength and reliability. The fracture lines were analyzed by scanning electron microscopy at magnifications of x50 and x500. The elemental compositions were compared with energy dispersive spectroscopy. A 1-way ANOVA and Tukey post hoc test were used for statistical analysis (alpha=.05). Results. Significant differences in FL values were found among the groups (P<.001). Gr(DLP) had the lowest FL (821 +/- 160 N), while the highest FL belonged to the control group, followed by Gr(LCM) (1132 +/- 209 N). Weibull analysis showed Gr(DLP) had the highest reliability. Failure analysis indicated that there were fractures and cracks in the pontic region in all groups. Conclusions. Although the control group performed better, the FL values of monolithic zirconia restorations fabricated by using different additive manufacturing methods exceeded the clinically relevant threshold (790 N), demonstrating their suitability for posterior use.