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    Optical properties, biaxial flexural strength, and reliability of new-generation lithium disilicate glass-ceramics after thermal cycling
    (WILEY, 2023) Türksayar, Almira Ada Diken; Demirel, Münir; Dönmez, Mustafa Borga
    PurposeTo investigate the color stability, translucency, biaxial flexural strength (BFS), and reliability of nano-lithium disilicate and fully crystallized lithium disilicate after thermal cycling and to compare with those of a commonly used lithium disilicate. Materials and methodsThree lithium disilicate glass-ceramics were used to prepare disk-shaped specimens (o:12 mm, thickness: 1.2 mm) from A2 shaded HT blocks (Amber Mill, AM; Initial LiSi Block, IN; IPS e.max CAD, EX). AM and EX specimens were crystallized, and all specimens were polished with a polishing paste (Diamond Polish Mint). A spectrophotometer (CM-26d) was used to measure color coordinates before and after thermal cycling. BFS test was performed after thermal cycling. Color differences (Delta E-00) and relative translucency parameter (RTP) values were calculated. One-way analysis of variance (ANOVA) (Delta E-00 and BFS), two-way ANOVA followed by Tukey's HSD tests (RTP), and chi-square tests (Weibull modulus and characteristic strength) were used for the statistical analyses (alpha = 0.05). ResultsNo significant differences were observed among the Delta E-00 values of tested materials (df = 2, F = 2.933, p = 0.070). RTP values were only affected by material type (p < 0.001) as AM had the highest RTP (p < 0.001), whereas IN and EX had similar values (p >= 0.165). BFS values varied among tested materials (df = 2, F = 21.341, p < 0.001). AM and EX had similar BFS values (p = 0.067) that were higher than that of IN (p <= 0.001). Weibull moduli of the materials were similar (p = 0.305), whereas EX had the highest and IN had the lowest characteristic strength values (p < 0.001) ConclusionsAlthough nano-lithium disilicate had the highest translucency, all materials had imperceptible color and translucency changes after thermal cycling when reported threshold values were considered. Newly introduced lithium disilicate glass-ceramics had adequate flexural strength as compared to the precursor material.
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    Stress behavior of an anterior single implant restored with high-performance polymer abutments under immediate and delayed loading: A 3D FEA study
    (WILEY, 2022) Türksayar, Almira Ada Diken; Dönmez, Mustafa Borga
    Purpose To evaluate the stress generated on peripheral bone, implant, and prosthetic components while using polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) hybrid abutments in two different loading situations with nonlinear 3D finite element analysis. Materials and methods Standard tessellation language (STL) files of original components were used for the in-silico modeling of implant, standard titanium abutment, and hybrid abutments (PEEK and PEKK). The implant was placed in the bone block to imitate immediate loading, in which a friction coefficient of 0.3 was set between the bone and the implant interface, or delayed loading, where the bone-implant interface was assumed to be perfect. In all models, both a horizontal force (25.5 N) and a 30-degree oblique force (178 N) were applied to the long axis of the implant to the palatal surface of the restoration. The stress distribution was evaluated. Results While more stress was observed in the prosthetic structures in the PEEK and PEKK models, the stresses on the implant and bone were similar in all models, regardless of the loading situation. Under immediate loading, PEEK hybrid abutments caused excessive stress accumulation on the titanium base abutment. Conclusions Even though abutment type did not affect the stresses on peripheral bone, PEEK and PEKK abutments generated greater stresses on the implant and the standard titanium abutment accumulated higher stresses. Oblique forces mostly generated greater stress than horizontal forces. Oblique forces on an immediately loaded implant led to stresses higher than the yield strength of a titanium implant when restored with PEEK hybrid abutment.
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    Translucency, color stability, and biaxial flexural strength of advanced lithium disilicate ceramic after coffee thermocycling
    (WILEY, 2022) Demirel, Münir; Türksayar, Almira Ada Diken; Dönmez, Mustafa Borga
    Objective To compare the color stability, translucency, and biaxial flexural strength (BFS) of differently glazed advanced lithium disilicate (ALDS) with those of lithium disilicate (LDS) and zirconia-reinforced lithium silicate (ZLS) after coffee thermocycling. Materials and methods Forty disk-shaped specimens were prepared from three lithium silicate based materials (CEREC Tessera, ALDS; IPS e.max CAD, LDS; Vita Suprinity, ZLS). ALDS specimens were divided into two subgroups according to glazing procedures (reduced glaze duration, ALDS-S and normal glaze duration, ALDS-N), while LDS and ZLS specimens were crystallized and glazed. Color coordinate measurements were performed before and after coffee thermocycling. Color differences (Delta E-00) and relative translucency parameters (RTP) were calculated. Specimens were then subjected to BFS test. Statistical analysis was performed by using 1- (Delta E-00 and BFS) and 2-way (RTP) ANOVA tests (alpha = 0.05). Results Delta E-00 values of tested materials were similar (df = 3, F = 0.150, p = 0.929). Two-way ANOVA showed the significant effect of material type, coffee thermocycling, and the interaction between these parameters on RTP values (p < 0.001). Both before and after thermocycling, LDS had the highest (p <= 0.001) and ZLS had the lowest (p < 0.001) RTP values, while ALDS-N had higher RTP than ALDS-S (p <= 0.001). Among tested materials, only LDS had similar RTP values before and after thermocycling (p = 0.865) as the other materials had lower RTP values after thermocycling (p < 0.001). ALDS-N had higher BFS values than ALDS-S (p = 0.005), while LDS had similar values to ALDS specimens (p >= 0.201). ZLS had the highest BFS (p <= 0.007). Conclusions ALDS had comparable values to those of other materials. However, reduced glazing duration resulted in decreased translucency and BFS of ALDS. Clinical significance ALDS may be an appropriate restorative material for those patients with increased coffee consumption considering its color stability and ability to maintain translucency, particularly when glazed by using a conventional porcelain furnace.