Two Independent Prospectively Planned Blinded Weibull Statistical Analyses of Flexural Strength Data of Zirconia Materials

Zirconia as a restoration dental material are gaining attention because of their high mechanical properties and good biocompatibility. Therefore, investigation of the flexural strength of zirconia is of great interest. For this purpose, Weibull statistics for description of the material reliability are frequently used. The aim of this work was to present a blinded data set to two independent statisticians for two parallel statistical analyses in order to find an optimal statistical approach for analysis of in-vitro measured flexural strength data of zirconia materials. A prospectively planned independent blinded statistical analysis implementing three quality control actions "blinded data set", "independent statistical analyses" and "parallel manuscript writing" was designed. Statistical analysis paths taken by both biostatisticians differed. They arrived at complementary results. The major difference was caused by two alternative distributional assumptions (Weibull/Normal) and alternative fitting methods (LS/ML). The parallel statistical analysis and manuscript writing approach on a blinded data set greatly supported our choice of statistical methods for analysis of flexural strength results of zirconia materials

Time-dependent degree of conversion, Martens parameters, and flexural strength of different dual-polymerizing resin composite luting materials

OBJECTIVE To investigate the degree of conversion (DC), Martens hardness (HM), elastic indentation modulus (EIT), and biaxial flexural strength (BFS) of six dual-polymerizing resin composite luting materials initially and after 2 and 7 days of aging. MATERIALS AND METHODS Specimens fabricated from Bifix QM (BIF; VOCO), Calibra Ceram (CAL; Dentsply Sirona), DuoCem (DUO; Coltène/Whaledent), G-CEM LinkForce (GCE; GC Europe), PANAVIA V5 (PAN; Kuraray Europe), and Variolink Esthetic DC (VAR; Ivoclar Vivadent) (n = 12 per material) were light-polymerized through 1~mm thick discs (Celtra Duo, Dentsply Sirona). DC, HM, and EIT were recorded directly after fabrication, and after 2 and 7~days of aging. As a final test, BFS was measured. Univariate ANOVAs, Kruskal-Wallis, Mann-Whitney U, Friedman, and Wilcoxon tests, and Weibull modulus were computed (p < 0.05). RESULTS While CAL presented low DC, HM, EIT, and BFS values, DUO and BIF showed high results. Highest Weibull moduli were observed for VAR and DUO. DC and Martens parameters increased between the initial measurement and 2~days of aging, while aging for 7~days provided no further improvement. CONCLUSIONS The choice of dual-polymerizing resin composite luting material plays an important role regarding chemical and mechanical properties, especially with patients sensitive to toxicological issues. DUO may be recommended for bonding fixed dental prostheses, as it demonstrated significantly highest and reliable results regarding DC, HM, and BFS. As DC and HM showed an increase in the first 48~h, it may be assumed that the polymerization reaction is not completed directly after initial polymerization, which is of practical importance to dentists and patients. CLINICAL RELEVANCE The chemical and mechanical properties of dual-polymerizing resin composite luting materials influence the overall stability and long-term performance of the restoration

Effect of final temperature and heating rate on the mechanical and optical properties of a zirconia veneering ceramic.

PURPOSE To evaluate the effect of firing temperature and heating rate on the volumetric shrinkage, translucency, flexural strength, hardness, and fracture toughness of a zirconia veneering ceramic. MATERIAL AND METHODS Zirconia veneering ceramic specimens (N = 45) with varying final temperatures (730 °C, 750 °C, and 770 °C) and heating rates (70 °C/min, 55 °C/min, and 40 °C/min) were fabricated (n = 5). Each specimen's shrinkage, translucency, flexural strength, hardness, and fracture toughness were determined. Two-way analysis of variance, Scheffé test, and Pearson's correlation analysis were used to evaluate data (α = 0.05). RESULTS The shrinkage (44.9 ± 3.1-47.5 ± 1.6 vol%) and flexural strength (74.1 ± 17.4-107.0 ± 27.1 MPa) were not affected by tested parameters (P ≥ 0.288). The interaction between the main factors affected the translucency, hardness, and fracture toughness of the specimens (P ≤ 0.007). Specimens with 770 °C final temperature and 70 °C/min heating rate had the lowest (21.8 ± 3.2 %) translucency (P ≤ 0.039). The hardness ranged between 4.98 ± 0.51 GPa (730 °C; 70 °C/min) and 5.60 ± 0.37 GPa (770 °C; 70 °C/min). Fracture toughness ranged between 0.54 ± 0.04 MPa√m and 0.67 ± 0.08 MPa√m with the highest values for specimens fired at 730 °C with 70 °C/min (P ≤ 0.001). There was a positive correlation between translucency and hardness (r = 0.335, P = 0.012), and a negative correlation between fracture toughness and all parameters other than shrinkage (translucency: r = -0.693/P < 0.001, flexural strength: r = -0.258/P = 0.046, hardness: r = -0.457/P < 0.001). CONCLUSIONS Heating rate and final temperature should be considered while fabricating veneered zirconia restorations with tested ceramic as they affected the translucency, hardness, and fracture toughness

Flexural Strength of Preheated Resin Composites and Bonding Properties to Glass-Ceramic and Dentin

To test the impact of preheating (25, 37, 54, or 68 degrees C) of TetricEvoCeram (TEC), FiltekSupremeXT (FSXT), and Venus (V) on flexural strength (FS), shear bond strength (SBS) and interfacial tension (IFT). FS was tested with TEC and FSXT. For SBS, glass-ceramic and human dentin substrate were fabricated and luted with the preheated resin composite (RC). SBSs of 1500 thermal cycled specimens were measured. For IFT, glass slides covered with the non-polymerized RC were prepared and contact angles were measured. Data were analyzed using 2/1-way ANOVA with Scheffe-test, and t-test (p < 0.05). Preheated TEC (37-68 degrees C) showed higher FS compared to the control-group (25 degrees C) (p < 0.001). FSXT presented higher FS than TEC (p < 0.001). For SBS to dentin higher values for FSXT than TEC were found. The preheating temperature showed no impact on SBS to dentin. SBS to glass-ceramic revealed a positive influence of temperature for TEC 25-68 degrees C (p = 0.015). TEC showed higher values than V and FSXT (p < 0.001). IFT values increased with the preheating temperature. A significant difference could be observed in every RC group between 25 and 68 degrees C (p < 0.001)

The effect of artificial aging on Martens hardness and indentation modulus of different dental CAD/CAM restorative materials

OBJECTIVES To determine the Martens hardness parameters for five different classes of CAD/CAM restorative materials after storage in water and thermo-cycling. MATERIALS AND METHODS Lithium disilicate ceramic IPS e.max CAD (EX), silicate ceramic IPS Empress CAD (EC), a polymer infiltrated interpenetrating network material (hybrid material) VITA Enamic (VE), two compact filled composites Lava Ultimate (LU), experimental material (EM), two low filled resin composites Katana Avencia (KA), Ambarino High-Class (AH) and ultra-low/unfilled acrylic polymers CAD-Temp (CT), Telio CAD (TC), breCAM.HIPC (BC) were tested. Specimens were stored in water at 37 °C for 30, 60, 90, 120 days and afterwards thermo-cycled (30,000×, 5 °C/55 °C). Martens hardness (HM) and indentation modulus (E$_{IT}$) were longitudinally investigated after each storage time. For structural analysis, each material was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). RESULTS The groups of unfilled polymers/ultra-low filled composite (CT, TC, BC) followed by low (KA, AH) and compact filled resin composites (LU, EM) showed the lowest HM and E$_{IT}$ values (p < 0.001). The highest values presented ceramics (EX, EC) followed by hybrid material (VE) (p < 0.001). High influence on the Martens hardness parameters was exerted by the aging duration (HM: η$_{P}$$^{2}$ = 0.108, p < 0.001; E$_{IT}$: η$_{P}$$^{2}$ = 0.074, p < 0.001). Structural analyses of resin composites revealed big differences in shape, size and distribution of filler particles. CONCLUSIONS The tested CAD/CAM materials showed differences in Martens hardness and indentation modulus pursuant to the material class. Ceramics showed highest values, followed by the hybrid material. For resin composites the Martens hardness and indentation modulus increased with the filler content. Artificial aging affected CAD/CAM materials differently. Some materials tested are prone to aging, the Martens hardness and indentation modulus decreased after thermo-cycling

Measuring the polymerization stress of self-adhesive resin composite cements by crack propagation

OBJECTIVES To test the polymerization stress of nine self-adhesive resin composite cements (G-CEM, iCEM, Bifix SE, Maxcem Elite, PANAVIA SA, SoloCem, SmartCem 2, SpeedCEM, RelyX Unicem 2) and one glass ionomer cement (control group; Ketac Cem). MATERIALS AND METHODS The crack propagation of a feldspar ceramic (n = 130) was determined by measuring crack lengths that originated from Vickers indentations, prior to and after the application and polymerization of the self-adhesive resin cements. Results for crack propagation were converted to polymerization stress values, and statistical analysis was performed using one-way ANOVA followed by Scheffé post hoc test. RESULTS SmartCem 2 presented higher stress values than iCEM, SoloCem, and Ketac Cem, while Ketac Cem showed lower values than Bifix SE, Maxcem Elite, SmartCem 2, SpeedCEM, and RelyX Unicem 2. CONCLUSIONS Self-adhesive resin composite cements differ in their polymerization stress, which may affect the durability of the restoration. For restorations made from ceramics with lower flexural strength, such as feldspar ceramics, resin composite cement materials with less polymerization stress should be preferred. CLINICAL RELEVANCE As a high polymerization shrinkage may increase crack propagation, the determination of the polymerization stress of self-adhesive resin composite cements employed for fixing all-ceramic restorations is an important factor

Surface properties of polyetheretherketone after different laboratory and chairside polishing protocols

STATEMENT OF PROBLEM Polyetheretherketone (PEEK) can be used as a framework material for fixed dental prostheses. However, information about laboratory and chairside polishing methods is still scarce. PURPOSE The purpose of this in vitro study was to determine the effects of laboratory and chairside polishing methods on the surface roughness (SR) and surface free energy (SFE) of PEEK, an autopolymerizing poly(methyl methacrylate), and a veneering composite resin. MATERIAL AND METHODS For each of the 3 materials, 80 specimens were prepared (N=240) and divided into 7 polishing groups and 1 control group (n=10). The 7 groups were split into 4 laboratory protocols: polishing paste (Abraso), a second polishing paste (Opal L), silicone polisher (Ceragum), and diamond grinder (Diagen-Turbo grinder). The other 3 groups were chairside protocols: rainbow technique (Super-Snap kit), polishing paste (Prisma gloss), and a polishing system (Enhance finishing). Machine polishing with SiC P4000 served as the control treatment. The protocols' average SRs and SFEs were measured, and their surface topographies were evaluated with scanning electron microscopy (SEM). The logarithmically transformed data were analyzed using covariance analysis, 2-way and 1-way ANOVA, and partial correlation (α=.05). RESULTS The polishing protocol exerted the highest influence on SR and SFE values (P<.001; SR: partial eta squared ηP(2)=.970; SFE: ηP(2)=.450), followed by material group (P<.001, SR: ηP(2)=.319; SFE: ηP(2)=.429). The interaction effect of the binary combinations of the 2 independent parameters (polishing protocol and material group) was also significant (P<.001, SR: ηP(2)=.681; SFE: ηP(2)=.365). CONCLUSIONS Chairside methods presented lower SR values than laboratory methods, and specimens polished using the 2-body mode showed higher SR than did specimens polished using the 3-body mode

Fracture load of 3D printed PEEK inlays compared with milled ones, direct resin composite fillings, and sound teeth

Objective!#!The objective of this in vitro study was to investigate fracture load, fracture types, and impact of chewing simulation of human molars restored with 3D printed indirect polyetheretherketone (PEEK) inlays and compare these with milled indirect PEEK inlays, direct resin composite fillings, and sound teeth.!##!Materials and methods!#!A total of 112 molars with form congruent class I cavities were restored with (n = 16/group) 3D printed indirect PEEK inlays via fused layer manufacturing (FLM): (1) Essentium PEEK (ESS), (2) KetaSpire PEEK MS-NT1 (KET), (3) VESTAKEEP i4 G (VES), (4) VICTREX PEEK 450G (VIC), (5) milled indirect PEEK inlays JUVORA Dental Disc 2 (JUV), and (6) direct resin composite fillings out of Tetric EvoCeram (TET). Sound teeth (7) acted as positive control group. Half of the specimens of each group (n = 8) were treated in a chewing simulator combined with thermal cycling (1.2 million × 50 N; 12,000 × 5 °C/55 °C). Fracture load and fracture types of all molars were determined. Statistical analyses using Kolmogorov-Smirnov test and two-way ANOVA with partial eta squared (η!##!Results!#!ESS and TET demonstrated the lowest fracture load with a minimum of 956 N, whereas sound molars showed the highest values of up to 2981 N. Chewing simulation indicated no impact (p = 0.132). With regard to Weibull modulus, KET presented a lower value after chewing simulation than JUV, whereas TET had the highest value without chewing simulation. All indirect restorations revealed a tooth fracture (75-100%), direct resin composite fillings showed a restoration fracture (87.5%), and 50% of the sound teeth fractured completely or had cusp fractures.!##!Conclusions!#!All 3D printed and milled indirect PEEK inlays as well as the direct resin composite fillings presented a higher fracture load than the expected physiological and maximum chewing forces.!##!Clinical relevance!#!3D printing of inlays out of PEEK via FLM provided promising results in mechanics, but improvements in terms of precision and esthetics will be required to be practicable in vivo to represent an alternative dental material

The Effect of Different Storage Media on Color Stability of Self-Adhesive Composite Resin Cements for up to One Year

The aim of this study was to analyze the long-term color stability of eight self-adhesive composite resin cements (SACRCs) after storage in diverse media for up to one year. 480 discs (diameter: 12 mm/thickness: 1.0 +/- 0.05 mm) were fabricated (n = 60/SACRC): (1) BeautyCem (BEA);(2) Bifix SE (BIF);(3) Clearfil SA Cement Automix (CLE);(4) RelyX Unicem 2 Automix (RXU);(5) SeT (SET);(6) SmartCem 2 (SMC);(7) SoloCem (SOC);and (8) SpeedCEM (SPC). After polishing, specimens were immersed in (a) red wine (RW);(b) curry-solution (CU);(c) cress-solution (CR);and (d) distilled water (DW) at 37 degrees C and measured after 7, 28, 90, 180, and 365 days for color differences (Delta E) and water absorption (WA). Non-aged specimens were used as baselines. After 365 days, all of the discs were polished and their Delta E was measured. Data were analyzed using Kolmogorov-Smirnov, partial-eta-squared/eta(2)(P), 3-/1-way ANOVA with Tukey-HSD post-hoc test (alpha = 0.05). Significant differences occurred between all SACRCs for WA (p <= 0.003), except in RXU and in SET and in Delta E (p <= 0.002), except in SET and SPC. The significantly highest WA presented in SOC;the lowest showed in BEA. Significant Delta E differences and a decrease after polishing between all storage media were found (p < 0.001) with highest values for RW, followed by CU, CR, and DW. The lowest Delta E was measured for CLE, followed by SOC, BIF, RXU, BEA, SPC, SET, and SMC (p < 0.001) and increased significantly during aging. The highest Delta E decrease presented in BEA. SACRCs showed an increase in WA/Delta E within total aging time. Discoloration could not be removed completely by polishing. SACRCs need to be carefully selected for restorations in the esthetical zone with visible restoration margins. Polishing can significantly reduce the marginal discoloration