Comparison of Contrast Ratio, Translucency Parameter, and Flexural Strength of Traditional and "Augmented Translucency" Zirconia for CEREC CAD/CAM System.

PURPOSE: Tetragonal zirconia polycrystals (TZP) can be used via CAD/CAM technique as metal replacement for fixed partial dentures. However, its intense white color and high opacity may represent an aesthetic limit. New TZPs with a claimed higher degree of translucency were recently marketed. The aim of the study was to investigate contrast ratio (CR), translucency parameter (TP), flexural strength (σ), Weibull characteristic strength (σ0 ), and Weibull modulus (m) of three "traditional" (IPS e.max Zir-CAD, inCoris ZI, VITA In-Ceram YZ) and two "increased translucency" (inCoris TZI, VITA In-Ceram YZ HT) Y-TZPs. METHODS: For flexural strength, ISO 6872:2008 was followed. Bars (N = 40) were cut from pre-sintered blocks. Dense-sintering, finishing, and polishing were performed in order to obtain specimens of 15 × 4 × 1.2 mm. Samples were tested with three-point bending setup in a universal testing machine. For CR and TP, specimens (N = 10) were cut perpendicularly to the long axis from pre-sintered blocks. After the dense-sintering, specimens were finished and polished in order to obtain tiles of 12 × 15 × 1 mm. CR and TP were measured with a spectrophotometer equipped with an integrating sphere. RESULTS: No significant difference was found regarding flexural strength. A significant difference was found both for CR and TP among tested groups. VITA In-Ceram YZ HT and inCoris TZI showed the higher translucency. The difference was not statistically significant when compared with VITA In-Ceram YZ, and statistically significant when compared with IPS e.max Zir-CAD and inCoris ZI. CONCLUSION: The new "augmented translucency" TZPs showed higher translucency and similar flexural strength than "traditional" TZPs. CLINICAL SIGNIFICANCE: Monolithic zirconia use is partially restricted due to the zirconia low translucency. The new "augmented translucency" zirconia showed a modest but perceptible increase in translucency and a similar flexural resistance, thus increasing the clinically suitable thickness range with optimized aesthetic and resistance. (J Esthet RestorDent 28:S32-S39, 2016).

Influence of coloring procedure on flexural resistance of zirconia blocks.

STATEMENT OF PROBLEM: The white color of zirconia limits the possibility of a natural-looking restoration. Industrially precolored blocks and green-stage coloring liquids are used to obtain shaded zirconia. Several authors have reported that pigments may negatively affect the mechanical characteristics of the material. PURPOSE: The purpose of this in vitro study was to investigate the effect of a recently marketed coloring system on the flexural strength (σ), Weibull characteristic strength (σ0), and Weibull modulus (m) of a zirconia for computer-aided design/computer-aided manufacturing (CAD/CAM) systems. MATERIAL AND METHODS: Noncolored white blocks (In-Ceram YZ), industrially precolored blocks (In-Ceram YZ col. LL1p), and green-stage infiltration-shaded blocks in 4 colors (In-Ceram YZ Coloring Liquids) were tested. Industrially precolored specimens (n = 30) were assigned to the PREC group. Noncolored specimens were divided into 5 groups (n = 30). Group CNTR was not treated (control). Groups INF-N, INF-L, INF-M, and INF-I were subject to green-stage infiltration (neutral, light, medium, and intense, respectively). Specimens were tested in a 3-point bending apparatus following ISO 6872:2008 specifications. Data were analyzed by 1-way ANOVA. RESULTS: The calculated flexural strengths (MPa) were CNTR 1232.56 ± 103.91; PREC 1215.16 ± 141.42; INF-N 1280.72 ± 160.10; INF-L 1218.92 ± 78.63; INF-M 1153.71 ± 176.80; and INF-I 1248.46 ± 111.73. No statistically significant differences were found among the tested groups (P = .195). CONCLUSIONS: Unlike what has been reported for other combinations of zirconia and coloring liquids, the coloring technique tested in the present study did not negatively influence the flexural characteristics of the tested zirconia.

Flexural resistance of Cerec CAD/CAM system ceramic blocks. Part 2: Outsourcing materials.

PURPOSE: To test different Cerec CAD/CAM system ceramic blocks, comparing mean flexural strength (sigma), Weibull modulus (m), and Weibull characteristic strength (sigma0) in an ISO standardized set-up. METHODS: Following the recent ISO Standard (ISO 6872:2008), 11 types of ceramic blocks were tested: IPS e.max CAD MO, IPS e.max CAD LT and IPS e.max CAD HT (lithium disilicate glass-ceramic); In-Ceram SPINELL, In-Ceram Alumina and In-Ceram Zirconia (glass-infiltrated materials); inCoris AL and In-Ceram AL (densely sintered alumina); In-Ceram YZ, IPS e.max Zir-CAD and inCoris ZI (densely sintered zirconia). Specimens were cut out from ceramic blocks, finished, crystallized/infiltrated/sintered, polished, and tested in a three-point bending test apparatus. Flexural strength, Weibull characteristic strength, and Weibull modulus were obtained. RESULTS: A statistically significant difference was found (P < 0.001) among lithium disilicate glass-ceramic (sigma = 272.6 +/- 376.8 MPa, m = 6.2 +/- 11.3, sigma0 = 294.0 +/- 394.1 MPa) and densely sintered alumina (sigma = 441.8 +/- 541.6 MPa, m = 11.9 +/- 19.0, sigma0 = 454.2 +/- 565.2 MPa). No statistically significant difference was found (P = 0.254) in glass infiltrated materials (sigma = 376.9 +/- 405.5 MPa, m = 7.5 +/- 11.5, sigma0 = 393.7 +/- 427.0 MPa). No statistically significant difference was found (P = 0.160) in densely sintered zirconia (sigma = 1,060.8 +/- 1,227.8 MPa, m = 5.8 +/- 7.4, sigma0 = 1,002.4 +/- 1,171.0 MPa). Not all the materials tested fulfilled the requirements for the clinical indications recommended by the manufacturer.

Flexural resistance of Cerec CAD/CAM system ceramic blocks. Part 1: Chairside materials.

PURPOSE: This study tested the materials available on the market for Cerec CAD/CAM, comparing the mean flexural strength in an ISO standardized set-up, since the ISO standard for testing such materials was issued later than the marketing of the materials tested. METHODS: Following the recent Standard ISO 6872:2008, eight types of ceramic blocks were tested: Paradigm C, IPS Empress CAD LT, IPS Empress CAD Multi, Cerec Blocs, Cerec Blocs PC, Triluxe, Triluxe Forte, Mark II. Specimens were cut out from ceramic blocks, finished, polished, and tested in a three-point bending test apparatus until failure. Flexural strength, Weibull characteristic strength, and Weibull modulus, were calculated. RESULTS: The results obtained from the materials for flexural strength were IPS Empress CAD (125.10 +/- 13.05), Cerec Blocs (112.68 +/- 7.97), Paradigm C (109.14 +/- 10.10), Cerec Blocs PC (105.40 +/- 5.39), Triluxe Forte (105.06 +/- 4.93), Mark II (102.77 +/- 3.60), Triluxe (101.95 +/- 7.28) and IPS Empress CAD Multi (100.86 +/- 15.82). All the tested materials had a flexural strength greater than 100 MPa, thereby satisfying the requirements of the ISO standard for the clinical indications of the materials tested. In all tested materials the Weibull characteristic strength was greater than 100 MPa.

Influence of resin composite mechanical properties on adhesive microtensile bond strength to dentin.

PURPOSE: To determine the influence of mechanical properties of resin-based composites on the microtensile bond strength to dentin of all-in-one adhesives. MATERIALS AND METHODS: Microtensile bond strengths were measured with the non-trimming technique for the experimental groups: 1) Bond Force/Estelite Σ (Tokuyama); 2) G-Bond Plus (GC)/Estelite Σ; 3) Bond Force/Gradia Direct Anterior (GC);4) G-Bond Plus/Gradia Direct Anterior; 5) Bond Force/Gradia Direct LoFlo (GC); 6) G-Bond Plus/Gradia Direct LoFlo. The following mechanical properties of the resin-based composites were assessed: tensile strength, flexural strength, tensile elastic modulus, shear elastic modulus, Poisson's ratio, Vicker's hardness, contraction stress. Three-dimensional models of microtensile beams were created for finite element analysis of the first principal stress values and distribution in the adhesive layer during microtensile testing. Statistical tests were applied to microtensile bond strength values (two-way ANOVA) and to data from mechanical tests (one-way ANOVA). In all the analyses, the level of significance was set at p < 0.05. RESULTS: While the adhesive did not significantly influence microtensile bond strength, the composite was a significant factor. Regardless of the adhesive, Estelite Σ yielded significantly higher bond strengths than Gradia Direct Anterior and Gradia Direct LoFlo, that were comparable. Adhesive-composite interactions were not statistically significant. Estelite Σ had the highest Vicker's hardness, the highest tensile and shear elastic moduli, the lowest and closest to dentin Poisson's ratio. A more favorable stress distribution in the adhesive layer occurred in the Estelite Σ model. CONCLUSIONS: When comparing the bonding potential of several adhesives with the microtensile technique, the same resin composite should be used in all the experimental groups for building up the coronal portion.

Evaluation of the fracture resistance of reattached incisal fragments using different materials and techniques.

OBJECTIVES: When coronal fracture occurs in anterior teeth, fragment reattachment can be a valid alternative to a direct restoration. The aim of this study was to evaluate the influence of the material and the technique used to reattach the fragment. MATERIALS AND METHODS: Eighty sound maxillary and mandibular incisors were selected and randomly divided into eight groups (n = 10). The incisal third of each tooth was removed using a saw machine. The fragments in groups 1-4 were reattached using resin-based materials: group 1 adhesive, group 2 flow, group 3 composite, group 4 cement; in groups 5-8, the same materials mentioned before were used but a bevel was also performed on both labial and lingual surfaces. Shear bond strength (SBS) was calculated by applying a load incisal to the reattachment line. A two-way Anova was used to evaluate the influence of materials and techniques on the SBS. RESULTS: The technique used was statistically significant (P < 0.001), while the material was not (P = 0.793). CONCLUSIONS: The choice of material seems to have no influence on the SBS, whereas a bevel performed on the labial and lingual surfaces can significantly improve the SBS of the reattached fragment.

Effect of post-cure heating on the flexural strength of two indirect resin composites.

The aim of this study was to evaluate whether a post-cure heat-treatment may improve the flexural strength of two indirect resin-based composites. Tested factors were: material (Gradia Indirect, Gradia Forte), mass (opaqus dentin, dentin, enamel) and curing mode (light, light and heat). A three-point bending test appliance was developed according to ISO 4049/2000. Three-Way ANOVA and 2-Pameter Weibull cumulative distribution function were performed. Factors material and curing mode were significant (p < 0.001), while the mass type was not (p = 0.181). A post-cure heat treatment may be useful for enhancing the flexural strength of both materials.

The influence of storage condition and duration on the resistance to fracture of different fiber post systems.

PURPOSE: To evaluate the effects of storage condition and duration on the resistance to fracture of different fiber post systems (and to morphologically assess the post structure before and after storage. METHODS: Three types of fiber posts (DT Light Post, GC Post, FRC Postect Plus) were divided in different groups (n = 12) according to the storage condition (dry at 37 degrees C; saline water at 37 degrees C; mineral oil at 37 degrees C and storage inside the roots of extracted human teeth immersed in saline water at 37 degrees C) and duration (6, 12 months). A universal testing machine loading at a 90 degrees angle was employed for the three-point bending test. The test was carried out until fracture of the post. A 3-way ANOVA and Tukey's test (alpha = 0.05) were used to compare the effect of the experimental factors on the fracture strength. Two posts of each group were observed before and after the storage using a scanning electron microscope. RESULTS: Storage condition and post type had a significant effect on post fracture strength (P < 0.05). The interaction between these factors was significant (P < 0.05). Water storage significantly decreased the fracture strength, regardless of the post type and the storage duration. Storage inside roots, in oil, and at dry conditions did not significantly affect post fracture strength. SEM micrographs revealed voids between fibers and resin matrix for posts stored in water. Posts stored under the other conditions showed a compact matrix without porosities.

Effect of storage time on the accuracy of casts made from different irreversible hydrocolloids.

AIM: Several new irreversible hydrocolloid formulations have recently become available with claims of an improved dimensional stability by the manufacturers. The aim of this study was to evaluate the accuracy of casts made from alginate impression materials poured immediately and after specific storage periods. METHODS AND MATERIALS: Five alginates were tested: CA 37 (Cavex); Jeltrate (Dentsply Caulk); Jeltrate Plus (Dentsply Latin America); Hydrogum 5 (Zhermack); and Alginoplast (Heraeus Kulzer). A master model was mounted on a special device and used to obtain the impressions. These impressions were stored at 23 degrees C and 100% relative humidity, then poured with gypsum immediately, and again after 24, 72 and 120 hours. The casts were measured and the data were analyzed by one way analysis of variance (ANOVA) and Tukey test at p<0.05. RESULTS: The dimensional stability of the alginate impressions was both material and time dependent (p<0.05). After 24 hours of storage, only Alginoplast and Hydrogum 5 comply with the master model (p>0.05). After 72 and 120 hours, only Hydrogum 5 was dimensionally stable (p>0.05). CONCLUSION: The dimensional stability of the alginate impressions is influenced by the selected material and the storage time. CLINICAL SIGNIFICANCE: Alginate impressions should generally be poured immediately. However, some new types of alginate may have the pouring delayed.

Flexural resistance of heat-pressed and CAD-CAM lithium disilicate with different translucencies.

OBJECTIVE: To compare flexural strength of CAD-CAM and heat-pressed lithium disilicate. METHODS: For Pressed specimens (Group A), acrylate polymer blocks were cut with a saw in bars shape. Sprueing, investing and preheating procedures were carried out following manufacturer's instructions. IPS e.max Press ingots (Ivoclar-Vivadent) were divided into subgroups (n=15) according to translucency: A.1=HT-A3; A.2=MT-A3; A.3=LT-A3; A.4=MO2. Ingots were then pressed following manufacturer's instructions. For CAD-CAM specimens (Group B) blocks of IPS e.max CAD (Ivoclar-Vivadent) were divided into subgroups: B.1=HT-A3; B.2=MT-A3; B.3=LT-A3; B.4=MO2. Specimens (n=15) were obtained by cutting the blocks with a saw. Final crystallization was performed following manufacturer's instructions. Both Press and CAD specimens were polished and finished with silica carbide papers of increasing grit. Final dimensions of the specimens were 4.0±0.2mm, 1.2±0.2mm, and 16.0±0.2mm. Specimens were tested using a three-point bending test. Flexural strength, Weibull modulus, and Weibull characteristic strength were calculated. Flexural strength data were statistically analyzed. RESULTS: The overall means of Press and CAD specimens did not differ significantly. Within the Press group different translucencies were found to have similar flexural strength. Within the CAD group, statistically significant differences emerged among the tested translucencies (p<0.001). Specifically, MT had significantly higher flexural strength than HT and MO. Also, LT exhibited significantly higher flexural strength than MO. SIGNIFICANCE: The choice between IPS e.max Press and IPS e.max CAD formulations can be based on different criteria than flexural resistance. Within each formulation, for IPS e.max Press translucency does not affect the flexural strength while for IPS e.max CAD it is an influential factor.