Impact of thermocycling on surface roughness,microhardness and optical properties of three different lithium disilicate ceramics

ObjectivesThis investigation was carried out to examine the influence of thermocycling aging on the surface roughness (R_a, µm), color parameters (L*, a*, b*), lightness change (ΔL*), chroma change (ΔC*_ab), color change (ΔE), and microhardness (VH) of three lithium disilicate ceramics.Materials and methodsForty-five specimens were prepared from three lithium disilicate materials (n = 15)—e.max CAD (EC), e.max Press (EP), and GC Initial LiSi Press (LP) ceramics—with dimensions of 6.0 × 1.2 × 16.0 ± 0.2 mm following the manufacturers’ instructions. All specimens were exposed to 5000 thermal cycles with bath temperatures ranging between 5 °C and 55 °C. Data of surface roughness, color parameters, and microhardness were obtained using an optical profiler, a spectrophotometer, and a Vickers hardness tester, respectively. One-way ANOVA, a post-hoc Tukey’s test, and a paired sample t-test were implemented for statistical analysis (p ≤ 0.05).ResultsFor surface roughness, insignificant differences were reported between the materials either before or after thermocycling (p > 0.05) while each material displayed a significant increase after being subjected to thermocycling (p < 0.05). For color parameters, LP showed significantly lower L* and b* after thermocycling while EC presented a significant reduction in a* in comparison with other materials (p < 0.05). EP showed a significant decrease in ΔL*, ΔC*_ab and ΔE compared with other materials (p < 0.05). Regarding microhardness, LP showed significantly increase value in comparison with other materials (p < 0.05).ConclusionsThermocycling had a major impact on the surface roughness, microhardness and optical characteristics of the tested materials. E.max Press displayed less changes in (ΔL*), (ΔC*_ab) and (ΔE), while GC LiSi Press had better behavior in terms of microhardness.     

Wear evaluation of the human enamel opposing different Y-TZP dental ceramics and other porcelains

PurposeThis study examined the wear resistance of human enamel and feldspathic porcelain after simulated mastication against 3 zirconia ceramics, heat-pressed ceramic and conventional feldspathic porcelain.Materials and methodsHuman teeth and feldspathic porcelain cusp were tested against ceramic discs. 5 brands were tested – 3 monolithic zirconia, Prettau, Lava, and Rainbow, one lithium disilicate, IPS e.max Press, and one feldspathic porcelain, Vita-Omega 900. The surface was polished using a 600 grit and 1200 grit SiC paper. Each group was loaded for 300,000 cycles in a chewing simulator. The wear resistance was analyzed by measuring the volume of substance lost. The wear surfaces were observed by scanning electron microscopy to determine the wear characteristics.ResultsVita-Omega 900 led to the greatest amount of enamel wears followed by IPS e.max Press, Prettau, Lava and Rainbow. There was a significant difference between Vita-Omega 900 and IPS e.max Press (p < 0.05). The wear values for human enamel were significantly greater than those for feldspathic porcelain, regardless of the surface roughness of the ceramic specimens (p < 0.05).ConclusionThe wear behaviour of human enamel and feldspathic porcelain varies according to the type of substrate materials. On the other hand, 3 zirconia ceramics caused less wear in the abrader than the conventional ceramic.Clinical significanceDental professionals should be aware of the wear effect of dental restorations on the opposing teeth or restorations. The amount of enamel wear was highest in feldspathic porcelains whereas zirconia ceramics caused less wear on the opposing teeth.     

The effect of core material, veneering porcelain, and fabrication technique on the biaxial flexural strength and weibull analysis of selected dental ceramics

Purpose: The objective of this study was to compare the effect of veneering porcelain (monolithic or bilayer specimens) and core fabrication technique (heat‐pressed or CAD/CAM) on the biaxial flexural strength and Weibull modulus of leucite‐reinforced and lithium‐disilicate glass ceramics. In addition, the effect of veneering technique (heat‐pressed or powder/liquid layering) for zirconia ceramics on the biaxial flexural strength and Weibull modulus was studied. Materials and Methods: Five ceramic core materials (IPS Empress Esthetic, IPS Empress CAD, IPS e.max Press, IPS e.max CAD, IPS e.max ZirCAD) and three corresponding veneering porcelains (IPS Empress Esthetic Veneer, IPS e.max Ceram, IPS e.max ZirPress) were selected for this study. Each core material group contained three subgroups based on the core material thickness and the presence of corresponding veneering porcelain as follows: 1.5 mm core material only (subgroup 1.5C), 0.8 mm core material only (subgroup 0.8C), and 1.5 mm core/veneer group: 0.8 mm core with 0.7 mm corresponding veneering porcelain with a powder/liquid layering technique (subgroup 0.8C‐0.7VL). The ZirCAD group had one additional 1.5 mm core/veneer subgroup with 0.7 mm heat‐pressed veneering porcelain (subgroup 0.8C‐0.7VP). The biaxial flexural strengths were compared for each subgroup (n = 10) according to ISO standard 6872:2008 with ANOVA and Tukey's post hoc multiple comparison test (p≤ 0.05). The reliability of strength was analyzed with the Weibull distribution. Results: For all core materials, the 1.5 mm core/veneer subgroups (0.8C‐0.7VL, 0.8C‐0.7VP) had significantly lower mean biaxial flexural strengths (p < 0.0001) than the other two subgroups (subgroups 1.5C and 0.8C). For the ZirCAD group, the 0.8C‐0.7VL subgroup had significantly lower flexural strength (p= 0.004) than subgroup 0.8C‐0.7VP. Nonetheless, both veneered ZirCAD groups showed greater flexural strength than the monolithic Empress and e.max groups, regardless of core thickness and fabrication techniques. Comparing fabrication techniques, Empress Esthetic/CAD, e.max Press/CAD had similar biaxial flexural strength (p= 0.28 for Empress pair; p= 0.87 for e.max pair); however, e.max CAD/Press groups had significantly higher flexural strength (p < 0.0001) than Empress Esthetic/CAD groups. Monolithic core specimens presented with higher Weibull modulus with all selected core materials. For the ZirCAD group, although the bilayer 0.8C‐0.7VL subgroup exhibited significantly lower flexural strength, it had highest Weibull modulus than the 0.8C‐0.7VP subgroup. Conclusions: The present study suggests that veneering porcelain onto a ceramic core material diminishes the flexural strength and the reliability of the bilayer specimens. Leucite‐reinforced glass‐ceramic cores have lower flexural strength than lithium‐disilicate ones, while fabrication techniques (heat‐pressed or CAD/CAM) and specimen thicknesses do not affect the flexural strength of all glass ceramics. Compared with the heat‐pressed veneering technique, the powder/liquid veneering technique exhibited lower flexural strength but increased reliability with a higher Weibull modulus for zirconia bilayer specimens. Zirconia‐veneered ceramics exhibited greater flexural strength than monolithic leucite‐reinforced and lithium‐disilicate ceramics regardless of zirconia veneering techniques (heat‐pressed or powder/liquid technique).     

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.

Microstructure,topography, surface roughness,fractal dimension,internal and marginal adaptation of pressed and milled lithium-disilicate monolithic restorations

PurposeTo characterize the effect of two processing techniques (pressing and CAD/CAM — Computer Aided Design/Computer Aided Machining) of lithium-disilicate (LD) based crowns on the microstructure, topography, roughness, fractal dimension, internal and marginal adaptation.MethodsOne-hundred identical preparations for monolithic crowns were made with dentin analogue material (G10 epoxy resin). One of the preparations was scanned and a monolithic crown in lithium-disilicate was planned in the CAD system. Fifty crowns were milled in a wax pattern and subjected to pressing (IPS e.max Press), while 50 crowns were machined at CAD/CAM (IPS e.max CAD) and posteriorly crystallized. Internal and marginal adaptation were assessed via replica technique at four manufacturing moments (Milled wax pattern; LD^PRESS; Milled LD^CAD; Crystallized LD^CAD) and considering 5 regions (margin, cervico-axial angle, axial wall, axial-occlusal angle and occlusal wall). Complementary analysis considering microstructure and topography, roughness and fractal dimension were performed in Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).ResultsThe processing technique resulted in different ceramic microstructure, topography, roughness and fractal dimension, whereas CAD/CAM lead to smoother, more homogeneous but more complex topography features (higher fractal dimension) in comparison to the pressing technique (P < 0.05). Regarding marginal and internal fit, LD^PRESS crowns showed to be more adapted at the margin, while LD^CAD were more adapted at the occluso-axial angle; other regions were not statistically different (α = 0.05).ConclusionsCAD/CAM and the pressing techniques for manufacturing LD crowns lead to completely different ceramic surface characteristics and affect crown adaptation at the margin and at occluso-axial angle.     

Three-dimensional trueness analysis of ceramic crowns fabricated using a chairside computer-aided design/manufacturing system: An in vitro study

PurposeThis study analyzed the trueness of polymer-infiltrated ceramic and glass ceramic crowns manufactured using the chairside computer-aided design/manufacturing (CAD/CAM) system.MethodsThe master model designs crowns using a CAD program after acquiring a digital impression with an intraoral scanner. Vita Enamic (VE), Vita Suprinity (VS), and IPS e.max CAD (IPS) were used to manufacture 10 crowns each (total: 30 crowns), using the chairside CAD/CAM system (inLab MC XL). Trueness was evaluated by superimposing the CAD data on the scan data using a three-dimensional program. The Kruskal–Wallis H test, a nonparametric test, and the Mann–Whitney U test were performed by applying the significance level (0.05/3 = 0.016), which was adjusted by post-analysis Bonferroni testing.ResultsThere was a significant difference in the trueness between the samples (p < 0.05). However, there was no statistically significant difference in the outer surface trueness between the samples (p > 0.05).ConclusionsThese findings show that the milling accuracy of VE is better than that of VS and IPS.     

Transmitted irradiance through ceramics: effect on the mechanical properties of a luting resin cement

Objectives

The study aims to characterise the curing behaviour of a light-curing luting composite (Variolink® Aesthetic LC, Ivoclar Vivadent) polymerised at different exposure times (10 s, 20 s) through different ceramics (IPS Empress CAD and IPS e.max CAD, Ivoclar Vivadent) and ceramic thicknesses (no ceramic, 0.5, 1, 1.5 and 2 mm).

Material and method

Curing units’ (Bluephase Style, Ivoclar Vivadent) variation in irradiance delivered up to 10-mm exposure distance as well as the incident and transmitted irradiance and radiant exposure up to 6-mm ceramic thickness were assessed on a laboratory-grade spectrometer. A total of 216 (18 groups, n = 12) thin and flat luting composite specimens of 500-μm thickness were prepared and stored after curing in a saturated vapour atmosphere for 24 h at 37 °C. Micro-mechanical properties (Vickers hardness, HV and indentation modulus, Y_HU) were determined by means of an automatic micro-hardness indenter.

Results

Within the study design, the radiant exposure received by the luting composite varied from 2.56 to 24.75 J/cm², showing a high impact on the measured properties. Comparing the effect of the parameters exposure time, ceramic thickness and type, the highest influence on the micro-mechanical parameters was identified for exposure time, while this influence was stronger on HV (p < 0.001, η _P ² = 0.452) than on Y_HU (p < 0.001, η _P ² = 0.178). The influence of ceramic type was significant but low (η _P ² = 0.161 on HV and 0.113 on Y_HU), while the influence of ceramic thickness was the lowest (η _P ² = 0.04 and 0.05, respectively).

Conclusions

Slightly higher irradiance values were transmitted through Empress CAD up to a ceramic thickness of 3 mm (p < 0.001), while being comparable with e.max for thicker slices. Differences in translucency between ceramics were reflected in the micro-mechanical properties of the luting composite.

Clinical relevance

The radiant exposure reaching the luting composite is determined by the incident irradiance, exposure time, ceramic type and ceramic thickness. At the analysed incident irradiance, exposure time was the most consistent parameter affecting the micro-mechanical properties of the luting composite, and this effect was strongly reflected in the more translucent ceramic Empress CAD. Within the curing conditions, an exposure time of 20 s is recommended.

     

Flexural strength,fracture toughness,three-body wear,and Martens parameters of pressable lithium-X-silicate ceramics

ObjectivesTo test and compare five pressable lithium-X-silicate-ceramics on their mechanical and wear properties.MethodsSpecimens were pressed and prepared from: i. Amber Press (AP), ii. Celtra Press (CP), iii. Initial LiSi Press (IL), iv. Livento Press (LP), and v. IPS e.max Press (IE). Four-point flexural strength (FS), SEVNB fracture toughness (K_IC), three-body wear (3BW), Martens hardness (HM) and indentation modulus (E_IT) were measured. For CP, FS and HM were measured with and without additional Power Firing. Each subgroup contained 15 specimens. Data were analyzed using Kolmogorov–Smirnov, one-way ANOVA followed by Scheffé test, Kruskal–Wallis-H-, Mann–Whitney-U-, and Spearman–Rho-test (p < 0.05). The Weibull modulus was calculated using the maximum likelihood estimation method.ResultsAP and CP presented higher FS than IL. LP presented the highest Weibull modulus. CP showed lower K_IC values than AP, and AP was not significant compared to LP and IE. The most 3BW material loss was observed for CP. CP revealed higher HM values than the remaining ceramics. IL presented lower E_IT compared to AP and CP. The following correlations were observed between the test parameters: 3BW with FS (r = 0.279, p = 0.015), with HM (r = −0.378, p = 0.001), and with E_IT (r = −0.344, p = 0.004); E_IT with FS (r = 0.203, p = 0.028); and HM with FT (r = −0.223, p = 0.027) and E_IT (r = 0.884, p < 0.001). No correlations were observed between FS and K_IC (r = 0.046; p = 0.346).SignificanceAP followed by LP showed the highest and IL followed by CP the lowest properties tested. Power Firing of CP improved the flexural strength. Ceramics with high flexural strength and Martens parameters showed lower wear. Materials with high Martens hardness presented lower fracture toughness values and ones with high indentation modulus showed high flexural strength.     

Load-bearing capacity of CAD/CAM 3D-printed zirconia,CAD/CAM milled zirconia,and heat-pressed lithium disilicate ultra-thin occlusal veneers on molars

ObjectivesThe load-bearing capacity of ultra-thin occlusal veneers made of 3D-printed zirconia were compared to the ones obtained by fabricating these reconstructions by CAD/CAM milling zirconia or heat-pressing lithium-disilicate.MethodsOn 60 extracted human molars, the occlusal enamel was removed and extended into dentin. Occlusal veneers of 0.5 mm thickness were digitally designed. The specimens were divided into 3 groups (n = 20 each) differing in the restorative material and the fabrication technique of the occlusal veneer. (1) 3DP: 3D-printed zirconia (Lithoz); (2): CAM: milled zirconia (Ceramill Zolid FX); (3) HPR: heat-pressed lithium disilicate (IPS e.max Press). After conditioning procedures, the restorations were adhesively bonded onto the conditioned tooth. Thereafter, all specimens were aged in a chewing simulator by exposure to cyclic fatigue and temperature variations. Subsequently the specimens were statically loaded and the load which was necessary to decrease the maximum load by 20% and initiate a crack (F_initial) and the load which was needed to fracture the specimen (F_max) were measured. Differences between the groups were compared applying the Kruskal-Wallis (KW) test and the Wilcoxon-Mann-Whitney-Test (WMW: p < 0.05).ResultsThe median F_initial values for the groups 3DP, CAM and HPR were 1’650 N, 1’250 N and 500 N. The differences between all three groups were statistically significant (KW: p < 0.0001). The median F_max values amounted to 2’026 N for the group 3DP, 1’500 N for the group CAM and 1’555 N for the group HPR. Significant differences were found between 3DP and CAM (WMW: p = 0.0238).SignificanceRegarding their load-bearing capacity, 3D-printed or milled zirconia as well as heat-pressed lithium disilicate can be recommended as restorative material for ultra-thin occlusal veneers to prosthetically compensate for occlusal tooth wear. Despite statistically significant differences between the restoration materials, all load-bearing capacities exceeded the clinically expected normal bite forces.     

Biaxial flexural strength and translucent characteristics of dental lithium disilicate glass ceramics with different translucencies

PurposeThe aim of this study was to evaluate the biaxial flexural strength and translucent characteristics of dental lithium disilicate glass ceramics with different translucencies.MethodsTwo heat pressed lithium disilicate glass ceramics (IPS e.max Press and an experimental ceramic) and one computer aided design/ computer aided manufacture (CAD/CAM) lithium disilicate glass ceramic (IPS e.max CAD) with different translucencies were evaluated. Disk-shaped specimens of each group were subjected to a biaxial flexural strength (BFS) test. Translucent parameters (TP) were also tested at 0.5 mm and 1.0 mm thickness, respectively. X-ray diffraction (XRD) and SEM were used for crystalline and microstructural analysis.ResultsBFS values of two heat pressed lithium disilicate glass ceramics were significantly higher than the CAD/CAM counterpart. No difference in BFS between two heat pressed glass ceramic was found. There were significant differences in BFS and TP values among the tested subgroups with different translucencies for IPS e.max Press and IPS e.max CAD. No difference in crystalline composition was found among the tested glass ceramics, but microstructure with shorter and wider crystal was revealed for IPS e.max CAD ceramics.ConclusionsLithium disilicate glass ceramics with different translucencies demonstrated different BFS and TP values.     

Effects of CAD/CAM ceramics and thicknesses on translucency and color masking of substrates

ObjectiveTo compare the translucency and masking of zirconia-reinforced lithium silicate with lithium disilicate glass-ceramic and hybrid composite.Materials and methodsOne hundred and twenty disc-shaped specimens were fabricated using Enamic, Celtra Duo, IPS E.max CAD, and Suprinity. Twelve groups were prepared according to material type and thickness (0.5, 1.0, and 1.5 mm). The specimens were tested over five substrates: composite resin-A3.5 shade (A3.5 control group), zirconia-A1 shade (ZR), nickel–chromium alloy (NC), black (B), and white (W). A spectrophotometer operating at wavelengths from 360 to 750 nm and a view-area size of 9.53 mm was used for color measurement.ResultsMean color difference values (ΔΕ) were found to be lowest in Suprinity and highest in IPS E.max. CAD. Color difference values were significantly related to substrate shade. The A3.5 substrate revealed the significantly lowest ΔΕ values of all the substrates (P = 0.05). Regarding the translucency parameters for ceramics of different thicknesses, a significant difference was observed among all groups except in Suprinity.ConclusionsDifferent ceramic types with different thicknesses and substrate strongly affect translucency and masking.Clinical significanceFabricating durable aesthetic restorations that also meets patients’ expectations is among the most significant challenges in dentistry. With high demand for more natural restorations, ceramics based on computer-aided design (CAD) and computer-aided manufacture (CAM) became popular and exhibited excellent results. However, various factors such as abutment shade, luting cement color, and ceramic type, thickness, and translucency may affect the prosthesis shade. The objective of this study was to evaluate the effects of these factors on the final shades of CAD/CAM-based ceramic restorations.     

Can we use the translucency parameter to predict the CAD/CAM ceramic restoration aesthetic?

ObjectivesTo evaluate the effects of background color, ceramic type and coping thickness on masking ability (ΔE) and translucency parameter (TP) of CAD/CAM lithium disilicate glass-ceramic/monolithic zirconia and, to determine the correlations between coping thickness, TP and ΔE.MethodsA total of 120 ceramic specimens (2 mm, 1 mm and 0.5 mm thickness; n = 10) of four CAD/CAM ceramics: IPS e.max, IPS ZirCAD, Upcera Li CAD and Upcera TT CAD, were studied. Specimens were tested over nine fabricated backgrounds: A1, A2, A3.5, ND2 and ND7 shade resin-based composites, cobalt-chromium alloy (CC), medium precious alloy (MPA), black (B) and white (W). CIELab values (L*, a* and b*), color difference (ΔE) and translucency parameter (TP) were measured and calculated using a digital spectrophotometer (color i7, X-Rite, Pantone®). Data were analyzed using the Shapiro-Wilk test, one-way ANOVA, three-way ANOVA, independent t-tests and Tukey post-hoc tests (p < 0.05).Results2 mm CAD/CAM ceramics showed ideal color matching (ΔE<2.6) over different backgrounds, except for CC, B and W backgrounds. Monolithic zirconia had lower ΔE values than lithium disilicate glass-ceramics. ΔE and TP values significantly reduced with the increased coping thickness (p < 0.05). Regardless of ceramic type and thickness, a strong TP-SD of ΔE correlation was observed.SignificanceCAD/CAM ceramic restoration color was significantly affected by background color, ceramic type and coping thickness. TP is a promising predictor for appropriate ceramic selection to receive an acceptable CAD/CAM ceramic restoration aesthetic.     

Four-point flexural strength and microtensile bond strength of digitally and conventionally veneered zirconia

This study intended to evaluate the effect of digital veneering on four-point flexural strength (FS) and microtensile bond strength (μTBS) of veneered zirconia. Two different zirconia blocks, a lithium disilicate and a feldspathic ceramic block, and two different layering ceramics were used. IPS e.max Zir CAD (ZC) and Vita In-Ceram YZ (YZ) with yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) were used as substructures. IPS e.max CAD (LD), Vita Mark II (VMII), IPS e.max Ceram (EC) and Vita VM9 (VM9) were used for veneering. Resin cement and fusion ceramic were placed between veneer and zirconia substructure for digital veneering. A total of one hundred and fifty specimens in five groups (n = 30) were prepared for FS and tested in universal machine at 1.0 mm/min. One hundred specimens in five groups (n = 20) were obtained for the μTBS and tested at 1.0 mm/min. Statistical analysis was made by one way ANOVA and Tukey HSD. Conventional veneering showed statistically significant FS. ZC veneered with EC had the highest mean FS and the lowest was obtained in groups veneered through resin cement. YZ layered with VM9 had the highest mean μTBS. ZC veneered through fusion ceramic and YZ veneered through resin cement showed significantly lower and similar μTBS.     

Fatigue resistance of ultrathin CAD/CAM ceramic and nanoceramic composite occlusal veneers

ObjectiveThe fracture resistance of different ultrathin occlusal computer-aided design/computer-aided manufacturing (CAD/CAM) veneers was investigated under cyclic mechanical loading to restore combined enamel-dentin defects.MethodsEighty-four molars were reduced occlusally until extensive dentin exposure occurred with a remaining enamel ring. Twenty-four molars were ground flat for examination of highly standardized specimens, of which 8 were treated with uniformly flat 0.3 mm IPS Empress CAD and 0.3 and 0.5 mm IPS e.max CAD restorations. Sixty-four molars were anatomically prepared until dentin exposure and were restored using occlusal veneers with fissure/cusp thicknesses of 0.3/0.5 mm from 3 different dental CAD/CAM materials: IPS Empress CAD, IPS e.max CAD and Lava Ultimate CAD/CAM. Teeth were etched with 37% phosphoric acid, and occlusal veneers were bonded using an adhesive luting system (Syntac Primer, Adhesive, Heliobond and Variolink II). Specimens were placed under cyclic mechanical loading in a chewing simulator (1 million cycles at 50 N) and were examined for cracks after each cyclic loading sequence. The anatomical 0.3/0.5 mm IPS e.max CAD specimens experienced an additional 1 million cycles at 100 N. Kaplan–Meier survival curves and log-rank tests were used for data analysis.ResultsAll highly standardized and 0.3/0.5 mm IPS e.max CAD specimens tolerated cyclic loading. One anatomical Lava Ultimate CAD/CAM and 10 IPS Empress CAD specimens showed cracks.SignificanceUltrathin occlusal veneers of lithium disilicate ceramic and nanoceramic composite showed remarkably high fracture strength under cyclic mechanical loading. These veneers might be a tooth substance preserving option for restoring combined dentin–enamel defects.     

An in-vitro comparison of fracture resistance of three CAD/CAM Ceramic materials for fabricating Veneer

AimsThis research aims to measure and compare the fracture resistance and modes of failure of the following three chemically varied computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic veneering materials: IPS e.max CAD, Vita Enamic, and Shofu HC.Materials and methodsTwenty-seven sound human upper premolars were collected and stored in saline at room temperature until the experiment started and were assigned to three groups at random (n = 9). Putty indices were prepared to ensure a standardized butt joint preparation. An InEos X5 scanner was used to scan all the samples, and the resulting data were transferred to a CAD/CAM milling machine for veneer fabrication based on the materials used. Twenty-seven machined ceramic veneers were milled from three different ceramic materials. The cementation process was conducted for each material according to the manufacturer's instructions. To quantify the fracture resistance, all the samples underwent 2000 water cycles in a thermocycler and were then mounted in a universal testing machine at a 90° angle at the occlusal part of the veneer. The modes of failure were determined under a stereomicroscope and grouped into type I, ceramic fracture; type II, combined ceramic and tooth fracture; and type III, root fracture.ResultsShofu HC had the highest mean (±standard deviation) fracture resistance (480.8 ± 92.8 N), followed by IPS e.max CAD (415.9 ± 147.2 N) and Vita Enamic (372.3 ± 123.9 N). However, the results of a one-way analysis of variance did not reveal statistically significant differences among the experimental groups (p = 0.194). The different groups exhibited different modes of failure, with ceramic fracture being the most common type of failure.ConclusionAll the materials tested in this study exhibited strong fracture resistance values, thereby indicating their use as veneering materials for the upper premolars.     

Properties of hot-pressed lithium silicate glass-ceramics

Objectives

New lithium silicate/disilicate hot-pressed glass-ceramics are introduced into the dental market. It is known that the mechanical properties of this material depend on the microstructure, chemical composition, glass matrix, morphology of crystals, volume ratio crystal/glass, additive, and treatments. This contribution investigates how these factors affect the properties of the new generation of lithium silicate/disilicate hot-pressed glass-ceramics.

Failure loads of heat-pressed versus milled lithium disilicate endocrowns

Objectives

This study aimed to compare the failure load of heat-pressed versus milled lithium disilicate endocrowns.

Materials and methods

Twenty extracted mandibular molars were sectioned 1.5 mm above the CEJ. Root canal treatment and endocrown preparation were done for all teeth. Samples were then divided into two groups: heat-pressed glass ceramic endocrowns (HP group) (n?=?10) and milled endocrowns (CAD group) (n?=?10). Cementation was done using self-adhesive resin cement, and a compressive load was applied on the occlusal surface of the specimens until failure occurred.

Results

The mean failure loads were significantly higher in the HP group (2546.5?±?339 N) compared to the CAD group (1759.9?±?114.2) (p?<?0.05), and majority of failures were due to fracture of the restoration.

Conclusions

Failure loads of heat-pressed lithium disilicate endocrown are superior to milled endocrown.

Clinical relevance

Molars restored with lithium disilicate endocrowns have higher failure loads than the maximum human bite force regardless of the fabrication method. Although heat-pressed endocrowns have superior failure loads to milled ones, both are indicated for restoring endodontically treated molar teeth.

     

Assessing Enamel Wear of Monolithic Ceramics With Micro-CT and Intra-oral Scanner

ObjectiveThis in vitro study aimed to investigate enamel wear against 3 monolithic ceramics using 2 methods of measurement.MethodsThree groups of standard flat monolithic ceramic specimens including zirconia-reinforced lithium silicate glass (Vita Suprinity, VITA Zahnfabrik), yttria-stabilised tetragonal zirconia (Lava Esthetic Zirconia), and lithium disilicate glass (IPS e.max Press, Ivoclar Vivadent) were prepared, with human enamel used as the control group. Each specimen was subjected to the 2-body wear test at 49 N for 250,000 cycles. Enamel antagonists were evaluated with micro-computed tomography (CT) and intra-oral scanner, allowing 3-dimensional images of vertical wear and volumetric loss of enamel antagonists to be calculated. One-way analysis of variance followed by Student–Newman–Keuls post hoc tests were used to examine the differences in vertical wear/volumetric loss amongst the groups. Paired t tests and intra-class correlations were used to compare vertical wear/volumetric loss between the micro-CT and intra-oral scanner groups.ResultsNo significant difference in vertical wear was found amongst all groups. More volumetric loss was found in all test groups than in the control group (P < .001), but no significant difference was found amongst the test groups. There was a moderate positive correlation (r = 0.535, P = .033) between the vertical wear and volumetric loss. No significant difference between the 2 methods of measurement was found.ConclusionsMonolithic ceramics induce more enamel wear than natural teeth. Both micro-CT and intra-oral scanners can be used for measuring tooth wear with similar performance.     

Effects of glucocorticoid-induced osteoporosis on bone tissue of rats with experimental periodontitis

ObjectiveTo evaluate the effects of osteoporosis induced by glucocorticoid (GIOP) on bone tissue of rats with experimental periodontitis (EP).Design48 male Wistar rats divided into groups: Naïve, EP, GIOP and GIOP + EP. Rats of GIOP and GIOP + EP groups received 7 mg/kg of dexamethasone intramuscularly once a week for 5 weeks. Following, EP and GIOP + EP groups were subjected to ligature-induced periodontitis. Naïve group experienced no manipulation. After 11 days, the animals were euthanized and left maxillae collected for macroscopic, radiographic, micro-tomographic and microscopic analysis of alveolar bone loss (ABL). Blood samples were collected for determination of bone-specific alkaline phosphatase (BALP) levels and the right femurs were removed for radiographic and biomechanical analysis.ResultsEP caused ABL and reduced BALP levels (p < 0,05), but it did not change the architecture or biomechanics of femur, compared to Naïve. GIOP did not cause ABL, but it significantly decreased alveolar bone mineral density (ABMD), bone percentage and trabecular thickness (Tb.Th) and increased alveolar bone porosity (p < 0.05) and significantly reduced BALP serum levels, as well as radiographic density and Young’s module of femur, compared to Naïve. There was a greater ABL in group GIOP + EP when compared to EP (p < 0.05). GIOP + EP caused a greater decrease on ABMD, Tb.Th, bone percentage and increased bone porosity (p < 0.05) and also presented a significant reduction in BALP levels (p < 0.05), in radiographic density and in Young’s module of femur compared to EP (p < 0.05).ConclusionsGIOP can potentiate the destructive effects of EP on alveolar bone and alter the systemic bone loss, by promoting bone resorption and reducing osteoblast activity.     

Cyclic contact fatigue resistance of ceramics for monolithic and multilayer dental restorations

ObjectiveTo evaluate the cyclic contact fatigue resistance and failure mode of ceramics for monolithic and multilayer restorations.MethodsCeramic structures (10 mm × 1.8 mm) were fabricated as follows (n = 28): (1) CAD-on- trilayer structure composed of Y-TZP (yttria stabilized tetragonal zirconia polycrystal- IPS e.max ZirCAD) infrastructure, fusion glass–ceramic (IPS e.max CAD Crystall/Connect) and lithium disilicate-based glass–ceramic (IPS e.max CAD); (2) ZFC- bilayer structure composed of Y-TZP infrastructure veneered by a fluorapatite glass–ceramic (IPS e.max Ceram); (3) LDC- monolithic lithium-disilicate glass–ceramic (IPS e.max CAD); and (4) YZW- monolithic Y-TZP (Zenostar Zr Translucent). All ceramics structures were bonded to a dentin analog substrate (G10). Specimens were submitted to cyclic contact fatigue test in a pneumatic cycling machine with 80 N load and 2 Hz frequency in distilled water at 37 °C. Test was interrupted after 10⁴, 10⁵, 5 × 10⁵ and 10⁶ cycles and the presence or absence of failure was recorded. Fatigue data were analyzed using Kaplan–Meier (log rank) and Holm–Sidak tests (α = 0.05). The relationship between the type of crack leading to failure and the experimental group was analyzed using chi-square test (α = 0.05).ResultsThere was no statistical difference between CAD-on and YZW groups (p = 0.516), which presented the highest survival rates after cyclic loading, followed by ZFC and LDC groups (p < 0.01). There was a significant relationship between type of crack and experimental group (p < 0.001). LDC specimens showed the greatest frequency of radial cracks, while cone cracks were more prevalent for ZFC and CAD-on specimens.SignificanceMonolithic Y-TZP (YZW) showed similar fatigue resistance to CAD-on multilayer specimens, but different failure mode. Monolithic lithium disilicate glass–ceramic (LDC) and Y-TZP conventionally veneered by glass–ceramic (ZFC) showed lower survival time under fatigue.