Zirconia-reinforced Lithium Silicate Research Articles

Evaluation of shear bond strength and shear stress on zirconia reinforced lithium silicate and high translucency zirconia.

This study evaluated the shear stress distribution on the adhesive interface and the bond strength between resin cement and two ceramics. For finite element analysis (FEA), a tridimensional model was made using computer-aided design software. This model consisted of a ceramic slice (10x10x2mm) partially embedded on acrylic resin with a resin cement cylinder (Ø=3.4 mm and h=3mm) cemented on the external surface. Results of maximum principal stress and maximum principal shear were obtained to evaluate the stress generated on the ceramic and the cylinder surfaces. In order to reproduce the in vitro test, similar samples to the computational model were manufactured according to ceramic material (Zirconia reinforced lithium silicate - ZLS and high translucency Zirconia - YZHT), (N=48, n=12). Half of the specimens were submitted to shear bond test after 24h using a universal testing machine (0.5 mm/min, 50kgf) until fracture. The other half was stored (a) (180 days, water, 37ºC) prior to the test. Bond strength was calculated in MPa and submitted to analysis of variance. The results showed that ceramic material influenced bond strength mean values (p=0.002), while aging did not: YZHT (19.80±6.44)a, YZHTa (17.95±7.21)a, ZLS (11.88±5.40)b, ZLSa (11.76±3.32)b. FEA results showed tensile and shear stress on ceramic and cylinder surfaces with more intensity on their periphery. Although the stress distribution was similar for both conditions, YZHT showed higher bond strength values; however, both materials seemed to promote durable bond strength.

Digital evaluation of the fit of zirconia-reinforced lithium silicate crowns with a new three-dimensional approach.

Several methods for the evaluation of fit of computer-aided design/computer-assisted manufacture (CAD/CAM)-fabricated restorations have been described. In the study, digital models were recorded with an intraoral scanning device and were measured using a new three-dimensional (3D) computer technique to evaluate restoration internal fit. The aim of the study was to evaluate the internal adaptation and fit of chairside CAD/CAM-fabricated zirconia-reinforced lithium silicate ceramic crowns fabricated with different post-milling protocols. The null hypothesis was that different post-milling protocols did not influence the fitting accuracy of zirconia-reinforced lithium silicate restorations. A master all-ceramic crown preparation was completed on a maxillary right first molar on a typodont. Twenty zirconia-reinforced lithium silicate ceramic crowns (Celtra Duo, Dentsply Sirona) were designed and milled using a chairside CAD/CAM system (CEREC Omnicam, Dentsply Sirona). The 20 crowns were randomly divided into two groups based on post-milling protocols: no manipulation after milling (Group MI) and oven fired-glazing after milling (Group FG). A 3D computer method was used to evaluate the internal adaptation of the crowns. This was based on a subtractive analysis of a digital scan of the crown preparation and a digital scan of the thickness of the cement space over the crown preparation as recorded by a polyvinylsiloxane (PVS) impression material. The preparation scan and PVS scan were matched in 3D and a 3D difference analysis was performed with a software program (OraCheck, Cyfex). Three areas of internal adaptation and fit were selected for analysis: margin (MA), axial wall (AX), and occlusal surface (OC). Statistical analysis was performed using 80% percentile and one-way ANOVA with post-hoc Scheffé test (P = .05). The closest internal adaptation of the crowns was measured at the axial wall with 102.0 ± 11.7 µm for group MI-AX and 106.3 ± 29.3 µm for group FG-AX. The largest internal adaptation of the crowns was measured for the occlusal surface with 258.9 ± 39.2 µm for group MI-OC and 260.6 ± 55.0 µm for group FG-OC. No statistically significant differences were found for the post-milling protocols (P > .05). The 3D difference pattern was visually analyzed for each area with a color-coded scheme. Post-milling processing did not affect the internal adaptation of zirconia-reinforced lithium silicate crowns fabricated with a chairside CAD/CAM technique. The new 3D computer technique for the evaluation of fit of restorations may be highly promising and has the opportunity to be applied to clinical studies.

Fracture Resistance of Monolithic Glass-Ceramics Versus Bilayered Zirconia-Based Restorations.

To compare the fracture resistance of monolithic reinforced glass-ceramic restorations with bilayer zirconia-based restorations. Fifteen ceramic crowns were fabricated on epoxy dies duplicated from a stainless steel master die. They were divided into 3 equal groups (n = 5) according to the type of ceramic material used: group I, monolithic lithium disilicate (IPS e.max CAD), group V, monolithic zirconia-reinforced lithium silicate (Vita Suprinity), and group B (bilayered zirconia substructure with veneering ceramic). All specimens were cemented on epoxy dies with a self-adhesive resin cement (Rely X Unicem), subjected to a chewing simulator, and then loaded until fracture in a universal testing machine. The results were tabulated and statistically analyzed using one-way ANOVA to compare among the 3 materials. The Bonferroni post hoc test was used for pairwise comparisons when the ANOVA test was significant. Zirconia-reinforced lithium silicate (Vita Suprinity) crowns showed the highest statistically significant (p < 0.05) mean fracture resistance values (1742.9 ± 102.7 N), followed by lithium disilicate (IPS e.max CAD) (1565.2 ± 89.7 N). Bilayered zirconia-based crowns showed the lowest statistically significantly mean fracture resistance values (1267.8 ± 86.1 N). Monolithic reinforced glass-ceramics (lithium disilicate and zirconia-reinforced lithium silicate) have better fracture resistance than bilayered zirconia-based ceramics. The use of monolithic reinforced ceramic restorations (lithium disilicate and zirconia-reinforced lithium silicate) is preferred to bilayered zirconia-based restorations to avoid chipping of the ceramic veneer.

EVALUATION OF ZIRCONIA-REINFORCED LITHIUM SILICATE CERAMIC SURFACE TREATMENT ON THEIR SHEAR BOND STRENGTH TO DENTINE FOLLOWING IMMEDIATE DENTIN SEALING

Objectives: The purpose of this study was to evaluate zirconia-reinforced lithium silicate ceramic surface treatment on their shear bond strength to dentine following immediate dentin sealing.Methods : One hundred sixty extracted molars were initially divided into two main groups each counting eighty molars: based on dentine sealing protocols (without immediate dentin sealing S- and with immediate dentin sealing S+), those groups were further subdivided into four subgroups each counting twenty based on the ceramic surface treatment protocol. Each were further subdivided into two subdivisions to evaluate the bonding durability after thermodynamic aging process each counting ten specimens. All restorations were adhesively bonded using a light curing resin cement. The thermo-mechanical group were subjected to 10,000 thermal cycles between (5-55oC) with a 30-s dwell time, 20 seconds transfer time. specimens were then subjected to maximum vertical load of 10 kg with cyclic frequency of 1.7 Hz for 240,000 cycles, which corresponds to one year of clinical service. Specimens were tested for shear bond strength using Instron testing machine. Data were statistically analyzed using two-way ANOVA and Tukey’s post-hoc tests.Result: A significantly higher shear bond strength of restorations (p ≤ 0.001) was obtained when immediate dentin sealing was followed regardless of the surface treatments of ceramics with a maximum value of 10.50±0.412 MPa. Both ceramic surface treatment and artificial aging had a statistically significant effect on the shear bond strength.Conclusion: Immediate dentin sealing protocol is recommended and HF surface treatment is recommended for ceramic restorations adhesion to achieve better durability.

Fatigue failure load of zirconia-reinforced lithium silicate glass ceramic cemented to a dentin analogue: Effect of etching time and hydrofluoric acid concentration.

This study aimed to evaluate the effect of etching time and hydrofluoric acid (HF) concentration on the fatigue failure load and surface characteristics of zirconia-reinforced lithium silicate glass (ZLS) ceramic cemented to a dentin-like, fiber reinforced epoxy resin. Ceramic (Suprinity, VITA) (1.0mm thick) and epoxy resin (2.5mm thick) discs (10mm diameter) were produced. The bonding surface of the ceramic samples was nonetched (control group), or etched for 30, 60 or 90s by 5% or 10% HF. The epoxy resin discs were etched by 10% HF for 30s followed by the application of an adhesive material (Single Bond Universal, 3M ESPE). Pairs of ceramic/epoxy resin discs were cemented with a dual cure resin cement. The fatigue failure load was determined by the staircase method (500,000 cycles at 20Hz; initial load = 925N; step size = 45N). In 10% HF the etching time was shown to influence the fatigue failure load, which increased as the etching time increased (30s < 60s < 90s), and in 5% HF the fatigue failure load was not shown to be affected by the etching time; the lowest fatigue failure loads were produced in the control group without ceramic etching followed by 10% HF acid etching for 30s. Topography analysis showed variations based on the etching protocols. All fractures (radial cracks) were shown to originate from defects at the ceramic surface on the cementing interface. For fatigue loading improvements of ZLS ceramic, 10% HF acid etching for 90s and silanization of the ceramic surface is recommended.

FLEXURAL STRENGTH AND ADHESION OF ZIRCONIA-REINFORCED LITHIUM SILICATE GLASS CERAMIC TO RESIN CEMENT AFTER THERMO-MECHANICAL LOAD CYCLING

Purpose: The aims of this study were to evaluate the flexural strength and adhesion of zirconia-reinforced lithium silicate glass ceramic with those of lithium disilicate after applying a combined thermo-mechanical load cycling. Materials and Methods: Zirconia-reinforced lithium silicate (vita suprinity; SV) and lithium disilicate glass ceramics (IPS e.max CAD; EM) were the materials used in this study. Specimens with the required dimensions for microtensile bond strength and flexural strength test were prepared and finished. The specimens were divided into two groups: control group that was stored in distilled water at 370C for 24 h (without thermo-mechanical load cycling) and test group (with thermo-mechanical load cycling). A total of 3,500 thermal cycles and 250,000 mechanical loading cycles were performed. Microtensile bond strength and flexural strength of each material were evaluated before and after thermo-mechanical load cycling. Moreover, additional micromorphological analysis such as those involving scanning electron microscopy and surface roughness of the etched ceramic bonded surfaces were performed for qualitative analysis. Data were analyzed using independent t-tests between the two glass ceramic groups, and paired t-test was used to detect significance within each group with and without thermo-mechanical load cycling.Results: The effect of thermo-mechanical load cycling on microtensile bond strength was statistically significant for both types of glass ceramics (EM and SV) (P<.001) and the most frequent failure type was mode I (adhesive failure between cement and ceramic type) with pronounced effect on EM (66.67%) than on SV (40%). Regarding thermo-mechanical load cycling effect on flexural strength, there was statically significant difference (P<.001) only for EM.Conclusions: SV glass ceramic showed higher bonding values than EM glass ceramic only after thermo-mechanical load cycling. However, it provides higher flexural strength values either before or after thermo-mechanical load cycling than EM glass ceramic.

Fracture strength of lithium disilicate crowns compared to polymer-infiltrated ceramic-network and zirconia reinforced lithium silicate crowns

ObjectivesThe aim of this study was to evaluate the fracture strength of crowns made from current CAD/CAM materials. In addition the influence of crown thickness and chewing simulation on the fracture strength was evaluated. MethodsCrowns were fabricated from lithium disilicate, zirconia reinforced lithium silicate (ZLS-ceramic) and a polymer-infiltrated ceramic-network (PICN) with an occlusal thickness of 1.0mm or 1.5mm, respectively (n=16). Crowns were cemented on composite dies. Subgroups of eight specimens were loaded with 5kg in a chewing simulator for 1,200,000 cycles with thermal cycling. Finally, all specimens were loaded until fracture in a universal testing machine. Three-way ANOVA was used to detect statistical interaction. Differences regarding the materials were tested with two-way ANOVA, following one-way ANOVA and a post-hoc Tukey's-Test. ResultsAll crowns survived the chewing simulation. The material had a significant influence on the fracture resistance (p≤0.05). Lithium disilicate achieved the highest values of fracture strength in almost all groups followed by ZLS-ceramic. PICN achieved the lowest values of fracture strength. Chewing simulation increased the fracture strength of thick lithium disilicate crown significantly. Greater occlusal thickness of all crown materials resulted in higher crown fracture strength before chewing simulation. After chewing simulation occlusal thickness of lithium disilicate and PICN crowns had no significant influence on the fracture strength. ConclusionsAll crowns revealed fracture strength above the clinically expected loading forces. Therefore the durability of the tested CAD/CAM materials seems promising also in an occlusal thickness of 1.0mm.

Fracture resistance of ceramic and polymer-based occlusal veneer restorations

ObjectivesThe purpose of this in vitro study was to evaluate the influence of thermodynamic loading on the durability and fracture resistance behavior of occlusal veneers fabricated from different biomedical dental CAD/CAM materials. MethodsThe occlusal surfaces of 64 extracted premolars were prepared in the enamel layer and restored with occlusal veneers with a fissure/cusp thickness of 0.5/0.8mm made from four different dental CAD/CAM materials: group LD lithium disilicate (e.max CAD), group LS zirconia-reinforced lithium silicate (Vita Suprinity), group PI polymer-infiltrated ceramic (Vita Enamic), and group PM polymethylmethacrylate PMMA (Telio CAD). The prepared teeth were etched with phosphoric acid. The occlusal veneers were then bonded using an adhesive luting system (Multilink Primer A/B and Multilink Automix luting resin). Half of the specimens were subjected to thermodynamic loading in a chewing simulator (1.2 million cycles at 98N). All specimens were quasi-statically loaded until fracture. The statistical analysis was made using the t-test and one-way ANOVA followed by the Tukey HSD test (α = 0.05). ResultsAll aged specimens survived the thermodynamic loading. Thermodynamic loading significantly raised the fracture resistance in groups LS, PI, and PM (P < 0.03). Occlusal veneers made from lithium disilicate and zirconia-reinforced lithium silicate recorded higher fracture resistance than those made from polymer-infiltrated ceramic and PMMA resin. ConclusionsAll tested dental CAD/CAM biomaterials exhibited a fracture resistance considerably exceeding the average occlusal force in the posterior dentition. Therefore, they might present a viable long-term treatment for restoring the occlusal surfaces of posterior teeth.

In-vitro fatigue and fracture testing of CAD/CAM-materials in implant-supported molar crowns

ObjectiveTo investigate the fatigue and fracture resistance of different CAD/CAM-materials as implant- or tooth-supported molar crowns with respect to the clinical procedure (screwed/bonded restoration). Methods168 crowns were fabricated from different CAD/CAM-materials (n=8/material): ZLS (zirconia-reinforced lithium silicate ceramic; Suprinity, Vita-Zahnfabrik), COB (composite; Brilliant Crios, Coltene), COL (composite; Lava Ultimate, 3M Espe), PMV/PPV (polyether ether ketone (PEEK)+milled composite veneer/composite paste veneer; BioHPP+HIPC veneer/Crealign veneer, Bredent), COH (composite; Block HC, Shofu), and ZIR (zirconia; IPS e.max ZirCAD, Ivoclar-Vivadent) as reference. Three groups were designed simulating the following clinical procedures: (a) chairside procedure ([CHAIR] implant crown bonded to abutment), (b) labside procedure ([LAB] abutment and implant crown bonded in laboratory, screwed chairside), and (c) reference ([TOOTH] crowns bonded on human teeth). Combined thermal cycling and mechanical loading (TCML) were performed simulating a 5-year clinical situation. Fracture force was determined and failures were documented. Data were statistically analyzed (Kolmogorov–Smirnov-test, one-way-ANOVA; post-hoc-Bonferroni, α=0.05). ResultsAll crowns of group LAB-PPV showed cracks after TCML. The other groups survived fatigue testing without failures. Fracture forces varied between 921.3N (PPV) and 4817.8N (ZIR) [CHAIR], 978.0N (COH) and 5081.4N (ZIR) [LAB], 746.7N (PPV) and 3313.5N (ZIR) [TOOTH]. Significantly (p<0.05) different fracture values were found between materials in all three groups. Only ZLS crowns provided no significant (p>0.05) differences between the individual groups. SignificanceDifferent ceramic and resin-based materials partly performed differently in implant or tooth situations. Individual resin-based materials (PPV, COB, COH) were weakened by inserting a screw channel. Most CAD/CAM-materials may be clinically applied in implant-supported crowns without restrictions. ​

Fracture resistance of glazed, full-contour ZLS incisor crowns

PurposeTo compare the failure behaviour of zirconia-reinforced lithium silicate (Celtra Duo, DeguDent) with that of lithium disilicate (IPS e.max CAD, Ivoclar Vivadent) and feldspar (Mark II, VITA) ceramics. MethodsThree groups of sixteen glazed maxillary incisor crowns were produced. The inner surfaces of the crowns were etched, then luted to metal dies with self-adhesive cement. Single load-to-failure tests were performed before and after thermo-mechanical ageing. To simulate clinical conditions, the specimens were thermocycled (10,000 cycles between 6.5°C and 60°C) and underwent chewing simulation (1,200,000 cycles, Fmax=86N). Statistical analyses were performed by use of non-parametric Kruskal–Wallis and Mann–Whitney U-tests. ResultsBefore ageing, all the monolithic incisor crowns fractured at test forces >285N. Mean fracture loads were highest for zirconia-reinforced lithium silicate (725N, SD 162N), slightly lower for lithium disilicate (701N, SD 276N), and lowest for feldspar (554N, SD 190N). The differences between the results were not statistically significant. After ageing, fracture resistance decreased for all materials except zirconia-reinforced lithium silicate. Mean fracture loads were highest for zirconia-reinforced lithium silicate (766N, SD 98N) and significantly lower for both lithium disilicate (485N, SD 64N) and feldspar (372N, SD 116N). ConclusionMonolithic restorations fabricated from zirconia-reinforced lithium silicate retain high fracture resistance after extensive thermo-mechanical ageing. This preclinical study suggests that cohesive failures of monolithic anterior crowns produced of these ceramics will not be a major problem in dental practice.

Indirect zirconia-reinforced lithium silicate ceramic CAD/CAM restorations: Preliminary clinical results after 12 months.

No clinical data are available for the new computer-aided design/computer-assisted manufacture (CAD/CAM) material zirconia-reinforced lithium silicate (ZLS) ceramic. This study describes preliminary clinical results for indirect ZLS CAD/CAM restorations after 12 months. Indirect restorations were fabricated, using the CEREC method and intraoral scanning (CEREC Omnicam, CEREC MCXL). Sixty-seven restorations were seated adhesively (baseline). Sixty restorations were evaluated after 12 months (follow-up), using modified FDI criteria. Two groups were established, according to ZLS restorations' post-processing procedure prior to adhesive seating: group I (three-step polishing, n = 32) and group II (fire glazing, n = 28). Statistical analysis was performed with Mann-Whitney U test and Wilcoxon test (P < .05). The success rate of indirect ZLS CAD/CAM restorations after 12 months was 96.7%. Two restorations clinically failed as a result of bulk fracture (failure rate 3.3%). No statistically significant differences were found for baseline and follow-up criteria (Wilcoxon test, P > .05). Statistically significant differences were found for criteria surface gloss for group I and group II (Mann-Whitney U test, P < .05). This study demonstrates ZLS CAD/CAM restorations have a high clinical success rate after 12 months. A longer clinical evaluation period is necessary to draw further conclusions.

Effect of professional dental prophylaxis on the surface gloss and roughness of CAD/CAM restorative materials.

BackgroundThis study aimed to evaluate the effect of dental prophylaxis on the surface gloss and roughness of different indirect restorative materials for computer-aided design/computer-aided manufacturing (CAD/CAM): two types of CAD/CAM composite resin blocks (Shofu Block HC and Estelite Block) and two types of CAD/CAM ceramic blocks (IPS Empress CAD and Celtra DUO).Material and MethodsAfter polishing the CAD/CAM blocks and applying prophylaxis pastes, professional dental prophylaxis was performed using four different experimental protocols (n = 5 each): mechanical cleaning with Merssage Regular for 10 s four times (Group 1); four cycles of mechanical cleaning with Merssage Regular for 10 s and Merssage Fine for 10 s (Group 2); four cycles of mechanical cleaning with Merssage Regular for 10 s and Merssage Fine for 30 s (Group 3); and mechanical cleaning with Merssage Fine for 10 s four times (Group 4). A glossmeter was used to measure surface gloss before and after mechanical cleaning, and a contact stylus profilometer was used to measure surface roughness (Ra).ResultsPolishing with prophylactic paste led to a significant reduction in surface gloss and increase in surface roughness among resin composite blocks, whereas the polishing-related change in surface gloss or roughness was smaller in Celtra DUO, a zirconia-reinforced lithium silicate block.ConclusionsChanges in surface gloss and roughness due to polishing with a prophylactic paste containing large particles were not improved by subsequent polishing with a prophylactic paste containing fine particles. Key words:CAD/CAM, professional dental prophylaxis, prophylactic paste, surface gloss, surface roughness.

Load-bearing capacity of various CAD/CAM monolithic molar crowns under recommended occlusal thickness and reduced occlusal thickness conditions.

PURPOSEThe goal of this study was to evaluate the fracture resistances of various monolithic crowns fabricated by computer-aided design and computer-aided manufacturing (CAD/CAM) with different thickness.MATERIALS AND METHODSTest dies were fabricated as mandibular molar forms with occlusal reductions using CAD/CAM. With different occlusal thickness (1.0 or 1.5 mm), a polymer-infiltrated ceramic network (Enamic, EN), and zirconia-reinforced lithium silicate (Suprinity, SU and Celtra-Duo, CD) were used to fabricate molar crowns. Lithium disilicate (e.max CAD, EM) crowns (occlusal: 1.5 mm) were fabricated as control. Seventy crowns (n=10 per group) were bonded to abutments and stored in water for 24 hours. A universal testing machine was used to apply load to crown until fracture. The fractured specimens were examined with a scanning electron microscopy.RESULTSThe type of ceramics and the occlusal thickness showed a significant interaction. With a recommended thickness (1.5 mm), the SU revealed the mean load similar to the EM, higher compared with those of the EN and CD. The fracture loads in a reduced thickness (1.0 mm) were similar among the SU, CD, and EN. The mean fracture load of the SU and CD enhanced significantly when the occlusal thickness increased, whereas that of the EN did not.CONCLUSIONThe fracture loads of monolithic crowns were differently influenced by the changes in occlusal thickness, depending on the type of ceramics. Within the limitations of this study, all the tested crowns withstood the physiological masticatory loads both at the recommended and reduced occlusal thickness.

In vitro performance and fracture resistance of CAD/CAM-fabricated implant supported molar crowns.

The aim of this study is to investigate the performance and fracture resistance of different CAD/CAM ceramic and composite materials as implant- or tooth-supported single crowns with respect to the clinical procedure (screwed/bonded restoration). One hundred twenty crowns were fabricated on implants or human molar teeth simulating (a) chairside procedure ([CHAIR] implant crown bonded to abutment), (b) labside procedure ([LAB] abutment and implant crown bonded in laboratory, screwed chairside), and (c) reference ([TOOTH] crowns luted on human teeth). Four materials were investigated: ZLS (zirconia-reinforced lithium silicate ceramic; Celtra Duo, Degudent: polished (P)/crystallized (C)), RB (resin-based composite; Cerasmart, GC), and RIC (resin-infiltrated ceramic; Enamic, Vita-Zahnfabrik). LiS (lithiumdisilicate; Emax CAD, Ivoclar-Vivadent) served as reference. Combined thermal cycling and mechanical loading (TCML) was performed simulating a 5-year clinical situation. Fracture force was determined. Data were statistically analyzed (Kolmogorov-Smirnov test, one-way ANOVA; post hoc Bonferroni, α = 0.05). One crown of ZLS_C[LAB] (1,200,000cycles) and RB[CHAIR] (890cycles) failed during TCML. Fracture values varied between 977.7N(RB) and 3070.4N(LiS)[CHAIR], 1130.6N(RB) and 2998.1N(LiS)[LAB], and 1802.4N(ZLS) and 2664.3N(LiS)[TOOTH]. Significantly (p < 0.003) different forces were found between the materials in all three groups. ZLS_C, RIC, and RB showed significantly (p < 0.014) different values for the individual groups. Partly ceramic and resin-based materials performed differently on implant or tooth abutments. The insertion of a screw channel reduced the stability for individual crown materials. Insertion of the screw channel should be performed carefully. All restorations were in a range where clinical application seems not restricted, but insertion of a screw channel might reduce stability of individual materials.

Microstructure characterization and SCG of newly engineered dental ceramics

ObjectivesThe aim of this study was to characterize the microstructure of four dental CAD-CAM ceramics and evaluate their susceptibility to stress corrosion. MethodsSEM and EDS were performed for microstructural characterization. For evaluation of the pattern of crystallization of the ceramics and the molecular composition, XRD and FTIR, respectively, were used. Elastic modulus, Poisson's ratio, density and fracture toughness were also measured. The specimens were subjected to biaxial flexure under five stress rates (0.006, 0.06, 0.6, 6 and 60MPa/s) to determine the subcritical crack growth parameters (n and D). Twenty-five specimens were further tested in mineral oil for determination of Weibull parameters. Two hundred forty ceramic discs (12mm diameter and 1.2mm thick) were made from four ceramics: feldspathic ceramic – FEL (Vita Mark II, Vita Zahnfabrik), ceramic-infiltrated polymer – PIC (Vita Enamic, Vita Zahnfabrik), lithium disilicate – LD (IPS e.max CAD, Ivoclar Vivadent) and zirconia-reinforced lithium silicate – LS (Vita Suprinity, Vita Zahnfabrik). ResultsPIC discs presented organic and inorganic phases (n=29.1±7.7) and Weibull modulus (m) of 8.96. The FEL discs showed n=36.6±6.8 and m=8.02. The LD discs showed a structure with needle-like disilicate grains in a glassy matrix and had the lowest value of n (8.4±0.8) and m=6.19. The ZLS discs showed similar rod-like grains, n=11.2±1.4 and m=9.98. SignificanceThe FEL and PIC discs showed the lowest susceptibility to slow crack growth (SCG), whereas the LD and ZLS discs presented the highest. PIC presented the lowest elastic modulus and no crystals in its composition, while ZLS presented tetragonal zirconia. The overall strength and SCG of the new materials did not benefit from the additional phase or microconstituents present in them.

Mechanical properties of zirconia reinforced lithium silicate glass-ceramic

ObjectiveThe aim of this study was to assess the mechanical properties of recently introduced zirconia reinforced lithium silicate glass-ceramic. MethodsTwo types of CAD/CAM glass-ceramics (Vita Suprinity (VS); zirconia reinforced lithium silicate and IPS e.max CAD (IC); lithium disilicate) were used. Fracture toughness, flexural strength, elastic modulus, hardness, brittleness index, and microstructures were evaluated. Data were analyzed using independent t tests. Weibull analysis of flexural strength data was also performed. ResultsVS had significantly higher fracture toughness (2.31±0.17MPam0.5), flexural strength (443.63±38.90MPa), elastic modulus (70.44±1.97GPa), and hardness (6.53±0.49GPa) than IC (P<0.001). On the other hand, VS glass-ceramic revealed significantly a higher brittleness index (2.84±0.26μm−1/2) (lower machinability) than IC glass-ceramic (P<0.05). VS demonstrated a homogeneous fine crystalline structure while, IC revealed a structure with needle-shaped fine-grained crystals embedded in a glassy matrix. The VS glass-ceramic revealed a lower probability of failure and a higher strength than IC glass-ceramic according to Weibull analysis. SignificanceThe VS zirconia reinforced lithium silicate glass-ceramic revealed higher mechanical properties compared with IC lithium disilicate glass-ceramic.

Fracture Strength of Monolithic All-Ceramic Crowns on Titanium Implant Abutments.

The fracture strengths of all-ceramic crowns cemented on titanium implant abutments may vary depending on crown materials and luting agents. The purpose of this study was to examine differences in fracture strength among crowns cemented on implant abutments using crowns made of seven different monolithic ceramic materials and five different luting agents. In total, 525 crowns (75 each of Vita Mark II, feldspathic ceramic [FSC]; Ivoclar Empress CAD, leucite-reinforced glass ceramic [LrGC]; Ivoclar e.max CAD, lithium disilicate [LiDS]; Vita Suprinity, presintered zirconia-reinforced lithium silicate ceramic [PSZirLS]; Vita Enamic, polymer-reinforced fine-structure feldspathic ceramic [PolyFSP], Lava Ultimate; resin nanoceramic [ResNC], Celtra Duo; fully crystallized zirconia-reinforced lithium silicate [FcZirLS]) were milled using a CAD/CAM system. The inner surfaces of the crowns were etched and silanized. Titanium implant abutments were fixed on implant analogs, and airborne-particle abrasion was used on their exterior specific adhesion surfaces (Al2O3, 50 μm). Then, the abutments were degreased and silanized. The crowns were cemented on the implant abutments using five luting agents (Multilink Implant, Variolink II, RelyX Unicem, GC FujiCEM, Panavia 2.0). After thermocycling for 5,000 cycles (5 to 55°C, 30 seconds dwell time), the crowns were subjected to fracture strength testing under static load using a universal testing machine. Statistical analyses were performed using analysis of variance (α = .0002) and the Bonferroni correction. No significant difference among the luting agents was found using the different all-ceramic materials. Ceramic materials LiDS, PSZirLS, PolyFSP, and ResNC showed significantly higher fracture strength values compared with FSC, FcZirLS, and LrGC. The PSZirLS especially showed significantly better results. Within the limitations of this study, fracture strength was not differentially affected by the various luting agents. However, the fracture strength was significantly higher for PSZirLS, PolyFSP, ResNC, and LiDS ceramics than for the FSP, LrGC, and the FcZirLS ceramic with all luting agents tested.

Evaluation of the shear bond strength of two resin cements on different CAD/CAM materials

Objective: This study investigated the bond strength of two resin cements (Panavia F 2.0 and Multilink N) to different CAD/CAM materials: resin nanoceramic (RNC; Lava Ultimate), hybrid ceramic (HC; Vita Enamic), zirconia-reinforced lithium silicate ceramic (ZLDC; Vita Suprinity), and lithium disilicate glass-ceramic (LDG; IPS e.max CAD HT).Material and methods: CAD/CAM blocks of 2-mm thickness were sectioned with a slow-speed diamond-saw sectioning machine. The slabs were then embedded in autopolymerizing acrylic resin (n = 12), and resin cements were applied to the surface of the specimens. All specimens were stored in water for 24 h and subjected to 5000 thermal cycles. Bond strength was measured by means of the shear bond strength test. The data were statistically analyzed by two-way ANOVA and Tukey LSD post hoc tests.Results: The results of the two-way ANOVA test indicated that the bond strength values varied significantly depending on the CAD/CAM restorative materials, resin cements, and interaction of these variables (p < 0.05). The RNC group showed the highest bond strength for Panavia F 2.0 (p < 0.05); there were no significant differences among other CAD/CAM materials for Panavia F 2.0 (p > 0.05). The LDG group showed the highest bond strength for Multilink N, it was followed by the ZLDC group (p < 0.05); there were no significant differences between RNC and HC groups (p > 0.05).Conclusions: Choosing resin cements for restorations should be done carefully because bond strength values vary significantly depending on the resin cement and CAD/CAM restorative material.

The zirconia-reinforced lithium silicate ceramic: lights and shadows of a new material.

This study aims to investigate the mechanical properties, composition and surface preparation for adhesive bonding of the recently introduced zirconia-reinforced lithium silicate (ZLS) glass-ceramic. One single block of ZLS was used to prepare the specimens (n=14). The fracture toughness (Ft) and the Vickers hardness (HV) were measured on specimens partially crystallized (PCs) (n=4) and fully crystallized (FCs) at 840°C for 8 min (n=4). The surface treatment was done using hydrofluoric-acid gel (HF) at different concentrations and times of action on FCs specimens (n=4). SEM-EDX was used to test elemental composition and crystalline phases (n=2). The new ZLS glass-ceramic showed significantly higher values of HV and Ft for FCs, PCs showed a brittle behavior. The surface etching should be made using HF at 4.9% for 20 s.

Chairside Fabrication of an All-Ceramic Partial Crown Using a Zirconia-Reinforced Lithium Silicate Ceramic.

The chairside fabrication of a monolithic partial crown using a zirconia-reinforced lithium silicate (ZLS) ceramic is described. The fully digitized model-free workflow in a dental practice is possible due to the use of a powder-free intraoral scanner and the computer-aided design/computer-assisted manufacturing (CAD/CAM) of the restorations. The innovative ZLS material offers a singular combination of fracture strength (>370 Mpa), optimum polishing characteristics, and excellent optical properties. Therefore, this ceramic is an interesting alternative material for monolithic restorations produced in a digital workflow.