Lithium Disilicate Ceramics Research Articles

The Effect of Dentin Desensitizer and Nd: YAG Laser Pre-Treatment on Bond Strength of Ceramic Restoration Cemented with Two Self Adhesive Cements

Objectives: This in-vitro study evaluated the effects of desensitizing treatments on the shear bond strength (SBS) of ceramic restoration cemented with two different self-adhesive resin cements (SARC). Materials and Methods: Sixty human molars’ occlusal surfaces were ground to expose dentin; and were randomly grouped as (n=10); Group CU: no surface treatment (control) and applied Rely X U200 SARC, Group CP: no surface treatment (control) and applied Panavia SA SARC, Group TU: treated with Teethmate and applied Rely X U200 SARC, Group TP: treated with Teethmate and applied Panavia SA SARC, Group LU: treated with Nd:YAG laser and applied Rely X U200 SARC, Group LP: treated with Nd:YAG laser and applied Panavia SA SARC. Then, lithium-disilicate ceramics (IPS e.max CAD Ivoclar Vivadent: n= 60; 5 mm in diameter; 2 mm in height) were cemented. SBS test was performed and the data were statically analyzed (?=0.05). Failure modes were determined with stereomicroscope. Results: Nd: YAG laser treatment groups showed significantly different SBS values than the control groups (p<0.05). However, there were no significant differences between TMD treatment groups and other groups (p>0.05). Multiple comparisons showed that no statically significant difference found between the SBS values of all groups (p>0.05). Group CP showed the lowest SBS value (14.97 MPa) and Group TU showed the highest SBS value (20.82 MPa) among all experimental groups. The overall failure types for specimens were “mixed” and“ adhesive”. Conclusions: Teethmate desensitizer and Nd:YAG laser pre-treatment increase the SBS of ceramic restoration cemented with two self adhesive cements.

Resin cements formulated with thio-urethanes can strengthen porcelain and increase bond strength to ceramics

ObjectivesThe use of thio-urethane oligomers has been shown to significantly improve the mechanical properties of resin cements (RCs). The aim of this study was to use thio-urethane-modified RC to potentially reinforce the porcelain-RC structure and to improve the bond strength to zirconia and lithium disilicate. MethodsSix oligomers were synthesized by combining thiols - pentaerythritol tetra-3-mercaptopropionate (PETMP, P) or trimethylol-tris-3-mercaptopropionate (TMP, T) – with di-functional isocyanates - 1,6-Hexanediol-diissocyante (HDDI) (aliphatic, AL) or 1,3-bis(1-isocyanato-1-methylethyl)benzene (BDI) (aromatic, AR) or Dicyclohexylmethane 4,4′-Diisocyanate (HMDI) (cyclic, CC). Thio-urethanes (20 wt%) were added to a BisGMA/UDMA/TEGDMA organic matrix. Filler was introduced at 60 wt%. The microshear bond strength (μSBS), Weibull modulus (m), and failure pattern of RCs bonded to zirconia (ZR) and lithium disilicate (LD) ceramics was evaluated. Biaxial flexural test and fractographic analysis of porcelain discs bonded to RCs were also performed. The biaxial flexural strength (σbf) and m were calculated in the tensile surfaces of porcelain and RC structures (Z = 0 and Z = −t2, respectively). ResultsThe μSBS was improved with RCs formulated with oligomers P_AL or T_AL bonded to LD and P_AL, P_AR or T_CC bonded to zirconia in comparison to controls. Mixed failures predominated in all groups. σbf had superior values at Z = 0 with RCs formulated with oligomers P_AL, P_AR, T_AL, or T_CC in comparison to control; σbf increased with all RCs composed by thio-urethanes at Z = −t2. Fractographic analysis revealed all fracture origins at Z = 0. ConclusionThe use of specific thio-urethane oligomers as components of RCs increased both the biaxial flexural strength of the porcelain-RC structure and the μSBS to LD and ZR. Clinical significanceThe current investigation suggests that it is possible to reinforce the porcelain-RC pair and obtain higher bond strength to LD and ZR with RCs formulated with selected types of thio-urethane oligomers.

Self-etching Primers vs Acid Conditioning: Impact on Bond Strength Between Ceramics and Resin Cement.

This study tested whether a self-etching surface agent and the conventional hydrofluoric acid (HF) would provide the same bonding capacity between resin cement and feldspathic (Fd) and lithium disilicate (Ld) ceramics. Ceramic blocks were cut with a low-speed diamond saw with water cooling (Isomet 1000, Buehler, Lake Bluff, IL, USA) into 20 blocks of 5 × 7 × 4 mm, which were ground flat in a polishing machine (EcoMet/AutoMet 250, Buehler) under water cooling. The blocks were randomly divided into eight groups (n=5), according to ceramic type (Ld or Fd), surface conditioning (HF + Monobond Plus or Etch and Prime), and aging by thermocycling (TC or absence-baseline). After 24 hours in 37°C distilled water, blocks were embedded into acrylic resin and 1-mm2 cross-section beams composed of ceramic/cement/composite were obtained. The microtensile test was performed in a universal testing machine (DL-1000, EMIC, São José dos Campos, Brazil; 0.5 mm.min-1, 50 kgf load cell). Bond strength (MPa) was calculated by dividing the load at failure (in N) by the bonded area (mm2). The fractured specimens were examined under stereomicroscopy, and one representative sample of each group was randomly selected before the cementation and was further used for analysis using scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). The self-etching agent showed the highest bond strength for Fd (24.66±4.5) and Ld (24.73±6.9) ceramics and a decrease in surface wettability. SEM and EDS showed the presence of similar components in the tested materials with different topographies for both. Therefore, the self-etching primer was able to deliver even higher bonding than HF+silane to a resin cement.

An in vitro evaluation of fracture load of implant‐supported zirconia‐based prostheses fabricated with different veneer materials

The purpose of this in vitro study was to evaluate fracture loads of implant-supported zirconia-based prostheses fabricated with different veneer materials (resin-based material and lithium disilicate ceramics). Forty-four zirconia-based molar prostheses were fabricated on dental implants and divided into four groups (n=11): zirconia-based prostheses veneered with feldspathic porcelain (ZVF), zirconia-based prostheses bonded with the lithium disilicate glass-ceramic veneer (ZBD), zirconia-based prostheses veneered with indirect composite resin (ZVC), and zirconia-based prostheses bonded with composite materials fabricated from a CAD/CAM resin block (ZBC). The zirconia-based prostheses and abutments were adhesively bonded with a dual-polymerized resin-based luting material. Fracture load was determined using compression load to the prostheses with a universal testing machine. The data were analyzed with one-way analysis of variance (ANOVA) and Tukey's HSD test (α=.05). The mean fracture load was significantly higher in the ZBC group (3.95 kN) than in the ZVC group (3.28 kN). No significant difference in fracture load was found among the ZVF (3.52 kN), ZBD (3.48 kN), and ZVC groups. The adhesively bonded veneering technique enhances fracture resistance of implant-supported zirconia-based prostheses fabricated with a resin-based material. All implant-supported zirconia-based restorations tested should resist physiologic masticatory forces in the oral environment.

Influence of repeated firings on the color parameters of two different all‐ceramic materials

AbstractAll‐ceramics materials have been widely used in dental practice due to advantages of esthetic outcome. Color parameters, one of the major factors for the esthetic outcome, are affected from different factors such as repeated firings, chemical composition and thickness. In clinical practice, ceramics were frequently subjected to the repeated firings, but the effects of the repeated firings on the color parameters have been underestimated or unknown, so the aim of the study was to evaluate the effects of the repeated firings on the color parameters of all‐ceramic materials. Two commercially available A2 shaded all‐ceramic systems were used in this study (lithium disilicate pressable ceramics and computer aided design/computer aided manufacturing [CAD/CAM] fabricated zirconia). Ten samples for each group (zirconia and lithium disilicate) were prepared and subjected to repeated firings, respectively (1st, 3rd, 5th). Color measurements were performed after each repeated firings using a colorimeter (Minolta CR 321, Konica Minolta, Tokyo, Japan). The perceptibility threshold and acceptability threshold for color changes (ΔE00) was defined as 0.8 and 1.8, respectively. Statistical analysis of the results was performed by using repeated measures ANOVA for color parameters and using non‐parametric Kruskal‐Wallis and Mann‐Whitney‐U test for ΔE00 values (P < .05). L*, a* values showed statistically significant differences for lithium disilicate pressable ceramics and were not significant the zirconia specimens. ΔE00 values were above the perceptibility level for both lithium disilicate and zirconia specimens. Repeated firings affect the color parameters of the lithium disilicate specimens. As a result of repeated firings, lithium disilicate ceramics become lighter and greener.

Disilicate Dental Ceramic Surface Preparation by 1070 nm Fiber Laser: Thermal and Ultrastructural Analysis.

Lithium disilicate dental ceramic bonding, realized by using different resins, is strictly dependent on micro-mechanical retention and chemical adhesion. The aim of this in vitro study was to investigate the capability of a 1070 nm fiber laser for their surface treatment. Samples were irradiated by a pulsed fiber laser at 1070 nm with different parameters (peak power of 5, 7.5 and 10 kW, repetition rate (RR) 20 kHz, speed of 10 and 50 mm/s, and total energy density from 1.3 to 27 kW/cm2) and the thermal elevation during the experiment was recorded by a fiber Bragg grating (FBG) temperature sensor. Subsequently, the surface modifications were analyzed by optical microscope, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS). With a peak power of 5 kW, RR of 20 kHz, and speed of 50 mm/s, the microscopic observation of the irradiated surface showed increased roughness with small areas of melting and carbonization. EDS analysis revealed that, with these parameters, there are no evident differences between laser-processed samples and controls. Thermal elevation during laser irradiation ranged between 5 °C and 9 °C. A 1070 nm fiber laser can be considered as a good device to increase the adhesion of lithium disilicate ceramics when optimum parameters are considered.

Effect of ceramic material and resin cement systems on the color stability of laminate veneers after accelerated aging

Statement of problemLaminate veneers are susceptible to color change during clinical service. Studies that compare the effects of different ceramic and resin cement systems on color stability are lacking. PurposeThe purpose of this in vitro study was to evaluate the color stability of laminate veneers after accelerated aging using different ceramic and resin cement systems. Material and methodsCeramic specimens (N=168; shade A1; thickness, 0.50 ±0.05 mm; diameter, 10.00 ±0.10 mm) were prepared using nanofluorapatite and lithium disilicate (high translucency [HT] to low translucency [LT]) ceramics. Light-polymerizing (LP) cements were classified by brightness (high or low). Dual-polymerizing cements were classified by composition (base-only [DB] or base-catalyst [DC]) for comparison of color stability on the basis of polymerization type. DB cement was light-polymerizing, whereas DC cement was dual-polymerizing. They were further classified by shade (transparent, white, or yellow [n=7, each]). Color difference (ΔE) values were obtained by spectrophotometric quantification of L* (lightness), a* (green-red), and b* (blue-yellow) values before and after aging. The Kruskal-Wallis, Mann-Whitney U, Wilcoxon signed rank, and Bonferroni post hoc tests were used for statistical analysis. ResultsAfter specimens were subjected to accelerated aging, HT ceramic specimens luted with yellow-shade DC cement exhibited the greatest color change (ΔE=2.11), whereas HT and LT ceramic specimens luted with low-brightness LP cement exhibited the least color change (ΔE=1.37). In HT ceramic specimens, which exhibited the greatest color change of the 3 ceramic types, transparent shade cement exhibited significantly lower ΔE values than the other shades with DB (P<.001) and DC cements (P=.010). High-brightness cement exhibited significantly higher ΔE values than low-brightness cement when used with NF (P=.017), HT (P<.001), and LT (P<.001) ceramics. The ΔE values of DB cement were not always lower than those of DC cement. For all specimens, the aging of laminate veneers decreased the L* values and increased the a* and b* values. ConclusionsCeramic and resin-cement systems affected the color stability of laminate veneers. Relative to other ceramics, HT lithium disilicate ceramics exhibited greater color changes upon aging. For HT ceramics, the use of transparent shade resin cement is recommended. The lower the brightness of resin cement, the higher the color stability of veneers. For luting of 0.5-mm-thick laminate veneers with dual-polymerizing cement, light polymerization did not yield better color stability than dual polymerization over time.

Comparative Evaluation of Flexural Strength of Nano-zirconia-integrated Pressable Feldspathic and Lithium Disilicate Ceramics

The purpose of the study was to evaluate and compare the flexural strength of nano-reinforced zirconia feldspathic porcelain, lithium disilicate ceramics, and zirconia. Ten bar-shaped specimens of computer-aided design (CAD)/computer-aided manufacturing (CAM) zirconia, reinforced feldspathic porcelain, and reinforced lithium disilicate were fabricated in accordance to International Organization for Standardization (ISO 6872; n = 10). Feldspathic porcelain and lithium disilicate ceramic specimens were reinforced with 5, 10, 15, and 20% of zirconia nanoparticles through a customized technique. The specimens were subjected to three-point flexural strength test using universal testing machine (UTM) and examined for crack propagation using a scanning electron microscope (SEM). Oneway analysis of variance (ANOVA) and Tukey test were used to analyze the data (p < 0.05). The flexural strength of feldsphatic porcelain increased with the increase in the concentration of zirconia particles. The mean flexural strength of 5, 10, 15, and 20% nano-zirconia-incorporated lithium disilicate was 93.8, 97.1, 100.6, and 100.8 MPa respectively, and was lower than the control group (221.7 MPa). A significant difference in the flexural strength was found with the incorporation of nano-zirconia particles. The flexural strength of zirconia-integrated feld-spathic porcelain increased and lithium disilicate ceramics decreased with the nano-zirconia reinforcement. The simplified approach of reinforcing feldspathic porcelain with zirconia nanoparticles can be adapted in clinical situations of higher masticatory forces.

Ceramic Surface Treatment with a Single-component Primer: Resin Adhesion to Glass Ceramics.

To evaluate the microshear bond strength (µSBS) of composite cement bonded to two machined glass ceramics and its durability, comparing conventional surface conditioning (hydrofluoric acid + silane) to a one-step primer (Monobond Etch & Prime). Machined slices of lithium disilicate ceramic (LDC) (IPS e.max CAD) and feldspathic ceramic (FC) (VITA Mark II) glass ceramics were divided into two groups (n = 10) according to two factors: 1. surface treatment: HF+S (ca 5% hydrofluoric acid [IPS Ceramic Etching GEL] + silane coupling agent [SIL; Monobond Plus]) or MEP (single-component ceramic conditioner; Monobond Etch & Prime); 2. storage condition: baseline (without aging; tested 24 h after cementing) or aged (70 days of water storage + 12,000 thermal cycles). Composite cement (Multilink Automix, Ivoclar Vivadent) was applied to starch matrices on the treated ceramic surfaces and photoactivated. A µSBS test was performed (0.5 mm/min) and the failure pattern was determined. Contact angle and micromorphological analyses were also performed. Data were analyzed with Student's t-test (α = 5%). For both ceramic materials, HF+S resulted in higher mean µSBS (MPa) at baseline (LDC: HF+S 21.2 ± 2.2 > MEP 10.4 ± 2.4; FC: HF+S 19.6 ± 4.3 > MEP 13.5 ± 5.4) and after aging (LDC: HF+S 14.64 ± 2.31 > MEP 9 ± 3.4; FC HF+S: 14.73 ± 3.33 > MEP 11.1 ± 3.3). HF+S resulted in a statistically significant decrease in mean µSBS after aging (p = 0.0001), while MEP yielded no significant reduction. The main failure type was adhesive between composite cement and ceramic. HF+S resuted in the lowest contact angle. Hydrofluoric acid + silane resulted in higher mean µSBS than Monobond Etch & Prime for both ceramics; however, Monobond Etch & Prime had stable bonding after aging.

Effect of Erbium-yttrium, scandium, gallium and garnet (Er-YSGG) laser on the bond strength of lithium disilicate ceramics.

Objectives:To assess the bond strength of LD ceramics with resin composite material and surface conditioning using Er: YSGG laser and HF acid.Methods:Thirty LD ceramic (Emax, Ivoclar vivadent) discs were prepared using hot pressing technique and treated with hydroflouric acid (Group-1-HF acid) (9%) (n=10) and Er- yttrium, scandium, gallium and garnet laser (Group-2-ER-YSGG laser) (Waterlase iPlus, 10 Hz and power of 0.5 W, pulse duration of 230 μs) (n=10). Ten specimens were left untreated to be included as controls (Group-3-Control). All the specimens were treated with Adper Single Bond adhesive (3MESPE, St. Paul, MN, USA). Multicore buildups (3mmx3mm) were performed using a rubber mold on the ceramic surfaces and cured using LED light-curing unit for 140 sec. All specimens were tested using shear bond test and failure modes were assessed with a stereomicroscope and scanning electron microscope. Data was analysed using ANOVA and Tukey Kramer multiple comparisons test.Results:The maximum and minimum shear bond strength values were achieved in HF Acid specimens (Group-1) (28.15±4.72 MPa) and control specimens (13.47± 3.14 MPa) respectively. Specimens treated with HF acid showed significantly higher bond strength in comparison to laser treated and control specimens (p<0.01). Laser treated specimens had significantly higher bond strength as compared to controls (p<0.01).Conclusions:Hydrofluoric (HF) acid treatment showed significantly better outcomes than YSGG laser surface treatment.

Complete rehabilitation of compromised full dentitions with adhesively bonded all-ceramic single-tooth restorations: Long-term outcome in patients with and without amelogenesis imperfecta

ObjectivesThis clinical follow-up evaluated the long-term outcome of full-mouth rehabilitations with adhesively bonded all-ceramic restorations in patients suffering from amelogenesis imperfecta (AI) or affected by extensive tooth wear including a loss of the vertical dimension of occlusion. Materials and methodsIncluded for evaluation were all patients treated with adhesively bonded monolithic single-tooth restorations made of silicate or lithium disilicate ceramics; allowing a maximum four missing teeth and a facial feldspathic veneering of LDS anterior crowns. After treatment, patients have been enrolled in a recall program for dental check-ups including quality assessment of the restorations. Patients answered the oral health impact profile (OHIP-14) at their last visit. ResultsSeventeen patients (mean age = 35 ± 18 years) were observed up to 16.5 years (mean: 6.2 ± 3.8 years). 12 out of 450 restorations failed due to core fracture (n = 7), tooth fracture (n = 2), one secondary caries, one chip-off grade 3, and one fixed dental prosthesis due to discomfort. The overall mean survival rate of the single-tooth restorations was estimated 99.4% at 5 and 91.4% at 10 years. The overall mean success rate was estimated 92.6% at 5 and 81.4% at 10 years, mainly due to chip-offs and crack formation (27 out of 31 relative failures). The mean annual failure rates (AFR) range between 1.5 and 2% over the years, but non-AI patients were affected more frequently by early technical complications in the facial veneering of anteriors, resulting in an AFR ranging between 5.2 and 4%. Quality assessment revealed stable color, form and marginal integrity in all patients up to ten years. The distribution of OHIP values is comparable to the representative sample of healthy patients. ConclusionAdhesively bonded single-tooth restorations provided a high clinical quality in the long-run. However, while the survival and success were excellent in AI patients, restorations in non-AI patients were affected by a higher complication rate, likely related to a higher risk profile due to a history of bruxism and tooth wear.

A Measurement Protocol for the Marginal and Internal Fit of All-Ceramic Crowns.

To evaluate in vitro the influence of firing on marginal and internal fit of all-ceramic milled and pressed lithium-disilicate crowns. One Standardized model with 1.6mm occlusal and 1.4mm axial reduction was used to fabricate 64 crowns. Using a factorial design, eight groups of lithium disilicate ceramics (n=8) using P=press, C=CAD/CAM, M=monolithic, O=coping, V=veneered, R=as produced: PMR, PMG, POR, PVG, CMR, CMG, COR, CVG. Crowns were produced and cemented on stone dies, then embedded in clear epoxy resin and sectioned into two plains. With a digital microscope, the distance between die and crowns was measured at the occlusal and axial walls. The horizontal/vertical fit at the finishing line of each section were measured as well. For the marginal fit, the analysis shows that the influence of material and design was significant on horizontal and vertical margins, and the influence of finish was significant with horizontal but not vertical margins (p=0.09). For the internal fit, the analysis showed that the axial gap was significantly influenced by material and finish but not by design (p=0.44). With a few exceptions, horizontal and vertical marginal discrepancies were below 100 μm. Additional firing increased the discrepancies.

Post-etching cleaning influences the resin shear bond strength to CAD/CAM lithium-disilicate ceramics

Statement of problemThe hydrofluoric acid (HF) is able to promote selective dissolution of the glassy phase in silica-based ceramic. However, the etching leaves insoluble silica-fluoride salts in the surface that affects negatively the bond, affirming the need of a post-etching cleaning.PurposeEvaluate the shear bond strength (SBS) of composite resin to CAD/CAM lithium-disilicate ceramics after different post-etching cleaning and silane treatments.MethodsTwenty-four 2 mm-thick slices of IPS e.max CAD (Ivoclar Vivadent, AG, Schann, Liechtenstein) were crystallized, embedded in acrylic resin, polished and cleaned in an ultrasonic bath. Each specimen was etched with 5% HF for 20 s, rinsed for 60 s, and treatment was completed using surface cleaning and silanization. The cleaning methods were: AW—air/water spray; UB—ultrasonic bath; PA—37% phosphoric acid; and ST—steam cleaning. The cleaned surface received: E—no silane treatment; E/S—silane application for 20 s, air drying for 20 s and hot drying (60 °C) for 20 s; E/S+—silane application for 60 s, air drying for 20 s, hot air drying (60 °C) for 20 s, rinsing with boiling water for 15 s and hot air drying for 20 s. Cylinders of composite resin (n = 12) (Z100, 3M-ESPE, Saint Paul, MN, USA) were bonded using an adhesive resin (Optibond FL adhesive, Kerr Corp, Orange, CA, USA). SBS testing was carried out after 24 h of storage in water. Samples for each post-etching cleaning regimen were analyzed by SEM.ResultsAccording to two-way ANOVA (Bonferroni-corrected post hoc tests, p < 0.05), the SBS was significantly influenced by the post-etching cleaning, with UB yielding the highest SBS (21 MPa for E/S); other post-etching cleaning regimens showed lower SBS values (12–17 MPa). The type of silane application was not significantly different. The SEM analysis showed a cleaner ceramic surface for UB when compared to the other groups.ConclusionsEtching lithium disilicate ceramics following by ultrasonic bath cleaning and regular application of a silane is recommended.

Bond strength and durability of universal adhesive agents with lithium disilicate ceramics: A shear bond strength study

The aim was to assess the shear bond strength (SBS) of lithium disilicate (LD) ceramic to resin composite with different universal adhesives, duration of ageing and silane. One hundred and twenty LD ceramic discs were processed, fired and etched (HF acid 5%) for 20 s (sec). All specimens were divided into 12 groups (n = 10), based on different combinations of, 3 different universal adhesives [Scotchbond (SB) Universal Adhesive, All-Bond (AB) Universal, and Futurabond U (FU)], silane and different duration of ageing [24 h and 3 months]. Composite resin cylinders (Tetric ceram) (3mm × 2 mm) were formed using bonding jig on ceramic and were light-cured. The specimens in groups 1–6 and 7–12 were stored in distilled water (37 °C) for 24 h and 3 months (thermocycling -5000 cycles 5–55 °C/30 s dwell time) before being subjected to bond strength testing respectively. Using universal testing machine shear bond test was performed at a crosshead speed of 1 mm/min. Failure modes and fracture patterns were assessed using stereomicroscope and scanning electron microscope. Analysis of variance was performed to analyze data. SBS was significantly higher with silane than without silane (p < 0.01), regardless of the type of adhesive or storage duration. Specimens tested at 24 h storage showed significantly higher (p < 0.01) SBS than specimens tested after 3-months. A comparison among different universal adhesives showed significantly distinct bond strength (p < 0.01). Optimal bonds to LD were achieved by application of silane. While ageing through storage had a negative impact on the SBS, it varied among different adhesives.

Color stability of lithium disilicate ceramics after aging and immersion in common beverages

Statement of problemThe color of an esthetic restoration and its color stability are important for long-term success. However, the impact of common beverages on lithium disilicate ceramic is not well known. PurposeThe purpose of this in vitro study was to investigate color variations of lithium disilicate ceramics after thermocycling (TC) and immersion in commonly consumed beverages. Material and methodsA total of 288 specimens (1×10×10 mm) were fabricated from IPS e-max computer-aided design (CAD) (n=72), IPS e-max CERAM ([CER] n=72), IPS e-max Press with glazing ([PG] n=72), and IPS e-max Press without glazing ([PNG] n=72) according to the manufacturer's instructions. Each group was divided into 4 subgroups (n=18): TC, coffee, black tea, and red wine. Thermocycling was performed at 21 900 cycles at 5°C, 37°C, 55°C, and 37°C (3 years’ clinical simulation), whereas the specimens were soaked in the staining solutions for up to 54 hours (3 years’ clinical simulation). Color parameters L*, a*, and b* were assessed with an ultraviolet-visible spectroscopy recording spectrophotometer. Color difference (ΔE) was calculated using the equation [ΔΕ= [(ΔL*)2 + (Δa*)2 + (Δb*)2]½]. Intraexaminer reliability was assessed by using the intraclass correlation coefficient. Two-way analysis of variance was used for the analysis of ΔΕ, and the parameters L*, a*, and b* were analyzed with linear mixed models for repeated measurements and the Bonferroni pair-wise comparison test (α=.05). ResultsParameters ΔΕ, L*, a*, and b* were significantly affected by the interaction between material and treatment (P<.001). A ΔΕ >1 was recorded for PG with tea, wine, and coffee, PG after TC and CER after TC. For L*, greater reduction was observed for PNG with tea and CER after TC, whereas for a* significant changes were positive (to red shades), except for PNG with TC, where PNG with wine showed the greatest positive change. For b*, significant changes were negative (to blue shades) except for PNG with tea and coffee and CAD with tea. ConclusionsAll groups demonstrated color changes below the clinically perceptible level (ΔΕ<3.7), except PNG in tea which showed statistically significant color differences (ΔΕ>4). CAD presented higher color stability compared with the nonglazed Press specimens.

Effects of Dentin Surface Treatments on Hypersensitivity to Bond Strength of Restorations: An In Vitro Study

This study evaluated the effects of desensitizing treatments on the shear bond strength (SBS) of adhesive resin cement (Rely X U100) applied to dentin. Human molars (n = 120) with exposed dentin were divided into 12 groups. In the experimental groups, dentin surfaces were treated with (1) an erbium:yttrium- aluminium-garnet (Er:YAG) laser, (2) a neodymium:yttrium-aluminium-garnet (Nd:YAG) laser, (3) glutaraldehyde (Gluma)-, (4) fluoride (Aqua Prep-F)-, and (5) oxalate (BisBlock)-containing desensitizing agents, (6) Gluma preceding the Er:YAG laser, (7) Aqua Prep-F preceding the Er:YAG laser, (8) BisBlock preceding the Er:YAG laser, (9) Gluma preceding the Nd:YAG laser, (10) Aqua Prep-F preceding the Nd:YAG laser, (11) and BisBlock preceding the Nd:YAG laser, in groups EL, NL, G, F, O, EL-G, EL-F, EL-O, NL-G , NL-F, and NL-O, respectively. Then, lithium disilicate ceramics were cemented to the treated surfaces. Subsequently, an SBS test was performed and the data were statistically analyzed (α = .001). The results suggested that the combined treatment of Gluma preceding Er:YAG laser increased the bond strength of ceramic to the dentin surface using a self-adhesive resin cement.

A Comparative Three- and Bi-dimensional Research of the Marginal Fit of Pressed Lithium Disilicate Inlays

The replacement of classical fillings, especially in the posterior area with different types of inlays has become a common solution used in order to improve all parameters which insure a long lasting treatment. Vrious ceramic materials and systems are available, but so far an ideal ceramic material suited for all clinical situations, has not been found. The range of ceramic materials as: lithium disilicate, aluminum oxide, zirconium oxide and hybrid ceramics enhance the possibilities of using ceramic inalys in various clinical situations. Marginal adaptation is one of the most important conditions for long-term success for any type of material. The marginal discrepancy of fixed restorations is one of the main factors which lead to failure of the prosthetic treatment.The purpose of the present study is to compare a 2D and 3D method for evaluating the marginal fit for pressed lithium dislicate inlays (Emax). The two used methods were: SEM- electronic microscopy and micro CT.

Effects of core and veneer thicknesses on the color of CAD-CAM lithium disilicate ceramics

Statement of problemThe color of dental ceramics is important for achieving successful esthetic restorations. However, insufficient studies are available of the color of recently introduced computer-aided design-computer-aided manufacturing (CAD-CAM) lithium disilicate ceramics as functions of the core and veneer thicknesses. PurposeThe purpose of this in vitro study was to evaluate the effects of the thickness of different core and veneer thicknesses on the color of CAD-CAM lithium disilicate ceramics. Material and methodsA total of 42 specimens from 2 groups of 7 ceramic cores at 3 thicknesses (0.8, 1.0, and 1.2 mm) were fabricated. The veneer was fabricated at 3 thicknesses (0.3, 0.5, and 0.7 mm). The group name was based on the name of the ceramic core (IPS e.max CAD; lithium disilicate [LD], IPS Empress CAD; leucite-reinforced glass-ceramic [LR]), and the associated number was determined by the combined thicknesses of the core and the veneer: 1=0.8+0.7; 2=1.0+0.5; and 3=1.2+0.3. The color coordinates and the color differences were calculated using a spectrophotometer. The color difference was analyzed using the CIEDE2000 chrominance and the acceptability threshold. Two-way ANOVA was used to identify the color difference based on the core/veneer thicknesses, and the Tukey honest significant differences and Games-Howell tests were conducted to verify the ΔE00 differences of the group (α=.05). In addition, regression analysis was carried out to estimate the causal relationship between the independent variables and the chrominance. ResultsAt a certain thickness, the color differences of LD1, LR1, and LR2 were not clinically acceptable based on the thicknesses of the core and the veneer. Results of 2-way ANOVA demonstrated that the different thicknesses of core/veneer combination significantly affected the color difference (P<.05). A significant interaction was present between the thickness and the material (P<.05). The results of multiple regression analyses showed that the average color difference of LR increased by 0.019 as the thickness of the core decreased by 0.2 mm. ConclusionsThe color is influenced by the thicknesses of the core and the veneer. With a certain thickness, the color differences increased as the thickness of the core decreased, and lithium disilicate ceramics were less vulnerable to standard deviation of color difference compared with the leucite-reinforced ceramics.

The effect of heat treatments applied to superstructure porcelain on the mechanical properties and microstructure of lithium disilicate glass ceramics

The aim of this study was to investigate that heat treatments with different numbers applied to superstructure porcelain whether effects microstructure and mechanical properties of lithium disilicate ceramic (LDC). Eighty disc-shaped specimens were fabricated from IPS e.max Press. Specimens were fired at heating values of porcelain in different numbers and divided four groups (n=5). Initial Vickers hardness were measured and X-ray diffraction (XRD) analysis was performed. Different surface treatment were applied and then Vickers hardness, surface roughness and environmental scanning electron microscopy (ESEM) analysis were performed. Data were analyzed with Varyans analysis and Tukey HSD test (α=0.05). Initial hardness among groups was no significant different (p>0.05), but hardness and surface roughness after surface treatments were significant different (p<0.05). Lithium disilicate (LD) peaks decrease depended on firing numbers. ESEM observations showed that firing number and surface treatments effect microstructure of LDC. Increasing firing numbers and surface treatments effect the microstructure of LDC.

Effect of self etching ceramic primer and universal adhesive on bond strength of lithium disilicate ceramic

The clinical success of ceramic restorations is affected by the ceramic bonding procedure. The objective of the study was to evaluate the effect of different surface treatments, including the use of self-etching ceramic primer (SECP), on resin cement-glass ceramic bond strength. Thirty lithium disilicate ceramic (LDC) rectangles (3 mm × 3 mm × 8 mm) were fabricated Specimens were randomly assigned into three experimental groups (n = 10) according to the surface treatment: Group 1-hydrofluoric acid [HF acid]+ silane + universal adhesive; Group 2-HF + universal adhesive; Group 3-SECP + universal adhesive. All specimens were stored in distilled water for 24 h at 37 °C and shear bond strength (SBS) was tested at a crosshead speed of 0.5 mm (Universal Testing machine-Instron). Failure modes were evaluated using a digital microscope for all specimens. Analysis of variance and the Tukey post hoc tests using SPSS (Version 22.0, IBM, New York, USA) were used to analyze data. The SBS of groups 1 (19.74 ± 1.28 MPa) and 3 (21.11 ± 2.07 MPa) were significant higher than group 2 (14.80 ± 1.94 MPa). The SBS values for specimens in groups 1 (19.74 ± 1.28 MPa) and 3 (21.11 ± 2.07 MPa) were comparable. Adhesive, mixed and cohesive failure modes were observed and mixed failure was the most common in all groups. Therefore, the use of SECP and universal adhesive is recommended as an alternative to the use of HF acid in combination with ceramic primer while bonding to LDC.