Targeting bonding protocols to increase the bond between acrylic resin or 3D printed denture bases and prefabricated or 3D printed denture teeth.

STATEMENT OF PROBLEM: The difference in chemical composition between denture base resin and denture teeth requires the development of bonding protocols that increase the union between the materials. PURPOSE: The purpose of this in vitro study was to evaluate the impact of different bonding protocols on the bond between heat-polymerized and 3-dimensionally (3D) printed acrylic resin denture bases and acrylic resin prefabricated and 3D printed artificial teeth. MATERIAL AND METHODS: Four types of artificial teeth were evaluated: prefabricated acrylic resin (VITA MFT) and 3D printed (Cosmos TEMP, PRIZMA 3D Bio Denture, and PrintaX AA Temp) bonded to 20×24-mm cylinders of heat-polymerized (VipiWave) and 3D printed (Cosmos Denture, PRIZMA 3D Bio Denture, and PrintaX BB Base) denture bases. Three bonding protocols were tested (n=20): mechanical retention with perforation + monomer (PT1), mechanical retention with perforation + airborne-particle abrasion with 50-µm aluminum oxide + monomer (PT2), and mechanical retention with perforation + Palabond (PT3). Half of the specimens in each group received 10 000 thermocycles and were then subjected to the bonding test at a crosshead speed of 1 mm/minute. The failure type was analyzed and scanning electron micrographs made. Additionally, surface roughness (Ra) and wettability (degree) were analyzed (n=15). ANOVA was used to evaluate the effect of the bonding protocol, and the Student t test was applied to compare the experimental groups with the control (α=.05). For type of failure, a descriptive analysis was carried out using absolute and relative frequency. The Kruskal-Wallis test was used to evaluate the surface changes (α=.05). RESULTS: Among the protocols, PT3 with in Yller and PT2 with Prizma had the highest bond strengths of the heat-polymerized denture base and 3D printed teeth (P<.05). When comparing the experimental groups with the control, PT3 and PT2 had greater union with the 3D printed denture base + 3D printed teeth (in Yller), with no difference from the heat-polymerized denture base + prefabricated teeth in acrylic resin. The treatment of the 3D printed tooth surfaces affected the surface roughness of Prizma (P<.001) and wettability (P<.001). CONCLUSIONS: To increase the bond between Yller 3D printed denture base + 3D printed teeth, a bonding protocol including mechanical retention with perforation + Palabond or mechanical retention with perforation + airborne-particle abrasion with aluminum oxide + monomer is indicated. For the other materials tested, further bonding protocols need to be investigated.

Effect of staining layer on roughness after progressive wear of monolithic ceramics.

PURPOSE: The aim of this study was to evaluate staining layer behavior applied to high-translucency zirconia (YZHT), feldspathic ceramics (FD), and zirconia-reinforced lithium silicate (ZLS) surfaces against different antagonists. METHODS AND MATERIALS: Monolithic ceramic discs (n = 120) (ø 12 mm; thickness, 1.2 mm; ISO 6872) were obtained, 30 from YZHT and FD, and 60 from ZLS CAD/CAM blocks (staining layer applied before or after the crystallization procedure). The specimens were divided into 12 subgroups (n = 10) according to the antagonists: steatite, polymer-infiltrated ceramic, or zirconia. Mechanical cycling (1.5 × 104 cycles; 15 N; horizontal displacement, 6 mm; 1.7 Hz) and flexural strength tests (1 mm/min-1000 kg cell) were performed. The differences between final and initial roughnesses (Ra, Rz, and Rsm), the mass loss, and the flexural strength data were individually analyzed by two-way ANOVA and Tukey's test (α = 0.05). RESULTS: The roughnesses of all ceramics did not present a statistically significant difference before wear simulation: Ra (p = 0.3348), Rz (p = 0.5590), and Rsm (p = 0.5330). After the wear simulation, the Ra parameter was not affected by an interaction between ceramic and antagonist (p = 0.595). The Rz and Rsm parameters were affected only by the antagonist pistons (both, p = 0.000). The ceramics used in this study showed statistically significant differences in mass loss after the wear test (p < 0.0001). The additional firing (2 steps) of the ZLS2 led to a higher lost mass quantity. CONCLUSION: All ceramics presented similar initial roughnesses and similar roughnesses after the wear simulation. The zirconia antagonist showed better performance against ceramics with high crystalline content. CLINICAL SIGNIFICANCE: It is clear that restorative materials must be carefully selected by dental practitioners according to indications, properties, and antagonists. The steatite antagonist, that is, an enamel analog, showed better performance against vitreous ceramics, while the zirconia antagonist showed better performance against ceramics with high crystalline content. Wear affects the surface roughnesses of the ceramics. Additional firing for the staining of the zirconia-reinforced lithium silicate ceramic led to a greater loss of mass.

Interface adhesion on layered zirconia: Effects of the veneering ceramic material and veneering technique.

PURPOSE: To evaluate the effect of different veneering ceramics and veneering techniques on the bond strength to zirconia. MATERIALS AND METHODS: 3Y-TZP zirconia blocks were sliced into 60 slabs, polished, and sintered. Each slab received one ceramic cylinder (Ø = 3.4 mm, 5 mm-high), according to the veneering ceramic type (feldspathic-FEL or lithium disilicate-based-LD) and the veneering technique (file-splitting with resin-based luting agent-RC, file-splitting with fusion ceramic-FC, or heat-pressing-HT), which resulted in six groups: FEL-RC, FEL-FC, FEL-HT, LD-RC, LD-FC, LD-HT. After preparation, the samples were immersed in distilled water for 24 h before the shear bond strength (SBS) test. The failure modes were classified as adhesive, predominantly adhesive, or cohesive. Representative failure mode images were taken in a Scanning Electron Microscope. The SBS data were analyzed by two-way ANOVA and Tukey's test. RESULTS: Both type of veneering ceramic and technique affected the bond strength. FC led to the highest SBS values. RC and HP provided similar results when compared within each veneering ceramic. Lithium disilicate achieved lower bond strength than feldspathic ceramic when the heat-pressing technique was applied. The most frequent failure modes were predominantly adhesive and adhesive for FEL and LD, respectively. CONCLUSION: File-splitting with fusion ceramic provided the highest adhesion to zirconia when feldspathic or lithium disilicate-based ceramics were used. The heat-pressing technique for veneering with lithium disilicate significantly decreased the bond strength when compared to the feldspathic ceramic.

Fatigue strength of 5Y-FSZ: glazing and polishing effects.

OBJECTIVE: The aim of this study was to evaluate the effect of four different finishing procedures on the fatigue strength of a fully stabilized zirconia (5Y-FSZ) material. MATERIALS AND METHODS: Disc-shaped specimens of a 5Y-FSZ (Katana UTML, Kuraray Noritake) were made (ISO 6872-2015), grinded with 600- and 1200-grit silicon carbide paper, sintered as recommended, and randomly assigned into four groups according to the finishing technique: C (control, as-sintered), P (polished with polishing rubbers), G (glaze application - powder/liquid technique), and PG (polished with polishing rubbers + glaze application - powder/liquid). Then fatigue strength (staircase method), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses were performed. RESULTS: The C group presented the lowest fatigue strength, while the PG group presented the highest. The P and G groups presented intermediate behavior, presenting similar statistical results. XRD showed similar crystalline phase patterns for all groups. SEM images revealed some changes in the zirconia surface, with the P group presenting some scratches on the surface, while the scratches in the PG group were filled with the glaze material. CONCLUSION: None of the techniques analyzed in this study impaired the fatigue strength of fully stabilized zirconia. Importantly, the polishing rubbers combined with glaze application (PG group) improved its fatigue strength. CLINICAL RELEVANCE: The polishing rubbers followed by glaze application improve the fatigue strength in ultra-translucent zirconia.

Sintering mode of a translucent Y-TZP: Effects on its biaxial flexure fatigue strength, surface morphology and translucency.

OBJECTIVE: This investigation evaluated the effect of two sintering modes of a translucent zirconia (Y-TZP) on its surface roughness, topography, phase-transformation (t → m), translucency and biaxial flexure fatigue strength. MATERIALS AND METHODS: To do so, 50 Y-TZP discs (Ø = 15 mm; thickness = 1.2 mm; IPS e.max ZirCAD LT) were prepared and divided into two groups: Standard mode (SM) and Fast mode (FM). Staircase fatigue testing was performed (piston-on-three balls set-up, ISO 6872:2015), as well as surface roughness, profilometry, scanning electron microscopy (SEM-FEG), energy dispersive X-ray spectroscopy (EDX), phase transformation (t → m) using X-ray diffraction analysis (XRD), translucency parameter analysis (TP and TP00 ) and fractography. RESULTS: The results showed no statistical significant differences for roughness parameters (p > 0.05, SM: Ra = 0.13 ± 0.02, Rz = 1.21 ± 0.26 and RSm = 24.91 ± 2.19; FM: Ra = 0.14 ± 0.03, Rz = 1.32 ± 0.25 and RSm = 24.68 ± 2.16) or flexural fatigue strength (SM: 512 (464-560) MPa; FM: 542 (472-611) MPa) between the groups. In addition, similarity in surface morphological features (SEM and profilometry), composition and phases (EDX and XRD) was observed between the firing protocols. Fractography showed that the failure origin occurred on the tensile side. Sintering mode did not affect the TP (F = 0.001, p = 0.97) and TP00 (F = 0.12, p = 0.72). CONCLUSIONS: Therefore, the fast-sintering mode is suggested as a viable alternative to the standard mode since it does not influence the evaluated surface morphology, microstructure, fatigue strength and translucency of a translucent monolithic zirconia. CLINICAL SIGNIFICANCE: The fast sintering mode is a viable alternative for zirconia without compromising its topography, microstructure, mechanical performance or translucency.

Effect of surface treatment and glaze application on shade characterized resin-modified ceramic after toothbrushing.

STATEMENT OF PROBLEM: The extrinsic characterization with pigments and glaze application on the surface of ceramic restorations promotes individualization and esthetics. However, whether this characterization is resistant to toothbrushing abrasive wear is unclear. PURPOSE: The purpose of this in vitro study was to investigate the abrasive wear resistance of characterized and glazed resin-modified ceramic with different surface treatments before characterization. MATERIAL AND METHODS: Eighty rectangular specimens (10×8×6 mm) were precision cut from Vita Enamic and randomly divided in 4 groups as per the surface treatment before the characterization technique. These groups included the following: no additional treatment or polishing only, acid etching, airborne-particle abrasion, and self-etching silanization. For each surface treatment, 2 subgroups were created considering the presence or absence of the glaze layer after shade characterization, totaling 8 groups (n=10). The specimens were submitted to toothbrushing simulation (150 000 cycles, 2.45-N, 180 strokes per minute) with a soft and straight toothbrush and a solution of toothpaste and distilled water (250 g/L). After each 50 000 cycles, the wear of the characterized surface was measured by using a contact profilometer in µm which was equivalent to 5, 10, and 15 years of simulated toothbrushing. The rates were analyzed by using 3-way ANOVA and the post hoc Tukey test (α=.05). Scanning electron microscopy analysis was performed to access the surface profile between the evaluated periods. RESULTS: The mean wear rate (Rz) of the characterized surface was affected by the isolated factors, including surface treatment, glaze, and time (P<.001), with no interactive effects noted. A higher mean value of Rz was observed for polishing only (12.9 ±4.4 µm), followed by airborne-particle abrasion (10.2 ±4.5 µm), acid etching (9.4 ±2.4 µm), and then self-etching silanization (7.6 ±2.9 µm). Mean wear rate was also increased by the glaze (11.1 ±4.7 µm) compared with its absence (9 ±3.2 µm) and by the length of time, with 15 years (11.3 ±4.5 µm) followed by 10 years (9.8 ±4.0 µm) and 5 years (9 ±3.6 µm). The scanning electron microscopy images showed similar worn surfaces for each subgroup, glaze removal after 150 000 cycles, and surface homogeneity in function of time. CONCLUSIONS: Self-etching silanization was found to be the treatment suitable for reducing the wear of characterized resin-modified ceramic during prolonged brushing of more than 5 years. Glaze application did not protect the characterization from surface wear, regardless of the ceramic surface treatment performed on the specimens.

Full-Crown Versus Endocrown Approach: A 3D-Analysis of Both Restorations and the Effect of Ferrule and Restoration Material.

PURPOSE: To assess stress distribution in full-crowns with a composite buildup and endocrowns under axial or oblique loads, both with different ferrules (1 or 2 mm) and ceramic materials (glass ceramic or hybrid ceramic). MATERIALS AND METHODS: Sixteen models were analyzed with finite element analysis. No-separation contacts were considered between restoration/resin cement and resin cement/tooth. The contact between the fixation cylinder and the root was considered perfectly bonded. The axial load was applied to the occlusal surface and the oblique load was applied to the buccal cusp. The resulting tensile stresses were shown for the crown, the cement layer and the tooth. RESULTS: Almost all factors influenced the stress distribution significantly in the crown and the cement layer, as well as the tooth. The only exception was found under oblique loading by the restoration material and the type of crown that were of no significant influence on the stress distribution in the tooth. CONCLUSIONS: Under axial load, the endocrown showed the least tensile stresses in the tooth, but under oblique loads, the full-crown showed less tensile stresses than the endocrown. With the hybrid ceramic material, lower stresses were found in the crown, but higher stresses were present in the cement layer. The 2 mm ferrule is beneficial for reducing the resulting tensile stresses in all modalities.

Effect of Consecutive Firings on the Optical and Mechanical Properties of Silicate and Lithium Disilicate Based Glass-Ceramics.

PURPOSE: To evaluate the effect of multiple firings on the optical and mechanical properties of two dental CAD/CAM glass-ceramics. MATERIALS AND METHODS: A total of 45 specimens of each lithium disilicate-LD (IPS E.max CAD, Ivoclar Vivadent) and zirconia lithium silicate-ZLS (Vita Suprinity, Vita Zahnfabrik) material were prepared in a disk shape. These specimens were divided into three groups according to two factors: "type of ceramic" (LD and ZLS) and "numbers of firings" (Control 2F-two firings, 5F-five firings and 7F-seven firings). The firing cycles were performed according to the manufacturer's recommendations. X-ray diffraction was additionally performed to determine crystalline phases in each group, spectrophotometry was used to determine color and translucency variation, and biaxial flexural strength (BFS) evaluated the mechanical behavior. The data were analyzed individually using two-way ANOVA tests and Tukey's test at α = 0.05. RESULTS: The crystalline phases did not present any change after multiple firings for either of the analyzed materials. Both commercial materials showed a significant difference regarding translucency at 7F (p = <0.01), and ZLS presented a difference in color higher than one (ΔE > 1) at 5F and 7F. Regardless of the number of firings, LD presented a higher BFS compared to ZLS (p = <0.001), and a significant increase in BFS comparing 2F and 7F (p = <0.024). CONCLUSION: The use of multiple firings can significantly alter the color, translucency, and mechanical strength of CAD/CAM ceramics.

Mouthguard use and TMJ injury prevention with different occlusions: A three-dimensional finite element analysis.

BACKGROUND/AIMS: There is a lack of data regarding the mechanical responses of the temporo-mandibular joints during an impact to the orofacial region. The aim of this study was to analyze the biomechanical effects of wearing a mouthguard (MG) on the impact response of the mandibular condyle and articular disk according to the type of occlusion. The hypothesis was that the MG would minimize the effect in those structures, regardless of the occlusion type. METHODS: Using modeling software, a human skull with jaw, teeth and articular disk was created. The models were divided according to the occlusion type (Class I, II, or III) and the presence of a mouthguard (with or without). The geometries were exported to analysis software, and the materials were considered ideal. Fixation occurred at the base of the foramen magnum. The load (0-500N, 1s) was applied to the upper central incisors with a steel ball. Maximum principal stress and Von Mises results (MPa) were obtained in the mandibular condyle and articular disk. Minimum principal stress and maximum shear stresses were also recorded in the articular disk. RESULTS: For both structures, the MG caused a decrease in stress concentration regardless of the occlusion and stress criteria. The condyle neck was the most tensile-stressed area while for the articular disk, both the superior and inferior surfaces were the most stressed areas. The highest stress peaks in the disk were found for compression followed by tensile and then shear stress. CONCLUSION: This biomechanical analysis of the effects of using a mouthguard exhibited considerably decreased stresses on the mandibular condyle and articular disk, regardless of the occlusion type.

Survival rate and load to failure of premolars restored with inlays: An evaluation of different inlay fabrication methods.

STATEMENT OF PROBLEM: Studies that evaluate the survival rate and load to fracture of premolars restored with inlays produced using different methods are lacking. PURPOSE: The purpose of this in vitro study was to compare the survival rate and fracture load of premolars restored with inlays fabricated using different methods. MATERIAL AND METHODS: Thirty maxillary premolars were selected, embedded, and prepared to receive inlays fabricated using different methods (n=10): LaCom-digital scanning with Lava C.O.S. scanner (3M ESPE), followed by milling of composite resin block (Lava Ultimate; 3M ESPE) in a milling unit; CeCom-digital scanning with Cerec 3D Bluecam scanner (Dentsply Sirona), followed by milling of a Lava Ultimate block in Cerec (Dentsply Sirona); PresDis-impression with polyvinyl siloxane, inlay made using the lost wax technique, and IPS e.max Press (Ivoclar Vivadent AG) pressed ceramic (lithium disilicate). A dual-polymerizing resin cement system was used to lute the inlays. Inlays were mechanically cycled (2 Hz, 106 mechanical pulses, 80 N) after 24 hours, and the specimens were stored in distilled water at 37°C for 11 months. Then, a fatigue test was conducted using a 10-Hz frequency and 400-N load on the inner inclines of the cusps. The test was complete when the specimen fractured or when the specimen reached 1.5×106 cycles. The specimens that survived fatigue testing were submitted to a single-load fracture test in a universal testing machine and analyzed using a stereoscope for failure classification. Survival rates were estimated using the Kaplan-Meier method and log-rank test (Mantel-Cox). Fracture load data were analyzed using 1-way ANOVA (α=.05). RESULTS: No significant differences were detected among the groups for the survival rate (P=.87) or for the load to fracture (P=.78). Most failures were longitudinal, catastrophic fractures. CONCLUSIONS: Premolars restored with inlays fabricated using the tested methods had similar survival rates and loads to fracture.

Different combinations of CAD/CAM materials on the biomechanical behavior of a two-piece prosthetic solution.

AIM: This study evaluated the stress distribution of implant-supported prostheses, varying the different combinations of computer-aided design/computer-aided manufacturing (CAD/CAM) materials between the hybrid abutment and the monolithic crown by three-dimensional (3D) finite element analysis (FEA). MATERIALS AND METHODS: Nine models were designed with Rhinoceros 3D and Ansys software. Each model contained a bone block of the molar area, including an implant (IH; Ø 3.75 × 11 mm) supporting a hybrid abutment (ceramic mesostructure (MS) cemented onto a titanium [Ti] base) and a monolithic crown. The occlusal load was applied to the fossa bottom (300 N; 30 degrees). The results were analyzed using the von Mises stress for each separated prosthetic structure and microstrain for the bone tissue. RESULT: Von Mises maps of the crown, ceramic MS, implant, screw, and cement layers showed a decreased stress concentration as the elastic modulus (E modulus) of the ceramic crown (CR) associated with a rigid ceramic MS decreased. No differences in bone tissue regarding microstrain were observed. CONCLUSION: Implant-supported crowns present less stress concentration when a rigid abutment is associated with resilient crowns.

Resin bond strength to zirconia: effects of surface treatments and resin cements.

This in vitro study evaluated the effect of surface treatments on the microshear bond strength between zirconia and 2 different resin cements. Thirty sintered zirconia blocks (15.5 × 19.0 × 39.0 mm) were allocated into 10 groups according to 2 factors: surface treatment (control [10% isopropyl alcohol], silica coating, primer, hot etching solution, or glaze) and resin cement (conventional dual-curing [Multilink Automix] or self-adhesive [RelyX U100]). Three cement cylinders (0.7-mm diameter × 1.5-mm height) were made on the surface of each zirconia block. The specimens were stored in water for 6 months at 37°C and then submitted to microshear bond strength tests (n = 9 per surface treatment group). The bond strength data were analyzed statistically with Kruskal-Wallis and Dunn tests (P < 0.05). The contact angle was measured with a goniometer on separate surface-treated disc specimens (n = 2 per group). The greatest mean (SD) bond strength values, regardless of cement type, were reported for the groups with the glaze surface treatment: conventional cement, 13.1 (0.26) MPa; and self-adhesive cement, 20.1 (0.23) MPa. The next greatest mean (SD) values were found in the silica coating groups: conventional cement, 7.94 (0.09) MPa; and self-adhesive cement, 9.8 (0.10) MPa. The self-adhesive cement groups presented the greatest bond strength values, except when the primer surface treatment was applied. The zirconia treated with the hot etching solution presented the greatest mean contact angle, 78.23 (SD 1.34) degrees, and bond strengths that were among the lowest achieved, suggesting that low wettability may have influenced bond strengths.

The effect of extended glaze firing on the flexural fatigue strength of hard-machined ceramics.

STATEMENT OF PROBLEM: It is unclear whether an extended glaze firing could improve the long-term mechanical performance of densely sintered CAD-CAM ceramics. PURPOSE: The purpose of this in vitro study was to analyze the effect of an extended glaze firing on the flexural fatigue strength (FFS) of densely sintered milled (hard-machined) leucite-based (LEU) and lithium disilicate-based (DIS) ceramics. MATERIAL AND METHODS: Disks were machined from ceramic blocks and divided into 6 groups (n=20) according to the material, LEU or DIS, and to the applied glaze firing: manufacturer-recommended glaze (G group), extended glaze (EG group), and control/no firing (C group). The surface roughness of the disks was measured before and after firing by using a contact profilometer, and data were compared by paired sample tests. Specimens were submitted to fatigue by using the staircase test design in water (piston-on-3 balls; 500 000 cycles, 20 Hz, and sinusoidal loading). Mean (±SD) FFS values were then calculated and analyzed by using 1-way analysis of variance and post hoc Tukey test (α=.05). RESULTS: Surface roughness did not change after the firing (P>.05). The highest FFS value in both ceramics was obtained after EG firing (LEU-EG=80.52 ±6.3 MPa; DIS-EG=147.25 ±10.5 MPa), which was statistically superior to G firing (LEU-G=73 ±6.8 MPa, P=.003; DIS-G=134.34 ±15.6 MPa; P=.023) and C group (LEU-C=61.94 ±6.3 MPa; P<.001; DIS-C=134.13 ±17.3 MPa; P=.023). CONCLUSIONS: EG firing optimized the biaxial flexural fatigue strength of hard-machined leucite and lithium disilicate ceramics compared with conventional glaze firing.

Influence of custom-made and stock mouthguard thickness on biomechanical response to a simulated impact.

BACKGROUND/AIMS: Mouthguards (MGs) are devices that can reduce the risks of facial trauma. However, the large variety of MG types and thicknesses raises the question of which type is the most effective and beneficial for the athletes. The aim of this study was to evaluate stress distribution in the skull, teeth, and jaws as a consequence of a direct impact. MATERIAL AND METHODS: Using modeling software, a human skull was modeled and a human jaw was created with all teeth inserted into the respective alveolus. The models were divided according to the MG type (custom-made or stock) and thickness (1, 2, and 4 mm). Two models without MG were evaluated with and without teeth contact. The geometries were exported to analysis software and the materials were considered ideal. Fixation occurred at the base of the foramen magnum. The load (500 N) was applied on the canine tooth with a ball. Maximum principal (MPa) and Von-Mises results were obtained. RESULTS: Without any protection, the generated tensile stress was of greater magnitude causing more damage in the absence of teeth contact. The presence of a MG significantly reduced the generated stress in all structures, and the customized/individualized type was more efficient than stock MGs. CONCLUSIONS: In extreme situations when it is impossible to use a MG, keeping the teeth in maximum intercuspal position is less harmful. Despite this, the use of any MG is beneficial and assists in dampening the generated stress. The thicker the device, the greater the capacity for decreasing the damage in all structures. The use of individual protectors for each patient is even more beneficial for preventing trauma during at-risk activities of impact.

Elastic Properties of Lithium Disilicate Versus Feldspathic Inlays: Effect on the Bonding by 3D Finite Element Analysis.

PURPOSE: To determine the elastic properties of five ceramic systems with different compositions (lithium disilicate vs. feldspathic ceramics) and processing methods and compare the stress distribution in premolars in the interface with inlays made with these systems loaded with the maximum normal bite force (665 N) using 3D finite element analysis (FEA). MATERIALS AND METHODS: The elastic properties of five ceramic restoration materials (IPS e.max Press, IPS e.max CAD, Vita PM9, Vita Mark II, Vita VM7) were obtained using the ultrasonic pulse-echo method. Three-dimensional FEA simplified models of maxillary premolars restored with these ceramic materials were created. The models were loaded with a load at the two nodes on the occlusal surface in the middle of the tooth, 2 mm from the outside of the tooth, simulating a loading ball with a radius of 6 mm. RESULTS: The means values of density (g/cm³), Young's modulus (GPa), and Poison's ratio was 2.6 ± 0.3, 82.3 ± 18.3, and 0.22 ± 0.01 for IPS e.max Press; 2.3 ± 0.1, 83.5 ± 15.0, and 0.21 ± 0.01 for IPS e.max CAD; 2.5 ± 0.1, 44.4 ± 11.5, and 0.26 ± 0.08 for PM9; 2.4 ± 0.1, 70.6 ± 4.9, and 0.22 ± 0.01 for Vitamark II; 2.4 ± 0.1, 63.3 ± 3.9, and 0.23 ± 0.01 for VM7, respectively. The 3D FEA showed the tensile stress at the interface between the tooth and the inlay was dependent on the elastic properties of the materials, since the Vita PM9 and IPS e.max CAD ceramics presented the lowest and the highest stress concentration in the interface, respectively. CONCLUSIONS: The elastic properties of ceramic materials were influenced by composition and processing methods, and these differences influenced the stress concentration at the bonding interface between tooth and restoration. The lower the elastic modulus of inlays, the lower is the stress concentration at the bonding interfaces.

Color stability of ceramic laminate veneers cemented with light-polymerizing and dual-polymerizing luting agent: A split-mouth randomized clinical trial.

STATEMENT OF PROBLEM: The color stability of luting agents influences the esthetics of ceramic laminate veneers. Clinical studies that have evaluated the color changes of veneers cemented to enamel with light- and dual-polymerizing resin cement are lacking. PURPOSE: The purpose of this split-mouth randomized clinical trial was to evaluate the color change and marginal discoloration of dual- and light-polymerizing cement used for cementation of ceramic laminate veneers. MATERIAL AND METHODS: In 10 participants, 0.3-mm-thick ceramic laminate veneers were cemented on the buccal surface of the second premolars without tooth preparation. A randomized application of light-polymerized cement was used on one side and a dual-polymerized cement on the contralateral side. The operator and participants were blinded to the activation mode. Color was evaluated by a blinded evaluator with a spectrophotometer at 24 hours and at 2, 6, 12, and 24 months after cementation. The CIELab (ΔE*ab) and CIEDE2000 (ΔE*00) formulas were used to quantify color alteration, and Δa*, Δb*, and ΔL* were calculated between the first and subsequent measurements. US Public Health Service guidelines were used to evaluate the marginal discoloration. RESULTS: Wilcoxon tests did not show a statistical difference in ΔE*ab and ΔE*00 between the groups (P>.05). At 24 months, the median ΔE*ab was 2.31 (interquartile ranges [IQR]: 3.34) for the light-polymerizing mode and 1.57 (IQR: 0.41) for the dual-polymerizing mode, while the median ΔE*00 was 1.65 for the light-polymerizing mode (IQR: 2.34) and 1.18 for the dual-polymerizing mode (IQR: 0.25). The thresholds for clinically acceptable color changes ΔE*ab>3.46 and ΔE*00>2.25 were found for both curing modes. Marginal discoloration was observed from the 2-year assessment. CONCLUSIONS: The color stability of ceramic laminate veneers was similar for both of the polymerizing modes for all evaluated periods. Marginal discoloration increased over a 2-year period for both the light- and the dual-polymerizing modes.

Zirconia-Reinforced Lithium Silicate Ceramic - A 2-Year Follow-up of a Clinical Experience with Anterior Crowns.

The aim of this manuscript is to describe 2-year follow-up of a clinical experience with a zirconia-reinforced lithium silicate ceramic for an anterior rehabilitation with single metal-free crowns. The maxillary-central incisor teeth crowns were made by zirconium-reinforced lithium silicate and covered with porcelain were obtained with a digital impression with the intra-oral scanner of the CEREC system as a basis for virtual design, as well as a laminate for the left lateral maxillary incisor, based on a "double scanning" technique. Lithium silicate material seems to be a safe and satisfactory alternative for anterior crowns' rehabilitation.

Effect of Jig Design and Assessment of Stress Distribution in Testing Metal-Ceramic Adhesion.

PURPOSE: In testing adhesion using shear bond test, a combination of shear and tensile forces occur at the interface, resulting in complex stresses. The jig designs used for this kind of test show variations in published studies, complicating direct comparison between studies. This study evaluated the effect of different jig designs on metal-ceramic bond strength and assessed the stress distribution at the interface using finite element analysis (FEA). MATERIALS AND METHODS: Metal-ceramic (Metal: Ni-Cr, Wiron 99, Bego; Ceramic: Vita Omega 900, Vita) specimens (N = 36) (diameter: 4 mm, veneer thickness: 4 mm; base diameter: 5 mm, thickness: 1 mm) were fabricated and randomly divided into three groups (n = 12 per group) to be tested using one of the following jig designs: (a) chisel (CH) (ISO 11405), (b) steel strip (SS), (c) piston (PI). Metal-ceramic interfaces were loaded under shear until debonding in a universal testing machine (0.5 mm/min). Failure types were evaluated using scanning electron microscopy (SEM). FEA was used to study the stress distribution using different jigs. Metal-ceramic bond strength data (MPa) were analyzed using ANOVA and Tukey's tests (α = 0.05). RESULTS: The jig type significantly affected the bond results (p = 0.0001). PI type of jig presented the highest results (MPa) (p < 0.05) (58.2 ± 14.8), followed by CH (38.7 ± 7.6) and SS jig type (23.3 ± 4.2) (p < 0.05). Failure types were exclusively a combination of cohesive failure in the opaque ceramic and adhesive interface failure. FEA analysis indicated that the SS jig presented slightly more stress formation than with the CH jig. The PI jig presented small stress concentration with more homogeneous force distribution compared to the CH jig where the stress concentrated in the area where the force was applied. CONCLUSION: Metal-ceramic bond strength was affected by the jig design. Accordingly, the results of in vitro studies on metal-ceramic adhesion should be evaluated with caution. CLINICAL SIGNIFICANCE: When adhesion of ceramic materials to metals is evaluated in in vitro studies, it should be noted that the loading jig type affects the results. Clinical observations should report on the location and type of ceramic fractures in metal-ceramic reconstructions so that the most relevant test method can be identified.

Fracture of Zirconia Abutment with Metallic Insertion on Anterior Single Titanium Implant with Internal Hexagon: Retrieval Analysis of a Failure.

This case report presents a retrieval analysis of a screw-retained one-piece restoration with the veneering ceramic fired directly onto the zirconia abutment that fractured during insertion. A patient who experienced root fracture of a maxillary left central incisor received a titanium implant on the same day as extraction. After delayed implant loading, a two-piece zirconia abutment with metallic insertion was customized. Upon installation, a horizontal fracture of the crown just above the metallic portion was detected. The retrieval analysis of a fractured zirconia abutment showed crack formation and diffusion of glaze material that expanded the crack line during firing.

Effect of Thickness, Processing Technique and Cooling Rate Protocol on the µTBS of a Bilayer Ceramic System.

PURPOSE: To evaluate the influence of different processing techniques, ceramic thicknesses, and cooling rate protocols on the µTBS of a veneering ceramic to zirconia (Y-TZP). MATERIALS AND METHODS: Eighty Y-TZP ceramic blocks (VITA In-Ceram 2000) with dimensions of 10 x 7 x 5 mm were obtained. The blocks were sintered in a special furnace at 1500° for 2 h, wet ground, and divided into 8 groups according to the factors "processing technique" (P: pressed/veneering ceramic PM9; or V: layered/ veneering ceramic VM9), "thickness" (2 mm and 4 mm), and "cooling protocol" (S: slow [10°C/s]; F: fast [50°C/s]). The Y-TZP/veneering ceramic blocks were sectioned to produce non-trimmed bar specimens (bonded area: 1±0.1 mm2), which were submitted to 1200 thermal cycles (5°C and 55°C, 30-s dwell time) and stored for 1 week in distilled water (37°C) before microtensile testing in a universal test machine (EMIC, 1 mm/min). The data in MPa were analyzed statistically using three-way ANOVA and Tukey's test. RESULTS: ANOVA revealed that only the factor processing technique was significant (p=0.015), unlike the factors thickness (p=0.111) and cooling protocol (p=0.202). The majority of the failures were classified as adhesive. CONCLUSION: Layered application of a thin veneering ceramic using a fast cooling rate resulted in improved bonding between veneering ceramic and zirconia.