Flexural strength and translucency of barium-silicate-filled resin nanoceramics for additive manufacturing.

OBJECTIVE: This in vitro study aimed to evaluate the flexural strength (FS) and translucency parameter (TP) of resin nanoceramics (RNCs) with barium silicate for additive manufacturing. MATERIALS AND METHODS: An RNC slurry was prepared by mixing a barium silicate filler and resin monomer. For the FS tests, specimens with three filler contents (0, 50, and 63 wt%) were designed according to ISO6872 for dental ceramics and ISO10477 for dental polymers. These specimens were then formed into discs with thicknesses of 1 and 2 mm for TP measurement. RESULTS: In the specimens prepared according to ISO6872, the FS increased significantly depending on the filler content. However, in the case of ISO10477, there was no significant difference between the FSs of the specimens with 0 and 50 wt% filler contents. The increase in thickness affected translucency, and the lowest translucency was obtained at a filler content of 63 wt%. The filler distribution was dense in the specimen with 63 wt% filler and uniform but relatively sparse in the specimen with 50 wt% filler. More voids were observed in the specimen with 63 wt% filler. The thickness and filler content of the specimen affected its TP. The TP of the specimen with 63 wt% filler was similar to that of human enamel. CONCLUSION: The FS was significantly higher at a filler content of 63 wt%. The lowest translucency was obtained at a filler content of 63 wt% for all tested thicknesses. CLINICAL SIGNIFICANCE: Increasing the filler content was advantageous for the mechanical properties of the RNCs. A high filler content led to low translucency in the RNCs. Therefore, the esthetics of human teeth can be reproduced if layering according to the filler content is performed in areas where esthetic characteristics are required.

Complete mouth rehabilitation in a patient with condylar fracture malunion: A clinical report.

Mandibular condyle fracture malunion and tooth loss can cause functional and esthetic problems. A patient with restricted mouth opening associated with muscle atrophy required prosthetic rehabilitation. Since the remaining teeth had a poor prognosis and the patient had difficulty adapting to the interim denture, complete mouth rehabilitation with implants was chosen. The implants were placed by using nerve lateralization and an autogenous bone graft. Prosthetic rehabilitation combines digital diagnosis and conventional prosthetic restorations. The definitive prosthesis was fabricated to ensure adequate oral hygiene and functional adaptation of the orofacial structures. Treatment resulted in stable masticatory function, occlusion, and esthetics and restored the function of the atrophied lips and restricted mouth opening.

Evaluation of shear bond strength based on substructure materials and ceramic veneering techniques.

PURPOSE: Bilayered restorations have both the strength of the substructure material and the esthetics of the veneer material; however, they should have appropriate bonding between the two materials. This study aimed to evaluate the shear bond strength (SBS) according to the substructure material and veneering technique used in bilayered restorations. MATERIALS AND METHODS: The experimental group was divided into four groups (n = 15 per group) based on the substructure materials (cobalt-chromium [Co-Cr] alloy and 3 mol% yttrium-stabilized tetragonal zirconia polycrystal [3Y-TZP]) and veneering techniques (pressing and layering). Veneering was performed with disk shape (diameter: 5 mm, height: 2 mm) on a substructure using each veneering technique. Shear stress was applied to the interface of the substructure and the veneering ceramic using a universal testing machine. The shear bond strength, according to the substructure and veneering technique, was analyzed using a two-way analysis of variance with a post-hoc Tukey's honestly significant difference test. The failure mode was observed, and the surface was analyzed using a scanning electron microscope and energy-dispersive spectroscopy. RESULTS: The shSBS of the Co-Cr alloy and 3Y-TZP substructure was not different (p > 0.05); however, the pressing technique showed a higher SBS than the layering technique (p < 0.05). The SBS did not differ depending on the veneering technique in the Co-Cr alloys (p > 0.05), whereas the SBS in the pressing technique was higher than that in the layering technique for 3Y-TZP (p < 0.05). In the layering technique, the Co-Cr alloy showed a higher SBS than 3Y-TZP (p < 0.05). In the failure mode, mixed failure occurred most frequently in all groups. Extensive elemental interdiffusion was observed through the opaque layer in the Co-Cr alloy, regardless of the veneering technique. In 3Y-TZP, a wider range of elemental interdiffusion was observed in the pressing technique than in the layering technique. CONCLUSIONS: In bilayered restorations with a 3Y-TZP substructure, the pressing technique yielded higher bonding strength than layering. Using the layering technique, 3Y-TZP showed a lower SBS than the Co-Cr alloy. In bilayered restorations using 3Y-TZP as a substructure, the veneering technique and thermal compatibility of the materials must be considered.

Fatigue resistance of anterior monolithic crowns produced from CAD-CAM materials: An in vitro study.

STATEMENT OF PROBLEM: Lithium disilicate and 5 mol% yttria partially stabilized zirconia (5Y-PSZ) are commonly used for anterior restorations. However, studies comparing the durability of 5Y-PSZ and lithium disilicates are sparse. PURPOSE: The purpose of this in vitro study was to investigate the fracture load of anterior monolithic crowns made of 2 lithium disilicates and a 5Y-PSZ under dynamic loading. MATERIAL AND METHODS: Titanium abutments of the maxillary incisors were prepared (N=48, 8 for each group). Monolithic anterior crowns were made from the lithium disilicates (e.max CAD, Rosetta SM) and 5Y-PSZ (Katana UTML). After cementation, the specimens were stored in water for 24 hours and then thermocycled 10 000 times. Dynamic loading (70 N, 200 000 cycles, 1 Hz) was applied to half the specimens. The fracture load was measured by using a universal testing machine. The fracture patterns were analyzed and fractography applied. Two-way ANOVA and the Fisher exact test were used for statistical analysis (α=.05). RESULTS: The material and dynamic loading affected the fracture load of the anterior monolithic crowns (P<.05). However, there was no interaction between the material and the dynamic loading (P=.079). Both lithium disilicates had higher fracture loads than 5Y-PSZ (P<.05). The fracture load of each specimen was reduced after dynamic loading (P<.05). Lithium disilicate showed marginal and bulk fractures, and 5Y-PSZ presented catastrophic fractures (P<.001). CONCLUSIONS: 5Y-PSZ materials with large grains and low flexural strength may be less resistant to fractures under dynamic loading than lithium disilicates.

Degree of conversion of light-polymerized composite resin in implant prosthesis screw access opening.

PURPOSE: The mechanical and physical properties of implant screw access opening deteriorate if composite resin is not polymerized properly. Therefore, this study aimed to analyze the effect of using composite resin in implant access opening on the degree of conversion (DC). MATERIALS AND METHODS: Two prosthetic materials (Co-Cr and zirconia), two types of composite resin (low and high viscosity), two light-cured resin depths (2 and 3 mm), and two polymerization methods (max-mode 10 s and mid-mode 20 s: 16 and 22 J/cm2 , respectively) were considered (n = 192). The DC of the polymerized composite resin was measured through Fourier-transform infrared spectroscopy. The top and bottom surfaces of the polymerized composite resin body were observed through scanning electron microscopy. Multiple linear regression analysis and analysis of variance were used to identify significant differences in DC (α = 0.05). RESULTS: The DC was lower when the low-viscosity composite resin (ß = -0.431), light-polymerized resin depth of 2 mm (ß = -0.430), zirconia prosthesis (ß = -0.191), and mid-mode polymerization method (ß = -0.164) were used. The resin type, depth of resin to be light-cured, prosthesis material, and polymerization method had an effect on the DC. CONCLUSIONS: Low-viscosity composite resin should be polymerized at a low irradiance and long polymerization time (such that the light-cured resin depth does not exceed 2 mm) to ensure proper composite resin polymerization in implant screw access opening.

Tensile bond strength of CAD-CAM all ceramic crowns before and after thermomechanical aging.

PURPOSE: The purpose of this in vitro study was to compare the tensile bond strength (TBS) of resin nanoceramics (RNC), zirconia, and lithium disilicate (LS2) restorations cemented to titanium abutments before and after thermomechanical aging. MATERIALS AND METHODS: Twelve specimens per group were fabricated to determine the TBS between a titanium abutment and four types of crown materials (2 RNCs, LS2, and translucent zirconia crowns for the maxillary molar). After milling, the abutments and crowns were cemented with resin cement after air-particle abrasion. In addition, thermomechanical aging (200,000 cycles, 50 N, 2 Hz) was applied to half of the specimens by using a mastication simulator. TBS was measured by using a universal testing machine. The interface between the crown and the cement was observed by using scanning electron microscopy (SEM). Two-way ANOVA was performed to analyze the effects of crown materials and thermomechanical aging. Failure-mode and interface analyses were also conducted. RESULTS: After thermomechanical aging, the TBS decreased in the LS2 specimens and increased in RNCs (p < 0.001). The ratio of mixed failure and debonding with the hole-sealing resin increased in the RNC group. SEM images showed the reduced gap between the crown and the resin cement after thermomechanical aging in the RNC group. CONCLUSIONS: Differences in TBS were affected by the crown materials after thermomechanical aging. After thermomechanical aging, the RNC crowns showed increased TBS, whereas LS2 and zirconia crowns exhibited decreased or similar TBS.

Correlation between occlusal contact area at various levels of interocclusal thicknesses and masticatory performance.

BACKGROUND: This study aimed to determine the correlation between occlusal contact area and masticatory performance using BiteEye® , a photo occlusal analysis device and the multiple sieve method. OBJECTIVES: To calculate the occlusal contact area at various levels of interocclusal thicknesses and to measure masticatory performance with peanuts as the test material. METHODS: Fifty-two adults (30 men and 22 women) were enrolled according to specific exclusion/inclusion criteria. The occlusal contact area was measured by obtaining the interocclusal record of the maximum intercuspal position (MIP) using silicone impression material. Occlusal contact area measurements were performed in the ranges of 0-149, 0-89, 0-59, 0-29 and 0-9 µm. Masticatory performance was measured by obtaining the median particle size (X 50 ) after converting the weight of comminuted peanuts into size using the multiple sieve method. Statistical analysis was performed at 95% significance level. RESULTS: Interocclusal thickness comparison revealed the highest correlation with X 50 in the 0-149 µm range. Stronger correlations between the occlusal contact area and X 50 were observed in cases of 20 strokes of mastication (r = -.451) than in cases of 10 strokes (r = -.383), in the posterior occlusal contact area (r = -.456) than in the full arch occlusal contact area (r = -.451) and the molar area (r = -.478) than in the premolar area (r = -.296). CONCLUSIONS: The larger the occlusal contact area, the higher the masticatory performance; this correlation was statistically significant. Regarding interocclusal thickness, the highest correlation between the occlusal contact area and masticatory performance was observed in the 0-149 µm range. CLINICAL TRIAL REGISTRATION NUMBER: GWNUDH IRB 2020-A001.

Effect of materials on axial displacement and internal discrepancy of cement-retained implant-supported prostheses.

STATEMENT OF PROBLEM: How axial displacement may be affected by the mechanical properties and internal discrepancy of a cement-retained implant-supported prosthesis is unclear. PURPOSE: The purpose of this in vitro study was to assess the difference in internal discrepancy and axial displacement according to the prosthesis material in cement-retained prostheses splinting nonparallel implants. MATERIAL AND METHODS: Computer-aided design and computer-aided manufacture (CAD-CAM) titanium abutments were fabricated for a vertically placed implant and a 15-degree tilted implant. Three types of prostheses, in zirconia, cobalt-chromium (Co-Cr) alloy, and polymethylmethacrylate resin (PMMA), were fabricated (n=10). The internal discrepancy between the CAD-CAM titanium abutment and the prosthesis was measured by using the replica technique. After luting with an interim cement, they were mounted in Type IV gypsum. The specimens were cyclic loaded, and axial displacement of the prosthesis was measured after 3, 10, 100, and 106 cycles. The internal discrepancy and cumulative axial displacement were assessed by using a 3-way analysis of variance and repeated measures analysis of variance (α=.05). RESULTS: The internal discrepancy of the prosthesis did not differ based on the prosthesis material (P=.869); however, it was significantly different based on the measurement location, with the occlusal discrepancy (224 ±29 µm) being greater than the axial discrepancy (21 ±10 µm) (P<.05). Implants with an angled placement exhibited less axial displacement than implants with vertical placement (P<.05). The PMMA prosthesis demonstrated significantly greater axial displacement than the zirconia or Co-Cr prostheses (P<.05), which were similar (P=.623). CONCLUSIONS: Prostheses made with high-elastic moduli materials exhibited less axial displacement than PMMA prostheses, even though the internal discrepancy was not different. Moreover, vertically placed implants presented a greater axial displacement of the prosthesis than implants with angled placement.

Effect of different ceramic materials and substructure designs on fracture resistance in anterior restorations.

STATEMENT OF PROBLEM: Materials have been developed to reduce the chipping of ceramic veneer and improve the esthetics of anterior ceramic veneered restorations. However, studies of the effects of material and substructure design on fracture resistance are sparse. PURPOSE: The purpose of this in vitro study was to investigate the fracture resistance of metal-ceramic (MC), zirconia-feldspathic porcelain (ZC), and zirconia-lithium disilicate (ZL) anterior restorations and evaluate the effect of material and substructure design. MATERIAL AND METHODS: After preparing and scanning artificial maxillary central incisor teeth, titanium abutments and restoration specimens (n=90) were fabricated. MC, ZC, and ZL materials were prepared with substructure designs A (two-third coverage of the palatal surface) and B (one-third coverage of the palatal surface). After cementation, the specimens were thermocycled (10 000 cycles, 5 and 55 °C). Fracture load measurements, failure mode analysis, energy dispersive X-ray spectroscopy (EDS), line scan analysis, fractography, finite element analysis (FEA), and Weibull analysis were performed. Two-way ANOVA was used to identify the effects of material and substructure design on fracture load. One-way ANOVA was used to identify significant differences of fracture load (α=.05). RESULTS: MC and ZL showed significantly higher fracture load than ZC (P<.05). MC_A showed a significantly higher fracture load than MC_B (P<.05). ZC_A exhibited the lowest Weibull modulus. FEA revealed that the maximum principal stress occurred near the loading area of the veneer. ZL displayed the lowest maximum principal stress among all the materials. CONCLUSIONS: ZL and MC_A exhibited more favorable fracture resistance. The substructure design of MC, with increased metal coverage of the palatal surface, improved fracture resistance significantly.

Connector design effects on the in vitro fracture resistance of 3-unit monolithic prostheses produced from 4 CAD-CAM materials.

STATEMENT OF PROBLEM: Studies that compared the fracture strength of monolithic lithium disilicate and 5-mol% yttria partially stabilized zirconia multiunit fixed dental prostheses are sparse. PURPOSE: As the connector is the weakest part of a fixed dental prosthesis, the purpose of this in vitro study was to investigate the effect of connector designs and material on the fracture strength of 3-unit monolithic fixed dental prostheses. MATERIAL AND METHODS: Resin-ceramic canine and premolar teeth (N=144) were prepared for fixed dental prosthesis abutments. Prostheses with 3 connector designs (width=height, widthheight) were made from 2 types of lithium disilicate (IPS e.max CAD and Amber Mill) and 5-mol% yttria partially stabilized zirconia (3M Lava Esthetic and Katana Zirconia UTML). Fracture strengths were measured after 200 000 cycles of dynamic loading of 50 N and thermocycling at 5 °C and 55 °C, and the fracture patterns were analyzed. Two-way analysis of variance and the Fisher exact test were used for statistical analysis (α=.05). RESULTS: The material and connector design affected the fracture strength of fixed dental prostheses (P<.05), and a significant interaction was found between the material and connector design (P<.05). The IPS e.max CAD material had significantly lower fracture strength than Amber Mill, 3M Lava Esthetic, or Katana Zirconia UTML (P<.05). Connector designs with a greater width versus height showed significantly lower fracture strengths than other designs (P<.05). CONCLUSIONS: The connector design of 3-unit fixed dental prostheses, particularly the connector height, may affect fracture strength depending on the prosthesis material.

A comparative study of the wear of dental alloys against monolithic zirconia.

STATEMENT OF PROBLEM: Materials used for dental restorations should cause wear similar to that of natural teeth. Studies on the wear of dental alloys against monolithic zirconia are lacking. PURPOSE: The purpose of this in vitro study was to compare the wear of Co-Cr, gold, and Ni-Cr alloys against monolithic zirconia of different surface roughness. MATERIAL AND METHODS: Cylindrical monolithic zirconia specimens were prepared by a sintering process. Sintered zirconia was then polished to prepare 30 zirconia substrate specimens with a smooth surface (Ra<0.1 µm) and 30 with a rough surface (3.5 µm

Effects of the Thickness Ratio of Zirconia-Lithium Disilicate Bilayered Ceramics on the Translucency and Flexural Strength.

PURPOSE: To determine the effects of the total thickness and core/veneer thickness ratio of bilayered ceramics on their three-point flexural strength and translucency. MATERIALS AND METHODS: Two groups of specimens were prepared with two different total thicknesses, 1.0 mm and 0.6 mm. These groups were divided into five and three subgroups with ten specimens each, respectively, having different core/veneer thickness ratios. Lithium disilicate was pressed on the zirconia surface using the "lost-wax technique." The translucency and three-point flexural strength were measured, and a one-way analysis of variance test (p < 0.05) was performed to determine whether the translucency and three-point flexural strength were affected by the total thickness and core/veneer thickness ratio of the specimens. RESULTS: For the same total thickness, translucency decreased with a increase in the zirconia core proportion (p < 0.001). For the same core/veneer ratio, the translucency decreased with an increase in the total thickness (p < 0.001). If the zirconia thickness was less than half of the total thickness, the bilayered ceramic specimens containing zirconia cores and monolithic lithium disilicate specimens exhibited a similar translucency. The three-point flexural strength increased with the increasing proportion of zirconia; however, it did not change significantly with the total thickness. However, for the same total thickness, the flexural strengths of the bilayered ceramics were higher than those of the monolithic specimens. CONCLUSIONS: At the same total thickness, increasing the zirconia core thickness decreased the translucency and increased the three-point flexural strength. Bilayered ceramic specimens with low zirconia ratios exhibited translucency similar to that of monolithic lithium disilicate ceramic but a higher flexural strength.

Impact of Intentional Overload on Joint Stability of Internal Implant-Abutment Connection System with Different Diameter.

PURPOSE: To evaluate the axial displacement of the implant-abutment assembly of different implant diameter after static and cyclic loading of overload condition. MATERIALS AND METHODS: An internal conical connection system with three diameters (Ø 4.0, 4.5, and 5.0) applying identical abutment dimension and the same abutment screw was evaluated. Axial displacement of abutment and reverse torque loss of abutment screw were evaluated under static and cyclic loading conditions. Static loading test groups were subjected to vertical static loading of 250, 400, 500, 600, 700, and 800 N consecutively. Cyclic loading test groups were subjected to 500 N cyclic loading to evaluate the effect of excessive masticatory loading. After abutment screw tightening for 30 Ncm, axial displacement was measured upon 1, 3, 10, and 1,000,000 cyclic loadings of 500 N. Repeated-measure ANOVA and 2-way ANOVA were used for statistical analysis (α = 0.05). RESULTS: The increasing magnitude of vertical load and thinner wall thickness of implant increased axial displacement of abutment and reverse torque loss of abutment screw (p < 0.05). Implants in the Ø 5.0 diameter group demonstrated significantly low axial displacement, and reverse torque loss after static loading than Ø 4.0 and Ø 4.5 diameter groups (p < 0.05). In the cyclic loading test, all diameter groups of implant showed significant axial displacement after 1 cycle of loading of 500 N (p < 0.05). There was no significant axial displacement after 3, 10, or 1,000,000 cycles of loading (p = 0.603). CONCLUSIONS: Implants with Ø 5.0 diameter demonstrated significantly low axial displacement and reverse torque loss after the cyclic and static loading of overload condition.

Displacement of Simulated Flabby Tissue by Different Tray Designs and Impression Materials.

PURPOSE: To compare the effect of 3 tray designs and 3 commonly used impression materials on the displacement of flabby tissue during maxillary edentulous impression by superimposition of 3D digital models. MATERIALS AND METHODS: Fifteen maxillary edentulous casts with simulated flabby tissue were fabricated by modifying a standard maxillary edentulous acrylic resin cast. Three types of impression trays were fabricated: trays with conventional relief, trays with additional relief, and trays with an open window. Three impression materials were tested: light-body polysulfide, light-body vinylpolysiloxane, and zinc oxide eugenol paste. For the analysis of tissue displacement during impression making, the test and control stone casts were scanned using a 3D laser scanner, and the 3D digital models were superimposed using metrology software. Statistical analyses were performed with an α = 0.05. RESULTS: Negative deviations were recorded at the areas of the alveolar crest, posterior part of flabby tissue, and middle of the palate. On the other hand, a positive deviation was recorded at the area of the anterior part of flabby tissue. A significant difference in the displacement of flabby tissue was found when using different tray designs (p < 0.0001). The tray with the open window showed significantly low tissue displacement at the flabby tissue region. Depending on sites, the amount of flabby tissue displacement showed different significances by the different impression materials used (anterior part: p < 0.0001; alveolar crest: p = 0.097; posterior part: p < 0.0001). Conventionally relieved trays showed significantly higher values of displacement at the anterior part of flabby tissue (p < 0.0001), while trays with open windows showed similar values of displacement at all measuring points, and no significant differences among different impression materials were found (p = 0.104). CONCLUSIONS: There were significant differences in the displacement of flabby tissue with different tray designs, especially with displacement occurring at the anterior and posterior parts of flabby tissue. Tray designs should be considered in order to make proper impressions when flabby tissue is present.

Effects of Lithium and Phosphorus on the Efficacy of a Liner for Increasing the Shear Bond Strength Between Lithium Disilicate and Zirconia.

PURPOSE: To evaluate the effect of the chemical formulation of liners on the shear bond strength (SBS) between lithium disilicate veneering ceramic and zirconia core. MATERIALS AND METHODS: Four experimental groups (n = 12) were designed according to liner composition: negative control group (lithium and phosphorus removed from the conventional liner), Li group (lithium added to the negative control group), P group (phosphorus added to the negative control group), and Li+P group as the positive control (conventional liner). After applying the liner, lithium disilicate was pressed on zirconia. Specimens were stored in distilled water (37°C, 24 h) before testing the SBS. To test the SBS, shear force was applied perpendicular to the lithium disilicate-zirconia interface. The differences in the SBS between the veneer lithium disilicate and zirconia substructure were evaluated with one-way ANOVA (significance level of 0.05). RESULTS: The presence or absence of lithium and phosphorus influenced the efficacy of the liner. The negative control and P groups showed mainly cohesive failures, and the Li group mainly showed mixed failures. Both adhesive and mixed failures were observed in the Li+P group. The groups including lithium showed significantly higher SBS than the negative control or Li+P group (p < 0.05). The group including phosphorus, which showed higher crystallinity, showed significantly lower SBS than the negative control and Li+P groups (p < 0.05). CONCLUSIONS: The differences in the composition of the liner can affect the wettability and reactivity, and as a result, the SBS was different.

Effect of silica-containing glass-ceramic liner treatment on zirconia coping retention.

STATEMENT OF PROBLEM: Zirconia prostheses show a high rate of retention loss, and more information is needed regarding the treatment of the intaglios of zirconia prostheses to improve the bond strength between zirconia and resin cement. PURPOSE: The purpose of this in vitro study was to evaluate the retention of titanium abutments and zirconia prostheses treated with silica-containing glass-ceramic liners. The effect of the abutment convergence angle on retention force was also examined. MATERIAL AND METHODS: Titanium abutments and zirconia copings (n=90) were fabricated with 3 different convergence angles (6, 12, and 24 degrees). Specimens were divided into 2 groups according to surface treatment: an airborne-particle-abraded control group and a group that was coated with a silica-containing glass-ceramic liner after airborne-particle abrasion (liner group). The thickness of the liner was measured, and the inner spacing of the zirconia coping was modified in the liner group. The coping was cemented, and the retention was evaluated with a tensile bond strength test by using a universal testing machine. Retention was analyzed by using a 2-way analysis of variance. Modes of failure were evaluated by examining the fracture surface. Elemental analysis of the interface was also performed. RESULTS: The liner group showed a significantly higher retention force for the zirconia prosthesis (P<.05). Regardless of surface treatment, the retention force at a convergence angle of 6 degrees was higher than that at 24 degrees (P<.05). The control group showed mostly adhesive type failures, whereas the liner group exhibited mostly mixed type failures. CONCLUSIONS: Silica-containing glass-ceramic liner treatment increased the retention compared with airborne-particle abrasion treatment alone. Tensile bond strength increased with decreasing abutment convergence angle.

Evaluation of the ceramic liner bonding effect between zirconia and lithium disilicate.

STATEMENT OF PROBLEM: Little information is available for the strength of bonding between zirconia and lithium disilicate as affected by surface pretreatment methods. PURPOSE: The purpose of this in vitro study was to investigate the shear bond strength (SBS) between zirconia core and lithium disilicate (LS2) veneered ceramic after surface pretreatments. MATERIAL AND METHODS: Fully sintered yttrium oxide partially stabilized tetragonal zirconia (Y-TZP) disk specimens were fabricated from zirconia ceramic materials. Specimens were divided into 4 groups with surface pretreatments applied (the as-received group, the liner group, the airborne-particle abrasion group, and the airborne-particle abrasion-plus-liner group). After pressing LS2 on a zirconia disk, shear force was applied perpendicular to the zirconia-LS2 interface. Data were analyzed using 2-way ANOVA and Tukey test (α=.05). For each group, the failure modes were measured by using optical microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction. RESULTS: Airborne-particle abrasion induced significantly lower interfacial strength between zirconia and lithium disilicate (P<.05). After airborne-particle abrasion of the surface, the increased monoclinic volume fraction and reduced coefficient of thermal expansion of zirconia may weaken the interfacial strength between zirconia and LS2. The liner treatment significantly improved the adhesion between zirconia core and veneering LS2 (P<.05). The SBS values decreased in the following order: liner group > airborne-particle abrasion-plus-liner group > airborne-particle abrasion group. The interfacial image of zirconia and LS2 showed a fusion of crystal structure between the 2 materials. Some components of the silica-containing glass-ceramic liner led to an increase in SBS as diffusion occurred on the zirconia surface. CONCLUSIONS: The bond strength between zirconia and veneering LS2 was significantly increased by application of silica-containing glass-ceramic liner but was decreased with airborne-particle abrasion.

In vitro evaluation of the polishing effect and optical properties of monolithic zirconia.

STATEMENT OF PROBLEM: The relationship between surface roughness and the optical characteristics of zirconia prostheses may be affected by the type of shaded block. PURPOSE: The purpose of this in vitro study was to investigate changes in surface roughness and brightness of monolithic zirconia blocks of different shades after polishing. MATERIAL AND METHODS: The surface roughness averages of 3 different kinds of shaded zirconia blocks (Zenostarof T0 [T0], Zenostar sun [Ts], and Zenostar sun chroma [Tsc]) were compared after surface polishing. Fifteen specimens of differing thicknesses were produced per block. (1 mm and 3 mm). Surface morphology and compositions were analyzed by using filed emission scanning electron microscopy (FE-SEM) and energy dispersive spectrometry. A 1-way ANOVA and the post hoc Scheffé test were performed (α=.05). The correlations between surface roughness and brightness were determined using the Pearson correlation analysis (α=.01). RESULTS: After phased polishing, Ts had the highest average roughness, followed by T0 and then Tsc. A statistically significant difference in roughness was observed between Ts and Tsc (P<.05). Ts exhibited multiple distinct layers in the FE-SEM image. Carbon was detected in the Ts specimens only. Brightness was highest in T0, followed by Ts and then Tsc. A positive correlation was observed between brightness and surface roughness for all specimens (P<.01). This correlation was stronger in the thicker specimens. CONCLUSIONS: The results of this study suggest that polishing affects monolithic zirconia differently depending on shade. The polishing of monolithic zirconia reduces both surface roughness and brightness. The optical properties of monolithic zirconia vary by thickness and can be opaque or translucent.

Evaluation of various polishing systems and the phase transformation of monolithic zirconia.

STATEMENT OF PROBLEM: Although a well-polished monolithic zirconia surface is essential, insufficient comparative studies on the constituents and efficacy of polishing systems have been conducted. PURPOSE: The purpose of this in vitro study was to analyze the abrasive constituents and compare the polishing effectiveness of 6 zirconia polishing systems, including their potential influence on the phase transformation of monolithic zirconia. MATERIAL AND METHODS: The compositions of 6 zirconia polishing systems were analyzed using energy dispersive spectroscopy (EDS). Sintered and high-speed ground monolithic zirconia specimens were used as control groups (n=14 specimens per group). Test groups (n=168) were pretreated identically to the control group and arbitrarily divided into 12 groups to examine 6 polishing systems for 2 polishing periods (60 or 120 seconds). The surfaces were characterized by a surface profiler and various analytic techniques, including x-ray diffraction (XRD) analysis. The data were analyzed using 2-way ANOVA and multiple comparisons and the Bonferroni method (α=.05). RESULTS: The abrasives were primarily composed of C, O, and Si. Diamond was identified as the main abrasive and SiC as the supplementary abrasive in the polishing systems. No significant differences were observed for the 60- or 120-second polishing times (P>.05). Four products had significantly lower surface roughness values than the other 2 (P<.001). The occlusal-adjustment-simulating pretreatment and polishing processes did not cause phase transformations in the zirconia specimens. CONCLUSIONS: The monolithic zirconia polishing systems contained diamond and SiC abrasives. All zirconia polishing systems showed clinically acceptable results, and 4 systems exhibited lower surface roughness. Phase transformation did not occur during polishing procedure.