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PURPOSE: To investigate the microscopic structure and fracture toughness of two pressable glass-ceramics comprising GC Initial LiSi Press (LiSi) and IPS e.max Press (e.max) with different levels of translucency. MATERIALS AND METHODS: Four groups of LiSi and e.max with medium opacity and high translucency levels were examined. The crystal morphology of acid-etched specimens was observed under a scanning electron microscope (SEM). Six specimens in each group were fabricated in square shape (12 mm '12 mm ' 1.5 mm) to measure translucency parameters (TP) using a spectrophotometer. Ten bar-shaped specimens each group with dimension of 23 mm ' 2 mm ' 4 mm were determined the fracture toughness (KIc) by a surface crack in flexure (SCF) using a universal testing machine. One-way ANOVA and Scheffe post-hoc tests were used for statistical analysis. RESULTS: LiSi showed fine dense crystals 1 - 1.5 µm in size, while e.max showed long rod-shaped crystals 3 - 4 µm in size. The TP values of all specimens were coincided with their translucency levels.There was no statistical difference in the KIc between different translucency for both ceramics (p<0.05). However, the KIc of e.max was significantly higher than that of LiSi at both translucency levels. As a result of larger and longer crystals in e.max, it could provide better crack deviation mechanism to resist the fracture. CONCLUSION: Within the limitations of this study, the translucency levels of both lithium disilicate ceramics did not affect the fracture toughness of the materials. The fracture toughness of e.max was statistically higher than LiSi.

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This study investigated the influence of different surface treatments on unfiring or firing zirconia-reinforced lithium silicate (ZLS) glass-ceramics. Celtra Duo and IPS e.max CAD blocks were cut and process following manufacturer protocols. The specimen surface was treated with seven different protocols. Two ceramic blocks with the same surface treatment were bonded with luting agent and prepared for mini-interfacial fracture toughness tests (mini-iFT). The specimens were tested after 1-week storage. The data was statistically analyzed using two-way ANOVA and Dunnett's T3 comparison (α=0.05). The highest mini-iFT of both Celtra Duo unfired and fired was shown in the HF+S group, which was not significantly different from HF+S+UA. For IPS e.max CAD, the mini-iFT was higher in the groups treated with hydrofluoric acid. Additional adhesive after silane application did not significantly improve bonding effectiveness. Therefore, surface treatment with hydrofluoric acid and silane is recommended for both unfiring and firing ZLS glass ceramics.

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BACKGROUND/PURPOSE: The colonization of microorganisms onto denture bases is one common problem that can contribute to oral diseases. Herein, three food preservatives, including zinc oxide, potassium sorbate, and sodium metabisulfite were introduced as anti-microbial additives into a heat-polymerized poly(methyl methacrylate) (PMMA). MATERIALS AND METHODS: Relative microbial reductions of the modified PMMA resins against Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans were evaluated. The in vitro cytotoxicity of the materials was measured against mouse fibroblast L929 cells. A three-point flexural test was performed to determine a flexural strength and modulus properties of the materials. RESULTS: The incorporation of all preservative agents into the material diminished the microbial growth of three microbial species. The PMMA resin combined with sodium metabisulfite exhibited the greatest anti-microbial activity that reduced almost all bacterial cells and about 40% of C. albicans. All modified resins showed no significant cytotoxicity against L929 cells. The addition of food preservatives did not significantly alter the flexural strength of the PMMA resin (∼84-92 MPa). However, the flexural modulus of the PMMA incorporated with food preservatives (∼2,024-2,144 MPa) was significantly lower than the unmodified PMMA. CONCLUSION: Three food preservatives, especially sodium metabisulfite, could be applied as anti-microbial additives into the denture base resin. The PMMA incorporated with the additives did not show cytotoxicity. Although, the addition of the food preservatives altered the mechanical properties, the materials still provided acceptable flexural properties.

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PURPOSE: To evaluate the influence of cyclic loading on phase transformation of zirconia abutments and to compare the effectiveness of three different quantitative ageing assessment techniques. MATERIALS AND METHODS: Thirty two Y-TZP prostheses fabricated from two brands, InCoris ZI and Ceramill ZI, were cemented to titanium bases and equally divided into two subgroups (n=8): control group without any treatment and aged group with cyclic loading between 20 N and 98 N for 100,000 cycles at 4 Hz in distilled water at 37℃. The tetragonal-to-monoclinic phase transformation was assessed by (i) conventional x-ray diffraction (XRD), (ii) micro x-ray diffraction (µXRD), and (iii) micro-Raman spectroscopy. The monoclinic-phase fractions (M%) were compared by two-way ANOVA. RESULTS: InCoris Zi presented significantly higher M% than Ceramill Zi in both control and aged groups (P<.001). Both materials exhibited significant phase transformation with monoclinicphase of 1 to 3% more in aged groups than controls for all thre e assessment techniques. The comparable M% was quantified by both µXRD and XRD. The highest M% was assessed with micro-Raman. CONCLUSION: Cyclic loading produced significant phase transformation in tested Y-TZP prostheses. The micro-Raman spectroscopy could be used as an alternative to XRD and µXRD.

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The mica-based glass-ceramics were prepared in the SiO2-Al2O3-MgO-MgF2-SrCO3-CaCO3-CaF2-P2O5 glass system. There were four mica-based glass-ceramics produced in this study according to the pigment added (CeO2 or Pr-ZrSiO4/Fe-ZrSiO4) and crystallization time (5-35 min). Four dental glass-ceramics, which were leucite-based, lithium disilicate-based and two zirconia reinforced lithium silicate ceramics, were also tested. The phase identification of mica-based glass-ceramics was performed using an X-ray diffractometer. The fracture toughness (KIC) was determined using the fractographic analysis approach. The one-way ANOVA was used to analyze the significant differences among the obtained KIC values at a=0.05. The results from the phase analysis showed that the mica glassceramics consisted of calcium-mica, fluorapatite and strontiumapatite. The KIC of mica-based glass-ceramics ranged between 1.36 to 1.53 MPa•m1/2 which were superior to only that of a leucite-based glass-ceramic. The shade and translucency of mica-based glassceramics appeared to be acceptable for dental application when compared with other dental glass-ceramics.

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PURPOSE: The objective of this study was to investigate the effect of surface treatments on microtensile bond strengths (MTBSs) of two types of indirect resin composites bonded to a conventional direct resin composite. MATERIALS AND METHODS: Indirect resin composite blocks of Ceramage and SR Nexco were prepared in a plastic mold having a dimension of 10 × 10 × 4 mm. These composite blocks were divided into three groups according to their surface treatments: Group1: Sandblast (SB); Group2: Sandblast and ultrasonically clean (SB+UL); Group3: Sandblast plus silane (SB+SI). After bonding with direct resin composite, indirect-direct resin composite blocks were kept in distilled water for 24 hours at 37℃ and cut into microbars with the dimension of 1 × 1 × 8 mm. Microbar specimens (n = 40 per group) were loaded using a universal testing machine. Failure modes and compositions were evaluated by SEM. The statistical analyses of MTBS were performed by two-way ANOVA and Dunnett's test at α = .05. RESULTS: Surface treatments and brands had effects on the MTBS without an interaction between these two factors. For SR Nexco, the MTBSs of SB and SB+SI group were significantly higher than that of SB+UL. For Ceramage, the MTBSs of SB and SB+SI were significantly higher than that of SB+UL. The mean MTBS of the Ceramage specimens was significantly higher than that of SR Nexco for all surface treatments. CONCLUSION: Sandblasting with or without silane application could improve the bond strengths of repaired indirect resin composites to a conventional direct resin composite.

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PURPOSE: The objective of this study was to determine the effect of thickness and brands on the contrast ratio of six zirconia dental ceramics. MATERIALS AND METHODS: Six brands of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics (ZENO® Translucent, Lava™ Plus High Translucency, inCoris TZI, Cercon® Base, Zeno®Zr, Lava™) were used in this study. Disc-shaped specimens with 15 mm diameter were prepared in five thickness levels (0.3, 0.6, 0.9, 1.2, 1.5 mm, n = 10) for each brand. The contrast ratio (CR = Y(b) /Y(w) ) was determined from the luminous reflectance over black (Y(b) ) and white (Y(w) ) backgrounds using a spectrophotometer. Two-way ANOVA was performed to determine the significant differences among thicknesses and brands at α = 0.05. RESULTS: The mean contrast ratio values of six zirconia ceramics were significantly different and influenced by both the thickness and brand. The mean contrast ratio values of all groups increased as their thickness increased from 0.3 to 1.5 mm. inCoris TZI was the most translucent, with the lowest contrast ratio at a thickness of 0.6 to 1.5 mm. The mean contrast ratio values of Lava™ and Lava™ Plus were significantly lower than those of Zeno®Zr, ZENO® Translucent, and Cercon® Base. CONCLUSIONS: The thickness and brands had significant effects on the contrast ratio of six zirconia dental ceramics. The mean contrast ratio values of inCoris TZI, Lava™, and Lava™ Plus High Translucency were significantly lower than those of Cercon® Base, Zeno®, and ZENO® Translucent at all thicknesses.

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PURPOSE: The objective of this study was to determine the effect of the color of a background substructure on the overall color of a zirconia-based all-ceramic crown. MATERIALS AND METHODS: Twenty one posterior zirconia crowns were made for twenty subjects. Seven premolar crowns and six molar crowns were cemented onto abutments with metal post and core in the first and second group. In the third group, eight molar crowns were cemented onto abutments with a prefabricated post and composite core build-up. The color measurements of all-ceramic crowns were made before try-in, before and after cementation. A repeated measure ANOVA was used for a statistical analysis of a color change of all-ceramic crowns at α=.05. Twenty four zirconia specimens, with different core thicknesses (0.4-1 mm) were also prepared to obtain the contrast ratio of zirconia materials after veneering. RESULTS: L(*) , a(*) , and b(*) values of all-ceramic crowns cemented either on a metal cast post and core or on a prefabricated post did not show significant changes (P>.05). However, the slight color changes of zirconia crowns were detected and represented by ΔE(*) ab values, ranging from 1.2 to 3.1. The contrast ratios of zirconia specimens were 0.92-0.95 after veneering. CONCLUSION: No significant differences were observed between the L(*) , a(*) , and b(*) values of zirconia crowns cemented either on a metal cast post and core or a prefabricated post and composite core. However, the color of a background substructure could affect the overall color of posterior zirconia restorations with clinically recommended core thickness according to ΔE(*) ab values.

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PURPOSE: The objective of this study was to compare the fracture toughness (KIc) obtained from the single edge V-notched beam (SEVNB) and the fractographic analysis (FTA) of a glass-infiltrated and a zirconia ceramic. MATERIALS AND METHODS: For each material, ten bar-shaped specimens were prepared for the SEVNB method (3 mm × 4 mm × 25 mm) and the FTA method (2 mm × 4 mm × 25 mm). The starter V-notch was prepared as the fracture initiating flaw for the SEVNB method. A Vickers indentation load of 49 N was used to create a controlled surface flaw on each FTA specimen. All specimens were loaded to fracture using a universal testing machine at a crosshead speed of 0.5-1 mm/min. The independent-samples t-test was used for the statistical analysis of the KIc values at α=0.05. RESULTS: The mean KIc of zirconia ceramic obtained from SEVNB method (5.4 ± 1.6 MPa·m(1/2)) was comparable to that obtained from FTA method (6.3 ± 1.6 MPa·m(1/2)). The mean KIc of glass-infiltrated ceramic obtained from SEVNB method (4.1 ± 0.6 MPa·m(1/2)) was significantly lower than that obtained from FTA method (5.1 ± 0.7 MPa·m(1/2)). CONCLUSION: The mean KIc of the glass-infiltrated and zirconia ceramics obtained from the SEVNB method were lower than those obtained from FTA method even they were not significantly different for the zirconia material. The differences in the KIc values could be a result of the differences in the characteristics of fracture initiating flaws of these two methods.

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OBJECTIVES: The objectives of this study were to characterize the clinical performance and wear characteristics of lithia-disilicate-based ceramic crowns. METHODS: Thirty posterior crowns were made using the heat-pressing technique and lithia-disilicate-based core ceramic. Subjects were recalled annually. The quality of crowns and adjacent gingival tissues were examined using nine criteria for acceptability. All crowns were examined and ranked from 4 (Excellent) to 1 (Unacceptable) for each criterion. Impressions were made for replica models at each appointment. Wear characteristics of dental ceramic and enamel were obtained by comparing the surface of the original model with the follow-up model using a laser scanner. RESULTS: Twenty-nine subjects returned for the 1-year recall examination. The maximum clenching force for the 30 subjects ranged from 125 to 815 N. All clinical criteria were ranked good to excellent at the 1-year recall exam and no fractures were observed. The mean occlusal wear volumes for the ceramic crowns after 1 year were 0.19 (0.065)mm3 for premolar sites and 0.34 (0.08)mm3 for molar sites. The mean occlusal wear volumes of opposing enamel after 1 year were 0.21 (0.06)mm3 for premolar teeth and 0.50 (0.22)mm3 for molar teeth. The mean occlusal wear volume of ceramic molar crowns was significantly lower than the volume of enamel wear of the opposing teeth (p

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