Effect of plasma treatment on zirconia adhesion properties

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Microhardness (GPa)

Superficial porosity (%)

VM7 C

VM7 G

VM7 L

VM7 C

VM7 G

5.3 (0.3)w

5.4 (0.3)w

5.4 (0.4)w

1.1 (0.3)X

1.5 (0.4)X

Microhardness (GPa)

16.5 (3.1)Y

Superficial porosity (%)

VM9 C

VM9 G

VM9 L

VM9 C

VM9 G

5.3 (0.3)B

5.6 (0.1)B

6.1 (0.4)A

1.3 (0.4)d

3.6 (1.0)e

Microhardness (GPa)

VM9 L 4.6 (2.6)e

Superficial porosity (%)

VM13 C

VM13 G

VM13 L

VM13 C

VM13 G

5.4 (0.4)b

5.7 (0.3)ab

5.8 (0.3)a

1.2 (0.4)x

1.37 (0.4)x

Conclusions: Diffractometry analysis suggested a slight increase in crystalline content for porcelain VM9 and VM13 after laser irradiation; however fracture toughness did not change. Depending on the studied porcelain the microhardness and the amount of pores increased after laser application. http://dx.doi.org/10.1016/j.dental.2012.07.087 81 Masking ability of ceramic materials used for fixed dental prostheses L.H. Silva 1,∗ , S.S. Favero 1 , E. Yoshimura 3 , P.F. Cesar 1

VM7 L

Lima 1 , M.M.

Pinto 2 , H.

1

University of São Paulo, Brazil University Nove de Julho, Brazil 3 University of ABC, Brazil 2

Objectives: To evaluate the influence of thickness and ceramic material on the masking ability (translucency parameter, TP) of ceramic specimens that simulate different prostheses configurations. Materials and methods: Four ceramic materials for fixed dental prostheses were used: two core materials (Y-TZP, YZ, and alumina polycrystal, AL) and their respective veneering porcelains (VM7 and VM9), all from Vita. Monolayers (n = 10) of YZ and AL were produced by sectioning pre-sintered blocks into plates with subsequent sintering to obtain specimens with 0.5, 1.0, 1.5, and 2.0 mm thicknesses (12 mm in length and width). Two bilayers were produced (n = 10): (a) 0.5-mm thick layer of core material with 0.5-mm thick porcelain and (b) 1.0-mm thick core layer veneered with 1.0-mm thick porcelain. Porcelain layer was applied using a silicone matrix. To simulate a bilayered restoration luted to a resin composite (RC) substrate, specimens with four layers (n = 10) were also produced by cementing the bilayer described in item (a) to a 1.0 mm thick RC plate. The resin cement used was All-Cem (FGM). All specimen surfaces were mirror polished (down to 1 ␮m finish) before testing. A spectrophotometer was used to measure L*/a*/b* coordinates over black and white backgrounds. Measurements were performed in diffuse reflectance (lambda range 400–700 nm/intervals of 10 nm). Fixed parameters were: illumination of CIE/D65

VM13 L 6.9 (4.0)y

(day light, 6500 K) and observer at 2◦ . TP was determined by: TP = [(Lb * − Lw *)2 + (ab * − aw *)2 + (bb * − bw *)2 ]1/2 , where subscripts b/w indicate background color (black/white). The clinically relevant threshold for TP was considered to be 3. The obtained data was submitted to one-way ANOVA and Tukey’s test (˛ = 0.05). Results: The TP values obtained showed that none of the evaluated specimen configurations could effectively mask the black background regardless of the thicknesses tested, as all TP values were above the clinically relevant threshold of 3. No significant difference was verified when the same thickness was considered for monolayer materials. Both AL + VM7 specimens with total thickness of 1.0 mm (TP = 10.4 ± 1.0) and 2.0 mm (TP = 4.8 ± 0.5) showed significantly better masking ability than YZ + VM9 specimens 1.0-mm thick (TP = 16.1 ± 0.8) and 2.0-mm thick (TP = 7.7 ± 0.8). Therefore, TP decreased with the increase in specimen thickness for the bilayers. Specimens with four layers resulted (YZ + VM9 + RC TP = 7.6 ± 0.6; AL + VM7 + RC TP = 5.2 ± 0.9) in similar TP values compared to bilayers with same thickness (2 mm). Conclusions: None of the specimen configurations tested showed an efficient masking ability (TP ≤ 3), regardless of thickness variation. However, TP values varied with specimen thickness. The 2 mm AL + VM7 materials showed the closest value to the clinically relevant threshold and therefore can be considered an efficient restoration configuration to mask dark substrates. The presence of the resin cement did not influence the final masking ability of the ceramic specimen. http://dx.doi.org/10.1016/j.dental.2012.07.088 82 Effect of plasma treatment on zirconia adhesion properties M. Silva ∗ , J.R.C. Queiroz, M. Massi, L. Nogueira Jr. University Estadual Paulista – UNESP, Brazil Objectives: This in vitro study evaluated the influence of different surface treatments on shear bond strength between a polycrystalline ceramic tetragonal zirconia stabilized with yttria (Y-TZP) and a resin cement.

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Materials and methods: Minimum number of blocks (1.5 cm × 1.5 cm) of a ceramic Y-TZP were prepared and synthesized according to the manufacturer’s recommendations, and sonically cleaned in distilled water for 10 min. According to the factors “surface treatment” and “presence of Si-based film”, the blocks were randomly divided into six groups: G1: polished; G2: polished film-coated, G3: blasting particles (110 ␮m) of alumina coated silica; G4: blasting particles (110 mM) of alumina-coated silica-coated film; G5: blasting particles (100 ␮m) of alumina and G6: sandblasting with alumina particles. The films were grown on the ceramic surface by chemical method using plasma deposition hexamethylsiloxane in vapor form. Cylinders (Ø2.4 mm × 4 mm thick) of a cement (Rely X U100 3M/ESPE) were prepared on the ceramic surface after the surface treatment (n = 10). The samples were submitted to shear bond strength in an universal testing machine (EMIC) at a speed of 1 mm/min. using a 50 kgf load cell. The data were subjected to two-factor ANOVA and Tukey test with acceptable variance of 0.05%. Results: The study revealed that the film had a negative influence on bond strength to the surface blasted with aluminum oxide and did not interfere with the results of other surface treatments. Conclusions: The surface treatment with plasma containing hexamethylsiloxane film in vapor form (HMDSO) did not produce better bond strength values by the method of shear type knife when compared to gold standard system blasting Rocatec (3M/ESPE). The thermal cycling diminished the bond strength values found in all treatments. http://dx.doi.org/10.1016/j.dental.2012.07.089 83 Edge chipping tests for veneered zirconia specimens: Finite element analysis C.B. Tanaka 1,∗ , J.B.C. Meira 1 , P.F. Cesar 1 , R.Y. Ballester 1 , G. Mendonc¸a 2 1

University of São Paulo, Brazil 2 University of Toronto, Canada

Objectives: The edge chipping fracture has been considered a practical and reliable test to evaluate chipping resistance and chipping toughness of dental ceramics. The aim of this study was to evaluate, by finite element analyses (FEA), the stress distribution of veneered zirconia specimens submitted to edge chipping test (ECT), simulating two different indenters: Rockwell (ECTR ) and Vickers (ECTV ). Materials and methods: 3D finite element models simulated bilayered bars (3.0 mm × 3.0 mm × 2.5 mm). Porcelain and zirconia (1.5 mm thickness each) were considered homogeneous, linear-elastic and isotropic. The ECTs were simulated by changing the vertical load (10 N) distances from the edge (six conditions: from 0.2 mm to 1.2 mm). For each distance, two models were created according to the indenter. To simulate ECTV , the force was applied in a single node, while the ECTR was simulated applying an equivalent pressure (1000 MPa) on the element free face (0.01 mm2 ). The nodes of the lower face of the zirconia layer were constrained in all degrees of freedom. The maximum and minimum principal stresses ( 1 and

Table 1 – Peak of  1 and  3 (MPa) for edge chipping simulations. Indenter

Edge distance (mm) 0.2

0.4

0.6

0.8

1.0

1.2

Vickers

 1 (MPa) 624.3 625.8 626.1 626.2 626.2 626.3  3 (MPa) 3125.0 3124.0 3124.6 3124.6 3124.6 3124.6

Rockwell

 1 (MPa)  3 (MPa)

75.0 783.0

68.8 782.6

67.8 782.5

67.9 782.5

68.0 782.5

68.0 782.5

 3 , respectively) peak and distribution were analyzed. The peaks of  1 and  3 represent the highest tensile and highest compressive stresses, respectively. Results: The FEA results showed that the highest compressive stress zone was located beneath the indenter, while the highest tensile was around this zone, regardless of the indenter type. However, for ECTR there was no tensile stress beneath the indenter, while for the ECTV the  1 at this region was relatively high. The  1 and  3 peaks from Vickers indenter (Table 1) were 4–8 times higher than those obtained with the Rockwell indenter. A higher stress peak indicates higher stress concentration, which would result in lower chipping resistance. Conclusions: The type of indenter influences the magnitude and distribution of  1 and  3 for ECT. The direct comparison between results from studies that used different indenters is not feasible. http://dx.doi.org/10.1016/j.dental.2012.07.090 84 Impedance spectroscopy analysis on anodization processes for CPTi grade 4 R.S. Williamson ∗ , M.D. Roach, J.A. Griggs Department of Biomedical Materials Sciences, UMMC, Jackson, MS, USA Objectives: Electrochemical impedance spectroscopy (EIS) is a tool used to analyze complex electrochemical systems through evaluation with equivalent circuit modeling. Impedance is a measurement of a circuit’s ability to resist electrical flow but also takes into account for frequency and out of phase signals (voltage and current). The purpose of this project was to evaluate the effect of oxide thickness and crystallinity on the surface oxide resistance of both anodized and non-anodized titanium. Materials and methods: The material used for this project was commercially pure titanium grade 4 (CPTi-4) sheet. An anodization process using a DC rectifier in 2 M sulfuric acid was completed at different voltage levels for six samples to produce varying oxide thicknesses (color) and crystallinity. One sample was cleaned only, leaving the natural forming oxide on the surface. X-ray diffraction was used to determine if any anatase and/or rutile peaks were present and JADE software was used to calculate the peak area. A Gamry ECM8 electrochemical multiplexer was used to run AC impedance with a sinusoidal excitation signal of 10 mV and a frequency range from 100 kHz to 500 ␮Hz. Bode and Nyquist plots were produced for each sample and equivalent circuit modeling was completed to determine the oxide integrity parameters.