Surface characterization of lithium disilicate ceramic after nonthermal plasma treatment Aljomar José Vechiato Filho, DDS,a Daniela Micheline dos Santos, DDS, DMD, PhD,b Marcelo Coelho Goiato, DDS, DMD, PhD,c Rodrigo Antonio de Medeiros, DDS,d Amália Moreno, DDS, DMD,e Liliane da Rocha Bonatto, DDS,f and Elidiane Cipriano Rangel, PhDg Araçatuba Dental School, São Paulo State University (UNESP), Araçatuba, São Paulo, Brazil; Engineering College, São Paulo State University (UNESP), Sorocaba, São Paulo, Brazil Statement of problem. Surface transformation with nonthermal plasma may be a suitable treatment for dental ceramics, because it does not affect the physical properties of the ceramic material. Purpose. The purpose of this study was to characterize the chemical composition of lithium disilicate ceramic and evaluate the surface of this material after nonthermal plasma treatment. Material and methods. A total of 21 specimens of lithium disilicate (10 mm in diameter and 3 mm thick) were fabricated and randomly divided into 3 groups (n¼7) according to surface treatment. The control group was not subjected to any treatment except surface polishing with abrasive paper. In the hydrofluoric acid group, the specimens were subjected to hydrofluoric acid gel before silane application. Specimens in the nonthermal plasma group were subjected to the nonthermal plasma treatment. The contact angle was measured to calculate surface energy. In addition, superficial roughness was measured and was examined with scanning electron microscopy, and the chemical composition was characterized with energy-dispersive spectroscopy analysis. The results were analyzed with ANOVA and the Tukey honestly significant difference test (a¼.05). Results. The water contact angle was decreased to 0 degrees after nonthermal plasma treatment. No significant difference in surface roughness was observed between the control and nonthermal plasma groups. Scanning electron microscopy and energy-dispersive spectroscopy images indicated higher amounts of oxygen (O) and silicon (Si) and a considerable reduction in carbon (C) in the specimens after nonthermal plasma treatment. Conclusions. Nonthermal plasma treatment can transform the characteristics of a ceramic surface without affecting its surface roughness. A reduction in C levels and an increase in O and Si levels were observed with the energy-dispersive spectroscopy analysis, indicating that the deposition of the thin silica film was efficient. (J Prosthet Dent 2014;-:---)
Clinical Implications Nonthermal plasma treatment may be useful in transforming the surface of lithium disilicate ceramic to increase the intimate contact of adhesive agents to its surface and, consequently, its ability to bond to luting resins, thus minimizing the etching procedure.
a
Graduate student, Graduate Program in Dentistry, Department of Dental Materials and Prosthodontics. Professor, Department of Dental Materials and Prosthodontics. c Professor, Department of Dental Materials and Prosthodontics. d Graduate student, Graduate Program in Dentistry, Department of Dental Materials and Prosthodontics. e Graduate student, Graduate Program in Dentistry, Department of Dental Materials and Prosthodontics. f Graduate student, Graduate Program in Dentistry, Department of Dental Materials and Prosthodontics. g Professor, Laboratory of Technological Plasmas. b
Vechiato Filho et al
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Volume Surface treatment with hydrofluoric acid (HF) gel is a well-established protocol for cementing glass ceramics that is supported by several studies.1,2 Some authors, however, advocate that HF be eliminated from the etching procedure3,4 because of its potential for crack formation5-7 and the production of insoluble silica-fluoride salts that might interfere with the adhesion of luting resins.8,9 This fact suggests the necessity of evaluating additional modifications and innovative strategies to maximize bonding properties.4,8,9 Nonthermal plasma (NTP) has been used as an alternative to HF for modifying the chemical behavior of a ceramic surface without damaging it because of its capacity to transform inert surfaces to chemically activated ones.10 NTP is in essence a gas that emits reactive electrons, ions, and free radicals when stimulated by glowdischarge. These emissions modify the surface of certain materials, physically or chemically, which improves their surface energy.10-14 This transformation may improve the union between the ceramic and the luting resin.10,11,15 Surface energy is measured by the contact angle of a liquid in contact with a substrate.10,16-18 Transformation of the ceramic surface can provide greater wettability, which is the first parameter to be analyzed when bonding protocols are evaluated.11,19,20 NTPs can be applied either by handheld units at atmospheric pressure11,13 or industrially in a vacuum.21 However, certain factors such as the distance between the handheld unit and the substrate surface can affect ion deposition.13 To control this parameter, industrial apparatus for NTP can be used. Hexamethyldisiloxane (HMDSO) is a monomer that is commonly used in these situations because it is safe, relatively inexpensive, and easy to obtain and manipulate.22-24 However, the thin film of organosiloxane created is hydrophobic,25,26 so the association of this monomer with other gases, such as Ar, O2, N2, and SO2, can transform the hydrophobic film to a hydrophilic layer of silica.3,11,24,27-29 In spite of the
advantages of HMDSO, little is known of this treatment,21,22 and the authors have not found any studies evaluating its effect on lithium disilicate ceramics. The present study, therefore, evaluated the surface energy of lithium disilicate ceramic after NTP treatment and characterized surface roughness with a profilometer and surface chemical composition with energy-dispersive spectroscopy (EDS) associated with scanning electron microscopy (SEM). The null hypothesis was that NTP treatment would not increase the surface energy, reduce the contact angle, increase the levels of O and Si, or decrease the carbon level of the ceramic surface and that the surface roughness would be unaffected.
MATERIAL AND METHODS Specimen preparation A total of 21 specimens of lithium disilicate (IPS e.max Press LT; Ivoclar Vivadent) were fabricated with the lost wax technique from disks (10 mm in diameter and 3 mm thick) of autopolymerizing acrylic resin (DuraLay; Polidental Ltda). For mechanical tests, 18 specimens were divided randomly into 3 groups of 6 each, and treatments were assigned accordingly by using the Research Randomizer website.30 Next, 1 specimen from each group was randomly selected for the SEM/EDS test. The sample size of 6 was determined by preliminary tests in which that number of specimens yielded adequate power (large-effect size according to the Cohen d effect-size statistics). At a¼.05, this sample size reached a power of 1 (surface roughness) and .996 (total surface energy) for detecting statistically significant differences. The power analysis was performed to determine the number of specimens required in each test group so that it could be ascertained whether statistical differences existed among groups; effect sizes were also analyzed to measure the magnitude of a treatment effect.31 The ceramic specimens were sequentially polished in an automatic
The Journal of Prosthetic Dentistry
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Issue
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polishing machine (Politriz Universal APL-4; Arotec) with 320-, 400-, 600-, and 800-grit abrasive papers (CarbiMet 2; Buehler) with constant water irrigation.32 Then the disks were washed in deionized water for 1 minute, in 99.3% ethyl alcohol for 5 minutes, and again in deionized water for 1 minute to remove the smear layer on the specimen surface. The control group was not subjected to any surface treatment. The NTP group was subjected to NTP treatment with HMDSO monomer (HMDSO; Sigma-Aldrich) associated with argon (Ar) gas (argon; White Martins) before the deposition of O2 (oxygen; White Martins). For the HF group, only 10% HF (Condicionador de porcelanas; Dentsply Intl) was applied for 20 seconds, followed by rinsing in distilled water for 1 minute.33-37 Specimens were then dried with compressed air before silane was applied (Silano Coupling Agent; Dentsply Intl) for 2 minutes. After silane application, the specimens were placed in an oven, heated at 100 C for 1 minute, and washed with water at 80 C for 15 seconds.9
NTP treatment The NTP group was subjected to NTP treatment by using a custom-made instrument created from drawings by an engineer from the Technological Plasma Laboratory (LapTec; São Paulo State University Engineering College) to create a highly hydrophilic thin film on the ceramic surface. The application plasmas were prepared from mixtures of 85% HMDSO vapor and 15% Ar at a radio frequency of 13.56 MHz (50 W), then applied to the specimen holder (inferior electrode) while the superior electrode was grounded. System pressure was maintained at a constant 8 Pa. Previous studies have indicated that this methodology provides excellent adhesion to metallic surfaces and that the thin organosilicon film is physically stable. However, once these films became hydrophobic, postdeposition treatment with plasma was required to transform the thin organosilicon film into a highly hydrophilic silica layer.
Vechiato Filho et al
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2014
3 used for the SEM/EDS tests. The Ra, Rq, Rz, and Rt values were obtained by using a cutoff of 500 mm for 12 seconds. Three readings were taken: 1 at the center of the specimen and 2 parallel readings at right and left of center. Then the average was calculated. Initial results were obtained in angstroms and converted to nanometers (nm).
Immediately after the last deposition, HMDSO and Ar were stopped and O2 was admitted to the system at 1.3 Pa. The plasma was established with a radio frequency of 13.56 MHz (50 W) applied to the specimen holder while the superior positive electrode was grounded. The substrate temperature was 31 C. The low temperature throughout the treatment was necessary to preserve the ceramic’s physical properties (Fig. 1).
Analysis of surface energy Surface energy was calculated with a goniometer (Ramé-Hart 100-00; RaméHart Instrument Co) by using the sessile drop method. Six specimens of each experimental group were used. Ten readings were made for each specimen to measure the water contact angle (polar component), and another 10
Analysis of surface roughness
Roughness parameters (nm)
Surface roughness was measured with a profilometer (Dektak D150; Veeco). Six specimens of each experimental group were used for the roughness test, and another specimen was
1000 900 800 700 600 500 400 300 200 100 0
** Ra Rq Rt Rz
* *
Group Co
Group HF
Group NTP
1 Main surface roughness (Ra) of control, hydrofluoric acid, and nonthermal plasma groups. Asterisks (* and **) represent statistical differences (P
Clinical Implications Nonthermal plasma treatment may be useful in transforming the surface of lithium disilicate ceramic to increase the intimate contact of adhesive agents to its surface and, consequently, its ability to bond to luting resins, thus minimizing the etching procedure.
a
Graduate student, Graduate Program in Dentistry, Department of Dental Materials and Prosthodontics. Professor, Department of Dental Materials and Prosthodontics. c Professor, Department of Dental Materials and Prosthodontics. d Graduate student, Graduate Program in Dentistry, Department of Dental Materials and Prosthodontics. e Graduate student, Graduate Program in Dentistry, Department of Dental Materials and Prosthodontics. f Graduate student, Graduate Program in Dentistry, Department of Dental Materials and Prosthodontics. g Professor, Laboratory of Technological Plasmas. b
Vechiato Filho et al
2
Volume Surface treatment with hydrofluoric acid (HF) gel is a well-established protocol for cementing glass ceramics that is supported by several studies.1,2 Some authors, however, advocate that HF be eliminated from the etching procedure3,4 because of its potential for crack formation5-7 and the production of insoluble silica-fluoride salts that might interfere with the adhesion of luting resins.8,9 This fact suggests the necessity of evaluating additional modifications and innovative strategies to maximize bonding properties.4,8,9 Nonthermal plasma (NTP) has been used as an alternative to HF for modifying the chemical behavior of a ceramic surface without damaging it because of its capacity to transform inert surfaces to chemically activated ones.10 NTP is in essence a gas that emits reactive electrons, ions, and free radicals when stimulated by glowdischarge. These emissions modify the surface of certain materials, physically or chemically, which improves their surface energy.10-14 This transformation may improve the union between the ceramic and the luting resin.10,11,15 Surface energy is measured by the contact angle of a liquid in contact with a substrate.10,16-18 Transformation of the ceramic surface can provide greater wettability, which is the first parameter to be analyzed when bonding protocols are evaluated.11,19,20 NTPs can be applied either by handheld units at atmospheric pressure11,13 or industrially in a vacuum.21 However, certain factors such as the distance between the handheld unit and the substrate surface can affect ion deposition.13 To control this parameter, industrial apparatus for NTP can be used. Hexamethyldisiloxane (HMDSO) is a monomer that is commonly used in these situations because it is safe, relatively inexpensive, and easy to obtain and manipulate.22-24 However, the thin film of organosiloxane created is hydrophobic,25,26 so the association of this monomer with other gases, such as Ar, O2, N2, and SO2, can transform the hydrophobic film to a hydrophilic layer of silica.3,11,24,27-29 In spite of the
advantages of HMDSO, little is known of this treatment,21,22 and the authors have not found any studies evaluating its effect on lithium disilicate ceramics. The present study, therefore, evaluated the surface energy of lithium disilicate ceramic after NTP treatment and characterized surface roughness with a profilometer and surface chemical composition with energy-dispersive spectroscopy (EDS) associated with scanning electron microscopy (SEM). The null hypothesis was that NTP treatment would not increase the surface energy, reduce the contact angle, increase the levels of O and Si, or decrease the carbon level of the ceramic surface and that the surface roughness would be unaffected.
MATERIAL AND METHODS Specimen preparation A total of 21 specimens of lithium disilicate (IPS e.max Press LT; Ivoclar Vivadent) were fabricated with the lost wax technique from disks (10 mm in diameter and 3 mm thick) of autopolymerizing acrylic resin (DuraLay; Polidental Ltda). For mechanical tests, 18 specimens were divided randomly into 3 groups of 6 each, and treatments were assigned accordingly by using the Research Randomizer website.30 Next, 1 specimen from each group was randomly selected for the SEM/EDS test. The sample size of 6 was determined by preliminary tests in which that number of specimens yielded adequate power (large-effect size according to the Cohen d effect-size statistics). At a¼.05, this sample size reached a power of 1 (surface roughness) and .996 (total surface energy) for detecting statistically significant differences. The power analysis was performed to determine the number of specimens required in each test group so that it could be ascertained whether statistical differences existed among groups; effect sizes were also analyzed to measure the magnitude of a treatment effect.31 The ceramic specimens were sequentially polished in an automatic
The Journal of Prosthetic Dentistry
-
Issue
-
polishing machine (Politriz Universal APL-4; Arotec) with 320-, 400-, 600-, and 800-grit abrasive papers (CarbiMet 2; Buehler) with constant water irrigation.32 Then the disks were washed in deionized water for 1 minute, in 99.3% ethyl alcohol for 5 minutes, and again in deionized water for 1 minute to remove the smear layer on the specimen surface. The control group was not subjected to any surface treatment. The NTP group was subjected to NTP treatment with HMDSO monomer (HMDSO; Sigma-Aldrich) associated with argon (Ar) gas (argon; White Martins) before the deposition of O2 (oxygen; White Martins). For the HF group, only 10% HF (Condicionador de porcelanas; Dentsply Intl) was applied for 20 seconds, followed by rinsing in distilled water for 1 minute.33-37 Specimens were then dried with compressed air before silane was applied (Silano Coupling Agent; Dentsply Intl) for 2 minutes. After silane application, the specimens were placed in an oven, heated at 100 C for 1 minute, and washed with water at 80 C for 15 seconds.9
NTP treatment The NTP group was subjected to NTP treatment by using a custom-made instrument created from drawings by an engineer from the Technological Plasma Laboratory (LapTec; São Paulo State University Engineering College) to create a highly hydrophilic thin film on the ceramic surface. The application plasmas were prepared from mixtures of 85% HMDSO vapor and 15% Ar at a radio frequency of 13.56 MHz (50 W), then applied to the specimen holder (inferior electrode) while the superior electrode was grounded. System pressure was maintained at a constant 8 Pa. Previous studies have indicated that this methodology provides excellent adhesion to metallic surfaces and that the thin organosilicon film is physically stable. However, once these films became hydrophobic, postdeposition treatment with plasma was required to transform the thin organosilicon film into a highly hydrophilic silica layer.
Vechiato Filho et al
-
2014
3 used for the SEM/EDS tests. The Ra, Rq, Rz, and Rt values were obtained by using a cutoff of 500 mm for 12 seconds. Three readings were taken: 1 at the center of the specimen and 2 parallel readings at right and left of center. Then the average was calculated. Initial results were obtained in angstroms and converted to nanometers (nm).
Immediately after the last deposition, HMDSO and Ar were stopped and O2 was admitted to the system at 1.3 Pa. The plasma was established with a radio frequency of 13.56 MHz (50 W) applied to the specimen holder while the superior positive electrode was grounded. The substrate temperature was 31 C. The low temperature throughout the treatment was necessary to preserve the ceramic’s physical properties (Fig. 1).
Analysis of surface energy Surface energy was calculated with a goniometer (Ramé-Hart 100-00; RaméHart Instrument Co) by using the sessile drop method. Six specimens of each experimental group were used. Ten readings were made for each specimen to measure the water contact angle (polar component), and another 10
Analysis of surface roughness
Roughness parameters (nm)
Surface roughness was measured with a profilometer (Dektak D150; Veeco). Six specimens of each experimental group were used for the roughness test, and another specimen was
1000 900 800 700 600 500 400 300 200 100 0
** Ra Rq Rt Rz
* *
Group Co
Group HF
Group NTP
1 Main surface roughness (Ra) of control, hydrofluoric acid, and nonthermal plasma groups. Asterisks (* and **) represent statistical differences (P
