Nd:YAG Laser Treatment of Bioglass-coated Zirconia Surface and Its Effect on Bond Strength and Phase Transformation

Fatemeh Soltaninejada / Azam Valianb / Maryam Moezizadehc / Mahdieh Khatirid / Hossein Razaghid / Hanieh Nojehdehiane

Purpose: To evaluate the morphological properties, phase transformation, and microshear bond strength of com- posite cement to bioglass-coated zirconia surfaces treated with Nd:YAG laser. Materials and Methods: Seventy-five zirconia disks were divided into five groups (n = 15). Group C received no sur- face treatment (control). Group S was subjected to sandblasting with 50-μm aluminum particles. Group B samples were coated with . Groups BL9 and BL5 received bioglass coating and laser irradiation with 9 J/cm2 and 5 J/cm2 energy density. Morphological assessment was done using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Zirconia phase transformation was assessed by XRD. Microhear bond strength testing was performed using a modified microtensile tester. The data were analyzed using the Welch test and the Games-Howell test (p < 0.05). Results: The sandblasted and bioglass-coated groups showed the highest bond strengths compared to other groups (p < 0.05). Group S showed the highest surface roughness and the highest frequency of cohesive failure. In all samples, the tetragonal phase decreased after surface treatment. Groups BL9 and BL5 showed some levels of tetragonal to cubic phase transformation. Conclusion: Bioglass coating of zirconia surfaces (using the slurry method) can increase its microshear bond strength comparable to that of sandblasting. Surface roughness of sandblasted zirconia was the highest among all methods. Irradiation of Nd:YAG laser on bioglass-coated zirconia surfaces is not effective and decreases its bond strength compared to sandblasting and bioglass coating. Increasing the Nd:YAG laser energy density cannot in- crease the surface roughness of bioglass-coated zirconia surfaces. Bioglass coating results in transformation of the tetragonal to the cubic phase. Keywords: Nd:YAG laser, bioglass, zirconia surface, bond strength, phase transformation.

J Adhes Dent 2018; 20: 379–387. Submitted for publication: 26.09.17; accepted for publication: 13.08.18 doi: 10.3290/j.jad.a41309

irconia is a crystalline oxide of zirconium with mechani- tetragonal phase, and the cubic phase.33 Yttrium-oxide te- Zcal properties very similar to those of metals and a color tragonal zirconia polycrystal (Y-TZP) has superior mechani- resembling that of natural teeth.39 It is an allotrope with cal properties and is the most widely studied zirconia com- three different crystalline structures depending on pressure pound.38,46 Transformation of one crystalline phase to and thermal conditions, namely, the monoclinic phase, the another depends on the stress applied to the zirconia sur-

a Postgraduate Student, Department of Endodontics, School of Dentistry, Shahid d Laser Engineer, Photonics and Quantum Technologies Research School, Beheshti University of Medical Sciences, Tehran, . Experimental design, per- NSTRI , Tehran, Iran. Performed laser application. formed the experiments in partial fulfillment of requirements for a degree, e Associate Professor, Dental Material Department, School of Dentistry, Shahid wrote the manuscript. Beheshti University of Medical Sciences, Tehran, Iran. Idea, hypothesis, exper- b Assistant Professor, Operative Dentistry Department, School of Dentistry, imental design, contributed to discussion. Shahid Beheshti University of Medical Sciences, Tehran, Iran. Contributed to discussion. c Professor, Operative Dentistry Department, School of Dentistry, Shahid Be- Correspondence: Hanieh Nojehdehian, Dental Material Department, School of heshti University of Medical Sciences, Tehran, Iran. Experimental design, con- Dentistry, Shahid Beheshti University of Medical Sciences, Velenjak, Tehran, tributed to discussion. Iran. Tel:+98-912-549-8634. e-mail: [email protected]

Vol 20, No 5, 2018 379 Soltaninejad et al face and causes volumetric changes in the crystalline struc- roughness and bond strength obtained by Nd:YAG laser ture at the site of load application. When stress is applied treatment compared to CO2 laser. to the zirconia surface, the energy released by crack forma- In a study on the effect of Nd:YAG laser on surface tion results in transformation of the tetragonal to the mono- roughness of zirconia and composite cement bond strength, clinic phase. This crystalline phase transformation causes sandblasting and glazing were compared. The highest sur- an expansion, which compensates for the crack; this prop- face roughness and bond strength were obtained by short erty is referred to as stress-induced transformation.33 This pulse Nd:YAG laser.46 Akyil et al1 concluded that Nd:YAG is a unique property of Y-TZP , explaining their su- laser can only increase the composite cement bond perior mechanical properties and thus the term “ strength when applied along with particle abrasion. Kirmali steel”.22 et al23 recommended the application of laser along with Despite all mechanical superiorities, the major drawback sandblasting. The problem with regard to Nd:YAG laser ap- of zirconia is its weak bond to different synthetic and non- plication is the destructive changes it causes on the zirco- synthetic substrates due to its neutral state. Thus, it can- nia surface. SEM analyses after laser treatment revealed not provide adequate bond strength for many clinical appli- small interlaced cracks. These cracks are created due to cations following conventional cementation techniques.7 An stresses caused by uncontrolled thermal changes during ideal method to achieve a long-term bond between zirconia laser treatment. They can induce tetragonal to monoclinic ceramic and tooth structure has yet to be found.22 phase transformation.47 Lee et al27 evaluated the effect of Several studies have evaluated the strength and durabil- Nd:YAG laser on a type of bioglass and its efficacy for treat- ity of different bonding protocols. Sandblasting, ie, air abra- ment of dentin hypersensitivity, and found that Nd:YAG sion, is a commonly used technique to enhance the ceramic laser irradiation at 160 mJ, 30 Hz/pulse and 330mJ, 30 bond to substrates.51,52 Air abrasion with aluminum oxide Hz/pulse increased the temperature of bioglass to approxi- particles is conventionally used to eliminate the superficial mately 600°C and no phase transformation occurred follow- contaminated layers to increase micromechanical retention ing its application. Thus, application of Nd:YAG laser im- between composite cement and the restoration.19,48 proved the properties of bioglass.27 Considering the Silanes can effectively increase the bond strength of sil- importance of this topic and diversity of the current meth- ica-based materials like . However, a silane cou- ods as well as the lack of confirmed superiority of any par- pling agent alone is not effective for non-silica-based resto- ticular method, this study sought to assess the effect of rations such as zirconia; these restorations require surface bioglass coating of zirconia (with thermal properties compat- treatment before bonding.29 ible with those of zirconia) with and without laser irradiation Hydrofluoric (HF) acid reacts with silica-containing on the bond strength of composite cement to zirconia. matrix to form hexafluorosilicate. This glass matrix is selec- The hypothesis of this study was that Nd:YAG laser treat- tively removed, exposing the crystalline structure to acid. As ment of bioglass-coated zirconia surfaces would improve a result, the ceramic surface becomes rough and irregular, the bond strength but possibly cause unwanted phase enabling mechanical retention of the ceramic surface.11 transformation. This rough surface provides higher surface energy for bond- ing to silane. In other words, application of a silane cou- pling agent on the etched ceramic surface increases the MATERIALS AND METHODS bond strength between composite and ceramic.16 Zirconia coating with and glass ceramics Ceramic Pieces has been suggested to enhance mechanical properties and Seventy-five zirconia disks were fabricated of Y-TZP zirconia achieve high bond strength.18 Among bioactive , bio- blocks (Zirkonzahn, Steger; Ahrntal, Italy) measuring 7 x 2 x glass 45S5 is known as the gold standard.20 Hench and 10 mm. The bonding surface was polished using silicon car- Paschall21 first introduced bioglass 45S5, with the chemi- bide abrasive papers (300-, 400-, and 600-grit) and sin- cal composition of 6 wt% P2O5, 24.5 wt% CaO, 24.5 wt% tered according to the manufacturer’s instructions. Prior to 21 Na2O, and 45 wt% SiO2. any surface treatment, all disks were cleaned in an ultra- Lasers have several applications in dentistry and are sonic bath containing 96% ethanol, followed by drying. used to enhance the bonding of dental materials to tooth structure. Laser has been used to modify and improve the Surface Treatments surface of dental materials,36 glaze ceramic surfaces,10 The samples were randomly divided into five groups (n = 15). extract fillings,37 and etch fillings and ceramic surfaces.32 y Group C: Fifteen control samples received no surface Nd:YAG lasers are a group of solid-state lasers widely used treatment or laser irradiation. in dentistry.43 Nd:YAG laser irradiation can provide a suit- y Group S: Fifteen disks in this group were sandblasted able ceramic surface to enhance the composite bond be- with 50-μm aluminum oxide particles (True etch, Ortho cause it increases the surface roughness by ablation and Technology; Tampa, FL, USA) with 4 kg/cm2 pressure at induction of random crystallization.40,41 Among three effec- a 10-mm distance for 15 s by a micro-etcher (Danville tive lasers, ie, Er:YAG, CO2, and Nd:YAG, the highest sur- Engineering; San Ramon, CA, USA) and washed in an face roughness of zirconia was noted following the use of ultrasonic bath containing 96% ethanol for 10 min in Nd:YAG laser.2 Paranhos et al38 reported higher surface order to remove loose particles on the zirconia surface.

380 The Journal of Adhesive Dentistry Soltaninejad et al y Group B: A bioglass coating was prepared as a slurry of Table 1 The mean surface roughness values in the five 500 μg bioglass, 1 ml of distilled water and 1 ml of PVA groups binder and applied on the surface of disks using a fine microbrush (TPC Advanced Technology). The samples Group Ra were then heated in a furnace (Materials and Energy Re- Control 40.06 ± 7.07 nm search Center; Alborz, Iran) at a rate of 100°C/h up to 1200°C, at which point the temperature was maintained Sandblasting 163.10 ± 30.01 nm for two hours before cooling at a rate of 200°C/h. The Bioglass coating 30.34 ± 5.02 nm bioglass powder had the same composition as 45S5 bio- Bioglass + 9 J/cm2 laser 55.43 ± 8.18 nm glass (6 wt% P2O5, 24.5 wt% Na2O, and 24.5 wt% SiO2) (Materials and Energy Research Center). Fifteen samples Bioglass + 5 J/cm2 laser 56.01 ± 7.10 nm were prepared in this manner. y Group BL5: The Nd:YAG laser parameters used in this group included 1.064 nm, Q-switched, 10- to 12-nano- second pulse duration, mean spot size of 400 μm and 100 mJ maximum energy. Fifteen zirconia disks were (Bisco; Schaumburg, IL, USA) for measurement of micro- coated with bioglass and then laser irradiated at 5 J/ shear bond strength. By soldering cast cylinders vertically cm2 energy density. onto the upper compartment of the tester, tensile load was y Group BL9: Fifteen zirconia disks were coated with bio- converted to shear load, which was applied at a crosshead glass and then laser irradiated at 9 J/cm2 energy density. speed of 0.5 mm/min. The load at failure was recorded. The microshear bond strength in MPa was calculated using the formula S = F/A in, where S is microshear bond Morphological Study strength, F is force in N (Newton), and A is area (mm2). For the assessment of surface morphology, one disk from each group was randomly subjected to AFM (atomic force Fracture Mode microscopy, Nanowizard II, JPK; Berlin, Germany) and SEM Debonded surfaces were then evaluated under a light ste- (Seron, AIS2100; Gyeonggi-do, Korea) at 1000X and 5000X reomicroscope (Carl Zeiss; Jena, Germany) with an external magnification. LED light source (LED Jansjo BO913, IKEA; Shanghai, ) at 3.6X magnification to determine the mode of failure, XRD Examination which was categorized as adhesive (failure at the cement- From each group, one disk was randomly selected for zirconia or cement-coating or zirconia-coating interface), co- phase analysis using an x-ray diffractometer (X’Pert Pro hesive (failure within the cement, coating, or zirconia sub- MPD, PANalytical 2009; Almelo, the Netherlands) with strate), or mixed (combination of adhesive and cohesive). Cu-Kα radiation of 40 kV.5 The data of diffraction intensity were scanned with a step scanning time of 20 s and a step Thickness of Coating size of 0.02 degrees in the 2θ range of 5 to 80 degrees, In coated samples, disk thickness was measured before four times for each specimen, and analyzed using X’Pert and after applying the coating using a digital micrometer HighScore Plus V3 software. (Mitutoyo; Kanagawa, Japan) with 1 μm accuracy, and the thickness of the coating was calculated as the difference Shear Bond Strength Test between these two values. The surface of all disks with bioglass coating was etched by HF acid (Ultradent Porcelain Etch, Ultradent; South Jordan, Statistical Analysis UT, USA) for 60 s, then rinsed and dried with water and air The microshear bond strengths in different groups were cal- spray, respectively, for 90 s. As recommended by the manu- culated and reported as means, standard deviation (SD), facturer, silane coupling agent (Ultradent Silane, Ultradent) minimum and maximum. Considering the non-homogeneity was applied to the surface and allowed to dry. After prepa- of variances in different study groups, the Welch test was ration of samples, a Tygon tube (Tygon, Norton Performance used for data analysis. To compare different groups, the Plastic; Cleveland, OH, USA) with an internal diameter of Games-Howell test was applied. This test was chosen for 0.7 mm and height of 1 mm was placed on zirconia blocks data analyses considering the non-homogeneity of vari- for application of composite cement. Panavia F 2.0 compos- ances, small (yet more than 5) sample size (n = 15) and ite cement (Kuraray Noritake; Osaka, Japan) was mixed ac- because it was less conservative than Tamhane’s test. cording to the manufacturer’s instructions, inserted into the Tygon tubes and light cured (Demetron LC, SDS, Kerr; Or- ange, CA, USA) for 40 s. The samples were immersed in RESULTS distilled water and incubated at 37°C for 24 h in an incuba- tor (PECO, model: PL-455G, Pooya Electronic; Teheran, Morphological Analysis Iran). Next, the Tygon tubes were separated from the ce- The resulting surface topographies for all groups showed ment and samples were transferred to a microtensile tester smoother surface profiles than the sandblast groups (Figs 1

Vol 20, No 5, 2018 381 Soltaninejad et al

abFig 1 AFM images: (a) control; (b) sand- blasted group; (c) bioglass-coated group; (d) bioglass+9 J/cm2 laser; (e) bioglass+5 J/cm2 laser. 600 nm 1.8 μm height height

0 nm 0 μm 0 μm fast 40 μm 40 μm fast 0 μm

cd

1 μm 900 nm height height

0 μm 0 nm 0 μm fast 40 μm 0 μm fast 40 μm

e

600 nm height

0 μm 0 μm fast 40 μm

Table 2 Shear bond strengths in MPa XRD Examination In all samples, the tetragonal phase decreased after sur- Group Mean Standard face treatment (Fig 4). The greatest reduction in tetragonal deviation phase was noted in samples coated with bioglass. In laser- Control 7.33 2.10 irradiated bioglass-coated samples, the reduction in tetrag- onal phase was not as great as that in the bioglass-coated Sandblast 48.26 8.27 group. Except for the bioglass-coated groups, no phase Bioglass 48.62 11.23 transformation was noted in any sample. Bioglass-coated samples with and without laser irradiation showed some Bioglass + 9 J/cm2 laser 37.92 4.17 levels of tetragonal to cubic phase transformation. Bioglass + 5 J/cm2 laser 37.26 5.43 Shear Bond Strength Test All experimental groups exhibited statistically significant dif- ferences vs the control group (p < 0.05, Table 2). Sand- blasted and bioglass-coated groups were not significantly different in terms of bond strength. Bioglass+ 9 J/cm2 laser and 2, Table 1). The sandblasted groups showed more and bioglass+ 5 J/cm2 laser groups also did not differ sta- changes in the surface texture with the formation of micro- tistically significantly; however, these two groups had sig- retentive grooves. The sandblasted samples showed the nificant differences compared to sandblasted and bioglass- highest and bioglass-coated samples the lowest surface coated groups (p < 0.05) and showed lower bond strengths. roughness (Table 1). In addition to pitted areas in the bioglass coating, small Fracture Mode cracks were noted on the bioglass surface due to the effect of All three failure modes were seen in most groups (Table 3). laser. Figure 3d (bioglass+ 9 J/cm2 laser) depicts pitted areas Adhesive failure had the highest frequency in the control and in the bioglass coating due to laser irradiation. These areas bioglass+ 5 J/cm2 laser groups, while the highest frequency were larger in the group subjected to 5 J/cm2 laser. The high- of cohesive failure was noted in the sandblasted group. Con- est surface roughness was found in the sandblasted group. trol and bioglass-coated groups showed no cohesive failure.

382 The Journal of Adhesive Dentistry Soltaninejad et al

Fig 2 SEM micrographs of the surface of samples at 1000X magnification: (a) con- trol; (b) sandblasted group; (c) bioglass-coated group; (d) bio- glass+ 9 J/cm2 laser; (e) bio- glass+ 5 J/cm2.

a b c

d e

Fig 3 SEM micrographs of the surface of samples at 5000X magnification: (a) con- trol; (b) sandblasted group; (c) bioglass-coated group; (d) bio- glass+9 J/cm2 laser; (e) bio- glass+ 5 J/cm2.

a b c

d e

DISCUSSION Some studies have shown that sandblasting can affect the long-term clinical service of zirconia by inducing tetrago- In this study, sandblasting surface treatment served as the nal to monoclinic phase transformation.25,54 Such phase positive control and other surface treatments were com- transformation can create a layer with compression stress pared with this method. Sandblasting or air abrasion with which counteracts the reduction in strength due to surface aluminum oxide particles has been reported to be the most defects.25 Moreover, phase transformation during the pro- effective surface treatment to improve the properties of cess of surface treatment can decrease the strength and bonding to zirconia; by increasing surface roughness, sand- increase the likelihood of zirconia fracture, as it decreases blasting results in micromechanical interlocking of the lut- the capacity of zirconia for phase transformation in future ing agent.8,24 Tsuo et al46 recommended sandblasting of critical situations (3-4 vt% increase when stress is applied sintered zirconia with 50-μm alumina particles. Similarly, to counteract crack propagation). Thus, during the process 50-μm alumina particles were used in the current study and of surface treatment, tetragonal to monoclinic phase trans- yielded high bond strength compared to the control group. formation must be minimized to ensure long-term success Roughening the internal surface of ceramic restorations can of restoration.44 In this study, the XRD pattern did not show increase the available surface for cement penetration and any tetragonal to monoclinic phase transformation in sand- consequently enhance mechanical bonding.9 Ersu et al17 blasted samples, which may be attributed to differences in showed that sandblasting created a rougher surface com- methods and types of zirconia used. Also, application of pared to other methods. In our study, the roughest surface Nd:YAG laser with the radiation parameters used here did was also obtained by sandblasting. not cause any unfavorable phase transformation in zirconia.

Vol 20, No 5, 2018 383 Soltaninejad et al

Table 3 The frequency distribution of modes of failure

Group Percentage

Adhesive Mixed Cohesive

Control 76.47% 23.52% 0.00%

Sandblasting 61.90% 28.57% 9.52%

Bioglass coating 64.70% 35.29% 0.00%

Bioglass+ 9 J/cm2 laser 50.00% 41.66% 8.33%

Bioglass+ 5 J/cm2 laser 86.66% 6.66% 6.66%

Fig 4 XRD diagram. counts

60000 control 40000 20000 0 10000 bioglass-coated 5000 0 20000 sandblasted 10000 0 bioglass + 20000 5 J/cm2 laser 10000 0 20000 bioglass + 10000 9 J/cm2 laser

0 10 20 30 40 50 60 70 Position ['2 Theta][Copper (Cu)] tetragonal phase

cubic phase

Thus, the study hypothesis stating that Nd:YAG laser treat- by this method.34 The coating thickness in our study was ment of bioglass-coated zirconia surface may cause un- similar to that of previous studies, and confirmed that the wanted phase transformation was rejected. bioglass slurry method yielded minimum coating thickness Bakry et al6 evaluated the application of bioglass on the (Table 4). This result also confirmed the efficacy of the bio- enamel surface and showed the XRD pattern of brushite glass slurry method, as it improved the bonding properties and hydroxyapatite crystals on the enamel specimen. In our to the level of sandblasting. study, we evaluated the application of bioglass on the zirco- When bioglass coating is applied, part of stabilized zirco- nium surface and showed the XRD pattern for phase trans- nia reacts with some of the Ca2+ ions to form zir- formation. conate. In XRD analysis, the coated surface showed a small In the current study, bioglass coating was applied as a percentage of calcium zirconate and some levels of mono- slurry fired onto the zirconia substrate to create an interme- clinic zirconia. It indicates that bioglass penetrated into sur- diate etchable layer on the zirconia surface.34 Many previ- face microstructure of ceramic and to a certain extent dis- ous studies have used such a coating to benefit from the solved the grains. Thus, the dissolved zirconia loses its properties of bioactive glass and good mechanical perfor- stability. During the cooling phase, zirconia dissolved in mance of zirconia.20,26 In the bioglass slurry method, the glass tends to crystallize. But since an adequate amount of bioglass coating and zirconia are in close contact; the inter- Y3+ ions is not available, it directly crystallizes to the mono- face between the two is uniform and without voids or de- clinic phase. Phase transformation at the interface can be fects. Also, a minimum coating thickness can be achieved controlled by precisely adjusting the time of each step of

384 The Journal of Adhesive Dentistry Soltaninejad et al

Table 4 Descriptive statistics for the thickness of bioglass coating in bioglass-coated group

Group Thickness of coating layer

Mean Median Standard deviation Minimum Maximum

Bioglass thickness 46.67 μm 37.00 μm 23.59 39 μm 91 μm

the bioglass application cycle. A cooling rate over 200°C/h prevents the formation of microcrystals in glass. Also, the 60.00 lower the temperature of applying bioglass coating, the fewer zirconia ions are released into the glass layer; how- 50.00 ever, the holding time of 2 h at 1200°C is longer.26 Accord- ingly, a cooling rate of 200°C/h is recommended for the 40.00 formation of microcrystals and 2 h at 1200°C is recom- 34 mended based on the thermal properties of bioglass. For 30.00 this reason, in our study, samples were heated in a furnace at 100°C/h to 1200°C and held at this temperature for 2 h 20.00 and then cooled at 200°C/h. By employing this technique, Mean microshear (MPa) no monoclinic phase transformation occurred in any of the samples. However, bioglass-coated samples showed some 10.00 degrees of cubic phase irrespective of the use or not of 0.00 laser; this phase transformation was probably due to ther- control sandblasted bioglass bioglass bioglass + 9 J/cm2 + 9 J/cm2 mal processes conducted on samples after bioglass coat- group laser laser ing and cannot be attributed to laser irradiation. Error bars ± 1 (SD) The main effect of laser energy is conversion of light to heat, and the most important interaction between laser and Fig 5 Microshear bond strength graph of the five groups. substrate is laser energy absorption by the substrate.50 Surface discoloration and water content along with some other surface properties determine the amount of energy absorbed by the irradiated surface.12 On dental surfaces, energy absorbed by water molecules manifests in the crys- and thus, bond strength increases. However, after laser ir- talline structure of dentin and organic compounds. Laser, radiation, numerous cracks are formed, which increase the during hard tissue destruction, creates micro-explosions risk of fragmentation of the coating and subsequently de- that to macroscopic and microscopic irregularities, pro- crease the bond strength. Some studies showed that viding a suitable surface for adhesion.31 Lasers can im- cracks are inevitably formed during local thermal changes, prove the properties of bioglass. Evidence shows that CO2 because volumetric changes occur during the process of laser can improve the interaction of 45S5 bioglass with freezing of the melted substrate.35,40 In this study, different dentin.4 Moreover, short pulse Nd:YAG laser with 5 and 9 energy densities of Nd:YAG laser were evaluated. The re- J/cm2 energy is effective in the deposition of bioactive sults revealed that by increasing laser energy, bond glass.14 Thus, in this study, the effect of Nd:YAG laser ir- strength did not significantly increase. In addition, the bond radiation was evaluated on zirconia coated with bioglass strengths resulting after bioglass+ 9 J/cm2 and bioglass+ and compared with the application of bioglass coating 5 J/cm2 laser treatment were not significantly different. alone. It was found that application of laser to bioglass- However, these two groups showed significantly lower bond coated zirconia compared to bioglass coating alone (with no strengths than did the sandblasted and bioglass-coated further surface treatment) did not significantly improve the groups (p < 0.05). Some studies on zirconia with no sur- bond strength. Although the bond strength in the former face treatment showed that increasing the energy density of group significantly increased compared to the control group, laser did not significantly increase the bond strength.29,42 the resutling bond strength was lower than the bond Assessment of SEM micrographs in groups with bioglass strength obtained both in the bioglass coating group with coating revealed pits and cracks on the bioglass surface no further treatment and in the sandblasted group. Thus, after laser irradiation. These defects decreased in size with the hypothesis stating that Nd:YAG laser treatment of bio- an increase in laser energy density, which is probably due to glass-coated zirconia surface would improve the bond the fact that by increasing energy density, a smaller surface strength was rejected. Due to the presence of SiO2 in bio- is irradiated. Thus, the size of defects (pits) decreases glass, silanization is effective in bioglass-containing groups while their depth probably increases. Meanwhile, an in-

Vol 20, No 5, 2018 385 Soltaninejad et al crease in energy density increases the size of cracks and Clinical studies are required to confirm our findings. fractures on the bioglass surface, which is also attributed to Moreover, the results with regard to one zirconia ceramic the increased energy per surface area and wider distribution may not be generalizable to other commercially available of energy and creation of larger cracks. However, further as- zirconia ceramics. Future studies on the effects of each sessments are required to confirm these assumptions. surface treatment on surface properties and bond strength Panavia F2.0 is a composite cement modified with MDP of other types of zirconia ceramics are required. phosphate monomer. MDP structural monomer is resistant to hydrolysis due to the presence of long carbonyl chains.48A recent study showed that Nd:YAG laser treat- CONCLUSIONS ment using MDP-containing primer can increase the bond strength of composite cement to zirconia.3 Furthermore, it y The application of bioglass coating on the zirconia sur- has been confirmed that composite cements containing face using the slurry method increases its shear bond MDP monomer can provide a durable bond irrespective of strength, making it comparable to that of sandblasting. the type of surface treatment.28,53 A different study also The surface roughness of sandblasted zirconia was the showed that when using MDP-containing primer, other sur- highest compared to other methods. face treatments are not required.19 However, some studies y Applying Nd:YAG laser on bioglass-coated zirconia was reported contrasting results. Mahmoodi et al30 reported not effective and decreased the bond strength compared that the MDP-containing primer did not improve the micro- to sandblasted and bioglass-coated groups. Increasing tensile bond strength when the zirconia ceramic surface the Nd:YAG laser energy did not increase the surface was sandblasted and treated with Nd:YAG laser. Another roughness of zirconia coated with bioglass and did not study showed that where MDP-containing primer was used cause a significant change in shear bond strength to zir- instead of silane, the etched glaze layer did not increase conia. the bond strength.13 In this study, Panavia composite ce- y The application of bioglass coating caused tetragonal to ment containing MDP monomer was applied on bioglass- cubic phase transformation. Applying Nd:YAG laser with coated samples after using etchant and silane; bioglass- the radiation parameters used in our study did not cause coated samples without laser treatment showed high bond any phase transformation in zirconia. strength comparable to that of the sandblasted group. Ap- plication of laser had a negative effect and decreased the bond strength compared to the sandblasted group. REFERENCES Due to the use of MDP-containing composite cement in 1. Akyıl MŞ, Uzun İH, Bayındır F. Bond strength of resin cement to yttrium- our study, a long-term bond may be guaranteed; however, stabilized tetragonal zirconia ceramic treated with air abrasion, silica thermocycling is often used to simulate the oral environ- coating, and laser irradiation. Photomed Laser Surg 2010;28: 801–808. ment to show the changes in cement bond to ceramic over 2. Arami S, Tabatabae MH, Namdar SF, Chiniforush N. Effects of different lasers and particle abrasion on surface characteristics of zirconia ceram- 15 time. Thus, future studies must employ aging protocols to ics. J Dent (Tehran) 2014;11: 233–241. confirm these results. 3. Asadzadeh N, Ghorbanian F, Ahrary F, Rajati Haghi H, Karamad R, Yari A, It is believed that shear loads are mainly responsible for Javan A. Bond Strength of Resin Cement and Glass Ionomer to Nd: YAG Laser-Treated Zirconia Ceramics. J Prosthodont 2017;0: 1–5. the failure of restorative materials. Thus, the shear bond 4. Bakry A, Takahashi H, Otsuki M, Sadr A, Yamashita K, Tagami J. CO2 laser strength test was performed to assess the quality of the improves 45S5 bioglass interaction with dentin. J Dent Res 2011;90: composite bond to zirconia.16 In our study, the shear bond 246–250. strength test was used to assess the bond of composite 5. Bakry A, Takahashi H, Otsuki M, Tagami J. The durability of phosphoric acid promoted bioglass-dentin interaction layer. 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