Journal of Investigative and Clinical Dentistry (2015), 0, 1–8
ORIGINAL ARTICLE Dental Biomaterials
Surface topography and bond strengths of feldspathic porcelain prepared using various sandblasting pressures Elham Moravej-Salehi1, Elahe Moravej-Salehi2 & Azam Valian3 1 Department of Restorative Dentistry, School of Dentistry, Shahed University, Tehran, Iran 2 Private Practice, Tehran, Iran 3 Department of Restorative Dentistry, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Keywords air abrasion, ceramic, sandblasting, scanning electron microscopy, shear bond strength. Correspondence Azam Valian, Assistant Professor, Department of Restorative Dentistry, School of Dentistry, Shahid Beheshti University of Medical Sciences, Daneshjou Blvd, Evin Ave, Tehran 19834, Iran. Tel: +989123163711 Email: [email protected] Received 9 December 2014; accepted 16 May 2015. doi: 10.1111/jicd.12171
Abstract Objective: The purpose of this study was to determine the bond strength of composite resin to feldspathic porcelain and its surface topography after sandblasting at different pressures. Methods: In this in vitro study, 68 porcelain disks were fabricated and randomly divided into four groups of 17. The porcelain surface in group 1 was etched with hydrofluoric acid. Groups 2, 3, and 4 were sandblasted at 2, 3 and 4 bars pressure, respectively. Surface topography of seven samples in each of the four groups was examined by a scanning electron microscope (SEM). The remaining 40 samples received the same silane agent, bonding agent, and composite resin and they were then subjected to 5000 thermal cycles and evaluated for shear bond strength. Data were analyzed using one-way ANOVA. The mode of failure was determined using stereomicroscope and SEM. Results: The highest shear bond strength was seen in group 4. however, statistically significant differences were not seen between the groups (P = 0.780). The most common mode of failure was cohesive in porcelain. The SEM showed different patterns of hydrofluoric acid etching and sandblasting. Conclusion: Increasing the sandblasting pressure increased the surface roughness of feldspathic porcelain but no difference in bond strength occurred.
Introduction Today, the use of materials that are aesthetically acceptable has become more popular in restorative dentistry.1 Ceramics are the most aesthetic materials available in restorative dentistry. For this reason, feldspathic ceramics are used in veneer frameworks and full ceramic restorations like inlays, onlays, laminates, and crowns.2 Ceramics are in a desirable range with respect to resistance to abrasion, chemical stability, biocompatibility, translucency, and fluorescency.2 The disadvantage of these materials is their low fracture strength.3 Porcelain fracture has been reported to be the second most common cause of failure after secondary caries.3,4 Porcelain fractures and chipping may be due to trauma, incomplete occlusal adjustments, parafunctional habits, ª 2015 Wiley Publishing Asia Pty Ltd
and fatigue failure. Incompatibility of the coefficient of thermal expansion between porcelain and the metal framework, failure of the adhesive bond, incomplete preparation, and inappropriate coping design may lead to failure.4 For intraoral repair of porcelain fractures, use of composite resin is recommended to avoid restoration replacement, time delay, and cost. It is also used to bond orthodontic brackets to porcelain. For this purpose, a standard method with optimal power and strength is needed to prepare the porcelain surface for repair without any detrimental effects.5 Many studies on the efficacy of ceramic surface treatment using burs, etching with hydrofluoric acid (HF), phosphoric acid, accidulated phosphate fluoride, ammonium bifluoride, lasers (CO2, Er-YAG, ND-YAG, Er,Cr-YSGG) and sandblasting have 1
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been published that reportedly increase the bond strength of resin material to porcelain.1,3,6,7 The use of HF followed by silane application is the standard clinical process for increasing the bond strength when repairing the porcelain surface with composite resin; this is because of the microporosities that hydrofluoric acid produces on the porcelain surface with selective dissolution of the glass matrix. This has been observed via scanning electron microscopy (SEM).2,3,8 Hydrofluoric acid acid is chemically poisonous and has higher tissue penetration ability compared to other etchants. It also has detrimental effects on soft tissues and causes caustic burns and necrosis. On the other hand, feldspathic porcelain surface etching with HF and unwanted contact with the enamel surfaces during work creates an insoluble fluoride salt that if not removed will lead to a lower bond strength.8,9 Sandblasting is a common method of surface treatment for increasing micromechanical retention because it produces a clean and active porcelain surface. On the other hand, it does not cause acute acid burns on the patient’s oral tissues. In this method the aluminum oxide particles remove the weakened phases of ceramic and create irregularities on the surface.10 These irregularities increase the surface area and improve the mechanical retention and bond.11 Surface topography analysis of treated ceramic with SEM provides qualitative information in this matter because this technique enables direct observation of the surface details with high resolution.12 The microsandblaster device allows for adjustment of different parameters such as the size of the abrasive particles, air pressure, time used, angle of nozzle, etc.5 Studies have shown that sandblasting for surface repair of ceramics is better performed with pure alumina particles between 30 and 250 lm, at high speed and with air pressure between 2 to 3 bars for nearly 15 sec.13 However, a study in 2013 showed that 5–15 sec of porcelain surface sandblasting produced almost similar shear bond strength.5 The results of Addison et al.14 showed that the best fracture strength of feldspathic porcelain laminates was produced with 50 lm alumina while 110 and 250 lm alumina particles reduced the bond strength. Also, the size of the particles, pressure, and angle of the machine affect the strength and life span of porcelain laminate restorations. A few studies have tried to evaluate the effect of different parameters of the sandblasting machine on the surface topography of feldspathic porcelain and the bond strength between composite and porcelain.5,15 On the other hand, different pressures of sandblasting machines have been used in previous studies for porcelain surface treatment. With respect to the lack of information on this matter, this study aimed to evaluate the effect of varying pressures of an intraoral sandblasting machine on the surface struc2
ture of feldspathic porcelain and bond strength to composite resin and compare it with the effect of hydrofluoric acid. The null hypothesis of this study was that sandblasting treatment at different pressures would not result in different shear bond strength and surface roughness. Materials and methods Sixty-eight porcelain discs (Ceramco 3; Dentsply Ceramco Co., Burlington, NJ, USA) (6 9 2 mm) were prepared in a mold according to the manufacturer’s instructions with a metal base of nickel chromium. The specimens were examined under a magnifying glass with 109 magnification to ensure absence of cracks. Initially the surfaces of the specimens were prepared using silicon carbide abrasive papers (400 and 600 grit) on a rotating metallographic polishing device under watercooling for 15 sec for the purpose of matching the specimens. Then they were rinsed with water and air-dried. The specimens were randomly divided into four groups of 17 and then coded. The below procedures were then carried out in sequence. 1 Control: 9.5% HF gel (Porcelain Etchant Gel, Bisco, Sachaumburg, IL, USA) was applied for 2 min to the surfaces of the specimens and then rinsed for 1 min and air-dried for another minute. 2 The surfaces of the specimens were sandblasted using an intraoral sandblasting device (Microsandblaster; Dento-Prop Ronvig, Denmark) with 50 lm alumina particles (Ronvig, Denmark) at a pressure of 2 bars for 10 sec from the constant distance of 5 mm with an angle of 90°. Jigs had been made for the purpose of uniformity. Next the specimens were washed for 1 min and air-dried for another minute. 3 Similar to group 2 but sandblasting pressure was at 3 bars. 4 Similar to group 3 but sandblasting pressure was at 4 bars. Evaluation of surface topography For analysis of the surface topography of the 20 treated specimens (six of each group), initially a 15-nm-thick gold coating was applied using a Sputter Coater (K450X; Emitech, Ashford, UK). Next the SEM (VEGA; TESCAN, Brno, Czech Republic) micrographs in top view were obtained in five random areas for each specimen at 5009, 20009, 40009, and 100009 magnifications. For evaluation of surface topography in the lateral view, eight surface-treated specimens (two of each group) were cut vertically in half with a diamond disk under watercooling. Then they were rinsed with water and air-dried. Next lateral surfaces of specimens were gold coated in the ª 2015 Wiley Publishing Asia Pty Ltd
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tion. The fracture mode of specimens was divided into three groups of adhesive, cohesive and mixed (adhesive/ cohesive). The cohesive fracture could have been in the porcelain or composite. One specimen of each group was observed randomly under SEM with 1009 and 10009 magnifications to evaluate the fracture mode. For this reason the specimens were gold coated (K450X; Emitech) and then observed with an electron microscope (VEGA; TESCAN) to evaluate their surface topography.
same way as mentioned above. The SEM micrographs were obtained at 15009 magnification. Evaluation of bond strength On the surface of 40 of the surface-treated specimens, a layer of silane agent (Bis-Silane Agent Parts A and B; Bisco) was applied using a microbrush. This was done for 1 min and dried with air-flow for 30 sec. Following this a layer of resin bond (D/E Resin; Bisco) was applied and cured with a light-curing unit (Starlight Pro, Mectron, Italy) with an intensity of 600 mW/cm2. Next, the composite resin (AELITETM All Purpose Body; Bisco) was applied in 2-mm-thick increments into clear plastic cylinders (Tygon tubes, 3 9 4 mm) over the bonding surface. Each layer was cured for 40 sec. The composite cylinders were light-cured from all three dimensions with an angle of 45° for an extra 120 sec from the porcelain surface. After the removal of Tygon tubes from the specimens under the stereomicroscope (Nikon SMZ800, Tokyo, Japan) with 109 magnification, the specimens were stored in sterile water in an incubator at 37°C for 24 h. Then specimens were subjected to 5000 thermal cycles at 5 and 55°C for 30 sec in each bath and a dwell time of 10 sec in a thermocycling machine (Malekteb, Tehran, Iran). Next, each specimen was mounted in cold cure acrylic resin. For the purpose of evaluation of shear bond strength, the specimens were moved to the universal testing machine (Zwick Roell Z050, Ulm, Germany) and force was applied at a crosshead speed of 1 mm/min to the interface of composite and porcelain. The bond strength was recorded in MPa. Normal distribution of data was ensured using the Kolmogorov–Smirnov test and with respect to the confidence interval of 95%, data were analyzed using Tukey’s test and one-way ANOVA by SPSS version 18.0 software (SPSS Inc., Chicago, IL, USA).
Results The mean values of shear bond strength are listed in Table 1. The highest shear bond strength was in group 4 (15.76 3.51). The lowest mean strength was in group 2 (14.11 3.36). There was no statistically significant difference between the groups (P = 0.780) (Table 2). The frequency of different fracture modes in the study groups (determined by stereomicroscope) can be seen in Table 3. All cohesive fractures were in the porcelain. Figure 1 shows evaluation of fracture mode under SEM at 1009 magnification. The results of SEM analysis of feldspathic porcelain surface etched with 9.5% HF gel for 2 min were compared to the sandblasted surfaces with 50-lm alumina particles at different pressures showing different surface morphology. In both methods the surface was rough and porous (Figure 2). Also, with the increase of sandblaster pressure from 2 to 4 bars, a slight increase in surface roughness was noted. Discussion Using intraoral repair technique and surface treatment, ceramic restorations can be repaired with composite resin with no need to replace the restoration.16 The adhesion mechanism of restorative materials is based on two theories: the chemical adhesion of molecules at the interface and micromechanical retention based on penetration of adhesive and mechanical interlocking.17 Acid-etching and sandblasting with alumina particles are among the most
Evaluating the mode of failure The mode of fracture of specimens was evaluated by a stereomicroscope (Nikon SMZ800) with 409 magnificaTable 1. Shear bond strength of samples in MPa
95% CI for the mean Group
Mean
Standard deviation
1 2 3 4
15.27 14.11 15.07 15.76
3.63 3.36 3.98 3.51
Lower bound
Upper bound
Minimum
Maximum
12.67 11.71 12.40 13.25
17.88 16.52 17.75 18.27
9.04 9.89 9.91 9.72
19.88 20.40 21.81 21.76
CI, confidence interval.
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Table 2. Statistical comparison of groups using Source of variation
Total sum of squares
Degrees of freedom
Mean squares
Intergroups Intragroups Total
14.408 489.978 504.386
3 37 40
4.803 13.243
ANOVA
F
Level of significance
0.363
0.780
Table 3. Frequency (percentage) of modes of failure of samples in the groups under study Mode of failure (%) Group
Cohesive
Adhesive
Cohesive/adhesive
1 2 3 4
90 60 70 90
– 20 10 –
10 20 20 10
common methods for surface treatment of silica-based ceramics.16 This study sought to determine the suitable sandblasting pressure for surface preparation of the feldspathic porcelain and to compare it with the effect of etching with hydrofluoric acid (HF). Within the limitations of this study, the results showed that the shear bond strength following sandblasting with 50-lm alumina particles at 2, 3 and 4 bar pressure was not significantly different and made no difference to the shear bond strength following acid etching with 9.5% HF (control group) (P = 0.780). Thus, the null hypothesis of the study regarding the bond strength was confirmed. Although increasing the sandblasting pressure from 2 to 4 bar slightly increased the bond strength. Previous studies have shown that all systems used for in-office porcelain repair should provide a minimum of 10 MPa bond strength at the interface.16 The bond strength values obtained in the present study in all surface treatment groups were within the acceptable range. It should be noted that all specimens underwent thermocycling before bond strength measurement in order to simulate the oral environment. Thermocycling has beenfound to be more accurate than water storage for simulating the effect of aging, and results in a reduction in bond strength greater than that due to long-term water storage and may even lead to spontaneous debonding.5 In the present study, similar to the study by Yung et al., thermocycling was done at 5000 cycles, which approximately corresponds to 6 months of clinical service of the restoration according to Gale and Dareell.18,19 The shear bond strength test is the most commonly used technique for evaluation of the efficacy of different 4
porcelain repair methods.16 This test is easy and quick and simulates the clinical situations.17 Moreover, it does not have the technical sensitivity of tensile and microtensile tests.20 In this study, the most common mode of failure was cohesive type in the porcelain; which is in accord with the results of many other studies.4,5,18 Studies have shown that if the bond strength between the porcelain and composite resin exceeds 13 MPa, cohesive failure may occur in the porcelain.21 In shear-bond strength testing, stress is heterogeneously distributed on the interface and more stresses are concentrated at regions far from the interface.This may lead to initiation of fracture on the porcelain surface.8,16,20 Application of 9.5% HF gel for 2 min along with silane is the most effective method for ceramic surface treatment. Thus, this technique was used for the control group specimens in this study.2,22 In the current study, SEM images showed irregularities and tunnel-like grooves and pores that seemed deeper than those seen on sandblasted surfaces. Such images have been reported in the majority of similar studies resembling honeycomb pattern.3,11,15,23 The reason for deeper porosities in HF group is that HF chemically reacts with the silica phase in between crystals and thus can penetrate to depth;3,7,10,15 while sandblasting has a mechanical mechanism based on the collision of particles as the result of air pressure and involves no chemical reaction. Thus, sandblasting increases surface porosities.12,13,15,21 Although HF is effective for porcelain surface conditioning, it has a corrosive nature,24 as it penetrates into the cells and disrupts their metabolism and subsequently kills them.3 Clinically, it can cause rash, burns, and deep tissue necrosis. Also, HF can severely traumatize tooth structure.3,24 Szep et al.25 found that HF leaves a layer of amorphous fluoride deposit on the tooth surface that interferes with the process of bonding and acid etching. Several studies have stated that this method cannot be applied in clinical dental practice especially for intraoral ceramic repair.2,8 On the other hand, acid etching with HF decreases the flexural strength of ceramics,22 whereas the sandblasting process is commonly used in prosthodontic laboratories and dental clinics.2 This process will result in micromechanical bonding and change in ceramic surface topography. It also increases surface roughness, surface area, and wettability of composite resin and ceramics.2,12 Studies have shown that sandblasting provides adequate bond strength.2,12,24 Scanning electron microscopy analyses of sandblasted ceramic surfaces showed irregular or hollow areas compared to surfaces subjected to acid etching.16 Profilometry, SEM and AFM analyses in different studies have shown that the mean surface roughness of sandblasted surfaces was greater and with prominently sharper points ª 2015 Wiley Publishing Asia Pty Ltd
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(a)
(b)
(c)
(d)
Figure 1. Scanning electron microscopy analysis of the mode of failure of samples in groups 1–4 (from (a) to (d) respectively) (1009 magnification): (a) cohesive failure (b) adhesive failure, (c) cohesive failure, and (d) cohesive failure.
compared to surfaces etched with HF or laser-irradiated surfaces.2,17,26,27 In the present study sandblasting provided rougher surfaces compared to HF but the shear bond strength was not different. Ersu et al.27 also stated that although sandblasting provides a rougher surface, this roughness does not ª 2015 Wiley Publishing Asia Pty Ltd
make the bond stronger. This is due to the fact that sandblasting treatment creates irregularities without undercuts on the surface and even the bond strength may diminish in the long-term.28 On the other hand, hydrolytic changes aggravate during storage. This change is more significant in sandblasted specimens than those treated with HF 5
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(a)
(b)
(c)
(d)
Figure 2. Scanning electron microscopy topography of the feldspathic porcelain surface in samples of groups 1–4 (from (a) to (d) respectively) (5009 magnification).
because the irregularities caused by acid etching are deeper. As a result resin is better preserved from the degradation process in HF treated specimens.29 In this study, the bond strengths of HF treated and sandblasted groups were found to be the same. This is due to the fact that the bond strength was compared in different groups after aging via thermocycling. 6
In sandblasting with alumina particles, by increasing the pressure from 20 to 100 psi a linear increase has been reported in the cutting rate on an enamel analogue.30 It has been discussed that in the sandblasting process very huge particles or very high pressures increase the bond strength but cause deformation of restoration because of abrasion.2 ª 2015 Wiley Publishing Asia Pty Ltd
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Therefore, in the present study 2–4 bar pressures (most commonly used in previous studies) were used and no significant difference was found in the resultant bond strength values. However, there was a very high percentage of cohesive fractures of the porcelain in the 4 bar pressure suggesting a possible weakening of the porcelain which may have impacted on the results. Also, SEM analysis showed increased surface roughness and depth of impact as the result of increased pressure. Similar results were obtained when evaluating the effect of two different pressures on zirconia ceramics after thermocycling. Although microscopic evaluations showed increased surface roughness, no difference occurred in bond strength.31 It should be noted that the shear bond strength is not solely dependent on surface roughness and other factors also play a role in this respect.3 Therefore, HF by creating microretentive areas and increasing the surface roughness enhances the bond strength.3,7,22 While, the sandblasting process is based on increasing the surface roughness and surface area and does not have the ability to cause retentive undercuts,12,28 even by increasing the pressure. Since there is a threshold for surface porosities limiting their effect on bond strength,3,15 by increasing the pressure, despite increased surface area, no significant increase in bond strength is achieved. Considering the results of the present study, it can be stated that the bond strength achieved via lower bar pressure sandblasting is essentially the same as the high bar sandblasting and the HF treatment, and low bar pressure results in less damage to the porcelain. Because although high pressure sandblasting increases surface roughness, it decreases the strength of porcelain restoration, can cause chipping of the porcelain or significant loss of porcelain material, and is also high risk for soft and hard tissues in the mouth such as damage to remineralized tooth surface
References 1 de Paula Eduardo C, Bello-Silva MS, Moretto SG, Cesar PF, de Freitas PM. Microtensile bond strength of composite resin to glass-infiltrated alumina composite conditioned with Er, Cr: YSGG laser. Lasers Med Sci 2012; 27: 7–14. 2 Yavuz T, Dilber E, Kara HB, Tuncdemir AR, Ozturk AN. Effects of different surface treatments on shear bond strength in two different ceramic systems. Lasers Med Sci 2013; 28: 1233–9. 3 Kukiattrakoon B, Thammasitboon K. Optimal acidulated phosphate fluo-
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layer.2,6,21,32 More studies are needed to confirm this clinically, but it would seem advantageous to use the lower pressure when working on porcelain repairs in the mouth. Last but not least, future studies are recommended to focus on the resultant strength of various porcelain specimens treated with air abrasion alone. Conclusions Within the limitations of this in vitro study: (a) sandblasting with 50 lm alumina particles at 2, 3 and 4 bar pressure from a constant distance of 5 mm for 10 s and 90° nozzle angulation did not significantly change the shear bond strength of feldspathic porcelain to composite resin; (b) the bond strength after sandblasting was similar to that after the application of 9.5% HF for 2 min; (c) SEM results demonstrated that a porous surface resulted from HF etching and sandblasting, however, HF caused deeper pores while sandblasting caused sharp points and more homogeneous pores; (d) SEM analysis of specimens sandblasted with 2–4 bar pressure showed slightly increased surface porosities and depth of pores; (e) the results of this study suggest that it may be advantageous to use a low bar pressure when sandblasting porcelain for intraoral repair. Acknowledgments This investigation was supported by Deputy of Research, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran. This article was based on a research project (number 310/2598).
ride gel etching time for surface treatment of feldspathic porcelain: on shear bond strength to resin composite. Eur J Dent 2012; 6: 63– 9. 4 El-Hosary MM, Shokry TE, Zaki DY, El-Shakour ASA. Bond strength of different intraoral repair systems for metal-ceramic restorations. J Am Sci 2011; 7: 383–8. 5 Amin Salehi E, Heshmat H, Moravej Salehi E, Kharazifard MJ. In vitro evaluation of the effect of different times of sandblasting on the bond strength of feldspathic porcelain to composite resin. J Islamic Dent Assoc Iran 2013; 25: 22–30.
6 Blatz MB, Sadan A, Kern M. Resinceramic bonding: a review of the literature. J Prosthet Dent 2003; 89: 268–74. 7 Dilber E, Yavuz T, Kara HB, Ozturk AN. Comparison of the effects of surface treatments on roughness of two ceramic systems. Photomed Laser Surg 2012; 30: 308–14. 8 Fabianelli A, Pollington S, Papacchini F et al. The effect of different surface treatments on bond strength between leucite reinforced feldspathic ceramic and composite resin. J Dent 2010; 38: 39–43. 9 Loomans BAC, Mine A, Roeters FJM et al. Hydrofluoric acid on dentin
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should be avoided. Dent Mater 2010; 26: 643–9. Ozcan M. Review: evaluation of alternative intra-oral repair techniques for fractured ceramic-fused-to-metal restorations. J Oral Rehabil 2003; 30: 194–203. Bottino MC, Ozcan M, Coelho PG, Valandro LF, Bressiani JC, Bressiani AHA. Micro-morphological changes prior to adhesive bonding: high-alumina and glassy-matrix ceramics. Braz Oral Res 2008; 22: 158–63. Kara HB, Dilber E, Koc O, Ozturk AN, Bulbul M. Effect of different surface treatments on roughness of IPS Empress 2 ceramic. Lasers Med Sci 2012; 27: 267–72. Reston EG, Filho SC, Arossi G, Cogo RB, Rocha CS, Closs LQ. Repairing ceramic restorations: final solution or alternative procedure? Oper Dent 2008; 33: 461–6. Addison O, Marquis PM, Fleming GJ. The impact of modifying alumina air abrasion parameters on the fracture strength of a porcelain laminate restorative material. Dent Mater 2007; 23: 1332–41. Valian A, Moravej-Salehi E. Surface treatment of feldspathic porcelain: scanning electron microscopy analysis. J Adv Prosthodont 2014; 6: 387–94. de Melo RM, Valandro LF, Bottino MA. Microtensile bond strength of a repair composite to leucite-reinforced feldspathic ceramic. Braz Dent J 2007; 18: 314–9. Kara HB, Ozturk AN, Aykent F, Koc O, Ozturk B. The effect of different surface treatments on roughness and
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bond strength in low fusing ceramics. Lasers Med Sci 2011; 26: 599–604. Yung J, Ha S, Lee J, kim S. Effect of sandblasting and various metal primers on the shear bond strength of a resin cement to Y-TZP ceramic. Dent Mater 2010; 26: 650–8. Gale MS, Darvell BW. Thermal cycling procedures for laboratory testing of dental restorations. J Dent 1999; 27: 89–99. Sakaguchi RL, Power JM. Craig’s restorative dental materials, 13th edn. United States: Mosby; 2012; 330, 97–8. Saracß Y, Elekdag-Turk S, Saracß D, Turk T. Surface conditioning methods and polishing techniques effect on surface roughness of a feldspar ceramic. Angle Orthod 2007; 77: 723–8. Zogheib LV, Bona AD, Kimpara ET, Mccabe JF. Effect of hydrofluoric acid etching duration on the roughness and flexural strength of a lithium disilicate-based glass ceramic. Braz Dent J 2011; 22: 45–50. Borges GA, Sophr AM, de Goes MF, Sobrinho LC, Chan DC. Effect of etching and airborne particle abrasion on the microstructure of different dental ceramics. J Prosthet Dent 2003; 89: 479–88. Saracß YSß, K€ ul€ unk T, Elekdag-T€ urk S, Saracß D, T€ urk T. Effects of surfaceconditioning methods on shear bond strength of brackets bonded to different all-ceramic materials. Eur J Orthod 2011; 33: 667–72. Szep S, Gerhardt T, Gockel HW, Ruppel M, Metzeltin D, Heidemann D. In vitro dentinal surface reaction of 9.5% buffered hydrofluoric acid in repair of
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ceramic restorations: a scanning electron microscopic investigation. J Prosthet Dent 2000; 83: 668–74. Schmage P, Nergiz I, Herrman W, € Ozcan M. Influence of various surface-conditioning methods on the bond Strength of metal brackets to ceramic surfaces. Am J Orthod Dentofacial Orthop 2003; 123: 540–6. Ersu B, Yuzugullu B, Yazici AR, Canay S. Surface roughness and bond strengths of glass-infiltrated alumina ceramics prepared using various surface treatments. J Dent 2009; 37: 848– 56. Wood DJ, Bubb NL, Millar BJ, Dunne SM. Preliminary investigation of a novel retentive system for hydrofluoric acid etching resistant dental ceramics. J Prosthet Dent 1997; 78: 275–80. Torres SMP, Borges GA, Spohr AM, Cury AADB, Yadav S, Platt JA. The effect of surface treatments on the micro-shear bond strength of a resin luting agent and four all-ceramic systems. Oper Dent 2009; 34: 399–407. Paolinelis G, Banerjee A, Watson TF. An in-vitro investigation of the effects of variable operating parameters on alumina air-abrasion cutting characteristics. Oper Dent 2009; 34: 87–92. Kern M, Barloi A, Yang B. Surface conditioning influences zirconia ceramic bonding. J Dent Res 2009; 88: 817–22. Khoroushi M, Eshghi A, Rezvani A. Effect of bioactive glass air abrasion on shear bond strength of two adhesive resins to decalcified enamel. J Dent (Tehran) 2014; 11: 644–54.
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ORIGINAL ARTICLE Dental Biomaterials
Surface topography and bond strengths of feldspathic porcelain prepared using various sandblasting pressures Elham Moravej-Salehi1, Elahe Moravej-Salehi2 & Azam Valian3 1 Department of Restorative Dentistry, School of Dentistry, Shahed University, Tehran, Iran 2 Private Practice, Tehran, Iran 3 Department of Restorative Dentistry, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Keywords air abrasion, ceramic, sandblasting, scanning electron microscopy, shear bond strength. Correspondence Azam Valian, Assistant Professor, Department of Restorative Dentistry, School of Dentistry, Shahid Beheshti University of Medical Sciences, Daneshjou Blvd, Evin Ave, Tehran 19834, Iran. Tel: +989123163711 Email: [email protected] Received 9 December 2014; accepted 16 May 2015. doi: 10.1111/jicd.12171
Abstract Objective: The purpose of this study was to determine the bond strength of composite resin to feldspathic porcelain and its surface topography after sandblasting at different pressures. Methods: In this in vitro study, 68 porcelain disks were fabricated and randomly divided into four groups of 17. The porcelain surface in group 1 was etched with hydrofluoric acid. Groups 2, 3, and 4 were sandblasted at 2, 3 and 4 bars pressure, respectively. Surface topography of seven samples in each of the four groups was examined by a scanning electron microscope (SEM). The remaining 40 samples received the same silane agent, bonding agent, and composite resin and they were then subjected to 5000 thermal cycles and evaluated for shear bond strength. Data were analyzed using one-way ANOVA. The mode of failure was determined using stereomicroscope and SEM. Results: The highest shear bond strength was seen in group 4. however, statistically significant differences were not seen between the groups (P = 0.780). The most common mode of failure was cohesive in porcelain. The SEM showed different patterns of hydrofluoric acid etching and sandblasting. Conclusion: Increasing the sandblasting pressure increased the surface roughness of feldspathic porcelain but no difference in bond strength occurred.
Introduction Today, the use of materials that are aesthetically acceptable has become more popular in restorative dentistry.1 Ceramics are the most aesthetic materials available in restorative dentistry. For this reason, feldspathic ceramics are used in veneer frameworks and full ceramic restorations like inlays, onlays, laminates, and crowns.2 Ceramics are in a desirable range with respect to resistance to abrasion, chemical stability, biocompatibility, translucency, and fluorescency.2 The disadvantage of these materials is their low fracture strength.3 Porcelain fracture has been reported to be the second most common cause of failure after secondary caries.3,4 Porcelain fractures and chipping may be due to trauma, incomplete occlusal adjustments, parafunctional habits, ª 2015 Wiley Publishing Asia Pty Ltd
and fatigue failure. Incompatibility of the coefficient of thermal expansion between porcelain and the metal framework, failure of the adhesive bond, incomplete preparation, and inappropriate coping design may lead to failure.4 For intraoral repair of porcelain fractures, use of composite resin is recommended to avoid restoration replacement, time delay, and cost. It is also used to bond orthodontic brackets to porcelain. For this purpose, a standard method with optimal power and strength is needed to prepare the porcelain surface for repair without any detrimental effects.5 Many studies on the efficacy of ceramic surface treatment using burs, etching with hydrofluoric acid (HF), phosphoric acid, accidulated phosphate fluoride, ammonium bifluoride, lasers (CO2, Er-YAG, ND-YAG, Er,Cr-YSGG) and sandblasting have 1
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been published that reportedly increase the bond strength of resin material to porcelain.1,3,6,7 The use of HF followed by silane application is the standard clinical process for increasing the bond strength when repairing the porcelain surface with composite resin; this is because of the microporosities that hydrofluoric acid produces on the porcelain surface with selective dissolution of the glass matrix. This has been observed via scanning electron microscopy (SEM).2,3,8 Hydrofluoric acid acid is chemically poisonous and has higher tissue penetration ability compared to other etchants. It also has detrimental effects on soft tissues and causes caustic burns and necrosis. On the other hand, feldspathic porcelain surface etching with HF and unwanted contact with the enamel surfaces during work creates an insoluble fluoride salt that if not removed will lead to a lower bond strength.8,9 Sandblasting is a common method of surface treatment for increasing micromechanical retention because it produces a clean and active porcelain surface. On the other hand, it does not cause acute acid burns on the patient’s oral tissues. In this method the aluminum oxide particles remove the weakened phases of ceramic and create irregularities on the surface.10 These irregularities increase the surface area and improve the mechanical retention and bond.11 Surface topography analysis of treated ceramic with SEM provides qualitative information in this matter because this technique enables direct observation of the surface details with high resolution.12 The microsandblaster device allows for adjustment of different parameters such as the size of the abrasive particles, air pressure, time used, angle of nozzle, etc.5 Studies have shown that sandblasting for surface repair of ceramics is better performed with pure alumina particles between 30 and 250 lm, at high speed and with air pressure between 2 to 3 bars for nearly 15 sec.13 However, a study in 2013 showed that 5–15 sec of porcelain surface sandblasting produced almost similar shear bond strength.5 The results of Addison et al.14 showed that the best fracture strength of feldspathic porcelain laminates was produced with 50 lm alumina while 110 and 250 lm alumina particles reduced the bond strength. Also, the size of the particles, pressure, and angle of the machine affect the strength and life span of porcelain laminate restorations. A few studies have tried to evaluate the effect of different parameters of the sandblasting machine on the surface topography of feldspathic porcelain and the bond strength between composite and porcelain.5,15 On the other hand, different pressures of sandblasting machines have been used in previous studies for porcelain surface treatment. With respect to the lack of information on this matter, this study aimed to evaluate the effect of varying pressures of an intraoral sandblasting machine on the surface struc2
ture of feldspathic porcelain and bond strength to composite resin and compare it with the effect of hydrofluoric acid. The null hypothesis of this study was that sandblasting treatment at different pressures would not result in different shear bond strength and surface roughness. Materials and methods Sixty-eight porcelain discs (Ceramco 3; Dentsply Ceramco Co., Burlington, NJ, USA) (6 9 2 mm) were prepared in a mold according to the manufacturer’s instructions with a metal base of nickel chromium. The specimens were examined under a magnifying glass with 109 magnification to ensure absence of cracks. Initially the surfaces of the specimens were prepared using silicon carbide abrasive papers (400 and 600 grit) on a rotating metallographic polishing device under watercooling for 15 sec for the purpose of matching the specimens. Then they were rinsed with water and air-dried. The specimens were randomly divided into four groups of 17 and then coded. The below procedures were then carried out in sequence. 1 Control: 9.5% HF gel (Porcelain Etchant Gel, Bisco, Sachaumburg, IL, USA) was applied for 2 min to the surfaces of the specimens and then rinsed for 1 min and air-dried for another minute. 2 The surfaces of the specimens were sandblasted using an intraoral sandblasting device (Microsandblaster; Dento-Prop Ronvig, Denmark) with 50 lm alumina particles (Ronvig, Denmark) at a pressure of 2 bars for 10 sec from the constant distance of 5 mm with an angle of 90°. Jigs had been made for the purpose of uniformity. Next the specimens were washed for 1 min and air-dried for another minute. 3 Similar to group 2 but sandblasting pressure was at 3 bars. 4 Similar to group 3 but sandblasting pressure was at 4 bars. Evaluation of surface topography For analysis of the surface topography of the 20 treated specimens (six of each group), initially a 15-nm-thick gold coating was applied using a Sputter Coater (K450X; Emitech, Ashford, UK). Next the SEM (VEGA; TESCAN, Brno, Czech Republic) micrographs in top view were obtained in five random areas for each specimen at 5009, 20009, 40009, and 100009 magnifications. For evaluation of surface topography in the lateral view, eight surface-treated specimens (two of each group) were cut vertically in half with a diamond disk under watercooling. Then they were rinsed with water and air-dried. Next lateral surfaces of specimens were gold coated in the ª 2015 Wiley Publishing Asia Pty Ltd
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Sandblasting pressures on porcelain
tion. The fracture mode of specimens was divided into three groups of adhesive, cohesive and mixed (adhesive/ cohesive). The cohesive fracture could have been in the porcelain or composite. One specimen of each group was observed randomly under SEM with 1009 and 10009 magnifications to evaluate the fracture mode. For this reason the specimens were gold coated (K450X; Emitech) and then observed with an electron microscope (VEGA; TESCAN) to evaluate their surface topography.
same way as mentioned above. The SEM micrographs were obtained at 15009 magnification. Evaluation of bond strength On the surface of 40 of the surface-treated specimens, a layer of silane agent (Bis-Silane Agent Parts A and B; Bisco) was applied using a microbrush. This was done for 1 min and dried with air-flow for 30 sec. Following this a layer of resin bond (D/E Resin; Bisco) was applied and cured with a light-curing unit (Starlight Pro, Mectron, Italy) with an intensity of 600 mW/cm2. Next, the composite resin (AELITETM All Purpose Body; Bisco) was applied in 2-mm-thick increments into clear plastic cylinders (Tygon tubes, 3 9 4 mm) over the bonding surface. Each layer was cured for 40 sec. The composite cylinders were light-cured from all three dimensions with an angle of 45° for an extra 120 sec from the porcelain surface. After the removal of Tygon tubes from the specimens under the stereomicroscope (Nikon SMZ800, Tokyo, Japan) with 109 magnification, the specimens were stored in sterile water in an incubator at 37°C for 24 h. Then specimens were subjected to 5000 thermal cycles at 5 and 55°C for 30 sec in each bath and a dwell time of 10 sec in a thermocycling machine (Malekteb, Tehran, Iran). Next, each specimen was mounted in cold cure acrylic resin. For the purpose of evaluation of shear bond strength, the specimens were moved to the universal testing machine (Zwick Roell Z050, Ulm, Germany) and force was applied at a crosshead speed of 1 mm/min to the interface of composite and porcelain. The bond strength was recorded in MPa. Normal distribution of data was ensured using the Kolmogorov–Smirnov test and with respect to the confidence interval of 95%, data were analyzed using Tukey’s test and one-way ANOVA by SPSS version 18.0 software (SPSS Inc., Chicago, IL, USA).
Results The mean values of shear bond strength are listed in Table 1. The highest shear bond strength was in group 4 (15.76 3.51). The lowest mean strength was in group 2 (14.11 3.36). There was no statistically significant difference between the groups (P = 0.780) (Table 2). The frequency of different fracture modes in the study groups (determined by stereomicroscope) can be seen in Table 3. All cohesive fractures were in the porcelain. Figure 1 shows evaluation of fracture mode under SEM at 1009 magnification. The results of SEM analysis of feldspathic porcelain surface etched with 9.5% HF gel for 2 min were compared to the sandblasted surfaces with 50-lm alumina particles at different pressures showing different surface morphology. In both methods the surface was rough and porous (Figure 2). Also, with the increase of sandblaster pressure from 2 to 4 bars, a slight increase in surface roughness was noted. Discussion Using intraoral repair technique and surface treatment, ceramic restorations can be repaired with composite resin with no need to replace the restoration.16 The adhesion mechanism of restorative materials is based on two theories: the chemical adhesion of molecules at the interface and micromechanical retention based on penetration of adhesive and mechanical interlocking.17 Acid-etching and sandblasting with alumina particles are among the most
Evaluating the mode of failure The mode of fracture of specimens was evaluated by a stereomicroscope (Nikon SMZ800) with 409 magnificaTable 1. Shear bond strength of samples in MPa
95% CI for the mean Group
Mean
Standard deviation
1 2 3 4
15.27 14.11 15.07 15.76
3.63 3.36 3.98 3.51
Lower bound
Upper bound
Minimum
Maximum
12.67 11.71 12.40 13.25
17.88 16.52 17.75 18.27
9.04 9.89 9.91 9.72
19.88 20.40 21.81 21.76
CI, confidence interval.
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Table 2. Statistical comparison of groups using Source of variation
Total sum of squares
Degrees of freedom
Mean squares
Intergroups Intragroups Total
14.408 489.978 504.386
3 37 40
4.803 13.243
ANOVA
F
Level of significance
0.363
0.780
Table 3. Frequency (percentage) of modes of failure of samples in the groups under study Mode of failure (%) Group
Cohesive
Adhesive
Cohesive/adhesive
1 2 3 4
90 60 70 90
– 20 10 –
10 20 20 10
common methods for surface treatment of silica-based ceramics.16 This study sought to determine the suitable sandblasting pressure for surface preparation of the feldspathic porcelain and to compare it with the effect of etching with hydrofluoric acid (HF). Within the limitations of this study, the results showed that the shear bond strength following sandblasting with 50-lm alumina particles at 2, 3 and 4 bar pressure was not significantly different and made no difference to the shear bond strength following acid etching with 9.5% HF (control group) (P = 0.780). Thus, the null hypothesis of the study regarding the bond strength was confirmed. Although increasing the sandblasting pressure from 2 to 4 bar slightly increased the bond strength. Previous studies have shown that all systems used for in-office porcelain repair should provide a minimum of 10 MPa bond strength at the interface.16 The bond strength values obtained in the present study in all surface treatment groups were within the acceptable range. It should be noted that all specimens underwent thermocycling before bond strength measurement in order to simulate the oral environment. Thermocycling has beenfound to be more accurate than water storage for simulating the effect of aging, and results in a reduction in bond strength greater than that due to long-term water storage and may even lead to spontaneous debonding.5 In the present study, similar to the study by Yung et al., thermocycling was done at 5000 cycles, which approximately corresponds to 6 months of clinical service of the restoration according to Gale and Dareell.18,19 The shear bond strength test is the most commonly used technique for evaluation of the efficacy of different 4
porcelain repair methods.16 This test is easy and quick and simulates the clinical situations.17 Moreover, it does not have the technical sensitivity of tensile and microtensile tests.20 In this study, the most common mode of failure was cohesive type in the porcelain; which is in accord with the results of many other studies.4,5,18 Studies have shown that if the bond strength between the porcelain and composite resin exceeds 13 MPa, cohesive failure may occur in the porcelain.21 In shear-bond strength testing, stress is heterogeneously distributed on the interface and more stresses are concentrated at regions far from the interface.This may lead to initiation of fracture on the porcelain surface.8,16,20 Application of 9.5% HF gel for 2 min along with silane is the most effective method for ceramic surface treatment. Thus, this technique was used for the control group specimens in this study.2,22 In the current study, SEM images showed irregularities and tunnel-like grooves and pores that seemed deeper than those seen on sandblasted surfaces. Such images have been reported in the majority of similar studies resembling honeycomb pattern.3,11,15,23 The reason for deeper porosities in HF group is that HF chemically reacts with the silica phase in between crystals and thus can penetrate to depth;3,7,10,15 while sandblasting has a mechanical mechanism based on the collision of particles as the result of air pressure and involves no chemical reaction. Thus, sandblasting increases surface porosities.12,13,15,21 Although HF is effective for porcelain surface conditioning, it has a corrosive nature,24 as it penetrates into the cells and disrupts their metabolism and subsequently kills them.3 Clinically, it can cause rash, burns, and deep tissue necrosis. Also, HF can severely traumatize tooth structure.3,24 Szep et al.25 found that HF leaves a layer of amorphous fluoride deposit on the tooth surface that interferes with the process of bonding and acid etching. Several studies have stated that this method cannot be applied in clinical dental practice especially for intraoral ceramic repair.2,8 On the other hand, acid etching with HF decreases the flexural strength of ceramics,22 whereas the sandblasting process is commonly used in prosthodontic laboratories and dental clinics.2 This process will result in micromechanical bonding and change in ceramic surface topography. It also increases surface roughness, surface area, and wettability of composite resin and ceramics.2,12 Studies have shown that sandblasting provides adequate bond strength.2,12,24 Scanning electron microscopy analyses of sandblasted ceramic surfaces showed irregular or hollow areas compared to surfaces subjected to acid etching.16 Profilometry, SEM and AFM analyses in different studies have shown that the mean surface roughness of sandblasted surfaces was greater and with prominently sharper points ª 2015 Wiley Publishing Asia Pty Ltd
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Sandblasting pressures on porcelain
(a)
(b)
(c)
(d)
Figure 1. Scanning electron microscopy analysis of the mode of failure of samples in groups 1–4 (from (a) to (d) respectively) (1009 magnification): (a) cohesive failure (b) adhesive failure, (c) cohesive failure, and (d) cohesive failure.
compared to surfaces etched with HF or laser-irradiated surfaces.2,17,26,27 In the present study sandblasting provided rougher surfaces compared to HF but the shear bond strength was not different. Ersu et al.27 also stated that although sandblasting provides a rougher surface, this roughness does not ª 2015 Wiley Publishing Asia Pty Ltd
make the bond stronger. This is due to the fact that sandblasting treatment creates irregularities without undercuts on the surface and even the bond strength may diminish in the long-term.28 On the other hand, hydrolytic changes aggravate during storage. This change is more significant in sandblasted specimens than those treated with HF 5
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Sandblasting pressures on porcelain
(a)
(b)
(c)
(d)
Figure 2. Scanning electron microscopy topography of the feldspathic porcelain surface in samples of groups 1–4 (from (a) to (d) respectively) (5009 magnification).
because the irregularities caused by acid etching are deeper. As a result resin is better preserved from the degradation process in HF treated specimens.29 In this study, the bond strengths of HF treated and sandblasted groups were found to be the same. This is due to the fact that the bond strength was compared in different groups after aging via thermocycling. 6
In sandblasting with alumina particles, by increasing the pressure from 20 to 100 psi a linear increase has been reported in the cutting rate on an enamel analogue.30 It has been discussed that in the sandblasting process very huge particles or very high pressures increase the bond strength but cause deformation of restoration because of abrasion.2 ª 2015 Wiley Publishing Asia Pty Ltd
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Sandblasting pressures on porcelain
Therefore, in the present study 2–4 bar pressures (most commonly used in previous studies) were used and no significant difference was found in the resultant bond strength values. However, there was a very high percentage of cohesive fractures of the porcelain in the 4 bar pressure suggesting a possible weakening of the porcelain which may have impacted on the results. Also, SEM analysis showed increased surface roughness and depth of impact as the result of increased pressure. Similar results were obtained when evaluating the effect of two different pressures on zirconia ceramics after thermocycling. Although microscopic evaluations showed increased surface roughness, no difference occurred in bond strength.31 It should be noted that the shear bond strength is not solely dependent on surface roughness and other factors also play a role in this respect.3 Therefore, HF by creating microretentive areas and increasing the surface roughness enhances the bond strength.3,7,22 While, the sandblasting process is based on increasing the surface roughness and surface area and does not have the ability to cause retentive undercuts,12,28 even by increasing the pressure. Since there is a threshold for surface porosities limiting their effect on bond strength,3,15 by increasing the pressure, despite increased surface area, no significant increase in bond strength is achieved. Considering the results of the present study, it can be stated that the bond strength achieved via lower bar pressure sandblasting is essentially the same as the high bar sandblasting and the HF treatment, and low bar pressure results in less damage to the porcelain. Because although high pressure sandblasting increases surface roughness, it decreases the strength of porcelain restoration, can cause chipping of the porcelain or significant loss of porcelain material, and is also high risk for soft and hard tissues in the mouth such as damage to remineralized tooth surface
References 1 de Paula Eduardo C, Bello-Silva MS, Moretto SG, Cesar PF, de Freitas PM. Microtensile bond strength of composite resin to glass-infiltrated alumina composite conditioned with Er, Cr: YSGG laser. Lasers Med Sci 2012; 27: 7–14. 2 Yavuz T, Dilber E, Kara HB, Tuncdemir AR, Ozturk AN. Effects of different surface treatments on shear bond strength in two different ceramic systems. Lasers Med Sci 2013; 28: 1233–9. 3 Kukiattrakoon B, Thammasitboon K. Optimal acidulated phosphate fluo-
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layer.2,6,21,32 More studies are needed to confirm this clinically, but it would seem advantageous to use the lower pressure when working on porcelain repairs in the mouth. Last but not least, future studies are recommended to focus on the resultant strength of various porcelain specimens treated with air abrasion alone. Conclusions Within the limitations of this in vitro study: (a) sandblasting with 50 lm alumina particles at 2, 3 and 4 bar pressure from a constant distance of 5 mm for 10 s and 90° nozzle angulation did not significantly change the shear bond strength of feldspathic porcelain to composite resin; (b) the bond strength after sandblasting was similar to that after the application of 9.5% HF for 2 min; (c) SEM results demonstrated that a porous surface resulted from HF etching and sandblasting, however, HF caused deeper pores while sandblasting caused sharp points and more homogeneous pores; (d) SEM analysis of specimens sandblasted with 2–4 bar pressure showed slightly increased surface porosities and depth of pores; (e) the results of this study suggest that it may be advantageous to use a low bar pressure when sandblasting porcelain for intraoral repair. Acknowledgments This investigation was supported by Deputy of Research, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran. This article was based on a research project (number 310/2598).
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ceramic restorations: a scanning electron microscopic investigation. J Prosthet Dent 2000; 83: 668–74. Schmage P, Nergiz I, Herrman W, € Ozcan M. Influence of various surface-conditioning methods on the bond Strength of metal brackets to ceramic surfaces. Am J Orthod Dentofacial Orthop 2003; 123: 540–6. Ersu B, Yuzugullu B, Yazici AR, Canay S. Surface roughness and bond strengths of glass-infiltrated alumina ceramics prepared using various surface treatments. J Dent 2009; 37: 848– 56. Wood DJ, Bubb NL, Millar BJ, Dunne SM. Preliminary investigation of a novel retentive system for hydrofluoric acid etching resistant dental ceramics. J Prosthet Dent 1997; 78: 275–80. Torres SMP, Borges GA, Spohr AM, Cury AADB, Yadav S, Platt JA. The effect of surface treatments on the micro-shear bond strength of a resin luting agent and four all-ceramic systems. Oper Dent 2009; 34: 399–407. Paolinelis G, Banerjee A, Watson TF. An in-vitro investigation of the effects of variable operating parameters on alumina air-abrasion cutting characteristics. Oper Dent 2009; 34: 87–92. Kern M, Barloi A, Yang B. Surface conditioning influences zirconia ceramic bonding. J Dent Res 2009; 88: 817–22. Khoroushi M, Eshghi A, Rezvani A. Effect of bioactive glass air abrasion on shear bond strength of two adhesive resins to decalcified enamel. J Dent (Tehran) 2014; 11: 644–54.
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