Original Article
Effects of different etching methods and bonding procedures on shear bond strength of orthodontic metal brackets applied to different CAD/CAM ceramic materials S. Kutalmıs Buyuka; Ahmet Serkan Kucukekencib ABSTRACT Objective: To investigate the shear bond strength (SBS) of orthodontic metal brackets applied to different types of ceramic surfaces treated with different etching procedures and bonding agents. Materials and Methods: Monolithic CAD/CAM ceramic specimens (N ¼ 120; n ¼ 40 each group) of feldspathic ceramic Vita Mark II, resin nanoceramic Lava Ultimate, and hybrid ceramic Vita Enamic were fabricated (14 3 12 3 3 mm). Ceramic specimens were separated into four subgroups (n ¼ 10) according to type of surface treatment and bonding onto the ceramic surface. Within each group, four subgroups were prepared by phosphoric acid, hydrofluoric acid, Transbond XT primer, and Clearfill Ceramic primer. Mandibular central incisor metal brackets were bonded with light-cure composite. The SBS data were analyzed using three-way analysis of variance (ANOVA) and Tukey HSD tests. Results: The highest SBS was found in the Vita Enamic group, which is a hybrid ceramic, etched with hydrofluoric acid and applied Transbond XT Adhesive primer (7.28 6 2.49 MPa). The lowest SBS was found in the Lava Ultimate group, which is a resin nano-ceramic etched with hydrofluoric acid and applied Clearfill ceramic primer (2.20 6 1.21 MPa). Conclusions: CAD/CAM material types and bonding procedures affected bond strength (P , .05), but the etching procedure did not (P . .05). The use of Transbond XT as a primer bonding agent resulted in higher SBS. (Angle Orthod. 2018;88:221–226.) KEY WORDS: CAD/CAM ceramic material; Orthodontic metal brackets; Shear bond strength; Surface treatment.
cient shear bond strength (SBS).1,3,4 Because the ceramic structure is inert, several processes are being performed on the ceramic surface to increase the bond strength of orthodontic brackets.5 Additionally, a sufficient bonding value for the bracket can be ensured by changing the bonding agents that provide the connection between the ceramic surface and the bracket.2,6,7 Different mechanical and chemical surface conditioning methods can be performed on the ceramic surface to enhance the bond strength of orthodontic brackets to ceramic restorations.8,9 One method is the use of hydrofluoric acid etching.10 However, because of its destructive nature, hydrofluoric acid may lead to trauma to the soft tissues and dental structures; therefore, the utmost care should be taken during its use.11 Phosphoric acid is also used to etch the ceramic surface, but the resulting bond strength was shown to be substantially lower than that of hydrofluoric acid.12 Although ceramic and other esthetic restorations are frequently used in prosthetic dentistry because of their advantages such as esthetic appearance, biocompat-
INTRODUCTION Dental ceramic restorations are frequently used in adults having severe substance loss from their teeth.1 In recent years, the need for bracket bonding to ceramic restorations has emerged with the increasing need for orthodontic treatment. In addition, orthodontists often experience difficulties with bracket bonding to ceramic restorations.2 Many studies have shown that bonding brackets to ceramic restorations has insuffia Assistant Professor, Department of Orthodontics, Faculty of Dentistry, Ordu University, Ordu, Turkey. b Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Ordu University, Ordu, Turkey.
Corresponding author: Dr S. Kutalmıs Buyuk, Department of Orthodontics, Faculty of Dentistry, Ordu University, Ordu 52100, Turkey (e-mail:
[email protected])
Accepted: October 2017. Submitted: July 2017. Published Online: November 15, 2017 Ó 2018 by The EH Angle Education and Research Foundation, Inc. DOI: 10.2319/070917-455.1
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Figure 1. Flowchart of the study groups.
ibility, and resistance to abrasion, they cause difficulties when used for adult bracket bonding.13,14 Recently, new types of computer-aided design and computeraided manufacturing (CAD/CAM) ceramic types have been developed for dental use. Differences arise from the type of production and the chemical and physical properties of ceramic material.15,16 The purpose of this in vitro study was to investigate the shear bond strength of orthodontic metal brackets applied to different types of ceramic surfaces treated with different etching procedures and bonding agents.
Turkey) with the polished surface exposed. Forty ceramic specimens in each CAD/CAM material group were divided equally into four subgroups of 10 specimens each according to the etching agents and primers used (Figure 1):
MATERIALS AND METHODS Monolithic CAD/CAM ceramic specimens (N ¼ 120; n ¼ 40 each group) of feldspathic ceramic Vita Mark II (VM), resin nanoceramic Lava Ultimate (LU), and hybrid ceramic Vita Enamic (VE) were produced (14 3 12 3 3 mm) from blocks using a low-speed cutting machine (Isomet 1000, Buehler, Ill). The upper side of all ceramic specimens was ground finished with 600-, 800-, 1000-, and 1200-grit silicon carbide paper (Atlas, Kocaeli, Turkey) on a sanding machine under a water cooling machine (Phoenix Beta, Buehler, Ill). Polishing procedures were performed using polishing discs and polishing paste with an electric handpiece at 10,000 rpm/min for 20 seconds. All specimens were ultrasonically cleaned and then embedded in autopolymerizing acrylic resin blocks (Panacryl; Incidental Istanbul, Angle Orthodontist, Vol 88, No 2, 2018
Hydrofluoric acid þ Clearfill ceramic primer (HFCL): specimens were conditioned with hydrofluoric acid (Ultradent Porcelain Etch 9.6 % Buffered, Ultradent Products, South Jordan, Utah) for 1 minute, then washed for 1 minute and air-dried. Clearfil ceramic primer (Kuraray Medical Inc, Okayama, Japan) was applied to the etched ceramic surface according to the manufacturer’s directions, and air-dried for 60 seconds. Phosphoric acid þ Clearfill ceramic primer (H3PO4CL): the specimens were etched with 40% phosphoric acid gel (K-etchant gel: 40% phosphoric acid, Kuraray) for 1 minute, then washed for 1 minute and air-dried. Clearfil ceramic primer was applied to the etched ceramic surface according to the manufacturer’s directions, and air-dried for 60 seconds. Hydrofluoric acid þ Transbond XT adhesive primer (HFTR): the specimens were conditioned with hydrofluoric acid for 1 minute, then washed for 1 minute and air-dried. Transbond XT adhesive primer (3M Unitek, Monrovia, Calif) was applied to the etched ceramic surface according
EFFECTS OF DIFFERENT METHODS AND PROCEDURES ON BOND STRENGTH
Figure 2. Experimental design of shear bond testing.
to the manufacturer’s directions, and air-dried for 60 seconds. Phosphoric acid þ Transbond XT adhesive primer (H3PO4TR): the specimens were etched with 40% phosphoric acid gel for 1 minute, then washed for 1 minute and air-dried. Transbond XT adhesive primer was applied to the etched ceramic surface according to the manufacturer’s directions and air-dried for 60 seconds.
Following application of surface conditioning and primer bonding agents, light cure bonding resin (Transbond XT, 3M Unitek) was applied to the base of standard stainless mandibular incisor metal brackets (Mini Master, American Orthodontics, Sheboygan, Wisc). The metal brackets were then placed on the ceramic surface and a standardized stable pressure was applied to the top surface of the bracket using a customized metallic bracket plier to obtain a uniform adhesive thickness. For consistency, all the attachments were bonded to the samples by the same clinician (S.K.B.). The light-cured adhesive paste was photopolymerized for a total of 20 seconds from two directions (mesial and distal aspects of bracket) using an LED device (Valo, standard mode, 1000 mW/cm2; Ultradent). The bonded specimens were stored in deionized water at 378C for 24 hours.
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The SBS test was done using a universal testing machine (Shimatsu Instron, Shimatsu Corp, Kyoto, Japan) at a crosshead speed of 0.5 mm/min. The shearing wedge was positioned vertically at the bracket base (Figure 2). The values of SBS data were calculated in MPa. After debonding, the fractured samples were examined under 103 magnification and the adhesive remnant index (ARI) was defined (5 ¼ no adhesive paste remained on the ceramic surface; 4 ¼ less than 10% of adhesive paste remained; 3 ¼ more than 10%; however, less than 90% of the adhesive paste remained; 2 ¼ more than 90% remained; 1 ¼ all the adhesive paste, with an impression of the bracket base, remained).17 Statistical analysis (SPSS 20.0; SPSS Inc, Chicago, Ill) of the SBS (MPa) data was performed using a threeway analysis of variance (ANOVA) and Tukey’s Honestly Significant Differences test, considering three factors (etching agent type, primer type, and ceramic type) and their interaction. Frequency distribution of the ARI scores among the 12 groups was assessed using the chi-square test. Statistical significance was performed at P , .05. RESULTS CAD/CAM material type and type of primer procedure affected the bond strength (P , .05), while the etching procedure did not (P . .05). There was no statistical relationship between CAD/CAM material and type of etching procedure nor CAD/CAM material and type of primer procedure (P . .05), but there was a statistically significant relationship between etching procedure and type of primer procedure using either the CAD/CAM material-etching or bonding procedure (P , .05; Table 1). The mean SBS values and standard deviation values are shown in Table 2. The highest SBS value was found in the Vita Enamic group, which is a hybrid ceramic, etched with hydrofluoric acid and Transbond XT adhesive primer. The lowest SBS value, however, was found in the Lava Ultimate group, which is a resin
Table 1. Results of Three-Way Analysis of Variance With Dependent Variable (MPa) Source of Variation Type of CAD/CAM material Type of etching procedure Type of primer procedure Type of CAD/CAM material 3 Type of etching procedure Type of CAD/CAM material 3 Type of primer procedure Type of Etching procedure 3 Type of primer procedure Type of CAD/CAM material 3 Type of etching procedure 3 Type of primer procedure Error Total
Mean Square
F
P
55.937 9.305 85.545 18.310 19.975 31.688 41.697
2 1 1 2 2 1 2
27.969 9.305 85.545 9.155 9.988 31.688 20.848
7.491 2.492 22.912 2.452 2.675 8.487 5.584
.001 .117 .000 .091 .073 .004 .005
403.233 3424.161
108 120
3.734
Type III Sum of Squares
df
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Table 2. Mean and Standard Deviation (SD) of the Shear Bond Strength (SBS) (MPa) of the Different Groups and Tukey Analysis 95% Confidence Interval for Mean N Hydrofluoric acid etching Clearfill Primer 10 VMf VE 10 LU 10 Transbond XT primer VM 10 VE 10 LU 10 Phosphoric acid etching Clearfill Primer VM 10 VE 10 LU 10 Transbond XT primer VM 10 VE 10 LU 10
Mean
Std Deviation
Std Error
Lower Bound
Upper Bound
6.34de 2.60ab 2.20a
2.40 2.15 1.21
0.76 0.68 0.38
4.63 1.06 1.33
8.06 4.14 3.07
6.36de 7.28e 5.66cde
2.19 2.49 1.15
0.69 0.79 0.36
4.79 5.49 4.84
7.92 9.06 6.48
4.16abd 5.01ade 3.38abc
1.92 2.48 1.21
0.61 0.78 0.38
2.79 3.24 2.52
5.53 6.79 4.25
5.23be 5.04ade 4.28abd
1.81 2.05 1.37
0.57 0.65 0.43
3.93 3.57 3.29
6.52 6.50 5.26
f VM indicates Feldspatic ceramic Vita Mark II; LU, Resin nanoceramic composite resin Lava Ultimate; VE, Hybrid ceramic Vita Enamic. Same superscript letters indicate not significantly different according to Tukey test, P . .05. Different superscript letters indicate significantly different according to Tukey test, P , .05.
nano-ceramic composite, etched with hydrofluoric acid and Clearfill ceramic primer. The ARI scores of the samples are shown in Table 3. There was a statistically significant difference in ARI scores among the groups (v2 ¼ 141.187; P , .001). DISCUSSION The aim of this study was to investigate the SBS of orthodontic metal brackets bonded to monolithic CAD/ CAM Vita Mark II, resin nano-ceramic, and hybrid ceramic materials in which different etching protocols and different bonding agents were applied. Reynolds reported that the clinically ideal bracket bond strength should be 5.8–7.8 MPa.18 In the current study, the SBS of the groups Vita Mark II HFCL, Vita Mark II HFTR, and Vita Enamic HFTR were greater than 5.8 MPa, while the SBS of the other groups was found to be less than 5.8 MPa. These differences might be due to the type of CAD/CAM ceramic material, the etching procedure, or the bonding material used. The study revealed that the CAD/CAM material type and bonding procedure affected the bond strength, while the etching procedure did not do so. To bond orthodontic brackets to ceramic surfaces with sufficient SBS, it is necessary to treat ceramic surfaces using different methods. These methods can be performed by mechanical means or chemically using strong acids such as hydrofluoric acid or with the help of phosphoric acid and bonding agents.5 In the study performed by Trakyali et al.,2 the optimum concentration of hydrofluoric acid was investigated in vitro. They found higher SBS in the 9.6% hydrofluoric Angle Orthodontist, Vol 88, No 2, 2018
acid etching group, but there was no statistically significant difference between the 9.6% and 5% hydrofluoric acid concentrations.2 In the current study, 9.6% hydrofluoric acid and 40% phosphoric acid were applied as a chemical etching agent to etch the surface of ceramic, which is frequently used in dentistry. Different etching durations also affected the bond strength of metal brackets applied to the ceramic surfaces. The groups etched for 60 seconds showed statistically higher SBS than did the groups etched for Table 3. Distribution of Adhesive Remnant Index (ARI) Scores Among the Groups ARI Scores 1 Hydrofluoric acid etching Clearfill Primer 7 VMa VE – LU – Transbond XT primer VM – VE LU – Phosphoric acid etching Clearfill Primer VM 5 VE – LU 1 Transbond XT primer VM 4 VE 10 LU 4 a
2
3
4
5
3 – –
– – –
2 4
8 6
1 1 –
– – –
2 2 1
7 7 9
4 1 –
– – –
– – –
1 9 9
2 – 6
1 – –
2 – –
1 – –
VM indicates Vita Mark II; LU, Lava Ultimate; VE, Vita Enamic.
EFFECTS OF DIFFERENT METHODS AND PROCEDURES ON BOND STRENGTH
20 seconds.19 In the current study, phosphoric acid and hydrofluoric acid were applied for 60 seconds, in accordance with the literature. SBS of orthodontic metal and ceramic brackets bonded to different CAD/CAM and conventional ceramic restorations have been evaluated previously.1,9,12,20 Abu Alhaija et al.1 compared alumina porcelain and lithium disilicate ceramic and did not find a statistically significant difference in any of the surface-treatment techniques. Turk et al.20 reported that lithium disilicate ceramic restorations had higher SBS than did feldspathic ceramic restorations. Abu Alhaija and Al-Wahadni9 compared lithium disilicate and feldspathic ceramic restorations and reported that feldspathic ceramic restorations had higher SBS. In a study performed by Elsaka,12 four different surface treatments were applied to Vita Enamic, and SBS was evaluated by bonding ceramic and metal brackets. Bonding ceramic and metal brackets to the Vita Enamic CAD/CAM material using a silica agent increased bond strength. In the current study, Clearfill and Transbond XT primer bonding agents were applied as bonding agents after etching. The groups treated with the Transbond XT primer bonding agent showed higher SBS. Studies revealed that the application of bonding agent such as silane increased the bond strength of orthodontic brackets to ceramic surfaces and composite restorations.2,6,21 Kim et al.22 evaluated the effects of various 10-methacryloyloxydecyl dihydrogen phosphate–containing primers and tribochemical silica coating on the SBS of metal orthodontic brackets to yttrium-stabilized tetragonal zirconia polycrystal (YTZP) ceramics. They found that, after alumina airborne-particle abrasion, the application of Clearfil ceramic primer, alloy primer, or Scotchbond Universal ensured stable bonding to Y-TZP ceramics. After tribochemical silica coating; however, only Clearfill ceramic primer produced a resistant bond to Y-TZP ceramics. Moreover, Zhang et al.23 reported that hydrofluoric acid etching followed by silane application was the ‘‘best suitable technique’’ for ideal bond strength for clinical practice on IPS Classic, a type of feldspathic porcelain. In the current study, Vita Mark II Lava ultimate, and Vita Enamic (a recently approved CAD/CAM ceramic material now on the market) ceramic materials were compared. Different SBSs were obtained in these ceramic groups wherein different etching processes and bonding agents were applied. This difference may be because of differences in the process of ceramic restoration and differences in their chemical and physical properties. The ARI scores showed that bond failure predominantly occurred with no composite remaining on the ceramic surface, because most of the adhesive
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remained on the bracket bases in most of the groups. These results are consistent with a previous study.1 Moreover, there was a statistically significant difference among the groups in terms of ARI scores (P , .001). CONCLUSIONS This in vitro study showed that
The type of CAD/CAM material and type of primer procedure influence SBS. There is a statistically significant relationship between types of etching procedure, primer procedure, and CAD/CAM material. The use of Transbond XT as a primer bonding agent resulted in higher SBS than did using Clearfill ceramic primer.
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