Author’s Accepted Manuscript Investigation of the fatigue behavior of adhesive bonding of the lithium disilicate glass ceramic with three resin cements using rotating fatigue method E. Yassini, M. Mirzaei, A. Alimi, M. Rahaeifard www.elsevier.com/locate/jmbbm

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S1751-6161(16)00016-3 http://dx.doi.org/10.1016/j.jmbbm.2016.01.013 JMBBM1774

To appear in: Journal of the Mechanical Behavior of Biomedical Materials Received date: 6 December 2015 Revised date: 13 January 2016 Accepted date: 18 January 2016 Cite this article as: E. Yassini, M. Mirzaei, A. Alimi and M. Rahaeifard, Investigation of the fatigue behavior of adhesive bonding of the lithium disilicate glass ceramic with three resin cements using rotating fatigue method, Journal of the Mechanical Behavior of Biomedical Materials, http://dx.doi.org/10.1016/j.jmbbm.2016.01.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Investigation of the fatigue behavior of adhesive bonding of the lithium disilicate glass ceramic with three resin cements using rotating fatigue method E .Yassinia, M. Mirzaeia, A. Alimib, M. Rahaeifardc * a

Department of Operative Dentistry, Dental Research Center, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. b

Department of Operative Dentistry, School of dentistry, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. c

Department of Mechanical Engineering, Golpayegan University of Technology, Golpayegan, Iran.

Abstract Objective: To investigate the fatigue behavior of bonding interface of lithium disilicate ceramic with three different dual cure resin cements. Material and Methods: Forty five bar shaped ceramic-resin-ceramic specimens were prepared and divided into 3 groups (n=15) according to the resin cement used (group1: Panavia F2.0, group 2: RelyX Ultimate, group 3: Duo-Link Universal). Three specimens of each group were tested using three point bending test and the fracture strength of the resin-ceramic bond was measured. Other specimens of each group were placed in the rotating fatigue testing machine at stresses equal to 30%, 40%, 50% and 60% of the fracture strength. The cyclic loading was continued until fracture or a maximum of 10000 cycles. For the specimens which did not fail until 10000 cycles, the cyclic loading was stopped and the fracture strength of the specimens was measured. Results: None of the specimens with cyclic loads of 30% and 40% of the fracture strength, have failed until 10000 cycles. After 10000 load cycles, the fracture strength of these specimens was significantly *

Corresponding author, Email: [email protected]

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lower than their initial fracture strength. On the other hand, all specimens with cyclic stresses equal to 50% and 60% of the fracture strength have failed before 10000 cycles so that the numbers of load cycles of RelyX specimens were significantly higher than those of Panavia ones and the numbers of cycles of Panavia specimens were significantly higher than those of Duo-Link specimens. Conclusion: The fatigue resistance of the ceramic-resin interface is significantly lower than its bond strength. Furthermore, RelyX Ultimate showed the highest fatigue resistance and Duo-Link Universal exhibited the weakest fatigue resistance. Since dental restorations are under cyclic loading caused by mastication forces, the results of this research can be used to select fatigue resistant resin cements for bonding of ceramic restorations. Keywords: Bonding; Fatigue; Resin cement; Lithium disilicate.

1. Introduction Dental ceramics are widely used for different types of restorations such as veneers, inlays, onlays and crowns. They have excellent properties such as chemical stability, biocompatibility, low thermal conductivity, high compressive strength, thermal diffusivity, translucency and fluorescence (Guarda et al., 2013; Song et al., 2016). Lithium disilicate glass ceramics are a new generation of heat pressed ceramics that have higher fracture toughness and flexural strength than the first generation of leucite based ceramics (Sakaguchi and Powers, 2012). They have enhanced mechanical properties and they are used in different types of restorations (Alao and Yin, 2015; Denry and Holloway, 2010). Resin based cements are the material of choice for luting ceramic restorations (Tolidis et al., 2012). There is a trend toward the use of the dual-polymerized luting agents for the restorations thicker than 2 mm (Akgungor et al., 2005). Dual cure cements have a high degree of polymerization due to their chemical activators (Blatz et al., 2003). The clinical success of ceramic restorations depends on various factors including the stability of the bonded interface with time. When ceramic restorations are cemented and

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exposed to oral environment, some factors can result in fatigue and influence on the physical and chemical properties of the resin-ceramic bonding (Guarda et al., 2013). Fatigue phenomenon is caused by cyclic loads produced by mastication forces or thermocycling. These cyclic stresses are repeated about 300000 time per year for an average person (Kawai et al., 2011; Lin et al., 2013). The cyclic load causes cracks to propagate along the material resulting weakening of the restoration (Guarda et al., 2013). Finally, at the last cycle of loading, the strength of the restoration becomes less than the magnitude of the cyclic stress and the fracture happens (Smyd, 1961; Wiskott et al., 1994b). In this situation, the restoration fails at the cyclic loads significantly lower than its fracture load (Lin et al., 2013; Mirmohammadi et al., 2010; Mirmohammadi et al., 2011). As the value of the cyclic stress increases, the failure occurs after lower number of cycles (Jung et al., 2000; Yahyazadehfar et al., 2013). An important characteristic of the fatigue behavior of materials is the relation between the magnitude of the cyclic stress and the number of cycles causing the fracture. This relation is usually presented by a curve known as S-N curve in which, for the various values of cyclic stress, the number of load cycles leading to the fracture is illustrated (Harik et al., 2002; Mutluay et al., 2013; Park et al., 2008). The vertical axis of this chart is the magnitude of cyclic stress and the horizontal axis shows the logarithm of number of load cycles which causes the failure of material. This curve is produced by interpolation of experimental data. The effect of fatigue phenomenon on the fracture of dental materials is widely investigated in the literature (Hayashi et al., 2008; Heintze et al., 2016; Michel et al., 1988; Patterson and Johns, 1991; Studart et al., 2007). A simple and efficient method to apply cyclic load, is the rotating fatigue approach (Keulemans et al., 2010; Scherrer et al., 2003). In this method, the specimens are prepared in the form of cantilevers and the cyclic load is applied by axially rotating this cantilever under a constant bending load (Mirmohammadi et al., 2010; Mirmohammadi et al., 2009). Due to the important role of fatigue in failure of dental restorations, in this work, the fatigue behavior of the bonding interface of the lithium disilicate ceramic with three different dual cure resin cements was investigated, using the rotating fatigue test. To this goal, bar shaped lithium disilicate specimens were

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prepared and bonded with three different resin cements (Panavia F2.0, RelyX Ultimate, Duo-Link Universal). Cyclic loads with magnitudes lower than the fracture strength of bonding were applied to the specimens and the loading continued until fracture or a maximum of 10000 load cycles. For the specimens which failed before 10000 cycles, the number of cycles leading to fracture was measured and for those which did not fail until 10000 cycles, the remained fracture strength after load cycling was measured and compared with the initial fracture strength. According to these quantities, the fatigue behavior of the interface of lithium disilicate ceramic with abovementioned resin cements were compared and discussed.

2. Materials and Methods 2.1. Preparation of the specimens Ninety lithium disilicate (IPS e.max Press, Ivoclar Vivadent) bars with length of 25 mm and circular cross section (d=3 mm) were prepared by heat-pressed technique. These bars were divided into 3 groups (each group contained 30 bars). For all groups the cross section of each bar was etched with 9.5% hydrofluoric acid (HF) for 90 seconds, and then rinsed with water. One layer of a silane coupling agent was applied onto etched surface of the specimens and then air dried for 5 seconds. In all groups, the specimens were divided into 15 couples which were bonded together from their cross section using different resin cements (group 1: Panavia F2.0, Kuraray; group 2: RelyX Ultimate, 3M ESPE; group 3: Duo-Link Universal, Bisco) so that 15 specimens were prepared for each group. The composition of the resin cements are presented in table 1.

Table 1.Resin cements and their compositions.

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The bars were bonded according to the manufacturers’ instruction and a split mold was used to obtain straight specimens. A schematic view of preparation of specimens is presented in figure 1.

Figure 1. Schematic view of specimen preparation.

2.2. Three-point bending fracture test The fracture strength of the resin-ceramic interface of the specimens was measured using three point bending test. Three specimens of each group were tested using universal testing machine (H10KS, TiniusOlsen, USA) at 0.5mm/min crosshead speed. The fracture stress of the specimens was calculated using the following relation (Beer et al., 2006).

(1)

In which, F is the fracture load and L is the support span.

2.3. Rotating fatigue test The 12 remained specimens of each group were placed in the rotating fatigue testing machine as shown in figure 2.

Figure 2. Rotating fatigue testing machine.

The specimens were cantilevered and the stress was produced in the interface by applying a constant load at the free end of the specimen. At the interface, the maximum of stress occurs at the top and bottom points (points A and B in the figure) noting that at the top point the tensile stress is produced while the 5

stress at the bottom point is compressive (Beer et al., 2006). The value of this stress is given by the following equation (Beer et al., 2006).

(2)

where, F is the applied load and L is the distance of the load from the interface. By rotating the cantilever, the location of top and bottom points are reversed and the stress alternates between compressive and tensile and the cyclic loading can be applied to the interface of the specimens. For each group, the 12 remained specimens were divided into 4 subgroups (each of 3 specimens) and different values of cyclic loading were applied to each subgroup (subgroup A: 30% of the fracture stress, subgroup B: 40% of the fracture stress, subgroup C: 50% of the fracture stress, subgroup D: 60% of the fracture stress). The cyclic loading was continued until failure or to a maximum of 10000 cycles. If the failure has not happen until 10000 cycles, the cyclic loading was stopped and the fracture strength of specimen was measured using three point bending test and the reduction of the fracture strength due to 10000 cycles of loading was obtained.

2.4. Scanning electron microscopy (SEM) The fractured surface (i.e. the interface shown in figure 1) of one specimen of each group was examined under vacuum condition using scanning electron microscope (XL 30; Philips, The Netherlands) to ensure that the fracture was happened in the ceramic-resin interface. The fractured surfaces were coated with gold using a sputter coater and scanned under SEM at the voltage of 20 kV and magnifications of 20 × and 40×.

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2.5. Statistical analysis Means and standard deviations of the data of all groups were calculated. Two way analysis of variance (ANOVA) and Tukey’s post hoc test were utilized to analyze the data. The analysis was performed using SPSS software (SPSS, Version 22, SPSS Inc., Chicago, IL, USA) and p values less than 0.05 were considered to show significant difference.

3. Results For all of the specimens under cyclic loads of 30% or 40% of the fracture strength (subgroups A and B), the failure did not happen until 10000 cycles. The fracture strength of these specimens was measured after 10000 cycles and compared with the initial fracture strength. The results of this comparison are presented in table 2.

Table 2- Initial and remained fracture strength of the specimens (MPa).

According to the results, after rotating fatigue test, the fracture strength of the specimens in subgroups A and B was significantly lower than the initial fracture strength (p

Investigation of the fatigue behavior of adhesive bonding of the lithium disilicate glass ceramic with three resin cements using rotating fatigue method.

To investigate the fatigue behavior of bonding interface of lithium disilicate ceramic with three different dual cure resin cements...
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