Department of Fixed Prosthodontics, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita-city, Osaka , Japan 2

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1 Dental Materials Journal 2016; 35(1): Bonding effectiveness of self-adhesive and conventional-type adhesive resin cements to CAD/CAM resin blocks. Part 1: Effects of sandblasting and silanization Mami HIGASHI 1 *, Mariko MATSUMOTO 1 *, Asuka KAWAGUCHI 1 *, Jiro MIURA 2, Takuya MINAMINO 1, Tomoshige KABETANI 1, Fumio TAKESHIGE 2, Atsushi MINE 1 and Hirofumi YATANI 1 1 Department of Fixed Prosthodontics, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita-city, Osaka , Japan 2 Division for Interdisciplinary Dentistry, Osaka University Dental Hospital, 1-8 Yamadaoka, Suita-city, Osaka , Japan Corresponding author, Atsushi MINE; mine@dent.osaka-u.ac.jp The present study assessed the effect of sandblasting and silanization on resin cement bond strengths to CAD/CAM resin blocks. Twenty four blocks (KATANA AVENCIA BLOCK) were divided into two resin cement groups (PANAVIA V5 [PV5] and PANAVIA SA CEMENT HANDMIX [PSA]), and further divided into four subgroups representing different surface treatment methods: no treatment (Ctl), silanization (Si), sandblasting (Sb), and Sb+Si. After resin application, microtensile bond strengths (μtbss) were measured immediately, 1, 3 and 6 months after water storage. In addition, surfaces resulting from each of the treatment methods were analyzed by scanning electron microscopy (SEM). Three-way analysis of variance revealed a statistically significant effect for the parameters surface treatment (p<0.001, F=370), resin cement (p<0.001, F=103, PSA<PV5), and water aging (p<0.001, F=18). Control treatment yielded significantly lower μtbs values compared to other treatment subgroups (p<0.001). The highest bond strength was achieved with Sb+Si treatment. SEM revealed that sandblasting roughened surfaces. Keywords: CAD/CAM resin blocks, Self-adhesive resin cement, Conventional resin cement, Sandblasting, Silanization INTRODUCTION Computer aided design/computer aided manufacturing (CAD/CAM) techniques in dentistry have been progressively developed permitting better standardization of techniques and improving the overall quality of dental restorations while simultaneously reducing costs of production. At present, CAD/CAM techniques can be used to produce not only inlays but also onlays, veneers and crowns 1). Many different materials including lithium disilicate glass ceramics, leucitereinforced glass ceramics, feldspathic glass ceramics, titanium, zirconia, and composite resin are conducive for production of dental restorations using CAD/CAM technology. In 2014, CAD/CAM manufactured resin fixed restorations for premolars started to be covered by Japanese social health insurance and have become extremely popular in Japan for several reasons. First, a tooth-colored restoration is preferable to a metal restoration for most patients. Second, the cost of CAD/ CAM resin blocks is reasonable compared to other esthetic materials such as zirconia. In addition, CAD/ CAM resin blocks exhibit similar color stability to glassceramic 2) because they are highly polymerized under standardized high pressure and temperature. Recent studies have shown that CAD/CAM manufactured resin fixed prostheses exhibit significantly higher fracture load values than conventionally-fabricated resin fixed *Authors who contributed equally to this work. Color figures can be viewed in the online issue, which is available at J-STAGE. Received Jul 9, 2015: Accepted Jul 28, 2015 doi: /dmj JOI JST.JSTAGE/dmj/ prostheses 3). A CAD/CAM resin block used in the present study was made with the new filler press and monomer infiltration method which increases the filler content compared to other CAD/CAM resin blocks and contain 62 wt% (48 vol%) inorganic filler 4). However, there is concern that these developments might lead to difficulties when bonding to resin cements is necessary or desirable. Indeed, Bähr et al. reported that if a high degree of conversion is achieved, no bond to resin composite can be established without conditioning 5). Therefore, the bonding for CAD/CAM manufactured resin fixed prostheses should be investigated more intensively. For enhanced bonding between CAD/CAM resin blocks and resin cements, sandblasting and silanization are recommended by manufacturers as necessary surface treatments. Sandblasting is expected to: 1) clean bonding surfaces; 2) create mechanical retention; and 3) increase the surface adherent area, resulting in higher bond strengths 6). Silanization is useful to promote the union of dissimilar materials by creating siloxane bonds (Si-O-Si) 7). However, insufficient evidence is available about these surface treatments 5,8) and many questions remain about the effect of sandblasting and silanization for bonding to CAD/CAM resin blocks. Moreover, manufacturers recommend both conventional-type adhesive resin cements and self-adhesive resin cements for bonding CAD/CAM resin blocks. Self-adhesive resin cements might be expected to show similar clinical performance as conventional-type adhesive resin cements when their high chemical and physical properties and

2 22 Dent Mater J 2016; 35(1): sufficient bond strengths to dentin are considered 9-11). Furthermore, in order to properly assess the clinical relevance and effectiveness of surface treatment on bonding, it is necessary to measure bond strengths after long-term water storage 12). In order to evaluate the bonding effectiveness, μtbs testing was used in the present study. Sirisha et al. reported that bonding effectiveness in the laboratory should be assessed by μtbs testing compared to other bond tests 13). The purpose of this study was to determine appropriate bonding procedures to CAD/CAM resin blocks. The null hypotheses were: (1) silanization and sandblasting have no effect on bonding effectiveness of resin cements to CAD/CAM resin blocks; (2) there are no differences between either conventional-type adhesive resin cement and self-adhesive resin cement in terms of bond strength of resin cements to CAD/CAM resin blocks or fracture mode when resin cements are used with CAD/CAM resin blocks; and (3) long-term water storage does not influence bond strength when resin cements are bonded to CAD/CAM resin blocks. MATERIALS AND METHODS Specimen preparation The materials used in the present study are listed in Table 1 and the experimental procedure is also schematically illustrated in Fig. 1. Twenty four CAD/CAM resin blocks (KATANA AVENCIA BLOCK, Kuraray Noritake Dental, Tokyo, Japan) with dimensions of mm were used. Each specimen was wet polished with #400- grit silicon-carbide paper (PRO-ACT, KOHNAN, Osaka, Japan). Specimens were divided so as to be bonded to one of two resin cement and each resin cement group was further divided into 4 subgroups according to the surface treatment method applied (n=3 per group). The surface treatment subgroups were: 1. Control (Ctl) subgroup: Specimens were air dried after polishing. 2. Silanization (Si) subgroup: Specimens were silanized with silane coupling agent (Clearfil Ceramic Primer Plus, Kuraray Noritake Dental) for 15 s and air dried. 3. Sandblasting (Sb) subgroup: Specimens were sandblasted with aluminum-oxide (Al 2O 3) particles of which mean particle size was 50 μm using airborne-particle abrasion (Adabrader, Table1 Materials used in this study with their application procedure Material Product (manufacturer) Composition Application procedure CAD/CAM resin block KATANA AVENCIA BLOCK (Kuraray Noritake) [227] Mixed filler with colloidal silica (Ø40 nm) and aluminum (Ø20 nm) oxide, Cured resins consisting of methacrylate monomer (Copolymer of Urethane dimethacrylate and other methacrylate monomers), Pigments Composite cement PANAVIA V5 (PV5) (Kuraray Noritake) [ U] PANAVIA SA CEMENT HANDMIX (PSA) (Kuraray Noritake) [1U0049] Paste A: Bis-GMA, TEGDMA, Hydrophobic aromatic dimethacrylate, Hydrophilic aliphatic dimethacrylate, Initiators, Accelerators, Silanated barium glass filler, Silanated, fluoroalminosilicate glass filler, Colloidal silica Paste B: Bis-GMA, Hydrophobic aromatic dimethacrylate, Hydrophilic aliphatic dimethacrylate, Silanated barium glass filler, Silanated alminium oxide filler, Accelerators, Dl-Camphorquinone, Pigments Paste A: 10-MDP, Bis-GMA, Triethyleneglycol dimethacrylate, Hydrophobic aromatic dimethacrylate, Silanated barium glass filler, Silanated colloidal silica, Dl-Camphorquinone, Benzoyl peroxide, Initiators Paste B: Bis-GMA, Hydrophobic aromatic dimethacrylate, Hydrophobic aliphatic dimethacrylate, Silanated barium glass filler, Silanated colloidal silica, Surface treated sodium fluoride, Accelerators, Pigments Build up on the CAD/CAM resin blocks and light-cure for 20 s for each 2 mm thick. Dispense equal amounts of paste A and paste B and mix for 10 s. Built up on the CAD/CAM resin blocks and light-cure for 20 s for each 2 mm thick. Other Clearfil Ceramic Primer Plus (Kuraray Noritake) [1F0005] 3-trimethoxysilylpropyl methacrylate, MDP, Ethanol Apply on the CAD/CAM resin blocks for 15 s and air-dry gently Bis-GMA: bisphenol A diglycidyl ether dimethacrylate, TEGDMA: triethyleneglycol dimethacrylate, MDP: 10-methacryloyloxi decyl phosphoate

3 Dent Mater J 2016; 35(1): Fig. 1 Schematic illustration of the experimental protocol polishing with a silicon-carbide paper. 2 Each group was further divided into 4 subgroups. 1. No treatment (Ctl) subgroup, 2. Silanization for 15 s (Si) subgroup, 3. Sandblasting for 15 s and ultrasonic cleaning for 120 s (Sb) subgroup, 4. 3 and silanization for 15 s (Sb+Si) subgroup. After each surface treatment, the surface was analyzed by SEM. 3 Resin cement increments were built up and light cured for 20 s. 4 Each specimen was stored in water at 37 C for 24 h. 5 Each specimen was then cut into approximately mm beams. 6 μtbs values of 24 beams per subgroup were measured immediately (0M), after one-month water storage (1M), after three-month water storage (3M), or after six-month water storage (6M). 7 Fractured surfaces after μtbs measurement were analyzed by SEM. Morita, Tokyo, Japan) for 15 s, ultrasonically cleaned for 120 s in distilled water, and air dried. 4. Sandblasting followed by silanization (Sb+Si) subgroup: Specimens were sandblasted and ultrasonically cleaned and then silanized. Sandblasting and silanization were performed in the same way as Sb subgroup and Si subgroup, respectively. After transparent partitions were put around the CAD/CAM resin blocks, PANAVIA V5 (PV5; Kuraray Noritake Dental) or PANAVIA SA CEMENT HANDMIX (PSA; Kuraray Noritake Dental) was applied to each treated surface and resin cement increments were built up (2 mm thick for each layer). Both cements were used following the manufacturers instructions (Table 1) and each cement layer was light-cured for 20 s using the same cordless light-emitting-diode curing light (Mini LED Ⅲ, Satelec, Merignac, France) which had a maximal light density of 2,200 mw/cm 2. Specimens were then stored in water at 37 C for 24 h. Micro-tensile bond strength (μtbs) test After water storage for 24 h, each specimen was cut into mm beams (0.5 mm 2, n=32 per blocks) with a slow-speed water-cooled diamond saw (MC-201N, MARUTO, Tokyo, Japan). Of the resulting 96 beams, 24 beams were randomly chosen for initial (0M) μtbs testing. Each beam was fixed to a jig with cyanoacrylate glue (Model Repair II Blue, Dentsply-Sankin, Tochigi, Japan) and subjected to a tensile force at a crosshead speed of 1.0 mm/min in a universal testing machine (EZtest SHORT, Shimadzu, Kyoto, Japan) until fracture occurred. Means and standard deviation were calculated and expressed in MPa. Remaining beams were randomly divided into 3 groups, and μtbs measured after 1 month (1M), 3 months (3M) or 6 months (6M). Among 6 months, the specimens were immersed and kept in the same water at 37 C in completely sealed containers. Scanning electron microscopy (SEM) observation The fractured surfaces after μtbs measurement and the representative surfaces of the CAD/CAM resin blocks after each surface treatment (n=4) were analyzed by SEM (JSM-6510LV, JEOL, Tokyo, Japan) to compare and contrast morphological differences (Fig. 1). For SEM observation, samples were mounted with carbon adhesion tape on a specimen holder and coated with platinum and SEM observation was operated at 15 kv. The fractured surfaces after μtbs measurement were examined under SEM to clarify the fracture mode. The fracture mode was classified into: [A] adhesive failure at the cement-block interface; [B] mixed failure; [C] cohesive failure in resin cement; or [D] cohesive failure in CAD/CAM resin block. Statistical analysis Microtensile bond strength values were analyzed using three-way analysis of variance (ANOVA) and Scheffé s method (α=0.05) using SPSS IBM version 21.0 (SPSS, Chicago, IL, USA). The level of statistical significance was set at α=0.05. RESULTS Observation of surface treatment effect SEM revealed that scars and debris were found after resin blocks were polished with the #400 grit siliconcarbide paper (Figs. 4a and b). Sandblasting removed the debris and increased surface roughness (Figs 4c and

4 24 Dent Mater J 2016; 35(1): d). Treatment with silane coupling agent application did not remove debris (Figs. 4e and f). There were no morphological differences between Ctl and Si subgroups. The surface seen on Sb+Si subgroup blocks was similar to that seen on the Sb subgroup blocks. Silanization did not produce any noticeable morphological changes. Microtensile bond strengths The mean μtbs and standard deviations (SD) are summarized per group in Table 2, and graphically presented in Fig. 2. No pre-testing failure was observed in the present study. Three-way ANOVA revealed a significant effect for the parameters surface treatment (p<0.001, F=370), resin cement (p<0.001, F=103), and water aging (p<0.001, F=18). μtbs values were significantly higher in the PV5 group than in the PSA group (p<0.001). In the PV5 cement group, the Ctl subgroup showed significantly lower μtbs values compared to the other groups (p<0.001). There was no significant difference in μtbs values between Si and Sb subgroups (p=0.48). The Sb+Si subgroup exhibited significantly higher μtbs values compared to the Si alone subgroup (p<0.001) or the Sb alone subgroup (p<0.001). Table 2 μtbs values (MPa) and types of failure mode PV5 PSA Ctl Si Sb Sb+Si Ctl Si Sb Sb+Si 0M (13.33) (12.36) [22/0/2/0] (12.65) [17/0/7/0] (6.40) [3/0/21/0] (11.36) [23/0/1/0] (11.90) [4/0/20/0] (10.67) [1/0/23/0] (13.44) [1/0/23/0] 1M (9.59) (13.57) [11/1/12/0] (13.37) [8/0/16/0] (11.43) [4/1/18/1] (16.45) (15.87) [11/2/11/0] (19.06) [5/0/19/0] (14.23) [0/3/21/0] 3M (12.39) (13.65) [16/0/8/0] (15.53) [8/0/16/0] (18.22) [0/0/24/0] (7.66) [22/0/2/0] (9.91) [12/3/9/0] (15.37) [5/0/19/0] (15.93) [4/0/20/0] 6M (13.57) (13.10) [23/0/1/0] (27.64) [8/0/16/0] (11.42) [3/0/18/3] (12.34) [22/0/2/0] (11.44) [14/0/10/0] (20.40) [5/0/19/0] (17.88) [4/0/20/0] Date are shown as mean (standard deviation). n=8 per group Numbers in square brackets show the number of specimens classified into four fracture modes [A/B/C/D]: [A] adhesive failure along the cement block interface; [B] mixed failure of cement and cement-block interface; [C] cohesive failure within resin cement; [D] cohesive failure within CAD/CAM resin block. Ctl: no treatment subgroup, Si: silanization subgroup, Sb: sandblasting subgroup, Sb+Si: silanization after sandblasting subgroup. 0M: immediately, 1M: after 1 month water storage, 3M: after 3 months water storage, 6M: after 6 months water storage. PV5: PANAVIA V5, PSA:PANAVIA SA CEMENT HANDMIX. Fig. 2 μtbs results of the PV5 group (a) and the PSA group (b). Columns connected by a line indicate significant difference (α<0.05). Ctl: no treatment subgroup, Si: silanization subgroup, Sb: sandblasting subgroup, Sb+Si: silanization after sandblasting subgroup. 0M: immediately, 1M: after 1 month water storage, 3M: after 3 months water storage, 6M: after 6 months water storage. PV5: PANAVIA V5, PSA:PANAVIA SA CEMENT HANDMIX.

5 Dent Mater J 2016; 35(1): In the PSA cement group, the Ctl subgroup demonstrated significantly lower μtbs values compared to the other subgroups (p<0.001). There was no significant difference in μtbs values between Si and Sb subgroups (p=0.39) and between Si and Sb+Si subgroups (p=0.43). Microtensile bond strength values decreased over time in both PV5 and PSA groups and the timedependent differences were statistically significant (0M vs. 1, 3 and 6M: p<0.001). Fig. 3 Fig Failure mode analysis cement comparison In the PV5 cement group, all samples showed adhesive failures in the Ctl subgroup while less than 40% adhesive failures were observed in the Sb and Sb+Si subgroups (Fig. 3a). A representative SEM image of adhesive failure is shown in Figs. 5a and b. The Si subgroup showed a higher number of adhesive failures than the Sb and Sb+Si subgroups (Fig. 3a). A higher number of cohesive failures within the PV5 resin cement was observed in the Sb+Si subgroup than other subgroups. The failure mode distribution of the PV5 group (a) and the PSA group (b). Ctl: no treatment subgroup, Si: silanization subgroup, Sb: sandblasting subgroup, Sb+Si: silanization after sandblasting subgroup. 0M: immediately, 1M: after 1 month water storage, 3M: after 3 months water storage, 6M: after 6 months water storage. PV5: PANAVIA V5, PSA:PANAVIA SA CEMENT HANDMIX. SEM observation of CAD/CAM blocks after surface treatment. a, b: Ctl subgroup. Scar and debris made by #400 polishing were observed on the surface. c, d: Sb subgroup. It was observed that the surface was markedly rough and no scar and debris remained. e, f: Si subgroup. As with a Ctl subgroup, the scar and debris were remained on the surface. Ctl: no treatment, Sb: sandblasting, Si: silanization.

6 26 Dent Mater J 2016; 35(1): subgroups after 1 month and this tendency continued to be observed after 3 and 6 months of water storage. DISCUSSION Fig. 5 SEM observation of fractured surfaces after μtbs test. a, b: PV5/Ctl/3M group. a: cement side; b: block side. SEM images demonstrated the adhesive failure. The scratch shown in Fig. 5a corresponds to that in Fig. 5b. c: PSA/Sb+Si/3M group (block side). The failure mode was the cohesive failure in cement. A lot of bubbles were observed on the surface (arrows). d: PV5/Si/1M (block side). Resin cements were found on the block surface. It meant that the fracture mode was the mixed failure. Ce: cement; Bl: block surface. Ctl: no treatment subgroup, Si: silanization subgroup, Sb+Si subgroup: silanization after sandblasting subgroup. 1M: after 1 month water storage, 3M: after 3 months water storage. PV5: PANAVIA V5, PSA:PANAVIA SA CEMENT HANDMIX. The number of adhesive failures decreased in both Si and Sb subgroups after 1 month of water storage. However, in the Si subgroup, the number of adhesive failures was increased at 3 and 6 months of water storage compared to 1 month of water storage. There were no time-dependent differences observed in the Ctl and Sb+Si subgroups. Only a few mixed failures were observed in both cement groups (Fig. 5d). In the PSA cement group (Fig. 3b), almost all samples showed cohesive failures within the resin cement in the Si, Sb and Sb+Si subgroups initially (0M), a notable difference from the Ctl subgroup which showed a higher number of adhesive failures. A lot of bubbles were observed on the surface in the cases where the fracture interfaces were within the resin cement (Fig. 5c). After water storage, the number of adhesive failures increased in the Si subgroup. Eighty percent of cohesive failures in the PSA resin cement were recorded in the Sb and Sb+Si The results of the present study dictate that the first null hypothesis that silanization and sandblasting have no effect on bonding effectiveness between CAD/CAM resin blocks and resin cements be rejected. Three-way ANOVA analysis revealed that surface treatment had the strongest effect on the bond strength (F=370). In the present study, the silanization improved the μtbs values in both PV5 and PSA cement groups. This may be due to the fact that the silane coupling agent created a chemical bond between the CAD/CAM resin blocks and resin cements, because silane coupling agents are adhesion promoters that facilitate chemical bonding between organic surfaces such as resin materials and inorganic surfaces 14). Yoshida et al. evaluated the shear bond strength of conventional-type adhesive cements to CAD/CAM resin block (GN-1, GC) using silane coupling agents and concluded that the application of silane coupling agents provided higher bond strength than without using silane coupling agents when evaluated after 50,000 time thermal cycling 15). In contrast, Zaghloul et al. reported that additional silanization did not increase bond strength between mechanically roughened CAD/CAM resins (Paradigm MZ100 and Paradigm C, 3M ESPE) and composite resin 9). However, the true effect of silanization cannot be correctly evaluated by a bond strength test when used on mechanically roughened surfaces. Sandblasting also significantly improved the μtbs values in both PV5 and PSA cement groups and SEM observation revealed that sandblasting produced micromechanically retentive surfaces and increased bonding surface area (Figs. 4c and d). The present study is the first article reporting on the bonding effectiveness between PV5/PSA and KATANA AVENCIA BLOCK. Shaymaa et al. evaluated the effect of surface treatments on the μtbs of self-adhesive resin cement to CAD/CAM resin blocks (Vita Enamic, Vita and Lava Ultimate, 3M ESPE) and the bond strength value achieved with sandblasting group was significantly higher than the control group for both types of CAD/CAM resin blocks 16). Stawarczyk et al. reported that sandblasting increased the bonding effectiveness for PMMA-based CAD/ CAM resin blocks 17). Furthermore, they reported that sandblasting before cementation of CAD/CAM crowns improved the tensile strength in both cements when polymeric CAD/CAM crowns luted on dentin abutment with self-adhesive cement or conventional-type adhesive cement 6). These results suggest that sandblasting is generally effective at increasing bond strengths when bonding to CAD/CAM resin blocks. There was no significant difference in μtbs values between the groups which treated with only sandblasting (Sb) and only silanization (Si). However, failure mode analysis revealed some important differences. Adhesive failures indicate that problems exist at the

7 Dent Mater J 2016; 35(1): adhesive interface as compared to cohesive failures or mixed failures. The frequency of adhesive failures in the Si subgroup tended to increase as the duration of water storage increased, a tendency was not observed in the Sb subgroup. For ceramics, the silanization procedure can improve resin ceramic bond even without micromechanical retention 10). However, for the CAD/CAM resin materials, micromechanical retention seemed to be essential not only for initial bond strength but also long-term durability. As with the present study, Wiegand et al. confirmed that adhesive conditioning alone for CAD/CAM polymer restorations without micromechanical retention is not adequate to obtain sufficient bond strength 18). The findings are supported by the result that a frequency of adhesive failures in the Sb+Si subgroup was the smallest observed in all subgroups. Therefore, it appears that the combination of sandblasting and silanization is necessary for bonding of CAD/CAM resin materials in the clinical setting in order to obtain maximal bond strengths that are maintained over time. The second null hypothesis that there are no differences between a conventional-type adhesive resin cement and a self-adhesive resin cement in terms of bond strength or fracture mode between CAD/CAM resin blocks and resin cements also was rejected when the results of the three-way ANOVA analysis (F=103) are considered. In the present study, a large number of cohesive failures in cement was observed especially in the PSA group indicating that this resin cement was the weak link during μtbs test. The tested PSA cement contains 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP), which is reported to decrease the mechanical properties of resin cements 19). On the other hand, PV5 is a conventional-type adhesive resin cement without 10-MDP and requires the pretreatment of a tooth with a primer containing 10-MDP which was not used in the present study. Moreover, PSA cement needs handmixing, possibly leading to the SEM observation that many more bubbles were incorporated into the cement (Fig. 5c). These bubbles also very likely played a role in decreasing the mechanical properties of this resin cements. Aksornmuang et al. reported that manipulation characteristics, e.g., hand-mix or auto-mix of the resin composite, could affect the strength of the material 20). It is important to evaluate the long-term durability and stability of bonding effectiveness. Durability and stability may be influenced by several factors, such as the physio-mechanical properties of luting materials, bonding strength between restorations and/or luting agents and/or dental tissues, and operator technique 9). The third null hypothesis that long-term water storage does not influence on bond strength between CAD/ CAM resin blocks and resin cements had to be rejected (F=18). Although the F-value was smaller than other two factors, three-way ANOVA revealed the significant effect of water aging and there were significant decrease of μtbs values obtained at 1M compared to at 0M (0M vs. 1, 3 and 6M: p<0.001). Keul et al. also reported that artificial water aging influenced CAD/CAM resin bonding 21) which corresponds to the present study. These results could be attributed to the degradation of the interface due to water penetration as aging in water is known to influence on restorative material/luting resin bond degradation 22). Several researchers have reported that in resin-based materials, the solubility of residual monomers and oligomers as well as filler particles and ions results in surface degradation 23,24). It is also reported that a typical polymeric dental restoration becomes saturated within one or two months after placement in water 23). Therefore, the results of these previous studies align well with those of the present study where μtbs values significantly decreased after 1M of water storage. In the present study, sandblasting was combined with ultrasonic cleaning. Although Attia et al. suggested the use of ultrasonic cleaning after sandblasting for durable bond strength 25), the influence of ultrasonic cleaning is still unclear. Kawaguchi et al. reported that ultrasonic and acid cleaning after sandblasting did not affect the long-term bonding durability between non-contaminated CAD/CAM resin blocks and resin cements 26). From these results, as long as restorations can be sandblasted in clinical situations after the tryin procedure, there is no need for ultrasonic and/or acid cleaning. Several CAD/CAM resin blocks and resin cements have been introduced to the dental market to date. One limitation of the present study that should be acknowledged is that only a single kind of resin block, conventional-type adhesive resin cement and selfadhesive resin cement were evaluated. Further studies should clarify whether sandblasting and silanization are also effective surface treatments with other CAD/CAM resin blocks and other resin cements. CONCLUSIONS 1) Sandblasting and silanization increased μtbs values between CAD/CAM resin blocks and adhesive resin cements. 2) A conventional-type adhesive resin cement showed higher μtbs values compared to a selfadhesive resin cement. 3) Long-term water storage influenced on bond strength between CAD/CAM resin blocks and resin cements. 4) Longer maintenance of bond strength was observed when CAD/CAM resin block surfaces were pretreated with a combination of both sandblasting and silanization. ACKNOWLEDGMENTS Kuraray Noritake Dental are acknowledged for supporting this work through generous donation of materials. Conflict of interest The authors report no conflicts of interest.

8 28 Dent Mater J 2016; 35(1): REFERENCES 1) Johnson AC, Versluis A, Tantbirojn D, Ahuja S. Fracture strength of CAD/CAM composite and composite-ceramic occlusal veneers. J Prosthodont Res 2014 ; 58: ) Bogna S, Beatrice S, Albert T, Malgorzata R, Mutlu Ö, Christoph H. F. H. Discoloration of manually fabricated resins and industrially fabricated CAD/CAM blocks versus glassceramic: Effect of storage media, duration, and subsequent polishing. Dent Mater J 2012; 31: ) Timea W, Andreas E, Malgorzata R, Bogna S. Fracture load of milled polymeric fixed dental prostheses as a function of connector cross-sectional areas. J Prosthet Dent 2013; 110: ) Okada K, Kameya T, Ishino H, Hayakawa T. A novel technique for preparing dental CAD/CAM composite resin blocks using the filler press and monomer infiltration method. Dent Mater J 2014; 33: ) Bähr N, Keul C, Edelhoff D, Eichberger M, Roos M, Gernet W, Stawarczyk B. Effect of different adhesives combined with two resin composite cements on shear bond strength to polymeric CAD/CAM materials. Dent Mater J 2013; 32: ) Stawarczyk B, Basler T, Ender A, Roos M, Ozcan M, Hämmerle C. Effect of surface conditioning with airborneparticle abrasion on the tensile strength of polymeric CAD/ CAM crowns luted with self-adhesive and conventional resin cements. J Prosthet Dent 2012; 107: ) Zaghloul H, Elkassas DW, Haridy MF. Effect of incorporation of silane in the bonding agent on the repair potential of machinable esthetic blocks. Eur J Dent 2014; 8: ) El Zohairy AA, De Gee AJ, Mohsen MM, Feilzer AJ. Microtensile bond strength testing of luting cements to prefabricated CAD/CAM ceramic and composite blocks. Dent Mater 2003; 19: ) Aguiar TR, André CB, Correr-Sobrinho L, Arrais CA, Ambrosano GM, Giannini M. Effect of storage times and mechanical load cycling on dentin bond strength of conventional and self-adhesive resin luting cements. J Prosthet Dent 2014; 111: ) Makkar S, Malhotra N. Self-adhesive resin cements: a new perspective in luting technology. Dent Update 2013; 40: , , ) Nakamura T, Wakabayashi K, Kinuta S, Nishida H, Miyamae M, Yatani H. Mechanical properties of new self-adhesive resin-based cement. J Prosthodont Res 2010; 54: ) Van Meerbeek B, Yoshihara K, Yoshida Y, Mine A, De Munck J, Van Landuyt KL. State of the art of self-etch adhesives. Dent Mater 2011; 27: ) Sirisha K, Rambabu T, Ravishankar Y, Ravikumar P. Validity of bond strength tests: A critical review-part II. J Conserv Dent 2014: ) Pollington S, Fabianelli A, van Noort R. Microtensile bond strength of a resin cement to a novel fluorcanasite glassceramic following different surface treatments. Dent Mater 2010; 26: ) Yoshida K, Kamada K, Atsuta M. Effects of two silane coupling agents, a bonding agent, and thermal cycling on the bond strength of a CAD/CAM composite material cemented with two resin luting agents. J Prosthet Dent 2001; 85: ) Elsaka SE. Bond strength of novel CAD/CAM restorative materials to self-adhesive resin cement: the effect of surface treatments. J Adhes Dent 2014; 16: ) Stawarczyk B, Trottmann A, Hämmerle CH, Özcan M. Adhesion of veneering resins to polymethylmethacrylatebased CAD/CAM polymers after various surface conditioning methods. Acta Odontol Scand 2013; 71: ) Wiegand A, Stucki L, Hoffmann R, Attin T, Stawarczyk B. Repairability of CAD/CAM high-density PMMA- and composite-based polymers. Clin Oral Investig 2015; 19: ) Yokokawa M, Takamizawa T, Tsujimoto A, Endo H, Iino M, Suzuki T, Shibasaki S, Myazaki M. Impact-sliding wear behavior of self-adhesive resin cements. Proceedings of the 141 st meeting of the Japanese society of conservative dentistry; 2014 Oct 30-31; Yamagata, Japan; p83. 20) Aksornmuang J, Nakajima M, Foxton RM, Tagami J. Mechanical properties and bond strength of dual-cure resin composites to root canal dentin. Dent Mater 2007; 23: ) Keul C, Kohen D, Eichberger M, Roos M, Gernet W, Stawarczyk B. The effect of different pretreatment methods of PMMA-based crowns on the long-term tensile bond strength to dentin abutments. Clin Oral Investig 2015; 19: ) Elsaka SE. Bond strength of novel CAD/CAM restorative materials to self-adhesive resin cement: the effect of surface treatments. J Adhes Dent 2014; 16: ) Ferracane JL. Hygroscopic and hydrolytic effects in dental polymer networks. Dent Mater 2006; 22: ) Santerre JP, Shajii L, Leung BW. Relation of dental composite formulations to their degradation and the release of hydrolyzed polymeric-resin-derived products. Crit Rev Oral Biol Med 2001; 12: ) Attia A, Lehmann F, Kerm M. Influence of surface conditioning and cleaning methods on resin bonding to zirconia ceramic. Dent Mater 2011; 27: ) Kawaguchi A, Higashi M, Matsumoto M, Miura J, Mine A, Yatani H. Effects of ultrasonic cleaning and etching on CAD/CAM resin bonding. 93rd IADR General Session and Exhibition, Boston, Massachusetts 2015; #3661.