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. 2024 Nov 1;24:1326. doi: 10.1186/s12903-024-05091-y

Bonding effectiveness of multi-step adhesive resin cements to CAD/CAM blocks: impact of thermal cycling and surface treatment methods

Seda Üstün Aladağ 1,✉, Elif Aydoğan Ayaz 2
PMCID: PMC11529232  PMID: 39487437

Abstract

Background

To investigate the effects of thermal cycling and surface treatment methods on the bonding effectiveness of multi-step resin cements to CAD/CAM blocks.

Methods

A total of 198 slices, 66 each from CAD/CAM blocks (feldspathic ceramic: Vitablocs TriLuxe Forte, V; resin matrix ceramics (RMCs): Cerasmart, C; and Shofu Block HC, S), were obtained and randomly divided into two subgroups for etching with hydrofluoric acid (HFA) and sandblasting with Al2O3 (SB). After the surface treatments, one etched and one sandblasted sample of each CAD/CAM block was observed via SEM analysis at 500× magnification. The remaining 32 etched and 32 sandblasted samples of each CAD/CAM block were divided into two subgroups to be cemented with total-etch (TE) and self-etch (SE) resin cements. Then, half of the 16 samples in all the subgroups were subjected to aging (TC) for 5000 cycles (n = 8). The shear bond strength (SBS) of each sample was measured. Four-way analysis of variance (ANOVA) and Tukey tests were used to analyze the data (p < 0.05).

Results

With or without TC, the highest SBS values for V were obtained with the HFA-TE and HFA-SE interactions, respectively. C presented the highest SBS values with HFA-SE and SB-TE interactions, whereas S presented the highest SBS values with SB-TE and HFA-TE interactions. Except the SB-SE interaction, C presented lower SBS values after TC than other materials. HFA created less porosity on the C and S surfaces than V. SB visibly roughened the surfaces of all the materials but caused fractures, cracks, and damage to the surfaces.

Conclusion

Similar SBS values can be achieved between feldspathics, RMCs, and multi-step adhesive resins with both HFA and SB treatments. However, the SBS values obtained from the SB-SE interaction may be below the recommended threshold values for all materials after TC. SB can cause distinctive cavities, fissures, and damage, especially on the surfaces of RMCs.

Keywords: Feldsphatic ceramic, Resin matrix ceramics, Surface treatments, Thermal cycling, Shear bond strength

Background

CAD/CAM is a technology that allows chairside production of restorations in a single visit, eliminating conventional impressions and laboratory procedures [1]. Glass ceramics are frequently preferred for the production of restorations by CAD/CAM because of their superior aesthetics, strength, and biocompatibility [2, 3]. Feldspathic restorations with a wide color gradient and translucency can be manufactured using multishade blocks (e.g., Vitablocs TriLuxe/TriLuxe Forte/RealLife blocks, Bad Säckingen, Germany), developed from monochromatic blocks over time [4]. In addition to these advantages, disadvantages such as brittleness, wear on the opposing dentition, and difficulty in milling limit the clinical and manufacturing success of glass ceramics [2, 5].

Recently, CAD/CAM blocks classified as ceramic-like [6] or indirect composite blocks [7–9] have been introduced to combine the advantages of ceramics and composites. Ceramic-like materials have been categorized as resin matrix ceramics (RMCs) [5]. RMCs are repaired with composite resins, milled easily, and the finishing and adjustment procedures are easier than those for glass ceramics [5, 10]. Cerasmart (GC Europe, Leuven, Belgium), a flexible hybrid nanoceramic, contains 71% silica filler by weight and barium glass particles in an organic resin matrix [10, 11]. Another RMC, the Shofu Block HC (Shofu Dental, Kyoto, Japan), contains 61% silica and zirconium silicate fillers in its UDMA- and TEGDMA-based organic matrix structure [12]. Cerasmart and Shofu Block HC are also described as indirect composite CAD/CAM blocks (ICs) with dispersed fillers. These blocks have desirable properties, such as an elasticity modulus close to that of dentin, the ability to absorb forces, and fatigue resistance [7–9].

Adhesive cementation of a restoration to dental tissues results in the formation of two interfaces: dental tissue-adhesive resin and adhesive resin-CAD/CAM restoration material [9]. Adhesive systems are classified into etch-rinse (TE), self-etch (SE), and self-adhesive (SA) systems according to their bonding properties and the pretreatment steps of dentin or enamel [13]. Adhesive luting cements are categorized as conventional multi-step cements (TEs and SEs), which can be combined with these adhesive systems according to the applied adhesion strategies, and SA resin cements [14–16]. To improve the bond strength between the restoration and adhesive resin cement, micromechanical and chemical surface treatments are applied. Frequently investigated mechanical surface treatment methods involve etching the cementation surface of the restoration with hydrofluoric acid (HFA) or sandblasting (SB) with aluminum oxide (Al2O3) particles [1, 12, 17–20]. HFA dissolves the glassy phase of ceramics, exposes the crystals and increases the surface area, creating a microporous surface through which the resin cement can penetrate [17, 21]. SB with Al2O3 increases the bonding area and surface energy of the material. The surface, which is cleared of any residue and organic matrix waste that may occur during the production process, becomes ready for micromechanical locking [22, 23].

When a prosthetic restoration is cemented, it is subjected to oral conditions that change thermally, chemically, and mechanically. Therefore, examining bond durability, which reflects long-term clinical service, is important; this can be achieved by subjecting test samples to artificial aging procedures [24]. Thermal cycling (TC) is an artificial aging method in which materials are subjected to hydrolytic and thermal changes, simulating intraoral conditions [25].

Knowing the properties of CAD/CAM blocks that can be included in different classifications is important in determining appropriate surface treatment and cementation protocols. According to the literature, no consensus exists on which cementation system and surface treatment method are used together to obtain higher bond strength in current CAD/CAM blocks. Additionally, studies comparing the effects of thermocycling on the initial bond strength of CAD/CAM blocks should be diversified. Therefore, the aims of this study were as follows: (1) To evaluate the shear bond strength (SBS) of multi-step resin cements applied to etched or sandblasted CAD/CAM blocks (Vitablocs TriLuxe Forte, Cerasmart, Shofu Block HC) with or without TC. (2) To examine etched and sandblasted material surfaces via scanning electron microscopy. The null hypothesis was that surface treatments, multi-step resin cements, and TC would not affect the SBS of CAD/CAM blocks.

Methods

Power analysis was performed via the GPower v3.1.9.7 program to determine the sample size. Using 95% confidence (1-α), 95% test power (1-β), and f = 0.354 effect size as a reference [26], 144 samples are required for the study, with a minimum of (128/24) ≅ 6 samples in each group. However, considering potential losses, the total final sample size was determined to be 192 (n = 8 for each group) for the SBS test.

The procedures applied to each subgroup and sample distribution are presented in the flowchart (Fig. 1). The types, compositions, and manufacturers’ information of the CAD/CAM blocks, adhesive resin cements, and materials used are listed in Table 1.

Fig. 1.

Fig. 1

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Flowchart presenting the procedure of this study

Table 1.

Information on the types, compositions and manufacturers of the materials used in this study

Materials Type Composition Manufacturer
Vitablocs TriLuxe Forte Feldspar ceramic block Silicon dioxide 56–64%, aluminum oxide 20–23%, sodium oxide 6–9%, potassium oxide 6–8%, calcium oxide 0.3–0.6%, titanium oxide 0.0–0.1% Vita Zahnfabrik, Bad Säckingen, Germany
Cerasmart Resin matrix ceramic or indirect composite block with dispersed fillers UDMA, Bis-MEPP, DMA, 71 wt% silica, barium glass GC Europe, Leuven, Belgium
Shofu Block HC Resin matrix ceramic or indirect composite block with dispersed fillers UDMA, TEGDMA, 61 wt% silica powder, micro fumed silica, zirconium silicate, pigments and others Shofu Dental, Kyoto, Japan
Vita Adiva F-Cem Dual cure, Total-etch adhesive resin cement Mixture of Bis-GMA-based resins, catalysts, stabilizers, pigments, and inorganic filler particles in a distribution of 0.05–1 μm. The filler content is 61% by weight or 41% by volume. Vita Zahnfabrik, Bad Säckingen, Germany
Multilink N Self-curing luting composite with light-curing option, Self-etch adhesive resin cement The monomer matrix is composed of DMA and HEMA. The inorganic fillers include barium glass, ytterbium trifluoride and spheroid mixed oxide. The particle size is 0.25–3.0 μm. The mean particle size measures 0.9 μm. The total volume of inorganic fillers is approximately 40%. Ivoclar Vivadent, Schaan, Liechtenstein
G-Multi Primer Priming agent, Universal primer Ethanol, γ-MPTMS, 10-MDP, MDTP, Bis-GMA, TEGDMA.

GC Corporation,

Tokyo, Japan
Vita Adiva Cera-Etch Hydrofluoric acid gel (HFA) 5% HFA Vita Zahnfabrik, Bad Säckingen, Germany
Airsonic Alu-Oxyd Aluminum oxide (Al2O3) powder 50 μm Al2O3 Hager Werken, Duisburg, Germany
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UDMA: urethane dimethacrylate; Bis-MEPP: 2.2-bis (4-methacryloxypolyethoxyphenyl) propane; DMA: dimethacrylate; TEGDMA: triethylene glycol dimethacrylate; Bis-GMA: bisphenol-A glycidyl methacrylate; HEMA: 2-hydroxyethyl methacrylate; γ-MPTMS: γ-methacryloxypropyl trimethoxy silane; 10-MDP: 10-methacryloyloxydecyl dihydrogen phosphate; MDTP: methacryloyloxydecyl dihydrogen thiophosphate

A total of 198 slices, 66 from each CAD/CAM block (Vitablocs TriLuxe Forte, V; Cerasmart, C; and Shofu Block HC, S) with a thickness of 2.5 mm, were obtained via a precision cutting device (Microcut, Metkon, Turkey). The thickness of the slices was checked with a digital caliper (IP54, Yamer, Turkey). To be fixed to the device during the SBS test, the cementation surfaces of the slices were left exposed and embedded in autopolymerizing acrylic resin (Imicyrl, Turkey). The cementation surfaces of all the samples were finished with waterproof silicon carbide abrasives (P600C, English Abrasives, England) in a polishing device (Grin PO 2 V grinder, Metkon, Turkey) for surface standardization. The samples were cleaned with distilled water for 5 min and air dried.

Surface treatments

Sixty-six samples prepared from each CAD-CAM block were randomly divided into 2 subgroups for HFA and SB surface treatments.

Thirty-three samples were etched with 5% HFA (Vita Adiva Cera-Etch, Vita Zahnfabrik, Germany) for 60 s, washed with an air‒water spray for 60 s, and dried with compressed air.

The other 33 samples were sandblasted with 50 μm Al2O3 (Airsonic Alu-Oxyd, Hager Werken, Germany) for 15 s from a distance of 10 mm at 2.5 bar pressure [20].

All the samples were cleaned with distilled water for 5 min to remove residues and particles and then air dried. One etched and sandblasted sample from each CAD/CAM block was selected for scanning electron microscopy (SEM) analysis.

Cementation procedures

The remaining 32 etched and 32 sandblasted samples of each CAD/CAM block were divided into two subgroups to be cemented with TE (Vita Adiva F-Cem, Vita Zahnfabrik, Germany) and SE (Multilink N, Ivoclar Vivadent, Liechtenstein) resin luting cements by the same operator. Before cementation, light-transmitting silicone tubes were prepared with a height and width of 3 mm. The silicone tubes were placed and secured in the center of the ceramic cementation surface.

A thin layer of universal primer (G-Multi Primer, GC Corp., Japan) was applied to the bonding areas of all the samples using a micro-tip applicator. Following this, the primer was air dried for 5 s according to the manufacturer’s instructions and then allowed to evaporate completely.

TE and SE resin luting cements were filled and condensed into the silicone tubes through auto-mix syringes. To prevent the formation of an oxygen inhibition layer during polymerization, the top surfaces of the silicone tubes were covered with a transparent strip. Excess cement was removed using a microbrush. All the samples were subsequently polymerized for 40 s with an LED light source (Woodpecker Led-B, Woodpecker, China) of 1000 mW/cm2. The silicone tubes were removed with a surgical blade, and each surface was polymerized again for 40 s to ensure proper polymerization at the bonding interface. The samples were stored in distilled water for 24 h to complete the polymerization.

Thermal cycling (TC) procedures

After the polymerization process, half of the 16 samples in all subgroups were subjected to thermal aging for 5000 cycles, reflecting approximately six months of clinical service (5–55 °C water bath with a dwell time of 30 s and a transfer time of 5 s) [25, 26]. The other half of the samples were kept in distilled water for 6 days until testing.

Shear bond strength (SBS) test

The SBS test of the samples fixed on a universal testing machine (Model 3343, Instron Corp., USA) was performed at a speed of 0.5 mm/min. The maximum load (L) reached was recorded in Newtons by the device. The bonding surface area (A) of ​​the samples was checked with a digital caliper, and the SBS values ​​were calculated in megapascals (MPa) according to the following formula: SBS = L/A.

Scanning electron microscopy (SEM) analysis

One etched and one sandblasted sample from each CAD/CAM block was examined by scanning electron microscopy (SEM). Before imaging, these samples were coated with gold-palladium. SEM (GeminiSEM 300, Zeiss, Germany) imaging was performed at 500× magnification to obtain the surface topography of the samples after surface treatment.

Statistical analysis

SPSS (V23, IBM Corp., USA) and Minitab (V14, State College, Pennsylvania) software were used for statistical data analysis. The conformity of the data for normal distribution was assessed via the Shapiro‒Wilk test. For data that did not meet the normality assumptions (p < 0.05), skewness and kurtosis tests were conducted. Parametric tests were performed for data analysis on the basis of previous studies [27, 28]. The SBS values ​​were compared according to the main effects and interactions of the material, surface treatment, adhesive resin, and thermal cycling via four-way analysis of variance (ANOVA). Multiple comparisons were examined via Tukey’s test. The significance level was set at p < 0.05.

Results

The SBS values (mean ± standard deviation) ​​are presented in Table 2; Fig. 2. The four-way ANOVA results are summarized in Table 3. SEM images of the etched and sandblasted materials are shown in Fig. 3

Table 2.

Descriptive statistics of SBS values ​​according to material, surface treatment, resin cement and thermal cycling variables

Material Surface treatments
Etching (HFA) Sandblasting (SB)
Resin cement Resin cement
Total-Etch (TE) Self-Etch (SE) Total Total-Etch (TE) Self-Etch (SE) Total

Without

thermal

cycling

Vita Triluxe Forte (V) 35.78 ± 1.21A 26.26 ± 1.26ABCD 30.65 ± 1.29A 23.77 ± 1.51ABCDE 26.19 ± 1.24ABCD 24.95 ± 1.38A
Cerasmart (C) 21.82 ± 1.29ABCDE 31.11 ± 1.11AB 26.05 ± 1.3A 27.1 ± 1.42ABC 16.35 ± 1.29CDEFG 21.21 ± 1.49AB
Shofu Block HC (S) 21.99 ± 1.2ABCDE 19.71 ± 1.24ABCDEF 20.82 ± 1.22AB 30.61 ± 1.29AB 20.82 ± 1.29ABCDE 25.24 ± 1.37A
Total 25.8 ± 1.36 25.25 ± 1.3 25.52 ± 1.33A 27.15 ± 1.42 20.73 ± 1.36 23.73 ± 1.42A

Thermal

cycling

(TC)

Vita Triluxe Forte (V) 24.59 ± 1.38ABCDE 19.48 ± 1.37ABCDEF 21.89 ± 1.39AB 14.58 ± 1.36DEFGH 10.28 ± 1.25GH 12.24 ± 1.37C
Cerasmart (C) 17.14 ± 1.54BCDEFG 16.06 ± 1.51CDEFG 16.59 ± 1.5BC 13.57 ± 1.72EFGH 10.72 ± 1.82FGH 12.06 ± 1.76C
Shofu Block HC (S) 23.5 ± 1.69ABCDE 18.86 ± 1.34BCDEFG 21.05 ± 1.53AB 18.15 ± 1.48BCDEFG 8.14 ± 1.21H 12.15 ± 1.67C
Total 21.48 ± 1.56 18.07 ± 1.4 19.7 ± 1.49B 15.31 ± 1.53 9.64 ± 1.47 12.15 ± 1.59C
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Mean ± standard deviation (SD); A-H: There is no difference between interactions with the same letter

Fig. 2.

Fig. 2

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The SBS values of the test groups (HFA: hydrofluoric acid, SB: sandblasting, TE: total-etch cement, SE: self-etch cement, TC: thermal cycling)

Table 3.

Four-way analysis of variance (ANOVA) results

Source Adj SS DF Adj MS F p Inline graphic
Material 0.797 2 0.398 3.562 0.031 0.041
Surface treatment 3.705 1 3.705 33.129 < 0.001 0.165
Resin cement 2.578 1 2.578 23.058 < 0.001 0.121
Thermal cycling 10.374 1 10.374 92.773 < 0.001 0.356
Material * Surface treatment 0.379 2 0.19 1.695 0.187 0.020
Material * Resin cement 0.582 2 0.291 2.604 0.077 0.030
Material * Thermal cycling 0.262 2 0.131 1.171 0.313 0.014
Surface treatment * Resin cement 0.873 1 0.873 7.811 0.006 0.044
Surface treatment * Thermal cycling 2.027 1 2.027 18.131 < 0.001 0.097
Resin cement * Thermal cycling 0.356 1 0.356 3.185 0.076 0.019
Material * Surface treatment * Resin cement 1.05 2 0.525 4.693 0.010 0.053
Material * Surface treatment * Thermal cycling 0.796 2 0.398 3.558 0.031 0.041
Material * Resin cement * Thermal cycling 0.08 2 0.04 0.356 0.701 0.004
Surface treatment * Resin cement * Thermal cycling 0.005 1 0.005 0.048 0.828 0.000
Material * Surface treatment * Resin cement * Thermal cycling 0.866 2 0.433 3.873 0.023 0.044
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F: four-way analysis of variance (ANOVA); : Partial Eta Squared; R-sq = 56.83%; R-sq(adj) = 50.92%

Fig. 3.

Fig. 3

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SEM images of etched and sandblasted materials (original 500× magnification) a) etched V, b) sandblasted V, c) etched C, d) sandblasted C, e) etched S, f) sandblasted S

According to the four-way ANOVA results (Table 3), the main effects of material (p < 0.05), surface treatment (p < 0.001), resin cement (p < 0.001), and thermal cycling (p < 0.001) on the mean SBS values ​​were statistically significant. There was a difference between the V (21.27) and C (18.23) materials; however, the S (19.15) material was similar to the other materials (p > 0.05). The main effect value of HFA (22.42) was significantly higher than that of SB (16.98) (p < 0.001). The main effect value ​​obtained with TE (21.91) was significantly higher than that obtained with SE (17.38) (p < 0.001). TC (15.47) significantly decreased the main value ​​of the without TC group (24.61) (p < 0.001).

The interactions between surface treatment × resin cement (p < 0.05), surface treatment × thermal cycling (p < 0.001), material × surface treatment × resin cement (p < 0.05), material × surface treatment × thermal cycling (p < 0.05), and material × surface treatment × resin cement × thermal cycling (p < 0.05) on the mean SBS values ​​were statistically significant (Table 3). Regardless of the material and TC variables, a significantly lower value​​ was obtained with the SB-SE (14.14) interaction (p < 0.05). There was no significant difference between the HFA-TE (23.54), HFA-SE (21.36), and SB-TE (20.39) (p > 0.05) interactions. When the resin type and material variables were not considered, there was no difference between HFA (25.52) and SB (23.73) in the without TC groups (p > 0.05). However, significantly lower values were obtained with SB (12.15) in the TC groups (p < 0.05).

According to multiple comparisons between groups (Table 2), both with and without TC, the highest SBS ​​was observed between etched V and TE. However, there was no difference between the groups cemented with TE (p > 0.05). The SBS between etched or sandblasted V and TE decreased after TC but was not significant (p > 0.05). However, the SBS between etched or sandblasted V and SE decreased after TC, which was significant between sandblasted samples V and SE (p < 0.05). After TC, the SBS between etched V and SE (19.48) was significantly higher than the SBS between sandblasted V and SE (10.28) (p < 0.05).

The highest SBS ​​was obtained for C when it was cemented with SE after HFA without TC (31.11). Compared to this group, significantly lower values ​​were obtained when sandblasted C was cemented with SE (16.35) (p < 0.05). However, there was no difference between the other groups cemented with SE (p > 0.05). When etched C was cemented with SE and when sandblasted C was cemented with TE, the SBS values ​​decreased significantly after TC (p < 0.05). After TC, no difference was observed in the SBS among the C groups (p > 0.05).

The highest SBS ​​for S occurred when it was cemented with TE after SB without TC. When etched S was cemented with TE, the SBS increased after TC, but the increase was insignificant (p > 0.05). When the sandblasted S was cemented with SE, the SBS ​decreased significantly after the TC (p < 0.05), and the lowest SBS values ​​were obtained among all the groups. The difference between this group and all the S groups was significant (p < 0.05).

HFA exposed the crystalline structure by dissolving the glassy phase of V (Fig. 3a). Craters, pits, and irregularities were dominant on the honeycomb-like surface. HFA created less porosity on the C and S surfaces (Fig. 3c and e). Small micro-pits were distributed over the entire surface on the C surface. The micro-pits on the S surface were more apparent on smooth surface areas. SB created irregular, rough and sharp-edged pores on all the material surfaces (Fig. 3b, d and f). One fracture line was observed on the surface of sample V (Fig. 3b). Thin cracks, fissures, and fracture lines were observed on the C surface (Fig. 3d). There were fracture lines, ring-shaped cavities, and deep holes on the surface of S (Fig. 3f).

Discussion

According to the results of this study, the effects of surface treatment, multi-step resin cement, and TC on the SBS of CAD/CAM blocks were significant (p < 0.001). Therefore, the null hypothesis was rejected.

When HFA is applied to the surface of silica-based, etchable, and vitreous ceramics, such as feldspathic ceramics, the HFA dissolves the glassy phase of the ceramic and reveals the crystalline structure [21, 29, 30]. HFA and the silica phase of feldspathic ceramics react to form hexafluorosilicates [30]. Topographic changes such as craters and pits occur on the ceramic surface, and a honeycomb-like appearance is formed, which is ideal for micromechanical interlocking [30, 31]. Queiroz-Lima et al. [17] reported that the etching effect cleans the material surface from oxides, residues, and debris and exposes critical hydroxyl groups for bonding with chemical agents such as silane. In this study, the highest SBS values for V, with and without TC, were obtained with the HFA-TE interaction, which can be attributed to the effects of HFA on feldsphatic ceramic surfaces.

In accordance with the SEM images from this study (Fig. 3c and e), researchers have argued that RMCs, i.e., ICs with dispersed fillers, cannot be sufficiently roughened with HFA [8, 19]. These blocks have two components: a polymer matrix phase and an inorganic glassy phase [9, 32]. HFA has an affinity for the silica phase of materials [21, 30]. However, the inorganic mineral structure of RMCs contains crystalline and polycrystalline components that are outside the mechanism of action of HFA [8]. Therefore, their lack of pure silicon dioxide may have limited the effect of HFA and caused them to exhibit smoother surfaces in the microscope images. The production of these blocks at high conversion rates under high temperature and pressure reduces the number of free carbon‒carbon double bonds participating in adhesive bonding on the material surface and increases the importance of surface treatments [22, 33, 34]. Nevertheless, the importance of chemical factors, free surface energy, and tension at the material‒adhesive interface, as well as mechanical variables, on the bond strength has been emphasized [35]. In this study, when etched with HFA, both RMCs presented bond strength values similar to those of feldspathic ceramics. Although RMCs are not roughened by HFA as much as the feldspathic, their surface chemistry and surface energy may have changed. As stated by Mittal [35], the increased surface energy may have reduced the interfacial tension and enabled the liquid adhesive to better wet the surface, thus increasing the bond strength. Studies have achieved higher bond strengths with etched RMCs [1, 12, 36, 37]. Cheunjit et al. [12] emphasized that the surface energy of CAD/CAM materials increased after HFA and found no difference between the bond strengths of sandblasted and etched C. Abdou et al. [34] correlated the ability of HFA to roughen ICs with dispersed fillers with critical surface energy and supported the application of HFA etching for these blocks. Additionally, a universal primer (UP) (G-Multi Primer) was preferred for silanization in this study. UPs contain acidic functional monomers such as MDP, silane coupling agents, and methacrylate monomers [32, 38]. In particular, the acidic components of MDP and copolymers support bonding with the polymer phase of the composite blocks [9, 33, 37]. Agingu et al. [39] reported that the MDP content of UPs enhances bonding with metals, alumina, and zirconium, which are ICs containing these components. Many researchers have recommended UPs for the silanization of these blocks [9, 33, 40]. On the basis of these findings, UP may be effective in increasing the SBS of etched RMCs and may have a synergistic effect with the slight porosity created by HFA.

Many scholars have suggested that SB is the most suitable surface treatment for RMCs [22, 33]. SB provides a clean, rough surface free of contaminants, creating a bonding area suitable for the micromechanical interlocking of resin cement [19, 23]. Both the resin matrix and fillers are exposed on the sandblasted surface [12, 23]. Strasser et al. [41] suggested the application of small-particle-size Al2O3 powder at low pressure (e.g., 50 μm/1 bar). Yoshihara et al. [23] reported that 0.1 MPa pressure was inadequate for surface modification and tested CAD/CAM materials at 0.2 MPa pressure. In line with these views, SB was carried out with the parameters of 50 μm/2.5 bar, taking a previous study as reference [20], and fractures, cracks and cavities were detected on the material surfaces in SEM images. Yoshihara et al. [23] reported damage to both the resin matrix structure and the resin matrix‒filler interface of CAD/CAM blocks after SB, especially progressive fractures on the S surface. El-Damanhoury et al. [19] also detected cracks on CAD/CAM block surfaces with similar parameters. Although there is no consensus in the literature regarding the acceptable bond strength value at the resin cement-material interface, Behr et al. [42] reported that a bond strength of over 10 MPa at the resin-restoration interface would be successful. Thurmund et al. [43] reported that a bond strength of ≤ 13 MPa at the porcelain-composite resin interface may result in adhesive failure. In this study, all materials presented SBS values below the recommended threshold value after the interaction of TC with SB-SE. This result suggested that SB may have resulted in damage, excessive roughness, and excessive deterioration of the bonding surface. Although the bonding area supported only with adhesive agents initially exhibited high SBS, low SBS may have occurred after TC. Abad-Coronel et al. [44] reported that SE systems reduce the number of clinical application steps and may degrade over time by acting as a permeable membrane at the bonding interface. Therefore, the low SBS of the SB-SE interaction can be attributed to the cumulative effect of SB and SE.

In this study, the main effect of TC on SBS was found to be significant, and a decrease in SBS was observed (p < 0.001). Reymus et al. [22] reported that S without SB or primer treatment exhibited bond failure during aging, which was attributed to the low filler content of S. In parallel, Cekic-Nagas et al. [32] obtained lower micro-SBS with CAD/CAM blocks containing low inorganic fillers and reported that water infiltration into the resin matrix structure of RMCs during aging may result in lower micro-SBS. In this study, although C (71%) contained more inorganic filler than S (61%), it presented a lower SBS after TC, and the main effect value (18.23) was lower than those of the other materials. This difference in findings may result from differences in the testing procedures, adhesive agents used, and internal structure of the materials. It is also possible that MDP, owing to its affinity for zirconia, may form a stronger bond with zirconium silicate, one of the inorganic components of S [39]. Interestingly, when etched S was cemented with TE, there was a nonsignificant increase in SBS after TC. This interaction between etched S and TE may have been triggered by the high temperature reached during TC, which increased postirradiation curing [22].

Studies have reported that the filler ratio of resin cement is associated with high bond strength [29, 32, 37]. Researchers have obtained lower bond strength values with resin cement having lower inorganic filler contents [32, 37]. The multi-step adhesive resins used in this study may have had similar inorganic filler amounts by volume (Vita Adiva F-Cem, 41% and Multilink N, 40%), resulting in similar SBS values before TC. Nevertheless, regarding the SBS values, the material*resin cement (p > 0.05) interaction is not significant, whereas the surface treatment*resin cement (p < 0.05) and material*surface treatment*resin cement (p < 0.05) interactions are significant. This suggests that the cumulative effect of the material, adhesive resin, and surface treatment rather than the type of cement used is important for SBS.

Limitations of this study include the fact that only TC was applied to reflect clinical use, the test samples were soaked in distilled water instead of saliva, and the bond strength between tooth tissue and the restoration was not evaluated. Additionally, in this study, two different surface treatments, HFA and SB, were applied to the bonding interface, while the effectiveness of various procedures such as dental laser and cold atmospheric plasma was not evaluated. Furthermore, the samples were subjected to macro bond strength testing. Therefore, further studies are needed to investigate the bond strength at the dentin-restoration interface using micro bond strength tests and to classify the fracture types as adhesive, cohesive, and mixed.

Conclusions

Within the limitations of this study, the following conclusions can be drawn:

  1. With or without TC, the highest SBS values for V were obtained with the HFA-TE and HFA-SE interactions, respectively.

  2. C presented the highest SBS values with HFA-SE and SB-TE interactions, whereas S presented the highest SBS values with SB-TE and HFA-TE interactions. Except for the SB‒SE interaction, C had lower SBS values after TC than did the other materials.

  3. Similar SBS values can be achieved between feldspathics, RMCs, and multi-step adhesive resins with both HFA and SB treatments. However, the SBS values obtained from the SB-SE interaction may be below the recommended threshold values for all materials after TC.

  4. SB can cause distinctive cavities, fissures, and damage, especially on the surfaces of RMCs.

Abbreviations

UDMA

Urethane dimethacrylate

bis-MEPP

2.2-bis (4-methacryloxypolyethoxyphenyl) propane

DMA

Dimethacrylate

TEGDMA

Triethylene glycol dimethacrylate

bis-GMA

Bisphenol-A glycidyl methacrylate

HEMA

2-hydroxyethyl methacrylate

γ-MPTMS

γ-Methacryloxypropyl trimethoxy silane

10-MDP

10-Methacryloyloxydecyl dihydrogen phosphate

MDTP

Methacryloyloxydecyl dihydrogen thiophosphate

Author contributions

All authors contributed equally to Conceptualization, Methodology, Formal analysis, Resources, Writing, Reviewing and Editing of the manuscript. Both authors read and approved the final manuscript.

Funding

This research was funded by the Scientific Research Projects Committee of Bursa Uludağ University with Grant #TGA-2022-815.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request due to privacy reasons and the large size of the data.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request due to privacy reasons and the large size of the data.

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