Effect of silane treatment and resin cement type on bond strength to 3D-printed restorative resin: an in vitro experimental study

Article information

Restor Dent Endod. 2026;.e34

Publication date (electronic) : 2026 July 7

doi : https://doi.org/10.5395/rde.2026.51.e34

Seul Ji Park¹, Eun Hye Lee², Ryan Jin Young Kim^2,, Joo Hee Shin^1,

¹Department of Conservative Dentistry, Korea University Guro Hospital, Seoul, Korea

²Department of Dental Science, Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Korea

^*Correspondence to Ryan Jin Young Kim, BDS, MSD, PhD Department of Dental Science, Dental Research Institute, School of Dentistry, Seoul National University, 101 Daehak-ro, Jongno-gu, Seoul 03080, Korea E-mail: ryankim05@snu.ac.kr

Joo Hee Shin, DDS, MSD, PhD Department of Conservative Dentistry, Korea University Guro Hospital, 148 Gurodong-ro, Guro-gu, Seoul 08308, Korea E-mail: endoshin@kumc.or.kr

Ryan Jin Young Kim and Joo Hee Shin contributed equally to this work as co-corresponding authors.

Citation: Park SJ, Lee EH, Kim RJ, Shin JH. Effect of silane treatment and resin cement type on bond strength to 3D-printed restorative resin: an in vitro experimental study. Restor Dent Endod 2026;51(3):e34.

Received 2025 October 19; Revised 2026 January 22; Accepted 2026 February 22.

Abstract

INTRODUCTION

Three-dimensional (3D) printing—also known as additive manufacturing—has emerged as an indispensable tool across diverse fields, notably revolutionizing workflows in dentistry [1]. It enables high precision and personalization in the fabrication of prostheses, surgical guides, orthodontic devices, and customized oral appliances such as mouthguards and splints by constructing each item layer-by-layer from digital models [2–4]. Furthermore, 3D printing facilitates the fabrication of dental restorations, streamlines treatment procedures, and reduces total treatment time. Recent advancements have made this fabrication suitable for producing long-term restorations.

3D-printed restorations rely on dental luting cements for secure bonding to tooth structures, making the bond strength of the cement essential for the durability of the restoration. The use of self-adhesive resin cements in indirect restorations has gained popularity, as they simplify clinical procedures while offering strong and durable bonds to both tooth structures and restorative materials [5]. To further enhance the adhesion of indirect restorations, conventional surface treatments such as etching, sandblasting, and the application of silane and resin bonding agents have been studied [6–8]. For glass-ceramics and resin-based substrates, silane treatment is commonly recommended to enhance the bond strength with resin cement [8,9]. Silane molecules contain two reactive groups that enable chemical bonding with both ceramic and resin materials: hydrolyzable groups bind to silicon hydroxyl groups (Si-OH) on ceramic surfaces, while organic groups interact with adhesive or composite resin monomers. This dual function makes silane a critical agent for strengthening the interface between inorganic and organic components in dental restorations [10].

3D-printing resins have distinct chemical compositions, and their physical and mechanical properties are largely determined by the types and ratios of monomers and fillers used. Unlike conventional dental restorative resins, 3D-printed resins typically contain no or lower filler content to minimize interference with light curing and to avoid excessive viscosity [11,12]. This altered composition may influence the efficacy of silane treatments and affect the bond strength with resin cements. Although previous studies have investigated the bond strength of provisional 3D-printed resins to repair materials or composite resins [7,13–15], no research to date has specifically examined the bond strength between 3D-printed resins and resin cements, or the effect of silane application prior to cementation.

While chemical compatibility plays a key role in bonding, another important factor is the surface wettability of the materials involved. This property is often assessed using contact angle measurements, which provide insight into how well a resin cement can spread across a given surface. In general, lower contact angles are associated with improved wettability, which can lead to improved adaptation and stronger adhesion at the interface [16,17]. Given the differences in filler content and surface chemistry between resin cements and 3D-printed materials, measuring the contact angles can help explain variations in bond strength observed across different material combinations.

Therefore, this study aimed to evaluate the bond strength of four different resin cements on two types of 3D-printed resins designed for permanent restorations both with and without silane treatment. Additionally, contact angle measurements were conducted to assess the wettability of each resin cement and 3D-printed substrate. The null hypothesis was that silane application and the type of 3D-printed resin would not significantly affect the bond strength among the resin cements.

METHODS

Institutional Review Board approval was not required because this was an in vitro study that did not involve human participants, human-derived materials, or identifiable personal information.

Sample preparation

The workflow of this study is illustrated in Figure 1. A total of 192 3D-printed resin cylinders (15 mm diameter, 15 mm height) were produced using a digital light processing printer (IMC 3D printer; Carmina, Seoul, Korea). All specimens were printed at a 0-degree orientation to the build platform with a layer thickness of 100 µm. After printing, the specimens were cleaned in isopropyl alcohol for 10 minutes (Form Wash; Formlabs, Somerville, MA, USA) to remove residual uncured resin, followed by post-curing for 30 minutes (Form Cure; Formlabs).

Figure 1.

Workflow of the study. The full names and manufacturers of the materials are provided in Table 1. The +S notation indicates silane application.

The resins used for printing consisted of ODS Permanent resin (OPR; C&B Permanent Resin; ODS, Incheon, Korea) and Graphy Permanent Resin C&B TC-80DP (GPR) (Graphy, Seoul, Korea), with 96 cylinders fabricated from each resin type. For bonding preparation, one side of each cylinder was sandblasted using 50 µm aluminum oxide particles at 0.2 MPa pressure for 10 seconds, followed by a 5-minute cleaning cycle in an ultrasonic unit and thorough air drying. After air abrasion, the surface morphologies of the 3D-printed resin substrates were observed using scanning electron microscopy (SEM; Apreo 2; Thermo Fisher Scientific, Waltham, MA, USA) at an accelerating voltage of 10 kV and a magnification of x500. Additional specimens that received silane treatment after air abrasion were also examined.

The GPR and OPR cylinders (n = 96 each) were divided into eight subgroups (n = 12 per subgroup) according to the type of resin cement used—G-CEM LinkAce (GL; GC Corp., Tokyo, Japan), RelyX U200 (RU; 3M ESPE, St. Paul, MN, USA), Clearfil SA (CS; Kuraray, Okayama, Japan), and RelyX Ultimate Clicker (UC; 3M ESPE)—and the presence or absence of silane treatment. In the silane-treated groups, RelyX Ceramic Primer (3M ESPE) was applied to the air-abraded 3D-printed resin surfaces using a microbrush and allowed to react for 60 seconds, and then air-dried for 15 seconds prior to cementation, in accordance with the manufacturer’s instructions. For the GL and UC groups, G-Multi PRIMER (GC) and Single Bond Universal Adhesive (3M ESPE) were applied, respectively, before placement of the corresponding resin cement, following the manufacturers’ recommended protocols.

Both the silane and resin cements were prepared according to the manufacturer’s instructions. The materials used in this study and their respective compositions are listed in Table 1. For cement application, specimens were prepared using a Bonding Clamp and a Bonding Mold Insert (Ultradent Products, Inc., South Jordan, UT, USA). The mold insert was designed to create a space with a 2.38 mm internal diameter and 2.67 mm height for resin cement, which was clamped against the cylinder. Resin cement was incrementally filled into the mold to a height of 2.0 mm. A light-emitting diode (LED) curing light unit (B&Lite S; B&L Biotech, Ansan, Korea) was fixed to the top surface of the mold insert and the resin cement was light-cured for 20 seconds. After removing the molds, the resin cement on the cylinders was light-cured for an additional 40 seconds—20 seconds on each of the two axial surfaces. All specimens were then stored in distilled water at 37°C in an incubator for 24 hours.

Table 1.

Test materials, manufacturers, and compositions used in the study

RESULTS

Shear bond strength

The SBS test results are presented in Table 2 and Figure 2. In the OPR group without silane application, the highest SBS was observed for GL, followed by UC, RU, and CS. Although no statistically significant differences were observed among the GL, UC, and RU groups (p > 0.05), the CS group exhibited a significantly lower SBS (p < 0.05). With the application of silane, RU showed the highest SBS, followed by GL, UC, and CS; however, no statistically significant differences were found between RU, GL, and UC, aside from CS, which showed a significantly lower bond strength (p < 0.05). In the GPR group without silane treatment, the highest SBS was observed for RU, followed by GL, UC, and CS. In the GPR group treated with silane application, RU exhibited the highest SBS value, followed by UC, GL, and CS. Similar to the OPR group, no statistically significant differences were noted between the RU, GL, and UC groups, whereas the CS group showed the lowest SBS (p < 0.05). When comparing SBS values between the OPR and GPR substrates under identical conditions (with or without silane), no statistically significant differences were observed for most cement types. According to the results of the three-way ANOVA (Table 3), resin cement type had a significant effect on SBS (p < 0.001). In contrast, resin substrate type and silane treatment did not show significant main effects (p > 0.05). Furthermore, no significant two-way or three-way interaction effects among resin cement type, resin substrate type, and silane treatment were observed (p > 0.05).

Table 2.

Shear bond strength (MPa) of the resin cements

Figure 2.

Shear bond strength of the resin cements. The full names and manufacturers of the materials are provided in Table 1.

Table 3.

Three-way analysis of variance results

In the OPR group, cohesive failure predominated across all subgroups. The GL, GL + S, RU, RU + S, UC, and UC + S exhibited 100% cohesive failures. In contrast, the CS subgroup showed a more varied distribution: 66.7% (8/12) were cohesive, 25.0% (3/12) were adhesive, and 8.3% (1/12) were mixed failures. The CS + S subgroup showed 83.3% (10/12) cohesive failures and 8.3% (1/12) mixed and adhesive failures. By contrast, the GPR group showed a broader distribution overall: 39.6% (38/96) cohesive, 30.2% (29/96) mixed, and 30.2% (29/96) adhesive failures. Notably, the CS subgroup showed no cohesive failures, with an equal distribution of adhesive and mixed failures (50.0% each). Cohesive failure was most frequently observed in the RU and UC subgroups (66.7%, 8/12, respectively) (Figure 3).

Figure 3.

Failure mode distribution. The full names and manufacturers of the materials are provided in Table 1. The +S notation indicates silane application.

Contact angle and surface evaluation

Figure 4 shows the contact angle values for the different resin cements and 3D-printed resin substrates. Among the resin cements, CS exhibited the highest contact angle (67.6°), followed by GL (59.2°), RU (51.8°), and UC (43.5°). All resin cement groups differed significantly from one another. For the substrates, GPR with silane treatment (GPR + S) exhibited a significantly higher contact angle (94.4°) than all other conditions. In contrast, GPR (68.8°), OPR (65.7°), and OPR with silane (62.0°) showed no significant differences.

Figure 4.

Contact angles among resin cements and three-dimensional printed substrates. The +S notation indicates silane application. Among the resin cements, G-Multi PRIMER and Single Bond Universal Adhesive were applied to GL and UC, respectively. The full names and manufacturers of the materials are provided in Table 1.

Figure 5 presents representative SEM images (×500) of the 3D-printed resin substrates after air abrasion and silane application. Microcracks were observed on both OPR and GPR surfaces after air abrasion. The OPR surface appeared relatively smooth and uniform, whereas the GPR surface exhibited a rougher and more irregular texture with deeper grooves and distinct surface features. Silane application produced minimal visible morphological changes compared to the air-abraded surfaces in both groups at this magnification.

Figure 5.

Representative scanning electron microscopy images (×500 magnification) of air-abraded and silane-treated OPR and GPR surfaces. (A) OPR after air abrasion without silane application, (B) OPR after air abrasion followed by silane application, (C) GPR after air abrasion without silane application, and (D) GPR after air abrasion followed by silane application. The full names and manufacturers of the materials are provided in Table 1.

DISCUSSION

As a form of indirect restoration, 3D-printed dental restorations require durable adhesion to luting cements to ensure clinical success. In this study, the SBS of three adhesive resin cements—GL, RU, and CS—and one adhesive resin cement, RelyX UC, were compared to two types of 3D-printed restorative resins. The effect of applying a silane coupling agent on bonding performance was also assessed. The null hypothesis proposed that the type of resin cement, use of silane, and type of 3D-printed resin did not significantly influence SBS. Thus, this hypothesis is only partially supported. The results demonstrated that the type of resin cement had a statistically significant effect on the bond strength, whereas the application of silane and choice of 3D-printed resin substrate did not have a significant impact.

In both the OPR and GPR resin groups, CS consistently showed a significantly lower bond strength than the other cements. According to manufacturer data, CS has a film thickness of 19 μm, which is notably greater than that of GL (3 μm), RU (13 μm), and UC (12 μm). A thicker cement layer can compromise mechanical interlocking by introducing interfacial gaps and cause uneven stress distribution during loading [18]. The CS exhibited the highest contact angle among the cements, indicating that its wettability was relatively poor. The combination of greater film thickness and limited wetting ability may have contributed to reduced bonding performance, resulting in a higher incidence of adhesive failure.

RU and UC are produced by the same manufacturer and are intended for different adhesive strategies. UC is an adhesive resin cement requiring the application of a separate bonding agent to achieve optimal adhesion, whereas RU is a self-adhesive resin cement that simplifies the clinical procedure by eliminating the need for additional bonding. Despite the added bonding step, UC did not exhibit superior bond strength compared with RU. The contact angle data further revealed that UC, when used in conjunction with a bonding agent, exhibited the lowest contact angle, indicating excellent wettability. RU also demonstrated relatively good wettability, which may have contributed to its ability to achieve a bond strength comparable to that of UC, despite not requiring an additional adhesive step. In addition to wettability, another possible explanation for the lack of significant difference in bond strength between UC and RU may lie in their inherent chemical composition, which enables effective bonding to the tested substrates, regardless of the bonding protocol used.

Regarding the silane coupling agents, no significant improvement in the SBS between the 3D-printed resins and resin cements was observed. This finding is consistent with previous studies that reported mixed results regarding the effectiveness of silane, often attributed to differences in the chemical composition of the materials being tested [19–22]. The absence of a noticeable bonding enhancement may be due to the unique chemical structure of the 3D-printed resins. Specifically, the types of monomers and fillers used in these materials can significantly influence their mechanical properties and adhesive compatibility with resin cements [23]. Compared to conventional composite resins, 3D printing resins contain different types and ratios of monomers [24], and only a limited number of studies have investigated the chemical composition of commercial 3D-printed resins used for dental prostheses [12,25]. Common monomers found in light-cured dental composites, such as bisphenol A-glycidyl methacrylate (bis-GMA) and urethane dimethacrylate (UDMA), are used in 3D printing resins [26]. Additionally, monomers such as ethoxylated bisphenol A-dimethacrylate (bis-EMA) and triethylene glycol dimethacrylate (TEGDMA) are often incorporated to reduce the viscosity of the liquid resin [24,27]. While monomer composition plays a key role in determining the mechanical properties, ceramic fillers are added to 3D-printed resins to enhance their strength [8,28]. These fillers vary in shape, size, and composition; however, increasing their size or percentage can not only reduce light transmission but also significantly increase viscosity, both of which may lead to undesirable outcomes [11,12]. The 3D printing resins used in this study, OPR and GPR, were urethane acrylate-based materials with no reported filler content. This composition limits the effectiveness of silane, which typically enhances adhesion through chemical interactions with silanol groups present on silica-containing surfaces [10,29]. Silane application on the GPR surface increased the contact angle, indicating reduced wettability and thus showed no clear beneficial effect on the bond strength. Similarly, previous studies reported that silane treatment has minimal or no effect on non-silica-based substrates, highlighting the substrate-dependent bonding mechanism [9,30]. In the present study, a commonly used air-drying protocol was employed to facilitate solvent evaporation from the applied silane; however, variations in drying duration or the use of heat-assisted evaporation may further influence the extent of silane condensation and surface energy. The absence of a significant improvement in bond strength following silane application may therefore be partially attributable to the selected drying protocol, in addition to the filler-deficient, urethane acrylate-based nature of the tested 3D-printed resins.

To further investigate the substrate-related differences in bonding performance, both the SBS results and SEM analysis were examined. Although SBS values between OPR and GPR were not significantly different, noticeable differences were observed in their failure patterns. The OPR groups predominantly exhibited cohesive failures, suggesting that failure occurred within the substrate material rather than at the interface, possibly because of the weaker interlayer cohesion in the OPR. In contrast, the GPR groups exhibited more frequent adhesive and mixed failures, indicating weaker adhesion at the resin-cement-substrate interface. The SEM analysis supports these observations. The OPR surfaces appeared relatively smooth and uniform after air abrasion and silane application, which may have allowed for a more consistent resin adaptation and stress distribution. Conversely, the GPR surfaces exhibited a rougher and more irregular morphology with microcracks, which may have compromised uniform resin infiltration despite the potential for mechanical interlocking. Additionally, the prevalence of cohesive failure in OPR suggests that the interlayer bonding within the printed substrate may be weaker than that in GPR. Although the resin cement achieved good adhesion to the OPR surface, internal structural weaknesses between the printed layers could have served as the primary failure site. In contrast, GPR may have stronger interlayer cohesion but a lower surface affinity for resin cements, as evidenced by the higher rate of adhesive failure. These morphological and structural differences likely contributed to the less favorable interfacial bonding behavior observed in the GPR substrate. These morphological differences also provide a framework for interpreting the contact angle results. The smoother and more uniform surface observed for OPR after air abrasion and silane application may have promoted more homogeneous wetting behavior, resulting in minimal changes in contact angle. In contrast, the rougher and more irregular surface morphology with microcracks observed in GPR may have facilitated non-uniform silane film distribution and possibly localized retention of organosilane components, leading to increased surface hydrophobicity and a higher water contact angle after silane treatment. Furthermore, both OPR and GPR are urethane acrylate-based materials with limited or no reported silica filler content, which restricts effective siloxane coupling. Under such conditions, silane is more likely to function as a superficial surface modifier rather than a true chemical coupling agent, explaining why material-dependent changes in wettability did not translate into significant improvements in bond strength. Therefore, while SBS values alone may suggest similar bonding performance, a more comprehensive evaluation that considers both quantitative bond strength and qualitative failure modes is essential for assessing the true integrity of adhesive interfaces in 3D-printed materials.

The findings of this study demonstrate that the type of resin cement has a significant impact on the SBS of 3D-printed resins, whereas silane treatment does not enhance the bonding performance under the conditions tested. These results suggest that careful selection of resin cement is critical for optimizing bonding to 3D-printed restorative materials with minimal or no filler content. However, this study has several limitations. First, only one silane coupling agent (RelyX Ceramic Primer) was evaluated using a single application and drying protocol. Variations in silane composition, solvent systems, or application methods among different products may influence interfacial chemistry and bonding performance. Therefore, the present findings should not be generalized to all silane agents. Second, thermocycling was not incorporated and should be included in future studies to better simulate clinical conditions and assess the long-term durability of the bond. In addition, only two 3D-printed restorative resins were investigated, both of which are urethane acrylate-based materials that were locally available at the time of the study. This limits the generalizability of the findings to other resin chemistries or commercially available materials in different regions. Furthermore, exploring a wider range of surface modifications, such as varying the air-abrasion pressure and application time, would provide further insights. Addressing these limitations in future research will help establish a more comprehensive understanding of the bonding behavior of 3D-printed resin materials.

CONCLUSIONS

Within the limitations of this study, it can be concluded that the type of resin cement significantly impacts the SBS to 3D-printed resins. Furthermore, silane treatment does not significantly enhance the SBS for either the OPR or GPR substrates, both of which lack filler content. Additionally, although no significant differences in SBS were found between the OPR and GPR substrates, the two substrates exhibited distinct failure patterns.

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