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Article

Comparison of the Bonding Strength of Denture Base Materials Obtained by Different Manufacturing Methods to Reline Materials

by
Neslihan Güntekin
,
Aslı Çiftçi
*,
Burcu Kızılırmak
and
Sema Ateşalp İleri
Department of Prosthodontics, Faculty of Dentistry, Necmettin Erbakan University, 42090 Konya, Turkey
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(17), 9543; https://doi.org/10.3390/app15179543 (registering DOI)
Submission received: 14 July 2025 / Revised: 23 August 2025 / Accepted: 28 August 2025 / Published: 30 August 2025
Browse Figures
Versions Notes

Abstract

The durability of bonding between the denture base and reline materials plays a critical role in the long-term success of removable prostheses. This study aimed to compare the bond strength of denture base resins fabricated by heat-polymerization, CAD-CAM milling, and 3D printing techniques after thermocycling and different surface treatments. A total of 216 specimens (10 × 10 × 20 mm) were prepared from three base materials and subjected to surface treatment via no treatment (control), alumina air abrasion, or an Er/YAG laser. Two reline materials (hard and soft) were applied according to manufacturers’ instructions. All samples underwent 5000 thermal cycles and were tested using a tensile bond strength test. SEM analysis was performed to evaluate failure modes. The highest bond strength was observed in the milled resin group combined with alumina air abrasion and the hard reline material, reaching up to 12.41 MPa. Statistically significant effects were found for the material type, surface treatment, and reline material (p < 0.001). The results indicate that material properties, surface preparation, and reline type critically influence bond performance. Milled PMMA bases and hard relining agents, particularly when combined with air abrasion, offer superior bonding outcomes.

1. Introduction

Complete dentures are removable prostheses designed to fit the upper and lower jaws with oral mucosa support in cases where all teeth have been lost due to various causes such as caries, bone resorption, or trauma [1]. The denture base materials used in complete dentures play a fundamental role in meeting the functional, aesthetic, and phonetic needs of edentulous patients. These materials must ensure biocompatible adaptation to the oral tissues, resistance to masticatory forces, and long-term dimensional stability. A denture base material with inadequate physical or mechanical properties may negatively affect the retention and stability of the prosthesis, potentially leading to clinical problems such as tissue irritation, prosthesis fractures, and decreased patient satisfaction [2].
Various methods have been employed in the fabrication of complete dentures using polymethyl methacrylate (PMMA) resin [3,4]. The most commonly used technique for producing complete denture bases is the conventional compression molding method. While this method offers advantages such as ease of application and low cost, it may also present drawbacks such as polymerization shrinkage and porosity [2].
Another method is subtractive manufacturing (milling) using computer-aided design and computer-aided manufacturing (CAD/CAM). With the increasing adoption of CAD/CAM technology in dentistry, complete denture bases can now be fabricated through subtractive manufacturing. In this technique, pre-polymerized industrial PMMA blocks are milled using machines to match the digitally designed denture form. The CAD/CAM method provides significant advantages, including high dimensional accuracy, a porosity-free structure, homogeneous polymerization, and enhanced mechanical strength. Additionally, digital archiving facilitates the easy reproduction of dentures and reduces the risk of cross-contamination. However, this method also has certain limitations, such as material waste and restricted ability to reproduce fine details [5].
While the CAD/CAM denture base fabricated by the subtractive method consists of DCL-filled PMMA, in this method the denture base is digitally designed, and the UDMA-based 3D denture base is produced by layer-by-layer photopolymerization of resins using light” [6].
In parallel with subtractive methods, advancements in additive manufacturing have further expanded the possibilities for denture base fabrication. In this method, the denture base is digitally designed and produced by layer-by-layer polymerization of photopolymer resins using light [7]. Dentures manufactured through 3D printing offer advantages such as high surface detail, reduced production time, and the potential for customization. However, the biological and mechanical adequacy of the resins used in the printing process remains an ongoing subject of research, and long-term clinical data are still limited [8].
While these manufacturing methods enhance prosthetic fabrication, the prolonged use of removable dentures continues to present biological and clinical challenges. One of the most critical issues is residual ridge resorption, which occurs with long-term denture use. This condition leads to pain, instability, and eventual prosthesis failure. In such situations, patients face two options: either complete replacement of the prosthesis or restoration with a relining material [9].
Replacement of prostheses is a difficult, costly procedure that requires several appointments for both the patient and the clinician [10]. Therefore, it is very important to maintain patients’ existing prostheses. It is usually preferred to restore the patient’s prosthesis with a relining material [11].
The bonding between the removable prostheses and the reline materials is of great importance during the procedure [12]. Many studies have been conducted on the bonding properties between denture reline materials and denture base polymers [13]. Tensile bond strength testing is frequently employed to evaluate the adhesion between denture base and reline materials as removable dentures are not only subjected to compressive masticatory forces but also to tensile stresses during insertion, removal, and functional vacuum effects in the oral cavity [9].
The bond strength is determined by a number of factors, including the type of denture base resin, the composition of the denture liner, and the bonding agent. In addition, different surface treatments applied to the prosthesis base affect the connection of the prosthesis. Mechanical surface treatments, including milling, airborne-particle abrasion, and lasers, have also been proposed to increase the contact area between the prosthesis and the reline material [14].
Denture liners are available in two types: silicone-based and acrylic-based resins, which can be further divided into heat-polymerizing or autopolymerizing categories [1]. Adhesives or primers are not required for denture liners made of acrylic resin because their chemical makeup is similar to that of the acrylic resins used in denture bases [13]. However, because debonding from the denture bases will be expected more frequently, adhesives would be necessary for silicone-based resilient denture liners because they have different fundamental chemical structures [15].
In the literature, while there are numerous studies on the restoration of conventionally fabricated denture bases with relining materials, there is a notable lack of data regarding the restoration of denture bases produced by CAD-CAM milling and 3D printing methods. Recent studies have highlighted the challenges of achieving durable bonding in 3D-printed denture bases and emphasized that additional surface or chemical modifications may be required to improve adhesion with relining materials [16]. The aim of this study is to investigate the bond strengths of three different types of bases by applying two different roughening processes and bonding them with two different relining materials.
The first null hypothesis is that the surface-treated base materials are no different from those of the control group. The second null hypothesis is that there is no difference in bond strength between the different base materials.

2. Materials and Methods

In this in vitro study, complete denture base specimens were prepared using three different manufacturing methods: conventional heat polymerization (HP), CAD/CAM milling (ML), and 3D printing (3D). The specimens in each manufacturing group were randomly divided into three subgroups based on the surface treatment method applied: control (C), airborne-particle abrasion (A), and laser surface treatment (L). The specimens were assigned to these subgroups using simple randomization with a computer-based random number generator (Microsoft Excel, RAND function). Two different relining materials were used: Tokuyama Rebase II (hard, acrylic-based; H) and Mucopren Soft (soft, silicone-based; S). Consequently, a total of 18 experimental groups were formed according to the 3 (manufacturing) × 3 (surface treatment) × 2 (reline material) design. The experimental groups are illustrated in Figure 1.
The methods, material compositions, and manufacturer information used in this study are presented in Table 1.
The sample size was determined using GPower (GPower 3.1 software; Heinrich Heine University, Düsseldorf, Germany) with a 5% margin of error, an effect size of 0.4, and a test power of 85%.
Each test specimen consisted of two base segments bonded together with the relining material and was subjected to a tensile test. To obtain six specimens (n = 6) per experimental group, twelve base segments were used. A total of 36 bar-shaped specimens were produced for each group by preparing 72 base segments. Accordingly, 108 bar-shaped test specimens were prepared for the entire study by combining 216 base segments in pairs using the reline materials.
The specimens were designed in STL (Standard Triangle Language) format using CAD-CAM software SolidWorks (Dassault Systèmes SolidWorks Corp., Waltham, MA, USA, Solidworks 2021),with the dimensions of 10 × 10 × 20 mm [17,18] and these files were used during the milling or 3D printing processes.
Specimens that were fabricated in accordance with the standardized dimensions (10 × 10 × 20 mm) and exhibited no defects during production were included in the study. Specimens presenting insufficiently roughened surfaces, sudden fracture during tensile testing, visible deformation, or incomplete bonding with the relining material were excluded from the analysis and subsequently remanufactured.
For the HP group, wax replicas were milled from CAD/CAM wax blocks (Bilkim, İzmir, Türkiye) using a milling machine (Coritec 350i, imes-icore, Eiterfeld, Germany). These wax patterns were invested in dental stone and placed into metal flasks (MD-135, Meta Dental, Ankara, Turkey). After wax elimination, the cavities were filled with a mixture of 14 mL liquid and 35 g powder of heat-polymerized acrylic resin (Integra, Birleşik Grup Dental, Ankara, Turkey) and prepared in accordance with the manufacturer’s instructions. Polymerization was carried out in boiling water at 100 °C for 30 min. This process was used to fabricate the denture base specimens for the conventional group.
For the milling group (M), IvoBase CAD PMMA discs (IvoBase CAD, Ivoclar Vivadent, Liechtenstein) were milled into 10 × 10 × 20 mm base specimens using a milling machine (Coritec 350i, imes-icore, Eiterfeld, Germany).
For the 3D printing group (3D), specimens measuring 10 × 10 × 20 mm were fabricated using a 3D denture base resin (Saremco Print Denturetec) with a 3D printer (Asiga MAX UV 3D), in accordance with the manufacturer’s instructions. Upon completion of the printing process, the specimens underwent a two-step cleaning protocol in 96% isopropyl alcohol. The first wash was conducted for 5 min, followed by a second wash in fresh solution for 3 min. After washing, the specimens were air-dried to ensure no solvent residues remained on the surface.
Subsequently, the specimens were subjected to a post-curing process for 20 min in an inert atmosphere (nitrogen gas) using a light source with a wavelength of 385 nm (Otoflash G171), as recommended by the manufacturer.
All specimens were stored in a water bath at 37 ± 1 °C (Nüve Incubator, Istanbul, Turkey) for 30 ± 2 days following fabrication. Afterwards, they were subjected to thermocycling for 5000 cycles between 5 °C and 55 °C, with a 60 s dwell time and a 30 s transfer time between baths [19].
The specimens in each manufacturing group were divided into three subgroups according to the surface treatment applied. In the control group (C), no surface treatment was performed. In the airborne-particle abrasion group (A), the specimens were sandblasted with 100 µm aluminum oxide (Al2O3) particles at a pressure of 2 bar, from a distance of 10 mm for 10 s (Basic Quattro, Renfert, Germany). After the procedure, the surfaces were cleaned with oil-free compressed air [14].
In the laser group (L), the bonding surfaces of the specimens were treated with an Er/YAG laser (LightWalker AT, Fotona, Slovenia) with a wavelength of 2940 nm, an energy of 150 mJ, and a power output of 1.5 W. The laser was applied with a pulse duration of 700 µs and a frequency of 10 Hz, using a 4 mm spot diameter from a 10 mm distance for 20 s.
Following the surface treatments, the specimen blocks were positioned facing each other with a 3 mm space between them (Figure 2a). Custom-designed boxes that could hold the denture base blocks were created in STL format and fabricated (Figure 2b). Using these boxes, the specimens were appropriately bonded with the designated reline materials (Figure 2c).
Tokuyama Rebase II was applied in accordance with the manufacturer’s instructions. First, an adhesive was applied to the bonding surfaces of the denture base materials. Then, two doses from the dropper of Tokuyama Rebase II liquid were mixed with approximately one dose of Tokuyama Rebase II powder in the measuring cup. To minimize air bubbles, the powder was added into the liquid. The mixture was gently stirred with a spatula for about 5–10 s. Then, the reline material was applied to the specimen surfaces within 20 to 60 s (at room temperature). For complete polymerization of the reline material, one dose of Tokuyama Resin Hardener II was dissolved in 200 mL of water at a temperature of 40–60 °C (104–140 °F) in a beaker, and the bonded specimen was immersed in this solution for 3 min.
Mucopren Soft was applied in accordance with the manufacturer’s instructions. First, a single layer of adhesive was applied to the bonding surfaces of the denture base materials and left to dry for 90 s, followed by a second adhesive layer. Then, Mucopren® Soft was mixed evenly using a dispensing gun and used to bond the two specimens together. The 3D-printed and milled specimens were kept in a warm water bath (30 °C/86 °F–35 °C/95 °F) for 2 h. Mucopren® Soft (Kettenbach GmbH & Co. KG, Eschenburg, Germany) was applied in accordance with the manufacturer’s instructions.
One hour after the application of the reline materials, the bonded specimens were immersed in a water bath (Nüve Incubator, Istanbul, Turkey) at (37 ± 1) °C for (23 ± 1) hours [17,20].
The specimens were then placed in a Universal Testing Machine (Devotrans, D.V.T. GPE 5 KN YBS, İstanbul, Turkey) for tensile testing, and the schematic representation of the test setup is shown in Figure 3.
The denture specimens were subjected to tensile force at a crosshead speed of 5 mm/min using a universal testing machine (Devotrans, D.V.T. GPE 5 KN YBS, Turkey) until failure occurred. The maximum tensile load prior to fracture was recorded in Newtons (N). The tensile bond strength values (in MPa) were calculated by dividing the maximum load (N) by the cross-sectional bonding area in mm2. The bonding area was taken as 100 mm2 (10 × 10 mm) for all denture base specimens.
To observe the effects of the surface treatments on the denture base materials, one specimen from each subgroup was randomly selected. The surfaces of these specimens were examined at various magnifications (500× to 10,000×) using a scanning electron microscope (Hitachi VP-SEM SU1510, Tokyo, Japan).

3. Results

3.1. Statistical Results

Statistical analyses were performed using the R statistical software (v.4.3.1). The normality of the data distribution was assessed using the Shapiro–Wilk test. For comparison of bond strength values that did not follow a normal distribution according to the material, surface treatment, and technique, a three-way robust ANOVA was employed, and pairwise comparisons were conducted using the Bonferroni test. The results of the analyses were presented as trimmed mean ± standard error. The significance level was set at p < 0.050.
As a result of the three-way robust ANOVA analysis, it was found that the type of denture base material, the surface treatment method, and the reline material technique all had statistically significant main effects on bond strength values (p < 0.001). Among the materials, the highest mean bond strength was observed in the CAD-CAM milled PMMA group (6.5 MPa), followed by the conventionally heat-polymerized group (6.03 MPa) and the 3D-printed group (4.91 MPa). However, no statistically significant differences were found in pairwise comparisons between these groups.
Regarding surface treatment methods, sandblasting provided the highest bond strength (6.76 MPa), followed by laser treatment (6.2 MPa) and the untreated control group (4.49 MPa). Although overall differences between groups were statistically significant (p < 0.001), no statistically significant differences were observed in pairwise comparisons. The type of relining material also showed a significant effect on bond strength (p = 0.001). The mean bond strength obtained with the hard acrylic-based reline material (H) (10.917 MPa) was significantly higher than that obtained with the soft silicone-based material (S) (0.911 MPa). The mean bond strength and standard error values (MPa) for all experimental groups are presented in Table 2.
The stress–strain curves of the tested relining materials reflect the intrinsic mechanical nature of each material. The Mucopren Soft, being a silicone-based resilient liner, exhibited a ductile behavior characterized by gradual elongation and a rounded curve before failure, which indicates its ability to undergo deformation and stretching without sudden fracture. In contrast, the Tokuyama Rebase II, an acrylic-based hard reline material, demonstrated a steep linear increase in stress with minimal elongation, followed by an abrupt drop, which is consistent with the brittle fracture behavior expected from rigid acrylic resins. These differences highlight the fundamental divergence in elasticity and fracture mechanisms between soft and hard relining materials. The stress-strain graphs of both relining materials have been shown in Figure 4.
The interaction between material and technique was found to be statistically significant in terms of bond strength (p = 0.001). The highest mean bond strength value was observed when the CAD-CAM material was combined with the hard liner (H) (12.229 MPa), which was statistically similar to the conventional group + H combination but significantly different from all other combinations. Bond strength values obtained with the soft liner (S) did not differ significantly among the materials.
The interaction between the surface treatment method and technique was also found to be statistically significant (p = 0.001). The highest mean bond strength was obtained with the combination of sandblasting + H technique (12.411 MPa). This group was statistically similar to the laser + H combination but significantly different from all other groups.
The three-way interaction of material × surface treatment × technique was not statistically significant (p = 0.226). The corresponding values are presented in Table 3 below.
As a result of the SEM analyses, distinct morphological differences were observed on the surfaces of the control groups, depending on the manufacturing method.

3.2. Surface Microstructure Analysis

The SEM images presented in Figure 5a–c illustrate the effects of different surface treatments on the surface morphology of denture base materials fabricated by 3D printing. In the control group (A), the surface appeared irregular, microporous, and heterogeneous, providing limited mechanical retention for bonding, which resulted in a low bond strength value (4.29 ± 1.34 MPa). In the group treated with Al2O3 sandblasting (B), pronounced micro-indentations and rough surface features were observed as a result of particle impingement.
This increased the surface area and promoted mechanical interlocking; however, due to the oligomeric structure of the 3D-printed material, chemical bonding remained limited, resulting in a moderate bond strength (5.33 ± 1.44 MPa). In the laser-treated group (C), regular micropores and microchannels were detected on the surface. Although this morphology allowed better penetration of viscous reline materials, the non-uniformity of the surface irregularities may have restricted effective bonding. These findings indicate that while surface morphology in 3D-printed materials is significantly affected by surface treatments, bond strength is also strongly dependent on the chemical composition of the material in addition to surface roughness.
The SEM images presented in Figure 5d–f demonstrate the effects of different surface treatments on the surface morphology of CAD-CAM milled denture base materials. In the control group (D), the surface exhibited a homogeneous, smooth structure with low porosity, which allowed for the formation of an effective chemical bond with the reline material, resulting in high bond strength values (e.g., 12.229 ± 0.78 MPa in group H). In the sandblasted group (E), the abrasive effect of Al2O3 particles created distinct surface irregularities and micro-retentions; this increased surface roughness, enhanced mechanical interlocking, and allowed better penetration of the reline material into the surface. In the laser-treated group (F), oriented micropores and undulating patterns were observed on the surface, increasing the surface area and providing a favorable environment for bonding. The generally homogeneous and controlled surface morphology of the CAD-CAM group is considered a significant micromorphological finding that supports the high bond strength observed in this group.
The SEM images presented in Figure 5g–i reveal the morphological responses of conventionally processed denture base materials to different surface treatments. In the control group (G), irregularly distributed, fibrous, and amorphous structures were observed on the surface; this heterogeneous surface morphology has the potential to create localized weak points at the bonding interface. In the group treated with Al2O3 sandblasting (H), widespread irregularities and distinct abrasion marks were evident across the surface; this structure, due to its increased surface area, supported mechanical retention and had a positive effect on bond strength. In the laser-treated group (J), characteristic micropores, crack-like lines, and fibrous areas were observed; although this morphology may enhance micromechanical interlocking potential, the presence of irregular structures in certain areas may compromise bonding. Notably, the fibrous crack patterns observed in this group are consistent with the low surface integrity reported in the literature and may indicate areas of bonding weakness. Overall, the surface morphology of the conventional group underwent significant changes after surface treatments, which were directly associated with bonding performance.

4. Discussion

In this study, the bond strength between denture base materials fabricated using different manufacturing methods and a reline material was evaluated following various surface treatment protocols. The findings revealed that bonding performance was significantly influenced by the type of material used, surface preparation, and relining technique; therefore, both null hypotheses were rejected.
The material type had a statistically significant effect on bond strength, with the highest values observed in the CAD-CAM milled group (p < 0.001). These results are consistent with previous studies reporting that CAD-CAM milled materials exhibit higher mechanical strength and bonding capacity due to their high density and low porosity [21].
In conventionally processed and CAD-CAM fabricated denture base materials, solvents or monomers are often applied to the base surface to promote chemical bonding with reline materials. This process induces swelling of the PMMA surface, facilitating monomer diffusion and enabling the formation of an interpenetrating polymer network (IPN) upon polymerization. The thickness of the IPN—and consequently the bond strength—is directly related to the degree of swelling of the PMMA [21]. Solvents such as acetone, chloroform, and dichloromethane enhance this swelling, thereby improving bond strength. The presence of acetone in the monomer content of Tokuyama Rebase II may have contributed to the high bond strength observed in both the CAD-CAM (12.229 ± 0.78 MPa) and conventional (11.465 ± 0.773 MPa) groups [22].
While polymerization in conventionally processed PMMA occurs through linear chain formation, 3D-printed resins typically incorporate multifunctional monomers such as bisphenol-A dimethacrylate (Bis-GMA) and urethane dimethacrylate (UDMA), resulting in highly cross-linked networks. These structures exhibit lower permeability and swelling in response to solvents, which restricts monomer diffusion and limits IPN formation. As a result, chemical bonding with hard reline materials may be adversely affected in 3D-printed denture base materials [21].
This may explain the lower bond strength observed in the 3D-printed denture base group. According to the literature, DLP resins containing UDMA exhibit high chemical stability against solvents and show no significant changes in surface morphology [21]. In line with the findings of the present study, previous research has also reported that bonding of hard reline materials to 3D-printed resin bases is less effective compared to conventionally processed bases [23,24].
SEM analysis results revealed that surface morphology was significantly affected by both the manufacturing method and the applied surface treatment. The smoother and more homogeneous surfaces observed in the CAD-CAM milled specimens support the higher bond strength found in this group [17]. This finding is consistent with studies reporting that CAD-CAM materials, due to their lower porosity and denser structure, offer improved chemical and mechanical bonding with reline materials [21].
Conversely, the pronounced microporosities observed in the control group of the 3D-printed specimens indicate a more heterogeneous surface structure, which may have reduced the interpenetration capacity and subsequently lowered bond strength [24].
Surface treatment methods also significantly affected bond strength (p < 0.001). Both sandblasting (6.76 MPa) and laser surface modification (6.2 MPa) significantly improved bonding compared to the untreated control group (4.49 MPa). The increase in surface roughness enhances mechanical interlocking, thereby contributing to improved bond strength [14,25]. Sandblasting not only removes surface contaminants but also increases surface roughness and the bonding area, which in turn enhances mechanical adhesion [18,22]. Following Al2O3 sandblasting, a high degree of surface roughness—particularly in the 3D-printed group—was observed due to intense particle embedding; while this improved mechanical retention, it also highlighted that chemical structure and monomer compatibility are critical determinants of bonding success [13].
Although laser treatment produced microporous and irregular surface morphologies in some groups, the increase in surface area did not contribute to bond strength as effectively as sandblasting. In the conventional group, in particular, the fibrous cracks observed after laser treatment (Figure 5i) suggest potential weak points for bonding [14,26]. However, a contrasting result was reported in a similar study by Korkmaz et al. (2013), where the control group exhibited higher bond strength than the specimens sandblasted with 50 µm Al2O3, which is inconsistent with the findings of the present study [27]. This discrepancy may be attributed to the particle size of the Al2O3 used for sandblasting. In our study, Li et al. (2024), who used a similar particle size of 110 μm Al2O3, reported a significant increase in bond strength following surface roughening, supporting our findings [18]. SEM analysis also confirmed that sandblasted surfaces exhibited greater roughness, further validating these results. Additionally, the presence of residual Al2O3 particles on the surface may negatively influence chemical bonding. Overall, the findings align with the existing literature, which supports the enhancement of bond strength through surface roughening techniques [28].
The Er/YAG laser has the capacity to modify surface morphology by inducing controlled ablation on substrates such as dentin, acrylic, and similar materials. During laser application, rapid water evaporation and volumetric expansion cause micro-ablation on the surface, thereby increasing the surface area and creating microscopic irregularities. The resulting roughness and elevated surface energy expand the adhesive material’s contact area, reduce the contact angle, and facilitate the penetration of especially viscous reline materials [14,26,27]. In line with these mechanisms, Moussa et al. (2024) reported that laser-treated denture base materials exhibited increased surface roughness and enhanced bond strength [23]. Similarly, in the present study, laser surface treatment resulted in higher bond strength compared to the untreated control group, supporting the beneficial effects of laser-induced surface modification.
In the results regarding Mukopren bond strength, sandblasting was found to be more effective than laser surface treatment. A review of the literature reveals mixed findings: while laser treatment has been reported to either enhance or have no significant effect on the bonding of soft liner materials, sandblasting has often been found to have little or even detrimental effect [25,29,30]. Consistent with our findings, Nakhaei et al. (2016) reported that air abrasion with 110 µm alumina particles created surface irregularities on the denture base, thereby increasing mechanical retention and improving bond strength [28]. In contrast, Gundogdu et al. (2014) found that Er/YAG laser treatment using 150 mJ energy and 100 µs pulse duration did not enhance the bond strength of PMMA resin to autopolymerized silicone-based soft liners [30]. One possible explanation for the lower bond strength observed with laser treatment could be the non-uniform surface irregularities caused by sweeping laser motions. These irregularities may have created voids that the soft liner material could not adequately flow into or adapt to, thereby reducing the effectiveness of bonding compared to the more consistent micro-retentive pattern achieved by sandblasting [31].
The choice of the relining material was one of the most influential factors affecting bond strength (p = 0.001). Bond strength values were significantly higher when Tokuyama Rebase II was used, with an average of 10.917 MPa, whereas this value was only 0.911 MPa with Mucopren Soft. In a study by Awad et al. (2023), similar trends were reported: the lowest bond strengths were observed with chairside soft reline materials, while the highest were achieved with hard laboratory-processed reline materials [17]. Autopolymerizing silicone-based soft liners are structurally classified as polysiloxanes and generally exhibit low bonding affinity to denture base resins. This is because their adhesion is not directly to the base surface but occurs through limited infiltration, often mediated by a primer or adhesive layer applied during surface treatment [21,24,30]. According to Craig and Gibbons (1961), a bond strength of 0.45 MPa is considered clinically acceptable for soft reline materials [32]. Although no statistically significant difference in bond strength was found between different base material fabrication methods for the soft liner, all groups in our study exceeded this clinically acceptable threshold [32].
In their in vitro study, Janyaprasert et al. (2024) compared the bond strength of denture base materials fabricated using heat polymerization, CAD/CAM milling, and 3D printing techniques after thermocycling, using various relining materials [33]. Higher bond strength values were observed in the heat-polymerized and milled groups, whereas the 3D-printed group exhibited the lowest values. This outcome can be attributed to the lower cross-linking density and oligomer-based composition of 3D-printed materials, which make them more susceptible to thermal stress. The repeated thermal fluctuations induced by thermocycling may cause microscopic degradation in these materials, weakening the interfacial bond. Conversely, the high bond strength values observed in the milled groups with certain relining materials suggest that these materials are more stable under thermal stress and may therefore be more suitable for clinical use [33].
The limitations of this study include the inability to fully replicate the complex dynamics of the intraoral environment, such as saliva, thermal fluctuations, and masticatory forces. This limits the direct clinical applicability and generalizability of the obtained bond strength results. Only two types of relining materials (hard and soft) and three different denture base materials were evaluated. Considering the broader range of materials available in the literature, the generalization of the findings to all clinical scenarios is constrained. Additionally, the bonding surface area in the specimens was standardized at 100 mm2. However, in actual prostheses, anatomical and morphological variations may significantly influence bonding behavior, which should be taken into account when interpreting the results.
In future studies, the variety of the denture base and relining materials should be expanded. Products from different manufacturers should be compared, with particular focus on the performance of advanced materials such as next-generation hybrid structures and nano-composite-based systems. The bonding characteristics and biomechanical behavior of these innovative materials, when compared to conventional systems, could provide valuable insights to guide clinical applications. Moreover, surface treatment should not be limited to mechanical methods alone. The integration of chemical agents—such as monomers, solvents, and silane-based modifiers—with mechanical surface treatments should be explored to evaluate potential synergistic effects. Such combination strategies may offer significant improvements, especially for 3D-printed resins, which tend to exhibit lower bond strength

5. Conclusions

This study revealed that CAD/CAM milled PMMA exhibited the highest bonding performance with relining materials. The application of surface treatments, including sandblasting and laser modification, significantly enhanced bond strength, highlighting the critical role of adequate surface preparation prior to clinical relining procedures. Hard acrylic-based relining materials demonstrated markedly superior bond strength compared with soft silicone-based liners, supporting their recommendation for long-term clinical durability. Conversely, 3D-printed denture bases displayed relatively low bond strength, indicating the necessity of additional surface or chemical modifications to optimize their performance. Among the tested protocols, the combination of CAD/CAM fabricated base materials with sandblasting and hard reline materials achieved the most favorable outcomes. These findings underscore the importance of deliberate selection of both the denture base material and surface treatment method to ensure predictable and durable bonding in clinical practice.

Author Contributions

Conceptualization, A.Ç.; Data curation, N.G., A.Ç., and B.K.; Formal analysis, N.G. and S.A.İ.; Funding acquisition, N.G., B.K., and S.A.İ.; Investigation, A.Ç.; Methodology, N.G., A.Ç., and B.K.; Project administration, N.G.; Resources, S.A.İ.; Software, A.Ç., B.K., and S.A.İ.; Supervision, N.G. and S.A.İ.; Validation, A.Ç.; Visualization, A.Ç.; Writing—original draft, A.Ç.; Writing—review and editing, B.K. and S.A.İ. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

The following abbreviations are used in this manuscript:
HPHeat-polymerized acrylic resin
MLMilled acrylic resin
3D3D-printed acrylic resin
CControl group (no surface treatment)
AAirborne-particle abrasion with aluminum oxide
LSurface treatment with laser
HHard reline material
SSoft reline material

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Figure 1. Schematic representation of the experimental groups.
Figure 1. Schematic representation of the experimental groups.
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Figure 2. (a) The arrangement of the specimens and the distance between them; (b) a specially designed mold box for aligning and bonding the specimens; (c) the specimens bonded with the reline material and prepared in their final form prior to testing. The colors are used to distinguish the components: blue = denture base material, yellow = reline material, gray = mold box.
Figure 2. (a) The arrangement of the specimens and the distance between them; (b) a specially designed mold box for aligning and bonding the specimens; (c) the specimens bonded with the reline material and prepared in their final form prior to testing. The colors are used to distinguish the components: blue = denture base material, yellow = reline material, gray = mold box.
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Figure 3. Schematic representation of the tensile bond strength test. The specimen was positioned between the upper and lower clamps, and a vertical tensile force was applied until failure occurred.
Figure 3. Schematic representation of the tensile bond strength test. The specimen was positioned between the upper and lower clamps, and a vertical tensile force was applied until failure occurred.
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Figure 4. Stress-strain graphs of the tested reline materials; (a) representative stress-strain curve of Mucopren Soft; (b) representative stress-strain curve of Tokuyama Rebaze.
Figure 4. Stress-strain graphs of the tested reline materials; (a) representative stress-strain curve of Mucopren Soft; (b) representative stress-strain curve of Tokuyama Rebaze.
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Figure 5. SEM images of denture base materials subjected to different surface treatments: (a–c) 3D-printed specimens: (a) control, (b) aluminum oxide (Al2O3) sandblasting, (c) laser surface modification; (d–f) CAD-CAM milled specimens: (d) control, (e) aluminum oxide (Al2O3) sandblasting, (f) laser surface modification; (g–i) conventionally processed specimens: (g) control, (h) aluminum oxide (Al2O3) sandblasting, (i) laser surface modification.
Figure 5. SEM images of denture base materials subjected to different surface treatments: (a–c) 3D-printed specimens: (a) control, (b) aluminum oxide (Al2O3) sandblasting, (c) laser surface modification; (d–f) CAD-CAM milled specimens: (d) control, (e) aluminum oxide (Al2O3) sandblasting, (f) laser surface modification; (g–i) conventionally processed specimens: (g) control, (h) aluminum oxide (Al2O3) sandblasting, (i) laser surface modification.
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Table 1. Summary of the base materials, surface treatments, and relining agents used in the study, including product information.
Table 1. Summary of the base materials, surface treatments, and relining agents used in the study, including product information.
CategoryProduct NameMaterial TypeCompositionManufacturer Abbreviation
Denture Base MaterialIntegraHeat-polymerized acrylic resin (PMMA)PMMABG Dental, Ankara, TurkeyHP4
IvoBase CADCAD/CAM milled pre-polymerized PMMAPMMAIvoclar Vivadent, LiechtensteinML6
Saremco Print DENTURETECLight-cured resin-based compositeOligomeric acrylate resins, inorganic filler particles, photoinitiators, stabilizersSaremco Dental AG, Switzerland3D5
Surface Treatment—No surface treatment (control)——C3
Al2O3 particle abrasionAirborne-particle abrasion (100 µm, 2 bar)Aluminum oxide particlesRenfert Basic Quattro, Hilzingen, GermanyA1
Er/YAG laserLaser surface treatment (2940 nm, 1.5 W)Er/YAG laser beam at 2940 nmFotona LightWalker AT, Ljubljana, SloveniaL2
Relining MaterialTokuyama Rebase IIHard, auto-polymerized acrylic-based linerBenzoyl peroxide, titanium dioxide, acetoacetoxyethyl methacrylate, mequinol, nonamethylene dimethacrylate, acetone, ethyl acetateTokuyama Dental Corporation, Tokyo, JapanH7
Mucopren® SoftSoft, auto-polymerized silicone-based linerVinyl polysiloxanes, hydrogen polysiloxanes, fillers, pigments, additives, platinum catalystKettenbach GmbH & Co. KG, Eschenburg, GermanyS8
A1: Airborne-particle abrasion with aluminum oxide, L2: Surface treatment with laser, C3: Control group (no surface treatment), HP4: Heat-polymerized acrylic resin, 3D5: 3D-printed acrylic resin, ML6: Milled acrylic resin, H7: Hard reline material, S8: Soft reline material.
Table 2. Mean ± standard error (MPa) bond strength values for different combinations of surface treatment methods, denture base materials, and reline materials.
Table 2. Mean ± standard error (MPa) bond strength values for different combinations of surface treatment methods, denture base materials, and reline materials.
RougheningTechnicalMaterialTotal
HP43D5ML6
A1H713.50 ± 0.909.49 ± 0.7414.24 ± 0.9912.41 ± 0.74 A
S81.46 ± 0.101.17 ± 0.201.42 ± 0.211.35 ± 0.10 B
Total7.48 ± 2.065.33 ± 1.447.83 ± 2.206.80 ± 1.09
L2H12.53 ± 0.79.58 ± 0.8213.09 ± 1.2411.73 ± 0.66 A
S0.58 ± 0.050.99 ± 0.071.15 ± 0.240.91 ± 0.10 C
Total6.55 ± 2.035.29 ± 1.497.12 ± 2.106.20 ± 1.05
C3H8.36 ± 1.068.07 ± 0.949.35 ± 0.678.59 ± 0.51 D
S0.52 ± 0.050.58 ± 0.070.55 ± 0.040.53 ± 0.03 E
Total4.44 ± 1.414.30 ± 1.344.95 ± 1.514.49 ± 0.79
TotalH11.46 ± 0.77 A9.04 ± 0.49 C12.23 ± 0.78 A10.92 ± 0.42
S0.85 ± 0.12 B0.89 ± 0.10 B1.04 ± 0.14 B0.91 ± 0.07
Total6.03 ± 1.054.91 ± 0.806.50 ± 1.115.68 ± 0.57
A1: Airborne-particle abrasion with aluminum oxide, L2: Surface treatment with laser, C3: Control group (no surface treatment), HP4: Heat-polymerized acrylic resin, 3D5: 3D-printed acrylic resin, ML6: Milled acrylic resin, H7: Hard reline material, S8: Soft reline material. Different superscript letters indicate statistically significant differences between groups (p < 0.05). The letters should be interpreted horizontally within each row.
Table 3. Comparison of bond strength values according to material, surface treatment, and reline technique.
Table 3. Comparison of bond strength values according to material, surface treatment, and reline technique.
Q*p
Material26.66<0.001
Roughening52.77<0.001
Technical1301.040.001
Material×Roughening7.910.158
Material×Technique23.940.001
Roughening×Technical24.740.001
Material×Roughening×Technique6.660.226
Q*: Robust ANOVA test statistic.
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Güntekin, N.; Çiftçi, A.; Kızılırmak, B.; Ateşalp İleri, S. Comparison of the Bonding Strength of Denture Base Materials Obtained by Different Manufacturing Methods to Reline Materials. Appl. Sci. 2025, 15, 9543. https://doi.org/10.3390/app15179543

AMA Style

Güntekin N, Çiftçi A, Kızılırmak B, Ateşalp İleri S. Comparison of the Bonding Strength of Denture Base Materials Obtained by Different Manufacturing Methods to Reline Materials. Applied Sciences. 2025; 15(17):9543. https://doi.org/10.3390/app15179543

Chicago/Turabian Style

Güntekin, Neslihan, Aslı Çiftçi, Burcu Kızılırmak, and Sema Ateşalp İleri. 2025. "Comparison of the Bonding Strength of Denture Base Materials Obtained by Different Manufacturing Methods to Reline Materials" Applied Sciences 15, no. 17: 9543. https://doi.org/10.3390/app15179543

APA Style

Güntekin, N., Çiftçi, A., Kızılırmak, B., & Ateşalp İleri, S. (2025). Comparison of the Bonding Strength of Denture Base Materials Obtained by Different Manufacturing Methods to Reline Materials. Applied Sciences, 15(17), 9543. https://doi.org/10.3390/app15179543

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