785 2025 final Comparison of Adhesion of So1-Liner between Conven8onal PMMA and 3D Printed Resin Denture Bases Vol 13 No 1 (2025) DOI 10.5195/d3000.2025.785 h#p://den*stry3000.pi#.edu Comparison of Adhesion of Soft-Liner between Conventional PMMA and 3D Printed Resin Denture Bases *Dawood Jadaan1,2, Juzailah Roffie2, Husniyati Roslan2, Nahas P3 ¹ College of Dentistry, Tikrit University, Tikrit, Salahddin , Iraq 2 Advanced Medical and Dental Institute, University Sains Malaysia, Kepala Batas, Pulau Pinang, Malaysia ³ Faculty of Dental Medicine, Lebanese University, Hadat, Beirut, Lebanon Abstract Aims: The purpose of this study was to evaluate the tensile strength of the so6-liner (Molloplast-B®) between the denture founda>on made of 3D printed resin and tradi>onal acrylic (PMMA). Materials and Methods: In this experiment, 60 acrylic specimens in the shape of reverse dumbbells were employed. The first group consisted of 24 specimens made from tradi>onal acrylic polymethyl methacrylate (PMMA) (Vertex, Veracril, and Duradent) while the second group consisted of 24 specimens made from 3D printed resin (Dentona). The third group consisted of 12 samples that were packed at the dough stage of acrylic and so6 liner at the same >me. A6er that, the samples from the first and second groups were split in two, with one half receiving no surface treatment and the other half undergoing sandblas>ng. Every sample is separated into two halves with precise measurements. The thickest and thinnest sec>ons were 80 mm in length (10 mm x 25 mm) and 8 mm x 15 mm, respec>vely, and were joined in the middle by the so6-liner material. The experiment's tensile strength was examined in two separate direc>ons to ascertain the so6-liner material's strength of adhesion to the sample's chosen materials. Results: The data analysis of the tensile strength test revealed a sta>s>cally significant difference in the so6-liner adhesion strength between the 3D-printed acrylic resin with sandblast treatment (0.2133 ± 0.03939 kN/mm²) and the 3D-printed acrylic resin without surface treatment (0.1567 ± 0.04677 kN/mm²). Similar results were observed for conven>onal acrylic PMMA, where the sandblasted acrylic PMMA (0.0950 ± 0.03606 kN/mm²) exhibited significantly be^er bond strength compared to the untreated acrylic PMMA (0.0875 ± 0.02491 kN/mm²). Dough stage samples had be^er values complared to tradi>onal acrylic (0.1483± 0.03689 kN/mm²). Conclusion: The results demonstrate that sandblast treatment significantly improves the so6-liner adhesion strength of both 3D- printed acrylic resin and conven>onal acrylic PMMA. Surface treatment enhances bond strength compared to untreated materials. These findings suggest that sandblas>ng is an effec>ve method for improving adhesion in acrylic-based materials. Keywords: Heat polymerized acrylic, Sandblast, So6-liner, Tensile strength. Cita:on: Jadaan D, et al. (2025) Comparison of Adhesion of SoH-Liner between Conven:onal PMMA and 3D Printed Resin Denture Bases. Den:stry 3000. 2.a001 doi:10.5195/d3000.2025.785 Received: November 29, 2024 Accepted: February 1, 2025 Published: February 5. 2025 Copyright: ©2025 Jadaan D, et al. This is an open access ar:cle licensed under a Crea:ve Commons AZribu:on Work 4.0 United States License. Email: dawoodsalmantech@gmail.com Introduction Long-term use of dentures can lead to significant changes in the supporting structures, often resulting in chronic pain and discomfort, particularly in the mandible [1]. Accelerated resorption of the alveolar ridges leads to the formation of a sharp, narrow crest, which generates excessive pressure, causing severe complications for the patient. As a result, it becomes essential to adopt denture design that provides adequate ridge protection [2]. Relining procedures play a critical role in addressing denture related problems [3]. This procedure is non-invasive, cost-effective, and offers greater patient comfort compared to fabricating new dentures [4,5]. There are two types of denture liners: stiff (usually made of polymethyl methacrylate) and resilient [6]. Resilient liners fall into two categories: short-term and long-term liners. In contrast to Comparison of Adhesion of So1-Liner between Conven8onal PMMA and 3D Printed Resin Denture Bases Vol 13 No 1 (2025) DOI 10.5195/d3000.2025.785 h#p://den*stry3000.pi#.edu short-term liners, which are intended to be worn for a maximum of 30 days, long-term liners can be worn for up to a year and maintain their durability for more than 30 days [7–9]. Resilient denture lining materials are preferred over hard denture liners because they engage soft tissue undercuts to increase prosthesis retention, relieve constrained pressure, and cushion the fitting surface of dental prostheses to enable more uniform force delivery [4]. However, surface imperfections and porosity, residual palatable after use, odor and water absorption, color instability, difficulties maintaining hygiene, and early thickening due to plasticizer solubility are some of the issues with resilient denture liners [7]. One major issue with denture liners is the liner's inability to adhere to the acrylic resins [10,11]. To prevent interfacial separation at the borders of the denture, it is recommended that the acrylic resins and denture liners retain a robust and durable binding. Additionally, the disintegration of the adhesive between the soft liners and the acrylic resins encourages the growth of bacteria and speeds up the deterioration of the soft lining material. [12,13]. Previous studies have suggested several techniques to increase the adhesion of liners to the denture base. These include airborne particle abrasion, bur roughening acrylic, chemical etching, and lasing to give the denture base a rougher surface [8, 14–18]. Denture processing techniques have changed dramatically in recent years due to the application of computer-aided design and manufacturing (CAD/CAM) technology [19–21]. Although dentures have been made using CAD/CAM technology since the 1990s, the lack of scientific evidence still makes them appear to be a relatively new technique [22]. CAD-CAM-fabricated dentures have better material properties and require fewer treatment visits, which saves money and time for both patients and physicians. Every day, more and more professional dentistry practices are utilizing CAD/CAM technology. Nevertheless, there is little scientific data on the bonding properties of denture liners to denture resins made using CAD/CAM technology [3]. Research on the use of 3D-printed denture resins is limited, with existing studies indicating that the adhesion strength of 3D-printed denture resins is generally lower than that of traditional acrylic. While many studies have focused on mixing powder and liquid soft- liner materials, this study utilizes a pre-made silicone-based soft liner (Molloplast B®), which is commonly used in maxillofacial prosthetics. The aim of this study is to evaluate the adhesion properties between resilient denture liners and various denture base materials, including those fabricated using traditional methods and advanced CAD/CAM or 3D printing technologies. Material and Methods Materials The materials used are listed in the following table (Table 1). Table 1. Materials used in the study. Item Brand Country Soft liner pest- silicon based Molloplast ® B (detax) Germany Heat cure acrylic polymer and monomer Duradant Turkey 3D printer resin denture base Dentona® Germany Dental stone type 4 Efes dental Turkey Wax disc milling for Vericom /Mazic wax Korea Comparison of Adhesion of So1-Liner between Conven8onal PMMA and 3D Printed Resin Denture Bases Vol 13 No 1 (2025) DOI 10.5195/d3000.2025.785 h#p://den*stry3000.pi#.edu CAD/CA M Separating medium Duradent Turkey Water Tap water Iraq Sand Renfert ® Germany Alcohol Clear logo Iraq Modeling wax Dura dent Turkey Fabrication of the samples Three types of samples were prepared: PMMA samples, 3D printed resin samples, and dough stage samples. Samples were prepared by joining two rectangular blocks of acrylic (PMMA) with a soft-liner material, while another group consisted of two rectangular blocks fabricated from 3D printed resin denture material connected by the soft liner (Figure 1). Figure 1. Sample measurements. The preparation of the samples involved two distinct groups: acrylic (PMMA) and 3D printed resin. For acrylic samples, a traditional technique was employed. A wax pattern was first designed and cut to the desired measurements. The wax pattern was placed inside a flask and fixed in position using dental stone (Figure 2). After the wax was eliminated, a mold space was created and was ready to be packed with acrylic material. After that, the acrylic was cured inside a water bath for one hour after reaching boiling state. Once curing was completed, the specimens were removed from the mold and finished. The acrylic samples were divided into two groups: one group underwent sandblasting with air pressure to treat the surface, while the other group was left untreated. Figure 2. Wax patterns inside the dental stone. For the 3D printed resin samples, the required dimensions for the tensile testing were designed using Autodesk (Figure 3). The design was then sent as an STL file to a 3D printer, which used Dentona® resin for removable dentures. After printing, the samples were removed from the machine and cleaned using an ultrasonic device with alcohol to ensure thorough cleaning. The samples were then light cured for two minutes and divided into two groups: one group was sandblasted to treat the surface, and the other remained untreated. Figure 3. Autodesk software. The next steps were similar for both groups. Acrylic samples (Those made by traditional method and 3D printed samples) were joined in the middle by wax and place inside a dental flask filled with dental stone (Figure 4). After wax elimination, a mold space was created to be packed with the soft- liner material. The soft-liner material (Molloplast-B®) was then packed into the mold space, with the flask placed under pressure for five minutes. It was transferred to a clamp to maintain pressure and submerged in a water bath at room temperature. The curing process involved dipping the flask into a water bath heated to 70°C for 90 minutes, followed by raising the temperature to 100°C for 30 minutes. After curing, the flask was removed and allowed to cool gradually to ambient temperature for 30 minutes, followed by an additional 15 minutes of cooling under running water. Comparison of Adhesion of So1-Liner between Conven8onal PMMA and 3D Printed Resin Denture Bases Vol 13 No 1 (2025) DOI 10.5195/d3000.2025.785 h#p://den*stry3000.pi#.edu Figure 4. Samples are connected by wax that was replaced by soft-liner. For dough stage samples, both the PMMA acrylic and the soft liner were packed together inside the dental mold at dough stage. This was followed by curing as mentioned earlier. In all cases, the preparation process involved careful handling, curing, and cooling to ensure the proper bonding of the soft-liner material with the acrylic or 3D printed resin base. Study design The experiment employed 60 specimens in the form of reverse rectangular blocks. 12 specimens were dough stage packed specimens which received no treatment. 24 of the specimens were made from 3D printed resin (Dentona® optiprint® laviva), while the other 24 specimens were made from traditional heat-cured acrylic PMMA resin (Veracril®, Duradent®). In line with Chladek et al. 2014 (Figure 1), the specimens were designed as follows: the entire length of 80 mm of resin (acrylic PMMA or 3D printed) was split into two sections of 40 mm each, separated by 3 mm. The surface was sanded and air- treated, with 25 mm having a thickness of 10 mm. On the other hand, the borders of 15mm were 8mm thick. Surface treatment Half of the sample underwent the surface treatment before the bonding of the soft reline material (Molloplast B®). The surface treatment was done using airborne-particle abrasion to the bonded surface by sandblast size 90–150-micron alumina with air pressure of 3- 4 bar. This was to increase the surface roughness to increase the mechanical boned between the materials. Tensile bond strength test The testing procedure was carried out at the University of Tikrit College of Engineering using a HOYTOM D1922fI testing machine (Figure 5) with a load cell capacity of 170 KN and a crosshead speed of 0.5mm/min. The readings obtained from the device's digital display represented the maximum load of failure, and the value bond strength was calculated by dividing the maximum load of failure by the cross-sectional area of each sample Figure 5. Hoytom testing machine. Statistical analysis The statistical analysis involved the use of One-Way ANOVA at P ≤0.05 to reveal if there were any differences between the groups. Results Tensile strength test The adhesion strength of soft liners was found to be significantly higher with 3D printed resin denture bases compared to conventional PMMA. There were highly significant differences between the five groups as revealed by one-way Anova test. Surface treated 3D printed resin samples had the highest value of tensile bond strength (0.2133) followed by untreated 3D printed resin (0.1567), dough stage samples (0.1483), surface treated PMMA samples (0.0950), while the lowest value was recorded for the untreated PMMA samples (0.0875) as indicated in (Tables 2 and 3). Comparison of Adhesion of So1-Liner between Conven8onal PMMA and 3D Printed Resin Denture Bases Vol 13 No 1 (2025) DOI 10.5195/d3000.2025.785 h#p://den*stry3000.pi#.edu Evaluation sample under the Scanning electron microscope (SEM). All samples were sent for SEM evaluation to determine the morphology of the denture bases before and after treatment by the sand airborne-particle abrasion surface treatment (Figure 6). Figure 6. Scanner electron microscopic (SEM), right are the untreated samples, left are the treated samples. Discussion This study compares the tensile strength of soft liners between conventional PMMA and 3D- printed resin denture bases. The results show that the soft liner, Molloplast-B®, adheres better to 3D-printed samples compared to conventional acrylic specimens. The tensile bond strength of 3D- printed samples was significantly higher than that of acrylic PMMA samples (traditional and dough stage), particularly when the 3D- printed surfaces were treated with sandblasting and air pressure (0.2133 ± 0.03939 kN/mm²), compared to untreated 3D-printed surfaces (0.1567 ± 0.04677 kN/mm²). This could be related to the printing process which can results in a micro-roughness and irregularities that can improve mechanical interlocking between the soft liner and the 3D printed sample. This roughness increases the surface area available for bonding, promoting stronger adhesion through mechanical bonding (micromechanical interlocking) between the liner and the resin [23]. In contrast, conventional PMMA samples, tends to have a smoother, more homogeneous surface. While sandblasting can induce surface roughness by creating micro- abrasions, the overall roughness of PMMA samples remains lower than that of 3D-printed resin surfaces, which may explain the lower bond strength observed in the untreated acrylic samples [24- 29]. In some cases, the sandblasted 3D-printed resin samples showed failure of the soft liner without separating from the bond surface, indicating strong adhesion. For conventional PMMA, sandblasting improved the bond strength of Molloplast-B® soft liner, with a bond strength of 0.0950 ± 0.03606 kN/mm², compared to untreated PMMA (0.0875 ± 0.02491 kN/mm²). In the case of the 3D-printed resins, surface treatments like sandblasting and air pressure can enhance the bonding sites by increasing surface energy [29, 30]. Sandblasting causes the surface to become microscopically rougher, which can expose more reactive functional groups, increasing the surface's affinity for chemical bonding with the liner [31-33]. Polymerization and the degree of crosslinking in the resin also play a role in determining the bond strength. 3D-printed resins generally exhibit better control over polymerization, allowing for a more uniform and complete curing process [34]. This results in a more stable, tightly packed polymer matrix that can provide superior adhesion. In contrast, PMMA, while also polymerized, may not have as consistent or efficient a curing process as 3D-printed resins, leading to slight variations in surface hardness and cohesion [36]. Traditional PMMA denture bases can also suffer from degradation over time due to the migration of plasticizers, which are used to modify the material's flexibility. This can weaken the surface and reduce its ability to maintain a strong bond with soft liners like Molloplast-B® [37]. 3D-printed resins, however, often have a more Comparison of Adhesion of So1-Liner between Conven8onal PMMA and 3D Printed Resin Denture Bases Vol 13 No 1 (2025) DOI 10.5195/d3000.2025.785 h#p://den*stry3000.pi#.edu stable polymer matrix and less plasticizer migration, which can result in better long-term adhesion [38]. In addition, the surface energy of a material is a key factor in determining how well it bonds to another material. 3D-printed resins typically have higher surface energy compared to PMMA, especially after surface treatments like sandblasting. This increased surface energy improves wettability, which enhances the ability of the soft liner to spread evenly over the denture base and form a stronger bond [39]. In comparison, untreated PMMA has lower surface energy, leading to poorer wetting and a weaker bond [40]. As mentioned above, dough stage samples had better tensile strength values compared to PMMA samples packed by the traditional methods. This is because packing both acrylic and soft liner at the dough stage allows the materials to intermingle or bond more effectively during the molding process. When packed with acrylic at the dough stage, the two materials have a better chance of distributing the applied tensile stress more evenly across the surface. This means that the soft liner can absorb some of the forces, reducing localized stress points. At the dough stage, both acrylic and soft liners are in a form that allows for better molecular interaction [41]. Acrylic resins are typically polymerized during curing, and when mixed with soft liners, the soft liner's material may undergo some crosslinking or slight interaction with the acrylic. This can result in a composite material with enhanced mechanical properties which explains the high tensile strength compared to PMMA [42]. 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Haghi HR, Shiehzadeh M, Gharechahi J, Nodehi D, Karazhian A. Comparison of tensile bond strength of sop liners to an acrylic resin denture base with various curing methods and surface treatments. Int J Prosthodont. 2020 Jan 1;33(1):56-62. Table 2. Statistical analysis for tensile bond strength. Vickers microhardness Group Mean ±SD Acrylic without sandblasting A 0.0875 0.02491 Acrylic with sandblasting B 0.0950 0.03606 3D printed resin without sandblasting C 0.1567 0.04677 3D printed resin with sandblasting D 0.2133 0.03939 Dough stage 0.1483 0.03689 ANOVA: F=22.448; p=0.000 Levene statistics=0.080, p-value=0.923 Comparison of Adhesion of So1-Liner between Conven8onal PMMA and 3D Printed Resin Denture Bases Vol 13 No 1 (2025) DOI 10.5195/d3000.2025.785 h#p://den*stry3000.pi#.edu Table 3. Post-hoc Tukey’s test results. I J Mean Difference (I-J) Standard Error p-value Acrylic without sandblasting Acrylic with -0.00750 0.01530 0.988 3D without -0.06917 0.01530 0.000 3D with -0.12583 0.01530 0.000 Dough stage -0.06083 0.01530 0.002 Acrylic with sandblasting Acrylic without 0.00750 0.01530 0.988 3D without -0.06167 0.01530 0.002 3D with -0.11833 0.01530 0.000 Dough stage -0.05333 0.01530 0.008 3D printed resin without sandblasting Acrylic without\ 0.06917 0.01530 0.000 Acrylic with 0.06167 0.01530 0.002 3D with -0.05667 0.01530 0.004 Dough stage 0.00833 0.01530 0.982 3D with sandblasting Acrylic without\ 0.12583 0.01530 0.000 Acrylic with 0.11833 0.01530 0.000 3D without 0.05667 0.01530 0.004 Dough stage 0.06500 0.01530 0.001