Comparative evaluation of sorption and solubility of contemporary light-cured resin cement, resin-modified glass ionomer, and self-adhesive resin luting cement in distilled water and artificial saliva

Introduction

The Latin word Lutum, meaning “mud,” is the origin of the English term “luting,” which is commonly used to describe the process of sealing a gap or joining two components with a moldable material [1]. In various clinical situations, dental treatments can utilize dental cement. It may serve as a luting agent, base material, or temporary filling substance. Different types of cement have also been developed for orthodontics and endodontics [2]. Strong functional and aesthetic acceptance is essential for the longevity of any permanent prosthesis luting cement. The form, whether powder-liquid or paste, affects luting cement’s mechanical, biological, and physical pro­perties [3]. Cement can be broadly categorized into two groups: conventional cement, which is water-based and includes polycarboxylate, zinc phosphate, glass ionomer, and resin-modified glass ionomer cement (RMGIC); and resin cement, which is polymer-based. Resin cement provides several advantages over conventional cement, including enhanced aesthetics, lower solubility, improved marginal integrity, strong adhesion, and superior mechanical properties [4]. Durability of luting agents is highly influenced by dental cement’s solubility and disintegration (SD) in patient saliva and other fluids. Hydrolytic breakdown of cement in oral fluids causes the release of critical components and debonding of repairs, posing risks for microleakage and ongoing deterioration. Component leaching significantly impacts luting cement’s structural stability and biocompatibility [5-7]. Furthermore, SD considerably affects the mechanical strength, thermal insulation capacity, surface roughness, and aesthetic appeal of luting agents. Recurrent caries, postoperative hypersensitivity, pulpal inflammation, and periodontal disease, are believed to be influenced by SD [8]. Several factors can contribute to cement-related SD, including the composition of cement, lower powder-to-liquid ratio, liberation of fluoride ions from specific cement, patient’s oral hygiene practices, composition of dentifrice, pH of patient’s food and beverage intake, and composition and pH of their saliva [7]. Consequently, patients with SD tend to consume more acidic beverages. This is linked to the release of protic acids from these beverages and decrease in salivary pH, which promotes the hydrolytic breakdown of cement in oral fluids. Maintaining saliva at a lower pH for extended periods may also increase SD [8]. Several studies have identified water as a potential factor contributing to failure of adhesives to bond with dentin [9]. Therefore, soluble cement plays a crucial role in assessing the clinical durability of dental cement, and has been the subject of considerable clinical and experimental studies [10, 11]. To investigate these changes, dental cement should be tested in saliva. Although pH of oral cavity can vary significantly based on the context, it is generally regarded as slightly alkaline. Since pH changes temporarily, it become more acidic due to microorganisms breaking down dental plaque. However, due to natural saliva’s fragility, it cannot be used for standardization in vitro research. Artificial saliva that resembles natural saliva in its reaction to test items is essential for creating an artificial oral environment. Since dental cement serves many diverse purposes, various types with different qualities have emerged, but no material has yet been found to meet all needs. Resin-based cement is crucial for adhesively cementing ceramic crowns and bridges, inlays, onlays, ceramic veneers, composite posts, and orthodontic braces, and its importance is increasing as aesthetic dentistry grows [12, 13]. Resin-modified glass-ionomer cement is widely used and effective for cementing ceramic restorations, posts, and metal-ceramic restorations. Similar to standard glass-ionomer cement, it offers good mechanical properties, easy handling, and fluoride release that helps protect against caries, limited solubility, and radiopacity [14, 15]. The longevity of fixed prosthodontic restorations can be enhanced by choosing luting cement with appropriate characteristics, reducing the risk of secondary caries, postoperative hypersensitivity, pulpal inflammation, and periodontal diseases [16, 17]. The choice of luting cement can significantly influence dental restorations’ mechanical stability and lifespan. It should be based on a specific clinical scenario and exposure to oral fluids. This thoughtful selection ultimately contributes to the long-term efficacy of dental restorations by enabling practitioners to make informed decisions about the appropriate luting cement for specific clinical situations [18]. Dental practitioners still disagree about whether to use resin or other cements for retaining single crowns in place. Cementation with non-adhesive resin cements is faster and easier, but the design of preparation will determine how well it remains in position [19]. On the other hand, luting with adhesive resin cements is more challenging, because is difficult to isolate the cement from the posterior teeth. Consequently, this study aimed to compare the sorption and solubility of various types of luting cement in distilled water and arti­ficial saliva, focusing on resin-modified glass-ionomer cement and resin adhesive.

Objectives

This in vitro study aimed to evaluate and compare the sorption and solubility of a contemporary light-cured resin luting cement with those of RMGIC and self-adhesive resin luting cement, when immersed in distilled water and artificial saliva.

Material and methods

Sample size

Sample size estimation used a priori power analysis for one-way ANOVA with three groups, a significance level of 0.05, statistical power of 80%, and a medium effect size (f = 0.25), based on Cohen’s convention to understand the sample size. It was assumed that around 30 specimens per group (total, n = 90) would be enough to identify statistically significant differences. However, due to limitations of in vitro experiments, such as availability of materials, laboratory resources, and cost limits, a sample size of 20 specimens in each group (total, n = 60) was employed. This aligns with previous investigations on dental materials (e.g., Vaz et al. 2023 [20]), and was adequate to demonstrate statistically significant differences among groups in this study.

Cement and specimen preparation

As presented in Table 1, the study analyzed three categories of luting cements: Group 1: Resin-modified glass ionomer luting cement (3M™ RelyX™); Group 2: Self-adhesive resin luting cement (G-CEM ONE); Group 3: Light-cured resin luting cement (PANAVIA™ Veneer LC). Sixty specimens were manufactured according to ISO 4049:2009 criteria (International Orga­nization for Standardization, ISO 4049:2009 Dentistry – Polymer-based restorative materials, Geneva: ISO, 2009) [21], with each type of cement allocated to a group of twenty specimens. Specimens were produced in Teflon molds, with an inner diameter of 8.0 ± 0.1 mm and a thickness of 1.0 ± 0.1 mm.

Polymerization

Polymerization was conducted using a curing light (Bluephase 20, Ivoclar Vivadent Ag, FL-9494; Schaan, Liechtenstein). The light tip of curing lamp was positioned over the center of specimens for a designated exposure time. Then, eight overlapping peripheral zones were irradiated for 20 seconds each, until the entire surface was covered. The upper surface was cured first, followed by the same procedure applied to the lower surface.

Storage following polymerization

Specimens were preserved in an incubator at 37.0 ± 1.0°C for sixty minutes following polymerization, to ensure complete polymerization [18].

Preliminary weight evaluation and immersion

Starting weight (W1 in µg) of each specimen was determined using a precision scale (0.0001 g digit) (Figure 1). Then, 10 out of 20 specimens from each category were immersed in 20 milliliters of artificial saliva with a pH of 7, for 30 days in a temperature-controlled incubator at 37°C (Figure 2). Ten other specimens from each group were immersed in 20 milliliters of distilled water under the same conditions (Figure 3). Petri dishes containing both specimen groups were kept at 37°C. Artificial saliva, according to the manufacturer, is composed of the following ingredients: aqua (water), xylitol, glyce­rin, PEG-40 hydrogenated castor oil, sodium benzoate, potassium sorbate, sodium phosphate, and citric acid. To evaluate the sorption and solubility characteristics, speci­mens were reweighed and measured (Figure 4) at speci­fied time intervals, such as first day, first week, second week, third week, and fourth week. These intervals provided observation of both instantaneous and cumulative material action throughout the time, but was not used in statistical analysis; they were employed as a way for evaluation and weight change observation of specimens. After four weeks of immersion, samples were placed in a desiccator with Sukh blue silica desiccant (Figure 5) for an additional 4 weeks. This enabled removal of absorbed water and assessment of long-term stability of solubility and sorption. In assessment of solubility and sorption, water sorption (WSP) and solubility (WSL) were computed using formulas from ISO 4049: WSP was calculated as (M2-M3)/V, while WSL was determined by (M1-M3)/V. M1 is the initial weight before immersion (mg), M2 indicates the weight after immersion (mg), M3 represents the weight post desiccation (mg), and V denotes the volume of the specimen. In data analysis, solubility and water absorption of several cements and storage mediums were analyzed using analysis of variance (ANOVA). Also, a two-way ANOVA test was performed to assess the effects of cement type and storage medium between groups, followed by post hoc tests. Post hoc analysis of least significant difference (LSD) test indicated substantial group discrepancies, while a p-value below 0.05 indicated statistical significance.

Results

Three varieties of dental cements in two separate storage media (distilled water and artificial saliva) were evaluated for solubility and sorption characteristics.

Results in distilled water

The resin-modified glass ionomer luting cement, 3M™ RelyX™, exhibited mean solubility value of 0.2741. Self-adhesive resin luting cement, G-CEM ONE, showed lower mean value of 0.1231, whereas contemporary re­sin luting cement, PANAVIA™ Veneer LC, demonstrated the lowest solubility, with mean value of 0.0262. Sorption results showed that the mean value of resin-modified glass ionomer luting cement was 0.3079, the mean value of G-CEM ONE self-adhesive resin luting cement was 0.1583, and PANAVIA™ Veneer LC resin cement exhibited the mean value of 0.0612. The detailed results are presented in Table 2. Moreover, the results demonstrated that resin-modified glass ionomer luting cement had the maximum solubility, followed by self-adhesive resin cement, and light-cured resin-luting cement, which had the lowest solubility. There was a significant group mean difference in solubility, as indicated by statistically significant results (p < 0.001). A one-way ANOVA was performed to compare the values among the three luting cements under distilled water condition. Post hoc comparisons were carried out for solubility using the LSD test, with differences considered statistically significant at p < 0.05. This is illustrated in Table 3, and for sorption in Table 4.

Results in artificial saliva

The resin-modified glass ionomer luting cement, 3M™ RelyX™, exhibited mean solubility values of 0.3467, self-adhesive resin luting cement, G-CEM ONE, showed lower mean values of 0.1482, and contemporary resin luting cement, PANAVIA™ Veneer LC, demonstrated the lowest solubility, with mean values of 0.0579. The sorption results demonstrated that the mean value of resin-modified glass ionomer luting cement was 0.3832, the mean value of G-CEM ONE self-adhesive resin luting cement was 0.1980, and PANAVIA™ Veneer LC resin cement had the mean value of 0.0655. The detailed results are presented in Table 5. A one-way ANOVA was performed to compare the values among the three luting cements under distilled water condition. Post hoc comparisons were carried out for solubility using the LSD test, with differences considered statistically significant at p < 0.05. This is shown in Table 6, and for sorption in Table 7.
In both distilled water and artificial saliva (p < 0.001), solubility and sorption assays revealed rather substantial variations across all groups. Solubility differences between the two media (distilled water and artificial saliva) demonstrated not statistically significant difference between the two media (t (58) = –1.470, p = 0.147), with the mean difference of –0.0431. The effect size (Cohen’s d = 0.114) showed that the effect was very slight, which means that the difference was not significant. In terms of sorption differences between the two media (distilled water and artificial saliva), there was no statistically significant difference in sorption values between the two media (t (58) = –1.297, p = 0.200), with the mean difference of –0.0398. The effect size (Cohen’s d = 0.119) showed a small effect with no actual significance (Table 8). Although artificial saliva demonstrated numerically higher sorption and solubility values than distilled water across all groups, these differences were not statistically signi­ficant.

Discussion

Both adsorption, which takes place on the surface of a material, and absorption, where water molecules diffuse into the internal structure of a material, define the phenomena of water sorption. Conversely, solubility, which is mostly affected by the saturation concentration between two substances, represents the degree to which one substance dissolves in a solvent. Since they influence restoration durability, biocompatibility, and marginal integrity, all of which are vital for long-term clinical success, these features are especially important in luting cements [22, 23]. Two primary theories explain water diffusion in polymeric dental materials: the free volume theory, in which water diffuses across micro voids without polar interaction, and the interaction theory, where water bonds to hydrophilic groups [23]. High solubility can compromise luting agents in clinical settings, leading to dimensional instability, low adhesion, and possible restorative failure. To guarantee dimensional stability and resistance to oral environmental stresses, ideal luting materials should indicate low water sorption and solubility [18].
In this study, three luting cements, i.e., RelyXTM, G-CEM ONE, and PANAVIATM Veneer LC, were evaluated and compared in distilled water and artificial saliva, based on solubility and sorption behaviors. The results showed that RelyXTM displayed the highest solubility and sorption, PANAVIATM Veneer LC displayed the lowest, while G-CEM ONETM produced intermediate values. In both the storage media, statistical analysis revealed that variations among the materials were significant (p < 0.05) (Tables 3, 4, 6 and 7). Our results confirm that the materials behave differently depending on their composition and polymerization technique, contradicting the expectation of equivalency. RelyXTM, a RMGIC, has a high solubility because of its hydrophilic character and the presence of HEMA and polyacrylic acid, which raise its affinity to water [20]. RMGIC still shows higher solubility than pure resin cements due to its ionic structure, even if adding resin components lowers water permeability compared to conventional glass ionomer cement [18, 24]. GICs are known for their susceptibility to moisture. Water has a crucial role in the setting reaction of glass ionomer cement and is extensively studied. It enables transportation of calcium and aluminum cations, allowing the polyacid and polyacrylate matrix to react and form a polyacrylate matrix [25]. Moisture exposure during the initial stages of maturation results in component’s leaching and deterioration of physical characteristics. The depletion of water leads to insufficient responses post hardening and desiccation, resulting in surface crazing. GICs are expected to readily absorb and release water [26]. Despite the established knowledge that G-CEM ONE and PANAVIATM resin luting cements exhibit reduced water absorption and solubility compared to glass ionomer cements, it remains essential to understand the mechanisms underlying these activities. When G-CEM ONE and PANAVIATM resin luting cements encounter water, the filler-matrix interface deteriorates, causing the cement to operate as a plasticizer, which may lead to swelling and subsequently undermine the mechanical properties. Disintegration may also occur due to the matrix alone or interaction of silane between the matrix and fillers [27]. As a light-cured resin cement, PANAVIATM Veneer LC demonstrated noticeably improved sorption and solubility. Its nano-cluster spherical silica fillers, which lower water absorption and improve mechanical integrity, could be the reason for this phenomenon. Its unique light-curing mode lowers unpolymerized monomers, thus affecting solubility [28]. By contrast, the dual-cure self-adhesive cement G-CEM ONE exhibited intermediate behavior. Its greater solubility and sorption in regions with low light exposure could be explained by incomplete polyme­rization [31, 32]. Delayed light activation in dual-cure systems has been found to lower the degree of conversion, so compromising mechanical performance [33]. Similar trends were confirmed by earlier studies, e.g., Kurdi et al. [30]. Furthermore, Meşe et al. [16] and Toledano et al. [34] reported that lower filler content and HEMA presence increased sorption and solubility for RMGIC. Meşe et al. [16] found that in aqueous solutions, RMGIC showed more degradation than resin-based cements. Attributed to the matrix composition and hydrophilicity, Kurdi et al. [30] observed that self-adhesive resin G-CEM ONE cement had more solubility than conventional resin cement [30]. G-CEM ONE and PANAVIATM resin cements may still release small amounts of unpolymerized monomers; therefore, their solubility is much influenced by their filler type, size, and coupling agents [24, 29]. Especially HEMA, hydrophilic moieties tend to raise solubility by drawing water molecules into the matrix [18]. Manufacturers’ guidelines state that ideal polymerization of dual-cure systems, such as G-CEM ONE, depends on appropriate light activation. Should light exposure be inadequate, self-curing by itself might not provide the required mechanical cha­racteristics [30, 32]. Therefore, clinical procedures have to consider light application timing, especially in areas with limited access. Under both media, PANAVIATM Veneer LC presented stable characteristics in this context, possibly due to its denser cross-linked polymer network and nanofiller technology. This composition probably limits micro void formation and water paths, thus restricting both solubility and sorption. The results also confirm the effect of filler content on cement behavior; solubility of G-CEM ONE cements with more filler loading usually showed lower value [35]. Giti et al. [10] underlined how the filler type and composition can affect the behavior of G-CEM ONE cement, even in terms of storage media [10, 36]. While cemented restoration failure frequently occurs at the cement-tooth or cement-restoration interface, the sorption and solubility tests assess the integrity of the cement. Clinically, excessive G-CEM ONE cement exposure is typically restricted to the repair margin, which is about 100 µm. The current investigation confirms the results of Meşe et al. [16] and Joshi et al. [20]. PANAVIATM luting exhibited a minor decrease in solubility and sorption under artificial saliva and distilled water conditions, over an extended period of four weeks. During that time, a slight weight reduction was recorded until the fourth week, while other groups recorded a higher degree of weight loss.
Although these results demonstrate considerable strength, some limitations must be acknowledged. Resin cements have significantly reduced solubility in both distilled water and artificial saliva media. However, upon collecting solubility data and assessing the relationship between solubility and immersion duration via regression analysis, a statistically nonsignificant positive correlation was observed. The markedly greater solubility of RMGI cement in an acidic solution, in contrast to resin cement, may be attributed to the hydrophilic charac­teristics of RMGIC. RMGI cement exhibited markedly greater solubility compared to G-CEM ONE and PANAVIATM cement in acidic media, as in artificial saliva was more than in distilled water. Nonetheless, the incorporation of a resin matrix in its formulation enables RMGI cement to restrict solvent diffusion, resulting in reduced solubility relative to traditional GI cement [37]. The findings of these investigations are crucial to dentistry, as the solubility of cement is a fundamental property influencing the success of dental restorations. The artificial saliva utilized in the study did not contain enzymes, such as anhydrase found in the oral cavity. This may clarify the low solubility and sorption values observed for all cement groups samples in artificial saliva [38]. The differences between the two storage media can be directly linked to the cement composition, the properties of the filler, and how effectively it poly­merizes. Furthermore, the presence of acidic bacteria in the oral cavity may have led to surface degradation, following extended contact with these enzymes [15]. Given the rather small sample size per group (n = 20), statistical robustness may be inadequate. Furthermore, artificial saliva lacks biological variables, such as enzymes, pH variability, and salivary flow, which may affect material behavior in vivo [20]. Finally, future research should include larger sample sizes, longer immersion times, and simulations of dynamic oral conditions in order to better understand the clinical implications of solubility and sorption in luting cements. PANAVIA™ Veneer LC, a material with low solubility, sorption, and high filler stability, is ideal for long-term clinical applications, particularly in environments with prolonged exposure to saliva and moisture.

Conclusions

Within the limitations of this in vitro study, it can be concluded that resin-based luting materials demonstrated the lowest values of water sorption and solu­bility. The light-cured resin cement, PANAVIA™ Veneer LC, exhibited markedly higher performance relative to all other materials evaluated. The study showed that PANAVIA™ was superior, while another, G-CEM ONE cement, was intermediate. Conversely, RMGIC presented the highest values, indicating greater susceptibility to water-induced degradation. The difference in behavior between storage in distilled water and artificial saliva highlights the impact of storage media on material stability. The findings indicate that environmental factors, such as moisture, pH fluctuations, and salivary composition, may significantly influence the long-term therapeutic efficacy of luting cements. Consequently, forthcoming research ought to incorporate more dynamic and therapeutically appropriate simulation environments, to enhance the prediction of long-term results. Although artificial saliva showed numerically higher sorption and solubility values than distilled water across all sample groups, these differences were not statistically significant.

Disclosures

1. Institutional review board statement: Not applicable.
2. Assistance with the article: None.
3. Financial support and sponsorship: None.
4. Conflicts of interest: None.

References