Effect of an alginate-based antacid and simulated gastric acid on the surface roughness and color stability of CAD/CAM resin-based materials

Abstract

Background

This in vitro study aimed to evaluate the effect of simulated gastric fluid (SGF) and an alginate-based antacid on the surface roughness and color stability of two additively manufactured (AM) and one subtractively manufactured (SM) resin-based restorative materials.

Methods

A total of 168 disc-shaped specimens (10 × 2 mm) were fabricated from two AM resin composites (Bego VarseoSmile TriniQ [AM-VS] and Saremco Crowntec [AM-C]) and one SM nano-ceramic hybrid (Voco Grandio blocs [SM-V]). Specimens were distributed into seven subgroups (n = 8) based on immersion media: distilled water (control); SGF mixed with artificial saliva (AS) at ratios of 1:1, 1:3, and 1:5; and the same mixtures with 10% alginate-based antacid (Gaviscon^®). All solutions were refreshed daily and maintained at 37 °C with gentle agitation for 48 h. Surface roughness (Ra) was measured with a contact profilometer, and color stability (ΔE₀₀) was assessed with a spectrophotometer. Data were analyzed using mixed-model ANOVA and post hoc tests (α = 0.05).

Results

Immersion in SGF + AS increased ΔE₀₀ and Ra values in all materials compared with distilled water (p<.001). The highest color change was observed in AM-C at SGF + AS (1:5) (1.87 ± 0.30), whereas SM-V showed the lowest ΔE₀₀ values (1.55 ± 0.04). Surface roughness increased under acidic conditions, with AM-C exhibiting the highest Ra values (1.30 ± 0.02 μm). The alginate-based antacid significantly reduced Ra values for all materials and reduced ΔE₀₀ values in AM-C (1:3 and 1:5) and AM-VS (1:5) (p<.05), with selected antacid-containing subgroups showing values approaching those of the control.

Conclusions

Simulated gastric fluid compromised the surface integrity and color stability of CAD/CAM resin-based restorative materials, with material-dependent differences. The addition of an alginate-based antacid mitigated these effects under selected experimental conditions, suggesting a potential protective role against acid-induced degradation.

Introduction

Computer-aided design and computer-aided manufacturing (CAD/CAM) technologies have become integral to modern dentistry, offering advantages such as improved efficiency, higher precision, and standardized production. These systems are compatible with a wide range of materials, including ceramics, polymers, and resin composites, processed either through additive or subtractive manufacturing techniques [1]. Despite these benefits, restorative materials may undergo chemical degradation and surface changes when exposed to acidic environments, leading to increased surface roughness and compromised color stability [2]. Such changes can negatively affect the longevity and esthetic performance of restorations, particularly in patients with chronic acid exposure [3].

The oral cavity represents a dynamic environment where saliva, pH fluctuations, and chemical challenges interact continuously [4]. Saliva plays a key role in maintaining oral homeostasis by buffering acids, facilitating remineralization, and lubricating oral tissues [5]. However, in patients with gastroesophageal reflux disease (GERD) or eating disorders associated with frequent vomiting, repeated exposure to gastric acid can dramatically reduce intraoral pH, reaching values as low as 1.0 during reflux episodes [6, 7]. This highly acidic environment not only accelerates the erosion of natural tooth tissues but also affects the structural integrity and surface properties of restorative dental materials [8–10].

In clinical practice, patients with GERD are often prescribed alginate-based formulations that form a floating barrier on the gastric contents and buffer the acid toward neutral pH [11]. Commercial examples include Gaviscon^®, an alginate-based antacid widely used to manage reflux symptoms. The presence of such buffering agents may modify the interaction between gastric acid and restorative materials, potentially reducing surface degradation and color change [11, 12]. Previous in-vitro investigations have demonstrated that exposure to simulated gastric acid can significantly increase surface roughness, reduce microhardness, and reduce color stability in conventional resin composites and ceramic restorations [13–15]. These findings highlight the vulnerability of polymer-based restorative materials to intrinsic acid challenges and provide a rationale for evaluating newer CAD/CAM resin-based systems under similar conditions [16, 17]. However, evidence regarding the effect of alginate-based antacids on CAD/CAM restorative materials under simulated gastric acid conditions remains limited [12].

Color stability and surface roughness are essential properties of restorative materials because they directly influence esthetic and functional outcomes [18]. Understanding how gastric acid and acid-buffering agents affect these parameters is critical for evidence-based material selection, especially in patients at high risk of intrinsic erosion [19]. Therefore, the aim of this study was to evaluate the effect of simulated gastric fluid (SGF) and an alginate-based antacid on the surface roughness and color stability of three CAD/CAM resin-based restorative materials: Saremco Crowntec, Bego VarseoSmile TriniQ, and Voco Grandio blocs. The null hypothesis (H₀) was that the presence of the antacid would not significantly affect surface roughness or color stability compared with acid exposure alone. The alternative hypothesis (H₁) was that the antacid would reduce surface roughness and improve color stability.

Methods

This in vitro study evaluated the effects of different immersion media on the surface roughness and color stability of two AM resin composites and one SM nano-ceramic hybrid. A total of 168 disc-shaped specimens (10 × 2 mm) were prepared using three restorative materials (n = 56 per material): Bego VarseoSmile TriniQ (AM-VS; Bego, Bremen, Germany), Saremco Crowntec (AM-C; Saremco Dental AG, Rebstein, Switzerland), and Voco Grandio blocs (SM-V; Voco GmbH, Cuxhaven, Germany). The specimens were subsequently divided into 7 subgroups based on immersion medium (n = 8 per subgroup). Details of the study materials are provided in Table 1, and the experimental workflow is depicted in Fig. 1.

Table 1.

Materials included in the study, their composition, manufacturing technology, and structural features

Material (Abbreviation)	Type / Manufacturer	Composition	Manufacturing technology	Structural features
VarseoSmile TriniQ (AM-VS)	3D-printed resin composite (BEGO, Bremen, Germany)	Methacrylate-based resin matrix with inorganic fillers (~ 50 wt%)	Additive manufacturing (AM), light-curing, layer-by-layer	Contains resin-rich matrix and interlayer interfaces; polymerization occurs during layer-by-layer printing
Crowntec (AM-C)	3D-printed resin composite (VOCO, Cuxhaven, Germany)	Urethane dimethacrylate, TEGDMA with ceramic and glass fillers (~ 55 wt%)	Additive manufacturing (AM), light-curing, layer-by-layer	Resin-based formulation with heterogeneous polymerization and mixed ceramic-glass filler content
Grandio blocs (SM-V)	Nano-hybrid ceramic composite block (VOCO, Cuxhaven, Germany)	~ 86 wt% nano-ceramic fillers (glass ceramics, silica, barium) in a polymer matrix (UDMA, TEGDMA)	Subtractive manufacturing (SM), industrial polymerization under high temperature and pressure	Densely polymerized hybrid structure with high filler loading and uniform filler distribution

Fig. 1.

Workflow of the study. Schematic representation of the experimental design, including specimen preparation, grouping according to storage media [Distilled Water (DW), simulated gastric fluid plus artificial saliva (SGF + AS) in ratios 1:1, 1:3, and 1:5, with or without 10% alginate-based antacid], immersion protocol (96 h at 37 °C), evaluation of surface roughness (Ra) and color difference (ΔE₀₀), followed by statistical analysis and outcome assessment

For specimen fabrication, discs were designed using Autodesk 123D Design software (Autodesk Inc., San Rafael, CA, USA) and exported as standard tessellation language (STL) files. AM specimens were fabricated with a DLP printer (Asiga Max 405; Asiga, Alexandria, Australia) at a layer thickness of 100 μm and a 90° build orientation. After printing, the specimens were ultrasonically cleaned in 99% ethanol for 5 min (3 min in reusable ethanol and 2 min in fresh ethanol) and post-cured in a polymerization unit (Otoflash G171; NK-Optik GmbH, Baierbrunn, Germany) according to the manufacturer’s instructions. SM-V specimens were milled from prefabricated blocks using a 5-axis milling unit (Imes-Icore 350i; Imes-Icore, Eiterfeld, Germany).

All specimens were stored in distilled water at 37 °C for 24 h prior to finishing. Surface standardization was performed by sequential polishing with silicon carbide papers of 240, 400, 600, and 1200 grit (English Abrasives Ltd, London, UK) under constant water irrigation. Polishing was conducted by a single operator to minimize variability [20]. After standardized polishing, all specimens were surface-glazed using Optiglaze Clear (GC Corp., Tokyo, Japan) to simulate a clinically finished CAD/CAM restoration. The specimens were sandblasted with 50 μm aluminum oxide particles (Korox; Bego GmbH & Co. KG, Bremen, Germany) at 0.15 MPa using an airborne-particle abrasion device (Basic quattro IS; Renfert GmbH, Hilzingen, Germany), followed by cleaning and air-drying. Optiglaze Clear was shaken thoroughly, dispensed into a clean dish, and applied as a thin, uniform layer using the manufacturer-provided brush without air thinning. Polymerization was performed using a laboratory light-curing unit (Otoflash G171; NK-Optik GmbH, Baierbrunn, Germany) for 5 min. All procedures were carried out in strict accordance with the manufacturer’s laboratory instructions to ensure standardized and reproducible surface characterization across all groups.

Specimens were immersed in six different media: distilled water (control); simulated gastric fluid (SGF) mixed with artificial saliva (AS) at ratios of 1:1 (50% SGF + 50% AS), 1:3 (25% SGF + 75% AS), and 1:5 (16.7% SGF + 83.3% AS); and the same three SGF: AS mixtures supplemented with 10% (v/v) alginate-based antacid (Gaviscon^®; Reckitt Benckiser, UK). SGF was prepared according to the United States Pharmacopeia formulation (0.1 N HCl, pH ≈ 1.2). Artificial saliva (pH ≈ 6.8) was prepared with xanthan gum (0.92 g/L), KCl (1.2 g/L), NaCl (0.85 g/L), MgCl₂ (0.05 g/L), CaCl₂ (0.13 g/L), NaH₂PO₄ (0.13 g/L), and C₈H₈O₃ (0.13 g/L). The initial pH values of SGF + AS mixtures were 2.4 (1:1), 2.7 (1:3), and 3.0 (1:5), which increased to 5.5, 5.8, and 6.1, respectively, after the addition of Gaviscon^®. To prepare the antacid-containing solutions, Gaviscon^® was added as 10% of the total volume, and the remaining 90% was composed of SGF and AS in the proportions described above to maintain the respective dilution ratios. Accordingly, specimens were immersed in distilled water (control); SGF mixed with artificial saliva (AS) at ratios of 1:1, 1:3, and 1:5; and the same three SGF: AS mixtures supplemented with 10% (v/v) alginate-based antacid. Each specimen was stored in 10 mL of the assigned medium in sealed glass vials at 37 ± 1 °C with constant agitation at 70 rpm. Solutions were refreshed every 24 h. The total immersion period was 48 h, representing an accelerated protocol estimated to approximate up to 5 years of cumulative acidic exposure in vivo, based on previous equivalences established for 96 h immersion (≈ 10 years) [9]. All solutions were freshly prepared daily, and their pH was measured with a calibrated pH meter (SevenCompact; Mettler-Toledo, Switzerland). After immersion, specimens were rinsed with deionized water, ultrasonically cleaned for 10 min, and air-dried before testing.

Color measurements were performed with a spectrophotometer (VITA Easyshade V; VITA Zahnfabrik, Bad Säckingen, Germany) against standardized white and black backgrounds, and the same backgrounds were consistently used for both baseline (T0) and post-immersion (T1) measurements to ensure valid ΔE₀₀ calculations. A custom silicone positioning mold was used to maintain consistent specimen orientation during repeated measurements. For each specimen, three readings were obtained from the central region, rotating the specimen 120° between measurements to minimize directional bias, and the mean value was used for analysis. The device was calibrated before each session according to the manufacturer’s instructions. T0 and T1 measurements were obtained under standardized illumination simulating D65 daylight, with an 8° observer angle. CIELab coordinates (L*, a*, b*) were recorded, and color differences (ΔE₀₀) were calculated using the CIEDE2000 formula [21]. Values exceeding 0.81 were considered perceptible, whereas values above 1.77 were deemed clinically unacceptable [22].

Surface roughness (Ra, µm) was evaluated after immersion using a portable contact profilometer (MarSurf PS 10; Mahr GmbH, Göttingen, Germany) with a cut-off value of 0.8 mm. Three linear scans were performed at predefined locations on each specimen, spaced 120° apart around the sample center. A custom acrylic positioning template was used to ensure consistent specimen placement and scan direction. The profilometer was calibrated before each session, and mean Ra values were used for analysis.

Representative specimens were sputter-coated with a 10-nm gold–palladium layer (EM ACE200; Leica Microsystems, Vienna, Austria) and examined under a scanning electron microscope (Hitachi High-Tech Corp., Tokyo, Japan) at 15 kV. Surface topography was recorded at ×2000 magnification.

All statistical analyses were performed using SPSS version 26.0 (IBM Corp., Chicago, IL, USA). The Shapiro–Wilk test was used to verify normality, and Levene’s test confirmed homogeneity of variances. A mixed-model analysis of variance (ANOVA) was applied, with time (T0, T1) as the within-subjects factor and material (three levels) and immersion medium (seven levels) as between-subjects factors. When statistically significant effects or interactions were found, post hoc comparisons were conducted with Tukey’s HSD or Bonferroni-adjusted paired t tests. The level of significance was set at α = 0.05.

Results

Color stability (ΔE₀₀)

The mean color difference (ΔE₀₀) values are summarized in Table 2. Immersion in SGF + AS significantly increased ΔE₀₀ values in all materials compared with the distilled water (DW) control (p<.001), with values across all groups ranging from 0.50 to 1.87. Although the SGF solutions were progressively diluted from 1:1 to 1:5, ΔE₀₀ values increased across these mixtures (p<.05). When comparing materials, no significant differences were observed in DW or SGF + AS (1:1) (p>.05). At SGF + AS (1:3), AM-C demonstrated significantly higher ΔE₀₀ values than both AM-VS and SM-V (p<.05). At SGF + AS (1:5), SM-V showed significantly lower ΔE₀₀ values than AM-VS and AM-C (p<.05). No other significant inter-material differences were found (p>.05). The addition of the alginate-based antacid reduced ΔE₀₀ values compared with the corresponding acid-only subgroups, with statistically significant reductions observed for AM-C at 1:3 and 1:5 and for AM-VS at 1:5 (p<.05). No significant reduction was observed for SM-V or for any 1:1 mixtures (p>.05). From a clinical perspective, ΔE₀₀ values in AM-C and AM-VS after immersion in SGF + AS at 1:3 and 1:5 exceeded the perceptibility threshold (> 0.81), with AM-C reaching the highest mean value (1.87 ± 0.30). SM-V, although more resistant, also showed perceptible changes under stronger acidic exposure (1.55 ± 0.04). Importantly, none of the antacid-containing subgroups exceeded the clinical acceptability threshold (> 1.77), confirming the protective effect of the alginate-based formulation.

Table 2.

Mean ± standard deviation of color difference (ΔE₀₀) values and statistical comparisons among groups

Material	DW	SGF + AS (1:1)	SGF + AS (1:3)	SGF + AS (1:5)	SGF + AS+antacid (1:1)	SGF + AS+antacid (1:3)	SGF + AS+antacid (1:5)
AM-VS	0.68 ± 0.08Aa	0.90 ± 0.06Bb	1.45 ± 0.17Bb	1.77 ± 0.13Cc	0.98 ± 0.16Bb	1.29 ± 0.15Bb	1.35 ± 0.19Bb
AM-C	0.74 ± 0.05Aa	0.99 ± 0.04Bb	1.77 ± 0.29Cc	1.87 ± 0.30Cc	1.00 ± 0.08Bb	1.39 ± 0.19Bb	1.50 ± 0.06Bb
SM-V	0.50 ± 0.02Aa	0.68 ± 0.07Bb	1.16 ± 0.09Bb	1.55 ± 0.04Bb	0.80 ± 0.09Bb	1.08 ± 0.09Bb	1.26 ± 0.26Bb

Different lowercase superscript letters indicate statistically significant differences among storage media within the same material (p<.05). Different uppercase superscript letters indicate statistically significant differences among materials within the same storage medium (p<.05). AM-VS Additively manufactured VarseoSmile TriniQ, AM-C Additively manufactured Crowntec, SM-V Subtractively manufactured Voco Grandio blocs, DW Distilled water, SGF Simulated gastric fluid, AS Artificial saliva

Surface roughness (Ra)

The mean Ra values are presented in Table 3. For all materials, immersion in SGF + AS resulted in significantly higher Ra values than in the DW control (p<.001), ranging from 0.18 μm to 1.30 μm. Within each material, statistically significant differences were observed among the immersion media (p<.05).

Table 3.

Mean ± standard deviation of surface roughness (Ra, µm) values and statistical comparisons among groups

Material	DW	SGF + AS (1:1)	SGF + AS (1:3)	SGF + AS (1:5)	SGF + AS+antacid (1:1)	SGF + AS+antacid (1:3)	SGF + AS+antacid (1:5)
AM-VS	0.19 ± 0.02Aa	0.28 ± 0.03Bb	0.74 ± 0.04Cc	0.98 ± 0.02Cc	0.20 ± 0.02Bb	0.39 ± 0.03Bb	0.45 ± 0.07Bb
AM-C	0.19 ± 0.01Aa	0.34 ± 0.05Bb	0.94 ± 0.18Cc	1.30 ± 0.02Dd	0.26 ± 0.01Bb	0.45 ± 0.02Bb	0.68 ± 0.04Bb
SM-V	0.18 ± 0.02Aa	0.21 ± 0.02Bb	0.60 ± 0.01Bb	0.90 ± 0.05Cc	0.18 ± 0.02Aa	0.30 ± 0.03Bb	0.37 ± 0.03Bb

Different lowercase superscript letters indicate statistically significant differences among storage media within the same material (p<.05). Different uppercase superscript letters indicate statistically significant differences among materials within the same storage medium (p<.05). AM-VS Additively manufactured VarseoSmile TriniQ, AM-C Additively manufactured Crowntec, SM-V Subtractively manufactured Voco Grandio blocs, DW Distilled water, SGF Simulated gastric fluid, AS Artificial saliva

For AM-VS, Ra values at SGF + AS (1:3) and SGF + AS (1:5) were significantly higher than those at DW and SGF + AS (1:1), with no significant difference between the 1:3 and 1:5 conditions (p<.05). For AM-C, Ra values differed significantly among all SGF + AS concentrations, with SGF + AS (1:5) showing significantly higher values than all other immersion conditions (p<.05). For SM-V, Ra values at SGF + AS (1:5) were significantly higher than those at DW and all other immersion media, whereas no significant difference was observed between DW, SGF + AS (1:1), and SGF + AS (1:3) (p>.05).

When materials were compared within the same immersion condition, AM-VS and AM-C exhibited significantly higher Ra values than SM-V at SGF + AS (1:3) (p<.05). At SGF + AS (1:5), AM-C showed significantly higher Ra values than both AM-VS and SM-V (p<.05), while no significant difference was observed between AM-VS and SM-V (p>.05). The addition of the alginate-based antacid significantly reduced Ra values for all materials compared with their corresponding antacid-free groups (p<.001). For SM-V, Ra values in the SGF + AS+antacid (1:1) group were not significantly different from the DW control (p>.05), whereas antacid-treated AM-VS and AM-C specimens remained significantly rougher than DW (p<.05).

Surface morphology (SEM Analysis)

Representative SEM images at 2000× magnification are shown in Figs. 2, 3 and 4. Specimens immersed in SGF + AS exhibited surface irregularities, micro-pits, and evidence of erosion, which became more pronounced with increasing acid concentration. These effects were especially visible in AM materials (AM-VS and AM-C), whereas the SM-V showed comparatively more homogeneous surfaces. In contrast, specimens stored in DW displayed relatively smooth and intact morphologies. The addition of the alginate-based antacid reduced the extent of surface degradation in all materials, with surface characteristics more closely resembling those of the control group.

Fig. 2.

Representative SEM micrographs (×2000) of the surface morphology of additively manufactured resin composite VarseoSmile TriniQ (AM-VS) after immersion in Distilled Water (DW), simulated gastric fluid plus artificial saliva (SGF + AS) at ratios 1:1, 1:3, and 1:5, and SGF + AS supplemented with alginate-based antacid (Gaviscon). All images represent typical specimens after 48 h of immersion in the respective media

Fig. 3.

Representative SEM micrographs (×2000) of the surface morphology of additively manufactured resin composite Crowntec (AM-C) after immersion in Distilled Water (DW), simulated gastric fluid plus artificial saliva (SGF + AS) at ratios 1:1, 1:3, and 1:5, and SGF + AS supplemented with alginate-based antacid (Gaviscon). All images represent typical specimens after 48 h of immersion in the respective media

Fig. 4.

Representative SEM micrographs (×2000) of the surface morphology of subtractively manufactured nano-ceramic hybrid block Grandio blocs (SM-V) after immersion in Distilled Water (DW), simulated gastric fluid plus artificial saliva (SGF + AS) at ratios 1:1, 1:3, and 1:5, and SGF + AS supplemented with alginate-based antacid (Gaviscon). All images represent typical specimens after 48 h of immersion in the respective media

Discussion

In this in vitro study, three CAD/CAM resin-based restorative materials—subtractive nanoceramic hybrid (SM-V) and two additively manufactured resin composites (AM-VS and AM-C)—were evaluated. The null hypothesis (H₀), which stated that the presence of an alginate-based antacid would not significantly influence surface roughness or color stability compared with simulated gastric acid exposure alone, was rejected. Instead, the findings partially supported the alternative hypothesis (H₁), as the alginate-based antacid mitigated surface roughness and discoloration in several experimental conditions, particularly in the AM materials.

Regarding optical stability, SGF + AS exposure increased ΔE₀₀ values, with AM-C and AM-VS showing the greatest overall discoloration, and SM-V exhibiting the greatest stability. Although the SGF solutions were progressively diluted from 1:1 to 1:5, color change increased across mixtures, indicating that discoloration was not solely dependent on acidity level. These differences reflect the material composition: AM materials contain a higher proportion of resin matrix, which increases susceptibility to water sorption, plasticization, and pigment uptake [23–25]. Furthermore, their layered printing process may create internal defects that exacerbate discoloration [26, 27]. SM-V, by contrast, contains a densely polymerized hybrid ceramic-polymer structure with smaller, uniformly distributed filler particles, limiting water uptake and pigment penetration [24, 25, 28]. The antacid addition reduced ΔE₀₀ under selected conditions, particularly for AM-C at 1:3 and 1:5, and for AM-VS at 1:5, while no significant effect was observed for SM-V, consistent with its intrinsic resistance. In the present study, specimens were polished and subsequently glazed, a protocol widely applied in clinical practice and also reported in in-vitro investigations on polymer-based CAD/CAM materials [29–31]. Glazing enhances surface quality by reducing porosity and increasing resistance to staining and degradation [27, 32]. However, methodological differences in the literature exist, as not all studies incorporate glazing, which may partially explain variations in reported color and surface roughness outcomes. In the current study, glazing was applied uniformly across all groups; therefore, any differences observed can be attributed to the immersion media rather than the surface finishing protocol, allowing a valid comparison of the effects of the alginate-based antacid.

These findings align with prior studies. Pîrvulescu et al. [9] reported that hybrid nanoceramics exhibited comparatively better stability than other CAD/CAM ceramics after immersion in simulated gastric juice. Similarly, Silva et al. [33] demonstrated that acidic beverages increase surface roughness and reduce the microhardness of resin composites, while Omara et al. [34] reported that high translucent zirconia exhibited the least color change, whereas veneered PEEK showed the greatest discoloration after gastric acid exposure. This is consistent with the present findings, as both PEEK-based restorations and resin-based CAD/CAM composites share a polymer-rich structure, which is more prone to water sorption, plasticization, and pigment uptake than ceramic-dominant materials such as the nano-ceramic hybrid SM-V.

Surface roughness values increased significantly after immersion in SGF + AS compared with DW, with higher Ra values frequently observed at the 1:5 condition; however, the pattern was material-dependent (e.g., at 1:3, AM-VS and AM-C showed higher Ra than SM-V, and at 1:5, AM-C exhibited higher Ra than AM-VS and SM-V). The incorporation of 10% Gaviscon^® into SGF plus artificial saliva mixtures significantly decreased surface roughness values relative to the corresponding antacid-free groups. These results are consistent with clinical evidence demonstrating the protective effect of alginate-based formulations in mitigating acid-induced damage. For instance, De Ruigh et al. [11] reported in a randomized crossover trial that Gaviscon Double Action Liquid, an alginate-antacid combination, effectively reduced distal esophageal acid exposure and increased nadir refluxate pH during the postprandial period compared to an antacid without alginate, despite no reduction in reflux frequency or proximal extension. This supports the hypothesis that the primary protective mechanism involves the co-localization and neutralization of the postprandial acid pocket rather than preventing reflux episodes entirely [35]. In vitro, the present findings corroborate this mechanism by suggesting that pH buffering and the raft-forming barrier provided by Gaviscon^® may mitigate acid-mediated roughness and SEM-visible surface changes on dental restorative materials. Roughness values above 0.20 μm have been associated with increased plaque accumulation, while values exceeding approximately 0.50 μm may be detectable by the tongue and contribute to patient discomfort and biofilm retention [36, 37]. In the present study, all specimens exposed to SGF + AS without antacid demonstrated Ra values exceeding these thresholds, particularly in the 1:5 condition, indicating a potentially increased risk of plaque retention and surface-related complications under acidic exposure. In contrast, the antacid-containing subgroups, especially for SM-V under specific conditions, maintained Ra values closer to clinically acceptable limits, suggesting that alginate-based formulations may help preserve surface quality under erosive challenges.

Previous studies have consistently shown that simulated gastric acid exposure adversely affects the surface characteristics of CAD/CAM restorative materials, including ceramics, hybrid ceramics, and resin composites [9, 15–17, 38]. Acidic conditions have been linked to increased surface roughness, reduced microhardness, and morphological changes visible under SEM [39]. These surface changes are clinically significant, as increased roughness can promote plaque accumulation, accelerate wear of opposing dentition, and impair esthetic outcomes [40]. In the present study, SGF + AS exposure increased Ra values across all materials, with AM-C and AM-VS showing greater increases in surface roughness and more pronounced SEM-visible surface alterations than SM-V. This difference can be attributed to manufacturing technology and material composition. AM composites, such as AM-VS and AM-C, are produced layer by layer, which may introduce interlayer interfaces and a heterogeneous degree of polymerization [25]. These interfaces, together with higher residual monomer content, increase susceptibility to hydrolytic degradation under acidic conditions [41, 42]. Their resin-rich matrices are also more prone to softening and filler leaching, resulting in greater surface irregularities [2, 43]. In contrast, SM-V is a pre-polymerized nano-ceramic hybrid block processed under high temperature and pressure, leading to a higher cross-linking density, reduced water sorption, and improved acid resistance [24, 25]. This explains why SM-V generally showed lower Ra values under comparable acidic conditions. Long-term experiments also indicate durability concerns, as Gil-Pozo et al. [15] demonstrated reduced flexural strength of resin-based CAD/CAM materials, along with greater wear rates, after prolonged exposure to gastric acid and thermal cycling. The present results extend this body of knowledge by demonstrating that, even under aggressive acidic conditions, partial surface degradation can be mitigated by incorporating an alginate-based antacid.

From a clinical perspective, these findings may be relevant for restorative treatment planning in patients with GERD or bulimia nervosa, where frequent acid challenges occur. Advising such patients on adjunctive use of alginate-based formulations could help preserve the functional and esthetic lifespan of resin-based restorations. Nonetheless, caution should be taken in extrapolating in vitro data to clinical conditions, as factors such as salivary flow, pellicle formation, and mechanical wear influence the protective effects in the oral environment [44].

In this study, a continuous immersion protocol was selected to provide a standardized and controlled erosive challenge, allowing the chemical effects of SGF and the alginate-based antacid to be isolated. Although this methodology is widely used in in-vitro erosion studies, it does not fully represent the dynamic intraoral environment, where cyclic exposure to gastric acid is followed by periods of neutralization and remineralization by saliva. Alternate immersion protocols have been proposed to better reproduce clinical conditions by simulating acid attacks interspersed with artificial saliva exposure and acquired pellicle formation. The present model, based on SGF mixed with artificial saliva, reproduces the ionic environment but cannot replicate continuous salivary flow, pellicle development, or the complex protective mechanisms of natural saliva, including buffering capacity, protein-mediated barrier effects, and mineral replenishment. The absence of unglazed control groups is a limitation, as glazing may partially mask the intrinsic susceptibility of resin-based materials to acidic degradation. However, the applied protocol reflects routine clinical practice and allowed standardized comparison of clinically relevant surfaces. Future investigations should focus on long-term cyclic acid challenges combined with mechanical loading and thermal cycling to better simulate oral conditions. Additionally, the impact of alginate-antacid exposure on other material properties, such as flexural strength, hardness, and bond integrity, warrants further evaluation.

Conclusions

Within the limitations of this in vitro study, it can be concluded that:

1. Exposure to simulated gastric fluid (SGF) increased surface roughness and color change (ΔE₀₀) in all CAD/CAM resin-based restorative materials tested.

2. The degree of changes was material-dependent, with the subtractively manufactured nano-ceramic hybrid (SM-V) demonstrating overall greater resistance to acid-induced surface and optical changes than the additively manufactured resin composites (AM-VS and AM-C).

3. The addition of an alginate-based antacid reduced surface roughness and discoloration in several experimental conditions, particularly in AM-C and AM-VS at higher dilution ratios; however, its effect on color stability was limited for SM-V.

4. In selected antacid-containing subgroups, particularly for SM-V under specific conditions, surface roughness and color change values approached those of the distilled water control, suggesting a protective effect against erosive and discoloration challenges.

Clinical significance

The findings suggest that alginate-based antacid formulations may offer adjunctive protection for resin-based dental restorations in patients exposed to gastric acid, such as individuals with gastroesophageal reflux disease (GERD) or eating disorders. Although the level of protection may vary depending on material composition and exposure conditions, such formulations could help preserve surface integrity and esthetic appearance in at-risk populations.

Authors’ contributions

Conceptualization: N.C. and R.S.; Methodology: N.C., R.S., and D.D.H.; Software: S.A.M. and M.A.B.; Validation: N.C., R.S., and D.D.H.; Formal analysis: D.D.H., M.A.B., and N.C.; Investigation: D.D.H., M.A.B., and N.C.; Resources: N.C. and R.S.; Data curation: D.D.H. and R.S.; Writing – original draft: N.C., D.D.H., and R.S.; Writing – review & editing: S.A.M. and R.S.; Visualization: S.A.M.; Supervision: R.S. and D.D.H.; Project administration: R.S. and D.D.H. All authors have read and approved the final version of the manuscript.

Funding

This study received no external funding.

Data availability

The data presented in this study are available on request from the corresponding author.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.