Effect of antacid gastric syrups on surface properties of dental restorative materials: an in vitro analysis of roughness and microhardness
The movement of acid from the stomach to the esophagus is controlled by an anti-reflux mechanism, which includes the lower esophageal sphincter. A disruption in this system leads to a chronic condition known as gastroesophageal reflux disease (GERD) . GERD is defined as the pathological passage of stomach contents into the esophagus and, in some cases, into the oral cavity. Its symptoms include insufficient stomach acid, heartburn, chest pain, chronic respiratory complications, and bronchial asthma . Heartburn is described as an uncomfortable burning sensation in the chest, behind the breastbone, or the upper abdomen, which may sometimes radiate to the throat . GERD, similar to other gastrointestinal disorders, is highly prevalent globally, exhibiting significant regional variations in its incidence. GERD prevalence has been reported to range from 18.1 to 27.8% in North America, 8.8–25.9% in Europe, 2.5–7.8% in East Asia, 8.7–33.1% in the Middle East, 11.6% in Australia, and 23.0% in South America. Additionally, the incidence rate of GERD is approximately 5 per 1,000 person-years in the UK and the US, while in children aged 1–17 years in the UK, this rate is 0.84 . Evidence suggests that GERD prevalence is increasing, particularly in North America and East Asia . The potential impact of GERD on oral health is significant, as the condition can affect not only the stomach and esophagus but also the oral cavity. It shows that the prevalence of GERD and the associated use of antacid syrups are expected to increase in the coming years due to lifestyle changes, dietary habits and an aging population. This highlights the need to understand the potential long-term effects of these syrups, particularly on oral health and dental materials, as their usage continues to increase. In the treatment of GERD, antacid medications work by neutralizing excess stomach acid and inhibiting proteolytic enzymes, thereby providing symptomatic relief . The effectiveness of these medications depends on their buffering and neutralizing capacities. Manufacturers are launching various formulations for better consumption and efficacy. These formulations often include agents such as calcium carbonate, sodium bicarbonate, and magnesium carbonate, which are effective in neutralizing acid . Some of these active ingredients are also found in toothpaste. For instance, calcium carbonate and sodium bicarbonate are added as abrasive agents due to their stain-removal and whitening properties, as demonstrated by previous studies [ – ]. Similarly, the abrasive effect of magnesium carbonate on tooth enamel crystals has been shown in studies . Studies have indicated that brushing teeth with water alone causes minimal wear, less than 0.1 microns. Thus, the active ingredients in toothpaste play a significant role in increasing abrasiveness . The interactions of composite resins with the oral environment have been investigated and reported by researchers for many years . To ensure the long-term success of aesthetic restorative treatments, it is desirable to use composite resins that can maintain their gloss over time. In this context, the interactions of composite resins with toothpaste, toothbrushes, chewing tablets, and syrups have frequently been the subject of research [ – ]. It has been stated that one way to whiten teeth is to remove stains from the enamel surface, which is why abrasives are added to toothpaste formulations . It has also been shown that these abrasives can lead to changes in the surface roughness and microhardness of composite resins . Studies in the literature have investigated the effects of syrups and effervescent tablets, used in the treatment of systemic diseases, on the surface roughness and microhardness of composite resins . Additionally, it is known that toothpaste containing agents effective in neutralizing acid, such as those found in antacid syrups, can alter the surface properties of composite resins . However, to the best of our knowledge, there is no study evaluating the potential effects of antacid syrups on the surface of composite restorative materials. Therefore, this in-vitro study aimed to evaluate the effect of antacid gastric syrups on the surface roughness and microhardness of restorative materials. The null hypotheses of the study were as follows: Antacid gastric syrups have no significant effect on the surface roughness of composite resins. Antacid gastric syrups have no significant effect on the surface microhardness of composite resins. 

This study is an in-vitro laboratory study. Table lists the three composite resins and their components, while Table shows the four antacid gastric syrups along with their components and pH values. The endogenous pH of all drugs was measured using a digital pH electrode meter (Growsan, Growkent, Turkey). Sample size calculation The sample size for this study was calculated using the G*Power software (Version 3.1.9.4, Germany). For the one-way ANOVA used to compare the groups, the effect size was set to 0.37 with a confidence level of 95% (α = 0.05) and a statistical power of 80% (β = 0.20). For the repeated measures ANOVA used to analyze time-dependent changes (baseline, day 7, day 15, and day 28), effect size of 0.16 was used to account for the inclusion of the time factor. Preparation of samples Three different types of composites were used in the study: nanohybrid, microhybrid, and giomer (Table ). A total of 150 disc-shaped samples, 50 of each composite type, were prepared in a special Teflon mold (10 mm x 2 mm). After the samples were placed in the molds, they were lightly pressed with mylar matrix and cured with a second-generation LED light device (Guilin Woodpecker Medical Instrument Co., Guilin, China) emitting light at 470 nm wavelength for 20 s (Light intensity 1200 mW/cm2). Disks removed from the molds were additionally cured on the other side for 20 s. The samples were then polished with extra thick, thick, medium, and thin discs (OptiDisc, Kerr, FL, USA) with a power tool running at 15.000 rpm according to user instructions. After polishing, the samples were measured with a digital caliper (Insize, Insize Ltd, China) to ensure that the samples had the same thickness. The pH of all tested liquids, including distilled water, was measured at a controlled temperature of 25 °C in accordance with standard laboratory protocols. In addition, samples were stored at 37 °C to simulate oral conditions. Randomization (blinding) According to the list created by https://www.random.org , all composite samples were numbered and randomly divided into 15 subgroups . The administration of antacid gastric syrups was carried out with the same technique. Calibration Surface roughness and microhardness analysis of all samples were performed by a single operator (FO). Accordingly, he was trained using a profilometer and a microhardness measuring device . For verification purposes, measurements of 10 composite samples excluded from the study were performed. Measurements were repeated at 1 week intervals and a repeatability agreement rate of %90 was obtained. Immersion cycles The immersion cycle protocol used in this study was adopted to imitate the actual consumption of antacid gastric syrups. The samples were immersed in 10 ml of antacid gastric syrup for 2 min daily at 24 h intervals for 28 days to simulate a period of 2 years and kept in an incubator at 37 °C . After each immersion cycle, the samples were washed under running water and stored in distilled water until the next cycle. The syrups were renewed before each cycle. The Control group samples were kept in distilled water for 28 days and the solution was renewed every other day. Surface roughness and microhardness measurements were performed at the beginning of the experiment, on days 7, 15, and 28. Measurement of surface roughness Surface roughness measurements of all samples were carried out using a mechanical profilometer (Surftest SJ-210 Mitutoyo, Tokyo, Japan). Measurements were performed at Baseline, day 7, day 15 and day 28. Measurements were carried out at 3 different points equidistant from the centre of each sample at a speed of 0.25 mm/sec and a cutting speed of 0.80 mm. The arithmetic mean of the obtained values (Ra, µm) was taken and recorded. Measurement of surface microhardness The surface microhardness of all samples was measured with a Vickers hardness tester (Shimadzu HMV-2000, Germany) and recorded as Vickers Microhardness Number (VHN). Measurements were carried out at baseline, day 7, day 15 and day 28. A dwell time of 15 s and a load of 0.49 N were applied to each sample . Hardness measurement was recorded in VHN by making 3 indentations 100 μm apart from the centre of the sample and from each other. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) One sample randomly selected from each group was subjected to examination in AFM and SEM devices. For SEM and AFM imaging, areas of the sample surface that were not impacted by microhardness indentations or surface roughness traces were carefully selected to ensure the integrity of the imaging results. An area of 10 × 10 μm was scanned in contact mode at a speed of 1 Hz with an AFM device (Nanomagnetics Instruments, Oxford, UK). The 3D image of the obtained surface and the corresponding average surface roughness value (Ra) are presented together. All imaging was performed from the center of the samples to ensure standardization. XEI Data Analysis Program, version 1.6 (Park Systems Inc.) analysis software was used to obtain surface topography from AFM images and for roughness calculations. The samples selected for SEM examination were coated with Au-Pd alloy in a coating device (BAL-TEC 050, Capovani Brothers, USA) to increase the conductivity. The samples were then placed in an SEM device (EVO 40 Carl Zeiss, Germany) and images were taken at x1000, x5000, and x10000 magnification and at a voltage rate of 20.00 kilovolts. Statistical analysis Data were analyzed using IBM SPSS V.27 (Chicago, USA). The Shapiro-Wilk test was used to determine the distribution, the Repeated Measures ANOVA test was used to compare parametric data between the beginning of the 28-day experiment and the measurements on days 7, 15 and 28, and the One-Way ANOVA test was used to compare independent groups. Homogeneous distribution was determined by Mauchly’s Test of Sphericity. Tukey and Games-Howell post-hoc tests were applied according to whether the data were homogeneously distributed or not. The significance level was determined as p < 0.05. 

The sample size for this study was calculated using the G*Power software (Version 3.1.9.4, Germany). For the one-way ANOVA used to compare the groups, the effect size was set to 0.37 with a confidence level of 95% (α = 0.05) and a statistical power of 80% (β = 0.20). For the repeated measures ANOVA used to analyze time-dependent changes (baseline, day 7, day 15, and day 28), effect size of 0.16 was used to account for the inclusion of the time factor. 

Three different types of composites were used in the study: nanohybrid, microhybrid, and giomer (Table ). A total of 150 disc-shaped samples, 50 of each composite type, were prepared in a special Teflon mold (10 mm x 2 mm). After the samples were placed in the molds, they were lightly pressed with mylar matrix and cured with a second-generation LED light device (Guilin Woodpecker Medical Instrument Co., Guilin, China) emitting light at 470 nm wavelength for 20 s (Light intensity 1200 mW/cm2). Disks removed from the molds were additionally cured on the other side for 20 s. The samples were then polished with extra thick, thick, medium, and thin discs (OptiDisc, Kerr, FL, USA) with a power tool running at 15.000 rpm according to user instructions. After polishing, the samples were measured with a digital caliper (Insize, Insize Ltd, China) to ensure that the samples had the same thickness. The pH of all tested liquids, including distilled water, was measured at a controlled temperature of 25 °C in accordance with standard laboratory protocols. In addition, samples were stored at 37 °C to simulate oral conditions. 

According to the list created by https://www.random.org , all composite samples were numbered and randomly divided into 15 subgroups . The administration of antacid gastric syrups was carried out with the same technique. 

Surface roughness and microhardness analysis of all samples were performed by a single operator (FO). Accordingly, he was trained using a profilometer and a microhardness measuring device . For verification purposes, measurements of 10 composite samples excluded from the study were performed. Measurements were repeated at 1 week intervals and a repeatability agreement rate of %90 was obtained. 

The immersion cycle protocol used in this study was adopted to imitate the actual consumption of antacid gastric syrups. The samples were immersed in 10 ml of antacid gastric syrup for 2 min daily at 24 h intervals for 28 days to simulate a period of 2 years and kept in an incubator at 37 °C . After each immersion cycle, the samples were washed under running water and stored in distilled water until the next cycle. The syrups were renewed before each cycle. The Control group samples were kept in distilled water for 28 days and the solution was renewed every other day. Surface roughness and microhardness measurements were performed at the beginning of the experiment, on days 7, 15, and 28. 

Surface roughness measurements of all samples were carried out using a mechanical profilometer (Surftest SJ-210 Mitutoyo, Tokyo, Japan). Measurements were performed at Baseline, day 7, day 15 and day 28. Measurements were carried out at 3 different points equidistant from the centre of each sample at a speed of 0.25 mm/sec and a cutting speed of 0.80 mm. The arithmetic mean of the obtained values (Ra, µm) was taken and recorded. 

The surface microhardness of all samples was measured with a Vickers hardness tester (Shimadzu HMV-2000, Germany) and recorded as Vickers Microhardness Number (VHN). Measurements were carried out at baseline, day 7, day 15 and day 28. A dwell time of 15 s and a load of 0.49 N were applied to each sample . Hardness measurement was recorded in VHN by making 3 indentations 100 μm apart from the centre of the sample and from each other. 

One sample randomly selected from each group was subjected to examination in AFM and SEM devices. For SEM and AFM imaging, areas of the sample surface that were not impacted by microhardness indentations or surface roughness traces were carefully selected to ensure the integrity of the imaging results. An area of 10 × 10 μm was scanned in contact mode at a speed of 1 Hz with an AFM device (Nanomagnetics Instruments, Oxford, UK). The 3D image of the obtained surface and the corresponding average surface roughness value (Ra) are presented together. All imaging was performed from the center of the samples to ensure standardization. XEI Data Analysis Program, version 1.6 (Park Systems Inc.) analysis software was used to obtain surface topography from AFM images and for roughness calculations. The samples selected for SEM examination were coated with Au-Pd alloy in a coating device (BAL-TEC 050, Capovani Brothers, USA) to increase the conductivity. The samples were then placed in an SEM device (EVO 40 Carl Zeiss, Germany) and images were taken at x1000, x5000, and x10000 magnification and at a voltage rate of 20.00 kilovolts. 

Data were analyzed using IBM SPSS V.27 (Chicago, USA). The Shapiro-Wilk test was used to determine the distribution, the Repeated Measures ANOVA test was used to compare parametric data between the beginning of the 28-day experiment and the measurements on days 7, 15 and 28, and the One-Way ANOVA test was used to compare independent groups. Homogeneous distribution was determined by Mauchly’s Test of Sphericity. Tukey and Games-Howell post-hoc tests were applied according to whether the data were homogeneously distributed or not. The significance level was determined as p < 0.05. 

Surface roughness analysis The analysis revealed significant changes in the surface roughness of the giomer composite after 28 days of exposure to antacid stomach syrups and distilled water, as well as in comparison to the Control group ( p < 0.05). Initially, the giomer composite exhibited the highest surface roughness values, while the microhybrid composite had the lowest. However, no significant changes were observed on the surfaces of the microhybrid and nanohybrid composites throughout the 28-day experimental period ( p > 0.05) (Table ). When treated with antacid syrups, the giomer composite showed pronounced reductions in surface roughness across all groups. For instance: Distilled Water : Significant decreases were observed (F(3,27) = 35.724, p < 0.001, η²=0.799, Observed Power (OP) = 1), with reductions between baseline and day 7 ( p < 0.001, d = 2.820, OP = 0.99), day 15 ( p < 0.001, d = 2.191, OP = 0.99), and day 28 ( p < 0.001, d = 3.236, OP = 0.99) (Table ). GL syrup : Significant decreases were observed (F(1.556,14.002) = 69.913, p < 0.001, η²=0.886, OP:1.00), with reductions between baseline and day 7 ( p < 0.001, d = 2.782, OP = 0.99), day 15 ( p < 0.001, d = 3.247, OP = 0.99), and day 28 ( p < 0.001, d = 2.758) (Table ). GD syrup : Surface roughness decreased significantly (F(3,27) = 47.202, p < 0.001, η²=0.84, OP = 0.99), with reductions observed between baseline and day 7 ( p < 0.001, d = 2.975, OP = 0.99), day 15 ( p < 0.001, d = 2.896, OP = 0.99), and day 28 ( p < 0.001, d = 2.159) (Table ). RD syrup : A notable decrease was recorded (F(3,27) = 68.307, p < 0.001, η²=0.884, OP = 0.99), with significant differences between baseline and day 7 ( p < 0.001, d = 2.679, OP = 0.99), day 15 ( p < 0.001, d = 3.216, OP = 0.99), and day 28 ( p < 0.001, d = 2.968, OP = 0.99) (Table ). MF syrup : A significant decline was observed (F(3,27) = 26.294, p < 0.001, η²=0.745, OP = 0.99), with reductions occurring between baseline and day 7 ( p < 0.001, d = 2.967, OP = 0.99), day 15 ( p < 0.001, d = 2.436, OP = 0.99), and day 28 ( p = 0.005, d = 1.546, OP = 0.90) (Table ). Overall, the giomer composite demonstrated a consistent reduction in surface roughness across all antacid syrup groups and the Control group. These findings suggest that the chemical composition and interaction of antacid syrups with the giomer’s surface may have contributed to this effect. Microhardness analysis The surface microhardness of the composites showed a significant decrease after 28 days of exposure to antacid gastric syrups, as well as to the Control group (distilled water). The findings for each composite and experimental group are summarized below (Table ). Among the antacid syrups, the following results were noted: Control Group (Distilled Water) : The significant reduction was observed in the nanohybrid composite (F(1.751,15.755) = 4.645, p = 0.03, η²=0.34, OP = 0.99 ), with significant differences between baseline and day 15 ( p = 0.046, d = 1.078, OP: 0.62), and baseline and day 28 ( p = 0.007, d = 1.483 OP = 0.87) (Table ). GL syrup : The significant reduction was observed in the microhybrid composite (F(3,27) = 23.934, p < 0.001, η²=0.72, OP = 0.99), with significant differences between baseline and day 15 ( p < 0.001, d = 2.137, OP = 0.99), and baseline and day 28 ( p = 0.001, d = 1.866, OP = 0.97). The giomer composite also showed a significant decrease (F(3,27) = 35.584, p < 0.001, η²=0.79, OP = 0.99), with reductions between baseline and day 15 ( p < 0.001, d = 2.569, OP = 0.99) and baseline and day 28 ( p = 0.001, d = 2.177, OP = 0.99) (Table ). GD syrup : The microhybrid composite exhibited the highest reduction in microhardness (F(3,27) = 77.096, p < 0.001, η²=0.89). Significant differences were observed between baseline and day 7 ( p = 0.005, d = 1.555), day 15 ( p < 0.001, d = 3.279, OP = 0.99), and day 28 ( p < 0.001, d = 3.955, OP = 1.00) (Table ). RD syrup : The microhardness of the microhybrid composite decreased significantly (F(3,27) = 21.374, p < 0.001, η²=0.7, OP = 0.99), with notable reductions between baseline and day 15 ( p = 0.024, d = 1.215, OP = 0.72), and baseline and day 28 ( p = 0.004, d = 1.618, OP = 0.92) (Table ). MF syrup : The most significant reduction in microhardness was observed in the giomer composite (F(3,27) = 79.461, p < 0.001, η²=0.9, OP = 0.99), with differences between baseline and day 15 ( p = 0.001, d = 1.916, OP = 0.98), and baseline and day 28 ( p < 0.001, d = 3.267, OP = 0.99). The microhybrid composite also experienced a significant decrease (F(3,27) = 19.260, p < 0.001, η²=0.68, OP = 0.99), with reductions between baseline and day 15 ( p = 0.003, d = 1.65, OP = 0.93), and baseline and day 28 ( p = 0.006, d = 1.505, OP = 0.88) (Table ). In summary, the microhybrid composite demonstrated the largest reduction in microhardness across multiple syrups, while the giomer composite also exhibited significant changes, particularly with MF syrup. These results highlight the variable effects of antacid syrups on composite materials depending on their chemical composition and filler content. SEM analysis Figures , and shows SEM images of the composite groups at x1000, x5000, and x10.000 magnification. The images were taken from near the center of the composite samples and recorded. During surface roughness measurements, precautions were taken to avoid areas with scratches or indentations caused by these measurements. Surface images of each composite group in the Control group and after 28 days of experiment are shown. In general, roughness increased in all 3 composite surface images. There is an increase in the number of scratches, pits, and residues in the surface layer. When the surface of the microhybrid composite is examined, it is seen that there is a significant increase in particle accumulation and irregularity on the surface after contact with GL. When the surface of the nanohybrid composite is examined, it is seen that there is a limited increase in surface irregularity in general. However, it is seen that the increase in surface irregularity is higher after contact with RD. The changes in the roughness of the surface after the antacid stomach syrups applied to the Giomer composite are significantly higher than the Control group. At the same time, changes are also observed on the surface significantly compared to other composite groups. There is an increase in the number of pits and holes on the surface after contact with syrups. Of these, the roughness changes caused by GD and MF syrups are higher than the others. AFM analysis Figures , and shows 3D AFM images of the composite groups. The images were taken from the near center section of the composite samples. During surface microhardnes measurements, precautions were taken to avoid areas with scratches or indentations caused by these measurements. The surface images of each composite group in the Control group and after 28 days of experimentation are shown. When the images of the microhybrid composite groups were examined, the surface treated with MF syrup showed the highest surface roughness. The Control group and the composite surfaces treated with other syrups showed similar roughness values. When the nanohybrid composite groups were analyzed, the group showing the highest surface roughness was the composite treated with MF syrup. The group with the least surface roughness was the group treated with GD. When the giomer composite groups were analyzed, the group showing the highest surface roughness was the composite treated with GD syrup. The group showing the least surface roughness was the Control group. 

The analysis revealed significant changes in the surface roughness of the giomer composite after 28 days of exposure to antacid stomach syrups and distilled water, as well as in comparison to the Control group ( p < 0.05). Initially, the giomer composite exhibited the highest surface roughness values, while the microhybrid composite had the lowest. However, no significant changes were observed on the surfaces of the microhybrid and nanohybrid composites throughout the 28-day experimental period ( p > 0.05) (Table ). When treated with antacid syrups, the giomer composite showed pronounced reductions in surface roughness across all groups. For instance: Distilled Water : Significant decreases were observed (F(3,27) = 35.724, p < 0.001, η²=0.799, Observed Power (OP) = 1), with reductions between baseline and day 7 ( p < 0.001, d = 2.820, OP = 0.99), day 15 ( p < 0.001, d = 2.191, OP = 0.99), and day 28 ( p < 0.001, d = 3.236, OP = 0.99) (Table ). GL syrup : Significant decreases were observed (F(1.556,14.002) = 69.913, p < 0.001, η²=0.886, OP:1.00), with reductions between baseline and day 7 ( p < 0.001, d = 2.782, OP = 0.99), day 15 ( p < 0.001, d = 3.247, OP = 0.99), and day 28 ( p < 0.001, d = 2.758) (Table ). GD syrup : Surface roughness decreased significantly (F(3,27) = 47.202, p < 0.001, η²=0.84, OP = 0.99), with reductions observed between baseline and day 7 ( p < 0.001, d = 2.975, OP = 0.99), day 15 ( p < 0.001, d = 2.896, OP = 0.99), and day 28 ( p < 0.001, d = 2.159) (Table ). RD syrup : A notable decrease was recorded (F(3,27) = 68.307, p < 0.001, η²=0.884, OP = 0.99), with significant differences between baseline and day 7 ( p < 0.001, d = 2.679, OP = 0.99), day 15 ( p < 0.001, d = 3.216, OP = 0.99), and day 28 ( p < 0.001, d = 2.968, OP = 0.99) (Table ). MF syrup : A significant decline was observed (F(3,27) = 26.294, p < 0.001, η²=0.745, OP = 0.99), with reductions occurring between baseline and day 7 ( p < 0.001, d = 2.967, OP = 0.99), day 15 ( p < 0.001, d = 2.436, OP = 0.99), and day 28 ( p = 0.005, d = 1.546, OP = 0.90) (Table ). Overall, the giomer composite demonstrated a consistent reduction in surface roughness across all antacid syrup groups and the Control group. These findings suggest that the chemical composition and interaction of antacid syrups with the giomer’s surface may have contributed to this effect. 

The surface microhardness of the composites showed a significant decrease after 28 days of exposure to antacid gastric syrups, as well as to the Control group (distilled water). The findings for each composite and experimental group are summarized below (Table ). Among the antacid syrups, the following results were noted: Control Group (Distilled Water) : The significant reduction was observed in the nanohybrid composite (F(1.751,15.755) = 4.645, p = 0.03, η²=0.34, OP = 0.99 ), with significant differences between baseline and day 15 ( p = 0.046, d = 1.078, OP: 0.62), and baseline and day 28 ( p = 0.007, d = 1.483 OP = 0.87) (Table ). GL syrup : The significant reduction was observed in the microhybrid composite (F(3,27) = 23.934, p < 0.001, η²=0.72, OP = 0.99), with significant differences between baseline and day 15 ( p < 0.001, d = 2.137, OP = 0.99), and baseline and day 28 ( p = 0.001, d = 1.866, OP = 0.97). The giomer composite also showed a significant decrease (F(3,27) = 35.584, p < 0.001, η²=0.79, OP = 0.99), with reductions between baseline and day 15 ( p < 0.001, d = 2.569, OP = 0.99) and baseline and day 28 ( p = 0.001, d = 2.177, OP = 0.99) (Table ). GD syrup : The microhybrid composite exhibited the highest reduction in microhardness (F(3,27) = 77.096, p < 0.001, η²=0.89). Significant differences were observed between baseline and day 7 ( p = 0.005, d = 1.555), day 15 ( p < 0.001, d = 3.279, OP = 0.99), and day 28 ( p < 0.001, d = 3.955, OP = 1.00) (Table ). RD syrup : The microhardness of the microhybrid composite decreased significantly (F(3,27) = 21.374, p < 0.001, η²=0.7, OP = 0.99), with notable reductions between baseline and day 15 ( p = 0.024, d = 1.215, OP = 0.72), and baseline and day 28 ( p = 0.004, d = 1.618, OP = 0.92) (Table ). MF syrup : The most significant reduction in microhardness was observed in the giomer composite (F(3,27) = 79.461, p < 0.001, η²=0.9, OP = 0.99), with differences between baseline and day 15 ( p = 0.001, d = 1.916, OP = 0.98), and baseline and day 28 ( p < 0.001, d = 3.267, OP = 0.99). The microhybrid composite also experienced a significant decrease (F(3,27) = 19.260, p < 0.001, η²=0.68, OP = 0.99), with reductions between baseline and day 15 ( p = 0.003, d = 1.65, OP = 0.93), and baseline and day 28 ( p = 0.006, d = 1.505, OP = 0.88) (Table ). In summary, the microhybrid composite demonstrated the largest reduction in microhardness across multiple syrups, while the giomer composite also exhibited significant changes, particularly with MF syrup. These results highlight the variable effects of antacid syrups on composite materials depending on their chemical composition and filler content. 

Figures , and shows SEM images of the composite groups at x1000, x5000, and x10.000 magnification. The images were taken from near the center of the composite samples and recorded. During surface roughness measurements, precautions were taken to avoid areas with scratches or indentations caused by these measurements. Surface images of each composite group in the Control group and after 28 days of experiment are shown. In general, roughness increased in all 3 composite surface images. There is an increase in the number of scratches, pits, and residues in the surface layer. When the surface of the microhybrid composite is examined, it is seen that there is a significant increase in particle accumulation and irregularity on the surface after contact with GL. When the surface of the nanohybrid composite is examined, it is seen that there is a limited increase in surface irregularity in general. However, it is seen that the increase in surface irregularity is higher after contact with RD. The changes in the roughness of the surface after the antacid stomach syrups applied to the Giomer composite are significantly higher than the Control group. At the same time, changes are also observed on the surface significantly compared to other composite groups. There is an increase in the number of pits and holes on the surface after contact with syrups. Of these, the roughness changes caused by GD and MF syrups are higher than the others. 

Figures , and shows 3D AFM images of the composite groups. The images were taken from the near center section of the composite samples. During surface microhardnes measurements, precautions were taken to avoid areas with scratches or indentations caused by these measurements. The surface images of each composite group in the Control group and after 28 days of experimentation are shown. When the images of the microhybrid composite groups were examined, the surface treated with MF syrup showed the highest surface roughness. The Control group and the composite surfaces treated with other syrups showed similar roughness values. When the nanohybrid composite groups were analyzed, the group showing the highest surface roughness was the composite treated with MF syrup. The group with the least surface roughness was the group treated with GD. When the giomer composite groups were analyzed, the group showing the highest surface roughness was the composite treated with GD syrup. The group showing the least surface roughness was the Control group. 

The aim of this in-vitro study was to evaluate the effects of antacid gastric syrups on the surface roughness and microhardness of composite resins. At the end of the 28-day experimental period, changes in the surface roughness and microhardness of the composite groups were observed. In this study, a period of 28 days was chosen to simulate the long-term and repetitive effect of antacid gastric syrups on composite surfaces. Composite samples were contacted with syrups for 2 min each day, followed by immersion in distilled water for the remainder of the day. This protocol reflects daily syrup consumption and allows for the assessment of cumulative effects over time. In similar studies involving beverages such as tea and coffee, a 28-day period was equated to approximately 2.5 years of real-life consumption, assuming an average daily contact time of 15 min . Although the contact dynamics of syrups differ from beverages, this standardised 28-day period remains a robust and widely accepted approach in the literature for assessing long-term effects on composites, particularly because of the shorter daily exposure time. In our study, mechanical profilometer, AFM, and SEM methods were used to evaluate the changes in surface roughness. The mechanical profilometer scans the indentations and protrusions on the surface with its sensitive tip and creates a 2D profile. Researchers have stated that due to the 3D structure of the surface topography of restorative materials, mechanical profilometers that can make 2D measurements may be insufficient for measuring surface irregularities . The use of 3D imaging with AFM in combination with a mechanical profilometer will provide more objective results in the evaluation of surface roughness . In addition, SEM examination for visual evaluation of microstructural changes, deposits, and deformations on the composite surface at the microscopic level will increase the objectivity of the results obtained . Antacid gastric syrups are medicines that can be purchased over-the-counter (OTC) and studies examining their effects on oral health are limited . Studies in the literature on antacid drugs have reported that they are effective in preventing wear that may occur on the tooth surface due to gastrointestinal disorders, aspirin intake, etc . These drugs contain agents such as calcium carbonate, sodium bicarbonate, magnesium, carbonate to neutralize the acid . It is also known that these active ingredients are added to toothpaste for their abrasive properties . Studies in the literature have shown that toothpaste containing these active ingredients increases the surface roughness of composites [ – ]. Suzuki et al. reported that a special slurry containing calcium carbonate was effective in eroding the surface of composites . Madeswaran et al. emphasized that sodium bicarbonate may wear dentin in addition to its anti-erosive effects . The common feature of these substances is that they contain carbonate; while their basic structure neutralizes acidic environments, their fine-grained structure may change the surface properties of tissues by physical abrasion. Lippert et al. reported that calcium carbonate and sodium bicarbonate may be present in toothpaste at ratios of %8–20 and more than %50, respectively . 10 ml of toothpaste with a density of 1.3 g/ml may contain an average of 1000–2500 mg calcium carbonate or 6500 mg sodium bicarbonate; those produced for whitening purposes may increase this ratio. Their abrasive effects vary depending on factors such as particle size, application method, and contact time. The RD and MF syrups used in our study contained 600 mg calcium carbonate, while GD contained 325 mg calcium carbonate and 213 mg sodium bicarbonate (Table ). Therefore, the corrosive effect of antacid gastric syrups may increase with the amount present in the formulation. After 28 days, changes in the surface roughness of the composites were observed. Therefore, hypothesis 1 of the study - antacid gastric syrups have no significant effect on the surface roughness of composite resins - was rejected. Microhybrid and nanohybrid composites showed a slight increase in roughness after contact with antacid syrups, while the giomer composite showed a significant decrease in mechanical profilometer analysis. Visual evaluations by SEM show that the irregularities on the surface of microhybrid and nanohybrid composites increased slightly, while the number of pits and indentations increased significantly in the giomer composite. AFM analysis generally showed an increase in the surface roughness of all groups. The researchers note that the differences between the measurement methods may be influenced by factors such as the length of the scanned area, the details of the methods and the film layer that may remain on the surface [ – ]. In a similar study, Alavi et al. reported the formation of voids on the surface as a result of solution application to the giomer composite . These results are similar to our study. The large voids in the SEM images can be attributed to the detachment of S-PRG filler particles of about 5 μm in size in the giomer composite from the surface after contact with antacid syrups. The observation of irregularities in the groups treated with antacid syrups, except for the Control group, suggests that the abrasive agents in these syrups may be responsible for the increase in roughness on the giomer surface. In studies where the surface roughness of the giomer composite was tested, it was shown to increase more than the other composite groups, in line with our findings . The microhardness test is an effective method for measuring the durability and hardness of a material. It is calculated by the static diamond tip in the device leaving a mark on the material under a certain load for a certain period . The Vickers test can be used to measure the hardness of brittle materials. In this test, the tip of the instrument is shorter than in other instruments and is less affected by the surface properties of the material . Due to these advantages, Vickers hardness tester was used in our study. The results of the analysis show that the microhardness values decreased in the microhybrid composite group after contact with antacid stomach syrups. For this reason, hypothesis 2 of the study - antacid gastric syrups have no significant effect on the surface roughness of composite resins - was rejected. A similar decrease was observed in some groups of the Giomer composite. The chemical structure and content of composite resins are important factors affecting the microhardness value. Karatas et al. stated that composites with high filler content have high surface microhardness, while Rodriguez et al. stated that the physical and mechanical properties of composites are related to filler content . In our study, the observation of a decrease in the microhardness values of microhybrid composites with lower filler content over time supports similar findings in the literature. The low microhardness of the Giomer composite despite its high filler content may be due to its glass ionomer-based structure as well as mechanical weaknesses due to water absorption and dissolution of monomers in its organic matrix. This may lead to separation between the polymer chains and a decrease in mechanical properties . The observed decrease in the microhardness values of microhybrid composite groups after treatment with antacid syrups is related to the basic nature of the syrups, chemical reactions, and corrosive components. In the literature, several studies have shown that solutions with acidic pH reduce the surface microhardness of composites . To our knowledge, basic solutions have not been shown to reduce surface microhardness. The abrasive substances in the antacid syrups may have been effective in the decrease in microhardness. The surface microhardness of composites also decreased after brushing with toothpaste with similar active ingredients . In this study, the interaction of commonly used oral composite types with OTC antacid gastric syrups was evaluated. For the evaluation, observational analyses were performed using mechanical profilometry, three-dimensional AFM, and SEM. The results of all three methods are consistent with each other. The most affected composite group is the giomer composite; this may be due to the special production of giomer with particles in the form of S-PRG. During the 28-day experiment, a slight increase in surface roughness was also observed in the microhybrid and nanohybrid composite groups. In general, slight microhardness reduction occurred in the tested composites and these changes were different when compared to the Control group (distilled water). As a result, carbonate-based agents in antacid gastric syrups may have played a role in these changes. This study has some limitations. The first limitation is that the composite types used in the study differ not only in filler type and size but also in matrix composition. This makes it difficult to examine the surface roughness and microhardness changes that occur after exposure to the same factor. Future studies can investigate materials with more homogeneous matrix compositions to further elucidate the role of organic matrices in surface and mechanical changes under similar conditions. Another limitation, It did not fully simulate the oral environment; factors such as saliva and pH variation were not taken into account. Future studies will allow for more realistic results by including these factors. The final limitation is that the experiment lasted 2 min a day for 28 days. Assuming an average contact time of 5 s with gastric syrups, a duration of action of approximately at least 2 years was calculated. In addition, the increase in the number of individuals using antacid gastric syrups for a long period reveals the need for longer experimental studies. 

The active ingredients added to gastric syrups to produce an antacid effect significantly change the surface roughness and microhardness of restorative materials. Especially giomer composites show more pronounced changes compared to other composite groups. The effects of the amount of substances such as calcium carbonate, sodium bicarbonate, and magnesium carbonate on teeth and restorative materials should be studied in depth with further research. 

