This study aimed to investigate the impact of varying concentrations of graphene oxide (GO) combined with two surface coating agents (SCAs) and two dental adhesives (DAHs) used as SCAs on microhardness. Two SCAs, Resin Glaze (ReG) and Coat-It (CoI) (Shofu Inc., Kyoto, Japan), along with two DAHs, Adper^TM Scotchbond^TM Multi-purpose Adhesive (AdA) (3M ESPE, Seefeld, Germany) and OptiBond^TM FL Adhesive (OpA) (Kuraray Noritake Dental Inc., Okayama, Japan), were tested. The ten concentrations of GO—0 wt % (control), 0.05 wt %, 0.1 wt %, 0.3 wt %, 0.5 wt %, 0.7 wt %, 1 wt %, 2 wt %, 5 wt %, and 10 wt %—were incorporated into the SCAs and DAHs to create the experimental formulations. These mixtures underwent centrifugation for homogenization, followed by sonication for dispersion. The mixture was poured into the 3D-printed resin mold (10 mm in diameter and 1 mm in height) and then cured with a light curing unit for 180 s. The cured specimens were then kept in distilled water at 37 ± 1 °C for 24 h. All specimens were then subjected to evaluation of their microhardness properties using a Knoop hardness testing machine. Data were collected, and the statistical analysis was conducted using Two-way ANOVA followed by Tukey’s post-hoc tests at a 0.05 level of significance. According to the results, surface hardness was significantly increased (p < 0.05) when 0.3–0.7 wt % of GO was added to ReG, CoI, and AdA, compared to the control group. However, surface hardness was significantly increased (p < 0.05) when 0.05–0.3 wt % of GO was added to OpA compared to the control group. In the control groups, the microhardness of OpA was significantly higher than that of the other groups (p < 0.05). In the 0.1 wt % groups, the microhardness of OpA was significantly higher than that of the other groups (p < 0.05). At 0.5 wt %, ReG, CoI, and AdA showed significantly higher microhardness compared to their respective control groups (p < 0.05). In the 1–10 wt % groups, the microhardness of ReG, CoI, and AdA demonstrated a gradual, significant decrease compared to the 0.7 wt % groups. Whereas in the 0.5–10 wt % groups, the microhardness of OpA showed a significant gradual decrease compared to the 0.3 wt % group. In summary, the optimal GO concentration could improve the surface hardness of ReG, CoI, AdA, and OpA.

Recurrent acidic exposure in patients with gastroesophageal reflux disease (GERD) accelerates the degradation of provisional restorative materials, whereas approaches to enhance the acid resistance of 3D-printed restorations remain inadequately characterized. This study aimed to evaluate the effect of graphene oxide (GO) incorporation on the surface properties and acid resistance of 3D-printed provisional restorative materials under simulated gastroesophageal reflux conditions. GO was synthesized using the Hummers’ method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. XRD analysis demonstrated a pronounced shift in the characteristic peak (2θ) from 26° to 12°, consistent with an expansion of interlayer spacing after oxidation. FTIR confirmed the presence of oxygen-containing functional groups (hydroxyl, carbonyl, and epoxy), while Raman spectroscopy identified the characteristic D and G bands, confirming successful GO synthesis. Temporary Crown & Bridge resin (TC100) was modified with GO at six concentrations (0, 0.025, 0.05, 0.1, 0.5, and 1.0 wt %) using a planetary ball milling technique. Standardized 3D-printed specimens (n = 24 per group) were fabricated. Surface roughness and Vickers microhardness were measured before and after 45 h of immersion in simulated gastric acid (pH 2). Data were analyzed using one-way ANOVA and paired t-tests (α = 0.05). After acid exposure, the control group (0 wt % GO) exhibited significant surface deterioration, showing the highest surface roughness and a marked reduction in hardness (p < 0.05). Conversely, GO-modified groups demonstrated a concentration-dependent improvement in resistance to acid-induced degradation. The 0.5 wt % GO group showed the most favorable performance, maintaining both surface roughness and hardness with no significant difference from baseline values (p > 0.05). These findings indicate that GO incorporation enhances the surface integrity and acid resistance of 3D-printed provisional resins, with 0.5 wt % identified as the optimal concentration for minimizing acid-induced surface deterioration.