Background <p>Medicinal plants have long been used in Anatolia for the management of infections and oral health–related conditions. Essential oils obtained from these plants are traditionally valued for their antimicrobial properties; however, their applicability in modern oral care formulations (mouthwashes) and their compatibility with oral biomaterials remain insufficiently explored. This study aimed to evaluate the antimicrobial activity of region-specific essential oil–based mouthwash formulations prepared using Salvia triloba, Origanum vulgare, Lavandula angustifolia, and Myrtus communis, and to assess their compatibility with commonly used restorative materials.</p> Methods <p>Glass ionomer and resin-based restorative materials were immersed in herbal essential oil–based mouthwash formulations to simulate 1- and 5-year clinical exposure periods. Weight change was recorded, while color stability was assessed using the CIEDE2000 (ΔE₀₀) formula, and antimicrobial activity was determined by the minimum inhibitory concentration (MIC) method.</p> Results <p>The physical effects of herbal mouthwash formulations were material-dependent; in glass ionomer cement, weight change was affected by mouthwash type and duration (p &lt; 0.05), while in resin-based materials color change remained within clinically acceptable limits (ΔE₀₀ &lt; 1.8). All herbal formulations exhibited antimicrobial activity, as indicated by MIC values, with the lowest MIC values observed for the O. vulgare mouthwash against S. mutans and C. albicans (0.02%), while the strongest antifungal activity against C. albicans was noted for the M. communis formulation (0.05%).</p> Conclusions <p>The demonstrated antimicrobial efficacy together with acceptable effects on restorative materials suggests that essential oil–based mouthwash formulations derived from Anatolian medicinal plants provide a favorable balance between antimicrobial activity and material compatibility.</p>