Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 23 0 2026 11 04 4865 4865 Manar Ramadhan Department of Prosthodontics, College of Dentistry, University of Baghdad, Baghdad, Iraq Faiza Abdul-Ameer Department of Prosthodontics, College of Dentistry, Mustansiriyah University, Baghdad, Iraq 2023 06 28 2024 10 29 Objectives: Silicone facial prostheses are replaced after a relatively short period of clinical service, mainly due to the decline in their physical and mechanical properties. This study aimed to investigate some mechanical and physical properties of VST-50 maxillofacial silicone after incorporating thymol micro-powder into its matrix. Materials and Methods: In this in vitro study, room-temperature vulcanised VST-50 maxillofacial silicone and thymol micro-powder were used to prepare the study specimens according to the findings of a pilot study. Sixty specimens were prepared and assigned equally and relevantly to three tests (tensile strength/elongation percentage test, and surface roughness test). Each test encompassed three groups (n=10). According to thymol content percentage, the study groups were customised as: group A: control (without additive), experimental groups B and C with 0.75wt% and 1wt.% thymol additive, respectively. An Instron universal testing machine was used to investigate the tensile strength and elongation percentage, and a profilometer was used to test the surface roughness. ANOVA and post-hoc test were used to analyze the results (alpha 0.05). Results: Statistically, group B showed a significantly higher mean tensile strength (mean difference: -3.055 N/mm2; P<0.001) and elongation percentage (mean difference: -157.9885%; P=0.003). However, group C showed a significantly lower surface roughness (mean difference: 0.1172µm; P<0.001). Conclusion: According to the results of this in vitro study, thymol micro-powder appears to be a promising additive that could reinforce some physical and mechanical properties of medical-grade maxillofacial silicone. https://fid.tums.ac.ir/index.php/fid/article/view/4865 https://fid.tums.ac.ir/index.php/fid/article/download/4865/2252