AN INVESTIGATION OF SURFACE CHARACTERISTICS OF ENAMEL TREATED WITH INFILTRATIVE RESIN: A SCANNING ELECTRON MICROSCOPY STUDY Danielle E. Easterly, Doctorate of Dental Surgery. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Dentistry at Virginia Commonwealth University. Virginia Commonwealth University. 2017. Director: Dr. Eser Tüfekçi D.D.S., M.S., Ph.D., M.S.H.A. Objective: To evaluate the microstructural changes of a resin infiltrant (ICON®, DMG America LLC, Englewood, NJ) after six months of simulated toothbrushing. Materials and Methods: Ten extracted third molars (n=10) were collected. Artificial white spot lesions were created and resin applied. Environmental SEM images at 250X and 500X were taken after application of Icon® (T1), and after six months of simulated toothbrushing (T2). Micrographs were evaluated for changes in surface characteristics. Results: SEM showed some changes in the surface characteristics of the resin after simulated toothbrushing. However, changes in presence of enamel rods, microcracks, or fractures were not statistically significant (p>0.05). The effects of polymerization shrinkage were noted on most samples in the form of clefts and fissures. Conclusions: Icon® resin seems to withstand challenge by toothbrush abrasion over a six-month period, with some evidence of microstructural wear.