Objective <p>Biofilm formation on dental restorative materials and implant surfaces plays a central role in the development of dental caries, periodontal disease, and peri-implantitis. Durable antimicrobial surface treatments that inhibit bacterial adhesion and biofilm formation remain a significant unmet need in restorative and implant dentistry. Therefore, this study aimed to develop a composite coating combining cetylpyridinium chloride and graphene oxide, and to evaluate its durable antibacterial surface modification under in vitro conditions.</p> Methods <p>A composite coating consisting of cetylpyridinium chloride and graphene oxide was prepared and applied to composite resin and titanium surfaces. Antibacterial activity against <i>Streptococcus mutans</i> and <i>Porphyromonas gingivalis</i> was evaluated using adenosine triphosphate assays and fluorescence-based live/dead staining. Coating retention after washing and air-drying was assessed by optical microscopy and Raman spectroscopy.</p> Results <p>Cetylpyridinium chloride-graphene oxide-coated surfaces showed a significant reduction in bacterial viability compared with phosphate-buffered saline, ethanol, and cetylpyridinium chloride-only controls. Antibacterial effects were maintained after rinsing and air-drying on both composite resin and titanium surfaces. Raman spectroscopy confirmed the persistence of characteristic graphene oxide bands after washing, indicating stable retention of the coating on the material surfaces.</p> Conclusions <p>Cetylpyridinium chloride–graphene oxide coatings demonstrate sustained surface-associated antibacterial activity against key cariogenic and periodontal pathogens and remain stably adhered to common dental restorative and implant materials after washing. These findings suggest that cetylpyridinium chloride–graphene oxide coatings may serve as a durable contact-active surface modification strategy to reduce biofilm formation associated with dental caries and peri-implantitis.</p>