: Dental biofilms play a major role in the pathogenesis of peri-implant mucositis. Biofilm reduction is a pre-requisite for a successful therapy of peri-implant mucosal lesions. In this study, we evaluated the effect of three different plasma devices on the reduction of Streptococcus mutans (S. mutans) and multispecies human saliva biofilms. Material and Methods: We assessed the efficacy of three different non-thermal atmospheric pressure plasma devices against biofilms of S. mutans and saliva multispecies grown on titanium discs in vitro in comparison with a chlorhexidine digluconate (CHX) rinse. Efficacy of plasma treatment was determined by the number of colony forming units (CFU) and by scanning electron microscopy. The results were reported as reduction of CFU (CFUuntreated−CFUtreated). Results: The application of plasma was much more effective than CHX against biofilms. The maximum reduction of CHX was 3.36 for S. mutans biofilm and 1.50 for saliva biofilm, whereas the colony forming units (CFU) reduction of the volume dielectric barrier discharge argon plasma was 5.38 for S. mutans biofilm and 5.67 for saliva biofilm. Conclusions: Treatment of single- and multispecies dental biofilms on titanium discs with non-thermal atmospheric pressure plasma was more efficient than CHX application in vitro. Thus, the development of plasma devices for the treatment of peri-implant mucositis may be fruitful.