In recent years, people have become more conscious about the side-effects of fluoride toothpastes and herbal products have drawn attention as alternatives in the struggle against caries. Studies have focused on the benefits of essential oils obtained from herbs because of their antibacterial effects. The aim of this study was to evaluate and compare the antibacterial activity of Origanum dubium and Cinnamomum cassia oils combined with herbal toothpastes against Streptococcus mutans. The antibacterial activity of the test materials was determined using the agar well diffusion method before and after the addition of essential oils. We tested the efficacy of Splat Organic and Splat Biocalcium against S. mutans (12 mm and 11 mm, respectively) doubled in combination with Origanum dubium (23 mm for both toothpastes) and tripled with Cinnamomum cassia (38 mm and 36 mm, respectively). Jack N’ Jill toothpaste, which did not initially show any antibacterial effect, exhibited the largest inhibition zones after the addition of the essential oils (38 mm for Origanum dubium and 39 mm for Cinnamomum cassia). The results of this study pointed out that herbal toothpastes exhibit statistically higher antibacterial activity against Streptococcus mutans (p < 0.05) than their initial forms after the addition of essential oils.