This study evaluated the effectiveness of a newly developed dental hygiene chew for dogs, with and without a natural antimicrobial additive, compared with a reference diet. Efficacy was determined by measuring the severity of gingivitis and the accumulation of dental plaque and calculus in dogs after 4-weeks of being fed the different dietary regimens. Dogs fed a single daily dental chew had significantly less gingivitis (P = 0. 02), plaque (P = 0. 0004), and calculus (P = 0.0001) compared with dogs in the control group that were fed an identical diet but received no chews. The inclusion of the antimicrobial agent did not improve the efficacy of the product. The dental hygiene chews tested in this study have potential to help reduce the incidence of periodontal disease in dogs.