Dental infections cause chronic diseases, such as periodontitis and dental caries, thereby leading to the tooth loss. Antibacterial and antibiofilm efficiencies of silver and zinc oxide nanoparticles combined with chitosan and erythromycin against several bacterial oral diseases have been, therefore, demonstrated. Silver nanoparticles (TVE-AgNPs) were compared with a commercial ZnONPs that conjugated with chitosan to form TVE-AgNPs-CS and ZnONPs-CS. The synergistic efficiency of TVE-AgNPs-CS or ZnONPs-CS combined with erythromycin against Streptococcus mutans (S. mutans), Bacillus subtilis (B. subtilis) and Pseudomonas aeruginosa (P. aeruginosa) was estimated by broth micro-dilution assays, agar diffusion and biofilm formation. Herein, TVE-AgNPs were produced using Thymus vulgaris extract (TVE) and the peak obtained of TVE-AgNPs at 450 nm indicated the formation of TVE-AgNPs. Furthermore, results displayed the creation of spherical TVE-AgNPs with diameters a ranging from 10 to 24 nm. The FTIR analysis suggested that TVE contains reducing agents that consequently had a function in silver ions reduction and TVE-AgNPs formation. The minimum Inhibitory Concentration (MIC) value of TVE-AgNPs-CS and ZnONPs-CS with erythromycin exhibited an MIC value of 4–8 and 8–16 μg mL⁻¹, respectively. The inhibition ratio versus biofilm was evaluated to be 75, 77.7, and 65.5% for S. mutans, B. subtilis and P. aeruginosa, respectively at TVE-AgNPs-CS/erythromycin concentration of 4 μg mL⁻¹, while it was 91.6, 83.3, and 79.3% at ZnONPs-CS/erythromycin concentration of 8 μg mL⁻¹. Our results provided an evidence of TVE-AgNPs-CS and ZnONPs-CS with erythromycin being antibacterial and antibiofilm agents against the tested bacteria. Also, they caused cell membrane damage of bacterial cells. Thus, ZnONPs-CS/erythromycin could be used in dental applications due to its non-toxicity profile and may be an important in the future development of more effective therapies for control of dental diseases.