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Abstract Background A manual toothbrush is an indispensable tool for promoting and maintaining oral health worldwide but given the non-biodegradable and non-recyclable thermoplastic materials from which it is made, it cannot be considered free of threats to the environment. Therefore, also in light of the World Dental Federation's goals to implement and initiate policies for sustainable dentistry, this study evaluates the sustainability of two materials most used for manual toothbrush bristles, namely nylon, and silicone. Objectives The objective is to investigate the optimal solution to reduce the environmental impact of toothbrushes, and how the environmental impact would change if only the brush head was changed instead of the entire toothbrush. Methods Life Cycle Assessment and Carbon Footprint were used. Four manual toothbrushes with nylon bristles, and a handle in polypropylene with/without silicone parts (N1, N2, N3, N4) and two manual toothbrushes, with silicone bristles, but one with polypropylene handle only (Si1), the other with polypropylene handle and silicone parts (Si2) were evaluated. Results A toothbrush with silicone bristles is more sustainable than one with nylon bristles in all 18 impact categories, with average values of − 14%. In addition, eliminating only the brush head instead of the entire toothbrush could result in savings of 4.69 × 10‒3 kg CO2 eq per toothbrush. Therefore, based on the results of this study and to meet Dentistry's need to reduce its environmental impact, the ideal toothbrush should be lightweight, with less superfluous material, and with less impactful materials such as silicone instead of nylon. Conclusions The concluding indications for improving the sustainability of toothbrushes are therefore: (i) eliminate the amount of superfluous material; (ii) develop lighter models; and (iii) develop models in which only the brush head is replaced rather than the entire toothbrush.