I accidentally used my moms toothbrush today and she has pretty bad periodontitis. im freaking out because i noticed that i have a little cut on my upper gum and im wondering if the bacteria from her toothbrush will infect my gums now?

It's unlikely. Do use an antibacterial mouth rinse. Also, rebrush with your own toothbrush and then disinfect it with boiling water. You may also apply hydrogen peroxide to the small cut, either 3% or 1.5%. You may purchase the 1.5% at the pharmacy or make your own by diluting the 3% solution 50/50 with water. Floss properly and rinse each day to prevent gum disease.

The bacteria that cause tooth decay and gum disease are easily transmissible from one person to another, and the transfer usually occurs in infancy. Presence nor absence nor a cut is of no consequence. If you want to prevent gum disease floss or WaterPik DAILY, brush 2 full minutes by the clock twice daily, and see your Dentist twice a year. Your mom should be under care of Periodontist.