Drying Matters More Than Disinfectant: Spacing and Airflow Rules for Storing Forty Toothbrushes in a Classroom

School toothbrushing programmes store dozens of brushes between sessions, and guidance often reaches for disinfectant soaking where the underlying problem is that brushes stay wet and touching. This study models drying under stated assumptions: a shaken brush head carries 2.0 mL of water, evaporation proceeds at 0.020 mL per minute with heads separated and at half that rate with heads touching, and the dry target is a residual of 0.2 mL. Separated brushes reach the target in 90.0 minutes; touching brushes need 180.0 minutes. A four-row rack at 25 mm spacing stores forty brushes in rows 250 mm long. Spacing, a one-time construction decision, replaces a recurring disinfectant cost. This study is simulated, not measured. SIMULATED, NOT MEASURED.