How clean are toothbrushes when new?

Run it under hot water and use soap.

every monthmy dentist told me that

Toothbrushes should be replaced as soon as the bristles show signs of wear, splay, fray or when the color indicator changes color. Generally, this is every 8 to 12 weeks. A worn toothbrush would not...

you need a new toothbrush every month because you dont want old bactira bilding up in your toothbrush