No, absolutely not. There is no 'emergency' that warrants sharing of a toothbrush. The is a fundamental issue of not transferring bacteria. An emergency is better dealth with through chomping on mint or a gum leaf or washing ones mouth with fresh water, any liquid infact, or scraping with a soft twig of a tree or rubbing some ash or bicarb on the gums. Do not do it. its not worth it when living in a developed context where a solution is literally just around the corner.......keep your distance, laugh about it but don't share a tooth brush