Oral thrush is caused by infection with the yeast Candida Albicans. It causes bright white patches, which wehn rubbed come away leaving angry red spots and pain. It is uncommon in healthy adults unless they have diabete or are taking steroid medication which suppresses the immune system. Anti-fungal creams or lozenges can be helpful.
The most common trigger for oral thrush is prolonged treatment with anti-biotics. They are not discriminatory and kill of all bacteria, both good and bad allowing yeast organisms to multiply in the mouth. Use of oral contraceptives and steroid inhalers may also be a cause of oral thrush. If you use a steroid inhaler rinse your mouth with cold water after each inhalation.
Anyone suffering from oral thrush should change their toothbrush at least every 2 months.
Tea tree can be diluted in water and used as a mouthwash to combat thrush.
Otherwise, follow the advice given in the article on Candida.