Tear stains are very common in the breed. Some are lucky enough not to have any staining but it is a real battle for some pet owners. Even the good lines can produce dogs that have staining. There's lots of info out there on the subject. There are several tricks and tips that maltese people use, I have tried a few of them but not all. Some people swear by giving distilled water as their daily drinking water, some people add vinegar to the water, avoiding any food with red dye, giving a daily (1/2 tab 2xday) dose of Tums to prevent stains (changes the PH level and helps keep yeast and bacteria production under control), Tetracycline or giving low dose of Tylan (the trick here is finding a vet that's willing to give you the prescription), over the counter eye drops such as Colloidal Silver (some show people swear by colloidal silver) or Collyrium, Omega 3 supplements, Missing Link, not using plastic water and food bowls, and treating with a mixture called MOM. MOM is a homemade recipe using equal amounts of Milk of Magnesia, corn starch and hydrogen peroxide to make a paste. Brush paste on the stained area ( I use a small flat artist brush), and work well into the stain. Allow paste to dry overnight. Wash out in the morning and condition. Repeat for several days until stains have disappeared. I have bought many over the counter eye stain products such as eye envy and have not had any luck with them on maltese hair. I use MOM and Tums and have found it work best for me. Tearstains in maltese is extremely common.
Here’s a great link for the causes and treatments of tearstains in malts.
http://www.bhejei.com/tearsta.htm
And here's an article written by Tonia H. of Rhapsody
http://www.malteseonly.com/teartonia.html
This forum has lots of info too.
http://www.spoiledmaltese.com/forum/