What is the white on the tips of some people's teeth?

To me it sounds a lot like Dental fluorosis.

Dental fluorosis is a developmental disturbance of dental enamel caused by excessive exposure to high concentrations of fluoride during tooth development. The risk of fluoride overexposure occurs between the ages of 3 months and 8 years. In its mild forms (which are its most common), fluorosis often appears as unnoticeable, tiny white streaks or specks in the enamel of the tooth. In its most severe form, tooth appearance is marred by discoloration or brown markings. The enamel may be pitted, rough and hard to clean. The spots and stains left by fluorosis are permanent and may darken over time.

Dentist's are researching as we speak the use of fluoride, some dentist's say it was a bad thing. We get fluoride in municipal drinking water and by ingesting fluoride in that form which is sodium fluoride can be lethal. That is why on this side of toothpaste tubes it say's do not swallow. It is lethal and we get this in water and it causes a host of medical problems, look them up, the internet has this info.

For more info on Dental fluorosis. Go to link

There is pictures so you can see if this is your issue. Good luck.