After general house maintenance in the last few years it is now time to do some wife maintenance. My missus has (on the surface) nice white teeth. Mine are grey from many years of drinking red wine. However, mine are in pretty good condition due to modern dentistry and belated knowledge of proper dental cleaning. After "her inside" complained about a bit of tooth ache I actually had a look inside her gob to see how the dental condition was going as, not being one who looks at the mantle piece when stoking the fire, I had never really thought this was important before. The result was a disaster, dental decay, cracked teeth, and a missing tooth. We have now started on a slow path of repair. She is 39 and if nothing is done I doubt she will have many teeth left by the time she is 50. She comes from a very poor farming background and cites this as her reason for not being aware of the importance of taking care of your teeth as she could not afford a toothbrush (used a piece of soft wood). 

I wonder if it is just her or if many Thai people have the same problem as my impression of Thai people is that most of them have very nice white teeth.

I think diet plays a major role in this, I agree that most Thai peoples teeth do not stand up to close inspection and many need lots of work done, Mrs CM was similar. Also, spending money on a scaling or cleaning is often a very low priority.