There is no real way to stop it. I've always taken really good care of my teeth and still do. once I was around 15 weeks they became very sensitive to heat+cold and pressure. I'm 35 weeks now and nothing has changed and my teeth still are having problems. my dentist tried having me change to a softer tooth brush and toothpaste for sensitive teeth and it has not helped at all. :(
Your teeth/gums do become more sensitive during pregnancy. no sugesstions, but it is common.