Dominant and recessive alleles?

I'm confused, possible: both my parents have long teeth, and how would my sister get wide teeth if my parents don't have wide teeth? Is it possible for my mom to have a dominant and recessive alleles for teeth. I think the dominant allele could be long teeth and wide would be recessive. I'm confused though because what if my dad doesn't have wide teeth but has a recessive allele and dominant, and in a punnett square if my moms recessive allele and my dads were together wouldn't it be different since to be able to have wide teeth it must be 2 recessive alleles but my dads recessive allele wouldn't be wide teeth