Will a dentist know there is a problem with your teeth just by looking at it?

I went to the dentist yesterday for a check up, sometimes after eating hard stuff my back tooth will kind of hurt so i tough i need feeling done on my teeth or something. I didn't tell the dentist this bcs i was kinda afraid. The dentist then just look around my teeth follow by cleaning my teeth then he said ok your done now.So i would like to know do dentist know there a problem with your teeth just by looking at them??