The large, flat teeth at the back of your mouth are called molars. They are the millstones in your mouth, which you use to grind food while chewing. So, they are the ones that do the heavier job and take heavy wear and tear. The back teeth on the lower jaw mesh with their corresponding back teeth on the upper jaw, each with the one just above it. While chewing, both the lower and the upper tooth press and scrape against each other.
Compared to the front teeth, molars do not show up much when you speak or laugh out loud. So, their appearance is not as important as, say, the cutting teeth in the front of the mouth, called the incisors.
When selecting the material for the crown for your back teeth, consider strength first and cosmetic value if the tooth is visible, or if you have receding gums. That way, you would ideally settle for a gold crown for the back teeth. However, some people do not like metallic presence in their mouth. The next best option would be metal with a ceramic outer casing.
Over the years, both dentists as well as patients have preferred the Porcelain-fused-to-metal (PFM) dental crown for the back teeth. PFMs offer high strength with better cosmetics. A thin cap that looks like a thimble, called the substructure is made from a metal alloy. It fits over the tooth. You get the shape of a crown when porcelain is fused over this cap. The outer porcelain gives it the appearance of a real natural tooth.
Recently, Zirconia crowns are gaining increasing prominence. They are very strong and a good option for people who are allergic to metals. However, they are on the pricier.
If everything else is okay then you could even consider an all metal crown for the back teeth. As I already said, the choice will vary from person to person. It also depends to a great extent on the expertise of your dentist.
Trust your dentist to decide which the best crown would be for you.