let's talk about tooth colored fillings...

Tooth colored [composite] fillings are one of the most elegant types of restorations. A number of other types of restorations require that the dentist remove parts of healthy tooth just to be able to accommodate the restoration. With composites, only the part of the tooth that has already been destroyed by the caries process is removed and replaced. Not all teeth can be restored with composite, but I recommend it where possible.

A basic explanation of how composite fillings adhere to teeth (bonding process): the tooth surface to be bonded is etched - this creates a porous surface, resin (liquid component of the filling) is then infiltrated within these porosities, micromechanically locking in to the tooth structure, a more putty like tooth colored filling material is then chemically bonded to this resin-tooth layer. 

As you can imagine, any amount of saliva will prevent the resin from infiltrating where the saliva is, and weaken the overall bond. This is why maintaining a dry, isolated tooth is extremely important (see future post on rubber dams).  

The tooth colored filling is initially doughy and adapts to the shape of the tooth. It is hardened by shining a blue light, with a specific wavelength range, onto it. You can think of the doughy state as being comprised of a soup of individual links. When the blue light activates them, they join together to form a chain.

The problem is, the chain's shorter than individual links next to each other - tooth colored materials slightly shrink when hardened (somewhere around1.5-3% depending on the type, small but not insignificant). In order to minimize the stress on the tooth, and to prevent the filling from pulling away from the tooth, the filling material needs to be placed a small increment at a time - this, you can imagine is quite tedious and time consuming, but worth the time and effort!

in case you're wondering how those fillings ended up from up top...