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...

what do you mean I have 10 cavities ??? ... or why you need to floss

Believe it or not, one of the scenarios I dread most is when a new patient who hasn't been to a dentist for a year or two, does not have any dental pain, comes in for an exam, and a large number of cavities appear on the radiographs ('x-rays'). First, the patient is skeptical - who wouldn't be - here she is lying down powerless, and a total stranger, who has every incentive in making a big deal of every little dark spot in her mouth, tells her that she needs a ton of dental care. Second, it's expensive (good dental care is time consuming and relatively pricy). Third, all the patient wanted in the first place is a cleaning and maybe whiter teeth. As you can imagine, tip-toing around this is quite challenging...

Why does this happen?

First a little tooth anatomy: Teeth are composed of three layers: the outer dense 'protective' layer is the enamel (the hardest substance in the human body), then there's dentin - the softer/'shock absorbong' layer, and finally, the pulp chamber - where the blood supply and nerve structure of the tooth is.

And some basic x-rayology: Dental x-rays show gradients of density - the denser the structure in which the x-ray is passing through, the brighter it appears on the radiograph (the x-ray film), so enamel appears the brightest, then there's dentin, then the pulp chamber, which appears very dark, because it's hollow and houses blood/nerve tissue. The most commonly used type of x-rays are two-dimensional - the entire three dimensional structure of the tooth is projected on a two-dimensional film.

Back to the discussion above:

Ironically, one of the culprits is Fluoride. One of the ways in which fluoride is thought to prevent caries is by making teeth denser, hence less prone to acid attacks - this is fantastic! but... one type of 'cavity' you can have is in between teeth (we'll talk about other kinds in later posts). It starts as a small de-calcification within enamel - because the entire tooth is being projected onto a 2D film, the denser areas obliterate the less dense decalcified area in the middle, and cavities are not seen on the x-ray. This creates a false sense of comfort for the patient - "I don't floss now, and I don't have any cavities...see, I don't need to floss..." But, just because it doesn't show up on the x-ray now, doesn't mean it's not there!

By not flossing, food particles are left in the area/fluoride is prevented access to that area (will discuss caries progression in a future post) advancing caries...you have 28-32 teeth in your mouth, unless you've lost more, and this process is going on in between each one of them. They won't be detectable on an x-ray until they've progressed large enough to destroy a significant amount of dentin (the softer stuff) and are impossible to see in your mouth visually, because they're in between teeth. So unless you're flossing semi-regularly, you may find yourself at the dental office being told you've got 10 cavities!

silver fillings

It's no secret that I'm not a fan of silver fillings, and not because of the mercury. After setting, all of the mercury is basically bound and don't get released in significant quantities, there are even some studies that report you get more mercury from seafood than that released from silver fillings.

I don't like them because they break teeth! ... and it's technology from the 1800's (here's the wiki link to amalgams if you're interested in reading more history). Metals don't bind to teeth, and so the way silver fillings stay in teeth is by preparing the teeth in such a way as to prevent them from coming out - see photo below.

Over time (with cyclic fatigue) the stress areas tend to fracture. If the tooth's lucky, the fracture will be superficial, and not involve the nerve - in such cases, the tooth may be restored by a tooth colored filling, an onlay ('porcelain filling'), or if more extensive, a crown. If the tooth's not so lucky, the fracture line may extend to the pulp chamber of the tooth (where the nerve lives), in which case, the tooth may require a root canal and then a crown. Sometimes these fracture lines extend through the entire tooth, in which case, the tooth will need to be extracted!

I don't advocate removal of ALL silver fillings because that comes with its own risks - every time a dentist alters a tooth, the nerve gets temporarily irritated and sometimes, the nerve gets permanently irritated and requires root canal treatment. In addition, every time you remove silver fillings, you risk exposure to mercury because the filling will now overheat and release mercury particles and vapors (look for my future blog on rubber dam isolation to minimize/eliminate this risk.) However, I do always advocate removal of silver fillings when there's evidence of fracture lines, because I prefer to address the fracture preemptively rather than wait for the tooth to fracture unpredictably, potentially risking losing the tooth.

There are some studies that show silver fillings last longer than tooth colored fillings. This was historically the case, since dental resins were first developed in the 60s and 70s and did not become clinically acceptable for posterior teeth until the 90s. The latest composites have significantly improved since then. Composites are very much more technique sensitive than silver fillings, and if not placed properly, they will fail in a short number of years. However, if proper technique is followed (to be discussed in a future post) they could last just as long, if not longer!