dental insurance

Friday, January 1, 2010

Teeth under a Microscope-Enamel

Dental Enamel is the outer part of a tooth; the part you see. It coveres the tooth like a thick eggshell. In baby teeth, it is quite thin. In permanent teeth, it is thicker, roughly 1-2mm. It is very hard. Under a microscope the enamel "rods" are arranged kind of like a stack of lumber with the surface being the ends of the stack. These rods have sort of a keyhole shape in crossection.

In order for a composite filling, sealant or other bonded material to adhere to the enamel, the surface is "etched". This is usually done by applying 37% phosphoric acid solution for about 15-20 seconds and then rinsed off. (No the acid does not hurt. In fact, you can touch it for a good while and nothing will happen. It's acid, but not that strong). The etchant removes inorganic material and parts of the enamel rods whose ends are exposed by demineralization. Yes, if you put an egg into vinegar it will eventually demineralize the eggshell. Same thing here, but a much shorter time, stronger acid and it's only the microscopic surface that is demineralized. This etching produces multiple areas for bonding material to mechanically adhere to the enamel surface. Visually the tooth has a frosted appearance. It's sort of like sandblasting or priming the surface. Bonding agent is then applied, flowing down into this rougher surface. Once curing occurs, this locks into the undercuts, and bonds the material to the tooth.

Unetched Enamel:

Etched Enamel:

Dentin can also be etched, but the bond strength is less than with the enamel. It is much more organic with dental tubules evident on microscopic view. Newer bonding agents bond to enamel and dentin. You can see from these photos how the surface is primed for bonding.

Etched Dentin:

Here is a good slide show on enamel: Enamel Histology

A good summary of the status of enamel and dentin bonding: JADA Article

Now, is the histology of enamel different with enamel flourosis? with hypoplasia? Basically, yes. That would be whole other post.

Sunday, November 8, 2009

Silver Fillings (Amalgam)

I don't want a silver filling! I hear this from time to time in the office. What are silver fillings (amalgam fillings)? They are sometimes called amalgam because they have a few different things in them amalgamated together to form something new.

Just so you know we do not do amalgam silver fillings anymore in our office and have not for many years. This mainly was a factor of the improvement in the strength and durability of white fillings and patient demand. We have found that the ability of the stonger newer composite white fillings that bond to the tooth (strengthening it) and the cosmetic benefits make it a very desirable restorative material.

Amalgam consists of a powder of ground up mainly silver and copper and some other metals mixed with a little drop of mercury. You shake it all together (amalgamate). After a few seconds of "trituration" the thing is kind of maleable and putty like. It is placed into the cavity preperation and initially hardens in a few minutes. It is very important to note that there is basically no murcury coming out of a silver filling once it is amalgamated. They are quite safe as determined by extensive scientific clinical studies-(See links below.)
Silver fillings were very common in the past and were the standard of care, and still are, because they hold up quite well to biting forces. If a dentist is still doing silver fillings, that is still an acceptable method of treatment. There are a few drawbacks to "silver" fillings: 1. They do not bond to the tooth, they basically just fill the cavity. 2. They are silver so there is a cosmetic concern. Now, how many people are looking at your back teeth trying to see in there? If you know them that well, it probably does not matter what your teeth look like. Still, we are all concerned with appearance and want the most cosmetic solution available. 3. thermal conductivity is better/lower with white fillings.