Now lets look a little further at the diagram on the right. It shows a cross section of the tooth, not unlike what you would see when reading one of your own radiographs, which we will do in a second.
The two main hard tissues of the tooth are the "enamel" and the "dentin." There is a third one, called the "cementum" which covers the root surfaces of the tooth and which the bone attaches to. In the most common dental diseases do not affect the cementum (it is after all not exposed to that hostile oral environment) lets concentrate on the first two instead.
The Uniqueness of Dental Enamel...
The crown portion of the tooth is covered with a material that is truly unique in the human body. The enamel is, first of all, the hardest substance in the body, with a crystalline density that creates a very durable, wear resistant surface on which to perform an important task for our survival - eating.
The most important thing to understand right off the bat is that the enamel forms very early in our lives and once the tooth erupts into the mouth (exposes itself) the enamel ceases to grow any more. That means that the enamel you get on your tooth is all you are going to get for the rest of your life. It is the only tissue in the body which does not regenerate, repair itself, or shed its surface.
What that means is that you must ensure that the enamel forms properly (something every pregnant mother must understand fully to protect their baby's teeth for a lifetime) and you must protect it throughout your life because you don't get any more.
Enamel has no living tissue within it, including nerves. It has no feeling and does not cause sensitivity or pain when it is touched. That means that when it gets damaged, you will not have any warning signs or symptoms. Only a dentist can tell you if your enamel is healthy or damaged.
So now we are going to get a little technical, but don't worry it is going to be fun, I promise!What is Enamel Made of...
What is the Enamel Made of?
96% of the enamel is made up of the mineral "hydroxylapatite" which is formed into very densely packed, crystalline rods. The other 4% of enamel is made up of water and organic material that is mostly a collagen sheath that surrounds each crystalline rod.
The brown stained image on the far left shows the densely packed enamel surface with the underlying dentin below it. Enamel is not stained like this normally, that was just so it would show up on the microscope. Enamel is actually clear and has no color at all.
The image to the right is highly magnified view of the enamel surface taken with an electron microscope. Here you can see the individual crystalline rods in their collagen sheaths. The width of each rod is only 5 microns or .005 millimeters.
Bonding to Enamel...
The very nature of enamel is very important if you want to understand how we use the new adhesive, bonded composite resins to seal and restore your teeth. When enamel gets etched with a very weak acid, it opens up some shallow spaces within the rods creating a very microscopically rough surface. When resins are flowed onto that surface they grip the enamel tenaciously and allow for things to "bond" to the tooth.
This process was actually developed by studying how the simple barnacle attaches to docks and the hulls of ships. It does it the exact same way - by secreting an acid onto the surface and then secreting an enamel like material to grip that roughened surface.
When enamel gets acid-etched it looks frosty white. That is how we know we will get a good bond to that surface. We also know that the enamel will not be harmed in any way by doing this - as long as you seal it well!
Bleaching the Enamel (Tooth Whitening)...
Tooth Whitening is a very popular technique used today. It is safe way to alter the enamel to appear lighter to the naked eye. So how is this achieved?
Look again at the image to the right, showing those rods. It doesn't look very smooth does it? Well it isn't - microscopically. All of those "interstitial spaces" between the rods will collect debris and stains from coffee, tea, red wine, fruit juices, and smoking to just name a few. When those materials fill in the spaces, the enamel becomes a little more smooth. When light bounces off the smoother surface it appears to the naked eye as a slightly darker surface.
I won't get into the physics of all of this - but color is a function of the wavelength of light which is picked up by the retinae in our eyes. The wavelength of light that reflects off of a stained surface is darker than the microscopically rough surface of healthy, clean enamel.
It just so happens that when we apply a mild cleanser to the enamel, one that will "bubble out" the stains from these microscopic nooks and crannies, the tooth gets a similar frosty white appearance as we do with acid etching. That is because the wavelength of the light reflects off of this rough surface in a "whiter" fashion. We really don't "bleach" the tooth, like you would your clothes. It is just a good microscopic cleaning.
The most common material to achieve enamel whitening is peroxide based. It can be applied as hydrogen peroxide gel over the counter, or as carbamyl peroxide gel when professionally supplied. We won't get into the details of that here, refer to the procedure section on bleaching to learn more.
So now you know how enamel forms and how it is made, lets take a closer look at the next material, that makes up most of your tooth - the dentin.
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