Tooth-bonding science. / How it works.
Etching a tooth's enamel surface is the key to this technique.
One of the hallmark characteristics of tooth bonding is the great strength with which it adheres to tooth enamel. And while you might anticipate that the creation of this bond is somewhat complicated, it is actually based on a science that is quite straightforward and easy to understand. Here's how tooth bonding works....
A) The tooth's enamel is treated with an acidic conditioner.
Tooth enamel is a highly mineralized tissue (tooth enamel has much more mineral content than bone). If an acidic solution is placed on an enamel surface the acid will dissolve (etch) away some of its mineral content. The net result of this etching process is that at a microscopic level the surface of the tooth enamel will have become very roughened.
In many ways etched tooth enamel is just like etched glass (frosted glass). You might have noticed that as you run your hand over frosted glass you can feel that its surface has a texture. This is because at a microscopic level the surface of the glass is very rough. You probably also know that etched glass has a whitish (frosted) appearance. Etched tooth enamel looks this same way. If you dry off an etched enamel surface, it will have the same distinctive "frosted" appearance.
B) Tooth bonding technique relies on a micromechanical attachment of the dental restorative to the etched enamel surface.
Dental bonding technique exploits the microscopic surface roughness of etched tooth enamel. A dentist will coat the tooth's etched surface with a liquid plastic (dentists usually refer to this resin as "bonding agent"). Since the bonding agent is a liquid it is able to seep in between the nooks and crannies of the tooth's etched surface and then once the resin is cured (hardened) it becomes locked onto the tooth's surface.
This attachment of the liquid resin to the enamel surface constitutes the "bonding" part of tooth bonding technique. And as you now know this bond is simply a mechanical one. It is a bond based on an interlocking of the cured liquid plastic bonding agent within the nooks can crannies of the etched enamel surface.
C) Once the initial bond with the tooth has been established, dental composite is added so to complete the restoration.
Now at this point the tooth's surface has only been covered with just a very thin layer of bonding agent. So to give the dental restoration its needed bulk and shape successive, layers of a dental restorative material called "dental composite" are added incrementally onto this bonded sublayer until the restoration takes its proper form.
Each additional of layer dental composite that is placed creates a chemical bond with the bonding agent sublayer and/or a previous layer of dental composite. Notice that we said a chemical bond is created as opposed to a mechanical bond like that which exists between the bonding agent and the etched enamel surface.
Bonding to tooth dentin.
What we have described so far only explains the process of creating a bond with tooth enamel. As we mentioned previously, creating a bond to tooth enamel is really a very straightforward process and one that dentists have understood since the 1960's. Creating a bond with tooth dentin is somewhat similar but in fact is a more complicated process and one whose understanding is still evolving.
Actually you might not even be aware that a type of tooth tissue called dentin exists. Teeth are not solid enamel but instead a tooth's enamel is really just a layer that encases the portion of the tooth that lies above the gum line. If a tooth has broken or decayed significantly, or if a tooth's gum line has receded very much, the portion of the tooth that is visible is actually dentin.
Creating a bond with dentin is a fairly complicated process to explain and is really beyond the scope of our discussion here. However, as a point of interest the steps your dentist takes when bonding to dentin are essentially the same as those they take when bonding to tooth enamel. And in fact both process are accomplished simultaneously using the same agents and materials.