Dental Procedure: Bonding

Watch Dental Video about Bonding in Dentistry

Bonding is an informal term in dentistry describing the gluing procedure in ceramic and/or plastic fillings.

Contrary to the cementing process, surfaces that are to going to be glued must first undergo a special preparatory treatment. The individual steps are explained below:

Step one: Etching the surfaces and the teeth. The etching process roughens up the surface of the tooth or the ceramic inlay, creating a so-called micro-retentive pattern. The animation shows a cross section of a tooth while the etching gel (blue) is being applied. At first, the surface of the tooth is smooth; as time passes, the etching gel “eats” its way into the dental enamel and creates small lacunas and caves. These structures remain even after the etching gel is rinsed off.

Let’s assume the initial surface of the tooth, including the inlay, amounts to a length of “x.” Examining the gluing surface closely after the etching procedure, we can see that this surface has been expanded by a factor of “y.”

However, since the etching pattern is not two-dimensional but three-dimensional, the gluing surface is actually enlarged even further.
But a word of caution: Not everything on the tooth can be etched equally. In the video "bonding", you see a tooth’s dental enamel being removed with a drill. Enamel is a mineral.

Below the enamel, there is dentin. Dentin consists of protein strands and small channels.

These structures are destroyed during the drilling procedure and literally form a pulp, for which the technical term is “smear layer” (represented by the gray mass in the animation). The smear layer prevents the glue from penetrating the dentin; however, if the etching gel were applied on the enamel and the dentin for an equal amount of time, then the proteins released in the dentin would form lumps because of the etching gel. This is called denaturization and is similar to chicken soup when it begins to boil: The gray film forming on the surface is made up of denaturized proteins. Again, the glue isn’t able to penetrate the dentin.


ceramic inlay bonding

This is why the etching gel is applied to the enamel first, is only applied to the dentin some time later, and is only left on the dentin for a few seconds. Not only does this remove the smear layer without denaturizing the proteins of the dentin, but it also creates the desired micro-retentive pattern in the enamel. Now the glue (green) can penetrate the dentin. This is the basis for an optimal bond.

Step two: The primer. The primer is used to remove water from the dentin in order to “dry out” the protein strands, because water prevents the glue from distributing well in the dentin.

Step three: The adhesive. Although the protein strands are dry now, they have collapsed. The adhesive makes the protein strands stand up again, thus promoting the distribution of the glue.

Step four: Bonding. The bonder is the “pre-glue;” since it’s very thin, it penetrates deeply into the cleaned and reestablished protein strands of the dentin and into the vacuoles/caverns of the dentin.

Finally, the actual glue is applied.

Although this is only a rough outline, it is clear that the gluing of dental fillings is an elaborate process. Good bonding results can only be achieved if the instructions of the manufacturer are followed and if the tooth remains clean throughout the procedure. This is why one should always work with a cofferdam. In the animation, you see what happens if, for example, saliva and/or blood comes in contact with the tooth – the porous surface is immediately closed and the glue  can no longer penetrate the structures created earlier.

The adhesion, and thus the tightness, of the filling/inlay are reduced. Well-glued ceramic inlays cannot be recognized, even by a dentist!
The risks of bonding are negligible. Nevertheless, complications may occur in individual cases, possibly requiring additional measures. Every additional measure may in turn lead to complications which may lead to a loss of teeth. At this point, we will only discuss the specific complications encountered in bonding. These are, for example:

  • Sensitive tooth necks
  • Toothache, for example due to an injury of the dental nerve
  • Leaking ceramic fillings/plastic fillings
  • Clogging of gaps between teeth
  • Gum inflammations, for example due to glue residue


Click here to see the video: Bonding


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