The composite resin is a plastic material having aesthetical properties and
being able to stick to the tooth surfaces. The glueing procedure can be
summarized in a defined sequence of chemicals that prepare the dental surfaces
in order to receive the filling material.
The choice of the colour is done by observing the tooth and trying to
harmonize the composite to the remaining structure. This is not always an easy
task because the composite has different light reflection and refraction
features from the tooth itself, nonetheless, an experienced dentist with a good
knowledge of the product he is using can reach satisfying results.
The first substance to take contact with the finished enamel and dentine
surface is an Acid that used as a conditioner (usually Orthophosphoric Acid 37%
concentration): its function is to render a raw surface allowing the grip of the
further substances. After its action, it's removed with a brief water spray.
According to the product used, there will be a Primer, which is a substance
charged with creating a connection layer between tooth and resin: as a matter of
fact it's a substance which is able of permeating the etched surface and connect
it to the next layer.
As for next, the Adhesive is used, which is actually a fluid transparent sort
of varnish and can be considered as the proper filling glue.
A thing to be pointed at is that some brands of dental adhesives mix these
substances in one bottle: they are the so called "one step" adhesives. Every
professional chooses his favourite product according to the published
information and to his experience.
The actual filling material (composite) is delivered in small tubes or
cartridges used with special dispensers. In any way, it is brought into the
cavity with progressive quantities: it needs stratification.
This is mainly done to minimize a particularly unwanted effect that all the
composites have, and that's to say polymerization retraction.
This issue deals with the fact that while the material hardens, it undergoes
a volume contraction: if this is too heavy, it may cause a micro leakage between
filling and cavity walls, too small to be noticeable but big enough to allow a
second caries to pass through the gap.
The composite hardening is achieved by exposing it to the light of a special
lamp with a specific wavelenght emission. aminimum strenght of 550 mW/sqcm is
required and below that value, a proper hardening cannot be guaranteed.
The final part of the filling leads to the removal of the wedge, of the
matrix and of the rubber dam. At this point the so called occlusal test is
fulfilled: that means that the proper chewing dimensions are controlled, or
easier said there's a check on the patient eventually feeling to be "touching"
the filled tooth before the others. With the appropriate burs, retouching is
done and as a next phase, the filling is polished using rubber burs, polishing
paste or similar. Now the filling is complete.