Introduction to Dental Composite Resins
A Dental Composite generally contains four components :
- The Matrix : the basic phase to which the other elements are added.
- The Filler : generally particle of some type of glass to improve physical properties.
- The Coupling agent : a silane to promote adhesion to the matrix.
- The initiator : activates the polymerization by chemical reaction or exposure to a blue light.
During the polymerization (transition from a soft to a hard state) the material shrinks. Reducing the amount of matrix and increasing the filler components reduces shrinkage up to a point where the mass is too dense and cannot be clinically handled. Shrinkage has practical consequences, such as transferring of tensile forces to the tooth or detachment of the filling from the cavity with gaps formation.
The size of the particles affects other properties: extra small particles (microfilled) can be polished to the higher luster with excellent aesthetic outcome but have generally inferior mechanical properties; bigger particles (macrofilled) are much stronger but tend to degranulate during finishing and therefore the fillings end up with a rather dull final look.
It is evident that there is not a perfect recipe and a lot of different approaches have been tried during the years. The modern trend is to use a highly variable mix of particle sizes (Hybrid) wich offers a good compromise of strength and aesthetic properties. The sizes and proportion of this mix is an individual choice of single manufacturers with the so called Nanohybrid being the last trend.
The combination of a moder Hybrid composite, the last bonding technique, and the hand of a skilled clinician, offer a valid restorative option for most of the cases at a very competitive price.
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