What Is A Composite Resin Filling Material?

What Is A Composite Resin Filling Material
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Composite filling materials were developed due to the demands for a more aesthetic filling material to be used in the anterior teeth. At the time, amalgam was the most widely used filling material. It was used in all surfaces for posterior teeth and was even used in anterior teeth such as buccal or palatal surfaces. I’ve even seen amalgam used as class III and class IV cavities.

Even nowadays it is very common to see a MO amalgam on an upper 1st premolar in wide view for everyone to see when the person smiles. The alternative to amalgam was to use silica based filling materials. Silicate resin was a poor filling material because it did not bond onto enamel and did not bond onto enamel and therefore micro leakage always occurred.

In addition, there was no filler added into the resin so it had weak mechanical properties and the filling material would quickly wear away with unsightly staining as it also absorbed water.

Composite Resins

This then led to the development of composite resins. Composite resin consists of a Bis- GMA resin with filler particles such as quartz. The very first composite resins were called macro filled composite filling materials.

They were called macro filled composite resin materials because the filler particles were relatively large. This gave the composite good mechanical properties but due to the large filler particles, it was difficult to obtain a good surface finish and polish. As a result, the composite resin would readily pick up stains and this was more apparent to avid smokers, tea and coffee drinkers.

As composite resin was primarily an aesthetic filling material, the particle size was reduced and this led to the formation of micro filled composite resins. These micro filled composite resins had good aesthetics and could be polished to a high degree for aesthetic longevity.

However there was a problem with these micro filled composite resins in that it was difficult to pack a lot of particles into the resin and this caused them to have poorer mechanical properties. These composites would wear away quicker and could not be used in areas where there was high occlusal loading.

Hybrid Composites

This then led to the development of hybrid composites which consisted of a mixture of large and small quartz particles within the base GMA resin. These were the first composite’s used for posterior teeth. The very first posterior composite filling material was developed by ICI and it was called Occlusion.

These early posterior composites had a problem in that they were not stiff enough to adequately pack against a matrix band and therefore a good contact point could not be obtained. In an effort to obtain good contact points, the clinician had to use wedges in order to create a good contact point with the adjacent tooth.

There were also other problems such as polymerisation shrinkage and lack of bonding onto enamel and dentine at the cavity box floor.

Further developments within composite resin technology for filling materials have included using nano-filled composites and flowable composite.