Covers how composite restorative materials measure up against the general requirements for restorations, set out in a table of properties such as mechanical strength, wear, thermal behaviour, aesthetics and biological safety. It then discusses polymerization shrinkage, with a bar chart comparing shrinkage across composite types, the biological effects of monomer release, and the causes of colour change. It closes by noting that no composite meets every requirement, which is why materials are often combined.
Topic 29 of 52 in the MU Sofia syllabus for Dental Materials (Dental Medicine, Year 1). The free AceMed note covers it in 6 sections, about 174 words (2 min of reading), with 14 flashcards.
In this note
Introduction
Requirements and how composites perform
Polymerization shrinkage
Biological requirements
Color stability
No material is ideal
Introduction
Composites must replace lost tooth tissue in appearance and in function, and they must last in a wet, acidic and mechanically loaded environment. They are held to the general requirements for restorative materials. This note shows how well they meet each one.
Polymerization shrinkage
Shrinkage is the main weakness of composites and has been the focus of research. Only the resin shrinks, so more filler means less shrinkage. Pure dimethacrylates shrink by about 20% at full conversion.
Biological requirements
In the mouth, only 40 to 70% of the monomer converts, so some is released. Some components can change hormonal balance, and resins can cause allergies. Materials with less filler contain more resin and are less well tolerated. Deep cavities need a calcium hydroxide liner under a glass-ionomer.
Color stability
Endogenous: in chemically cured composites, the amine-peroxide system oxidizes and turns brown-yellow.
Exogenous: stains on the surface, and at margins where gaps have opened.
No material is ideal
No composite meets every requirement. This is why restorations often combine materials, with a biologically active layer on living tissue and a strong, esthetic layer on top.
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