dental Silorane composite resin 2 pages only 2011 simply discussed

1. * RBC = resin-based composite , RBCs = resin-based composites.
Silorane resin-based composite
Silorane resin-based composite ( silorane RBC* ): good biocombatibility and low mutagenic potential
( in comparison with oxirane RBC )
Note: silorane resin = siloxane & oxirane .
Oxirane : Cationic ring opening addition polymerization reaction ( while other methacrylate RBCs are
free radical addition polymerization reaction ).
Low polymerization shrinkage ( less than 1% shrinkage, while other composites more than
1.5% shrinkage )
Less microleakage and better marginal integrity.
Less polymerization stress.
Siloxane : Increased hydrophobicity
Less water sorption ( water sorption may result in hydrolytic degradation and
filler-matrix debonding ).
Less absorption to dyes and less sensitive towards exogenic staining
( about 50% less than other composites ).
Less bacterial adhesion ( about 50% less than other composites ).
Less solubility.
Initiating system : Combines between ( balance between )
High polymerization reactivity ( better than oxirane RBC ).
( note: a reactive material develops its strength directly after light cure )
Highest ambient light stability ( 10 min , while other composites were
less than 2 min ).
( this allows the dentist to place the composite restoration under
full operatory light )
Note: The electron donor decomposes the iodonium salt to an acidic cation , which opens the oxirane ring , and
starts the ring opening polymerization reaction.
A critical mass of cations has to be formed to start the polymerization reaction. This is the reason for the
highest ambient light stability. ( ambient = surrounding ) , ( ambient light = operatory light )
( camphorquinone,
iodonium salt,
electron donor )

2. * RBC = resin-based composite , RBCs = resin-based composites.
Advantages of silorane RBC :
1 , 2 : Low polymerization shrinkage and stress ( less than 1% polymerization shrinkage, while other
composites more than 1.5% polymerization shrinkage ).
3 : Less microleakage and better marginal integrity.
4 , 5 : Less water sorption and solubility.
6 : Less absorption to dyes and less sensitive towards exogenic staining ( about 50% less than other
composites ).
7 : Less bacterial adhesion ( about 50% less than other composites ).
8 : Highest ambient light stability ( 10 min , while other composites were less than 2 min ).
Note : Ambient = surrounding.
Ambient light = operatory light.
( this allows the dentist to place the composite restoration under full operatory light )
9 : Good biocombatibility and low mutagenic potential ( in comparison with oxirane RBC ).
What is the cause of polymerization shrinkage ?
The resin molecules move toward each other to form chemical bond polymerization shrinkage.
Why cationic ring-opening addition polymerization reaction resuls in lower
polymerization shrinkage than free radical addition polymerization reaction ?
Because ring opening (opening the ring) gains space and compensate shrinkage which occurs in the
subsequent step ( when the resin molecules move toward each other to form chemical bond ).
How can we reduce polymerization stress ?
Reducing polymerization shrinkage ( from seminar ), reducing stiffness (elastic modulus),
reducing C-factor, incremental placement, curing technique and polymerization speed (e.g soft-start
to allow for sress relaxation).