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 )

* RBC = resin-based composite , RBCs = resin-based composites.

( camphorquinone,

iodonium salt,

electron donor )

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).

* RBC = resin-based composite , RBCs = resin-based composites.