Silanation of Compliant Aggregates Improves Mechanical Properties of Composite Resin

Commercially available dental composite resins undergo polymerization shrinkage during curing, setting up internal stress that can result in debonding at the tooth-composite interface, tooth fracture and composite failure.  These materials also suffer from low toughness.  We previously showed that compliant aggregates composed of polybutadiene and silica reduced contraction stress and increased modulus, flexural strength and energy to break of an experimental composite resin.  Objective: This study was intended to determine if silanation of compliant aggregates further improves mechanical properties of the composite resin.  Methods: A series of aggregate fillers were formed by adsorption of polybutadiene of MW 2-3 million onto fumed silica (300m²/g) from dichloromethane and subsequently dried and sieved to particle size <25 micrometers.  Aggregates were silanated using a 2% solution of 3-methacryloxypropyltrimethoxysilane in ethanol.  Fillers with polybutadiene:silica ratios ranging from 0.00005:1 to 0.5:1 were added to a bis-GMA/bis-EMA/TEGDMA resin system at 9 volume % and light cured in bar form.  Bars were tested in an Instron Universal Testing machine in 3-point bend test mode.  Results: Results indicate that silanation of aggregates significantly increases flexural modulus and flexural strength when compared to unsilanated aggregates (P<0.05).  No significant increase in energy to break was found.  Conclusions: Silanation is an effective method for increasing modulus and strength in this monomer/initiator/filler system.  Supported by NIDCR T32 Grant #DE14318 and NIDCR Grant #R21DE018353.