title: Polymerization stress development in dental composites: Effect of cavity design factor.
abstract: The objective of the study was to assess the effect of the cavity design factor (C-factor) on polymerization stress development (PSD) in resin composites. An experimental resin (BT resin) was prepared, which contained 2,2-bis[p-(2'hydroxy-3'-methacryloxypropoxy)phenylene]propane (B) and triethylene glycol dimethacrylate (T) in 1:1 mass ratio, and an activator for visible light polymerization. Also an experimental composite with demonstrated remineralizing potential was formulated by inclusion into the BT resin of zirconia-hybridized amorphous calcium phosphate (ACP) filler at a mass fraction of 40 % (BT/ACP composite). A commercial glass-filled composite (TPH) was used as a control. To assess the effect of the test geometry on PSD, C-factor was systematically varied between 0.8 and 6.0 by varying the height of the cylindrical composite specimens. The measured PSD values obtained by cantilever beam tensometry for specimens with variable C-factors were normalized for mass to specimens with a C-factor of 1.33 (h=2.25 mm) as controls to give calculated PSD values. Degrees of vinyl conversions (DC) attained in the TPH control and in the experimental BT/ACP composites were measured by near-infrared spectroscopy. In both the TPH and BT/ACP composite series, PSDcalcincreased with the increasing C-factor, confirming the hypothesis that the C-factor value influences PSD values. The higher PSDmeasand PSDcalcvalues for the experimental BT/ACP composite compared to the commercial TPH composite probably reflect differences in the type and mass of the resin and filler phases in the two types of composite. These differences also account for the observed variation (21 %) in DC attained in a BT/ACP composite 2 h after cure (69.5 %) and in the DC of the TPH composite (57.5 %) having the same C-factor. The cavity design factor seems to play a key role in influencing the PSD of bonded composites, but other factors such as composite mass and composition also must be considered for their effects on PSD.
authors.affiliation: Polymers Division, National Institute of Standards and Technology, Gaithersburg, 20899, MD, USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Antonucci
authors.affiliation: Paffenbarger Research Center, American Dental Association Foundation, Gaithersburg, 20899, MD, USA.
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Giuseppetti
authors.affiliation: Paffenbarger Research Center, American Dental Association Foundation, Gaithersburg, 20899, MD, USA.
authors.forename: Justin N R
authors.initials: JN
authors.lastname: O'Donnell
authors.affiliation: Paffenbarger Research Center, American Dental Association Foundation, Gaithersburg, 20899, MD, USA.
authors.forename: Gary E
authors.initials: GE
authors.lastname: Schumacher
authors.affiliation: Paffenbarger Research Center, American Dental Association Foundation, Gaithersburg, 20899, MD, USA.
authors.forename: Drago
authors.initials: D
authors.lastname: Skrtic
keywords: amorphous calcium phosphate; cavity design factor; composite; polymerization stress; resin; tensometry