Wear and Polymerization Shrinkage of Highly-Filled and Flowable Composite Materials

Flowable composite materials are less filled than traditional composites.  Their composition allows ease of manipulation but makes these materials susceptible to increased polymerization shrinkage and increased wear.  Objective: To compare the wear and polymerization shrinkage of 4 highly-filled and 4 flowable materials.  Methods:  Six mm thick flat composite specimens (n=10) were prepared and polymerized with a curing light (560mW/cm²) in 2mm intervals. Specimens were mounted in brass holders and stored at 37°C. Specimens were loaded into an Alabama Wear Testing Device for 40,000 cycles at 72 Hz applying a 75N force. The test was performed with a ceramic antagonist and in a slurry of 50um PMMA beads. The volumetric and depth loss through wear of the specimens was determined using a non-contact light profilometer (Proscan 2000).  Specimens (n=5) were placed into an ACUVOL volumetric shrinkage device and polymerized with a curing light (800mW/cm²).  Values of shrinkage were recorded and averaged between 7 to 8 minutes following polymerization and reported as polymerization shrinkage (%vol). Data were analyzed with repeated ANOVA and post-hoc Tukey/Kramer test (p=.05). Results:

Material	Wear depth (um)	Wear volume (mm3)	Polymerization shrinkage (%)
Estelite S (Tokuyama Dental)	39.1±19.5	0.005±0.003	1.9±0.1
Filtek Supreme (3M ESPE)	45.2±15.1	0.021±0.014	1.9±.1
Esthet X Plus (Dentsply Caulk)	40±8.8	0.008±0.001	3.1±0.1
Premise (Kerr)	38.9±12.6	0.009±0.003	2.±0.1
Estelite Flow Quick (Tokuyama Dental)	16.4±3.9	0.002±0.001	4.02±0.2
Filtek Supreme Plus Flow (3M ESPE)	62.6±7.6	0.037±0.018	5.01±0.8
Esthet X Flow (Dentsply)	72±21.2	0.019±0.007	5.08±0.9
Revolution 2 (Kerr)	42.1±18.2	0.015±0.009	6.39±0.3

As expected, polymerization shrinkage was statistically greater for flowable materials.  Flowable materials did not present statistically greater volumetric or depth wear. Conclusions:  Clinically, flowable materials should be avoided in large restorations where extreme polymerization shrinkage could cause marginal gaps. Supported in part by a grant from Tokuyama Dental.