Physical Properties of Hybrid Composite Resins Containing Prepolymerized-Filler Particles

New hybrid composite resin restorative materials containing prepolymerized filler particles have been marketed for both anterior and posterior restorations.  Objectives: The purpose of this study was to compare the physical properties of the new hybrid composite resins with prepolymerized-filler particles (Premise, Kerr; Gradia Direct, GC) to traditional microhybrids (Esthet-X, Dentsply; Z250, 3M/ESPE) and a microfill composite (Durafill VS, Kulzer) (see table).  Methods: Eight specimens were created per composite group (n=8).  Diametral Tensile Strength: composite was placed in 3x6 mm diameter aluminum mold, light cured on four sides (Bluephase 16i, Ivoclar) for 20 seconds each, stored in 37^oC water for 24 hours and loaded to failure in compression in a universal testing machine (Model 5543, Instron) at a crosshead speed of 1.0 mm/min.  Flexural Strength: composite was placed in a 2x2x25 mm aluminum mold, light cured in three over-lapping segments per side, stored and tested in 3-point flexure as above at a crosshead speed of 0.25 mm/min.  Knoop hardness: composite was placed in a 2x8 mm diameter polyetrafluorethylene mold, light cured on both sides as above, stored dry for 24 hours, and indented (LM 300AT, Leco) using a 200-gram load and 10-second dwell time.  Three hardness measurements were made for each specimen.  Polymerization shrinkage: composite was placed on the pedestal in the AcuVol volumetric shrinkage device (Bisco) and light cured for 40 seconds. Shrinkage was recorded at 5 minutes.  A mean and standard deviation were determined per group.  A one-way ANOVA/Tukey was performed per physical property (alpha=0.05).  Results:  Significant differences were found between groups per property (p<0.001).  See table.  Conclusions:  In general, the traditional microhybrid composites (Z250, Esthet-X) had higher strength, the composites containing prepolymerized fillers (Gradia Direct, Premise) performed more moderately and the microfill (Durafill VS) had lower strength.  Premise and Durafill VS had the lowest polymerization shrinkage.

Composite (Shade A-2)	Composite Type	Physical Property: Mean (st dev)
		Diametral Tensile Strength (MPa)	Flexural Strength (MPa)	Knoop Hardness (KHN)	Shrinkage (%)
Z250 (3M/ESPE)	Microhybrid	62.3 (12.7) a	159.2 (15.4) a	69.6 (1.7) a	3.22 (0.25) a
Esthet-X (Dentsply)	Microhybrid	49.6 (9.7) b	135.9 (9.0) b	46.1 (1.1) b	3.24 (0.30) a
Premise (Kerr)	Nanofilled Hybrid	44.7 (6.4) bc	105.3 (4.8) c	44.3 (3.6) b	2.30 (0.08) b
Gradia Direct (GC)	Microfilled Hybrid	37.6 (4.5) c	91.4 (6.6) d	31.8 (2.1) c	3.17 (0.24) a
Durafill VS (Kulzer)	Microfill	36.0 (3.0) c	59.6 (5.3) e	14.5 (1.3) d	2.44 (0.09) b
		Groups with same letter (by column) are not significantly different (p>0.05)

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