Tooth colored restorative materials have been responsible for the advancement of esthetic dentistry.  Flowable composites were introduced in 1996 and have been proposed as an elastic liner to reduce polymerization stress.  The clinical characteristics of such a technique is relatively unknown.  Few studies were performed on the microtensile strength of flowable and hybrid composite.

 

Objectives: The purpose of this study was to investigate the microtensile strength of flowable composite and hybrid composites. 

 

Methods:  Ninety rectangular sticks (2X2X20 mm) were fabricated in a PVS mold by filling the mold with flowable composites and hybrid composites and cured for 40s.  Material tested were: Esthet.X, DyractFlow (Dentsply Caulk), HeliomolarHB, Heliomolarflow (Vivadent Ivoclar)  Prodigy, Revolution (Kerr).   No other treatment was performed after light curing.  The sticks were sandpapered to remove flash after demolding and stored in water for 7 days.  A micro-specimen former (U of Iowa) was used to trim the flowable composite-composite interface to a circular cross-section (d~1 mm; 0.78 mm² cross sectional area) with a 2mm gage length.  Specimens were subjected to tensile forces in a passive-gripping fixture (Dirck's device) mounted on a Vitrodyne machine and operated at 10 microns/s. 

 

Results: The results are expressed in MPa (Standard Deviation).  Kruskal-Wallis One-way ANOVA on ranks demonstrated significant differences among groups (p<0.001). 

Materials	MPa (SD)	Dunn's Multiple Comparison
Prodigy	15.51 (6.85)	a
Revolution	14.91 (3.41)	a,b
Heliomolar HB	12.42 (2.58)	a,b,c
HeliomolarFlow	10.72 (2.66)	b,c,d
Esthet.X	10.37 (3.17)	c,d,e
Dyractflow	8.38 (3.29)	c,d,e

Conclusions: The microtensile strengths are material dependent.  Flowable and hybrid composites from the same manufacturer have comparable microtensile strengths.