The purpose of this study was to determine if air thinning three denti
n adhesives would affect bond strength to dentin. Ninety human molars
were mounted in acrylic and the occlusal surfaces ground to expose a f
lat dentin surface. Thirty teeth were randomly assigned to one of the
following dentin bonding agent/composite combinations: A) Universal Bo
nd 3/TPH (Caulk), B) All-Bond 2/Bis-Fil-P (Bisco), and C) Scotchbond M
ulti-Purpose/Z-100 (3M). The primers were applied following the manufa
cturers' instructions. The adhesives were applied by two methods. A th
in layer of adhesive was applied with a brush to 15 specimens in each
group and light cured. Adhesive was brushed on to the remaining 15 tee
th in the group, air thinned for 3 seconds, and then polymerized. The
appropriate composite was applied in 2 mm increments and light cured u
tilizing a 5 mm-in-diameter split Teflon mold. Following 3 months of w
ater storage, all groups were shear tested to failure on an Instron Un
iversal Testing Machine. Bond strength was significantly higher in all
groups when the dentin bonding agent was painted on without being air
thinned. Scotchbond Multi-Purpose had significantly higher bond stren
gth than All-Bond 2, which had significantly higher bond strength than
Universal Bond 3.