Photopolymerizing intensity and duration effect on adhesive bond strength

Objectives: to test the effect of photopolymerizing intensity and duration on shear bond strength of two adhesive/composite systems to dentine.

Methods: Two adhesive/composite systems were tested: (1) Adper Single Bond Plus & Z100  (3M ESPE); and (2) XP Bond & Ceram-x mono (Dentsply). Extracted human teeth were embedded in acrylic cylindrical bases. The coronal aspect of each tooth was sliced to expose a flat surface of dentine. Adhesives were applied according to instructions. A special jig (Ultradent) in combination with Teflon inserts (2.3 mm diameter aperture) were used to apply composite to dentine surfaces. Two photopolymerizing units were used: Elipar Free light 2 (3M ESPE), LED type with 600 mw/cm² output, and Astralis 10 (Ivoclar), halogen type with 1100 mw/cm² output. Each of the 2 materials groups was divided into 4 subgroups for curing with each of the curing units at two curing durations: 10 sec and 40 sec. All specimens were stored in water for 24 hours. Shear bond strength was tested using an Instron machine with crosshead speed of 0.5 mm/min.

Results: Mean SBS and SD (MPa) for the different experimental groups are shown below:

Material	XP Bond/Ceram X mono		Adper/Z100
Time Intensity	10 Sec	40 Sec	10 Sec	40 Sec
600 mw/cm2	7.667 (1.12)	14.774 (3.28)	12.529 (1.45)	20.794 (4.39)
1100 mw/cm2	16.926 (3.87)	17.926 (5.26)	22.459 (3.42)	24.384 (3.74)

Conclusions: Both curing time and intensity had a significant effect on SBS (p=0.000). Longer curing duration significantly enhanced bond strength for the 600 mw/cm² intensity (p=0.000) but not for the 1100 mw/cm².