Effect of convergent light-irradiation on microtensile bond strength of resin composite to dentin

Shinichiro Ogisu, DDS,(a) Ryuzo Kishikawa, DDS, PhD,(a) Alireza Sadr, DDS, PhD,(b) Kazunari Matoba, BEng,(c) Norimichi Inai, DDS, PhD,(d) Masayuki Otsuki, DDS, PhD,(a) and Junji Tagami, DDS, PhD(a),(b)

(a)Cariology and Operative Dentistry, Department of Restorative Sciences, Graduate School, (b)Global Center of Excellence (GCOE) Program; International Research Center for Molecular Science in Tooth and Bone Diseases, Tokyo Medical and Dental University, Tokyo, (c)Department of Research and Development, J. Morita Mfg. Corp., Kyoto, and (d)Medical Office, Welfare Division, Minister’s Secretariat, The Ministry of Agriculture, Forestry and Fisheries of Japan, Tokyo, Japan

Purpose: This study investigated the effects of curing light convergence and irradiation distance on the microtensile bond strength of resin composite to dentin using three light emitted diode (LED) light-curing units.
Materials and Methods: Three light curing units were investigated in this study; Flash Lite (FL), Pencure (PN), and an experimental light-curing hand-piece developed for Dentaport ZX (DP), which was designed to emit convergent light. The light intensity of each unit was measured at irradiation distances up to 10 mm. For bond strength test, bonding area was demarcated on prepared dentin using black plastic rings, in which a self-etching adhesive and a resin composite (Clearfil Liner Bond IIΣ and Clearfil Photo Core) were light-cured at different distances (2, 4, 6, 8, and 10 mm). After 24 hours storage in 37oC water, the specimens were sectioned into beams. Microtensile bond strength was then measured and failure modes were observed.
Results: The light intensity of all units significantly decreased with increasing irradiation distance. DP showed a smaller range of decrease, significantly higher intensity values at irradiation distances over 2 mm and significantly higher bond strengths at 8 and 10 mm compared to FL and PN (p<0.05). Percentage of cohesive failures in dentin decreased at 8 and 10 mm for FL and PN. Irradiation distance did not significantly affect light curing performance of DP.
Conclusion: Convergent light-irradiation was effective in maintaining adequate light intensity and bond strength as the irradiation distance increased. (Int Chin J Dent 2009; 9: 45-53.)

Key Words: irradiation distance, light intensity, microtensile bond strength.