J Korean Acad Conserv Dent JKACD Journal of Korean Academy of Conservative Dentistry 1225-0864 2093-8179 The Korean Academy of Conservative Dentistry 10.5395/JKACD.2008.33.4.405 Original Article Is an oxygen inhibition layer essential for the interfacial bonding between resin composite layers? Kim Sun-Young Cho Byeong-Hoon Baek Seung-Ho Lee In-Bog Department of Conservative Dentistry, School of Dentistry, Seoul National University, Korea. Corresponding Author: In-Bog Lee. Department of Conservative Dentistry, School of Dentistry, Seoul National University, 275-1 Yeongeon-Dong, Jongno-Gu, Seoul, 110-768, Korea. Tel: 82-2-2072-3953, Fax: 82-2-2072-3859, inboglee@snu.ac.kr 07 2008 31 07 2008 33 4 405 412 04 06 2008 04 07 2008 08 07 2008 Copyright © 2008 The Korean Academy of Conservative Dentistry 2008

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This study was aimed to investigate whether an oxygen inhibition layer (OIL) is essential for the interfacial bonding between resin composite layers or not.

A composite (Z-250, 3M ESPE) was filled in two layers using two aluminum plate molds with a hole of 3.7 mm diameter. The surface of first layer of cured composite was prepared by one of five methods as followings, thereafter second layer of composite was filled and cured: Group 1 - OIL is allowed to remain on the surface of cured composite; Group 2 - OIL was removed by rubbing with acetone-soaked cotton; Group 3 - formation of the OIL was inhibited using a Mylar strip; Group 4 - OIL was covered with glycerin and light-cured; Group 5 (control) - composite was bulk-filled in a layer. The interfacial shear bond strength between two layers was tested and the fracture modes were observed. To investigate the propagation of polymerization reaction from active area having a photo-initiator to inactive area without the initiator, a flowable composite (Aelite Flow) or an adhesive resin (Adhesive of ScotchBond Multipurpose) was placed over an experimental composite (Exp_Com) which does not include a photoinitiator and light-cured. After sectioning the specimen, the cured thickness of the Exp_Com was measured.

The bond strength of group 2, 3 and 4 did not show statistically significant difference with group 1. Groups 3 and 4 were not statistically significant different with control group 5. The cured thicknesses of Exp_Com under the flowable resin and adhesive resin were 20.95 (0.90) um and 42.13 (2.09), respectively.

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Arrangements of two molds for testing the interfacial shear bond strength. A: aluminum mold, B: hole for composite (diameter = 3.7 mm), C: hole for mounting jig connecting to an universal testing machine.

Specimen preparations for measuring the thickness of the interfacial polymerization propagation.

Interfacial shear bond strength between two resin composite layers according to the interfacial treatments. Group 1: remained oxygen inhibition layer at the interface, Group 2: removed oxygen inhibition layer with acetone, Group 3: inhibited the formation of oxygen inhibition layer by Mylar strip, Group 4: OIL was covered with glycerin and light-cured, Group 5: control group of bulk-filled composite. Groups within same bar did not show statistically significant differences.

Distribution of the interfacial fracture modes according to the interfacial treatments (n = 20).

(a) Cured layer of Exp_Com by the propagation of the polymerization reaction induced from Aelite Flow, or (b) from Adhesive resin of ScotchBond Multipurpose, (c) cured layer thickness of Exp_Com according to the interfacing resins. (AF, Aelite Flow; AR, Adhesive resin of ScotchBond Multipurpose.)