C o p y r i g h t b y N o t f o r Q u i n t e s s e n c e Not for Publication Fracture Strength of Indirect Resin Composite Laminates to Teeth with Existing Restorations: An Evaluation of Conditioning Protocols Mutlu Özcan a /Ayse Mese b Purpose: This study evaluated the fracture strength and failure types of indirect resin-based composite laminates bonded to teeth with aged Class III composite restorations that were conditioned according to various protocols. Materials and Methods: Maxillary central incisors (N = 60) with window-type preparations received laminates made of a highly-filled resin composite material (Estenia) (10 per group).On the mesial and distal side, Class III cavities (3 x 3 mm) were prepared using ultrasonic burs and filled with resin composite (Quadrant Anterior Shine). The unrestored teeth served as a control group (group 6). All restored teeth (n=50) were thermocycled (5°C to 55°C, 6000X) and sub- jected to one of the conditioning protocols: (1) air-particle abrasion with alumina particles coated with silica (30-μm SiO 2 , CoJet)+silanization, (2) air-particle abrasion with alumina particles (50 μm, Al 2 O 3 )+silanization, (3) 9.5% hydro- fluoric acid (HF) for 90 s (Ultradent)+silanization and (4) protocol of Clearfil Repair Kit, (5) adhesive resin (Quadrant Unibond Sealer). A three-step bonding procedure and dual-polymerizing resin cement (Panavia F 2.0) were employed. The inner surfaces of the laminates were conditioned (CoJet-Sand, 30 μm SiO 2 ) and silanized (ESPE-Sil). All speci- mens were stored in water at 37°C for one month prior to the fracture test. Results: A significant difference was observed in fracture strength values between the groups (ANOVA, p = 0.0261). The only significant difference was between group 2 (299 ± 103 N) and group 3 (471 ± 126 N) (p = 0.0239) (Tukey’s test, α = 0.05). The majority of failures were type C (35/60) (chipping of the laminate with enamel exposure), followed by type B (21/60) (cohesive failure within the composite laminate). Conclusion: The fracture strengths of the laminates tested did not show significant differences, whether they were bonded to existing, aged Class III composite restorations or to intact teeth. The failure types, however, varied between the groups. The lowest strengths were obtained from the air-particle abraded (50 μm, Al 2 O 3 ) and silanized group. Keywords: indirect composite, fracture strength, laminates, surface conditioning. J Adhes Dent 2009; 11: 391-397. Submitted for publication: 10.02.08; accepted for publication: 12.06.08. W ith the advances in adhesive technologies, polymer- ization systems, and improvement in mechanical and physical properties of the resin systems, the use of resin composites have become routine practice in restorative dentistry. Unfortunately, during their service life in the oral environment, resin-based composite materials are prone to degradation, due to water absorption, softening and de- composition of the monomer matrix, filler detachment from the matrix, or microcrack formation. 3,18 Clinically, this may lead to compromised esthetics due to wear, discol- oration, or loss of surface properties of the resin-based restorations, especially in the anterior region. In such situ- ations, laminate restorations made of resin-based com- posite fabricated directly or indirectly, or ceramics serve as good alternatives to re-establish esthetics in a minimally invasive manner. 13 When a laminate is indicated for a tooth that contains multiple discoloured resin restorations with a history of several restoration cycles, the replace- ment of underlying pre-existing resin composite restora- tions first requires their removal by drilling. This may also result in the removal of sound enamel and dentin tissues. Clinical evidence indicates that failures related to adhe- sively bonded ceramic laminates are more frequent on ex- isting composite restorations. 17 These failures were mainly due to the difference in thermal expansion coefficient be- tween ceramic and the composite. Such failures could be observed in the form of severe marginal defects and mar- ginal discoloration at the transition between ceramic and composite restoration. Vol 11, No 5, 2009 391 a Professor and Research Associate, University Medical Center Groningen, Uni- versity of Groningen, Department of Dentistry and Dental Hygiene, Clinical Dental Biomaterials, Groningen, The Netherlands. b Assistant Professor, Faculty of Dentistry, Department of Prosthodontics, Uni- versity of Dicle, Diyarbakr, Turkey. Correspondence: Prof. Dr.med.dent. Mutlu Özcan, University Medical Center Groningen, University of Groningen, Department of Dentistry and Dental Hy- giene, Clinical Dental Materials, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands. Tel: +31-50-363-85-28, Fax: +31-50-363-26-96. e-mail: mut- luozcan@hotmail.com