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Aim of the study: This study was directed to evaluate the microleakage of different types of composite resin in class II posterior restoration at the cement-enamel junction CEJ. Materials and methods: Eighty one freshly extracted molars were selected. The teeth were divided into three main groups (27 each) according to the material used. Group 1: samples were restored with packable resin composite. Group 2: samples were restored with packable resin composite lined with 1-1.5mm layer of flowable resin composite. Group 3: samples were restored with hybrid resin composite. Each group was divided into three subgroups (9 each) according to the storage time. Subgroup A, B and C: storage time was 24 hours, 1 month and 3 months respectively. The gingival margin was located at the CEJ. The teeth were restored and microleakage testing was performed using dye penetration method. The data were collected and statistically analyzed. Results: The packable composite group recorded the highest microleakage values followed by hybrid composite group then flowable-lined packable composite group and this was statistically with high significance (p<0.001). The three groups showed the least microleakage values after one month followed by three months storage while the highest values were after 24 hours storage. Conclusion: None of the tested materials was able to completely eliminate marginal microleakage at CEJ but the use of flowable resin composite as a liner under packable resin composite showed a reduction in microleakage compared to the other types. KEYWORD: CEJ, class II restoration, packable composite, flowable composite, hybrid composite, microleakage, storage time. (30) Hadeel A. Sabry and Ebaa I Al-Agha E.D.J. Vol. 62, No. 1 the coefficients of thermal expansion of the tooth and the composite or between the elastic modulus of the tooth and the composite. Although some degree of microleakage will occur with most dental materials, slight leakage can be tolerated by the pulp and irritants are often removed by pulpal blood flow. However in some circumstances, microleakage becomes a source of postoperative sensitivity, recurrent caries and subsequently an eventual failure of the restoration. (2) Significant advances provided by adhesive systems and improvement in the physical and mechanical properties of resin composites, along with the increasing esthetic demand by the patients, have made esthetic direct restorations on the posterior segment a common procedure in the dental practice. However, there are advantages and disadvantages to using resin composites on posterior teeth. The advantages are conservative preparation, esthetics and adhesion to the dental structure. The disadvantages are technique sensitivity, polymerization shrinkage, postoperative sensitivity and marginal microleakage. (3) One of the recent composite resin materials is the packable resin composite which provide improved handling properties by changing the filler phase or matrix system, the viscosity of these materials was increased to resist a greater condensing force. (4) Also, flowable resin composite have been suggested as a liner beneath composites, assuming that the low viscosity material will better fill irregular internal surfaces and proximal boxes, thereby improving final marginal integrity.(5) The literature has shown that major marginal microleakage occurs on the gingival surfaces located in dentin or cementum. This is because these two structures do not show the same conditions for adhesion to resin composites, of which enamel has better results. In addition, difficulty in accessing the proximal boxes of the preparations and the control of contamination are complicating factors for restorative technique. In addition, dentin bonding is more difficult because the heterogeneous nature of the tissue requires the bonding system to accommodate simultaneously the properties of the hydroxyapatite, collagen, smear layer, dentinal tubules and fluids. (6) MATERIALS AND METHODS A total number of eighty one freshly extracted human molars were selected for this study. The selected teeth were cleaned from both tissue and calculus deposits then scrubbed with hard tooth brush under running water and finally dried with oil-free compressed air. Any defected tooth was discarded and replaced by another one. Class II cavity was prepared in one proximal surface for each molar following the general principles of cavity preparation. The cavities were prepared by using carbide round bur revolving at a high speed with water air spray in the central fossa of each tooth, the bur was changed to carbide tapered fissure bur revolving at a high speed then a carbide inverted cone bur was used to finish the floor of the cavity. The cavities were approximately 4mm in width and 4mm in depth and the gingival margin was about 1.5mm from the axial wall. The depth of the gingival floor was placed at CEJ. The cavo-surface margins for all walls were prepared without bevels. The teeth were randomly divided into three main groups (27 each) according to the material used. Group 1: samples were restored with packable resin composite (Tetric Ceram HB, Ivoclar-Vivadent). Group 2: samples were restored with packable resin composite lined with a 11.5mm layer of flowable resin composite (Tetric Flow, Ivoclar-Vivadent). Group 3: samples were restored with hybrid resin composite (Prime Dent, Prime Dent.USA). Each group was divided into three subgroups (9 each) according to the storage time. Subgroup A: storage time was 24 hours. Subgroup B: storage time was 1 month. Subgroup C: storage time was 3 months. The cavity walls for each tooth were etched with 37% phosphoric acid gel (Total Etch, IvoclarVivadent) for 20 seconds, rinsed thoroughly for 30 seconds with water according to the manufacturer’s MICROLEAKAGE OF DIFFERENT RESIN COMPOSITES OF CLASS II POSTERIOR (31) instructions then dried for 5 seconds with oil free air syringe. Bonding agent (Prime Dent Adhesive bonding system.USA) was applied to the cavities by a brush and spreading was done by a gentle blow of oil free air then light cured for 20 seconds according to the manufacturer’s instructions using a visible light curing unit (3H, Fit-Light S.China). In group A, after placing celluloid matrix band (GoMat, IvoclarViva Dent), packable resin composite was placed in increments by a plastic instrument then each increment was light cured for 20 seconds according to the manufacturer’s instructions. In Group B, 1-1.5mm thick layer of flowable resin composite was placed without a celluloid matrix band in order to easily manipulate and standardize the thickness of the increment then light cured for 20 seconds according to the manufacturer’s instructions then packable resin composite was placed in increments over the flowable liner to fill the prepared cavity with the aid of the celluloid band. In Group C, after placing celluloid matrix band, hybrid resin composite was placed in increments by a plastic instrument then light cured for 20 seconds according to the manufacturer’s instructions. After restoration, samples were finished by finishing bur and rubber flame in a low speed hand piece. Specimens were stored in distilled water at 37oC and humidity 100% in an incubator for one day, one month and three months according to each storage interval until microleakage testing. All teeth surfaces except the restoration and 1mm away from the cavity margins were coated with nail varnish then by sticky wax to insure complete sealing of the samples. After sealing, samples were immersed in 2.5% methylene blue dye at 37oC for 24 hours, removed from the dye, cleaned under tap water then left to dry for another 24 hours. Samples were sectioned mesio-distally by using a double-sided diamond disk rotating at a low speed then the crown of each tooth was splitted longitudinally in two halves by a bi-beveled chisel. Each sample was examined microscopically by a stereomicroscope using a computerized image analyzing system. A digital image of the restoration was captured by a digital camera mounted on a stereomicroscope (Olympus SZ-PT-Japan) at a 25X magnification. Image analysis software was used to measure the linear dye penetration in microns at four different points (cervical, mesio-occlusal, disto-occlusal and at the center of the occlusal surface). Microleakage was measured in microns and the results were statistically analyzed.

MICROLEAKAGE OF DIFFERENT RESIN COMPOSITES OF CLASS II POSTERIOR RESTORATIONS PLACED AT THE CEMENTO-ENAMEL JUNCTION