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Aim: This study was carried out to investigate the effect of some surface treatment protocols on bond strength of different types of composites to indirect composite blocks at different aging periods

Materials and methods: One hundred and eight discs were obtained from indirect esthetic restorative blocks (Grandio Blocs, VOCO GmbH, Germany) which are designed for Cerec CAD/ CAM system, shade A2, size 14. Three millimeters thick discs were obtained by sectioning the blocks using a low speed isomet saw (Isomet 1000, Buehler Ltd., Lake Bluff, IL, USA). The discs were divided into six groups (18 each) according the surface pre-treatment employed. Group 1: no treatment as control, group 2: roughening with diamond stone, group 3: sandblasting and silica coating. Group 4: etching with phosphoric acid %30 for one minute, group 5: combination of roughening and etching and group 6: combination of sandblasting and etching. Each group was further subdivided to three subgroups (6 each) according to the repair material used either nanohybrid composite, bulk fill composite and organically modified ceramic restorative material (Ormocer). Finally each subgroup was divided into two classes (3 each) according to the aging time either 24 hours or 3 months. After surface treatments, Futurabond U (VOCO GmbH, Cuxhaven, Germany) was applied. Before curing, small cylinders were cut from tygon tubes (Norton Performance Plastic Co. Cleveland of USA) with an internal diameter of 0.8 mm and a height of 1 mm. Five cylinders were mounted on the treated surfaces of each disc (n = 30). Finally, the adhesive was light cured for 20 seconds using LED light curing unit. Three repair materials were used in this study. Nano-hybrid resin composite (Grandio) shade A2, regular bulk fill resin composite (x-tra fil) universal shade and organically modified ceramic restorative material (Ormocer) (Admira Fusion). All materials used were of the same manufacturer (VOCO GmbH, Cuxhaven, Germany). Each material was packed into the cylinder lumen using endodontic plugger and light-cured for 20 seconds using the same light curing unit. For the three-month group, the specimens were stored for three months in distilled water at room temperature. Using a universal testing machine (Llyod instruments Ltd, fareham UK), the μ-SBS were measured. A wire of 0.2mm diameter was looped around the resin composite cylinder. Shear force was applied to each specimen at a cross-head speed of 0.5 mm/min until failure occurred.

Results: Regarding 24-hour storage time, One-way ANOVA and post-hoc Tukey’s HSD test showed that within Nanohybrid group, Bulk fill group and Ormocer group; Group 6 had the signifi- cantly highest μSBS. While Regarding three months storage time, One-way ANOVA and post-hoc Tukey’s HSD test showed that within Nanohybrid group, Bulk fill group; Group 6 had the signifi- cantly highest μSBS. Within Ormocer group; Group 5 had the significantly highest μSBS. There were no significant differences in μSBS detected between the different repair material within each surface treatment group Independent Student-t test revealed that within all study groups, μSBS mean values at 24-hour storage time were significantly higher than those of 3-month ageing time (P0.05).

Conclusions: Within the limitation of this invitro study the following conclusions could be drawn: 1- Combination of surface treatment protocols significantly increased the repair bond strength. 2- There was no difference between the three direct resin composite materials on repairing the composite blocks after 24 hours. 3- The bond strength of the repaired composite blocks after 24 hours storage showed higher micro-shear bond strength than after 3 months aging.