Statement of Problem: Composite reins have recently become popular for posterior teeth restorations.Gap formation and subsequent microleakage are of the complications resulting from such restorations.One of the techniques to overcome polymerization shrinkage of composite resins is sandwich technique (application of glass ionomer as a base beneath the composite resin). Since polymerization patterns in two types of composite resins (light CURE and self CURE) differ from each other, various effects on the bond strength between glass ionomer and dentin are expected.Purpose: The aim of this in vitro study was to evaluate the effects of self- CURE and light- CURE composite resins in sandwich technique on the bond strength of light CURE glass ionomer and dentin.Materials and Methods: 40 extracted human premolars were selected and divided into four groups:Group 1: Light CURE glass ionomer of 1mm thickness was placed on dentin.Group 2: 1mm thickness of light CURE glass ionomer plus a mass of self CURE composite resin of 2mm thickness were placed.Group 3: 1mm thickness of light CURE glass ionomer plus light CURE composite resin as two separate 1mm layer were placed.Group 4: 1mm thickness of light CURE glass ionomer with 37% phosphoric acid etching followed by two separate layers of light CURE composite resin of 1mm thickness were placed.SEM was used to determine gap size at GI- dentin and GI- composite interfaces. The findings were analyzed by ANOVA and t-student tests.Results: Groups 1 and 2 showed no gap at GI-dentin interface and also cracks were not observed in all these specimens. In group 3, there was gap between light CURE GI and light CURE composite resin and cracks were seen in GI, too. Group 4 showed gap at both interfaces and more cracks were seen in GI. Groups 1 and 2 showed the least gap formation and group 4 showed the most. Statistically significant difference was found between groups 3, 4 and group 1 (control), 2.Conclusion: Base on this study, the application of self-CURE composite resin on light CURE GI showed no gap and crack formation on GI-dentin and GI-composite interfaces and GI itself. However, light CURE composite resins and glass ionomer etching aggregated crack and gap formation.

Background and purpose: In orthodontic brackets, unlike restorative materials or porcelain, the shear bond strength of the adhesives used is important because the oblique forces from food or objects or the tension of the adhesive food affect the brackets. This study aimed at measuring and comparing shear bond strength and adhesive remnant index of light CURE composite, no mix (self-CURE) composite, and no bond composite (GC Orthoconnect). Materials and methods: A total of 27 non-carious and sound human premolar teeth were used. The samples were divided into three groups, including light CURE composite, self-CURE composite, and no bond composite (GC Orthoconnect). After bonding and thermocycling process, the metal brackets (American Orthodontics) were then debonded using universal testing machine. Adhesive remnant index (ARI) score was assessed. Results: The highest and lowest SBS mean values were seen in self-CURE group (18. 0402±, 5. 71665) and light CURE group (7. 7890±, 3. 98995), respectively. There were significant differences in SBS values between all groups except between the no bond group and the self-CURE group (P= 0. 18, P>0. 05). The highest ARI scores were 0 in the self-CURE group and 3 in the no bond group and the light CURE group. Conclusion: The no bond composite provided acceptable overall shear bond strength and compared to light CURE composite showed higher shear bond strength and lower bond failure.

Background and Aim: Nonmetallic tooth- colored posts adhere to canal walls by dentin bonding agents and resin cements. Better retention and proper distribution of stress result from enough and proper bonding. The purpose of this study was to evaluate bond strength of D.T. Light - post with two different resin cements (selfCURE & dual-CURE) and to investigate the effect of irrigating solutions applied in root canal on bond strength of the resin cements and D.T.Light- post to root canal wall.Materials and Methods: In this experimental study 40 single root teeth (maxillary canine & central) were selected and stored in 0.1% thymol solution for one week and transferred to distilled water. The teeth were decoronated 2mm above CEJ. The canal space was mechanically enlarged using k-files (up to # 70). The teeth were randomly divided into two groups. The first group was irrigated with 2.6% NaOCl, and the second was irrigated with normal saline. After drying, the teeth were filled with gutta percha cones using lateral condensing method. After two weeks the post space was prepared and D.T.Light- post was inserted in each subgroup using self or dual-CURE cements according to manufacturer's instructions. After thermocycling, the apical part was cut 1cm below CEJ. The remained length was divided into 9 equal sequential sections. Each section was submitted to shear push-out test in universal testing machine. Statistical analysis of the bond strength data was performed using ANOVA and post hoc tests with p<0.05 as the level of significance. All failed specimens were examined under stereomicroscope. Degrees of conversion (DC) of the cements were determined by FTIR.Results: Significant difference in bond strength values were found among sites (P=0.001) and cements (P=0.03). With increasing in depth, bond strength decreased. The mean bond strength value in dual-CURE resin cement was higher than self-CURE cement. The irrigating solutions caused no significant difference in bond strength (P=0.46). DC% had significant difference in various depths.Conclusion: According to the results of this investigation, bond strength of dual-CURE cement is higher than self-CURE one in D.T Light- post because of post's translucency. 2.6% sodium hypochlorite does not affect the bond strength.

Background and Aim: Cementation is one of the most critical steps of the porcelain restoration technique. However, limited information is available concerning the bond strength of current ceramic bonding systems. The aim of this study was to evaluate the shear bond strength of three dual-CURE resin cements to IPS-Empress2 ceramics. Materials and Methods: In this experimental study, 30 pairs of IPS-Empress 2 ceramic discs were fabricated with 10 and 8 mm diameters and 2.5 mm thickness. After sandblasting and ultrasonic cleaning, the surfaces of all specimens were etched with 9% hydrofluoric acid for 60 seconds. Then, the three groups of 10 bonded specimens were prepared ceramic bonding resin systems including Panavia F2, Variolink II and Rely X ARC. After storage in 37±1o c water for 24 hours and thermocycling in 5o c and 55o c water for 500 cycles with 1-minute dwell time, the shear bond strengths were determined using Instron machine at speed of 0.5mm/min. Data were analyzed by One Way ANOVA test. For multiple paired comparisons, the Tukey HSD method was used. The mode of failure was evaluated by scanning electro microscope (SEM). P<0.05 was considered as the limit of significance. Result: Significant differences were found between different cement types (P<0.05). Variolink II provided the highest bonding values with IPS-Empress2. A combination of different modes of failure was observed. Conclusion: Based on the results of this study, according to the highest mode of cohesive failure, Variolink II seems to have the strongest bond with IPS-Empress2 ceramics.

A sandwich structure must have thin, dense, high strength facings, a low density core, which is usually thick, relatively weak, a rigid and strong attachment between them. Sandwich structures are being increasingly used in aerospace, buildings, and automotive industries, because they have high specific strength, stiffness, good thermal and acoustical insulation properties. Because of potentially low cost and high thermal resistance of phenolic resins they are attractive for using as the matrix in the facings and the core materials. Having a little knowledge of the manufacturing of phenolic sandwich, structures, in this research we have manufactured sandwich panels by compression molding employing two alternative methods: Co-CURE and counter CURE processes. In a co-CURE process, the core and composite skins CUREd simultaneously but, in counter CURE process the core with certain density and thickness are first prepared and CUREd with the skins as the second stage. The influence of the selected process on the flexural properties of the sandwich panels has been experimentally investigated, leading to the identification of the preferred processing conditions.