Comparison of Cuspal Deflection and Microleakage of Premolar Teeth restored with Three Restorative Materials.

AIM: This study aimed to assess cuspal deflection and micro-leakage of mesio-occluso-distal (MOD) cavities in premolar teeth restored with three different tooth-colored restorative materials to determine the effect of polymerization shrinkage stress over time. MATERIALS AND METHODS: The MOD cavities (4 mm depth) were prepared in 30 sound human maxillary premolars. The teeth were randomly divided into three groups (n = 10). The teeth were then restored with Filtek P60 (group I), X-tra fil (group II), and Admira Fusion x-tra (group III). Cuspal deflection was assessed after 5 minutes, 24 hours, 48 hours, and 7 days by measuring the intercuspal distance. After restoring the teeth, they were subjected to 1,000 thermal cycles and were then immersed in 2% methylene blue for 24 hours. After vertical section of teeth, they were observed under a stereomicroscope to assess micro-leakage. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey's honest significant difference (HSD) post hoc test. Friedman test was used to compare different time points in each group and nonparametric Mann-Whitney test was applied to assess microleakage (a < 0.05). RESULTS: The mean cuspal deflection was significantly different in the three groups (p < 0.001). The highest deflection was noted in Filtek P60 (14.8 ± 1.9) and the lowest was noted in Admira Fusion x-tra (7.4 ± 1.4 µm). Cuspal deflection significantly decreased after 7 days, but did not return to the baseline value. Admira Fusion x-tra showed significantly less deflection after 7 days (p < 0.001), but the other two groups were the same (p = 0.3). Microleakage was not significantly different among the three groups (p > 0.05). CONCLUSION: The lowest cuspal deflection was noted in Admira Fusion x-tra, although marginal microleakage was not significantly different among the groups. CLINICAL SIGNIFICANCE: As the lowest cusp deflection was noted in Admira Fusion x-tra, this restorative material can be suitable for esthetic restoration of extensive posterior cavities.

Comparative Evaluation of Application of Universal Bonding on the Microtensile Bond Strength of Light Cure and Dual Cure Composites Bonded to Dentin.

Objectives: There is limited knowledge on the efficacy of universal adhesives when used in different etching modes. The aim of this study was to evaluate the microtensile bond strength (µTBS) to dentin using universal adhesives with light-cure and dual-cure composites. Materials and Methods: In this in vitro experimental study, the occlusal third of 60 caries-free human molars were removed and the exposed surfaces were treated and allocated to 10 groups (N=6). Two different bonding agents (Single Bond Universal, G-Premio) were used to bond 2 different composite resins (Z250 light-cure and CoreFlo DC dual-cure) to dentin, using etch-and-rinse (E&R) and self-etch (SE) modes. Single Bond 2 was applied in E&R mode on wet dentin to serve as control. The specimens were sectioned into 1×1 mm2 sticks with a precision saw. A microtensile testing machine was used to measure the µTBS of the specimens with a crosshead speed of 0.5 mm/min. Data were analyzed using three-way ANOVA and Bonferroni post-hoc test (α=0.05). Results: The Single Bond Universal group in SE mode with light-cure composite yielded the highest (39.24MPa), and the G-Premio SE group with dual-cure composite produced the lowest (13.65MPa) mean µTBS (P<0.05). The dominant failure mode was adhesive, in all groups. Conclusion: The bonding agent had a significant effect on µTBS of composite to dentin, but different composites and different etching modes were not significantly different in this respect.

Effect of 940nm Diode Laser Irradiation on Microtensile Bond Strength of an Etch and Rinse Adhesive (Single Bond 2) to Dentin.

STATEMENT OF THE PROBLEM: Laser can influence bonding mechanism by increasing the penetration depth of adhesive in smear layer. The effect of 940 nm diode laser on microtensile bond strength of adhesive to dentin has not been investigated in previous studies. PURPOSE: The aim of this study was to evaluate the effect of 940 nm diode laser irradiation on microtensile bond strength of Single Bond 2 to dentin. MATERIALS AND METHOD: Thirty sound premolars extracted for orthodontic reasons were randomly divided into five groups as follows: G1 or control: etching+ Single Bond2 (SB); G2: diode laser (940 nm wavelength, 1W power, continuous mode)+ etching+ SB; G3: etching+ laser irradiation+ SB; G4: etching+ SB+ laser irradiation+ adhesive curing; G5: etching+ laser irradiation+ SB +laser irradiation +adhesive curing. After the bonding procedure, Z250 composite resin was applied on the dentin surface in three layers of 2 mm thickness. After 24 hours of immersion in distilled water at 37°C and thermocycling for 1000 thermal cycles, the teeth were sectioned into 1mm2 sticks. The microtensile bond strength was measured using a universal testing machine. Bond strength (MPs) was analyzed by one-way ANOVA followed by HSD post hoc Tukey's test (α=0.05). RESULTS: G4 (38.35±8.99) showed the significant highest bond strength compared to other groups (p= 0.000). G5 (25.16±6.14) showed significantly higher bondstrength than the control group (18.85±4.79) (p= 0.032).Bond strength of G2 (23.39±6.07) and G3 (22.85±5.11) groups was the same and similar to that in the control group (p> 0.05). CONCLUSION: Based on the results of this study, it may be concluded that dentin surface irradiation with 940 nm diode laser after adhesive application and prior to curing can significantly increase the bond strength of composite to dentin.

Multiple in vitro analyses of fracture resistance in maxillary central incisors restored with fiber posts.

INTRODUCTION: The resistance to fracture of endodontically treated teeth restored with esthetic post systems has not been extensively researched. This in vitro study compared the fracture patterns of endodontically treated teeth with esthetic post systems with different analysis methods. MATERIALS AND METHODS: A total of 26 recently extracted human maxillary central incisors were decoronated and then endodontically treated. Teeth were restored with quartz fiber posts. All posts were cemented with Panavia dual curing adhesive resin cement and subsequently restored with composite cores. Three methods were used to test fracture resistance. Each specimen was embedded in acrylic resin and then secured in a universal load-testing machine. A compressive load was applied at 135º degree angle at a crosshead speed of 1 mm/min to the long axis of the tooth until fracture occurred. The two other methods, finite element analysis (FEA) and photo elastic study used the same angulation and 90 N force to simulate the first method. The data were then compared. RESULTS: Clinical results indicated that fracture was most likely to occur between core and dentin, and then in the cervical 1/3 of the root. Photo elastic study demonstrated similar results; the highest stresses occurred at the junction of dentin and core contralateral to the side where force was applied. FEA also confirmed these results; however it also showed that the highest stresses arise at the dentin/core junction contralateral to the force point. CONCLUSION: All three techniques reiterate that the risk of fracture is greatest at the cervical dentin/core junction.