This study evaluated ascending order of light attenuation distance (0,2,4,8 mm) and specimen dimensions (2x2x10, 2x2x12, 2x2x15 mm3) differing from requirements of ISO 4049 (2x2x25 mm3) on the flexural strength of nano-hybrid resin composite. Specimens (N=160) were prepared accordingly and randomly assigned into groups for the factors studied. Specimens were photo-polymerized from increased distances through 1, 2, 3 and 5 overlapping cycles depending on the specimen length after which they were subjected to three-point bending test (0.5 mm/min). Data were statistically analyzed using one-way, twoway ANOVA and Tukey's HSD post-hoc tests (=0.05). Two-parameter Weibull modulus, scale (m) and shape (0) were calculated. Both light attenuation distance (p0.001) and specimen dimensions (p0.001) significantly affected the results. Regardless of the specimen dimensions, 0, 2 mm polymerization distance resulted in significantly higher mean flexural strength compared to 4 and 8 mm. Polymerization distance did not significantly affect the mean flexural strength of specimens prepared according to ISO norms (p>0.05). Weibull distribution presented the highest shape (m) for 10-8 mm (24.65), 12-4 mm (14.54), 15-2 mm (12.32), 25-2 mm (17.56), length-light distance combinations. Specimen dimensions prepared in accordance with ISO 4049 do not allow for comparison of the effect of light attenuation distance on the flexural strength of resin composite tested.

No abstract

Aim. To evaluate the bond durability of two universal adhesives; mild and ultra-mild in both etch-and-rinse and self-etch modes after simulated in-vitro degradation by long-term water storage or thermocycling. Methods. A total of 144 specimens were used in this study; 120 specimens (prepared from 30 teeth) for microshear bond strength testing and fracture mode assessment, and 24 specimens for scanning electron microscopic evaluation (prepared from 24 teeth). Specimens were prepared from 54 recently extracted caries free third molars and randomly divided into 12 groups, according to the adhesive treatment (All Bond or Scotchbond Universal), etching mode (etch-andrinse or self-etch) and aging method (thermocycling or water storage). Each tooth was sectioned mesio-distally into two halves exposing free dentin surface for bonding where dentin substrate 1 mm below the dentino-enamel junction was used. After adhesive application and composite build up, specimens were tested in shear mode after storing in distilled water at 37˚C for 24 hours or 1 year, or after being thermocycled between 5 and 55 °C for 10,000 cycles (n=10). Microshear bond strength (μSBS) was tested using a universal testing machine. Adhesive-dentin interface was examined using scanning electron microscope (SEM) (n=2). Data were analyzed using 3 way AN0VA and pairwise comparisons was performed using Bonferroni correction at significance level of α ≤0.05. Results. Statistical analysis revealed non-significant difference for etching mode in both adhesives (p=0.596). After aging, the bond strength was only reduced in Scotchbond Universal after one year of water storage in both modes (p<0.001). SEM evaluation revealed intact hybrid layer and longer resin tags for etch-and-rinse mode than selfetch mode of both adhesives. Conclusion. The bond strength of universal adhesives is not affected by the etching mode, however its durability was shown to be material dependent.

INTRODUCTION: The use of short implants has been introduced as an alternative treatment for posterior regions, however, it leads to serious prosthetic complications. Using CAD/CAM, materials like zirconia and Bio-HPP can be used to fabricate implant supported restorations. OBJECTIVES: This study aimed to evaluate and compare the strains developed around short and standard implant length using two different crown materials. MATERIALS AND METHODS: Polyurethane blocks (n=20) were used as alternative materials for human cancellous bone. Blocks were divided into two groups, group A received ten standard length implants 12 mm, and group B received ten short implants 7 mm. Each group was equally subdivided into two subgroups, according to crown material (BioHPP and zirconia). Universal testing machine was used to apply a load of 100 N axially and obliquely at 45° on the restorations. Microstrains were measured using strain meter. RESULTS: The difference in microstrain values between BioHPP and zirconia was statistically insignificant for both group A and group B. Comparing between group A and group B having the same restorative materials, it was found that, the difference was statistically significant for zirconia in axial loading only. A significant difference was observed between oblique and axial loads in standard implant length for both BioHPP and zirconia restorations, and for zirconia in short implants as well (p value=0.043), while the difference was insignificant for BioHPP in short implants. CONCLUSIONS: Short implants are comparable treatment modality to standard implant lengths for single tooth restoration. Oblique forces produce more stresses than vertical forces. According to the average of loads, there is no significant difference between BioHPP and zirconia for both short and standard implant length. However, it is advisable not to use zirconia restorations with short implants.

No abstract