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Abstract
The present study was conducted to compare in vitro between the use of Consepsis V (Chlorhexidine cavity disinfectant) prior to Clearfil SE Bond and the use of the new antibacterial adhesive system Clearfil Protect Bond alone regarding their antibacterial effect against Streptococcus mutans, in addition to their microleakage, shear bond strength and fracture mode pattern.
A- Microbiology Test:
Specimens from coronal carious lesions were taken by means of a sterile sharp excavator and then transported to the laboratory to be promptly inoculated on Mitis-Salivarius agar plates for isolation of Streptococcus mutans. Colonies proved to be Streptococcus mutans were inoculated and cultivated in Brain Heart Infusion (BHI) broth. After incubation for 24 hrs bacterial suspension (stock solution) was obtained.
Twelve BHI agar plates were prepared according to manufacture’s instructions and standardized wells with a diameter of 6 mm were punched into the agar with a blunt end of a sterile Pasteur pipette. Approximately 0.5 ml of Streptococcus mutans suspension was inoculated by swabbing over the agar surface and the test material Clearfil Protect Bond primer (single- bottle self-etching primer solution with the antibacterial monomer (MDPB), Concepsis V (Chlorhexidine antibacterial solution) and Clearfil SE Bond primer (single-bottle self-etching primer solution) were filled in the wells and tested separately. After 48 hours of incubation, the diameter of circular inhibition zones produced around the materials was measured using a caliper. The test was repeated twelve times for each material.
B- Microleakage Test:
A total of sixty extracted caries-free permanent human premolars stored in normal saline were used in this study. After class V preparation on the facial surface of the test specimens, they were randomly divided into three groups, according to the mode of dentin surface treatment and bonding agent used:
• Group I: using Clearfil Protect Bond.
• Group II: using Concepsis V (chlorohexidine) to disinfect the cavity followed by Clearfil SE Bond.
• Group III: using Clearfil SE Bond without surface disinfection.
Restored teeth were stored in distilled water for 2 weeks. During this time they were thermocycled in a thermocycling machine, 1000 cycles between 5°C and 55 °C with a dwell time of 15 seconds at each temperature. Then they were immersed in 0.5 % aqueous basic fuchsin dye for 24 hours. After immersion, the specimens were then sectioned longitudinally (buccolingually) through the center of the restoration. Each tooth half obtained was evaluated using a stereomicroscope and scored from 1 to 4 depending on the extent of dye penetration for the occlusal and the gingival walls separately.
Scoring system used:
• 1= no leakage
• 2= penetration to ½ of the distance from the cavosurface to the axial surface
• 3= penetration more than ½ of the distance from the surface to the axial wall
• 4= penetration along the axial wall
C- Shear Bond Strength Test:
A total of Forty-five caries-free permanent molars prepared in forty-fives acrylic molds were used in this study. They were divided into three groups, of fifteen specimens each, according to the dentin surface treatment and the adhesive system used to adhere composite to dentin:
• Group I: using Clearfil Protect Bond.
• Group II: using Concepsis V (chlorohexidine) to disinfect the surface followed by Clearfil SE Bond.
• Group III: using Clearfil SE Bond without surface disinfection.
The specimens were obtained by fabrication of cylindrical acrylic molds with molar teeth crowns embedded in them, with their occlusal surfaces facing upwards.
The shear bond strength of all specimens was determined using the universal testing machine. The load was applied perpendicular to the composite-tooth interface at a crosshead speed of 0.5 mm/minute. The force was applied until de-bonding occurred giving the maximum load (failure load that the specimen could withstand until failure occurred). This load was recorded from the screen in Kilograms to be the failure load divided by the surface area of the bonded surface, giving the shear bond strength in Kg/cm2
The maximum load that the specimen could withstand until failure will be determined and shear bond strength values will be calculated by dividing the load of failure to the surface area of bonding and expressed in Kg/cm².
Shear bond strength (Kg/cm²) = Failure Load (P) Kg / Surface area (A) (cm²)
Then these values were converted to MPa using the following equation: MPa =Kg /cm² × 0.09807
After testing the shear bond strength, the fracture sites were viewed by a stereomicroscope to determine if the mode of bond failure was:
• Adhesive
• Cohesive
• Mixed adhesive cohesive
The results of these tests showed the following:
1) The difference in inhibition zone among the three materials was statistically significant.
2) The differences in microleakage scores between occlusal and gingival walls in groups I and II were statistically significant. However, the difference between occlusal and gingival walls in group II was not statistically significant. In addition, differences in microleakage scores between every two groups were statistically significant in all cases except between groups I and III in gingival wall.
3) Comparison of shear bond strength among the three groups showed that, statistically significant differences existed between all groups except between groups I and III.
4) Only adhesive and mixed modes of fracture were observed in the three groups. A significantly greater percent of specimens (100%) had mixed mode of failure in group I compared to the percent of specimens with the same mode of fracture in groups II and IIII (60%).