INFLUENCE OF BLEACHING ON COLOUR AND SURFACE ROUGHNESS, AND MIRCOSHEAR BOND STRENGTH OF REPAIR, FOR NOVEL HYBRID CERAMIC

Objective: This study investigated the effect of bleaching on the colour, surface roughness,
and microshear bond strength of repair composite to a hybrid ceramic material, CERASMART.
Methods: This study was conducted in two parts; first effect of bleach on the colour and surface roughness, secondly effect of bleaching on mirco-shear (µSBS) bond strength. 8 Plate specimens of a CAD/CAM hybrid ceramic (CERASMART, GC) were cut using isomet saw (Beuhler, Germany). To assess colour (ΔE) and surface roughness (Ra) (n= 6) were used; and to assess microshear bond strength (µSBS) 18 specimens were prepared; (n=9) composite micro-cylinders were bonded each to an unbleached and bleached CERASMART plate. Colour and surface roughness were evaluated before, and after bleaching. A spectrophotometer was used to assess colour, surface roughness was assessed using a digital microscope at 120X magnification and an image software were analyzed using WSxM software. MicroShear bond strength (µSBS) was tested in a universal testing machine at a crosshead speed of 0.5 mm/min, using orthodontic wire loop (0.014” in diameter) wrapped around the bonded micro-cylinder. Failure modes were investigated with a digital camera at 35X. Data were analyzed with Test with α = 0.05.
Results: (ΔE1.54) was more than 1 and less than 2. Mean (Ra) values were [0.2516 ± 0.0024µm] for unbleached, and [0.2511 ± 0.0025µm] for bleached, showing no statistically significant difference between resultant (Ra) values. Mean microshear bond strength (µSBS) values showed [19.6 ± 5.2 MPa] for unbleached, and [20.1 ± 3.7MPa] for bleached, showing no statistically significant difference between resultant (µSBS). Failure modes were predominately mixed (combined adhesive and cohesive in the repair material).
Conclusion: Bleaching did not affect the repair potential of CERASMART material. Colour was affected however, it is not clinically perceptible. Bleaching did not affect surface roughness.
Clinical implications repair can be safely performed on bleached hybrid ceramic, even immediately after bleaching without influencing the bond strength.