Objectives: To determine the effect of laser surface treatment on the mode of debonding (adhesive or cohesive) of Ni-Cr alloy (Wiron 99) in comparison to conventional sandblasting techniques.

Methods: Eighty Ni-Cr cylinders were randomly allocated into 5 groups: Group I – sandblasted; Group II – low laser fluence (3.0 J/cm2); Group III – medium laser fluence (4.0 J/cm2); Group IV – High laser fluence (4.9 J/cm2); Group V – combined sandblasting and medium laser fluence (4.0 J/cm2). Optical and scanning electron microscopy was performed up to a magnification of x1000. Specimens within groups were bonded into pairs with a composite luting cement (Panavia-21) as per manufacturer's instructions prior to tensile debonding. Following bond failure further images were taken of the debonded surfaces.

Results: Low and medium laser fluences alone failed to fully ablate the oxidation layer - in places a crystalline layer remained. The highest laser fluence (group IV) melted the surface of the Ni-Cr cylinders, covering the oxidation layer. A combination of sandblasting and lasing allowed for full removal of the surface oxidation layer due to abrasion followed by roughening of the surface with the laser. The higher tensile bond strength of Group V (Attrill et al.) is reflected in the method of bond failure. Groups I – IV underwent partial adhesive failure at both surfaces. For lased surfaces often the treated surface was removed with the adhesive, exposing untreated alloy. Group V, in the main, underwent cohesive failure with a layer of adhesive remaining on both surfaces.

Conclusions: Laser pre-treatment of Ni-Cr alloy in combination with sandblasting optimises bonding to composite luting agents, resulting in a high proportion of cohesive failures when compared to sandblasting or lasing alone. This study supports the possibility of laser etching of non-precious metal surfaces to enhance bonding.

Project funded by Engineering and Physical Science Research Council grant.

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