Qualitative assessment of surface topography of XeCl laser etched Ni-Cr alloy.

OBJECTIVES: The aims of this study were to compare the mode of debonding (adhesive or cohesive) of laser-etched Ni-Cr alloy (Wiron 99) to a standard sandblasting technique, and to a combination of sandblasting and laser etching. The etched surfaces were examined using optical and electron microscopy techniques. METHODS: Five groups of randomly allocated Ni-Cr cylinders were prepared: Group I-sandblasted; Groups II-IV-laser etched at three fluences (3.0, 4.0 and 4.9 J/cm2), Group V-combination sandblasting and laser etching (4.0 J/cm2). Within groups specimens were bonded into pairs (N=8) with composite luting cement (Panavia 21) prior to tensile debonding. Optical and scanning electron microscopy were performed both prior to and following debonding. RESULTS: An oxide layer was observed on sample surfaces before surface preparation by lasing or abrasion. Sandblasting removed the oxidation layer, which low and medium laser fluences alone failed to fully ablate. The highest (4.9 J/cm2) laser fluence melted the surface of the Ni-Cr alloy, covering the oxidation layer. A combination of sandblasting and lasing at 4.0 J/cm2 allowed full removal of the surface oxidation layer due to abrasion, followed by roughening of the surface with the laser. This resulted in greater mean tensile debonding strengths [Murray, A, Attrill, D, Dickinson, M. Dent Mater, 2004, In press] and a tendency for cohesive rather than adhesive interface failures. Groups I-IV underwent partial adhesive failure at both surfaces. Group V, in the main, underwent cohesive failure with a layer of adhesive remaining on both surfaces. SIGNIFICANCE: Laser etching 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.

The effects of XeCl laser etching of Ni-Cr alloy on bond strengths to composite resin: a comparison with sandblasting procedures.

OBJECTIVES: The aim of this study was to determine the effect of laser surface treatment of Ni-Cr alloy on the tensile bond strength of a proprietary composite resin (Panavia 21) in comparison with a conventional sandblasting technique. METHODS: Eighty cylinders of Ni-Cr were randomly allocated into the following groups: Group I-sandblasting only; Group II-low laser fluence (3.0 J/cm(2)); Group III-medium laser fluence (4.0 J/cm(2)); Group IV-high laser fluence (4.9 J/cm(2)); Group V-sandblasting in combination with medium laser fluence (4.0 J/cm(2)). Specimens within groups were bonded into pairs with resin cement as per manufacturer's instructions. They were then de-bonded using a tensile test. RESULTS: The mean de-bond strengths (SD) were: Group I-13.1 (4.2)MPa; Group II-17.6 (5.8)MPa; Group III-25.7 (11.8)MPa; Group IV-22.6 (6.6)MPa; Group V-41.8 (13.2)MPa. A statistically significant improvement (Bonferroni, p<0.05) in bond strength was found for the specimens which had been both lased and sandblasted (Group V) compared to all other groups, including those which were only sandblasted. SIGNIFICANCE: Laser pre-treatment of Ni-Cr alloy increases bond strength to composite resin compared with sandblasting; laser pre-treatment in combination with sandblasting further increases the de-bond strengths.