Penetration of bonding resins into fibre‐reinforced composite posts: a confocal microscopic study

Abstract

To compare the penetration of two different bonding resins applied for different contact times, on glass reinforced-reinforced composite root canal posts showing an interpenetrating polymer network (IPN) or cross-linked polymer matrix. The research hypothesis was that the bonding resins were equally able to penetrate into the IPN post whereas less penetration was evident into the cross-linked post. In addition, the prolonged contact time of the bonding resin on the surface of post was assumed to increase the resin penetration. A total of 36 posts, comprising 18 IPN posts (everStick Post) and 18 cross-linked posts (C Post Millennium) were divided into 12 groups of three posts. All posts had a diameter of 1.2 mm. Both bonding resins (Scotchbond Multi Purpose Plus and Stick Resin) were labelled with Rhodamine B for determination of the resin penetration into the post. After contact times of 1, 30 and 300 s the bonding resins were light cured for 60 s. Penetration of bonding resins into three sections of each post was measured by confocal scanning light microscope. The influences of post and type of adhesive resin on resin diffusion into the polymer matrix of the post were assessed by nonparametric methods. For C Post Millennium and for 1 s contact time, no penetration of bonding resins into the polymer matrix of posts occurred in any section of any post. For the everStick Post, penetration was always noted after 300 s contact (mean 22.8 microm) and nearly always after 30 s contact (mean 3.5 microm), with very little difference between the two adhesives. The degree of penetration into everStick Posts was invariably greater after 300 s contact than after 30 s (P < 0.001). Both sets of results were highly significantly greater than the zero penetration recorded using C Post Millennium or 1 s contact time (P < 0.001). The ability of bonding resins to penetrate into everStick Post with IPN polymer matrix may give the opportunity to establish a good link between fibre-reinforced composite posts, luting cements and composite cores.