Fluoride-releasing resin bonding of amalgam restorations in primary teeth: in vitro secondary caries effect

To evaluate the effects of a fluoride-releasing resin designed for amalgam bonding on secondary caries formation in primary teeth restored with amalgams.

Primary teeth with caries-free buccal and lingual surfaces were selected and underwent a fluoride-free prophylaxis. Cavity preparations were performed in the buccal and lingual smooth surfaces of 20 primary teeth. A fluoride-releasing dimethacrylate resin bonding agent (Alloybond) was placed prior to amalgam restoration (Dispersalloy) of the cavity preparations in 10 teeth. Amalgam restorations placed in 10 teeth following copal cavity varnish (Copalite) served as controls. The teeth were thermocycled in synthetic saliva (500 cycles, 5 degrees-50 degrees C), and then coated with an acid-resistant coating, leaving a 1mm rim of sound enamel surrounding the restorations. Artificial secondary caries were created (2.2 mM calcium, 2.2 mM phosphate, 50 mM acetic acid, 0.5 ppm fluoride, pH 3.90). Following lesion formation, longitudinal sections (five per tooth) were prepared for polarized light evaluation. Mean depths for the primary surface lesions were determined using a computer-interfaced digitized tablet. Cavity wall lesion frequencies were also evaluated. Comparisons were made between groups (ANOVA, DMR).

Primary surface lesion depth was reduced significantly (P < 0.05) with Alloybond-amalgams (135 +/- 14 microm) when compared with Copalite-amalgams (184 +/- 21 microm). Cavity wall lesion frequency was decreased (P < 0.05) significantly with Alloybond-amalgams (57%) compared with Copalite-amalgams (89%). The beneficial effect of the fluoride-releasing amalgam bonding agent was not limited to the cavosurface enamel. The caries susceptibility of enamel surfaces adjacent to amalgams with the fluoride-releasing bonding agent was decreased considerably. The incorporation of the amalgam-bonding resin with fluoride-releasing capabilities provided greater protection against a constant cariogenic attack over that for a conventional amalgam restoration.