Adhesive systems and secondary caries formation: Assessment of dentin bond strength, caries lesions depth and fluoride release

Abstract 

Objectives

The present study evaluated the microtensile bond strength and caries formation on adhesive/dentin interfaces before and after dynamic chemical formation of secondary caries.

Methods

Restorations were prepared on the dentin surface of 80 bovine incisors using four adhesive systems: two fluoride-free (Single Bond and Clearfil SE Bond) and two fluoride containing (Optibond Solo Plus and Clearfil Protect Bond). The restored teeth were then sectioned into multiple slabs that were further trimmed at the bonded interface to a cross-sectional area of 1mm². Half of the slabs were subjected to secondary caries formation using a pH cycling model (treated groups); while the other half was used as the control group (no pH cycling). The specimens designated for bond strength evaluation were subjected to microtensile bond strength test (μTBS). Caries lesions formation was assesses by polarized light microscopy at different depths from the adhesive–dentin bonded interface. The fluoride ion concentration was evaluated using the de/remineralization solutions (De/Re).

Results

No differences in μTBS were observed among the adhesive systems in both the control and treated conditions. Secondary caries significantly reduced the values of μTBS for all adhesives (p<0.05). Optibond Solo Plus presented the lowest caries formation at 5μm depth. Fluoride concentrations present in the De/Re were less than 0.03ppm, regardless of the adhesive system tested.

Significance

Bond strength values significantly decreased after in vitro secondary caries formation. Fluoride present in adhesive systems is not capable of inhibiting secondary caries or maintaining bond strength values following caries formation.

Keywords: Fluoride releasing materials, Microtensile bond strength, In vitro secondary caries, Depth of caries formation