Purpose: To investigate the influence of uremia on the shear bond strength (SBS) of composite resin to enamel and dentin substrates with assessment of the micromorphological pattern of etched enamel and dentin surfaces using atomic force microscopy (AFM). Materials and Methods: A total of 44 natural molars was collected from healthy individuals (n = 22 molars) and uremic patients (n = 22 molars). Each set of teeth was then divided into 2 equal subsets (n = 11 molars) relative to the bonding substrate to be tested. In each subset, the surfaces of 7 molars were flattened and polished up to 2000-grit roughness using wet silicon carbide (SiC) abrasive papers. A three-step adhesive was used to bond Tetric Ceram composite buildups to the prepared tooth surfaces. All specimens were thermocycled before they were stressed in shear using a universal testing machine. Fractured specimens were stereomicroscopically examined to detect the mode of bond failure. In the remaining 4 molars, enamel and dentin specimens were prepared for AFM examination to assess the micromorphological patterns of acid-etched surfaces. Results: The mean bond strength values in MPa to enamel (22.40 ± 4.30) and dentin (17.97 ± 4.65) of teeth of healthy individuals were significantly different (p < 0.001) from those to enamel (12.40 ± 2.81) and dentin (7.83 ± 2.05) of teeth of uremic patients. Most of the tested enamel specimens showed a mixed type of bond failure, but the adhesive type was predominant with dentin specimens. AFM examinations revealed a shallow etching pattern for uremic enamel and dentin specimens compared to those of healthy individuals. The mean roughness average (Ra) values after etching of healthy enamel (238.0 ± 4.65) and dentin (267.0 ± 4.79) were significantly different (p < 0.001) from those to etched uremic enamel (111.0 ± 5.24) and dentin (143.0 ± 2.16). Conclusion: Uremia adversely affects bonding of composite resin to enamel and dentin and confers an altered micromorphological etching pattern.
Keywords: uremia, resin composite, shear bond strength, enamel and dentin, acid-etch pattern