Effect of dentin conditioners on wet bonding of 4-META/MMA-TBB resin

By altering either ferric chloride concentration in 10% citric acid (1% ferric chloride = 10-1; 5% ferric chloride = 10-5; 10% ferric chloride = 10-10) or conditioning periods with an aqueous mixture of 1% citric acid and 1% ferric chloride (1-1), the influence of dentin substrate on bond strength and hybridized dentin in wet bonding of 4-META/MMA-TBB resin was examined.

Dentin surfaces of fresh bovine incisors were conditioned either with 10-1, 10-5, or 10-10 mixtures for 10 s (10-1-10s, 10-5-10s, 10-10-10s groups) or with a 1-1 mixture for 5, 10, 30 or 60 s (1-1-5s, 1-1-10s, 1-1-30s, 1-1-60s groups). Rinsed, demineralized dentin samples were kept wet, primed with 5% 4-META in acetone for 60 s, and bonded with 4-META/MMA-TBB resin. Bonded specimens were trimmed to a mini-dumbbell shape for tensile testing. The cross sections of bonded specimens were modified with HCl and NaOCl in order to assess the hybrid layer. The fractured surfaces of specimens and the hybridized dentin were investigated with SEM.

No significant difference (p > 0.01) in tensile strength was identified between 10-1-10s and 10-5-10s groups (30 MPa), 10-10-10s and 1-1-5s groups (15 MPa), and the three groups conditioned by 1-1-10s, -30s and -60s (40 MPa). The thickness of the hybrid layer increased with increasing either ferric chloride or conditioning periods.

The concentration of ferric chloride in 10% citric acid for wet bonding must be less than 5% in order to provide a reliable bond. When applied from 10 to 60 s, the 1-1 conditioner provided hybridized dentin with reliable tensile bond strength. The thickness of the hybrid layer did not influence the tensile bond strength.