Acid resistance and bond strength of calcium-containing adhesive on enamel

Marginal sealing by enamel bonding is important to enhance the durability of the restoration and prevent secondary caries after operative procedure. This study aimed to evaluate the enamel acid resistance and bond strength of an experimental calcium-containing adhesive system.

All materials were provided by Kuraray Noritake Dental, Inc. (Tokyo, Japan). A calcium-containing primer (CaP) was formulated by blending 10% CaCl₂ into Clearfil SE Bond2 primer. The original primer (SEP) served as a control. Clearfil SE Bond2 Bond and Clearfil Protect Bond (PBB) were used as bonding agents. Human molar enamel was used for acid-resistance evaluation. After the adhesive was applied, a resin composite was built and light-cured. The samples were then subjected to an acid-base challenge and observed under scanning electron microscopy after 1 day and 3 months of storage. Mechanical strength was evaluated using microshear bond strength (microSBS) testing on bovine incisor enamel, with tests conducted 1 day after bonding (TC0) and after 5000 thermal cycles (TC5000). Statistical analysis was performed using two-way ANOVA and t tests (α = 0.05).

Acid-base resistant zones (ABRZs) formed in all groups, with thicker ABRZ formation in the CaP groups than in the SEP groups. A slope formation at the bottom of the outer lesion was noted in the PBB group. No morphological differences were found between the immediate and 3-month storage groups. The thermal cycling mode did not significantly affect the microSBS between the CaP and SEP groups.

The experimental calcium-containing adhesive system formed a thicker ABRZ on enamel without affecting the microSBS.

The study suggests that the experimental adhesive system enhances enamel acid resistance, forming a thicker ABRZ while maintaining bond strength, offering improved long-term protection against caries for clinical use.