Effect of Limonene on the Bond Strength of a Universal Adhesive System to Caries-Affected Dentin

This study aimed to evaluate the effect of limonene (LIM) on the bond strength of a universal adhesive system in self-etch mode to caries-affected dentin (CAD).

Class I cavities were prepared in eighty sound human molars and divided into four groups (n = 20): Sound dentin (SD), SD + LIM (SD treated with LIM), CAD, and CAD + LIM (CAD treated with LIM). Following pH cycling, two layers of a universal adhesive system (Single Bond Universal, 3MESPE) were applied. After restoration (Filtek Z350, 3MESPE), samples were sectioned into 0.9 mm² sticks and stored in distilled water at 37°C for 24 h and 6 months. Subsequently, sticks were subjected to microtensile bond strength testing. Data were analyzed using 2-way ANOVA and Bonferroni's test (p < 0.05). Fracture patterns were examined under optical and scanning electron microscopes.

After 24 h, SD + LIM showed lower bond strength than CAD but remained higher than CAD + LIM. CAD + LIM exhibited the lowest bond strength, regardless of aging. In SD + LIM, widened dentinal tubules were observed, accompanied by resin tags. In CAD + LIM, disorganized and unprotected collagen fibrils were identified, with fewer resin tags.

Limonene decreased the bond strength of the universal adhesive system in self-etch mode to caries-affected dentin.

Limonene as a pretreatment in self-etch adhesive protocols shows potential for enhancing the durability of adhesive restorations on sound dentin. However, its use on caries-affected dentin could compromise adhesion, highlighting the need for careful consideration when applying it to compromised substrates.