Shear Bond Strength of a Light-Cured and a Dual-Cured Universal Adhesive to Primary and Permanent Dentin: An In Vitro Study

The aim of the study was to evaluate the immediate and aged shear bond strength (SBS) of a dual-cured and a light-cured universal adhesive to primary and permanent dentin. Twenty caries-free primary molars and twenty permanent third molars were selected and sectioned to expose mid-coronal dentin. Specimens were assigned to four groups (n = 10) according to dentition type and adhesive agent used: Group 1—primary teeth/Scotchbond Universal; Group 2—permanent teeth/Scotchbond Universal; Group 3—primary teeth/Futurabond U; and Group 4—permanent teeth/Futurabond U. Two resin micro-rods were fabricated and bonded with the same adhesive on each specimen. The SBS test was applied after 24 h (first micro-rod) and after thermocycling (second micro-rod). Failure modes were assessed under an optical microscope and scanning electron microscopy. Shear bond strength was significantly higher in permanent teeth than in primary teeth (p < 0.001). No statistically significant differences were found between the two adhesives (p = 0.194). Adhesive failures predominated across all groups. Both adhesives exhibited comparable SBS to primary and permanent dentin. These findings support the suitability of both universal adhesives for the restoration of primary and permanent teeth, though long-term clinical studies are warranted.