Qualitative Enhancement of the Tooth–Filling Interface Using Cold Atmospheric Plasma

<b>Objective</b>: To evaluate the effects of cold atmospheric plasma (CAP) on adhesive bonding in Class II composite restorations in vitro. <b>Methods</b>: Forty-eight standardized Class II cavities were assigned to six groups (<i>n</i> = 8), varying in phosphoric acid conditioning, CAP treatment (1.5 W or 3 W), composite filling, and thermo-mechanical loading (TML). Evaluations included dye penetration, adhesive layer morphology, resin tag length, and hybrid layer thickness. <b>Results</b>: CAP combined with phosphoric acid (H₃PO₄) significantly increased hybrid layer thickness and resin tag length (<i>p</i> < 0.006). The lowest dye penetration was observed in Groups 1 and 4. <b>Conclusions</b>: CAP in combination with phosphoric acid improved the adhesive interface in Class II cavities. CAP alone showed limited benefits, and higher power levels may negatively affect bonding.