Mechanical behavior of repaired resin composites, zirconia, and hybrid ceramics fabricated by additive and subtractive manufacturing technologies: An in vitro study

The aim of this study was to evaluate the effects of substrate material and repair composite on surface wettability, shear‐bond strength (SBS), and interfacial stress distribution of direct repairs to digitally fabricated restorations. One hundred and twenty disk‐shaped specimens (Ø 10 × 2 mm) were divided into six substrate groups (n = 20): two additively manufactured resin composites (Crowntec, C; NextDent C&B, ND), two printed zirconias (LithaCon 3Y‐TZP, LI; INNI‐Cera 3Y‐TZP, IN) and two subtractively manufactured ceramics (Vita Enamic PICN, EN; IPS e.max ZirCAD MT, IPZ). Each group was repaired with either a microhybrid (Clearfil Majesty Esthetic, CL) or a nanofilled composite (Filtek Z350 XT, FZ; n = 10). Contact angles were measured post-conditioning via sessile drop. Specimens were thermocycled, then SBS was evaluated at 0.5 mm/min. Two-way ANOVA with Tukey post-hoc (α = 0.05) analyzed angle and SBS. Finite element analysis of a 200 N shear load mapped interfacial stress distributions. Contact angles ranged from 58.5 ± 6.1° (IN–FZ) to 71.2 ± 7.7° (C–CL), with significant effects of substrate ( p = 0.018), composite ( p = 0.041), and their interaction ( p = 0.036). SBS was highest on IN (CL: 26.9 ± 4.0 MPa; FZ: 28.5 ± 3.6 MPa) and lowest on C (15.0 ± 2.0 MPa; 15.2 ± 1.8 MPa; p < 0.05). FZ tended toward higher SBS than CL, although within-substrate differences were non-significant. FEA revealed that FZ repairs produced more centralized tensile‐stress cores than CL repairs, and stiffer substrates (IPZ) showed higher compressive stresses. Both substrate and composite type significantly influence wettability, shear-bond strength, and interfacial stress distribution. Nanofilled composites paired with MDP‐based adhesives optimize repair performance on ceramic substrates.