OBJECTIVE: To evaluate the effect of the manufacturing trinomial (technology, printer, and resin) and preparation design on the fabrication and fit accuracy (trueness and precision) of additively manufactured (AM) resin-based overlays compared to subtractively manufactured (SM) overlays. METHODS: Six mandibular right first molar typodont teeth were prepared with varying designs: (A) 1 mm occlusal reduction, (B) 1.5 mm occlusal reduction, (C) B + contrabevel finish line, (D) B + chamfer finish line, (E) C + proximal box, and (F) D + proximal box. Overlays were fabricated using AM-IX (tilting stereolithography), AM-VS (digital light processing), or SM-EN and digitized for fabrication (overall, external, intaglio, marginal) and internal fit accuracy analyses. Data were analyzed with two-way analysis of variance and Bonferroni-corrected post-hoc tests (α = 0.05). RESULTS: The interaction between the manufacturing trinomial and preparation design affected fabrication accuracy of overall, external, and intaglio surfaces, and the precision of marginal surface deviations and average gaps (P ≤ 0.034). AM-IX overlays mostly had higher overall, external, and marginal fabrication accuracy, whereas SM-EN overlays mostly had lower accuracy across these surfaces (P ≤ 0.019). Preparation designs A, B, and C mostly led to lower overall, external, and intaglio surface trueness within SM-EN overlays (P ≤ 0.014). AM-IX overlays had the lowest and preparation design E led to the highest gaps (P ≤ 0.023). CONCLUSIONS: AM overlays fabricated with tilting stereolithography mostly had higher fabrication and fit accuracy. Increased axial preparation improved fabrication trueness but did not consistently enhance fit.