Effect of polymerization unit and support bar design on the trueness and fit of additively manufactured implant-supported complete-arch fixed frameworks: An in vitro study.

OBJECTIVE: This study evaluated the influence of polymerization units and support bar design on the trueness and fit of complete-arch implant-supported frameworks fabricated using digital light processing (DLP) additive manufacturing (AM) and compared their performance with a subtractively manufactured (SM) control. METHODS: A maxillary complete-arch framework was designed and fabricated using six conditions combining two polymerization units (xenon-flash light under nitrogen [XFN] and light-emitting diode [LED]) and three support bar designs (no-bar, Y-shaped bar, horizontal-bar), along with an SM reference framework (n = 10). Fabrication trueness was evaluated by analyzing surface deviations across predefined regions (overall framework, occlusal, non-occlusal, and abutment surfaces) and by measuring linear abutment-level and interimplant distance deviations using metrology software. Marginal gap, used as a fit indicator, was assessed using a digital triple-scan protocol. Test and control group differences were analyzed by one-way ANOVA (Dunnett), and those across AM groups by two-way ANOVA (Bonferroni; α = 0.05). RESULTS: Support bar design significantly influenced trueness (p < 0.001); no-bar frameworks generally demonstrated the highest trueness. The polymerization unit showed limited main effects on trueness, although a significant effect was observed for overall RMS (p = 0.024). For linear deviation, interimplant distance, and marginal gap, outcome-dependent polymerization unit × support bar design interactions were identified (p < 0.05). XFN polymerization yielded lower linear deviations at selected implant sites, whereas LED polymerization was associated with lower interimplant distance deviations and reduced marginal gaps at specific locations. CONCLUSIONS: Support bar design was the primary factor influencing dimensional trueness, with no-bar configurations generally demonstrating higher trueness. Polymerization unit effects were outcome- and geometry-dependent, with no consistent overall difference between XFN and LED. CLINICAL SIGNIFICANCE: Under the tested laboratory conditions, omitting support bars was associated with lower surface deviations in DLP-printed frameworks. However, the site- and geometry-dependent marginal gap findings do not establish a clinically preferable support or polymerization protocol and require mechanical and clinical validation.