3D Printing Techniques and Digital Workflow Integration in Orthodontics: A Systematic Review of Accuracy, Clinical Protocols, and Quality Assurance

Background: Three-dimensional (3D) printing has significantly transformed orthodontic practice by enabling digital workflows that enhance precision, efficiency, and treatment personalization. However, no comprehensive systematic review has synthesized open-access evidence on accuracy, clinical protocols, and quality assurance across all orthodontic applications. Objectives: This systematic review aims to: (1) evaluate the accuracy of 3D-printed orthodontic models compared to conventional methods; (2) assess factors affecting print accuracy across different technologies; (3) synthesize evidence for direct-printed aligners versus thermoformed aligners; (4) evaluate accuracy of 3D-printed surgical guides; and (5) identify quality assurance protocols and their impact on clinical outcomes using only open-access literature. This approach enhances reproducibility and ensures accessibility of evidence for clinicians in resource-limited settings. Methods: This systematic review was conducted following PRISMA 2020 guidelines. Due to the rapid evolution of digital orthodontic technologies and the focused scope on open-access literature, the review protocol was finalized prior to registration. Measures to ensure transparency and methodological rigor were implemented throughout the review process. Electronic searches were performed in PubMed/MEDLINE (with free full text filter), Directory of Open Access Journals (DOAJ), and Google Scholar from January 2015 to January 2026. The search strategy combined controlled vocabulary and keywords related to orthodontics, 3D printing, and workflow techniques. Only open-access, freely available peer-reviewed literature was included. Study selection, data extraction, and risk-of-bias assessment were performed independently by two reviewers. The Cochrane Risk of Bias tool (RoB 2) was used for randomized controlled trials, ROBINS-I for non-randomized studies, and a customized tool for in vitro studies. Certainty of evidence was assessed using GRADE. Results: The search identified 214 records from open-access sources. After removing 28 duplicates, 186 records were screened, 94 full-text articles were assessed, and 82 studies met inclusion criteria. Included studies comprised 18 randomized controlled trials (22.0%), 24 prospective cohort studies (29.3%), 31 in vitro accuracy studies (37.8%), and 9 systematic reviews (11.0%). Meta-analysis of 6 studies with low risk of bias showed pooled mean difference of 0.22 mm (95% CI: 0.09–0.36 mm) between 3D-printed models and plaster standards. PolyJet and SLA technologies demonstrated superior accuracy. Direct-printed aligners showed comparable dimensional accuracy to thermoformed aligners (mean difference 0.08 mm, 95% CI: -0.02–0.18 mm) but lacked long-term clinical data. Surgical guides achieved mean linear deviations of 0.81 mm (95% CI: 0.62–1.00 mm) for orthognathic surgery and 0.47 mm (95% CI: 0.32–0.62 mm) for TAD placement. Quality assurance protocols reduced printing errors by 30–40%. GRADE assessment indicated moderate certainty for model accuracy outcomes and low certainty for direct-printed aligner outcomes. Conclusions: Current open-access evidence supports the clinical acceptability of 3D-printed orthodontic models and surgical guides. Direct-printed aligners represent an emerging technology requiring further clinical validation. Standardized protocols for parameter optimization, post-processing, and quality assurance are essential for consistent outcomes. The availability of reliable open-access evidence supports evidence-based orthodontic practice globally, particularly in low- and middle-income settings where subscription access may be limited. Future research should prioritize randomized controlled trials for emerging applications and long-term clinical outcomes. PROSPERO Registration: Not registered