Why does digitally predicted tooth movement fail? the biology-digital mismatch in orthodontics: a critical narrative review.

Digital orthodontics has advanced through intraoral scanning, CAD/CAM, virtual planning, and clear aligners; however, discrepancies remain between predicted and actual tooth movements. This narrative review critically examined the biological and biomechanical factors underlying the limited predictability of digitally planned orthodontic treatment. A structured literature search of PubMed, Scopus, and Google Scholar was conducted and peer-reviewed articles were critically analyzed. Current digital systems primarily operate on geometric and algorithm-based models that assume linear and standardized tooth movements, whereas actual orthodontic tooth movements are governed by nonlinear biological processes, including periodontal ligament remodeling, bone turnover, mechanotransduction pathways, and substantial patient-specific variability. Clinical evidence shows a lower predictability for torque, extrusion, intrusion, and rotation than for tipping and expansion. The limitations of biomechanical models, force decay, and tracking loss are discussed along with AI applications in treatment planning. Future progress will require the integration of biological profiling, adaptive biomechanics, and AI-driven systems to enhance precision and manage patient expectations.