Serum Vitamin D Status and Risk of Early and Late Dental Implant Failure: A Systematic Review of Multivariate-Adjusted Primary Studies with Explicit Vitamin D Cut-off Classification

ABSTRACT Statement of problem Dental implant failure remains a significant clinical concern, with early loss often attributed to impaired osseointegration. Recent research has considered the role of serum vitamin D in implant integration, yet the precise relationship between vitamin D status and implant loss, particularly when distinguishing early and late failures, is not fully established. Purpose The objective of this analysis was to evaluate the association between explicit serum vitamin D cut-off values and clinically confirmed dental implant failure, with a particular focus on differentiating early (pre-loading) from late (post-loading) failures. The review also sought to determine whether primary studies used multivariate adjustment for potential confounders. Material and methods The draft of this revision was registered in PROSPERO (CRD420251049631, https://www.crd.york.ac.uk/PROSPERO/view/CRD420251049631 ). A comprehensive literature search was conducted using AI-assisted tools to identify primary research studies, including randomized controlled trials and cohort studies, published in English, Spanish, French, German, or Italian. Eligible studies required explicit vitamin D threshold categorization, clinically verified implant loss, and clear differentiation of early and late failures. Data extraction included study design, vitamin D categorization, analytical methods, and outcomes. Results Identified studies predominantly consisted of retrospective and prospective cohorts examining early implant failures, frequently using cut-offs such as >30 ng/mL, 10–30 ng/mL, and