Purpose of Review <p>The position of full-crown preparation margins remains a critical topic of debate. While subgingival margins are occasionally necessary for aesthetic or functional reasons, they have been linked to increased gingival inflammation, deeper probing depths and potential clinical attachment loss. This review aimed to evaluate the influence of subgingival versus supragingival crown margin position on periodontal parameters in adult patients.</p> Recent Findings <p>Electronic and grey literature searches identified analytical and interventional human studies comparing periodontal outcomes—such as probing depth, bleeding on probing (BoP), and gingival recession—between subgingival and supragingival /equigingival crown margins or intact teeth. The quality of evidence was assessed using the GRADE approach. Data were pooled using a random-effects model, and an Analytic Hierarchy Process (AHP) framework was applied to rank the impact of crown margin position on periodontal health. Twenty-three studies (<i>n</i> = 1,725 participants; 5,615 teeth/surfaces) met the inclusion criteria. Risk of bias was low in 7 studies, moderate in 12, and high in 4. Meta-analysis revealed significantly greater probing depth (mean difference: 0.57&#xa0;mm; 95% CI: 0.44–0.70) and higher gingival index scores (mean difference: 0.44; 95% CI: 0.16–0.71) at subgingival crown margins, with no significant difference in plaque index. The AHP analysis confirmed a greater periodontal impact of subgingival margins, particularly concerning gingival inflammation. Certainty of evidence was graded as low for probing depth and very low for gingival and plaque indices.</p> Summary <p>Current evidence suggests that subgingival full-crown margins are associated with increased gingival inflammation and greater probing depths. Whenever feasible, supragingival crown margins should be preferred to promote long-term periodontal health.</p>