Space changes after premature loss of mandibular second primary molars: a systematic review and meta-analysis

Background Deciduous dentition plays a crucial role in mastication, phonetics, and maintaining arch space for permanent successors. While several systematic reviews have quantified spatial changes following first primary molar loss, specific evidence synthesis for second primary molars is lacking. This systematic review and meta-analysis aimed to quantify space loss following premature extraction of second primary molars and evaluate the clinical necessity of space maintenance. Methods Five electronic databases (PubMed, Web of Science, LILACS, EMBASE, and Cochrane libraries) were searched without date restrictions (last search 03/06/2025). Inclusion criteria included randomized, quasi-randomized, and non-randomized clinical trials involving children aged 4–9 years with second primary molar indicated for extraction. Two independent investigators assessed studies for inclusion, evaluated risk of bias using ROBINS-I tool, and extracted data. Random-effects models with 95% confidence intervals calculated mean differences as effect measures. Results Four studies were included in qualitative synthesis, with three studies involving 38 children included in meta-analysis. Meta-analysis demonstrated mean mandibular space loss of 0.80 mm (95% CI: -1.00 to -0.60; p < 0.0001) at 3 months, 1.10 mm (95% CI: -1.24 to -0.96; p < 0.0001) at 6 months, and 1.24 mm (95% CI: -1.48 to -1.02; p < 0.0001) at 9–10 months post-extraction. Arch hemi-perimeter decreased by 1.06 mm (95% CI: -1.26 to -0.31; p = 0.001) at 6 months. Conclusions Current limited short‑term evidence suggests that premature mandibular second primary molar loss in children with erupted first permanent molars results in mean space loss of approximately 1.24 mm over 9‑10 months. Whether this short‑term space loss translates into long‑term malocclusion or orthodontic treatment need remains unknown. Therefore, clinical decisions regarding space maintenance should remain individualized and based on arch length discrepancy, occlusal development, crowding, molar relationship, and long‑term orthodontic risk. The current evidence is insufficient to support routine space maintainer use. Maxillary arch evidence is too limited to support any conclusion. Protocol registration PROSPERO CRD42025640491.