To investigate proximal contact loss and marginal bone resorption following delayed posterior implant restoration, and to analyze associated factors and their interrelationship.

This retrospective cohort study included 204 patients with 261 delayed posterior implant restoration units treated between January 2023 and January 2025. Restoration units were used as the analytical units. Proximal contact loss and mesiodistal marginal bone resorption (≥ 1.0 mm) were assessed during a median follow-up of 17.9 months [interquartile range ( IQR ): 14.7–21.8]. Generalized estimating equation (GEE) models were used to identify factors associated with both outcomes.

Among 261 units with a median follow-up of 17.9 months ( IQR : 14.7–21.8), the incidence of proximal contact loss was 40.6% (106/261), and marginal bone resorption ≥ 1.0 mm occurred in 30.7% (80/261) of units. In multivariable GEE models, compromised periodontal support of adjacent teeth was associated with proximal contact loss [odds ratio ( OR ) = 2.15, 95% confidence interval ( CI ): 1.21–3.82]. Proximal contact loss was independently associated with marginal bone resorption ≥ 1.0 mm ( OR  = 2.33, 95% CI : 1.28–4.23), and compromised periodontal support of adjacent teeth was also associated with marginal bone resorption ( OR  = 3.18, 95% CI : 1.76–5.74).

Proximal contact loss and marginal bone resorption were relatively common during mid-term follow-up after delayed posterior implant restoration. Proximal contact loss was associated with marginal bone resorption. Compromised periodontal support of adjacent teeth was associated with both outcomes. Shared underlying risk factors may contribute to this association; the retrospective design cannot establish causality.