Peri-Implant Inflammation Varies With Different Restorative Emergence Angles: An Histological Evaluation

To histologically evaluate peri-implant inflammatory responses associated with varying restorative emergence angles and to assess differences between buccal and lingual implant sites.

Six healthy male mongrel dogs received four bone-level implants (3.8 × 7 mm) per hemi-mandible in the posterior mandible. Customized abutments with standardized restorative angles of 20°, 40°, 60°, and 80° were immediately connected. After 24 weeks, all implants were retrieved for histological processing and quantitative analysis of inflammatory cell infiltration within three defined peri-implant soft tissue regions. A linear mixed-effects model was used to compare the groups to account for within-subject correlations.

Histological sections were obtained for all specimens (N = 48). Inflammatory cell counts increased progressively with wider restorative angles, demonstrating a significant dose-dependent relationship (p < 0.001). At buccal sites, inflammation remained low up to 40° (20° = 3%; 40° = 6%) but increased sharply at 60° (≈10%) and 80° (≈13%) (p < 0.001), indicating a threshold beyond which wider emergence angles markedly intensified the inflammatory response. Lingual sites exhibited a similar, though less pronounced pattern. Values were stable up to 40° (20° = 4%; 40° = 3.1%), followed by a moderate rise at 60° (≈7%) and a pronounced increase at 80° (≈12%) (p < 0.001). When both aspects were analyzed together, significant angle-by-site interactions emerged at 40° and 60°, indicating a consistently higher inflammatory response on the buccal compared with the lingual side.

Wider restorative emergence angles (> 40°) are associated with increased peri-implant inflammatory cell infiltration, particularly at buccal sites.

Wide restorative emergence angles (> 40°) favor peri-implant inflammation, potentially compromising the long-term stability of peri-implant tissues.