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

Abstract

Objectives: To histologically evaluate peri-implant inflammatory responses associated with varying restorative emergence angles and to assess differences between buccal and lingual implant sites. Materials and methods: Six healthy male mongrel dogs received four bone-level implants (3.8 x 7 mm) per hemi-mandible in the posterior mandible. Customized abutments with standardized restorative angles of 20 degrees, 40 degrees, 60 degrees, and 80 degrees 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. Results: 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 degrees (20 degrees = 3%; 40 degrees = 6%) but increased sharply at 60 degrees (approximate to 10%) and 80 degrees (approximate to 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 degrees (20 degrees = 4%; 40 degrees = 3.1%), followed by a moderate rise at 60 degrees (approximate to 7%) and a pronounced increase at 80 degrees (approximate to 12%) (p < 0.001). When both aspects were analyzed together, significant angle-by-site interactions emerged at 40 degrees and 60 degrees, indicating a consistently higher inflammatory response on the buccal compared with the lingual side. Conclusions: Wider restorative emergence angles (> 40 degrees) are associated with increased peri-implant inflammatory cell infiltration, particularly at buccal sites. Clinical relevance: Wide restorative emergence angles (> 40 degrees) favor peri-implant inflammation, potentially compromising the long-term stability of peri-implant tissues.