Histological and immunohistochemical soft-tissue response to cylindrical and concave abutments: multicenter randomized clinical trial

Abstract

Background:This study aimed to analyze the influence of concave andcylindrical abutments on peri-implant soft tissue. Dimensions, collagen fiberorientation, and immunohistochemical data were assessed.Methods:A multicenter, split-mouth, double-blind randomized clinical trialwas conducted. Two groups were analyzed: cylindrical abutments and concaveabutments. After a 12-week healing period, peri-implant soft tissue samples werecollected, processed, and evaluated for dimensions, collagen fiber orientation,and immunohistochemical data. Inflammatory infiltration and vascularizationwere assessed, and the abutment surfaces were analyzed using scanning elec-tron microscopy. The statistical analysis was performed using the SPSS version20.0 statistical package.Results:A total of 74 samples in 37 patients were evaluated. Histologicalevaluation of peri-implant soft tissue dimensions revealed significant differ-encesbetweenconcaveandcylindricalabutments.Concaveabutmentsexhibitedgreater total height (concave: 3.57±0.28 – cylindrical: 2.95±0.27) and bar-rier epithelium extension (concave: 2.46±0.17 – cylindrical: 1.89±0.21)(p<0.05),whilethesupracrestalconnectivetissueextension(concave:1.11±0.17– cylindrical: 1.03±0.16) was slightly greater (p>0.05). Collagen fiber ori-entation favored concave abutments (23.76±5.86), with significantly moretransverse/perpendicular fibers than for cylindrical abutments (15.68±4.57).The immunohistochemical analysis evidenced greater inflammatory and vascu-lar intensity in the lower portion for both abutments, though concave abutmentsshowed lower overall intensity (concave: 1.05±0.78 – cylindrical: 1.97±0.68) (p<0.05). The abutment surface analysis demonstrated a higher percentage oftissue remnants on concave abutments (42.47±1.32; 45.12±3.03) (p<0.05).Conclusions:Within the limitations of this study, concave abutments pre-sented significantly greater peri-implant tissue height, linked to an extendedbarrier epithelium, versus cylindrical abutments in thick tissue phenotype.This enhanced soft tissue sealing, favoring a greater percentage of transverselyoriented collagen fibers. The concave design reduced chronic inflammatoryexudation with T and B cells, thus minimizing the risk of chronic inflammation.