Tissue response to implants placed in contact with retained roots: a histology report after 10 and 12 weeks in the pig mandible

Purpose The biological responses of dental tissues to implants placed in contact with retained roots is poorly documented. The aim of this study is to present the histological findings of three implants that inadvertently came into contact with retained root fragments for periods of 10 and 12 weeks in the pig mandible. Materials and Methods Three implants were retrieved from a preclinical pig model in which fractured root remnants were unintentionally left following tooth extractions. Implants were placed after a three-month healing period; they were subsequently retrieved after 10 and 12 weeks. Histological analyses were performed using optical microscopy, polarized light microscopy, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) to characterize the tissue responses at the implant interface. Three distinct configurations of implant–root contact were observed: 1) an implant entirely embedded within a retained root composed of dentin and osteodentin; 2) an implant exhibiting apical contact with a retained root; and 3) an implant apex contacting debris from a fractured root. Results The implant fully embedded within the retained root displayed continuous contact with dentin and osteodentin, without any intervening soft tissue. Direct implant–dentin contact areas showed no evidence of cellular activity. In contrast, osteodentin displayed active modeling and remodeling along the implant surface in regions where space and microgaps were present between the implant and dental tissues. In the second and third cases, full osseointegration was achieved along the implant body despite apical contact with residual root tissues. Newly formed osteodentin was closely adapted to the implant apex, while the periodontal ligament that was present did not extend significantly onto the implant surface. Conclusions This report documents for the first time the histological response to an implant entirely embedded within a retained root. The findings show that implants can achieve a form of mineralized integration with dentin and osteodentin. Moreover, contact with non-infected root fragments does not appear to compromise osseointegration. These observations may have some clinical implications for implant placement strategies when encountering residual root fragments during surgery.