Differences in Soft Tissue Wound Healing between Immediate and Delayed Implant Placement: An Experimental Preclinical In Vivo Investigation

The dynamics of tissue wound healing associated with dental implants placed in fresh extraction sockets or in healed alveolar ridges are not fully understood. Therefore, the aim of this preclinical in vivo investigation was to evaluate soft tissue healing and osseointegration after immediate implant placement, compared with delayed implant placement, using histomorphometric and immunohistochemical analyses. Methods: In 8 dogs, immediate postextraction implants and delayed implants were evaluated. After 2 and 8 weeks of healing, dissected tissue blocks were processed for calcified and decalcified histological analysis. Histometric measurements for soft tissue height and width were performed. Immunohistochemical analysis for the evaluation of bone metabolism, immune response and angiogenesis was performed. Results: At 2 weeks, histometric analysis showed that peri-implant soft tissue height was significantly greater in the immediate implant group (4.47 mm ± 0.78) compared to the delayed implant group (2.92 mm ± 0.51, p = 0.028), primarily due to the connective tissue height. Immunohistochemical analysis indicated significantly higher alkaline phosphatase (ALP) (6.85 ± 5.17 vs. 3.56 ± 2.31, p < 0.05) and matrix metalloproteinase (MMP2) activity (1.59 ± 1.64 vs. 0.58 ± 0.48, p < 0.05) in immediate implants, suggesting increased osteogenic and matrix metalloproteinase activity. At 8 weeks, the peri-implant soft tissue height remained higher in the immediate implant group (3.43 mm ± 0.83) compared to the delayed implant group (2.4 mm ± 0.37, p = 0.088), although the difference was less pronounced. Immunohistochemical differences between groups diminished in late healing stages. Conclusions: Soft tissue dimensions around immediate implants differ from those established around staged implants placed on healed alveolar ridges. Moreover, osseointegration dynamics around immediate implants may occur at a different rate compared with staged implants.