Immediate dental implant placement of occlusal restorations has garnered the interest of dentists and patients (De Bruyn et al., 2014, Strub et al., 2012). The main underlying reason for this trend is patient satisfaction due to a shorter treatment time and improved aesthetic aspects (Bahat and Sullivan, 2010, De Rouck et al., 2009, Misch et al., 2004). Indeed, clinical researches demonstrate that immediate loading prevents crestal bone loss and preserves the extracted socket (Becker et al., 1998). However, some studies have raised concerns regarding infection and the quality of soft-tissue closure or bony housing (Ibbott et al., 1993, Paolantonio et al., 2001, Rosenquist and Grenthe, 1996).

Different survival rates of immediate loadings ranging from 85 to 100 percent have been reported and compared with the gold standard tooth replacement strategy, namely delayed loading, for nearly two decades (Bali et al., 2019, Calandriello et al., 2003, Glauser et al., 2004). It has also been reported that delayed loading placements have survival rates ranging from 85 to 99 percent (Romanos et al., 2010). The delayed loading strategy (placing abutment and crown in occlusal contact at least three months post-surgery) is primarily based on achieving sufficient primary stability to ensure osseointegration (Bali et al., 2019). In contrast, it is asserted that recent advancements in certain role-playing factors, such as mechanical design, surface characteristics, and the clinician’s experience, are able to provide primary stability during the immediate loading (Romanos, 2009).

Osseointegration, a term used interchangeably in the literature for the secondary stability of dental implants, has been the subject of numerous histological or numerical studies. Some histological or histomorphometric studies indicate that immediately loaded cases have greater bone density and/or less average bone loss around the implant than delayed cases (Romanos, 2005, Romanos et al., 2002). The bone-to-implant contact, a functional measure of secondary stability, is better in the immediate loading strategy, resulting in more excellent osseointegration (Tumedei et al., 2020).

Besides the histological studies, numerical investigations have elucidated the post-insertion biological changes within the peri-implant site. Davis (2003) proposed employing mechanobiological models (Davies, 2003) that had previously been utilized exclusively for long bone fracture healing processes (Claes and Heigele, 1999, Gómez-Benito et al., 2005, Huiskes et al., 1997, Prendergast et al., 1997). Geris and her colleagues simulated the osseointegration around an implant using mechanobiological models of fracture healing in a bone chamber modeled experimentally in a rabbit tibia. They evaluated the effects of two cyclic micromovements during four weeks post-surgery and demonstrated the existence of cartilage and endochondral ossification. In addition, Geris and her colleagues demonstrated the feasibility of using mechanobiological models in a two-dimensional geometry due to their appropriate coincidence of the numerical and experimental outcomes (Geris et al., 2004, Geris et al., 2003).

Chou and Müftü (2013) simulated an immediately loaded dental implant using a mechanobiological model in order to investigate the role of micromovement amplitude and the gap size in the osteotomy cylinder. In addition, they utilized a two-dimensional axisymmetric model that included a callus space between the implant and the host bone (Chou & Müftü, 2013). Recently, Irandoust and Müftü (2020) added bone remodeling to the osseointegration simulation of an immediately loaded dental implant. The results demonstrated that the roots of threads receive less mechanical stimulation, resulting in possible bone resorptions, which compromise the overall secondary stability over the long term (Irandoust & Müftü, 2020).

In recent years, the literature on numerical simulations of osseointegration for dental implants appears to have expanded. Although some previous studies have utilized precise mechanoregulatory models, they assumed unrealistic geometry for the callus, the main region of these models. The extracted osteotomy site for the implant insertion is generally drilled using a smaller bit than the implant diameter. Hence, the oversized gaps between the implant and the host bone not only created exaggerated callus space for cellular evolutions but also eliminated the thread engagement between the bone and implant. This considerably changes the mechanical stress distribution through the callus.

Furthermore, a numerical investigation of the role of implant loading strategies in osseointegration is lacking in the literature. Therefore, this paper aimed to simulate the osseointegration of an inserted dental implant under immediate and delayed loadings using a mechanobiological model implemented by finite element analysis. It was hypothesized that the immediate loading strategy would provide comparable bony anchorage for the dental implants to the delayed loading strategy.