Abstract
The purpose of this research is to study the biomechanical response of dental implants in bone-level type locations, 0.5 mm above and below the bone level. In addition, the influence of the thickness of the cortical bone on osseointegration is determined due to the mechanical loads transfer from the dental implant to the cortical and trabecular bone. The thicknesses studied were 1.5 mm and 2.5 mm. Numerical simulations were performed using a finite element method (FEM)-based model. In order to verify the FEM model, the in silico results were compared with the results obtained from a histological analysis performed in an in vivo study with 30 New Zealand rabbits. FEM was performed using a computerized 3D model of bone-level dental implants inserted in the lower jawbone with an applied axial load of 100 N. The analysis was performed using different distances from the bone level and different thicknesses of cortical bone. The interface area of bone growth was evaluated by analyzing the bone–implant contact (BIC), region of interest (ROI) and total bone area (BAT) parameters obtained through an in vivo histological process and analyzed by scanning electron microscopy (SEM). Bone-level implants were inserted in the rabbit tibiae, with two implants placed per tibia. These parameters were evaluated after three or six weeks of implantation. FEM studies showed that placements 0.5 mm below the bone level presented lower values of stress distribution compared to the other studied placements. The lower levels of mechanical stress were then correlated with the in vivo studies, showing that this position presented the highest BIC value after three or six weeks of implantation. In this placement, vertical bone growth could be observed up the bone level. The smallest thickness of the study showed a better transfer of mechanical loads, which leads to a better osseointegration. In silico and in vivo results both concluded that the implants placed 0.5 mm below the cortical bone and with lower thicknesses presented the best biomechanical and histological behavior in terms of new bone formation, enhanced mechanical stability and optimum osseointegration.
Highlights
Different factors will affect bone behavior, growth or loss when dental implants are placed at the osseous level
Since the stability of the implant can vary according to cortical-bone thickness, the three cases mentioned above were analyzed for two different thicknesses of the cortical bone: t = 1.5 mm
finite element method (FEM) simulation studies showed that bone-level dental implants placed subcrestally had a lower load transfer to the bone than dental implants at bone level and above the bone crest
Summary
Different factors will affect bone behavior, growth or loss when dental implants are placed at the osseous level. These factors are: macro and micro implant design [1–4], the separation between placed implants [5], periodontal and bone quality [6], occlusal loading [7], the microgap prone to bacteria colonization in the implant abutment connection and, in consequence, the location of this connection in relation to the bone crest [8–12]. Some studies show peri-implant bone losses of between 1 and 2 mm after the first year of occlusal loading, and from 0.1 to 0.2 mm over successive years [13–15]. Pellicer et al observed that different placement of the bone-level implant could produce bone growth with different behavior in an analysis of different clinical studies [16]. As early as 1969, Branemark [17] recommended placing the implant below the bone crest to prevent implant exposure during bone remodeling
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