Implant dimensions greatly influence load transfer characteristics and the lifetime of a dental system. Excessive stresses at peri-implant area may result in bone failure. Finding the critical point at the implant-bone interface and evaluating the influence of implant diameter-to-length ratio on adjacent bone stresses makes it possible to select implant dimensions. For this, different cylindrical implants were numerically analysed using geometrical models generated from computed tomography images of mandible with osseointegrated implants. All materials were assumed to be linearly elastic and isotropic. Masticatory load was applied in its natural direction, oblique to occlusal plane. Maximum von Mises stresses were located around the implant neck at the critical point of its intersection with the plane of loading and were functions of implant diameter-to-length ratio. It was demonstrated that there exists a certain spectrum of diameter-to-length ratios, which will keep maximum bone stresses at a preset level chosen in accordance with patient's bone strength.

Extreme stresses in surrounding bone are among the most important reasons for implant failure. Bone density (quality) is a variable that plays a decisive role in achieving predictable osseointegration and long-term survival of implants. The magnitudes of ultimate occlusal load, which generate ultimate von Mises stress at the critical point of peri-implant area for the spectrum of implants inserted into mandible with four different bone qualities (Lekholm and Zarb classification), were calculated. Geometric models of mandible segment were generated from computed tomography images and analysed with osseointegrated cylindrical implants of various dimensions. Occlusal loads were applied in their natural direction. All materials were assumed to be linearly elastic and isotropic. The investigation suggests that an implant's ultimate occlusal load indicates its load-carrying capacity. As a result, bone loss can be predicted, and viable implants can be selected by comparing the values of their ultimate occlusal load in different clinical conditions.

Dental implant failure is mainly the consequence of bone loss at peri-implant area. It usually begins in crestal bone. Due to this gradual loss, implants cannot withstand functional force without bone overload, which promotes complementary loss. As a result, implant lifetime is significantly decreased. To estimate implant success prognosis, taking into account 0.2 mm annual bone loss for successful implantation, ultimate occlusal forces for the range of commercial cylindrical implants were determined and changes of the force value for each implant due to gradual bone loss were studied. For this purpose, finite element method was applied and von Mises stresses in implant-bone interface under 118.2 N functional occlusal load were calculated. Geometrical models of mandible segment, which corresponded to Type II bone (Lekholm & Zarb classification), were generated from computed tomography images. The models were analyzed both for completely and partially osseointegrated implants (bone loss simulation). The ultimate value of occlusal load, which generated 100 MPa von Mises stresses in the critical point of adjacent bone, was calculated for each implant. To estimate longevity of implants, ultimate occlusal loads were correlated with an experimentally measured 275 N occlusal load (Mericske-Stern & Zarb). These findings generally provide prediction of dental implants success.

Background : Edentulous posterior maxilla is often associated with placement of short plateau implants due to limited available bone. However, their usage results in higher stresses in crestal cortical bone, which leads to its overload and subsequent implant failure. Biomechanical evaluation of bone-implant conglomerate and influence of bone quality and implant size on bone stresses by finite element (FE) analysis allows to compare load-bearing capacity of various implants. Aim/Hypothesis : The aim of the study was to assess stress magnitudes in cortical bone of critical thickness to verify bone capability to withstand functional loading on short plateau implants. Materials and Methods : Two short Bicon Integra-CP ™ implants of minimal (4.5x5.0 mm) and maximal (6.0x5.0 mm) diameter were analyzed. Their 3D models were placed in posterior maxilla segment models with type III and IV bone and 0.2-1.5 crestal cortical bone thickness and were completely osseointegrated. These models were designed in Solidworks 2016 software using 4-node 3D FE. Implants and bone were assumed as linearly elastic and isotropic. Elasticity modulus of cortical bone was 13.7 GPa, cancellous bone-1.37 (type III) and 0.69 (type IV) GPa. Bone-implant assemblies were analyzed in FE software Solidworks Simulation. 120.92 N mean maximal oblique load (molar area) was applied to the center of 7 Series Low 0° abutment. Von Mises equivalent stresses (MESs) in surrounding bone were calculated and compared with 100 MPa cortical bone ultimate strength to determine the ultimate functional load (UFL) for both implants. UFL magnitudes were then correlated with 275 N maximum experimental load for molar site. Results : It was found that MESs maximal magnitudes were located in crestal cortical bone. The spectrum of maximal MESs was between 14.0 and 54.0 MPa. The highest MESs were found for 4.5x5.0 mm implant placed in type IV bone with 0.2 mm crestal cortical bone, while the smallest magnitudes were calculated for 6.0x5.0 mm implant in type III bone with 1.5 mm crestal cortical bone. UFL values were in range 222…860 N. For 6.0x5.0 mm implant, UFL magnitudes were higher than 275 N for the spectrum of bone parameters: 576 N/860 N and 448 N/712 N for type III and IV bone, 0.2 mm/1.5 mm cortical bone thickness. UFL difference between 0.2 and 1.5 mm corresponded to 33% and 37% for type III and IV bone. 4.5x5.0 mm implant produced much lower UFL values: 281 N/526 N and 222 N/466 N. In order to be successful, requires at least 0.2 mm cortical layer in type III bone and 0.7 mm in type IV bone. Cortical bone decrease to around 0 mm resulted in UFL drop to 550 and 432 N (6.0x5.0 mm), 270 and 216 N (4.5x5.0 mm). Conclusions and Clinical Implications : This FE study provides a rationale for appropriate implant selection. It generally approves the clinical success of plateau implants in posterior maxilla due to their low susceptibility to poor bone quality and cortical bone thickness. It also enhances perception of implant/bone system biomechanics. The proposed method is a...

Crestal cortical bone at the implant neck is the key structural element of the jaw, which withstands the functional loading. Bone loss progression results in overloading of "soft" cancellous bone with the risk of implant failure. Comparing to conventional ones, short implants should be more sensitive to this issue. Plateau implants reduce the impact of bone loss, but there is no quantitative confirmation to this.The aim of this study was to assess the load-bearing ability of cancellous bone on several levels of bone loss after it propagates through the crestal cortical bone.Cancellous bone von Mises stresses (MESs) were proposed to evaluate loadbearing ability of fully and partially osseointegrated 4.5 (N), 5.0 (M), 6.0 mm (W) diameter and 5.0 mm length Bicon SHORT® implant on 5 levels of bone loss from 1.2 to 2.0 mm. Implant 3D models were placed crestally and bicortically in posterior maxilla segment models with type III bone and 1.0 mm cortical crestal and sinus bone. Bone models were drawn in Solidworks 2016 software. Materials were assumed to be linearly elastic and isotropic. Elasticity moduli of cortical/cancellous bone were 13.7/1.37 GPa. Bone-implant assemblies were analyzed in finite element (FE) software Solidworks Simulation. 4-node 3D FEs were generated with a total number of up to 2,516,000. 120.92 N oblique load was applied to the center of 7 Series Low 0°a butment. MESs were evaluated in cancellous bone-implant interface for fully and partially osseointegrated implant and were compared.6.0, 5.0, 3.5 MPa maximal MESs for the osseointegrated N, M, W implants were found in cancellous bone at the first fin. For 1.2, 1.4, 1.6, 1.8, 2.0 mm bone loss, maximal MESs were calculated in migrating critical points of cancellous bone-implant interface, which were located on the border of disosseointegrated-osseointegrated cancellous bone