The critical cases of posterior maxilla: the lack of cortical bone versus short plateau implants success

Abstract

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...

An experimental study on the effects of the cortical thickness and bone density on initial mechanical anchorage of different Straumann® implant designs

“…Several studies have also clearly showed that improving primary stability via bi-cortical anchorage plays a great role in the success of immediate loading protocols such as All-on-4™ [ 12 ] and All-on-3 [ 13 ] and implant placements following sinus floor augmentation. However, 70% of all age-related bone loss is cortical [ 14 ] and the lack of cortical bone especially in the posterior maxillae could pose a great challenge for the clinician [ 15 ], especially in elderly dental implant patients.…”