Variations in the implant thread shape and occlusal load behavior may result in significant changes in the biological and mechanical properties of dental implants and surrounding bone tissue. Most previous studies consider a single implant thread design, an isotropic bone structure, and a static occlusal load. However, the effects of different thread designs, bone material properties, and loading conditions are important concerns in clinical practice. Accordingly, the present study performs Finite Element Analysis (FEA) simulations to investigate the static, quasi-static and dynamic response of the implant and implanted bone material under various thread designs and occlusal loading directions (buccal-lingual, mesiodistal and apical). The simulations focus specifically on the von Mises stress, displacement, shear stress, compressive stress and tensile stress within the implant and the surrounding bone. The results show that the thread design and occlusal loading rate have a significant effect on the stress distribution and deformation of the implant and bone structure during clinical applications. Overall, the results provide a useful insight into the design of enhanced dental implants for an improved load transfer efficiency and success rate.

Background: To compare the loss of preload in absence of loading and after a fixed number of ideal masticatory cycles in two different connection systems using all-on-four prosthetic model. Methods: Two equal models of an edentulous mandible rehabilitated with all-on-four technique with two types of abutment system (MUA and OT-Bridge) supporting a hybrid prosthesis, were used. Initial torque values of the prosthetic fixing screw, after ten minutes from initial screw tightening and after 400000 masticatory cycles were registered using a mechanical torque gauge. Differences between initial and final torque values were reported for each anchoring system and the two systems were finally compared. Results: No statistically significant differences regarding the loss of preload between MUA and OT-Bridge system were found after 400000 masticatory cycles; however, in MUA system it was found between anterior and posterior implant screws. A significant difference in preload loss was found only for MUA system comparing the initial screw torque to that measured after 10 minutes from the tightening in absence of cyclic loadings. Conclusions: MUA and OT-Bridge are reliable prosthetic anchoring systems able to tolerate repeated masticatory cycles also on distal cantilever in all-on-four rehabilitation model without any significant loss of preload in screw tightening

Peri-implant bone resorption has been reported around some implants after loading and this could create problems for the long-term stability of peri-implant soft and hard tissues. The causes are still not completely known, but a relevant importance could be assumed by the presence of a bacterial contamination at the micro-gap level of the implant-abutment junction. In this regard, external and internal implant-abutment assemblies have been shown to be much more permeable to bacterial colonization than Cone-Morse or conical connections. A subcrestal implant placement could have aesthetic advantages allowing a better prosthetic emergence profile. In literature controversial experimental and clinical results have been reported about bone resorption around implants placed equicrestally and subcrestally. Interestingly, Finite Element Analysis (FEA) studies revealed to be extremely useful for assessing the peri-implant bone strain and stress. Thus, the aim of this study was a FEA evaluation of implants with a Cone-Morse implant-abutment assembly (Implacil De Bortoli, São Paulo, Brazil) inserted into a bone block model (width: 10 mm, vertical height: 17.5 mm, thickness of the cortical area: 1.5 mm) mimicking equicrestal and subcrestal placements (1 and 2 mm). The results demonstrated that maximum stresses were observed within the cortical bone around the equicrestally placed implants, the lowest in the implant placed 2-mm subcrestally and intermediate stresses within the implant placed 1-mm subcrestally. Cortical bone was more stressed under lateral loads than axial loads. In conclusion, this FEA study suggested that implant placement at -1 mm could be recommended.

Background and Objectives: Mechanical and biological complications can lead to system fracture or screw loss on dental implants. Narrow and regular platforms have been used without a consensus about the effect of distance the abutment from the prosthetic platform margin. The aim of this study is to evaluate different insertion torques in the deformation of tri-channel platform connections through two- and three-dimensional measurements with micro-CT. Materials and Methods: 164 implants were divided into groups (platform diameter and type): 3.5, 3.75, and 4.3 mm NP (Narrow Platform), and 4.3 mm RP (Regular Platform). Each implant-platform group was then divided into four subgroups (n = 10) with different torques: T45 (45 Ncm), T80 (80 Ncm), T120 (120 Ncm) and T150 (150 Ncm). The implant-abutment-screw assemblies were scanned and the images obtained were analyzed. Results: A significant difference was observed for the linear and volume measures between the different platforms (p <0.01) and the different implant insertion torques (p <0.01). Qualitative analysis suggested higher deformation resistance for the 3.75 NP compared to the 3.5 NP, and RP was more resistant compared to the NP. Conclusions: The 0.25-mm increment in the implant platform did not increase the resistance to the applied insertion torques; the 4.3-mm implant was significantly stronger compared to the 3.5-mm implant and the proposed micro-CT analysis was considered valid for both 2D and 3D analyses of micro gaps, qualitatively and quantitatively.

Background: One challenge in implant dentistry is to reduce marginal bone resorption to avoid long-term esthetic and biological complications. Sub-gingival implant placement has been suggested as a suitable strategy. Methods: 38 healthy patients were enrolled to receive bone level (BL – Control group) or 2 mm sub-crestal (SC - Test group) conical connection, platform-switched implants. An immediate tissue level abutment was used in the Test group by following a One Time Abutment (OTA) restorative procedure. Marginal Bone Modification (MBM) was calcu-latied on standardized radiographs at surgery (T0), loading (T1), and 6 months (T2) and 12 months after loading (T3), and cathegorised in Bone Loss (BL) if the resorption occurred below the implant neck and Bone Remodeling (BR) if above. Pocket probing depth (PPD), Bleeding on probing (BoP) and Plaque Index (PI) were also collected. Results: The mean MBM in the test group after 12 months was 0.61mm, compared to 0.52mm in the control group. However, no BL was observed in the test group, as the MBM completely occurred above the implant neck as BR, whilst in the control group MBM corresponded in total to BL. The average PPD was 2.38mm in the test group and 3.04mm in the control group after 12 months, BoP 50% and 43%, PI 33% and 19.44% respectively. Conclusions: Sub-crestal conical connection, platform-switched implants could be a suitable clinical choice to avoid BL with exposure of the treated implants surfaces.

Implant-supported-screw-retained prostheses are really popular. Some of the most frequent complications have been mechanical complications. These include abutment screw loosening or even screw fracture. Using an intermediate abutment can offer several advantages. However, little literature has been found regarding how this affects the mechanical behavior of dental restorations. This study focuses on understanding the mechanical behavior of implant-supported restorations with a transepithelial component compared to those with a direct implant-supported restoration. It was carried out by using the Finite Element Method (FEM) and was experi-mentally validated. The results showed that in the case of transepithelial-supported restoration, the prosthetic screw mounted over the transepithelial component suffers higher stress than the one screwed directly to the implant. After applying a cyclic fatigue load, it is experimentally proven that, in the transepithelial-supported restorations, the fuse changes from being the screw that goes to the implant, to being the upper one. As a conclusion we can say that the use of an intermediate abutment in dental restoration not only provides better protection to the rest of the dental restoration but also allows easier repair in the event of a fracture. This can potentially lead to more efficient procedures and improved patient outcomes.

Purpose: The objective of the study was to qualitatively assess micro-gap dimensions, connecting fitting surface profile and bacterial leakage of machined and cast high gold alloy UCLA abutments, with or without electrodeposited gold coatings attached to external hexagon implants. Materials and methods: 16 plastic UCLA (PUCLA) and 5 machined cast-to UCLA (GUCLA) abutments were cast with a high gold content alloy. 10 were electrolytically gold plated (8 - PUCLA, 2 - GUCLA). All abutments were attached to implants giving 21 implant-abutment combinations (IACs). External perimeter micro-gaps measured with SEM under different illumination and magnification conditions were averaged over three regions. The IACs were examined for E.coli leakage following an initial sterility test. Disassembled combinations were examined with SEM and surface profiles qualitatively assessed. Results: External micro-gap measurements did not reflect the variable connecting surface profiles but average values < 3.5 μm were observed for all IACs. Bacterial transfer was observed in 3 of 5 PUCLA plated and 2 of 5 PUCLA non-plated IACs. No transfer occurred in the 3 GUCLA non-plated or 2 GUCLA plated IACs. Abutment connecting surfaces, both Au plated and not Au plated, showed plastic deformation (smearing) in variable mosaic patterns across the micro-gap. External micro-gap dimensions although not truly reflective of surface connecting profiles averaged < 3.5 μm measured under shadow eliminating silhouette illumination for both cast and pre-machined external hexagon abutments with and without Au plating. Conclusions: Micro-gap dimensions < 5 μm were obtained with both high noble metal cast and pre-machined external hexagon abutments with and without Au electrodeposited on the abutment connecting surface. Regions of intimate contact due to plastic deformation (smearing) of these surfaces was observed. A continuous smeared region around the circumference of the surfaces can provide an effective barrier to egress of E.coli bacteria from the internal regions of the implant under static loading.