Influence of Bone-Level Dental Implants Placement and of Cortical Thickness on Osseointegration: In Silico and In Vivo Analyses

Design Factors of Ti-Base Abutments Related to the Biomechanics Behavior of Dental Implant Prostheses: Finite Element Analysis and Validation via In Vitro Load Creeping Tests

This study has been carried out to analyze the influence of the design of three geometric elements (wall thickness, platform width, and chamfer) of Ti-base abutments on the distribution of stresses and strains on the implant, the retention screw, the Ti base, and the bone. This study was carried out using FEA, analyzing eight different Ti-base models based on combinations of the geometric factors under study. The model was adapted to the standard Dynamic Loading Test For Endosseous Dental Implants. A force of 360 N with a direction of 30° was simulated and the maximum load values were calculated for each model, which are related to a result higher than the proportional elastic limit of the implant. The transferred stresses according to von Mises and microdeformations were measured for all the alloplastic elements and the simulated support bone, respectively. These results were validated with a static load test using a creep testing machine. The results show that the design factors involved with the most appropriate stress distribution are the chamfer, a thick wall, and a narrow platform. A greater thickness (0.4 mm) is also related to lower stress values according to von Mises at the level of the retaining screws. In general, the distributions of tension at the implants and microdeformation at the level of the cortical and trabecular bone are similar in all study models. The in vitro study on a Ti-base control model determined that the maximum load before the mechanical failure of the implant is 360 N, in accordance with the results obtained for all the Ti-base designs analyzed in the FEA. The results of this FEA study show that modifications to the Ti-base design influence the biomechanical behavior and, ultimately, the way in which tension is transferred to the entire prosthesis-implant-bone system.

PCAT-1' s role in wound healing impairment: Mitochondrial dysfunction and bone marrow stem cell differentiation inhibition via PKM2/β-catenin pathway and its impact on implant osseo-integration

This study focused on unravelling the role of PCAT-1 in wound-healing process, particularly its impact on regenerative and osteogenic abilities of mesenchymal stem cells (MSCs). We delved into how PCAT-1 regulates mitochondrial oxidative phosphorylation (OXPHOS) and interacts with pivotal molecular pathways, especially β-catenin and PKM2, using human bone marrow-derived MSCs. MSCs were cultured under specific conditions and PCAT-1 expression was modified through transfection. We thoroughly assessed several critical parameters: MSC proliferation, mitochondrial functionality, ATP production and expression of wound healing and osteogenic differentiation markers. Further, we evaluated alkaline phosphatase (ALP) activity and mineral deposition, essential for bone healing. Our findings revealed that overexpressing PCAT-1 significantly reduced MSC proliferation, hampered mitochondrial performance and lowered ATP levels, suggesting the clear inhibitory effect of PCAT-1 on these vital wound-healing processes. Additionally, PCAT-1 overexpression notably decreased ALP activity and calcium accumulation in MSCs, crucial for effective bone regeneration. This overexpression also led to the reduction in osteogenic marker expression, indicating suppression of osteogenic differentiation, essential in wound-healing scenarios. Moreover, our study uncovered a direct interaction between PCAT-1 and the PKM2/β-catenin pathway, where PCAT-1 overexpression intensified PKM2 activity while inhibiting β-catenin, thereby adversely affecting osteogenesis. This research thus highlights PCAT-1's significant role in impairing wound healing, offering insights into the molecular mechanisms that may guide future therapeutic strategies for enhancing wound repair and bone regeneration.

Influence of the Tube Angle on the Measurement Accuracy of Peri-Implant Bone Defects in Rectangular Intraoral X-ray Imaging

BACKGROUND

Intraoral radiography in the right-angle technique is the standard procedure to examine the peri-implant bone level in implant follow-up and implant-related studies. For the implementation of the right-angle or parallel technique, mostly ready-made image receptor holders are used. The aim of this experimental study is to analyze changes in the measurement of standardized peri-implant defects caused by a deviation in the position of the image receptor.

METHODS

Eleven Xive® implants (Dentsply Sirona, Bensheim, Germany) were placed in bovine bone, and peri-implant defects of varying depths were created. The preparations were fixed in a specially made test stand, and intraoral radiographs were taken using the right-angle technique with standard film holders at various horizontal and vertical projection angles. Defect measurement was carried out with the imaging software Sidexis 4 V 4.3 (Dentsply Sirona, Bensheim, Germany).

RESULTS

With increasing angular deviation, larger deviations between the measured and the real extent of the defect occurred. Vertical tilting caused significant distortion, while horizontal rotation showed less effect.

CONCLUSION

Intraoral radiography only provides a valid representation of the peri-implant bone level for follow-up or as a tool in implant-related studies if a reproducible projection direction is assured.

Investigation of the Influence of Roughness and Dental Implant Design on Primary Stability via Analysis of Insertion Torque and Implant Stability Quotient: An In Vitro Study

In the placement of dental implants, the primary fixation between the dental implant and the bone is of great importance and corresponds to compressive mechanical fixation that aims to prevent micromovement of the implant. The aim of this research was to determine the role of roughness and the type of dental implant (tissue-level or bone-level) in implant stability, measured using resonance frequency analysis (RFA) and insertion torque (IT). We analyzed 234 titanium dental implants, placed in fresh calf ribs, at the half-tissue level and half-bone level. The implant surface was subjected to grit-blasting treatments with alumina particles of 120, 300, and 600 μm at a projection pressure of 2.5 bar, resulting in three types of roughness. Roughness was determined via optical interferometry. The wettability of the surfaces was also determined. Implant stability was measured using a high-precision torquemeter to obtain IT, and RFA was used to determine the implant stability quotient (ISQ). The results show that rough surfaces with Sa values of 0.5 to 4 μm do not affect the primary stability. However, the type of implant is important; bone-level implants obtained the highest primary stability values. A good correlation between the primary stability values obtained via IT and ISQ was demonstrated. New in vivo studies are necessary to know whether these results can be maintained in the long term.

Bacteriostatic Poly Ethylene Glycol Plasma Coatings for Orthodontic Titanium Mini-Implants

Titanium mini-implants are used as anchorage for orthodontic tooth movements. However, these implants present problems due to the infection of surrounding tissues. The aim of this work was to obtain a polyethylene glycol (PEG) layer by plasma in order to achieve a bacteriostatic surface. Titanium surfaces were activated by argon plasma and, after, by PEG plasma with different powers (100, 150 and 200 W) for 30 and 60 min. The roughness was determined by white light interferometer microscopy and the wettability was determined by the contact angle technique. Surface chemical compositions were characterized by X-ray photoelectron spectroscopy (XPS) and cytocompatibility and cell adhesion studies were performed with fibroblast (hFFs) and osteoblast (SAOS-2) cells. Bacterial cultures with Spectrococcus Sanguinis and Lactobacillus Salivarius were performed, and bacterial colonization was determined. The results showed that plasma treatments do not affect the roughness. Plasma makes the surfaces more hydrophilic by decreasing the contact angles from 64.2° for titanium to 5.2° for argon-activated titanium, with values ranging from 12° to 25° for the different PEG treatments. The plasma has two effects: the cleaning of the surface and the formation of the PEG layer. The biocompatibility results were, for all cases, higher than 80%. The polymerization treatment with PEG reduced the adhesion of hFFs from 7000 to 6000 and, for SAOS-2, from 14,000 to 6500, for pure titanium and those treated with PEG, respectively. Bacterial adhesion was also reduced from 600 to 300 CFU/mm² for Spetrococcuns Sanguinis and from 10,000 to 900 CFU/mm² for Lactobacillus Salivarius. The best bacteriostatic treatment corresponded to PEG at 100 W and 30 s. As a consequence, the PEG coating would significantly prevent the formation of bacterial biofilm on the surface of titanium mini-implants.

Stress Distribution Pattern in Zygomatic Implants Supporting Different Superstructure Materials

The aim of this study was to assess and compare the stress–strain pattern of zygomatic dental implants supporting different superstructures using 3D finite element analysis (FEA). A model of a tridimensional edentulous maxilla with four dental implants was designed using the computer-aided design (CAD) software. Two standard and two zygomatic implants were positioned to support the U-shaped bar superstructure. In the computer-aided engineering (CAE) software, different materials have been simulated for the superstructure: cobalt–chrome (CoCr) alloy, titanium alloy (Ti), zirconia (Zr), carbon-fiber polymers (CF) and polyetheretherketone (PEEK). An axial load of 500 N was applied in the posterior regions near the zygomatic implants. Considering the mechanical response of the bone tissue, all superstructure materials resulted in homogeneous strain and thus could reconstruct the edentulous maxilla. However, with the aim to reduce the stress in the zygomatic implants and prosthetic screws, stiffer materials, such Zr, CoCr and Ti, appeared to be a preferable option.

The Characterization of Titanium Particles Released from Bone-Level Titanium Dental Implants: Effect of the Size of Particles on the Ion Release and Cytotoxicity Behaviour

Many studies are being carried out on the particles released during the implantoplasty process in the machining of dental implants to remove bacterial biofilms. However, there are no studies on the release of particles produced by the insertion of bone-level dental implants due to the high compressive frictional loads between the rough titanium implant and the bone tissue. This paper aims to characterize the released particles and determine the release of titanium ions into the physiological environment and their cytocompatibility. For this purpose, 90 dental implants with a neck diameter of 4 mm and a torque of 22 Ncm were placed in 7 fresh cow ribs. The placement was carried out according to the established protocols. The implants had a roughness Ra of 1.92 μm. The arrangement of the particles in the bone tissue was studied by micro-CT, and no particle clusters were observed. The different granulometries of 5, 15, and 30 μm were obtained; the specific surface area was determined by laser diffraction; the topography was determined by scanning electron microcopy; and the particles were chemically analysed by X-ray energy microanalysis. The residual stresses of the particles were obtained by X-ray diffraction using the Bragg-Bentano configuration. The release of titanium ions to the physiological medium was performed using ICP-MS at 1, 3, 7, 14, and 21 days. The cytocompatibility of the particles with HFF-1 fibroblast and SAOS-2 osteoblast cultures was characterized. The results showed that the lowest specific surface area (0.2109 m²/g) corresponds to the particles larger than 30 μm being higher than 0.4969 and 0.4802 m²/g of those that are 5 and 15 μm, respectively, observing in all cases that the particles have irregular morphologies without contamination of the drills used in the surgery. The highest residual stresses were found for the small particles, -395 MPa for the 5 μm particles, and -369 for the 15 μm particles, and the lowest residual stresses were found for the 30 μm particles with values of -267 MPa. In all cases, the residual stresses were compressive. The lowest ion release was for the 30 μm samples, as they have the lowest specific surface area. Cytocompatibility studies showed that the particles are cytocompatible, but it is the smallest ones that are lower and very close to the 70% survival limit in both fibroblasts and osteoblasts.