The Influence of Type 2 Diabetes Mellitus on the Osseointegration of Titanium Implants With Different Surface Modifications-A Histomorphometric Study in High-Fat Diet/Low-Dose Streptozotocin-Treated Rats

Strategies for Improving Impaired Osseointegration in Compromised Animal Models

Implant osseointegration is reduced in patients with systemic conditions that compromise bone quality, such as osteoporosis, disuse syndrome, and type 2 diabetes. Studies using rodent models designed to mimic these compromised conditions demonstrated reduced bone-to-implant contact (BIC) or a decline in bone mineral density. These adverse effects are a consequence of disrupted intercellular communication. A variety of approaches have been developed to compensate for the altered microenvironment inherent in compromised conditions, including the use of biologics and implant surface modification. Chemical and physical modification of surface properties at the microscale, mesoscale, and nanoscale levels to closely resemble the surface topography of osteoclast resorption pits found in bone has proven to be a highly effective strategy for improving implant osseointegration. The addition of hydrophilicity to the surface further enhances osteoblast response at the bone-implant interface. These surface modifications, applied either alone or in combination, improve osseointegration by increasing proliferation and osteoblastic differentiation of osteoprogenitor cells and enhancing angiogenesis while modulating osteoclast activity to achieve net new bone formation, although the specific effects vary with surface treatment. In addition to direct effects on surface-attached cells, the communication between bone marrow stromal cells and immunomodulatory cells is sensitive to these surface properties. This article reports on the advances in titanium surface modifications, alone and in combination with novel therapeutics in animal models of human disease affecting bone quality. It offers clinically translatable perspectives for clinicians to consider when using different surface modification strategies to improve long-term implant performance in compromised patients. This review supports the use of surface modifications, bioactive coatings, and localized therapeutics as pragmatic approaches to improve BIC and enhance osteogenic activity from both structural and molecular standpoints.

Dental Implant Placement in Medically Compromised Patients: A Literature Review

As a discipline of dentistry, oral implantology deals with the diagnosis, design, insertion, restoration, and/or management of alloplastic or autogenous oral structures for the purpose of regaining contour, function, aesthetics, and speech in a partially or completely edentulous patient. The present review aims to provide the currently available knowledge about the impact of certain systemic disorders and the usage of some medications on the survival rate of dental implant therapy and to highlight the importance of patient management under these conditions. Diabetes, osteoporosis, cardiovascular diseases, and the intake of some medications can increase the risk of the failure of a dental implant. Even though there are relatively few medical contraindications to dental implant treatment, certain conditions may increase the risk of failure or complications.

Fluoride-modified implant surfaces improves osseointegration in the tibias of rats with induced diabetes

This study evaluated the influence of a fluoride-modified titanium surface on osseointegration in rats with induced diabetes. One hundred and eighty rats were randomly allocated into 3 groups with 60 animals each: Control group (C): Animals without diabetes; Diabetes Group (D): Animals with uncontrolled induced diabetes; Controlled Diabetes Group (CD): Animals with diabetes induced controlled by the insulin administration. Diabetes was induced by streptozotocin injection. Each animal received 2 implants in the proximal tibial metaphysis, one with the machined surface (M) and the other one with a fluoride-modified titanium surface (F), after 4 weeks of induction of diabetes. The animals were submitted to euthanasia 2, 4, and 6 weeks after the implant placement (n = 20 animals/group). The osseointegration was evaluated by the implant removal torque test and the histometric analysis of the non-decalcified histological sections: 1) Contact bone/implant (%BIC); 2) Bone tissue area between implant threads (%BBT). Implants with F surface showed a higher removal torque than implants with surface M in all groups. There was no difference in %BIC between the groups regardless of the surface used. The F surface showed a tendency to present higher %BBT values for the 3 evaluation periods in the D group. The fluoride-modified implant surface has no impact on the %BIC and %BBT. However, the fluoride-modified implant surface increases the locking of the implants with the bone. The hyperglycemia was associated with lower removal torque values despite the surfaces of the implant used.

Effect of autologous platelet-rich plasma on new bone formation and viability of a Marburg bone graft

This study aimed to compare the new bone formation, the process of remodeling, and the viability of bone grafts, using a combination of platelet-rich plasma (PRP) and Marburg bone graft versus bone grafts without any additional elements. For this study, 48 rabbits (with 24 rabbits in each group) were used. Bone defects were made in the femur, and the bone graft used was the human femoral head prepared according to the Marburg Bone Bank. Rabbits were divided into the following groups: heat-treated bone graft (HTBG group) and HTBG with PRP (HTBG + PRP group). After 14, 30, and 60 days post-surgery, the assessment of the results involved X-ray, histopathological, and histomorphometric analyses. The greater new bone formation was detected in the HTBG + PRP group on the 14 and 30 day (p < 0.001). Furthermore, the group using bone grafts with PRP demonstrated notably enhanced remodeling, characterized by stronger bone integration, more significant graft remineralization, and a circular pattern of newly formed bone. The PRP-bone graft complex improves bone tissue repair in the bone defect in the initial stages of bone regeneration. PRP has been identified to enhance the remodeling process and amplify the osteoconductive and osteoinductive capabilities of HTBGs.

Bone healing around implants placed in subjects with metabolically compromised systemic conditions

The aim of this study was to evaluate the bone healing of tight-fit implants placed in the maxilla and mandible of subjects compromised with metabolic syndrome (MS) and type-2 Diabetes Mellitus (T2DM). Eighteen Göttingen minipigs were randomly distributed into three groups: (i) control (normal diet), (ii) MS (cafeteria diet for obesity induction), (iii) T2DM (cafeteria diet for obesity induction + Streptozotocin for T2DM induction). Maxillary and mandibular premolars and molar were extracted. After 8 weeks of healing, implants with progressive small buttress threads were placed, and allowed to integrate for 6 weeks after which the implant/bone blocks were retrieved for histological processing. Qualitative and quantitative histomorphometric analyses (percentage of bone-to-implant contact, %BIC, and bone area fraction occupancy within implant threads, %BAFO) were performed. The bone healing process around the implant occurred predominantly through interfacial remodeling with subsequent bone apposition. Data as a function of systemic condition yielded significantly higher %BIC and %BAFO values for healthy and MS relative to T2DM. Data as a function of maxilla and mandible did not yield significant differences for either %BIC and %BAFO. When considering both factors, healthy and MS subjects had %BIC and %BAFO trend towards higher values in the mandible relative to maxilla, whereas T2DM yielded higher %BIC and %BAFO in the maxilla relative to mandible. All systemic conditions presented comparable levels of %BIC and %BAFO in the maxilla; healthy and MS presented significantly higher %BIC and %BAFO relative to T2DM in the mandible. T2DM presented lower amounts of bone formation around implants relative to MS and healthy. Implants placed in the maxilla and in the mandible showed comparable amounts of bone in proximity to implants.

Osseointegration of Titanium Implants in a Botox-Induced Muscle Paralysis Rat Model Is Sensitive to Surface Topography and Semaphorin 3A Treatment

Reduced skeletal loading associated with many conditions, such as neuromuscular injuries, can lead to bone fragility and may threaten the success of implant therapy. Our group has developed a botulinum toxin A (botox) injection model to imitate disease-reduced skeletal loading and reported that botox dramatically impaired the bone formation and osseointegration of titanium implants. Semaphorin 3A (sema3A) is an osteoprotective factor that increases bone formation and inhibits bone resorption, indicating its potential therapeutic role in improving osseointegration in vivo. We first evaluated the sema3A effect on whole bone morphology following botox injections by delivering sema3A via injection. We then evaluated the sema3A effect on the osseointegration of titanium implants with two different surface topographies by delivering sema3A to cortical bone defect sites prepared for implant insertion and above the implants after insertion using a copper-free click hydrogel that polymerizes rapidly in situ. Implants had hydrophobic smooth surfaces (PT) or multiscale biomimetic micro/nano topography (SLAnano). Sema3A rescued the botox-impaired bone formation. Furthermore, biomimetic Ti implants improved the bone-to-implant contact (BIC) and mechanical properties of the integrated bone in the botox-treated rats, which sema3A enhanced. This study demonstrated the value of biomimetic approaches combining multiscale topography and biologics in improving the clinical outcomes of implant therapy.

Semaphorin 3A delivered by a rapidly polymerizing click hydrogel overcomes impaired implant osseointegration in a rat type 2 diabetes model

Semaphorin 3A (sema3A) is an osteoprotective factor that enhances bone formation while inhibiting osteoclast bone resorption. It is produced by rat calvarial osteoblasts cultured on grit-blasted/acid-etched microtextured (SLA) titanium surfaces at higher levels than on tissue culture polystyrene, suggesting that it may improve performance of titanium implants in vivo, particularly in conditions characterized by compromised bone quality. To test this, we established a clinically relevant type 2 diabetes mellitus (T2DM) rat model and used a non-toxic click hydrogel that rapidly polymerizes in situ (GEL) to provide localized controlled delivery of sema3A. In vitro studies confirmed that sema3A released from GEL was biologically active, increasing osteoblast differentiation of a pre-osteoblast cell-line. Whereas increased sema3A production was not observed in T2DM calvarial osteoblasts cultured on SLA, exogenous sema3A enhanced surface-induced osteoblast differentiation, indicating that it would be a viable candidate for in vivo use. Delivery of sema3A either by GEL or by local injection to bone defects enhanced osseointegration of SLA implants in the T2DM rats. Trabecular bone mass and bone-to-implant contact were decreased in T2DM rats compared to normal rats; sema3A delivered locally improved both parameters. These findings suggest that reduced trabecular bone contributes to poor osseointegration in T2DM patients and support GEL as a promising treatment option for sustained release of therapeutic doses of sema3A. Moreover, using this clinically translatable T2DM model and developing a biocompatible, Cu-free click chemistry hydrogel platform for the non-invasive delivery of therapeutics has major implications for regenerative medicine as a whole. STATEMENT OF SIGNIFICANCE: Osseointegration is compromised in patients with poor bone quality due to conditions like type 2 diabetes mellitus (T2DM). Previously, we showed that semaphorin 3A (sema3A) production is increased when human bone marrow stromal cells are cultured on titanium substrates that support osseointegration in vivo, suggesting it may enhance peri-implant osteogenesis in diabetes. Here we established a spontaneously developing T2DM rat model with clinical translatability and used it to assess sema3A effectiveness. Sema3A was delivered to the implant site via a novel copper-free click hydrogel, which has minimal swelling behavior and superior rheological properties. Osseointegration was successfully restored, and enhanced compared to burst release through injections. This study provides scientific evidence for using sema3A to treat impaired osseointegration in T2DM patients.

Effect of Anti-Diabetic Medications on Dental Implants: A Scoping Review of Animal Studies and Their Relevance to Humans

Animal studies have ascertained that hyperglycemia adversely affects bone metabolism and dental implant osseointegration. However, diabetic patients show low occurrence of unfavorable hard or soft peri-implant tissue changes, differences that are possibly due to treatment with anti-diabetic medications. This scoping review aimed to systematically examine the effects of these drugs on implant outcomes and explore the predictive modality of animal studies for clinical practice according to type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). Three electronic databases (MEDLINE, EBSCOHost, and Cochrane) were searched according to the PRISMA-ScR standards for studies on diabetic animals that received titanium implants and anti-diabetic treatments. Risk assessment was performed using the SYRCLE Risk-of-Bias (RoB) tool. Twenty-one papers were included, encompassing six types of medications. Fifteen studies were on T1DM animals, and only six involved T2DM models. T1DM animals were treated with non-insulin drugs in four investigations, while insulin was utilized in 11 other studies. In T2DM experiments, five administered non-insulin drugs, and only one applied locally delivered insulin. Only insulin in T1DM studies produced a positive influence on bone-implant contact (BIC), bone mineral content, and removal torque values. Inappropriate drug selection, inadequate glycemic control, and high RoB depict a mismatch between the research focus and the translational rationale to clinical practice. There remains a knowledge gap regarding T2DM investigations due to the lack of studies. More data are needed concerning intraoral implants and the performance of osseointegrated implants in patients with a later onset of diabetes. Future research should reflect the pathophysiology and treatment of each type of diabetes to ensure clinical applicability.

Silk Fibroin/Hydroxyapatite Coating Improved Osseointegration of Porous Titanium Implants under Diabetic Conditions via Activation of the PI3K/Akt Signaling Pathway

The application of three-dimensional printed porous titanium implants (TIs) is compromised in patients suffering from diabetes mellitus (DM), which disturbs the normal process of implant osseointegration, resulting in fixation failure. It was possibly because of reactive oxygen species (ROS) overproduction at the bone-implant interface. A silk fibroin-based hydroxyapatite (SF/HA) hybrid material emerged as a novel biological material for accelerating new bone formation. We proposed that the SF/HA hybrid coated titanium implant (SHT) could mitigate DM-mediated impaired osseointegration, which had never been reported previously. To test this assumption and further elucidate the mechanisms, primary rabbit osteoblasts were seeded on TIs or SHTs and cultured with normal serum, diabetic serum (DS), DS + N-acetyl-L-cysteine (NAC) (a potent ROS inhibitor), and DS + LY294002 (a specific PI3K/Akt inhibitor) for osteoblast behavior examinations. An animal study was performed on diabetic rabbits implanted with the two kinds of implants for osseointegration tests. DM-mediated ROS overproduction caused osteoblastic biological dysfunctions and apoptotic injury, associated with suppression of PI3K/Akt signaling in osteoblasts cultured on a TI substrate. Of note, the SHT substrate significantly suppressed ROS overproduction under diabetic conditions, improved osteoblast functional recovery including ameliorative osteoblast adhesion and morphology, improved cellular proliferation and differentiation, and abrogated apoptosis, which exhibited the same effect as NAC administration on the TI. The in vitro results were further corroborated in vivo by enhanced osteogenesis and osseointegration of SHTs in diabetic rabbits. Moreover, the aforesaid promotive effects afforded by the SF/HA coating were totally abolished with administration of LY294002 for blocking PI3K/Akt signaling. The above results collectively demonstrated that the SF/HA hybrid coating significantly ameliorated DM-mediated impaired osseointegration of the TI via reactivation of the ROS-mediated PI3K/Akt signaling pathway. The hybrid coating elicited a novel surface biofunctionalization strategy to attain favorable clinical performance of TI in diabetics.

Cytotoxic effects of submicron- and nano-scale titanium debris released from dental implants: an integrative review

OBJECTIVE

This integrative review aimed to report the toxic effect of submicron and nano-scale commercially pure titanium (cp Ti) debris on cells of peri-implant tissues.

MATERIALS AND METHODS

A systematic search was carried out on the PubMed electronic platform using the following key terms: Ti "OR" titanium "AND" dental implants "AND" nanoparticles "OR" nano-scale debris "OR" nanometric debris "AND" osteoblasts "OR "cytotoxicity" OR "macrophage" OR "mutagenic" OR "peri-implantitis". The inclusion criteria involved articles published in the English language, until December 26, 2020, reporting the effect of nano-scale titanium particles as released from dental implants on the toxicity and damage of osteoblasts.

RESULTS

Of 258 articles identified, 14 articles were selected for this integrative review. Submicron and nano-scale cp Ti particles altered the behavior of cells in culture medium. An inflammatory response was triggered by macrophages, fibroblasts, osteoblasts, mesenchymal cells, and odontoblasts as indicated by the detection of several inflammatory mediators such as IL-6, IL-1β, TNF-α, and PGE2. The formation of a bioactive complex composed of calcium and phosphorus on titanium nanoparticles allowed their binding to proteins leading to the cell internalization phenomenon. The nanoparticles induced mutagenic and carcinogenic effects into the cells.

CONCLUSIONS

The cytotoxic effect of debris released from dental implants depends on the size, concentration, and chemical composition of the particles. A high concentration of particles on nanometric scale intensifies the inflammatory responses with mutagenic potential of the surrounding cells.

CLINICAL RELEVANCE

Titanium ions and debris have been detected in peri-implant tissues with different size, concentration, and forms. The presence of metallic debris at peri-implant tissues also stimulates the migration of immune cells and inflammatory reactions. Cp Ti and TiO₂ micro- and nano-scale particles can reach the bloodstream, accumulating in lungs, liver, spleen, and bone marrow.

Influence of nano-hydroxyapatite coating implants on gene expression of osteogenic markers and micro-CT parameters. An in vivo study in diabetic rats

This study evaluated the response of a nano-hydroxyapatite coating implant through gene expression analysis (runt-related transcription factor 2 (Runx2), alkaline phosphatase (Alp), osteopontin (Opn), osteocalcin (Oc), receptor activator of nuclear factor-kappa B (Rank), receptor activator of nuclear factor-kappa B ligand (Rank-L), and osteoprotegerin (Opg)). Three-dimensional evaluation (percent bone volume (BV/TV); percent intersection surface (BIC); bone surface/volume ratio (BS/BV); and total porosity (To.Po)) were also analyzed. Mini implants were surgically placed in tibias of both healthy and diabetic rats. The animals were euthanized at 7 and 30 days. Evaluating all factors the relative expression of Rank showed that NANO surface presented the best results at 7 days (diabetic rats). Furthermore the levels of Runx2, Alp, Oc, and Opn suggest an increase in osteoblasts proliferation, especially in early stages of osseointegration. %BIC in healthy and diabetic (7 days) depicted statistically significant differences for NANO group. BV/TV, BS/BV and To.Po demonstrated higher values for NANO group in all evaluated time point and irrespective of systemic condition, but BS/BV 30 days (healthy rat) and 7 and 30 days (diabetic rat). Microtomographic and gene expression analyses have shown the benefits of nano-hydroxyapatite coated implants in promoting new bone formation in diabetic rats.

TiO2 Nanotubes Alleviate Diabetes-Induced Osteogenetic Inhibition

Background

Patients with diabetes mellitus (DM) have a higher failure rate of dental implant treatments. However, whether titanium (Ti) implants with TiO₂ nanotubes (TNT) surface can retain their biocompatibility and osteogenetic ability under DM conditions has not been investigated; in addition, their behavior in DM conditions is not well characterized.

Materials and Methods

Pure Ti discs were surface treated into the polishing (mechanically polished, MP), sandblasted and acid-etched (SLA), and TNT groups. Scanning electron microscopy was used to examine the surface morphology. The cell adhesion and proliferation ability on different modified Ti surfaces at various glucose concentrations (5.5, 11, 16.5, and 22 mM) was detected by the CCK-8 assay. The osteogenetic ability on different modified Ti surfaces under high-glucose conditions was evaluated by alkaline phosphatase (ALP), osteopontin (OPN) immunofluorescence, Western blot, and Alizarin Red staining in vitro. Detection of cell apoptosis and intracellular reactive oxygen species (ROS) was undertaken both before and after N-acetylcysteine (NAC) treatment to assess the oxidative stress associated with different modified Ti surfaces under high-glucose conditions. An in vivo study was conducted in DM rats with different modified Ti femoral implants. The osteogenetic ability of different modified Ti implants in DM rats was assessed using a micro-CT scan.

Results

High-glucose conditions inhibited cell adhesion, proliferation, and osteogenetic ability of different modified Ti surfaces. High-glucose conditions induced higher apoptosis rate and intracellular ROS level on different modified Ti surfaces; these effects were alleviated by NAC. Compared with the SLA surface, the TNT surface alleviated the osteogenetic inhibition induced by high-glucose states by reversing the overproduction of ROS in vitro. In the in vivo experiment, micro-CT scan analysis further confirmed the best osteogenetic ability of TNT surface in rats with DM.

Conclusion

TNT surface modification alleviates osteogenetic inhibition induced by DM. It may provide a more favorable Ti implant surface for patients with DM.

An In Vivo Study in Rat Femurs of Bioactive Silicate Coatings on Titanium Dental Implants

Silica-based ceramics have been proposed for coating purposes to enhance dental and orthopedic titanium (Ti) implant bioactivity. The aim of this study was to investigate the influence of sphene-based bioceramic (CaO.TiO₂.SiO₂) coatings on implant osseointegration in vivo. Sphene coatings were obtained from preceramic polymers and nano-sized active precursors and deposited by an automatic airbrush. Twenty customized Ti implants, ten sphene-coated and ten uncoated rough implants were implanted into the proximal femurs of ten Sprague-Dawley rats. Overall, cortical and cancellous bone-to-implant contact (BIC) were determined using micro-computed tomography (micro-CT) at 14 and 28 days. Moreover, peri-implant bone healing was histologically and histomorphometrically evaluated. The white blood cell count in the synovial fluid of the knee joints, if present, was also assessed. No difference in the BIC values was observed between the sphene-coated and uncoated implants, overall and in the two bone compartments (p > 0.05). Delamination of the coating occurred in three cases. Consistently with micro-CT data, the histological evaluation revealed no differences between the two groups. In addition, no synovial fluid could be collected on the test side, thus confirming sphene biocompatibility. In conclusion, sphene coating was found to be a suitable material for biomedical applications. Further studies are needed to improve coating adhesion to the implants.