Tissue engineering strategies for the future generation of dental implants

Effects of Argon Gas Plasma Treatment on Biocompatibility of Nanostructured Titanium

In this study, we applied argon plasma treatment to titanium surfaces with nanostructures deposited by concentrated alkali treatment and investigated the effects on the surface of the material and the tissue surrounding an implant site. The results showed that the treatment with argon plasma removed carbon contaminants and increased the surface energy of the material while the nanoscale network structure deposited on the titanium surface remained in place. Reactive oxygen species reduced the oxidative stress of bone marrow cells on the treated titanium surface, creating a favorable environment for cell proliferation. Good results were observed in vitro evaluations using rat bone marrow cells. The group treated with argon plasma exhibited the highest apatite formation in experiments using simulated body fluids. The results of in vivo evaluation using rat femurs revealed that the treatment improved the amount of new bone formation around an implant. Thus, the results demonstrate that argon plasma treatment enhances the ability of nanostructured titanium surfaces to induce hard tissue differentiation and supports new bone formation around an implant site.

Effect of the amnion-chorion or collagen membrane as a matrix on the microenvironment during a regenerative endodontic procedure

INTRODUCTION

During regenerative endodontic procedures, the microenvironment of the canal is formed by the degree of disinfection and release of ions from the applied materials onto the top surface. This study aimed to characterize the effects of amnion-chorion membrane (ACM) and collagen membrane (CM) on pulp-dentin regeneration compared to calcium silicate cements (CSCs), focusing on cell migration, mineralization potential, anti-inflammation, and angiogenesis.

METHODS

Two CSCs and two membranes were used: ProRoot_® MTA (PM; Dentsply, Tulsa, OK, USA), RetroMTA_® (RM; BioMTA, Seoul, Korea), Collagen Membrane_® (CM; Genoss, Suwon, Korea), and BioXclude_® (ACM; Snoasis Medical, Colorado, USA). Transwell and scratch assays were used to evaluate cell migration and wound healing. Mineralization potential was evaluated using alkaline phosphatase (ALP) activity, alizarin red S staining, and quantitative real-time-polymerase chain reaction (qRT-PCR) for the expression of marker genes. qRT-PCR was used to measure the levels of angiogenic genes and inflammatory mediators. An endothelial tube formation assay was used to assess angiogenesis.

RESULTS

The membranes showed superior migration and wound healing compared with CSCs. Except for RM, PM and the two membranes showed high ALP activity and mineralization nodule formation and upregulated mRNA expression of markers for mineralization. Membranes upregulated the mRNA of angiogenesis genes and increased the capillary tube formation of endothelial cells compared to CSCs. Furthermore, the membrane matrix decreased the expression of inflammatory genes.

CONCLUSIONS

CM and ACM showed prominent cell migration, angiogenesis, and healing effects against inflammation, as well as comparable mineralization potential compared to CSCs, recommending the use of membrane as a matrix.

Effect of Argon-Based Atmospheric Pressure Plasma Treatment on Hard Tissue Formation on Titanium Surface

In this paper, we suggest that the atmospheric pressure plasma treatment of pure titanium metal may be useful for improving the ability of rat bone marrow cells (RBMCs) to induce hard tissue differentiation. Previous studies have reported that the use of argon gas induces a higher degree of hard tissue formation. Therefore, this study compares the effects of plasma treatment with argon gas on the initial adhesion ability and hard tissue differentiation-inducing ability of RBMCs. A commercially available titanium metal plate was used as the experimental material. A plate polished using water-resistant abrasive paper #1500 was used as the control, and a plate irradiated with argon mixed with atmospheric pressure plasma was used as the experimental plate. No structural change was observed on the surface of the titanium metal plate in the scanning electron microscopy results, and no change in the surface roughness was observed via scanning probe microscopy. X-ray photoelectron spectroscopy showed a decrease in the carbon peak and the formation of hydroxide in the experimental group. In the distilled water drop test, a significant decrease in the contact angle was observed for the experimental group, and the results indicated superhydrophilicity. Furthermore, the bovine serum albumin adsorption, initial adhesion of RBMCs, alkaline phosphatase activity, calcium deposition, and genetic marker expression of rat bone marrow cells were higher in the experimental group than those in the control group at all time points. Rat distal femur model are used as in vivo model. Additionally, microcomputed tomography analysis showed significantly higher results for the experimental group, indicating a large amount of the formed hard tissue. Histopathological evaluation also confirmed the presence of a prominent newly formed bone seen in the images of the experimental group. These results indicate that the atmospheric pressure plasma treatment with argon gas imparts superhydrophilicity, without changing the properties of the pure titanium plate surface. It was also clarified that it affects the initial adhesion of bone marrow cells and the induction of hard tissue differentiation.

Dental Implant Bioactive Surface Modifiers: An Update

Objectives:

Main purpose of this review was to present an update on various coating materials utilized in improving the surface chemistry of the dental implants.

Methods:

Literature search was carried out in various on-line databases such as PubMed, Medline, Google scholar, EBSCO, Wiley Science Library, and Saudi Digital Library using appropriate keywords (dental implant surface coatings, dental implant surface modifiers, and dental surface coatings).

Results:

Total of 569 studies were retrieved. All the relevant studies among them were reviewed and compiled.

Conclusion:

Current implant surface's biomimetic coatings offer many benefits compared to the traditional plasma sprayed coatings. Further incorporation of biomimetic coatings with various material has lead improvement in mechanical and biological properties of implants.

Enhanced Bioactivity of Collagen Fiber Functionalized with Room Temperature Atomic Layer Deposited Titania

Surface modifications of a biomaterial like collagen are crucial in improving the surface properties and thus enhancing the functionality and performance of such a material for a variety of biomedical applications. In this study, a commercially available collagen membrane's surface was functionalized by depositing an ultrathin film of titania or titanium dioxide (TiO₂) using a room temperature atomic layer deposition (ALD) process. A novel titanium precursor-oxidizer combination was used for this process in a custom-made ALD reactor. Surface characterizations revealed successful deposition of uniform, conformal TiO₂ thin film on the collagen fibrillar surface, and consequently, the fibers became thicker making the membrane pores smaller. The in vitro bioactivity of the ALD-TiO₂ thin film coated collagen was investigated for the first time using cell proliferation and a calcium phosphate mineralization assay. The TiO₂-coated collagen demonstrated improved biocompatibility promoting higher growth and proliferation of human osteoblastic and mesenchymal stem cells when compared to that of noncoated collagen. A higher level of calcium phosphate or apatite formation was observed on ALD modified collagen surface as compared to that on noncoated collagen. Therefore, this novel material can be promising in bone tissue engineering applications.

Effect of Amelogenin Coating of a Nano-Modified Titanium Surface on Bioactivity

The interactions between implants and host tissues depend on several factors. In particular, a growing body of evidence has demonstrated that the surface texture of an implant influences the response of the surrounding cells. The purpose of this study is to develop new implant materials aiming at the regeneration of periodontal tissues as well as hard tissues by coating nano-modified titanium with amelogenin, which is one of the main proteins contained in Emdogain®. We confirmed by quartz crystal microbalance evaluation that amelogenin is easy to adsorb onto the nano-modified titanium surface as a coating. Scanning electron microscopy, scanning probe microscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy analyses confirmed that amelogenin coated the nano-modified titanium surface following alkali-treatment. In vitro evaluation using rat bone marrow and periodontal ligament cells revealed that the initial adhesion of both cell types and the induction of hard tissue differentiation such as cementum were improved by amelogenin coating. Additionally, the formation of new bone in implanted surrounding tissues was observed in in vivo evaluation using rat femurs. Together, these results suggest that this material may serve as a new implant material with the potential to play a major role in the advancement of clinical dentistry.

Periostin promotes migration, proliferation, and differentiation of human periodontal ligament mesenchymal stem cells

OVERVIEW

Periostin (POSTN) is critical to bone and dental tissue morphogenesis, postnatal development, and maintenance; however, its roles in tissue repair and regeneration mediated by human periodontal ligament mesenchymal stem cells (PDLSCs) remain unclear. The present study was designed to evaluate the effects of POSTN on hPDLSCs in vitro.

MATERIALS AND METHODS

hPDLSCs were isolated and characterized by their expression of the cell surface markers CD44, CD90, CD105, CD34, and CD45. Next, 100 ng/mL recombinant human POSTN protein (rhPOSTN) was used to stimulate the hPDLSCs. Lentiviral POSTN shRNA was used to knockdown POSTN. The cell counting kit-8 (CCK8) and scratch assay were used to analyze cell proliferation and migration, respectively. Osteogenic differentiation was investigated using an alkaline phosphatase (ALP) activity assay, alizarin staining, and quantitative calcium analysis and related genes/protein expression assays.

RESULTS

Isolated hPDLSCs were positive for CD44, CD90, and CD105 and negative for CD34 and CD45. In addition, 100 ng/mL rhPOSTN significantly accelerated scratch closure, and POSTN-knockdown cells presented slower closure at 24 h and 48 h. Furthermore, the integrin inhibitor Cilengitide depressed the scratch closure that was enhanced by POSTN at 24 h. The CCK8 assay showed that 100 ng/mL rhPOSTN promoted hPDLSC proliferation. Moreover, 100 ng/mL rhPOSTN increased the expression of RUNX2, OSX, OPN, OCN, and VEGF and enhanced ALP activity and mineralization. POSTN silencing decreased the expression of RUNX2, OSX, OPN, OCN, and VEGF and inhibited ALP activity and mineralization.

CONCLUSIONS

POSTN accelerated the migration, proliferation, and osteogenic differentiation of hPDLSCs.

Reduction of bacterial adhesion on dental composite resins by silicon-oxygen thin film coatings

Adhesion of bacteria on dental materials can be reduced by modifying the physical and chemical characteristics of their surfaces, either through the application of specific surface treatments or by the deposition of thin film coatings. Since this approach does not rely on the use of drugs or antimicrobial agents embedded in the materials, its duration is not limited by their possible depletion. Moreover it avoids the risks related to possible cytotoxic effects elicited by antibacterial substances released from the surface and diffused in the surrounding tissues. In this work, the adhesion of Streptococcus mutans and Streptococcus mitis was studied on four composite resins, commonly used for manufacturing dental prostheses. The surfaces of dental materials were modified through the deposition of a-SiO(x) thin films by plasma enhanced chemical vapor deposition. The chemical bonding structure of the coatings was analyzed by Fourier-transform infrared spectroscopy. The morphology of the dental materials before and after the coating deposition was assessed by means of optical microscopy and high-resolution mechanical profilometry, while their wettability was investigated by contact angle measurements. The sample roughness was not altered after coating deposition, while a noticeable increase of wettability was detected for all the samples. Also, the adhesion of S. mitis decreased in a statistically significant way on the coated samples, when compared to the uncoated ones, which did not occur for S. mutans. Within the limitations of this study, a-SiO(x) coatings may affect the adhesion of bacteria such as S. mitis, possibly by changing the wettability of the composite resins investigated.

Genetic networks in osseointegration

Osseointegration-based dental implants have become a well-accepted treatment modality for complete and partial edentulism. The success of this treatment largely depends on the stable integration and maintenance of implant fixtures in alveolar bone; however, the molecular and cellular mechanisms regulating this unique tissue reaction have not yet been fully uncovered. Radiographic and histologic observations suggest the sustained retention of peri-implant bone without an apparent susceptibility to catabolic bone remodeling; therefore, implant-induced bone formation continues to be intensively investigated. Increasing numbers of whole-genome transcriptome studies suggest complex molecular pathways that may play putative roles in osseointegration. This review highlights genetic networks related to bone quality, the transient chondrogenic phase, the vitamin D axis, and the peripheral circadian rhythm to elute the regulatory mechanisms underlying the establishment and maintenance of osseointegration.

Effects of Protein-Simulated Body Fluid Mixing Methods on Characteristics of Bone-Like Mineral

This study examined effects of protein mixing methods into modified simulated body fluid (mSBF) on the crystalline structure and morphology of bone-like mineral (BLM) coated on poly(lactic-co-glycolic acid) PLGA. Using bovine serum albumin (BSA) as a model protein, four sample groups were prepared: the N-BLM group was coated by soaking substrates in mSBF without BSA; the B-BLM group was coated by soaking in mSBF with BSA added immediately before soaking; the Ca-BLM group was coated by soaking in Ca-mSBF prepared by premixing BSA with a CaCl(2) solution before preparing the mSBF; the P-BLM group was coated by soaking in P-mSBF made by premixing the BSA with a KH(2)PO(4) solution. The B-BLM and Ca-BLM groups exhibited densely coated, thick BLM layers, whereas the P-BLM group exhibited loosely connected BLM clusters. The hydroxyapatite (HAp) crystallites of the B-BLM and Ca-BLM groups were aligned along the c-axis, but those of the P-BLM group were disordered and had a lower crystallinity. The alignment to the c-axis of Ca-BLM and the disordered orientation of P-BLM was caused by calcium ions bound to BSA in Ca-mSBF and phosphate ions bound to BSA in P-mSBF, respectively. These results show that the crystallinity and morphology of BLM can be controlled by the mixing of BSA in mSBF. The crystallinity of BLM is closely connected to its solubility. Therefore, the release characteristics of growth factors and cell regulation on BLM could be affected by the changes in the crystalinity of BLM.

Potential feasibility of dental stem cells for regenerative therapies: stem cell transplantation and whole-tooth engineering

Multipotent mesenchymal stem cells from bone marrow are expected to be a somatic stem cell source for the development of new cell-based therapy in regenerative medicine. However, dental clinicians are unlikely to carry out autologous cell/tissue collection from patients (i.e., marrow aspiration) as a routine procedure in their clinics; hence, the utilization of bone marrow stem cells seems impractical in the dental field. Dental tissues harvested from extracted human teeth are well known to contain highly proliferative and multipotent stem cell compartments and are considered to be an alternative autologous cell source in cell-based medicine. This article provides a short overview of the ongoing studies for the potential application of dental stem cells and suggests the utilization of 2 concepts in future regenerative medicine: (1) dental stem cell-based therapy for hepatic and other systemic diseases and (2) tooth replacement therapy using the bioengineered human whole tooth, called the "test-tube dental implant." Regenerative therapies will bring new insights and benefits to the fields of clinical medicine and dentistry.

Bioengineered periodontal tissue formed on titanium dental implants

The ability to use autologous dental progenitor cells (DPCs) to form organized periodontal tissues on titanium implants would be a significant improvement over current implant therapies. Based on prior experimental results, we hypothesized that rat periodontal ligament (PDL)-derived DPCs can be used to bioengineer PDL tissues on titanium implants in a novel, in vivo rat maxillary molar implant model. Analyses of recovered implants revealed organized PDL tissues surrounding titanium implant surfaces in PDL-cell-seeded, and not in unseeded control, implants. Rat PDL DPCs also exhibited differentiative potential characteristic of stem cells. These proof-of-principle findings suggest that PDL DPCs can organize periodontal tissues in the jaw, at the site of previously lost teeth, indicating that this method holds potential as an alternative approach to osseointegrated dental implants. Further refinement of this approach will facilitate the development of clinically relevant methods for autologous PDL regeneration on titanium implants in humans.

Surface modification of biomedical and dental implants and the processes of inflammation, wound healing and bone formation

Bone adaptation or integration of an implant is characterized by a series of biological reactions that start with bone turnover at the interface (a process of localized necrosis), followed by rapid repair. The wound healing response is guided by a complex activation of macrophages leading to tissue turnover and new osteoblast differentiation on the implant surface. The complex role of implant surface topography and impact on healing response plays a role in biological criteria that can guide the design and development of future tissue-implant surface interfaces.

Ridge augmentation and maxillary sinus grafting with a biphasic calcium phosphate: histologic and histomorphometric observations

OBJECTIVES

This retrospective study reports on histologic and histomorphometric observations performed on human biopsies harvested from sites augmented exclusively by biphasic calcium phosphate [BCP: hydroxyapatite (HA)/ tricalcium phosphate (TCP) 60/40] and healed for a minimum of 6 months.

MATERIALS AND METHODS

Five patients benefited from three augmentation regimens (i.e.: one-stage lateral augmentation; two-stage lateral augmentation; and two-stage sinus grafting). In all patients, a degradable collagen membrane served as a cell-occlusive barrier. Core biopsies were obtained from lateral as from crestal aspects 6-10 months after augmentation surgeries. For histologic and histomorphometric evaluations, the non-decalcified tissue processing was performed.

RESULTS

The histological examination of 11 biopsies showed graft particles frequently being bridged by the new bone, and a close contact between the graft particles and newly formed bone was seen in all samples. The mean percentages of newly formed bone, soft tissue compartment, and graft material were 38.8% (+/-5.89%), 41.75% (+/-6.08%), and 19.63% (+/-4.85%), respectively. Regarding bone-to-graft contact values, the percentage of bone coverage of graft particles for all biopsies ranged from 27.83% to 80.17%. The mean percentage of bone coverage was 55.39% (+/-13.03%).

CONCLUSIONS

Data from the present study demonstrated osteoconductivity scores for the BCP material (HA/TCP 60/40) in patients resembling those previously shown for grafting materials of xenogenic and alloplastic origin.

Surface modifications of dental implants

Dental implant surface technologies have been evolving rapidly to enhance a more rapid bone formation on their surface and hold a potential to increase the predictability of expedited implant therapy. While implant outcomes have become highly predictable, there are sites and conditions that result in elevated implant loss. This paper reviews the impact of macro-retentive features which includes approaches to surface oxide modification, thread design, press-fit and sintered-bead technologies to increase predictability of outcomes. Implant designs that lead to controlled lateral compression of the bone can improve primary stability as long as the stress does not exceed the localized yield strength of the cortical bone. Some implant designs have reduced crestal bone loss by use of multiple cutting threads that are closely spaced, smoothed on the tip but designed to create a hoop-stress stability of the implant as it is completely seated in the osteotomy. Following the placement of the implant, there is a predictable sequence of bone turnover and replacement at the interface that allows the newly formed bone to adapt to microscopic roughness on the implant surface, and on some surfaces, a nanotopography (<10(-9) m scale) that has been shown to preferably influence the formation of bone. Newly emerging studies show that bone cells are exquisitely sensitive to these topographical features and will upregulate the expression of bone related genes for new bone formation when grown on these surfaces. We live in an exciting time of rapid changes in the modalities we can offer patients for tooth replacement therapy. Given this, it is our responsibility to be critical when claims are made, incorporate into our practice what is proven and worthwhile, and to continue to support and provide the best patient care possible.

Selfprotective smart orthopedic implants

In this review, we discuss current advances leading to an exciting change in implant design for orthopedic surgery. The initial biomaterial approaches in implant design are being replaced by cellular-molecular interactions and nanoscale chemistry. New designs address implant complications, particularly loosening and infection. For infection, local delivery systems are an important first step in the process. Selfprotective 'smart' devices are an example of the next generation of orthopedic implants. If proven to be effective, antibiotics or other active molecules that are tethered to the implant surface through a permanent covalent bond and tethering of antibiotics or other biofactors are likely to transform the practice of orthopedic surgery and other medical specialties. This new technology has the potential to eliminate periprosthetic infection, a major and growing problem in orthopedic practice.