Improvement in the osteoblastic cellular response to a commercial collagen membrane and demineralized freeze-dried bone by an amino acid derivative: an in vitro study

The role of N-acetylcysteine in osteogenic microenvironment for bone tissue engineering

Bone defect is a common clinical symptom which can arise from various causes. Currently, bone tissue engineering has demonstrated positive therapeutic effects for bone defect repair by using seeding cells such as mesenchymal stem cells and precursor cells. N-acetylcysteine (NAC) is a stable, safe and highly bioavailable antioxidant that shows promising prospects in bone tissue engineering due to the ability to attenuate oxidative stress and enhance the osteogenic potential and immune regulatory function of cells. This review systematically introduces the antioxidant mechanism of NAC, analyzes the advancements in NAC-related research involving mesenchymal stem cells, precursor cells, innate immune cells and animal models, discusses its function using the classic oral microenvironment as an example, and places particular emphasis on the innovative applications of NAC-modified tissue engineering biomaterials. Finally, current limitations and future prospects are proposed, with the aim of providing inspiration for targeted readers in the field.

Conditional Mitigation of Dental-Composite Material-Induced Cytotoxicity by Increasing the Cure Time

Light-cured composite resins are widely used in dental restorations to fill cavities and fabricate temporary crowns. After curing, the residual monomer is a known to be cytotoxic, but increasing the curing time should improve biocompatibility. However, a biologically optimized cure time has not been determined through systematic experimentation. The objective of this study was to examine the behavior and function of human gingival fibroblasts cultured with flowable and bulk-fill composites cured for different periods of time, while considering the physical location of the cells with regard to the materials. Biological effects were separately evaluated for cells in direct contact with, and in close proximity to, the two composite materials. Curing time varied from the recommended 20 s to 40, 60, and 80 s. Pre-cured, milled-acrylic resin was used as a control. No cell survived and attached to or around the flowable composite, regardless of curing time. Some cells survived and attached close to (but not on) the bulk-fill composite, with survival increasing with a longer curing time, albeit to <20% of the numbers growing on milled acrylic even after 80 s of curing. A few cells (<5% of milled acrylic) survived and attached around the flowable composite after removal of the surface layer, but attachment was not cure-time dependent. Removing the surface layer increased cell survival and attachment around the bulk-fill composite after a 20-s cure, but survival was reduced after an 80-s cure. Dental-composite materials are lethal to contacting fibroblasts, regardless of curing time. However, longer curing times mitigated material cytotoxicity exclusively for bulk-fill composites when the cells were not in direct contact. Removing the surface layer slightly improved biocompatibility for cells in proximity to the materials, but not in proportion to cure time. In conclusion, mitigating the cytotoxicity of composite materials by increasing cure time is conditional on the physical location of cells, the type of material, and the finish of the surface layer. This study provides valuable information for clinical decision making and novel insights into the polymerization behavior of composite materials.

N-Acetyl Cysteine-Mediated Improvements in Dental Restorative Material Biocompatibility

The fibroblast-rich gingival tissue is usually in contact with or adjacent to cytotoxic polymer-based dental restoration materials. The objective of this study was to determine whether the antioxidant amino acid, N-acetyl cysteine (NAC), reduces the toxicity of dental restorative materials. Human oral fibroblasts were cultured with bis-acrylic, flowable composite, bulk-fill composite, self-curing acrylic, and titanium alloy test specimens. Cellular behavior and function were analyzed on and around the materials. Impregnation of the bulk-fill composite and self-curing acrylic with NAC reduced their toxicity, improving the attachment, growth, and function of human oral fibroblasts on and around the materials. These mitigating effects were NAC dose dependent. However, NAC impregnation of the bis-acrylic and flowable composite was ineffective, with no cells attaching to nor around the materials. Although supplementing the culture medium with NAC also effectively improved fibroblast behaviors, direct impregnation of materials with NAC was more effective than supplementing the cultures. NAC-mediated improvements in fibroblast behavior were associated with reduced production of reactive oxygen species and oxidized glutathione together with increased glutathione reserves, indicating that NAC effectively directly scavenged ROS from materials and reinforced the cellular antioxidant defense system. These results establish a proof of concept of NAC-mediated improvements in biocompatibility in the selected dental restorative materials.

Clinical applications of concentrated growth factors membrane for sealing the socket in alveolar ridge preservation: a randomized controlled trial

The purpose of this study was to evaluate the efficacy of concentrated growth factor (CGF) membrane for the sealing of alveolar socket in alveolar ridge preservation (ARP). A total of 22 patients with 24 alveolar sockets were recruited and divided randomly into CGF group and Bio-Gide collagen membrane group. The soft tissue wound healing rate was calculated using intraoral scanner at 3, 7, and 14 days after ARP, and the bone resorption volume at 1, 3, and 5 mm below the alveolar ridge was measured by CBCT at 6 months postoperation. The keratinized gingival width was also measured before and 6 months after ridge preservation. In terms of soft tissue healing rate, the CGF group exhibited significant higher than that of Bio-Gide group at both 7 and 14 days after surgery (P < 0.05). However, there was no significantly different in bone resorption rate and the width of keratinized gingival after 6 months (P > 0.05). Therefore, the use of CGFs membranes for wound closure in ARP is a reliable method, but more clinical data are needed to prove it.

Clinical applications of concentrated growth factors combined with bone substitutes for alveolar ridge preservation in maxillary molar area: a randomized controlled trial

PURPOSE

To evaluate the clinical effects of concentrated growth factors (CGFs) combined with bone substitutes for alveolar ridge preservation (ARP) in the maxillary molar area.

METHODS

Thirty-six patients who underwent extraction of the upper molars were recruited and randomly divided into three groups: 1. Grafted with CGFs combined with deproteinized bovine bone mineral (DBBM) and covered with CGFs membrane (CGFs/DBBM group), 2. Grafted with DBBM alone and covered with collagen membrane (DBBM group), 3. Control group spontaneous healing. The area of the alveolar bone in center (C-), mesial (M-) and distal (D-) section was compared with preoperative in radiography. Bone cores were obtained for histopathology observation and comparison.

RESULTS

In C-, M- and D-section, the alveolar ridge area in all three groups was significantly reduced at 8 months postoperatively compared to the baseline (P < 0.05). The alveolar ridge area declines in the CGFs/DBBM group (C-12.75 ± 2.22 mm2, M-14.69 ± 2.82 mm2, D-16.95 ± 4.17 mm2) and DBBM group (C-14.08 ± 2.51 mm2, M-15.42 ± 3.47 mm2, D-16.09 ± 3.97 mm2) were non-significant differences. They were significantly less than the decline in the control group (C-45.04 ± 8.38 mm2 M-31.98 ± 8.34 mm2, D-31.85 ± 8.52 mm2) (P < 0.05). The percentage of newly formed bone in the CGFs/DBBM group (41.99 ± 12.99%) was significantly greater than that in DBBM group (30.68 ± 10.95%) (P < 0.05). The percentage of residual materials in the CGFs/DBBM group (16.19 ± 6.63%) was significantly less than that in the DBBM group (28.35 ± 11.70%) (P < 0.05).

CONCLUSION

Combined application of CGFs and DBBM effectively reduced the resorption of alveolar ridge and resulted in more newly formed bone than the use of DBBM with collagen membranes.

UV-Photofunctionalization of Titanium Promotes Mechanical Anchorage in A Rat Osteoporosis Model

Effects of UV-photofunctionalization on bone-to-titanium integration under challenging systemic conditions remain unclear. We examined the behavior and response of osteoblasts from sham-operated and ovariectomized (OVX) rats on titanium surfaces with or without UV light pre-treatment and the strength of bone-implant integration. Osteoblasts from OVX rats showed significantly lower alkaline phosphatase, osteogenic gene expression, and mineralization activities than those from sham rats. Bone density variables in the spine were consistently lower in OVX rats. UV-treated titanium was superhydrophilic and the contact angle of ddH₂O was ≤5°. Titanium without UV treatment was hydrophobic with a contact angle of ≥80°. Initial attachment to titanium, proliferation, alkaline phosphatase activity, and gene expression were significantly increased on UV-treated titanium compared to that on control titanium in osteoblasts from sham and OVX rats. Osteoblastic functions compromised by OVX were elevated to levels equivalent to or higher than those of sham-operated osteoblasts following culture on UV-treated titanium. The strength of in vivo bone-implant integration for UV-treated titanium was 80% higher than that of control titanium in OVX rats and even higher than that of control implants in sham-operated rats. Thus, UV-photofunctionalization effectively enhanced bone-implant integration in OVX rats to overcome post-menopausal osteoporosis-like conditions.

Fabrication and in-vitro Investigation of Polycaprolactone - (Polyvinyl Alcohol/Collagen) Hybrid Nanofiber as Anti-Inflammatory Guided Tissue Regeneration Membrane

Background:

Periodontal disease is the most common oral condition that affects the tissue surrounding the teeth. The oral cavity is colonized by an impressive array of micro-organisms, many of which can colonize the implants such as Guided Tissue Regeneration (GTR) often utilized in recovering procedures that result in inflammation interfering with the bone regeneration.

Methods:

In the current study, a nano-hybrid GTR membrane is developed as a heliacal structure scaffold with localized drug delivery function (Ibuprofen) as an anti-inflammatory agent. Polycaprolactone (PCL) and a blend of Polyvinyl alcohol (PVA)/collagen (Col) (50/50) were electrospun by electrospinning. Ibuprofen (Ibu) was loaded once in the PCL context and once in the hydrophilic portion (PVA/Col).

Results:

The in vitro release behavior was investigated in each case. Chemical and physical properties were studied for each item. Morphology investigation indicated a heliacal structure with the total average diameter of 1266 nm consististing of porous pores with the average diameter of 256nm.

Conclusion:

The membranes indicated proper mechanical properties and appropriate biodegradation rate as a potential GTR membrane. The controlled and sustained release of Ibu was obtained from both PCL and PVA/COL loaded membranes. Kinetic model study indicated the following zero-order and Higuchi models for the optimum case of PCL loaded and PVA/Col Ibu loaded scaffolds respectively.

Beneficial Effects of Vitamins K and D3 on Redox Balance of Human Osteoblasts Cultured with Hydroxyapatite-Based Biomaterials

Hydroxyapatite-based biomaterials are commonly used in surgery to repair bone damage. However, the introduction of biomaterials into the body can cause metabolic alterations, including redox imbalance. Because vitamins D3 and K (K1, MK-4, MK-7) have pronounced osteoinductive, anti-inflammatory, and antioxidant properties, it is suggested that they may reduce the adverse effects of biomaterials. The aim of this study was to investigate the effects of vitamins D3 and K, used alone and in combination, on the redox metabolism of human osteoblasts (hFOB 1.19 cell line) cultured in the presence of hydroxyapatite-based biomaterials (Maxgraft, Cerabone, Apatos, and Gen-Os). Culturing of the osteoblasts in the presence of hydroxyapatite-based biomaterials resulted in oxidative stress manifested by increased production of reactive oxygen species and decrease of glutathione level and glutathione peroxidase activity. Such redox imbalance leads to lipid peroxidation manifested by an increase of 4-hydroxynonenal level, which is known to influence the growth of bone cells. Vitamins D3 and K were shown to help maintain redox balance and prevent lipid peroxidation in osteoblasts cultured with hydroxyapatite-based biomaterials. The strongest effect was observed for the combination of vitamin D3 and MK-7. Moreover, vitamins promoted growth of the osteoblasts, manifested by increased DNA biosynthesis. Therefore, it is suggested that the use of vitamins D3 and K may protect redox balance and support the growth of osteoblasts affected by hydroxyapatite-based biomaterials.

Impaired osteoblastic behavior and function on saliva-contaminated titanium and its restoration by UV treatment

The objective of this study was to examine behavior and function of osteoblasts on saliva-contaminated titanium and its potential improvement after UV light treatment. Acid-etched titanium disks were contaminated with human saliva. Osteoblasts derived from rat femur were cultured on contaminated and clean titanium disks. Contaminated disks further treated with UV light were also tested. The number of attached cells, the degree of cell spreading, and the expression of adhesion protein were significantly decreased on saliva-contaminated surfaces compared with clean surfaces. The gene expression of osteocalcin was also downregulated on contaminated surfaces, whereas ALP activity and mineralization were not significantly influenced. The impaired functions on contaminated surfaces were significantly increased if the surfaces were further treated with UV and even outperformed the ones on clean titanium surfaces. XPS analysis revealed that the atomic percentage of carbon and nitrogen detected on contaminated surfaces were substantially decreased after UV treatment. These results suggest that osteoblastic behavior and function were compromised on titanium surfaces contaminated with saliva. The compromised functions no longer happened if the surfaces were further treated with UV light, providing the basis to understand the effect of biological contamination on osseointegration and to explore UV treatment as a decontaminating technology.

Current bone substitutes for implant dentistry

PURPOSE

Alveolar ridge augmentation is essential for success in implant therapy and depends on the biological performance of bone graft materials. This literature review aims to comprehensively explain the clinically relevant capabilities and limitations of currently available bone substitutes for bone augmentation in light of biomaterial science.

STUDY SELECTION

The biological performance of calcium phosphate-based bone substitutes was categorized according to space-making capability, biocompatibility, bioabsorption, and volume maintenance over time. Each category was reviewed based on clinical studies, preclinical animal studies, and in vitro studies.

RESULTS

Currently available bone substitutes provide only osteoconduction as a scaffold but not osteoinduction. Particle size, sensitivity to enzymatic or chemical dissolution, and mechanical properties affect the space-making capability of bone substitutes. The nature of collagen fibers, particulate size, and release of calcium ions influence the biocompatibility of bone substitutes. Bioabsorption of bone substitutes is determined by water solubility (chemical composition) and acid resistance (integrity of apatite structure). Bioabsorption of remnant bone substitute material and volume maintenance of the augmented bone are inversely related.

CONCLUSION

It is necessary to improve the biocompatibility of currently available bone substitutes and to strike an appropriate balance between bioabsorption and volume maintenance to achieve ideal bone remodeling.

N-acetyl cysteine as an osteogenesis-enhancing molecule for bone regeneration

Bone regeneration often requires cues from osteogenesis-inducing factors for successful outcome. N-acetyl cysteine (NAC), an anti-oxidant small molecule, possibly modulates osteoblastic differentiation. This study investigated the potential of NAC as an osteogenesis-enhancing molecule in vitro and in vivo. Various concentrations of NAC (0, 2.5, 5.0, and 10 mM) were added to rat bone marrow stromal cell or osteoblastic cell culture in media with or without dexamethasone. The results showed marked enhancement of alkaline phosphatase activity and mineralized matrix formation together with consistent upregulation of bone-related gene markers such as collagen I, osteopontin, and osteocalcin in the osteoblastic culture with addition of 2.5 or 5.0 mM NAC regardless of the presence of dexamethasone. Micro-CT-based analysis and histological observation revealed that addition of NAC to a collagenous sponge implanted in a critical size cortical bone defect (3.0 mm × 5.0 mm) in rat femur yielded acceleration and completion of defect closure, with thick, compact, and contiguous bone after 6 weeks of healing. In contrast, with sponge alone, only sparse and incomplete bone regeneration was observed during the matching healing period. These results indicate that NAC can function as an osteogenesis-enhancing molecule to accelerate bone regeneration by activating differentiation of osteogenic lineages.