Biological characterization of surface-treated dental implant materials in contact with mammalian host and bacterial cells: titanium versus zirconia

Development of a Coculture Model for Assessing Competing Host Mammalian Cell and Bacterial Attachment on Zirconia versus Titanium

Objectives: Coculture models are limited by bacteria rapidly outcompeting host mammalian cells for nutrients in vitro, resulting in mammalian cell death. The goal of this study was to develop a coculture model enabling survival of mammalian cells and oral bacterial species to assess their competition for growth on dental implant materials. Methods: Two early colonizing oral bacterial species, Streptococcus mutans or Actinomyces naeslundii, were grown in coculture with primary human macrophages or human gingival fibroblasts for up to 7 days on tissue-culture treated polystyrene or polished titanium and zirconia disks. Chloramphenicol was supplemented in cell culture medium at bacteriostatic concentrations to maintain stable bacterial inoculum size. Planktonic and adherent bacterial growth was assessed via spot plating while mammalian cell growth and attachment were evaluated using colorimetric metabolic assay and confocal fluorescence microscopy, respectively. Results: Macrophages and fibroblasts proliferated in the presence of S. mutans and maintained viability above 70% during coculture for up to 7 days on tissue-culture treated polystyrene and polished titanium and zirconia. In contrast, both mammalian cell types exhibited decreasing proliferation and surface coverage on titanium and zirconia over time in coculture with A. naeslundii versus control. S. mutans and A. naeslundii were maintained within an order of magnitude of seeding inoculum sizes throughout coculture. Significance: Cell culture medium supplemented with antibiotics at bacteriostatic concentrations can suppress bacterial overgrowth and facilitate mammalian cell viability in coculture model systems. Within the study's limitations, oral bacteria and mammalian cell growth in coculture are comparable on polished titanium and zirconia surfaces.

Overview of strategies to improve the antibacterial property of dental implants

The increasing number of peri-implant diseases and the unsatisfactory results of conventional treatment are causing great concern to patients and medical staff. The effective removal of plaque which is one of the key causes of peri-implant disease from the surface of implants has become one of the main problems to be solved urgently in the field of peri-implant disease prevention and treatment. In recent years, with the advancement of materials science and pharmacology, a lot of research has been conducted to enhance the implant antimicrobial properties, including the addition of antimicrobial coatings on the implant surface, the adjustment of implant surface topography, and the development of new implant materials, and significant progress has been made in various aspects. Antimicrobial materials have shown promising applications in the prevention of peri-implant diseases, but meanwhile, there are some shortcomings, which leads to the lack of clinical widespread use of antimicrobial materials. This paper summarizes the research on antimicrobial materials applied to implants in recent years and presents an outlook on the future development.

Succession of oral bacterial colonizers on dental implant materials: An in vitro biofilm model

OBJECTIVES

Oral bacterial adhesion on dental implant materials has been extensively studied using in vitro systems but has yielded results restricted to in vitro growth patterns due to limitations in species selection, sustained fastidious anaerobe growth, and mixed culture longevity. The aim of this study was to develop an oral bacterial biofilm model consisting of colonizers representative of the oral microbiome exhibiting temporal shifts characteristic of plaque development and maturation in vivo.

METHODS

Streptococcus oralis, Actinomyces naeslundii, Aggregatibacter actinomycetemcomitans, Veillonella parvula, Fusobacterium nucleatum, and Porphyromonas gingivalis were grown in monoculture prior to combination in mixed culture. Commercially pure titanium (cpTi) and yttria-stabilized zirconia (ZrO2) disks with polished, acid-etched, or sandblasted surfaces were prepared to evaluate oral bacterial adhesion. After 6 h, 1, 3, 7, 14 and 21 days, genomic DNA from planktonic and adherent bacteria was isolated. Quantitative polymerase chain reaction (qPCR) was used to enumerate the amount and proportion of each species.

RESULTS

Early-colonizing S. oralis and A. actinomycetemcomitans, dominated after 6 h prior to secondary colonization by F. nucleatum and V. parvula in planktonic (1 day) and sessile (3 days) form. A. naeslundii maintained relatively low but stable bacterial counts throughout testing. After 14 days, late-colonizing P. gingivalis became established in mixed culture and persisted, becoming the dominant species after 21 days. The composition of adherent bacteria across all substrates was statistically similar at all timepoints with notable exceptions including lower S. oralis bacterial counts on polished cpTi (3 days).

SIGNIFICANCE

Within the present model's limitations, multispecies oral bacterial attachment is similar on surface-treated cpTi and ZrO2.

Stable sol-gel hydroxyapatite coating on zirconia dental implant for improved osseointegration

Aside from being known for its excellent mechanical properties and aesthetic effect, zirconia has recently attracted attention as a new dental implant material. Many studies have focused on hydroxyapatite (HA) coating for obtaining improved biocompatibility, however the coating stability was reduced by a byproduct produced during the high-temperature sintering process. In this study, to overcome this problem, we simply coated the zirconia surface with a sol-gel-derived hydroxyapatite (HA) layer and then sintered it at a varied temperature (<1000 °C). The surface showed a nanoporous structure, and there was no crystalline phase other than HA and zirconia when the sintering temperature was 800 °C. The adhesion strength of the HA layer (>40 MPa) was also appropriate as a dental implant application. In addition, in vitro cell experiments using a preosteoblast cell line revealed that the HA-coated zirconia surface acts as a preferable surface for cell attachment and proliferation than bare zirconia surface. In vivo animal experiments also demonstrated that the osteoconductivity of zirconia were dramatically enhanced by HA coating, which was comparable to that of Ti implant. These results suggest that the sol-gel-based HA-coated zirconia has a great potential for use as a dental implant material.

In vitro biocompatibility of a sandblasted, acid-etched HA composite coating on ultrafine-grained titanium

A sandblasted, acid-etching hydroxyapatite (SLA-HA) composite coating on ultrafine-grained titanium was synthesized by the sandblasting, acid etching and electrophoresis deposition. Mouse osteoblasts (MC3T3-E1) were cultured in vitro and inoculated on the SLA-HA composite coating of the ultrafine-grained titanium. Using ultrafine-grained titanium with SLA coating as the control group, the adhesion and proliferation of the osteoblasts were analyzed using the CCK-8 assay. The number and morphology of the cells were observed using a laser confocal microscope. Cells toxicity of the cytotoxicity to osteoblasts was studied by culturing them in an immersion solution of the SLA-HA composite coating. The hemolysis properties of the obtained material were assessed using fresh rabbit blood. Ultrafine-grained titanium with the SLA-HA composite coating was found to have no significant toxicity to osteoblasts, as well as good blood compatibility, playing a positive role in the adhesion of osteoblasts and promoting their proliferation and differentiation.

Development of a Surface-Functionalized Titanium Implant for Promoting Osseointegration: Surface Characteristics, Hemocompatibility, and In Vivo Evaluation

This study aimed to evaluate the impact of surface-modified biomedical titanium (Ti) dental implant on osseointegration. The surfaces were modified using an innovative dip-coating technique (IDCT; sandblasted, large-grit, and acid-etched, then followed by coating with the modified pluronic F127 biodegradable polymer). The surface morphology and hemocompatibility evaluations were investigated by field-emission scanning electron microscopy, while the contact analysis was observed by goniometer. The IDCT-modified Ti implant was also implanted in patients with missing teeth by single-stage surgical procedure then observed immediately and again four months after placement by cone-beam computerized tomography (CBCT) imaging. It was found that the IDCT-modified Ti implant was rougher than the dental implant without surface modification. Contact angle analysis showed the IDCT-modified Ti implant was lower than the dental implant without surface modification. The hemocompatibility evaluations showed greater red blood cell aggregation and fibrin filament formation on the IDCT-modified Ti implant. The radiographic and CBCT image displayed new bone formation at four months after the IDCT-modified Ti implant placement. Therefore, this study suggests that the IDCT-modified Ti dental implant has great potential to accelerate osseointegration.