Lyndon F. Cooper

Advancing dental implant surface technology--from micron- to nanotopography.

Current trends in clinical dental implant therapy include use of endosseous dental implant surfaces embellished with nanoscale topographies. The goal of this review is to consider the role of nanoscale topographic modification of titanium substrates for the purpose of improving osseointegration. Nanotechnology offers engineers and biologists new ways of interacting with relevant biological processes. Moreover, nanotechnology has provided means of understanding and achieving cell specific functions. The various techniques that can impart nanoscale topographic features to titanium endosseous implants are described. Existing data supporting the role of nanotopography suggest that critical steps in osseointegration can be modulated by nanoscale modification of the implant surface. Important distinctions between nanoscale and micron-scale modification of the implant surface are presently considered. The advantages and disadvantages of nanoscale modification of the dental implant surface are discussed. Finally, available data concerning the current dental implant surfaces that utilize nanotopography in clinical dentistry are described. Nanoscale modification of titanium endosseous implant surfaces can alter cellular and tissue responses that may benefit osseointegration and dental implant therapy.

Macrophage cell lines produce osteoinductive signals that include bone morphogenetic protein-2

Bone wound healing requires osteoinductive signals that are attributed to (the) bone morphogenetic proteins (BMPs). The cellular origin of such osteoinductive signals has only been partially elucidated. Because of the central role of the macrophage in cutaneous wound healing, we hypothesized that the macrophage could play a similar role in osseous healing. It was the aim of the present investigation to examine the possible expression of BMP by the macrophage, and to evaluate the contribution of macrophage products to an early step of bone formation modeled in an in vitro culture system. The synthesis of BMP-2 and BMP-6 by cultured human and murine macrophages was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). When human mesenchymal stem cells (hMSCs) were grown in conditioned media from J774A.1 cells, alkaline phosphatase expression increased. This induction was blocked by anti-BMP-2 antibody and by anti-transforming growth factor-beta1 (TGF-beta1) antibody. Modeling of the macrophage expression of osteoinductive signals by potential physiological situations was evaluated by treatments with lipopolysaccharide (LPS) or macrophage chemotactic peptide-1 (MCP-1). Macrophage BMP-2 expression was reduced by proinflammatory LPS stimulation (which was confirmed to induce release of the proinflammatory cytokine, TNF-alpha), and conditioned media from LPS-treated macrophages had no ability to increase alkaline phosphatase activity in hMSCs. This first study of macrophage BMP-2 expression indicates that the macrophage is capable of physiological regulation consistent with a key role in osteoinduction for osseous wound healing.

The effects of implant surface nanoscale features on osteoblast- specific gene expression

This study investigated the influence of nanoscale implant surface features on osteoblast differentiation. Titanium disks (20.0 x 1.0 mm) with different nanoscale materials were prepared using sol-gel-derived coatings and characterized by scanning electron microscopy, atomic force microscopy and analyzed by X-ray Photoelectron Spectrometer. Human Mesenchymal Stem Cells (hMSCs) were cultured on the disks for 3-28 days. The levels of ALP, BSP, Runx2, OCN, OPG, and OSX mRNA and a panel of 76 genes related to osteogenesis were evaluated. Topographical and chemical evaluation confirmed nanoscale features present on the coated surfaces only. Bone-specific mRNAs were increased on surfaces with superimposed nanoscale features compared to Machined (M) and Acid etched (Ac). At day 14, OSX mRNA levels were increased by 2-, 3.5-, 4- and 3-fold for Anatase (An), Rutile (Ru), Alumina (Al), and Zirconia (Zr), respectively. OSX expression levels for M and Ac approximated baseline levels. At days 14 and 28 the BSP relative mRNA expression was significantly up-regulated for all surfaces with nanoscale coated features (up to 45-fold increase for Al). The PCR array showed an up-regulation on Al coated implants when compared to M. An improved response of cells adhered to nanostructured-coated implant surfaces was represented by increased OSX and BSP expressions. Furthermore, nanostructured surfaces produced using aluminum oxide significantly enhanced the hMSC gene expression representative of osteoblast differentiation. Nanoscale features on Ti implant substrates may improve the osseointegration response by altering adherent cell response.

Biologic determinants of bone formation for osseointegration: Clues for future clinical improvements

STATEMENT OF PROBLEM Further improvement in and expansion of the application of dental implants requires control and improvement of bone mass for implant support. PURPOSE Although osseointegration involves both the formation and the maintenance of bone at implant surfaces, the aim of this article is to identify cellular and molecular determinants of bone formation that may be used in clinical attempts to enhance or expand the application of endosseous implants for dental and craniofacial prosthetics. METHODS A review of bone biology and dental and orthopedic implant literature was performed using Medline and published monographs. RESULTS This spectrum of information indicates that molecular and cellular approaches to creating and maintaining bone mass may be used to expand the application of dental implants and to improve dental implant success in bone-deficient sites.

In vivo evaluation of hsp27 as an inhibitor of actin polymerization: Hsp27 limits actin stress fiber and focal adhesion formation after heat shock

The role of hsp27 as an inhibitor of actin polymerization was considered in the context of the actin cytoskeleton and its relationship with focal adhesion formation. The aim of this study was to evaluate the potential effects of hsp27 on focal adhesion formation as a relevant biological consequence of actin stress fiber formation. When hsp27 was overexpressed in stably transfected cells, cell attachment was delayed and recovery of disrupted stress fibers and focal adhesions was limited. In ROS 17/2.8 cells, heat shock caused the reversible disruption of stress fibers and focal adhesions. The loss of stress fibers and focal adhesions was associated with reduced phosphotyrosine on the focal adhesion kinase (FAK). Microinjection of recombinant 6‐His hsp27 and phosphorylated 6‐His hsp27 was used to demonstrate that nonphosphorylated hsp27 prevented the recovery of stress fibers and focal adhesions. These results provide in vivo evidence that hsp27 acts as an inhibitor of actin polymerization that can alter cellular interactions with extracellular environments by perturbation of stress fibers, and subsequently focal adhesions. J Cell Physiol 177:575–584, 1998.

Incipient Analysis of Mesenchymal Stem-cell-derived Osteogenesis

Tissue regeneration strategies invoke cell-based therapies for effective tissue formation. Current assessment of mesenchymal stem cell (MSC) directed bone regeneration during in vivo assays is dependent on histologic determination of bone formation. It was the aim of this study to determine the relationship between bone sialoprotein (BSP) expression and osteocalcin expression with subsequent osteogenesis occurring in MSC-based implants. RT-PCR assessment of human actin, collagen type I, BSP, and osteocalcin indicated that undifferentiated cells did not express BSP or osteocalcin. Three weeks following implantation, human BSP could be identified in RNAs isolated from the retrieved implants. For every implant from which human BSP cDNA was amplified, parallel implants harvested at 6 weeks demonstrated bone formation at the histologic level. This study confirms that, in the context of the severe combined immunodeficiency disease (SCID) mouse model, culture-expanded, cryopreserved human MSCs have osteogenic potential and demonstrates that implanted cell gene expression can reveal the early onset of bone formation.

The combination of micron and nanotopography by H2SO4/H2O2 treatment and its effects on osteoblast-specific gene expression of hMSCs

H(2)SO(4)/H(2)O(2) treatment of titanium implants imparts nanofeatures to the surface and alters the osteoblast response. The aim of this study was to evaluate the effect of H(2)SO(4)/H(2)O(2) treatment of commercially pure Titanium (cpTi) surfaces on gene expression of human mesenchymal stem cells (hMSCs) differentiated into osteoblasts. Commercially pure grade IV titanium disks (20.0 mm x 1.0 mm) were polished or polished and subsequently treated by grit blasting or grit-blasting/acid etching with an H(2)SO(4)/H(2)O(2) solution. The surfaces were divided into three groups: smooth (S), grit-blasted (Gb), and nanostructured: grit-blasted/acid etched (Nano). Surfaces were examined by scanning electron microscopy and atomic force microscopy. HMSCs were grown on the disks. The data points analyzed were at 3, 7, 14, and 28 days. Real-time PCR was used to measure the mRNA levels of ALP, BSP, Runx2, OCN, OPN, and OSX. The housekeeping gene GAPDH was used as a control. Descriptive statistics were calculated using Microsoft Excel. T-test was performed for comparison of mRNA levels when compared with S surfaces (p < 0.05). All osteoblast-specific genes were regulated in surface-dependent patterns and most of them were upregulated on the Nano surfaces. Runx2 and OSX mRNAs were more than threefold upregulated at days 14 and 28 on Nano. Higher levels for ALP (38-fold), BSP (76-fold), and OCN (3-fold) were also observed on the Nano surfaces. A grit-blasted surface imparted with nanofeatures by H(2)SO(4)/H(2)O(2) treatment affected adherent cell bone-specific gene expression. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Fracture resistance of yttria-stabilized zirconia dental implant abutments

PURPOSE An in vitro study was performed to assess the effect of different degrees of clinical reduction of zirconia abutments on the failure load of clinical assemblies. MATERIALS AND METHODS Zirconia abutments (Y-TZP Ceramic Abutment, Astra Tech) were prepared with 0, 0.5, or 1 mm of external axial reduction starting 1 mm above the height-of-contour. Abutments (n = 10) were attached to implant analogs (25 Ncm torque) embedded in a stainless steel cylinder using Fields metal. Fracture loads (N) were determined when assemblies were loaded at 60 degrees off-axis until failure (Instron, CHS = 0.1 mm/min). Groups were statistically compared using ANOVA (p < 0.05). RESULTS Fracture loads for all assemblies displayed large variations within groups. There were no statistically significant differences (p > 0.05) among different abutment groups with a mean fracture load of 429 N (+/-140) for the control group, 576 N (+/-120) for 0.5-mm margins, and 547 (+/-139) for 1.0-mm margins. All fractures occurred at the interface where the abutment was connected to the analog. CONCLUSION In this in vitro study of simulated ultimate assembly strength, the preparation of zirconia abutments did not significantly impair the fracture resistance of simulated implant assemblies. All implant abutments fractured at rates higher than the maximum incisal forces (90-370 N) estimated to occur in the anterior region of the mouth.

The Current and Future Treatment of Edentulism

The purpose of this review and summary is to focus the clinicians attention on existing potential limitations regarding the management of edentulism. The current published data and opinions concerning the need for treating edentulism, the quality of dentures, related morbidity, and alternative or related therapeutics (e.g., dental implants) suggest there are opportunities for improvement in the treatment of the edentulous population. This may be achieved by adopting a broader therapeutic strategy focused not solely on technical aspects of an oral prosthesis. Instead, a wider array of clinical features of the edentulous patient should be addressed. A contemporary strategy may include concerns for prevention of tooth loss, evaluation of residual alveolar ridge resorption, and related issues of denture function, continual evaluation of oral mucosal health, compassionate management of maladaptive patients, a rationale for timely replacement of dentures, and continued development of dental implant therapies. The importance of therapeutic technical quality can be underscored, but should not overwhelm the broader concerns for assuring the overall health and well-being of the edentulous population.

Restricted and coordinated expression of β3-integrin and bone sialoprotein during cultured osteoblast differentiation

In this study, the expression of beta3-integrin was examined in relationship to the restricted expression of bone sialoprotein (BSP). Immunohistochemical analysis indicated that the alpha(v)beta3-integrin was coincident and proximal to BSP expression in the fetal mandible bovine osteoblast culture model. Alpha(v)beta3-integrin expression was expressed predominantly in a region proximal to, but not including, the substrate adherent cells. In comparison, the alpha5beta1-integrin was expressed in a generalized pattern throughout the culture layers in a coordinated fashion to fibronectin. The temporal expression of beta1- and beta3-integrin was evaluated using RT-PCR and southern blot analysis. Unlike the generalized expression of beta1-integrin, beta3-integrin was restricted to days 3 and 5 of the culture period. The previous demonstration of similar restriction of BSP expression and the present colocalization of BSP suggests the potential coordinated expression of a specific extracellular matrix ligand with a select integrin. Beta3-integrin/BSP adhesion-mediated signaling may play a significant role in the process of osteoblast morphodifferentiation.