Journal of Oral Implantology June 2014 - (Page 294)

CLINICAL Cellular Responses to Metal Ions Released From Implants Thomas B. Kardos, MDS, PhD In the process of calcified tissue formation, cells secrete a protein-rich matrix into which they add a metal ion that nucleates in the presence of phosphorus to form an inorganic salt (usually calcium hydroxyapatite). Cellular and tissue responses to metal ions-released from implants, for example-can therefore be considered from the perspective of how cells handle calcium ions. A critical factor in determining cellular toxicity will be free ion concentrations and the competitive interactions that occur in a physicochemical manner. Three of the parameters used to assess the biocompatibility of implant materials are (1) the ability to influence mitotic activity, (2) intercellular adhesion, and (3) promotion of cell death. A spectrum of responses to free intracellular calcium ions can be identified, ranging from presence of the ion being essential for cell division through to an excess of the free ion that results in cell death (apoptosis). In between these extremes, cells may become postmitotic and express phenotypic variations as they adapt to their environment and establish equilibrium to maintain intracellular calcium homeostasis. The response of cells to implants can be linked to ions released and interactions between these and other ions and/or molecules present in the tissues, similar to the manner in which cells handle calcium ions. Key Words: metal ions, calcium, titanium, bone formation, bone growth INTRODUCTION S ince Branemark coined the term ''osseointegration'' for the tissue responses to placement of a dental implant, there has been intensive research into the development of biocompatible materials for a wide range of biomedical applications. The definition of the term osseointegration has, however, been modified since its introduction to broadly encompass clinical success. There is general agreement that the process of osseointegration depends on several factors, and clinical success is well documented for titanium and titanium-based alloys. Critical to the success of osseointegration is the response of cells that results in the formation of hard tissues, either through the processes of bone formation (osseoinduction-matrix secretion and initiation of mineralization de novo) and/or bone growth (osseoconduction-matrix secretion and addition or removal of mineral to or from an existing mineralized tissue). However, concerns Department of Oral Rehabilitation, University of Otago, Faculty of Dentistry, P.O. Box 647, Dunedin, New Zealand. Corresponding author, e-mail: tom.kardos@otago.ac.nz DOI: 10.1563/AAID-JOI-D-11-00249 294 Vol. XL /No. Three /2014 have been raised over potential adverse effects of some of these implanted materials-in particular, metals-arising from their release of ions into the tissues.1 As all biomaterials will evoke biological responses, a variety of studies have been undertaken to determine significant biological properties of materials. These studies have shown that surface morphology, topography, roughness, chemical composition, surface energy, chemical potential, strain hardening, the presence of impurities, thickness of titanium oxide layer, and the presence of metal and nonmetal composites have a significant influence on responses within the tissues, as reviewed by Elias and Meirelles.1 In an attempt to closely match the physical properties of the implants with those of host bone, a number of titanium alloy scaffolds have been developed to provide ''bone-mimicking'' properties.2 Commonly used metallic elements are tantalum (Ta), niobium (Nb), zirconium (Zr), tin (Sn), molybdenum (Mo), and the semi-metal silicon (Si). The cytotoxicity of these elements has been recently investigated and ''safe'' ion concentrations determined using a range of cell culture assays.2 In these studies, the metallic elements were considered biocompatible if the cell viability in the

Table of Contents for the Digital Edition of Journal of Oral Implantology June 2014

Controlled Early Inflammation and Bone Healing—Potential New Treatments
Zygomatic Implants: The Impact of Zygoma Bone Support on Biomechanics
A Comparative Study on Microgap of Premade Abutments and Abutments Cast in Base Metal Alloys
Topical Simvastatin Improves the Pro-Angiogenic and Pro-Osteogenic Properties of Bioglass Putty in the Rat Calvaria Critical-Size Model
Assessment of the Correlation Between Insertion Torque and Resonance Frequency Analysis of Implants Placed in Bone Tissue of Different Densities
Benefits of Rehabilitation With Implants in Masticatory Function: Is Patient Perception of Change in Accordance With the Real Improvement?
A Method for Fabrication of Implant-Supported Fixed Partial Dentures
Safe Sinus Lift: Use of Acrylic Stone Trimmer to Avoid Sinus Lining Perforation
The Effects of Sinus Membrane Pathology on Bone Augmentation and Procedural Outcome Using Minimal Invasive Antral Membrane Balloon Elevation
Cellular Responses to Metal Ions Released From Implants
A Two-Stage Surgical Approach to the Treatment of Severe Peri-Implant Defect: A 30-Month Clinical Follow-Up Report
Eight-Year Follow-Up of a Fixed-Detachable Maxillary Prosthesis Utilizing an Attachment System: Clinical Protocol for Individuals With Skeletal Class III Malocclusions
Active Implant Peri-Apical Lesion: A Case Report Treated Via Guided Bone Regeneration With a 5-year Clinical and Radiographic Follow-up
Flapless Implant Placement: A Case Report
Active Implant Periapical Lesions Leading to Implant Failure: Two Case Reports
A Review of Platelet Derived Growth Factor Playing Pivotal Role in Bone Regeneration
LETTER TO THE EDITOR
REVIEW OF CURRENT LITERATURE

Journal of Oral Implantology June 2014