Handbook of A dhesive Techn ology Second Edition, Revised and Expanded edited by A Pizzi Universite' de Nancy I Epinal, France K L Mittal Hopewell Junction, New York, U.S.A MARCEL MARCEL DEKKER, INC D E K K E R Copyright © 2003 by Taylor & Francis Group, LLC NEWYORK BASEL Although great care has been taken to provide accurate and current information, neither the author(s) nor the publisher, nor anyone else associated with this publication, shall be liable for any loss, damage, or liability directly or indirectly caused or alleged to be caused by this book The material contained herein is not intended to provide specific advice or recommendations for any specific situation Trademark notice: Product or corporate names may be trademarks or registered trademarks and are used only for identification and explanation without intent to infringe Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 0-8247-0986-1 This book is printed on acid-free paper Headquarters Marcel Dekker, Inc., 270 Madison Avenue, New York, NY 10016, U.S.A tel: 212-696-9000; fax: 212-685-4540 Distribution and Customer Service Marcel Dekker, Inc., Cimarron Road, Monticello, New York 12701, U.S.A tel: 800-228-1160; fax: 845-796-1772 Eastern Hemisphere Distribution Marcel Dekker AG, Hutgasse 4, Postfach 812, CH-4001 Basel, Switzerland tel: 41-61-260-6300; fax: 41-61-260-6333 World Wide Web http://www.dekker.com The publisher offers discounts on this book when ordered in bulk quantities For more information, write to Special Sales/Professional Marketing at the headquarters address above Copyright ß 2003 by Marcel Dekker, Inc All Rights Reserved Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher Current printing (last digit): 10 PRINTED IN THE UNITED STATES OF AMERICA Copyright © 2003 by Taylor & Francis Group, LLC Preface to the Second Edition What can one say about the second edition of any book, especially one like this compendium that contains 50% more material and pages than the rather popular first edition, is heavily revised, expanded, and modernized, and contains 10 new chapters? As editors we can simply say we are elated This is all true, of course, but it sounds so dull! Some readers (particularly younger ones) may expect some profound truth in a preface, a noteworthy dedication, or even an unusual phrase to remember such as the one that graced the preface of another book (Advanced Wood Adhesives Technology, Marcel Dekker, Inc., 1994) So here it is: On my (AP) first day as a university professor (at the University of the Witwatersrand in Johannesburg), I was profoundly impressed by the motto printed on the paper bookmark that was given to me by the administration clerk, ‘‘Wherever a site of higher learning stands, there stands a light in the darkness of human folly.’’ The university meant this to signify how good they were (and they were good, too) It goes much deeper than this, however A site of learning does not need to be a university, or an industrial/research laboratory, but it can be more broadly defined as any source of learning, even, for instance, a book in such an arcane, specialized, but always fascinating, field as adhesives It is for this reason that this volume has been revised and expanded, to function as a site of learning and a springboard for budding adhesive technologists It is dedicated to next generations in the hope that they may build, and build rapidly, on the cumulative wisdom of many specialists distilled in this handbook This book, containing bountiful information, should serve for veterans as a commentary on the current state of knowledge regarding adhesives, and as a Baedeker for those who wish to make their maiden voyage into the wonderful and technologically important area of adhesives In essence it should be valued by and of use to everyone interested, centrally or peripherally, in adhesives and should appeal to polymer chemists, surface chemists, adhesionists, and engineers, as well as users of adhesives We now have the pleasant task of thanking all those who helped in many and varied ways to bring this project to fruition First, we are profoundly thankful to all the authors of the first edition for consenting to again be part of this much enlarged effort Many contributors devoted time and effort to update their chapters As any handbook can benefit from an injection of new blood, so our particular thanks must go to the contributors of new chapters Our appreciation is extended to the staff of Marcel Dekker, Inc for giving this book its form In closing, we can happily say that it has been great fun working with all involved in this project A Pizzi K L Mittal Copyright © 2003 by Taylor & Francis Group, LLC Preface to the First Edition Bonding different materials together by means of an adhesive may appear to most people as a mundane occurrence In reality a great deal of technology backs the apparently simple action of bonding Thus, a complex and advanced technology, or series of technologies, has arisen to deal with adhesives and their applications in many fields The diversity of substrates and the continuous introduction of new processes and materials has ensured that the field of adhesives technology is one of the more swiftly expanding manufacturing endeavors Some excellent handbooks on adhesives already exist although there are very few indeed However, the expansion and diversity of this field has by necessity limited the number of technologies and relevant aspects described in such volumes This volume is no exception to such a trend The editors and authors not pretend that overlaps with other similar works not exist since basic background is often necessary to understand more advanced concepts This volume however covers some aspects of technology that are not described in other volumes of this type It also often looks at already reported technologies from a very different angle It is hoped that such a volume will help to fill some of the technological gaps between the existing literature and industrial reality The volume is divided into four main sections, the first being an introductory overview The remaining three sections are concerned with (1) fundamental aspects, (2) adhesive classes, and (3) some fields in which application of adhesives is very extensive All the contributors are known specialists in their fields who practice their specialties on a daily basis Their chapters are the results of considerable knowledge and experience in their particular niches It is a pleasant duty for the editors and authors, on completing a volume of this nature, to acknowledge the help willingly given by friends, colleagues, their companies, and their institutions Without their help and encouragement most of the chapters presented would not have seen the light of day Last, but definitely not least, our thanks go to Marcel Dekker, Inc and its staff for originating this book, for their help and encouragement, and for prompting us to finish it A Pizzi K L Mittal Copyright © 2003 by Taylor & Francis Group, LLC Contents Preface to the Second Edition Preface to the First Edition Contributors Part 1: Review Topics Historical Development of Adhesives and Adhesive Bonding Fred A Keimel Information Resources William F Harrington Part 2: Fundamental Aspects Theories and Mechanisms of Adhesion J Schultz and M Nardin The Mechanical Theory of Adhesion D E Packham Acid–Base Interactions: Relevance to Adhesion and Adhesive Bonding Mohamed M Chehimi, Ammar Azioune, and Eva Cabet-Deliry Interactions of Polymers in Solution with Surfaces Jean-Franc¸ois Joanny Tailoring Adhesion of Adhesive Formulations by Molecular Mechanics/Dynamics A Pizzi Principles of Polymer Networking and Gel Theory in Thermosetting Adhesive Formulations A Pizzi Application of Plasma Technology for Improved Adhesion of Materials Om S Kolluri 10 Silane and Other Adhesion Promoters in Adhesive Technology Peter Walker 11 Testing of Adhesives K L DeVries and P R Borgmeier 12 The Physical Testing of Pressure-Sensitive Adhesive Systems John Johnston 13 Durability of Adhesive Joints Guy D Davis 14 Analysis of Adhesives David N.-S Hon Copyright © 2003 by Taylor & Francis Group, LLC 15 16 17 18 19 Fracture of Adhesive-Bonded Wood Joints Bryan H River Fracture Mechanics Methods for Interface Bond Evaluations of Fiber-Reinforced Plastic/Wood Hybrid Composites Julio F Davalos and Pizhong Qiao Spectroscopic Techniques in Adhesive Bonding W J van Ooij Ultraviolet Stabilization of Adhesives Douglas Horsey Thermal Stabilization of Adhesives Neal J Earhart, Ambu Patel, and Gerrit Knobloch Part 3: Adhesive Classes 20 Protein Adhesives for Wood Alan L Lambuth 21 Animal Glues and Adhesives Charles L Pearson 22 Carbohydrate Polymers as Adhesives Melissa G D Baumann and Anthony H Conner 23 Natural Rubber-Based Adhesives Sadhan K De 24 Elastomeric Adhesives William F Harrington 25 Polysulfide Sealants and Adhesives Naim Akmal and A M Usmani 26 Phenolic Resin Adhesives A Pizzi 27 Natural Phenolic Adhesives I: Tannin A Pizzi 28 Natural Phenolic Adhesives II: Lignin A Pizzi 29 Resorcinol Adhesives A Pizzi 30 Furan-Based Adhesives Mohamed Naceur Belgacem and Alessandro Gandini 31 Urea–Formaldehyde Adhesives A Pizzi 32 Melamine–Formaldehyde Adhesives A Pizzi 33 Isocyanate Wood Binders Charles E Frazier 34 Polyurethane Adhesives Dennis G Lay and Paul Cranley 35 Polyvinyl and Ethylene–Vinyl Acetates Ken Geddes 36 Unsaturated Polyester Adhesives A Pizzi 37 Hot-Melt Adhesives A Pizzi Copyright © 2003 by Taylor & Francis Group, LLC 38 39 40 41 42 43 44 45 Reactive Acrylic Adhesives Dennis J Damico Anaerobic Adhesives Richard D Rich Aerobic Acrylics: Increasing Quality and Productivity with Customization and Adhesive/Process Integration Andrew G Bachmann Technology of Cyanoacrylate Adhesives for Industrial Assembly William G Repensek Silicone Adhesives and Sealants Loren D Lower and Jerome M Klosowski Epoxy Resin Adhesives T M Goulding Pressure-Sensitive Adhesives T M Goulding Electrically Conductive Adhesives Alan M Lyons and D W Dahringer Part 4: Application of Adhesives 46 Adhesives in the Electronics Industry Monika Bauer and Juărgen Schneider 47 Adhesives in the Wood Industry Manfred Dunky 48 Bioadhesives in Drug Delivery Brian K Irons and Joseph R Robinson 49 Bonding Materials and Techniques in Dentistry Eberhard W Neuse and Eliakim Mizrahi 50 Adhesives in the Automotive Industry Eckhard H Cordes Copyright © 2003 by Taylor & Francis Group, LLC Contributors Naim Akmal* University of Cincinnati, Cincinnati, Ohio, U.S.A Ammar Azioune Interfaces, Traitement, Organisation et Dynamique des Syste`mes (ITODYS), Universite´ Paris 7–Denis Diderot, Paris, France Andrew G Bachmann Dymax Corporation, Torrington, Connecticut, U.S.A Monika Bauer Fraunhofer Institute of Applied Materials Research, Teltow, Germany Melissa G D Baumann Forest Products Laboratory, USDA–Forest Service, Madison, Wisconsin, U.S.A Mohamed Naceur Belgacem Ecole Franc¸aise de Papeterie et des Industries Graphiques (INPG), St Martin d’He`res, France P R Borgmeier University of Utah, Salt Lake City, Utah, U.S.A Eva Cabet-Deliry Laboratoire d’Electrochimie Mole´culaire, Universite´ Paris 7–Denis Diderot, Paris, France Mohamed M Chehimi Interfaces, Traitement, Organisation et Dynamique des Syste`mes (ITODYS), Universite´ Paris 7–Denis Diderot, Paris, France Anthony H Conner Forest Products Laboratory, USDA–Forest Service, Madison, Wisconsin, U.S.A Eckhard H Cordes Mercedes-Benz AG, Bremen, Germany Paul Cranley The Dow Chemical Company, Freeport, Texas, U.S.A D W Dahringer AT&T Bell Laboratories, Murray Hill, New Jersey, U.S.A Dennis J Damico Lord Corporation, Erie, Pennsylvania, U.S.A Julio F Davalos West Virginia University, Morgantown, West Virginia, U.S.A Guy D Davis DACCO SCI, Inc., Columbia, Maryland, U.S.A Sadhan K De Indian Institute of Technology, Kharagpur, India K L DeVries University of Utah, Salt Lake City, Utah, U.S.A Manfred Dunky Dynea Austria GmbH, Krems, Austria Neal J Earhart CIBA-GEIGY Corporation, Ardsley, New York, U.S.A Charles E Frazier Virginia Polytechnic Institute and State University, Blacksburg, Virginia, U.S.A Alessandro Gandini Ecole Franc¸aise de Papeterie et des Industries Graphiques (INPG), St Martin d’He`res, France Ken Geddes Crown Berger Limited, Darwen, Lancashire, England T M Goulding Consultant, Johannesburg, South Africa *Current affiliation: Teledyne Analytical Instruments, City of Industry, California, U.S.A Copyright © 2003 by Taylor & Francis Group, LLC William F Harrington Adhesive Information Services, Mishawaka, Indiana, U.S.A David N.-S Hon Clemson University, Clemson, South Carolina, U.S.A Douglas Horsey CIBA-GEIGY Corporation, Ardsley, New York, U.S.A Brian K Irons* Columbia Research Laboratories, Madison, Wisconsin, U.S.A Jean-Franc¸ois Joanny Institut Charles Sadron, Strasbourg, France John Johnston Consultant, Charlotte, North Carolina, U.S.A Fred A Keimel Adhesives and Sealants Consultants, Berkeley Heights, New Jersey, U.S.A Jerome M Klosowski Dow Corning Corporation, Midland, Michigan, U.S.A Gerrit Knobloch CIBA-GEIGY Corporation, Basel, Switzerland Om S Kolluri HIMONT Plasma Science, Foster City, California, U.S.A Alan L Lambuthy Boise Cascade Corporation, Boise, Idaho, U.S.A Dennis G Lay The Dow Chemical Company, Freeport, Texas, U.S.A Loren D Lower Dow Corning Corporation, Midland, Michigan, U.S.A Alan M Lyons AT&T Bell Laboratories, Murray Hill, New Jersey, U.S.A Eliakim Mizrahi University of the Witwatersrand, Johannesburg, South Africa M Nardin Centre de Recherches sur la Physico-Chimie des Surfaces Solides, CNRS, Mulhouse, France Eberhard W Neuse University of the Witwatersrand, Johannesburg, South Africa D E Packham Center for Materials Research, University of Bath, Bath, England Ambu Patel CIBA-GEIGY Corporation, Ardsley, New York, U.S.A Charles L Pearson Swift Adhesives Division, Reichhold Chemicals, Inc., Downers Grove, Illinois, U.S.A A Pizzi Ecole Nationale Supe´rieure des Technologies et Industries du Bois, Universite´ de Nancy I, Epinal, France Pizhong Qiao The University of Akron, Akron, Ohio, U.S.A William G Repensek National Starch and Chemical Company, Oak Creek, Wisconsin, U.S.A Richard D Rich Loctite Corporation, Rocky Hill, Connecticut, U.S.A Bryan H River Forest Products Laboratory, USDA–Forest Service, Madison, Wisconsin, U.S.A Joseph R Robinson University of Wisconsin, Madison, Wisconsin, U.S.A Juărgen Schneider Fraunhofer Institute of Applied Materials Research, Teltow, Germany J Schultz Centre de Recherches sur la Physico-Chimie des Surfaces Solides, CNRS, Mulhouse, France A M Usmani Firestone, Carmel, Indiana, U.S.A W J van Ooij University of Cincinnati, Cincinnati, Ohio, U.S.A Peter Walker Atomic Weapons Establishment Plc, Aldermaston, Berkshire, England *Current affiliation: University of Wisconsin, Madison, Wisconsin, U.S.A y Deceased Copyright © 2003 by Taylor & Francis Group, LLC Historical Development of Adhesives and Adhesive Bonding Fred A Keimel Adhesives and Sealants Consultants, Berkeley Heights, New Jersey, U.S.A I INTRODUCTION The history of adhesives and sealants is closely related to the history of humankind Some of what are thought of as relatively ‘‘new’’ uses of adhesives have their origins in ancient times, and although most of these materials have been subject to vast changes, others have been changed very little over time As new materials are developed, a review of the history of uses can lead one to see where they might be applied to improve old applications, and sometimes to satisfy requirements of entirely new applications II EARLY HISTORY OF ADHESIVES AND SEALANTS ‘‘Insects, fish and birds know the art of producing mucous body fluids suitable for gluing The load-carrying capacity of the hardened glue, as exemplified by egg-fastening and nest-building, is comparable to that of modern structural adhesives’’ [1, p 1] As humankind evolved, inquisitive persons observed and thought about insect and bird building and repair of nests with mud and clay They encountered spider webs and naturally occurring ‘‘sticky’’ plant and asphaltic materials that entrapped insects, birds, and small mammals Unlike species that use an inherited instinct to perform a single task, human beings adopted the techniques of many species They observed the natural phenomenon of sticky substances, then gathered and used these materials in locations away from their origins, exemplified today by the recently discovered Stone Age natives of South America’s Amazon region and those in the interior of Borneo and New Guinea As rains fell, and then drying set in, many sticky materials regained their sticky properties, and some of the leaves used by ancient peoples to wipe sticky residues from their hands retained small quantities of water Observing this, the first crude waterproof containers were manufactured using what we now call pressure-sensitive adhesives Our early ancestors used mud, clay, snow, and other natural materials to keep vermin, wind, and inclement weather out of their dens, warrens, caves, and other Copyright © 2003 by Taylor & Francis Group, LLC calcium cation–carboxylate interaction, proceeds at a conveniently slow rate After completed placement, the material may be light activated, which initiates polymerization of the methacrylate side groups and entails rapid hardening The presence of residual free carboxyl groups ensures chemical cement bonding to the enamel–dentin adherend as in the conventional products Slow continuing reaction of polyacid and glass filler, following the light-curing step, leads to further maturation of the cement Typical shear bond strength values for light-cured GI cements bonded to dentin range from about to MPa (occasionally even higher [20]), and similar values are obtained for bonds to amalgam Numerous other so-called ‘‘light-curing’’ GI cements have recently been commercialized that are related to the glass ionomers only insofar as they contain a powdery filler made up of GI powder and calcium phosphate as the principal ingredients The matrix component of these materials is a light-curing mixture of mono- and diacrylate monomers As a consequence, their setting shrinkage is considerably larger than that of the conventional GI cements [21] Furthermore, containing no polyacids, these materials are unable to undergo the chemical bonding reaction to enamel–dentin characteristic of the glass ionomers proper, although other bonding mechanisms associated with the acrylate monomers may be quite efficacious Procedural details for GI liner application have been described [22], and a good review of developments in this field is available [23] V CAVITY FILLING While dental amalgam is still the most widely used cavity filling material for the direct restoration of defects in posterior teeth, the retention of amalgam filling is due entirely to macromechanical containment in the undercut cavity The same holds true for the silicate filling materials, which have for many decades been used for anterior restoration These two classes of restoratives are therefore outside the scope of this chapter Of interest as adhesion-active filling materials under the present heading are the glass ionomer cements, including their metal-reinforced varieties (cermets), and the composite resins A Requirements In addition to certain biological requirements, such as cariostatic properties and lack of pulp irritability or systemic toxicity, a filling material should possess low water absorption and should not dissolve in the oral fluids The dimensional changes (generally involving contraction) on hardening of the material should be minimal so as to preclude tensile and/or shear stress concentrations at the interface with tooth structure with resultant development of microleakage, and the thermal properties (e.g., coefficient of thermal expansion and thermal diffusivity) should resemble as far as possible those of the tooth substance so as to minimize the development of interfacial shear and tensile stresses Ideally, the mechanical properties, notably strength and stiffness, should match those of enamel and dentin, and some bonding mechanisms, micromechanical and/or chemical, should be operative between cement and cavosurface Additional requirements, of no major interest in the present context, are concerned with cosmetic considerations, radiopacity, and rheological behavior, the last-named two features being of importance in the clinical application Copyright © 2003 by Taylor & Francis Group, LLC B Materials Glass Ionomers Although prevalently used as luting and cavity-lining cements, the glass ionomers play a moderate part as cavity-filling materials, largely on the strength of their adhesion to the enamel and dentin of the tooth structure, the polyacid components participating in ionic bond formation with calcium cations of the hydroxyapatite in addition to undergoing weak ionic and/or covalent bonding with basic or nucleophilic sites in the dentinal collagen The structural features and bonding mechanisms were discussed in Sections II.B.6 and IV.B.5 The compositions and properties of the GI filling materials are quite similar to those of the luting and lining varieties, the main difference being a more viscous consistency of the filling material, brought about by increased filler/liquid ratios and/or varied types and sizes of the glass–particulate fillers As pointed out earlier, the weak link in GI– enamel bonding frequently is not so much the interface but the cement itself, which is quite brittle and possesses low flexural (15 to 20 MPa) and diametral tensile (8 to 12 MPa) strengths It is largely for this reason that the GI cements are not routinely employed for restoration of permanent teeth, where premature failure would be expected under the load of masticating forces Metal-containing GI materials, known as cermets, are the latest in specialty development in the field of dental ionomer cements The cermets contain a filler phase obtained by fusing silver and other metals or alloys together with aluminosilicate glass and pulverizing the molten mass This is then combined with poly(acrylic acid) in one- or two-part fashion as described in Section II.B.6 The cermets display setting and bonding characteristics resembling those of the metal-free parent cements while displaying better fatigue limits, and in properly poly(acrylic acid)-conditioned cavities, cause significantly less marginal leakage However, there appears to be no clear superiority with respect to other strength characteristics, both tensile and compressive strength values being in the same ranges as observed for representative GI cements, although for a silver–tin–zinc alloy as the metal component, encouraging compressive and diametral tensile strength data (187 and 18 MPa, respectively) have been reported [24] An interesting potential application for reinforced-glass ionomers in restorative dentistry suggests itself for building up cores in severely destructed teeth prior to the placement of crowns Perfect dimensional stability is required for a core to support a superimposed crown efficaciously Conventional composites exposed to moisture are not sufficiently stable dimensionally for this kind of application as a consequence of unduly high water sorption, and there are indications that reinforced GI cements, on account of better dimensional stability, may more adequately fulfill that requirement [25] Composites The shortcomings of the unfilled acrylic resins as luting agents were emphasized in Section II.B.7, and for similar reasons, these clear acrylics have failed to establish themselves as restorative materials The composite resins on the other hand, after a lengthy development period have come to be recognized as one of the most useful and versatile classes of dental materials now available to the clinician for both anterior and posterior restorations [26] Composite resins are essentially ceramic-filled, polymerizable dimethacrylates, the curing (hardening) of which, as pointed out before, involves three-dimensional cross-linking through free-radical polymerization of the acrylic groups, initiated either chemically (i.e., through peroxide–amine redox initiation) or Copyright © 2003 by Taylor & Francis Group, LLC photolytically (i.e., through a light-activated process commonly involving a-diketone photooxidants and amine-type photoreductants) Contrasted with the unfilled acrylic, the present-day composite resin systems feature low exotherms and comparatively low polymerization shrinkage (typically, 1.5%), low water absorption and solubility, yet improved thermal properties, esthetics, biocompatibility, and mechanical stiffness The dimethacrylate resins constituting the matrix generally contain aromatic ring structures to impart rigidity and high viscosity The most common representative, bisGMA, a bisphenol A derivative, was introduced in Section II.B.7 Other partly aromatic and highly viscous, yet less hydrophilic dimethacrylates as currently used matrix components, imparting enhanced dimensional stability, are 2,2-bis(4-methacryloyloxyphenyl) propane (bis-MA) and 2,2-bis[4-(3-methacryloyloxypropoxy)phenyl]propane (bis-PMA) To optimize clinical manipulation, the matrix contains low-viscosity comonomers, including the previously introduced TEGDMA and a large variety of aliphatic and aromatic urethanedimethacrylates Although the degree of conversion and cross-linking increases with raised concentrations of the low-viscosity monomers, at the same time it causes increased polymerization shrinkage with obvious detrimental effects on adhesion to the tooth material Although incremental placement of the composite, with intermittent partial curing of the individual layers, is being practiced in an effort to minimize contraction on curing, this technique tends to reduce the ultimate fracture toughness within the interface between the layers of the restorative A recently described method of compensating for contraction during polymerization utilizes ammonia-treated montmorillonite as a low-percentage additive [27] More promising pointers toward overcoming the polymerization shrinkage problem are found in the excellent work currently performed, inter alia, in the laboratories of Eick [6,28,29] and of Stansbury and Bailey [30] on cyclic monomers consisting of spiro-orthocarbonates, such as the cis–trans isomers of 2,3,8,9-di(tetramethylene)-1,5,7,11-tetraoxaspiro[5.5]undecane or similar structures possessing exocyclic polymerizable double bonds Monomers of this type undergo polymerization with volume expansion, and the reaction can be photoinitiated, for example, with (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate Structural design features have been discussed and methods for volume change measurement presented [31] The presence of exocyclic double bonds may facilitate polymerization, and methacryloyloxy-substituted spiro-orthocarbonates, which also polymerize with volume expansion, offer the potential for copolymerization reactions with conventional resin systems Further advancement in this field can be expected, and this should contribute significantly to the retention properties of composite materials The discontinuous, reinforcing phase of the composites, which on a mass basis constitutes some 50 to 85% of the total cement, consists of siliceous ceramic filler particles, generally crystalline quartz, barium or strontium aluminoborate silica, aluminosilicate glasses, prepolymerized composite material, and specialty biphasic glasses Depending on filler particle size, one distinguishes the conventional composites, with a filler size of to 50 mm, from an important intermediate class of composites featuring 1to 5-mm filler size, a third class known as microfilled composites with a mean particle size of 0.04 mm, and finally, the so-called hybrid composites, which for most efficient packing and highest fracture toughness, typically incorporate some 70 to 75% of conventional filler and to 10% of submicron-size silica filler These variations of filler type, size, and concentration play a major part in affecting the physical and performance characteristics and thus the optimal clinical conditions for application of each one of the numerous types of compositions on the market Copyright © 2003 by Taylor & Francis Group, LLC The strength, fracture toughness, and general durability of the resin–filler combinations in the oral environment are all critically dependent on a strong bond between resin matrix and reinforcement particles Weak interfacial bonding leads to marginal degradation, penetration of oral fluids, and premature wear under the masticatory forces Untreated filler materials are anchored to the matrix essentially by the micromechanical mode, as the polymerizing resin locks into the surface voids and crevasses of the filler or penetrates into the pores of especially porous filler materials Introduction of a chemical adhesion component in the form of coupling agents improves the bonding dramatically The commonly utilized compounds are methacrylate-terminated alkoxysilanes [e.g., 3-methacryloyloxypropyl(trimethoxy)silane], occasionally in combination with zirconates and other co-coupling agents The rationale behind this structural choice is the expectation that, upon treatment of the filler materials (glassy fillers requiring preetching) with coupling agents of this type, silyl ether bonds are formed with surface hydroxyl groups of the filler, while polymerizable vinyl groups protrude from the surface layer and, on compounding with the resin, should be available for copolymerization and cross-linking with the embedding matrix In practice, however, most of the vinyl groups of the silanized filler surface appear to undergo homopolymerization, and the actual resin bonding involves formation of an interpenetrating, rather than cross-linking, network on the interface as the polymerizing matrix resin diffuses into the polymethacrylate surface layer Irrespective of the actual bonding mechanism operative in the interface, silanizing of filler materials prior to compounding with the matrix is generally the accepted method of efficaciously enhancing resin–filler adhesion Typical diametral tensile bond strength values reported for a light-cured, zirconate-treated bis-GMA resin composite containing a silanized glass filler are 55 to 56 MPa, as against 32 MPa for a composite containing untreated glass [32] Bonding Agents One of the most intensely pursued objectives in dental materials research over the past three decades is the achievement of clinically acceptable retention, by micromechanical and/or chemical bonding mechanisms, of the restorative to the prepared enamel and dentinal tooth structure Perfect retention, in addition to providing a major contribution to the longevity of the restoration, would offer the best protection against microleakage of oral fluids along the tooth–restorative interface, with its detrimental consequences of bacterial ingress and secondary caries development Optimally effective interfacial bonding requires complete wetting of the adherend surfaces by the adhesive and the attainment of durable bond strengths matching the inherent strength levels of the dental and restorative components of the joint Although materials science is still a long way from reaching such perfection, much has been accomplished in recent years in pursuit of this goal In view of the importance of dentinal and enamel bonding in restorative practice, the subject is being treated in this section under its own separate heading Also covered here briefly are bonding methods used for prosthodontic and orthodontic attachments and repair The retention of restoratives and restorations to the tooth structure is customarily measured in terms of shear bond strength and, less commonly, tensile bond strength Peel strength measurements, as routinely performed in other segments of adhesion technology, are not particularly predictive here and hence are seldom utilized in restorative dentistry The bond strength data reported in the dental materials literature tend to show considerable variability because of marked sensitivity to the materials and techniques employed Type, age, and preconditioning of the tooth material, type and geometry of the prepared Copyright © 2003 by Taylor & Francis Group, LLC cavity (or other adhesion surface), and the application variables of primer and filling material all are of critical importance, and so are the details of postconditioning (e.g., storage in saline and thermocycling) of the prepared joints, and the techniques and devices used for bond strength testing.* The strength data given in the text should thus be accepted at best as representative, useful indicators of general bonding performance It is equally important to realize that the data reported in the literature have been derived almost entirely from in vitro tests and thus cannot simply be correlated with in vivo results, although their value as predictors of clinical performance remains undisputed The composite materials presently on the market not per se possess adhesive properties conducive to bonding to the hard tissue of tooth structure Auxiliary techniques are available, however, which enable the clinician to overcome this inherent deficiency, and composite-type restorations are routinely placed nowadays under conditions leading to an acceptable, if not perfect degree of bond formation with the cavosurface Thanks to these advances in dental material technology, cavity preparation with large undercuts, as with amalgam fillings, is no longer a necessity for successful restoration, and the beneficial consequences in terms of preservation of healthy tooth structure and minimization of secondary caries through reduction of microleakage are obvious Because of differences in some of the bonding mechanisms between the resin–enamel and resin–dentin adherend pairs, the techniques required for resin bonding to enamel on the one hand, and to the dentinal tooth component on the other, differ in certain aspects Enamel is a biomaterial of low free surface energy and thus will resist wetting by a potential adhesive Moreover, as pointed out before, it consists of 97 wt % mineral constituent, essentially hydroxyapatite Any adhesion process would therefore have to rely almost exclusively on reactions with the exposed apatitic hydroxyl groups, as has been established for the polycarboxylate and ionomer cements (Sections II.B.5 and II.B.6) Reactive partners of this type, however, are absent in the resin-based materials For a mechanical joint, on the other hand, the cut enamel surface, having grooves substantially shallower than 100 nm, lacks the roughness required for retention of the intruding resin tags The advent of the acid etch technique, developed by Buonocore in 1955, changed the situation dramatically Acid etching, in essence an enamel-conditioning process, and by now a standard clinical procedure, involves a brief treatment of the clinically prepared enamel surface with acids, most commonly phosphoric acid, applied as an aqueous (30 to 50%) solution or, more conveniently, as an aqueous gel The resultant increase in free surface energy enhances the wetting characteristics and so enlarges the interfacial contact area In addition, the etching creates microporosity, which allows the subsequently placed resin to flow into the pores, *The divergence of test methods currently employed in different laboratories has prompted numerous calls for international standardization, exemplified by recent proposals to standardize methods for dentinal bond strength determination and, herewith related, for the evaluation of microleakage and marginal gap dimensions [33] On a more universal scale, several years ago, with the aim of developing standardized test methods, a working group was convened by D.R Beech of the Australian Dental Standards Laboratory under the auspices of the International Standards Organisation (ISO) Technical Committee 106 (Dentistry) A draft report, completed in 1991, CD TR 11405, entitled Dental Materials Guidance on Testing of Adhesion to Tooth Structure, presents precise details of screening tests, bond strength measurements, gap and microleakage tests, and clinical usage tests A useful tool for assessment of the reliability of a bond is the Weibull analysis approach [34] The method, utilized now in many laboratories, allows for determination of the probability of bond failure as a function of applied stress Copyright © 2003 by Taylor & Francis Group, LLC forming resin tags with a typical length of 25 mm, thus efficaciously anchoring the composite to the enamel in a micromechanical fashion The depth of hard-tissue penetration is not necessarily, however, the prime contributor to the bonding effect; tag density and inherent strength both are of at least equal importance The placement of heavily filled and viscous composites, including the hybrid types, which may find it difficult to penetrate into the pores, is frequently preceded by application of a layer of unfilled resin of low viscosity compatible with the composite, although the success of this method is questioned by others Typical tensile bond strengths attained between composite resin and acid-etched enamel range from 16 to 23 MPa, highest bond strength values generally being associated with surfaces cut transversely to the enamel crystallites [35] The topic of acid etching has been reviewed by Gwinnett [36] and by Retief [37] In addition to the acid etching technique, methods of enamel etching by laser treatment have more recently been introduced and in general appear to be similarly effective, or even superior, although more cumbersome in clinical practice The development of chemical coupling or bonding agents for resin adhesion to hard tooth structure, pioneered by Bowen several decades ago [38] and more recently reviewed by that author [39], represents a challenging chapter in contemporary dental materials research Although applicable to resin–enamel bonding, the chemical adhesive materials currently available find their major use in resin–dentin bonding applications Contrasted with enamel, dentin contains only 69% hydroxyapatite matter in addition to an increased percentage of organic substance of low surface energy and aqueous fluids, which occupy the dental tubules (Table 1) On a volume basis, the overall organic– aqueous domain makes up more than one-half of the dentinal substance The dentin surface is thus a strongly hydrophilic adherend The bis-GMA and related resin components of the composite, on the other hand, represent hydrophobic constituents A bonding agent intended to join dentinal and composite adherends durably must therefore be hydrophilic enough to displace the aqueous phase from the dentinal surface for subsequent bonding, by whatever mechanism, to the dentinal substrate At the same time, however, it must comprise hydrophobic molecular entities compatible with, and capable of bonding to, the resinous restorative Based on this rationale, early biphasic, surface-active dentin bonding agents, developed in Bowen’s laboratory [38], were of the type N-[2-hydroxy-3(methacryloyloxy)propyl]-N-phenylglycine (NPG-GMA), N-[2-hydroxy-3-(methacryloyloxy)propyl]-N-(4-tolyl)glycine (NTG-GMA), and related structures These compounds are distinguished (1) by the presence of hydrophilic functional amino acid groups capable of chelating or ionic bonding to the apatitic surface calcium and other multivalent cations and to reactive amino groups in the organic (collagen) domains of dentin, and (2) by the presence of reactive vinyl groups capable of copolymerization with composite resin Other first-generation bonding agents contained isocyanatoacrylates or diisocyanate-terminated oligourethanes designed so as to form cross-links between dentinal hydroxyl and amine functions and filler hydroxyl groups Halogenated phosphate esters of bis-GMA, HEMA, and other methacrylate substrates, believed to function through calcium phosphate bonding to dentin and vinyl-type copolymerization with composite resin, were also developed at that time The compounds were applied as thin layers to variously conditioned dentinal surfaces, followed by the placement of standard composites Athough initial results were by no means impressive, shear bond strengths at the very best attaining 10 MPa, these early pioneering investigations provided a powerful impetus to dental bonding research activities worldwide, and although many a development product fell by the wayside for reasons of poor long-term clinical performance, others were developed in the following years to a fairly high level of effectiveness and produced encouraging (although not Copyright © 2003 by Taylor & Francis Group, LLC necessarily clinically acceptable) results Among the bonding systems that have reached the third-generation stage and compete for present-day clinical acceptance are those based on combinations of (1) glutaraldehyde with HEMA; (2) arylglycine-type surface-active monomers with PMDM, the adduct of HEMA to pyromellitic dianhydride; (3) hydrophilic HEMA with hydrophobic bis-GMA; and (4) methyl methacrylate with 4-META, the adduct of HEMA to trimellitic acid anhydride A brief discussion of these examplify bonding systems follows The original glutaraldehyde–HEMA system, developed in Asmussen’s laboratory [40] and commonly known as GLUMA, contains as the critical component a primer consisting of an aqueous solution of glutaraldehyde (5%) and HEMA (35%), which was applied onto the dental surface precleansed with alkali-neutralized (pH 7.4) ethylenediaminetetraacetic acid (17% in water) for smear layer removal and superficial decalcification This was overlaid with a sealer consisting of unfilled, light-cured resin of the bis-GMA type, onto which in turn the composite was placed The primer mixture in this system interpenetrates and forms bonds with the top zone of the partly demineralized dentin matrix, to which it anchors the resinous overlays upon free-radical homo- and copolymerization The bonding effects achieved with this early system were unsatisfactory; average shear bond strengths generally failed to exceed 10 MPa even after the implementation of further (minor) improvements Bond failure occurred along the weakened decalcified dentin zone, as neither the primer nor the sealer diffused through that zone into the underlying calcified matrix Adhesive failure at the sealer–composite interface was also observed [41] Subsequent improvements and simplifications of the GLUMA system included changes in pre-treatment and conversion of the primer into a self-contained bonding resin through inclusion of bis-GMA monomer and initiator A typical presentday GLUMA bonding procedure [42] comprises the following steps: Cavosurface cleansing by treatment with an aqueous solution of aluminum oxalate (ca 5%) and glycine (2.5%) adjusted to pH 1.5 This results in both enamel and dentin etching and in amino acid infiltration into the etched dentin Brush application of bonding resin consisting of glutaraldehyde (5%), HEMA (33%), bis-GMA (2%), camphorquinone photoinitiator (0.1%), water (55%), and acetone (5%), followed by light curing Conventional placement of composite resin In this and similar systems (e.g., with pyruvic acid and glycine as cleanser components) [43,44] the amino acid infiltrated into the dentinal surface zone adds to the concentration of amino groups in that layer and thus contributes to glutaraldehyde bonding; in addition, it is believed to act as the reductant in conjunction with the camphorquinone photooxidant component in the interpenetrating resin, thus upon photoirradiation, initiating resin polymerization right along the contact surface with the cleanser Shear bond strength values as high as 16 to 18 MPa to dentin, and up to 23 MPa to enamel, can be attained with this and similar third-generation GLUMA recipes In the field of bonding agents based on arylglycine–PMDM combinations, numerous advanced versions have originated from Bowen’s early concept of biphasic monomers with both hydrophilic and hydrophobic functional sites as exemplified by the aforementioned NPG-GMA system In our initial version, a second biphasic monomer, 2,5-bis[2-(methacryloyloxy)ethoxycarbonyl]terephthalic acid (PMDM), an addition product of HEMA to pyromellitic dianhydride, was added The dentinal surface was first conditioned with an aqueous acidic solution of iron(III) oxalate, which removed the smear layer and deposited iron cations, contributing to the bonding effect through chelation Next, an acetone soluCopyright © 2003 by Taylor & Francis Group, LLC tion of NPG-GMA or NTG-GMA was applied, followed by treatment with an acetone solution of PMDM and placement of the composite The PMDM comonomer interacted synergistically with the precursor component, spontaneously inducing free-radical polymerization Having passed through various stages of improvement, a current version, available commercially, comprises dentin conditioning with aluminum oxalate (6%) in dilute (2.5%) aqueous nitric acid, followed by application of a premixed acetone solution of NTG-GMA and PMDM After solvent volatilization, this is overlaid with an unfilled, light-curing bis-GMA resin of low viscosity, to be followed by composite placement [39] The micromechanical processes constituting the overall bonding effect have been studied by transmission and scanning electron microscopy* techniques [41,46] Mean shear bond strengths of 17 to 18 MPa have been reported [47,48]; however, lower and quite variable values are also on record, once again stressing the need for standardization of bonding and testing techniques [49] The recent finding in Bowen’s laboratory that the oxalate conditioning and subsequent NPG-GMA coating steps can be replaced by a treatment with acidic NPG without loss of bonding strength has led to a related bonding system, also available commercially, in which the dentin is pretreated with a dilute (2.5%) aqueous nitric acid containing NPG (4%) [39] This removes the smear layer, partially decalcifies the upper dentin layer, and permits interpenetration of the amino acid Subsequent application of a 5% acetone solution of PMDM, with or without added HEMA, provides an overlay of resin, which penetrates into, and through, the decalcified zone and polymerizes spontaneously in contact with the amino acid, forming a resin-reinforced demineralized zone, which then bonds to the subsequently placed composite [46] Tensile bond strengths are 12 to 16 MPa at best, and frequently much lower On the other hand, and in contrast to the behavior of most other contemporary bonding agents, strength tends to increase slightly upon saline storage and thermocycling [50] Failure typically occurs along the adhesive–tooth surface, and the adhesive resin itself is probably the weakest part of the joint Outstanding adhesion perfomance has recently been documented for a modified system in which the key ingredient is a combination of NTG-GMA and BPDM, a biphenyldimethacrylate derivative related to PMDM The two components (called primers), dissolved in acetone, are premixed just prior to multiple-brush application onto the dentinal surface preconditioned either by etching with 10% aqueous phosphoric acid or by treatment with a succinic anhydride-modified HEMA (SA-HEMA) (a hydrophilic/hydrophobic methacrylate possessing a propanoic acid terminal) The low-viscosity primer mixture displaces surface moisture on the dentin and interpenetrates the partly demineralized collagen layer exposed by the etching process and fills the dentinal tubule orifices Subsequent application of an unfilled, photocuring methacrylate bonding resin causes further resin reinforcement of the demineralized zone and subsequent copolymerization This is followed by conventional composite application Mean shear bond strengths range from about 27 to nearly 40 MPa, depending on details of the application technique, and failure is cohesive in dentin The phosphoric acid-etching pre-treatment and tolerance of a *Although not specifically indicated in the text, the techniques of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) represent indispensable tools in the study of bonding processes and are widely used for the qualitative and quantitative evaluation of adherend surfaces, wetting and penetration, gap dimensions, and fracture mechanisms Roulet et al [45] have discussed the use of SEM in margin analysis, and publications dealing with preparatory methods for TEM and SEM investigations have been referenced by Eick et al [46] Copyright © 2003 by Taylor & Francis Group, LLC certain degree of surface moisture (by blotting or mild air drying) both combine to result in optimal bonding, whereas aggressively air-dried surfaces give considerably weaker bonds [51] The system described also lends itself exceedingly well to metal and porcelain bonding and has therefore found application in luting operations and prosthodontics [51,52] For example, a Ni–Cr–Be base metal alloy is bonded to composite with a mean shear bond strength in the vicinity of 25 MPa Key aspects of the NTG-GMA–BPDM primer application have recently been discussed in some detail [52] The development of HEMA–bis-GMA combinations as bonding agents has culminated in a number of recipes showing encouraging performance, and one major representative now on the market, defined as a dentin–enamel bonding system, has received wide attention In a typical protocol, the enamel portions of the prepared cavity are conventionally acid etched, and the dentinal surfaces are primed with an aqueous solution of the hydrophilic HEMA and maleic acid as comonomers This removes the smear layer and provides dentin interpenetration by the two monomers Priming is followed by brush application, in a fairly thick layer (75 to 100 mm), of a resin adhesive composed of HEMA, bis-GMA, and a photoinitiator, with a few percent of a low-viscosity monomer added for viscosity reduction After brief light curing of the adhesive coat, the composite is placed conventionally Because of polymerization inhibition by oxygen, a reactive surface layer containing incompletely polymerized resin is left on the adhesive coat, and subsequent copolymerization with the composite resin overlay affords effective adhesive–composite bonding Although earlier strength data reported were not particularly convincing, recent publications [41] cite mean shear bond strength values as high as 23 MPa, well on a par with enamel bonding data, with fracture for the major part cohesive in dentin or composite Excellent performance with respect to minimal microleakage and marginal gap dimensions relative to competitive bonding systems tested are also on record [53] On the other hand, this bonding system has been found to weaken on storage and thermocycling [41,50] A combination of modified features of the last-named two bonding systems is realized in an adhesive application known as the Kanca technique, in which dentin and enamel pre-treatment by phosphoric acid etching is followed by the consecutive layering of NTG-GMA, PMDM, and HEMA–bis-GMA adhesive resins, onto which the restorative is placed by conventional manipulation Low microleakage, and composite shear bond strengths to enamel/dentin at the 18-MPa level, have been reported [54] The last bonding system to be dealt with in this section, presented in Section II.B.8 as a luting agent, contains as the key monomer the addition product of HEMA to trimellitic acid anhydride, 4-(2-methacryloyloxyethoxycarbonyl)phthalic anhydride (4-META) Following early reports of excellent dentin–composite bonding results with 4-METAcontaining adhesives (tensile bond strengths typically 17 to 18 MPa), preeminently from Nakabayashi’s group and reviewed by that researcher [55], the 4-META system has since been refined to the stage of commercialization and routine clinical use [10,56] It typically comprises the following steps: Short (10 to 30 s) pre-treatment of prepared dentinal surface with the familiar citric acid–iron(III) chloride system (10% and 3%, respectively, in water) Application of bonding resin, composed of 5% 4-META in MMA and premixed with the initiator, a partially oxidized tri-n-butylborane [57] Overlaying of bonding resin coat with a thin layer of powdered poly(methyl methacrylate), followed by placement of composite Copyright © 2003 by Taylor & Francis Group, LLC The acidic iron(III) chloride etchant, as pointed out before, removes the smear layer and acts as a decalcifying agent In addition, just like 4-META itself, it appears to promote acrylate monomer penetration into the etched and partly demineralized dentinal surface The interpenetrated bonding agent containing the hydrophilic–hydrophobic 4-META comonomer may be retained inside the demineralized zone by adsorption onto the hydrophilic and hydrophobic domains present in that zone so that, upon polymerization, a hybrid zone is generated, which consists of resin-reinforced dentinal matter capable of copolymerization with the adjacent overlay of composite restorative Restricting the duration of the etching treatment to the short period indicated is a vital prerequisite for strong dentin–composite bond formation, as this will keep the depth of demineralization to less than 5mm (ca mm in noncarious dentin) and maintain the collagen phase in a reactive (nondenatured) state, thus ensuring complete penetration of the demineralized stratum by the MMA/4-META agent down to the virgin (calcified) dentin matrix before polymerization sets in under the influence of the borane initiator This, in turn, will ensure that no interlayer of decalcified and weakened dentinal material is left between virgin dentin and resin-impregnated stratum, as the exposed collagen, unprotected by infiltrated resin, is susceptible to degradation in an aqueous environment and thus would represent a weak link of the joint [56,58] An outstanding advantage of the borane derivative as the initiator of this 4-META bonding system rests on its activation by water and oxygen as described by Nakabayashi et al [58] The moisture on the dental surfaces in combination with air triggers free-radical generation and thus the initiation of polymerization by the borane at the dentin interface rather than throughout the bulk of the resin layer as in other free-radical-initiated systems This ensures that resin shrinkage proceeds toward the dentin adherend rather than away from it and so provides forceful counteraction against microleakage In a further (commercialized) version, etching with citric acid–iron(III) chloride [containing poly(vinyl alcohol) for viscosity control] is followed by brush application of HEMA monomer (containing hydroquinone monomethyl ether), a subsequent application of the HEMA–4-META combination premixed with the tributylborane initiator, and the final placement of the restorative resin [59] Excellent shear bond strength data, up to nearly 23 MPa, paired with a remarkably low degree of microleakage, have variously been reported [10,41,59,60], and fracture is cohesive in dentine and/or composite The last-named adhesive system is also quite efficacious in prosthodontic and orthodontic bonding applications [61] and in the bonding of amalgam fillings, which in general practice, plugging into an undercut cavity, are retained solely by a micromechanical mode Although dentin–amalgam shear bond strengths, just above MPa, are weak in relation to corresponding dentin–composite strength data, the bond is effective in reducing microleakage appreciably in comparison to conventionally placed amalgam restorative Representative shear bond strength ranges for the bonding agents discussed in the foregoing are listed in Table 5, and the structural representations and universally used abbreviations for the principal methacrylate and dimethacrylate monomers are found in Tables and Detailed characterization techniques for methacrylates and derived polymers have been described by Ruyter and Øysaed [62] VI CONCLUSIONS The foremost objective of operative dentistry is the durable placement of restoratives and the seating of restorations and prosthetic appliances with minimal loss of healthy tooth Copyright © 2003 by Taylor & Francis Group, LLC Table Representative Bond Strength Data for Present-Day Dentin Bonding Agents Dentin conditioning Composite–dentin shear bond strength (MPa) Al oxalate, glycine Al oxalate, diluted HNO3 NPG, diluted HNO3 SA-HEMA or diluted H3PO4 HEMA, maleic acid Fe(III) chloride, citric acid Fe(III) chloride, citric acid, then HEMA 10–18 8–18 7–16 15–29 8–23 10–23 9–22 Bonding agenta Glutaraldehyde, HEMA NTG-GMA, PMDM PMDM NTG-GMA, BPDM HEMA, bis-GMA 4-META, MMA 4-META, HEMA a See Section V.B.3 and Table Source: Literature in period 1989–1993 Table Structures and Abbreviations of Representative Monomethacrylate Monomers Structure Abbreviation MMA HEMA SA-HEMA NPG-GMA NTG-GMA 4-META Copyright © 2003 by Taylor & Francis Group, LLC Table Structures and Abbreviations of Representative Dimethacrylate Monomers Structure Abbreviation Bis-GMA Bis-MA Bis-PMA TEGDMA PMDM BPDM substance With the realization that adhesion technology can be a powerful ally in this endeavor, advanced bonding techniques have in recent years been placed in ever-increasing numbers at the clinician’s disposal in an effort to approach, and ultimately attain, this goal Promising results are evident particularly in the design of bonding techniques permitting enhanced retention of composite restoratives to the enamel and dentinal phases of the tooth substance Progress is also apparent in the development of adhesive systems allowing for the simplified and more efficacious attachment of bridges, inlays, onlays, and veneers to the tooth structure Emphasis in future development work will focus less on the achievement of ever-greater bond strengths than on perfection of adhesion in terms of complete surface wetting, absence of interfacial microleakage with associated cariogenic factors, and enhanced durability of both the adhesive interface and the restorative adherend ACKNOWLEDGMENTS The authors are much indebted to Drs W W Barkmeier, R L Bowen, R L Cooley, J D Eick, N Nakabayashi, D H Retief, and B I Suh for helpful and informative Copyright © 2003 by Taylor & Francis Group, LLC correspondence Thanks are also due to the numerous colleagues who provided reprints or preprints of their latest work, notably Drs E Asmussen, K Hirota, K Hotta, G Øilo, J F Roulet, I E Ruyter, J W Stansbury, M Suzuki, S Takagi, and M J Tyas Mrs Mollie Pearmain is thanked for the proficient typing of the manuscript REFERENCES J F McCabe, Applied Dental Materials, 7th ed., Blackwell, London, 1990 H J Wilson, J McLean, and D Brown, Dental Materials and Their Clinical Applications, British 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Abstr 1000 16 L C Chow, S Takagi, P D Costatino, and C D Friedman, Mater Res Soc Symp Proc 179: (1991) 17 R L Cooley and J W Court, J Esthet Dent 2: 114 (1990) 18 R L Cooley, and V A Sandoval, and S E Barnwell, Quintessence Intern 19: 899 (1988) 19 J W McLean, H J Prosser, and A D Wilson, Brit Dent J 158: 410 (1985) 20 R A McCaghren, D H Retief, E L Bradley, and F R Denys, J Dent Res 69: 40 (1990) 21 M Irie, J Tanaka, H Nakai, K Hirota, and K Tomioka, J Dent Res 69: 311 (1990), Abstr 1620 22 M Suzuki and R E Jordan, J Am Dent Assoc 120: 55 (1990) 23 M J Tyas, Current Opinion Dent 2: 137 (1992) 24 N K Sarkar, B F El Mallakh, and A A Kamar, J Dent Res 69: 366 (1990), Abstr 2061 25 R L Cooley, J W Robbins, and S Barnwell, J Prosthet Dent 64: 651 (1990) 26 R E Jordan and M Suzuki, J Am Dent Assoc 122: 31 (1991) 27 S M Collard, C F Liu, and C D Armeniades, J Dent Res 69: 309 (1990), Abstr 1603 28 F Millich, J D Eick, L Jeang, and T S Byerley, J Polymer Sci A: Polym Chem 31: 1667 (1993) 29 J D Eick, S J Robinson, T S Byerley, and C C Chappellow, Quintessence Intern 24: 632 (1993) 30 J W Stansbury, J Dent Res 70: 527 (1991), Abstr 2088; J Dent Res 71: 239 (1992), Abstr 1070 31 H W Christie, C C Chappellow, T J Byerley, and J D Eick, J Dent Res 69: 309 (1990) F Millich, J D Eick, G P Chen, T J Byerley, and E W Hellmuth, J Polymer Sci B: Polym Phys 31: 729 (1993) 32 H E Strassler, J M Antonucci, and J Marsh, J Dent Res 69: 232 (1990), Abstr 987 33 D H Retief, Am J Dent 4: 231 (1991) 34 S M Aasen, J D Oxman, and F A Ubel, J Dent Res 69: 230 (1990), Abstr 974 Copyright © 2003 by Taylor & Francis Group, LLC 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 T Munechika, K Suzuki, M Nishiyama, M Ohashi, and K Horie, J Dent Res 63: 1079 (1984) A J Gwinnett, Intern Dent J 38: 91 (1988) D H Retief, Operative Dent 12: 140 (1987) R L Bowen, J Dent Res 44: 895, 903, 906, 1369 (1965) R L Bowen and W A Marjenhoff, J Esthet Dent 3: 86 (1991) E C Munksgaard and E Asmussen, J Dent Res 63: 1087 (1984) R P Chappell, J D Eick, J M Mixson, and F C Theisen, Quintessence Intern 21: 303 (1990) J D Eick, S J Robinson, R P Chappell, C M Cobb, and P Spencer, ibid 24: 571 (1993) P A De Aranjo and E Asmussen, Intern Dent J 39: 253 (1989) S Uno and E Asmussen, Acta Odontol Scand 49: 297 (1991) S E Strickland, D H Retief, R S Mandras, and C M Russell, J Dent Res 70 (1991) 396, Abstr No 1043 J F Roulet, T Reich, U Blunck, and M Noack, Scanning Microsc 3: 147 (1989); see also A J E Qualtrough, A Cramer, N H F Wilson, J F Roulet, and M Noack, Intern J Prosthodont 6: 517 (1991) J D Eick, S J Robinson, C M Cobb, R P Chappell, and P Spencer, Quintessence Intern 23: 43 (1992) W W Barkmeier and R L Cooley, Am J Dent 2: 263 (1989) W W Barkmeier, C.-T Huang, P D Hammesfahr, and S R Jefferies, J Esthet Dent 2: 134 (1990) D H Retief, J Esthet Dent 3: 106 (1991) A J L Carracho, R P Chappell, A G Glaros, J H Purk, and J D Eick, Quintessence Intern 22: 745 (1991) W W Barkmeier, B I Suh, and R L Cooley, J Esthet Dent 3: 148 (1991) B I Suh and F A Cincione, Esthet Dent Update 3: 61 (1992) D F Rigsby, D H Retief, C M Russell, and F R Denys, Am J Dent 3: 289 (1990) J Kanca, J Dent Res 69: 231 (1990), Abstr 984 N Nakabayashi, CRC Crit Rev Biocompatibility 1: 25 (1984); Multiphase Biomedical Materials (T Tsuruta and A Nakajima, eds.), Utrecht, The Netherlands, 1989, Chap N Nakabayashi, M Ashizawa, and M Nakamura, Quintessence Intern 23: 135 (1992) N Nakabayashi and E Masuhara, J Biomet Mater Res 12: 149 (1978) N Nakabayashi, M Nakamura, and N Yasuda, J Esthet Dent 3: 33 (1991) R L Cooley, E Y Tseng, and W W Barkmeier, Quintessence Intern 22: 979 (1991) R P Chappell, J D Eick, F C Theisen, and A J L Carracho, Quintessence Intern 22: 831 (1991) K Hotta, M Mogi, F Miura, and N Nakabayashi, Dent Mater 8: 173 (1992) K Hotta, J Jpn Orthodont Soc 52: 360 (1993) I E Ruyter and H Øysaed, CRC Crit Rev Biocompatibility 4: 247 (1988) Copyright © 2003 by Taylor & Francis Group, LLC 50 Adhesives in the Automotive Industry Eckhard H Cordes Mercedes-Benz AG, Bremen, Germany I INTRODUCTION Adhesive bonding and sealing are used for various applications in the modern automotive industry, ranging from flexible car body sealings to high-performance structural adhesives (Fig 1) Adhesive types with specific properties are available for miscellaneous processing The requirements for adhesive bonds have increased due to the extended life of the car In adhesive processing, industrial health and environmental protection aspects have become more and more important Therefore, it is more difficult but nevertheless necessary to determine requirements for the adhesives to be used in the future In addition, the demand for quality standards requiring better quality management is increasing II ADHESIVE APPLICATIONS IN THE AUTOMOTIVE INDUSTRY In this chapter, adhesive bonding and sealing in automobile production are subdivided schematically into five ranges of application: (1) mechanical parts production, (2) the body shop, (3) the paint shop, (4) the assembly shop, and (5) the manufacturing of components Depending on the variety of applications, adhesives must satisfy a wide range of requirements On principle, all body shop adhesives must be usable without risk to the paint shop and they must resist the high temperature of the paint bake ovens Generally, the bond strength and/or sealing ability must perform under severe conditions for the life of the car Further requirements depend on: Function of the material (e.g., spot-weld sealants): good corrosion protection, weldability, no HCl or chlorine emitted to cause corrosion when overbaked, good adhesion on the substrates Processing technique: manual or automatic application, bonding at the assembly line or at a separate working site Specific material characteristics (e.g., moisture and/or hot-curing adhesive): curing time, stability in storage, flexibility at low temperatures, hydrolytic stability, aging resistance, adhesion properties Copyright © 2003 by Taylor & Francis Group, LLC ... hundreds of adhesive manufacturing companies in the United States alone The result of this startling array of diversity is hundreds of thousands of formulations that leave little pockets of knowledge... and materials has ensured that the field of adhesives technology is one of the more swiftly expanding manufacturing endeavors Some excellent handbooks on adhesives already exist although there... Adhesion of Adhesive Formulations by Molecular Mechanics/Dynamics A Pizzi Principles of Polymer Networking and Gel Theory in Thermosetting Adhesive Formulations A Pizzi Application of Plasma Technology