UNIVERSITÀ DEGLI STUDI DI TRIESTE Sede Amministrativa del Dottorato di Ricerca DOTTORATO DI RICERCA INGEGNERIA E SCIENZA DEI MATERIALI XXI CICLO RAMAN ANALYSIS OF DENTIN-ADHESIVE INTERFACE (Settore Scientifico Disciplinare Med 28) DOTTORANDA: COORDINATORE DEL COL. DEI DOC.: Dott.ssa Chiara NAVARRA Chiar.mo Prof. Sergio MERIANI RELATORE: Chiar.ma Prof.ssa Milena CADENARO CORRELATORE: Chiar.mo Prof. Lorenzo BRESCHI ANNO ACCADEMICO 2007 - 2008 TABLE OF CONTENTS Chapter 1: Introduction ......................................................................... 1 Chapter 2: Tooth anatomy ................................................................... 11 Chapter 3: Dental adhesion. ................................................................. 19 Chapter 4: Raman spectroscopy: a useful tool for polymerisation monitoring and chemical investigating. .............................. 35 Chapter 5: Degree of conversion of Filtek Silorane Adhesive System and Clearfil SE bond within the hybrid and adhesive layer: an in-situ Raman analysis. .................................................. 51 Chapter 6: Degree of conversion influences interfacial nanoleakage expression of one-step self-etch adhesives.. ....................... 75 Chapter 7: The effect of curing mode on extent of polymerization and microhardness of dual-cured, self-adhesive resin cements.. ............................................................................. 99 Chapter 8: Enamel and Dentin Bond Strength Following Gaseous Ozone Application. ........................................................... 115 Chapter 9: Summary, conclusions and future directions ................... 137 Riassunto, conclusioni e direzioni future ......................................... 145 Curriculum Vitae The thesis was written based upon the publications and articles reported below: Chapter 1: Introduction Chapter 2: Tooth anatomy Perdigão J, Breschi L - Chapter 11 Current Perspectives on Dental Adhesion, 1st edition, 2008, Montage Media Corporation, 1000 Wyckoff Avenue, Mahwah NJ 07430, USA; ISBN 0-9673009-4-0. Chapter 3: Dental adhesion. Chapter 4: Raman spectroscopy: a useful tool for polymerisation monitoring and chemical investigating. L. A. Lyon, C. D. Keating, A. P. Fox, B. E. Baker, L. He, S. R.. Nicewarner, S. P. Mulvaney, M. J. Natan. Raman Spectroscopy. Anal. Chem. 1998, 70, 341R-361R J. R. Ferraro K. Nakamoto. Introductory Raman Spectroscopy. 2nd edition, 1994, Academic Press, San Diego . Chapter 5: Degree of conversion of Filtek Silorane Adhesive System and Clearfil SE Bond within the hybrid and adhesive layer: an in-situ Raman analysis. C.O. Navarra, M. Cadenaro, S.R.. Armstrong, J. Jessop, F. Antoniolli, V. Sergo, R.. Di Lenarda, L. Breschi. Degree of conversion of Filtek Silorane Adhesive system and Clearfil SE Bond within the hybrid and adhesive layer: an in-situ Raman analysis. (Submitted). Chapter 6: Degree of conversion influences interfacial nanoleakage expression one-step self-etch adhesives: a correlative micro- Raman and FEI-SEM analysis. C.O. Navarra, M. Cadenaro, B. Codan, A. Mazzoni, V. Sergo, E. De Stefano Dorigo R.. L. Breschi. Degree of conversion influences interfacial nanoleakage expression one-step self-etch adhesives: a correlative micro- Raman and FEI-SEM analysis. (Submitted). Chapter 7: The effect of curing mode on extent of polymerization and microhardness of dual-cured, self-adhesive resin cements. M. Cadenaro, C.O. Navarra, F. Antoniolli, R.. Di Lenarda, F. Rueggeberg, L. Breschi. The effect of curing mode on extent of polymerization and microhardness of dual-cured, self-adhesive resin cements. (Submitted). Chapter 8: Enamel and dentin bond strength following gaseous ozone application. M. Cadenaro, C. Delise, F. Antoniolli, C.O. Navarra, R. Di Lenarda, L. Breschi. Enamel and dentin bond strength following gaseous ozone application. (In press) CHAPTER 1: INTRODUCTION 1 2 Analysis of the dentin/adhesive interface using Raman spectroscopy The concept of adhesion on dental tissues was introduced in dentistry in the middle of the past century, when the swiss chemist Oskar Hagger developed the archetype of the adhesive monomers [1], a system based on glycerophosphoric acid dimethacrylate, used for the first time by McLean and Kramer for a dental filling: in 1952 they published the first paper on dentinal bonding agents (DBA) [2]. Because of poor adhesion of restorative materials to prepared tooth, early attempts to restore teeth emphasized surgical removal of sound tissue by preparing the cavity to provide mechanical retention through such features as dovetails, grooves, undercuts, sharp internal angles and so forth. But the real “adhesive revolution” began in the Fifty after Michael Buonocore introduced acid etch on dental hard tissues as preconditioning process of the enamel before restoration to increase the fillings retention on the tooth surface [3]; at that time the “Adhesive Dentistry age” started: traditional mechanical methods of preparing the teeth for filling based on the concept “extension for prevention” proposed by Black [4] were replaced by more conservative approaches. Though adhesive techniques were initially employed in operative dentistry to bond fillings to the tooth, in recent times they are used also in prosthetics, orthodontics, and pediatric dentistry. Indication of Adhesive Dentistry The development of materials able to create a tight bond with dental tissues and to resist to the oral environment brought a radical transformation of the dentistry techniques, especially in operative dentistry: now it is possible not only to fill the teeth without sacrificing sound tissue for the mechanical retention to the tooth, but also to correct esthetic flaws (of colour, shape, dimension, etc) without a prosthetic approach, saving sound tissue, time and money. The introduction of endodontic posts which are capable to reach a 3 Analysis of the dentin/adhesive interface using Raman spectroscopy good bond with the dentin in the canal permits to create the core build-up for crowns. In prosthetics bonding agents can be used to cement crowns or partial dentures; in orthodontics using adhesives to place brackets is easier and faster for dentist and patient than in the past. The use of adhesives material in pediatric dentistry leads to fill the baby-teeth very fast, a necessary requirement with children and the use of sealants is worldwide part of preventive programs against the childhood caries. The concept of adhesion The etymology of “adhesion” is derived from the latin word adhaerere, which is a compound verb of ad (to) and haerere (to stick, to attach). The American Society for Testing and Materials, one of the most important society of coding and regulation of the commercial material in the world, defines adhesion between two material as “the condition in which two surfaces are held together by interfacial forces which may consist of valence forces (physical and chemical) or interlocking action (mechanical), or both of them” [6]. Two materials can be defined as adhesive materials if they are able to join, to resist separation and to transmit loads across the interface. The adhesive in adhesive terminology is the adherent, and the substrate which is locked is the adherend. The bond strength is the strength necessary to divide the two adherends. The durability is the time in which the bond is effective. Five theories have been proposed to explain the mechanism of adhesion: 1. Mechanical Adhesion Adhesive materials fill the voids or pores of the surfaces and hold surfaces together by micromechanical interlocking. 4 Analysis of the dentin/adhesive interface using Raman spectroscopy 2. Chemical Adhesion Two materials may form a compound at the interface. The strongest joins are where atoms of the two materials swap (ionic bonding) or share (covalent bonding) outer electrons. A weaker bond is formed if oxygen, nitrogen or fluorine atoms of the two materials share a hydrogen nucleus (hydrogen bonding). 3. Dispersive Adhesion or Adsorption Two materials may be held together by Van der Waals forces. A Van der Waals force is the attraction between two molecules, each with has a region of a positive or negative charge. In the simplest case, such molecules are therefore polar with respect to average charge density, although in larger or more complex molecules, there may be multiple "poles" or regions of greater positive or negative charge. These positive and negative poles may be a permanent property of a molecule (Keesom forces) or a transient effect which can occur in any molecule, as the random movement of electrons within the molecules may result in a temporary concentration of electrons in one region (London forces). 4. Electrostatic Adhesion Some conducting materials may pass electrons to form a difference in electrical charge at the join. This results in a structure creates an attractive electrostatic force between the materials. 5. Diffusive Adhesion When the molecules of both materials are mobile and soluble in each other the materials may merge at the interface by diffusion. This would be 5 Analysis of the dentin/adhesive interface using Raman spectroscopy particularly effective with polymer chains where one end of the molecule diffuses into the other material. It is also the mechanism involved in sintering. When metal or ceramic powders are pressed together and heated, atoms diffuse from one particle to the next, joining the particles into one. The strength of the adhesion between two materials depends on which of the above-said mechanisms occurs between the two materials, on the surface area over which the two materials get in contact and on the wetting of the adherends: materials that wet against each other tend to have a larger contact area than those that don't. The amount of wetting depends on the surface tensions of the materials. The theory of wetting claims that a solid with high surface tension is more wettable than one with low surface tension, and the energy of the adhesive should be smaller than the one of the solid to obtain a good adhesion; this means that the free energy of the bonding agent should be as big as possible to let it penetrate into the surface gaps. The angle between the adhesive and the surface is the contact angle (θ), and it describes the degree of wetting: if the contact angle is low, the wetting will be very favorable because the fluid cover a larger area of the surface; if the angle is high, the wetting will be unfavorable, because the fluid will remain compact on the surface (Fig. 1). Fig.1a: Wetting theory in Fig. 1b: Fluids with crescent wetting (from a to c). relationship with the contact angle (θ). 6