Contents

Contents

Preface - 2nd Ed. Advanced Level

Preface - 1st Ed. Advanced Level

Preface - Book Series

Literature/Trademarks/Other

Introduction

Abbreviations

Terms and Definitions

1 Chemistry/Polymer Chemistry

2 Radiometry

Resin Materials in Dentistry

1 Introduction

2 Modern Dental Resins

Matrix Resins

1 Introduction

2 Functional Groups and Monomer Links

3 Polyreactions

3.1 Polymerization Reactions

3.1.1 Free Radical Polymerization

3.1.1.1 Oxygen Inhibition

3.1.2 Cationic Polymerization

3.1.3 Anionic Polymerization

3.1.4 Ring-Opening Polymerization

3.1.5 Thiol-Ene Polymerization

3.1.6 Technical Polymerization Processes

3.2 Polycondensation

3.3 Polyaddition

4 Matrix Resins According to Links

4.1 Carbon-Carbon Link

4.1.1 Acrylates and Methacrylates

4.1.2 Other Important C-C-Linked Polymers

4.1.2.1 Polyethylene

4.1.2.2 Polypropylene

4.1.2.3 Polyvinyl chloride

4.1.2.4 Polytetrafluoroethylene

4.1.2.5 Polyvinyl acetate

4.1.2.6 Polystyrene

4.1.2.7 Synthetic Rubbers

4.2 Ester Link

4.2.1 Saturated Polyesters

4.2.2 Unsaturated Polyesters

4.2.3 Polycarbonates

4.3 Amide Link

4.4 Urethane Link

4.5 Ether Link

4.5.1 Polyphenylene oxide (PPO)/Polyphenylene ether (PPE)

4.5.2 Poly(aryl-ether-ether-ketone) (PEEK)

4.5.3 Polyoxymethylene (POM)

4.5.4 Epoxide Polymers (EP)

4.6 Siloxane Link

4.7 Sulfone Link

5 Structures and Properties of Monomers and Oligomers

5.1 Acrylates and Methacrylates

5.2 Other Monomers

5.3 Degree of Conversion (DC)

5.3.1 Degree of Conversion of Methacrylate-Based Composites

5.3.2 Degree of Conversion of Silorane-Based Composites

5.3.3 Degree of Conversion of Anionic Polymerization

5.3.4 Degree of Conversion of Polyaddition and Polycondensation

6 Structures and Properties of Polymers

6.1 Types of Chemical Bonds/Forces

6.2 Primary Polymer Structures

6.3 Secondary Polymer Structures

6.4 Tertiary Polymer Structures

6.5 Thermoplastics

6.6 Elastomers

6.7 Duromers

6.8 Interpenetrating Polymer Networks

6.9 Polymer Blends

7 Chemical Reactions of Polymers

7.1 Grafting

7.2 Cross-Linking of Polymers and Vulcanization

7.3 Layering/Incremental Technique and Repair of Resin Composites

Initiators and Catalysts

1 Introduction

2 Initiators

2.1 Thermal/Heat Initiators

2.2 Redox Initiators

2.2.1 Peroxide/Amine-Based Redox Initiators

2.2.2 Barbituric Acid-Based Redox Initiators

2.2.3 Sulfinic Acid-Based Redox Initiators

2.3 Photoinitiators

2.3.1 Conventional Radical Photoinitiators

2.3.2 Tailor-Made Radical Photoinitiators

2.3.3 Cationic Photoinitiators

2.3.4 Radical/Cationic Hybrid Photoinitiators

3 Synergists

4 Catalysts

Fillers

1 Introduction

2 General Effects of Fillers on Material Properties

3 Effect of Refractive Index on Optical Properties

4 Effect of Filler Shape on Mechanical Properties

5 Particle Reinforcement and Material Properties

6 Fiber Reinforcement and Material Properties

7 Organic Fillers

7.1 Adhesion Organic Filler/Resin Matrix

8 Inorganic Fillers

8.1 Adhesion Inorganic Filler/Resin Matrix

8.1.1 Adhesion of Inorganic Filler/Organic Matrix by Silanization

8.1.2 Other Surface Treatments for Adhesion Inorganic Filler/Organic Matrix

Pigments and Dyes

1 Introduction

2 Pigments

3 Dyes

Additives

1 Introduction

2 Stabilizers

3 Antioxidants

4 UV-Stabilizers

5 Plasticizers

Physical and Chemical Properties of Polymers - General Aspects

1 Introduction

2 Physical Properties

3 Chemical Properties

4 Ageing Processes/Depolymerization

Material Testing/Standards

1 Introduction

2 Parameters of Material Testing

3 Standards

4 Some Standard Tests

4.1 Methods to Test Mechanical Properties

4.1.1 Flexural Strength and Modulus of Elasticity

4.1.2 Tensile/Tear Strength and Modulus of Elasticity

4.1.3 Compressive Strength

4.1.4 Impact Strength

4.1.4.1 Izod Impact Strength

4.1.4.2 Charpey Impact Strength

4.1.5 Hardness Tests

4.1.5.1 Brinell Hardness

4.1.5.2 Knoop Hardness

4.1.5.3 Rockwell Hardness

4.1.5.4 Shore Hardness

4.1.5.5 Vickers Hardness

4.2 Chemical Properties

4.3 Other Physical Properties

4.3.1 Color Stability

4.3.2 X-Ray Opacity

4.4 Adhesion Testing

4.4.1 Micro-Tensile Bond Strength (µTBS) Test

4.4.2 Shear Bond Strength (SBS) Test

4.5 Statistics

Toxicology/Clinics/Standards

1 Introduction

2 Toxicology

2.1 Toxic Events

2.2 Toxicity Tests

2.3 Toxicity of Some Raw Materials for Dental Resins

2.3.1 (Meth)acrylic Monomers

2.3.2 (Meth)acrylate-Based Dental Resins - Other Components

2.4 Toxicity of Dental Resins - Evaluation and Summary

2.4.1 (Meth)acrylate-Based Dental Resins

2.4.2 Polysiloxanes and Polyethers

3 Standards for Laboratory Testing

4 Standards for Clinical Testing

Denture Base Resins

1 Introduction

2 Classification and Properties

3 Principal Processing Methods

3.1 Full and Partial Embedment

3.1.1 Pack and Press Technique

3.1.2 Injection Technique

3.1.3 Injection Molding

3.1.4 Pouring/Casting Technique

3.1.5 Melt and Press Technique

3.2 No Embedment

3.2.1 Light-Curing Resins

3.2.2 CAD/CAM Technique

3.3 Insulation of Plaster

4 Polymethyl (meth)acrylates

4.1 Powder/Liquid Products

4.1.1 Powder/Liquid Products - Formulation

4.1.1.1 Heat-Curing Products

4.1.1.2 Self-/Cold-Curing Products

4.1.1.3 Microwave-Curing Products

4.1.2 Powder/Liquid Products - Processing

4.1.2.1 Heat-/Microwave-Curing Products

4.1.2.2 Self-/Cold-Curing Products

4.2 One-Component Products

4.2.1 Polymerizable Products - Formulation and Processing

4.2.1.1 Light-Curing Products - Processing

4.2.1.2 Heat-/Microwave-Curing Products - Processing

4.2.2 Thermoplastic Products - Formulation and Processing

5 Other Denture Base Resins - Formulation and Processing

6 Fit of Dentures

7 Residual Monomer and Denture Intolerance

Resin Teeth

1 Introduction

2 Formulation and Production

3 Properties

4 Processing

Denture Reline Resins

1 Introduction

2 Indications and Requirements

3 Poly(meth)acrylate-Based Reline Materials

4 Polysiloxane-Based Reline Materials

Crown and Bridge Veneer Resins

1 Introduction

2 Classification, Formulation and Processing

2.1 Powder/Liquid Veneer Resins

2.2 One-Component Veneer Resins

3 Properties and Performance of Veneer Resins

3.1 Powder/Liquid Veneer Resins

3.2 One-Component Veneer Resins

Resins for Provisional/Temporary Crowns and Bridges

1 Introduction

2 Formulation and Processing

3 Properties

Resins for Crown Copings and Bridge Frames

Impression Materials

1 Introduction

2 Classification, Processing and Performance

3 Polysulfides

4 Polyethers

5 Polysiloxanes (Silicones)

Resin-Based Filling Composites

1 Introduction

2 Classification

3 Formulation

3.1 General Aspects and Overview

3.2 Microfill Filling Composites

3.3 Hybrid/Micro-Hybrid Filling Composites

3.4 Compomer Filling Composites

3.5 Ormocer Filling Composites

3.6 Nanoparticle Filling Composites

3.7 Silorane Filling Composites

3.8 Bulk-Fill Filling Composites

3.9 Giomer Filling Composites

3.10 Flowable Filling Composites

4 Properties and Performance

4.1 Flexural Strength and Flexural Modulus

4.2 Polymerization Shrinkage and Shrinkage Stress

4.3 Depth of Cure

4.4 Water Sorption, Solubility and Hygroscopic Expansion

4.5 Color Stability

4.6 X-Ray Opacity

4.7 Antibacterial Effects

5 Resins for Prophylaxis

Other Dental Polymers

Light-Curing Devices

1 Introduction

2 Light-Curing Devices for the Dental Practice

3 Light-Curing Devices for the Dental Laboratory

CAD/CAM Technology

1 Introduction

2 Intraoral Scanning

3 Grinding and Milling

4 3D Printing

Adhesion and Adhesives

1 Introduction

2 Theoretical Aspects of Adhesion

2.1 Surface Pretreatment

2.2 Adhesive Bond

2.3 Mechanical Bond

2.4 Chemical Bond

2.5 Geometrical Design of Bonding Surfaces

3 Special Surface Pretreatment Techniques

3.1 Silicatization Processes

3.1.1 Pyrolytic Silicatization

3.1.2 Tribochenical Silicatization

4 Metal/Resin Bond

5 Ceramic/Resin Bond

6 Resin/Resin Bond

7 Hard Tooth Tissues/Resin Bond

7.1 Mechanism of Resin/Enamel-Dentin Bond

7.2 Etchants and Etching Process

7.3 Classification

7.4 Formulation

7.5 Total-Etch Adhesives

7.5.1 3-Step Adhesives

7.5.2 2-Step Adhesives

7.6 Self-Etch Adhesives

7.6.1 2-Step Adhesives

7.6.2 1-Step Adhesives

7.7 Requirements and Properties

7.8 Creation of Dentin Bond - Smear and Hybrid Layer

7.8.1 Total-Etch Technique - Smear Layer Removal

7.8.2 Self-Etch Technique - Smear Layer Fixation and Hybrid Layer Creation

7.8.3 Adverse Effects on the Adhesive/Dentin Bonding Zone

7.9 Biocompatibility

8 Resin-Based Luting Composites

8.1 Conventional Luting Resin Composites

8.2 Self-Etch Luting Resin Composites

8.3 Self-Adhesive Luting Resin Composites

9 Bacterial Adhesion to Resins

Curriculum Vitae

Literature

Index

Preface - 2nd Ed. Advanced Level

Many mistakes and errors were corrected and some chapters reorganized or a little bit extended. Figures and tables were improved. Links were corrected or repaired.

Best regards

Ralf

November 2021

Preface - 1st Ed. Advanced Level

The “Advanced Level” is the second book of the series “Dental Resins - Material Science & Technology”. It comprises around 670 manuscript pages, 253 figures and 57 tables. The Advanced Level presents a very comprehensive and detailed insight into the material science and technology of dental resin polymers and their application and thus enormously extended the knowledge base of the Basic Level. It mainly addresses very interested dentists, teachers of dental universities/schools, postgraduate students, PhD candidates, researchers, material scientists, industrial developers or experts of adjoining professional disciplines.

Many thanks for your interest and best regards

Ralf

January 2021

Preface - Book Series

Resin materials are broadly used in dentistry for almost all indications and they will gain even more importance in future. Especially the increasing performance and efficiency of CAD/CAM technology and 3D-printing open possibilities to use resins not used up to now for dental applications. Besides of dentists, dental technicians, dental students, teachers of dental universities/schools, postgraduate students and PhD candidates there are many other specialists such as researchers, material scientists, industrial developers or experts of adjoining professional disciplines who are technically engaged in dental resins. Mainly two reasons are responsible for this interest: a) many persons dealing with dentistry feel a large desire for deeper knowledge in dental resins, b) the knowledge of many different specialists is requested to develop, to investigate, to test and to evaluate dental resins; c) dental resins offer very sophisticated highly developed properties so that they are also used in other disciplines for other purposes or are the base to develop tailor-made products for other very special non-dental applications.

The idea of this e-Book is to present a three-level textbook dealing with material science and technology of dental resins:

a) The Basic Level addresses students, dental technicians, teachers or all those interested in dental resins. The Basic Level gives a comprehensive insight into chemistry, physics and toxicology of dental resins and their technical application.

b) The Advanced Level broadens the information of the Basic Level significantly and mainly addresses teachers of dental universities/schools, postgraduate students, PhD candidates, researchers, material scientists, industrial developers or experts of adjoining professional disciplines.

c) The Expert Level gives a very deep insight into the science of dental resins and mainly addresses scientists doing research on dental resins, industrial developers or scientists of adjoining professional disciplines who are very strongly interested to become also specialists in dental resin material science. The Expert Level describes also the industrial processes that are used to manufacture dental resins. Furthermore, some exact formulations for some dental products are given; this includes know-how that has never been published before as far as the author knows.

Contrarily to print books, it is the great advantage of e-Books that improvements, corrections, additions or enhancements can be done swiftly so that new improved editions can be produced and distributed rapidly and cheaply. Therefore, the e-Book is the ideal format to update the content immediately whenever errors or mistakes must be eliminated or the scientific progress makes it necessary. It is the desired and planned scenario that the content of this e-Book will not become obsolete as fast as it usually happens with conventional print books but will be refreshed in shorter periods of time.

Illustrations and tables will increase in number with each level. The information they give is - hopefully - clear and understandable but certainly they will not become prettier or colored. This is a low-cost book and everything is done keeping costs to a minimum.

The author is aware that there will be errors, inaccuracies and ambiguousness but hopefully no incorrect or even misleading information in the text despite of all the care taken. The honorable readership is kindly asked for understanding and the author will be very grateful for any hints and proposals to improve the content of the book or the book at all. Therefore, every type of constructive criticism will be highly appreciated.

Having said all this, I hope you will enjoy the book and you will get the information that is helpful and valuable for you and your work.

Many thanks and best regards

Ralf

Literature/Trademarks/Other

Not all the literature used to write this book is specifically cited. Common dental, chemical or material science knowledge taken from textbooks is not specifically cited in the text. Such textbooks are

- dentistry and dental materials [1-20]

- chemistry [21-46]

- adhesives and adhesive technology [47-50]

- material science [50-52]

Also information, figures or tables taken from the author’s sole publications are not specifically cited; these are [53-79].

Information (terms, definitions, etc.) deriving from scientific organizations is not always specifically cited; these organizations are [80-83].

Specific information given is specifically cited.

Product names are not specifically marked as registered even if they are so. Principally brand names are only used when they are important in connection with the described subjects. This might be the case when only one product of a specific product category is available. Apart from that representatives of product categories presented in tables or graphics are anonymized.

Introduction

Besides of metals, alloys and ceramics plastics and composite resins have become to one of the most important material categories in all areas of daily life such as engineering, electronics, building and construction industry, car industry and many other industries as well as in medicine and dentistry. In 1922 Hermann Staudinger discovered these high molecular compounds and called them macromolecules [84]. This was the start of a new until then unknown chemistry called polymer chemistry. The development of numerous polymeric materials and combinations thereof with other organic or inorganic substances or materials gave birth to a huge number of advanced materials with exceptional properties.

In the early years plastics were considered to be cheap and inferior materials but today composite resins and high-performance plastics are very valuable and indispensable in all industries. The most important aspect for the resin materials’ breakthrough is certainly the fact that for nearly every usage custom-made, often also called tailor-made, products can be developed and finally provided. For sure, more and more new, until now unknown, resins or resin composites will be tailor-made for further or today even unknown applications in future.

Resin materials (plastics, composite plastics, composite resins, resin composites) are high molecular mass products (polymers). They are manufactured by transformation of naturally occurring or by synthesis from low molecular mass substances (monomers). These low molecular mass substances (monomers) are the smallest multiple recurring units building the high molecular mass substances (polymers). The properties of each of the resulting polymers depend on how the monomers are linked, on their chemical structure as well as on the spatial configuration of the formed macromolecules. Polymers or macromolecules do not have an exact but an average molecular mass because the single chains building the polymer/macromolecule are growing randomly and not in a well-defined manner.

Abbreviations

Abbreviations important in the context of this book or the dental literature are given in accordance with IUPAC [80-83]. Information given here is important for all levels of this book series.

Monomers

4-Met = 4-methacryloyloxypropyl trimellitic acid

4-Meta = 4-methacryloyloxypropyl trimellitic anhydride

AA = acrylic acid

BDMA = butanediol dimethacrylates

Bis-EDMA (2) = bis-EMA(2) = 2,2-bis[4(3'-methacryloyloxy)ethoxyphenyl)]propane

Bis-GMA = 2,2-bis[4(3'-methacryloyloxy-2'-hydroxy)propoxyphenyl]propane

EDMA = ethylene glycol dimethacrylate

EMA = ethyl methacrylate

GDM = glycerol dimethacrylate

GPDM = glycerol phosphate dimethacrylates

HEMA = hydroxyethyl methacrylate

HPMA = hydroxypropyl methacrylate

i-BuMA = iso-butyl methacrylate

MA = methyl acrylate

MDP = 10-methacryloyloxydecyl dihydrogen phosphate

MMA = methyl methacrylate

PENTA = dipentaerythritol pentaacrylate monophosphate

PMDM = pyromellitic dihydroxethyl methacrylate

TEGDMA = triethylene glycol dimethacrylate

TTEGDMA = tetraethylene glycol dimethacrylates

UDA = 7,7,9-trimethyl-4,13-dioxo-3,14-dioxa-5,12diazahexadecane-1,16-dioxy-diacrylate

UDMA = 7,7,9-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecane-1,16-dioxy-dimethacrylate

Thermoplastics/Duromers

ABS = acrylonitrile butadiene styrene copolymer

APE = aromatic polyester

CA = cellulose acetate

E/P = ethylene propylene copolymer

EP = epoxy polymer

EVA = ethylene vinyl acetate copolymer

HDPE = high density polyethylene

HMWPE = high molecular weight polyethylene

LDPE = low density polyethylene

LLDPE = linear low density polyethylene

PA = polyamide

PAA = polyacrylic acid

PAN = polyacrylonitrile

PBTP = polybutylene terephthalate

PC = polycarbonate

PDMS = polydimethylsiloxane

PE = polyethylene

PEEK = polyaryletheretherketone

PEMA = polyethyl methacrylate

PEO = polyethylene oxide

PES = polyethersulfone

PETP = polyethylene terephthalate

PF = phenol formaldehyde resin

PI = polyimide

PMMA = polymethyl methacrylate

POM = polyoxymethylene

PP = polypropylene

PS = polystyrene

PSU = polysulfone

PTFE = polytetrafluoroethylene

PU = polyurethane

PVAC = polyvinyl acetate

PVAL = polyvinyl alcohol

PVC = polyvinyl chloride

PVC-P = soft PVC - plasticized

PVC-U = hard PVC - unplasticized

SAN = styrene acrylonitrile copolymer

SB = styrene butadiene copolymer, high impact PS = HIPS

TPU = thermoplastic polyurethane

UF = urea-formaldehyde resin

UHMWPE = ultra high molecular weight polyethylene

UP = unsaturated polyester

VPE or XLPE = cross-linked polyethylene

Elastomers/Rubbers

ABR = acrylate butadiene rubber

AU = polyester urethane rubber

BR = butadiene rubber

EPR = ethylene propylene rubber

E-SBR = styrene-butadiene rubber

EU = polyether urethane rubber

FKM = fluoro rubber

IIR = isoprene isobutene rubber = butyl rubber

IR = cis-1,4-polyisoprene = synthetic rubber

NBR = acrylonitrile butadiene rubber = nitrile rubber

NCR = acrylonitrile chloroprene rubber

NIR = acrylonitrile isoprene rubber

NR = natural rubber

PBR = vinylpyridine butadiene

PDMS = polydimethylsiloxane

Composite Resins/Composite Plastics

AFP = asbestos fiber-reinforced plastic

BFK = boric fiber-reinforced plastic

CFK = carbon fiber-reinforced plastic

FK = fiber-reinforced plastic

GFK = glass fiber-reinforced plastic

MFK = metal fiber-reinforced plastic

MWK = metal whiskers fiber-reinforced plastic

SFK = synthetic fiber-reinforced plastic

UD = unidirectional fiber-reinforced plastic

Other

BPO = DBPO = dibenzoyl peroxide

CQ = camphorquinone

HQ = hydroquinone

HQME = hydroquinone monomethyl ether

M = molecular mass [g mol-1]

mass% = percent by mass, often also called wt% = percent by weight

mol = molar mass [mol] is the mass of 1 mole of a given substance divided by the amount of the substance and is expressed in g mol-1. Example: 100 g of water is about (100 g)/(18.015 g mol-1) = 5.551 mol of water

mol% = percent of mole

SEM = scanning electron microscopy

TEM = transmission electron microscopy

tert. arom. amine = tertiary aromatic amine

TPO = (2, 4, 6,-trimethylbenzoyl)diphenylphosphine oxide

vol% = percent by volume

Terms and Definitions

1 Chemistry/Polymer Chemistry

Terms and definitions important in the context of this ebook or the dental literature are explained in accordance with the IUPAC definitions [80-83] or with the literature [29-32, 85, 86].

Additive: Any type of substance that is added in very small quantities to a monomer, oligomer or polymer to improve, alter, and stabilize or to change its properties in any requested direction.

Antioxidant: A substance that inhibits or reduces the oxidation of other molecules or macromolecules, respectively. Primary and secondary antioxidants are differentiated. Primary antioxidants (mostly sterically hindered phenols or amine derivatives of higher molecular mass) are radical scavengers but secondary are not. Secondary antioxidants (sterically hindered phenols of lower molecular mass, organic phosphites or organic sulfides) decompose hydroperoxides to form stable alcohols and, thereby, chain branching can be avoided. It is the common purpose of all antioxidants to hinder or to diminish polymer degradation due to oxidative processes and to preserve the polymer’s properties.

Catalyst: Atoms, molecules or ions which diminish the activation energy with the result that a specific chemical reaction can occur. The catalyst does not participate in the reaction but exists before and after the reaction in the same chemical condition.

Comonomer: A second monomer added to the main monomer.

Constitutional unit: A species of atoms or atomic groups in a macromolecule, polymer or oligomer.

Composite resin/composite plastic: A resin/plastic that contains organic and/or inorganic fillers in all kinds of shapes (fibers, splinters, platelets, crystals, spheres, ligaments, etc.).

Copolymer: A polymer derived from more than one species of monomer.

Copolymerization: Polymerization of more than one species of monomer in which a copolymer is formed.

Cross-linkers: Cross-linkers are multifunctional monomers which form covalent chemical bonds between two separately growing polymeric chains to form a firm polymeric network. For polymerization reaction at least bifunctional monomers are requested, for polyaddition and polycondensation the monomers must be trifunctional at least.

Degree of crystallinity: The percentage of crystalline amount in a thermoplastic polymer.

Degree of conversion: The percentage of monomers that polymerize and form the polymer.

Degree of cross-linking: Relates to the number of groups that interconnect two materials. It is generally expressed in mole percent (mol%).

Degree of polymerization: The number of monomeric units/repeat units in a macromolecule, an oligomer or chain. For homopolymers the number of monomeric units corresponds with the number of repeat units. For copolymers this is not always true and sometimes the degree of polymerization is defined as the number of repeat units. Considering polyamide 66 (PA 66), for instance, the repeat unit consists of two monomeric units (-NH-(CH2)6-NH-OC-(CH2)4-CO-) with the result that a chain of two thousand monomeric units have only one thousand repeat units.

Functional group: A group of atoms in a molecule which significantly determines the reactivity or properties of the molecule (e.g. double bonds, triple bonds, aromatic compounds and hydroxyl or carboxyl groups).

Homopolymer: A polymer derived from only one specific monomer.

Inhibitor = Stabilizer: A molecule which deactivates radicals to inhibit a premature or unintended free radical polymerization. Inhibitors/stabilizers act similar to primary antioxidants.

Initiator: One or more molecules or ions forming radicals under the influence of energy and, thereby, start the free radical polymerization. The initiator takes part in the reaction and is consumed. In case the energy involved is light the initiator is called photoinitiator or light-initiator, in case it is heat it is called thermal or heat initiator, and in case it is “chemical” energy it is called redox initiator.

Ligand: Atom, molecule, ion or radical chemically bonded to a central atom.

Macromolecule/polymer molecule: A molecule of high relative molecular mass, the structure of which derives essentially of the multiple repetitions of molecule units with relatively low molecular mass.

Macroradical: A macromolecule which is a radical.

Matrix resin: Unpolymerized monomer/oligomer blend or polymerized material that may contain different types of fillers (organic or inorganic), initiators, catalysts, stabilizers, pigments or various types of other additives.

Molecule: Two or more identical or different atoms chemically bonded to each other.

Monomer molecule, functionality: It is differentiated between mono-, bi-, tri-, tetra- or penta-functional monomer molecules. Monofunctional molecules have one reactive group, bifunctional have two, trifunctional have three and so on reactive groups to run a polyreaction. Monomers with more than one functional group are also called multifunctional or higher functional monomers; they function as cross-linkers.

Monomer molecule: A molecule which can polymerize and contributes a constitutional unit to the structure of a macromolecule. In other words: the smallest molecule which repeats oneself during a polymerization to form a polymer/macromolecule.

Monomer: A substance composed of molecules each of which can provide one or more constitutional units to a polymer.

Monomeric unit/monomer unit: The largest constitutional unit contributed by a single monomer molecule in a polymerization process to the structure of a macromolecule or oligomer molecule.

Oligomer molecule: A substance of intermediate relative molecular mass composed of a few or more constitutional units repetitively linked to each other. The properties of an oligomer vary with the addition or removal of one or a few of the constitutional units.

Oligomer: A substance composed of oligomer molecules.

Polymer: A substance composed of macromolecules.

Polyaddition: The process of converting a monomer or a mixture of monomers into a polymer by polyaddition reaction.

Polycondensation: The process of converting a monomer or a mixture of monomers into a polymer by polycondensation reaction.

Polymerization: The process of converting a monomer or a mixture of monomers into a polymer by free radical, anionic or cationic polymerization reaction.

Polymerization rate: Can be measured and mathematically expressed. The polymerization rate describes the kinetics/growth rate of the chain propagation.

Polymerization shrinkage (often only called shrinkage): (a) Volumetric Shrinkage: The percentage of volumetric change of the unpolymerized monomer, oligomer or substance during the polymerization. (b)Linear Shrinkage: The percentage of linear change of the unpolymerized monomer, oligomer or substance during the polymerization. The randomly distributed monomer or oligomer molecules move towards each other when polymerized (density increases) and, therefore, need less room. In other words: The density/specific weight of the polymer is higher than of the monomer.

Polyreaction: Any type of process converting a monomer or a mixture of monomers into a polymer.

Pre-polymer molecule: A macromolecule or oligomeric molecule that provides reactive groups for further polymerization and contributes more than one monomeric unit to at least one chain of the final macromolecule.

Pre-polymer: A substance composed of macromolecules or oligomer molecules having reactive polymerizable groups.

Radical (often called: free radical): An atom or molecule that contains an unpaired electron. Mostly, radicals are very reactive substances. They are usually formed when a covalent bond breaks to leave an unpaired electron on each of the two species created by the bond breaking. The symbol is “R•”; the dot symbolizes the free unpaired electron.

Relative molecular mass (often only called molecular mass, obsolete is molecular weight): The sum of the relative atomic masses of all atoms forming a molecule.

Residual monomer: Monomeric molecules of the same or of different species that do not participate in the polymerization but remain in the polymer in their original state.

Residual monomer content: Percentage of monomer that did not participate in the polymerization but remains unpolymerized in the polymer.

Resin/plastic: No consistent and comprehensive definition was found in the literature or the internet. Therefore, it is tried to combine what was found and to formulate a definition to meet the needs of this book and of dental material science. Resin/plastic materials are polymeric materials whose main components are organic or silicon organic macromolecules. These macromolecules can be made synthetically or by transformation of natural products. To become a resin or a plastic material the macromolecule/polymer contains additional ingredients as for instance additives (stabilizers, UV-stabilizers, plasticizers, antioxidants), pigments, dies or fillers. The differentiation between resin/plastic and polymer is not always precise because also homogeneous polymers (e.g. polyethylene, polypropylene, polyvinylchloride or polyaryletheretherketone) are called resins or plastics in case their technical application and thus their properties as a product are considered. Organic macromolecular compounds have a carbon-carbon backbone but the silicon macromolecular ones, the so called polysiloxanes (trivial names: silicones, silicon rubbers) have a silicon-oxygen-silicon backbone with organic ligands or side chains.

Synergist = Accelerator: A substance that increases the polymerization rate. More generally: a substance that increases the rate of a chemical reaction. The synergist/accelerator takes part in the reaction.

UV-stabilizer: A substance that protects the polymer against UV-light.

2 Radiometry

Radiometry is the science and technology of radiation measurement of all wavelengths within the optical spectrum. The radiometric terminology is important to understand the performance of light-curing devices. The most important radiometric terms and their definitions for dental curing-lights are taken from [87-90].

Illuminance: is measured in lux [lx] and describes the total luminous flux incident on a surface per unit area.

Irradiance: Is expressed in Watt per square centimeter [W cm-2] and describes the radiant power [W] an object receives per unit area [cm-2].

Radiant energy: Is expressed in Joule [J] and describes the energy from the light source delivered per unit time [W s-1].

Radiant exitance/radiant emittance: Is expressed in Watt per square centimeter [W cm-2] and describes the radiant power [W] emitted from a known surface area of a light source.

Radiant exposure: Is expressed in Joule per square centimeter [J cm-2] and describes the energy an object receives per unit area [cm-2].

Radiant power/radiant flux: Is expressed in Watt [W] and describes the radiant energy delivered per unit time [J s-1].

Spectral irradiance: Is expressed in Watt per square centimeter and nanometer [W cm-2 nm-1] and describes the irradiance [W cm-2] at each wavelength [nm] of an electromagnetic spectrum.

Spectral radiant power: Is expressed in Watt per nanometer [W nm-1] and describes the radiant power [W] at each wavelength [nm] of an electromagnetic spectrum.

Resin Materials in Dentistry

1 Introduction

Resin materials are of high interest and importance in dentistry. They are used for numerous applications such as dentures, partial dentures, relining of dentures, artificial teeth, fillings, inlays, crowns, bridges, temporary restorations, sealants, luting purposes, adhesives, impressions etc.

Charles Goodyear ran the vulcanization of natural rubber the first time in 1839 and as a result the first resin material was born [64, 91-93]. This process served to manufacture denture bases in the following period of time. Although the natural rubber used for this purpose was pink-colored the esthetic appearance of the denture was very poor because of the rubber’s high opacity. Yet, this process was used till the thirties of the 20th century. Since approx. 1870 celluloid, synthesized from nitrocellulose and camphor, was used for denture bases aside from rubber. Celluloid denture base materials entered the market in the USA under the trademarks Hecolite and Coralite [91, 94, 95]. Around 1900 phenolic resins, developed by Baekeland and, therefore, often called bakelite, with the trademarks Aldenol and Walkerit were also used as denture base materials [53, 64, 91, 95-97].

In 1934 Pierre Castan synthesized the first epoxy polymer resin (trademark: Epoxolon) in the laboratories of DeTrey Fréres Co. (today: DeTrey/Dentsply GmbH, Germany) in Switzerland while he was searching for an improved denture base material and obtained a patent in 1940 [53, 64, 91, 98]. Although they were never used for dentures since then epoxy polymers were used for products of highest quality demands. Other plastics like benzyl cellulose (trademark: Pertax), polyamides (trademark: Protenyl), polystyrenes (trademark: Polystein), polyvinyl chloride (trademark: Hekodent, Hewodent) or polyolefins (trademark: Odenta) had similar destinies. They were only used for a short period of time as denture base materials [39, 53, 64, 91, 95-97].

The crucial ascent of polymer chemistry started in the thirties of the 20th century with Otto Röhm’s development of methyl methacrylate (also called: methacrylic acid methyl ester or MMA) from which he synthesized via polymerization polymethyl methacrylate (also called: polymethacrylic acid methyl ester or PMMA) [91, 99]. PPMA has the well-known trademark Plexiglas. In 1936 PMMA determined the great breakthrough in dental materials. The dental technician Gottfried Roth mixed milled PMMA with its monomer MMA and stirred the mixture until it becomes dough-like. Then he processed it the same way as it was commonly done to manufacture rubber dentures. He pressed the dough between two halves of a plaster mold representing the denture and boiled the whole assembly in a water bath until the dough was hardened [91]. This was the first time esthetically satisfying dentures were obtained and the method as well as the materials were patented in 1936 [91, 100]. This process was improved and optimized in the following years and decades and it is broadly used to manufacture dentures up to now. Later developments substituted MMA by numerous newly synthesized methacrylates, dimethacrylates or multifunctional methacrylates with sometimes very high molecular masses. This led to totally new high-performance composite resins that can be used for nearly almost all indications in the oral cavity.

Later MMA/PMMA composites [101-103] and newly developed high molecular mass methacrylates [104-106] were the base of modern resin-based filling materials and adhesives. R. L. Bowen laid the foundation stone for modern resin composite filling materials by his crucial research work and inventions and thus revolutionized restorative dentistry [104-111].

It was and it is still tried to use other polymers such as polycarbonates or polyacetals (also called polyoxymethylene or POM) to manufacture dentures. These products are processed via injection molding technique but they did not succeed on the market and are only occasionally used.

POM and polyaryletheretherketone (PEEK) processed via CAD/CAM are used today to manufacture denture bases or suprastructures which are usually made from metal. Very likely other polymers will be used for dental purposes in future due to the upcoming innovative processing techniques like CAD/CAM grinding or milling or 3D-printing.

Since 1955 the elastomeric polymers, the polysulfides, and in 1958 [112] the polysiloxanes (also called silicones) entered the dental market and were predominantly applied in the oral cavity for performing impressions. Today, the polysiloxanes dominate this segment. Since 1966 the polyether impression materials also took a great part of this segment [113, 114]. But polysiloxanes are also used in the dental laboratory for duplicating or embedding purposes.

2 Modern Dental Resins

1b

The chemical and physical properties of polymers are determined by the

- type of monomers

- type of monomeric links

- alignment of the monomers (primary structure)

- spatial alignment of the monomers in the polymeric chains (secondary structure)

- spatial alignment of the chains’ secondary structures against each other (tertiary structure)

There are numerous different monomers available to create the resin matrix. Depending on the type of monomer different resins with different chemical and physical properties emerge. The chosen monomers determine the type of link by the functional groups reacting with each other and thus also the type of polyreaction as well. The type of link determines the name of the polymer. The next chapter presents various polymers, also called matrix resins, their links and the respective polyreaction.

Fig. 1b: Principal composition of composite resins.