craig's restorative dental materials 13th ed. - r. sakaguchi, j. powers (mosby, 2012)

Craig’s
RESTORATIVE
DENTAL
MATERIALS
THIRTEENTH EDITION
EDITED BY
Ronald L. Sakaguchi, DDS, MS, PhD, MBA
Associate Dean for Research and Innovation
Professor
Division of Biomaterials and Biomechanics
Department of Restorative Dentistry
School of Dentistry
Oregon Health and Science University
Portland, Oregon
John M. Powers, PhD
Editor
The Dental Advisor
Dental Consultants, Inc
Ann Arbor, Michigan
Professor of Oral Biomaterials
Department of Restorative Dentistry and Biomaterials
UTHealth School of Dentistry
The University of Texas Health Science Center at Houston
Houston, Texas
1600 John F. Kennedy Blvd.
Ste 1800
Philadelphia, PA 19103-2899

CRAIG’S RESTORATIVE DENTAL MATERIALS ISBN: 978-0-3230-8108-5
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Library of Congress Cataloging-in-Publication Data
Craig’s restorative dental materials / edited by Ronald L. Sakaguchi, John M. Powers. 13th ed.
p. ; cm.
Restorative dental materials
Order of editors reversed on prev. ed.
Includes bibliographical references and index.

ISBN 978-0-323-08108-5 (pbk. : alk. paper) 1. Dental materials. I. Sakaguchi, Ronald L.
II. Powers, John M., 1946- III. Title: Restorative dental materials.
[DNLM: 1. Dental Materials. 2. Dental Atraumatic Restorative Treatment. WU 190]
RK652.5.P47 2012
617.6’95 dc23
2011015522
Vice President and Publishing Director: Linda Duncan
Executive Editor: John J. Dolan
Developmental Editor: Brian S. Loehr
Publishing Services Manager: Catherine Jackson/Hemamalini Rajendrababu
Project Manager: Sara Alsup/Divya Krish
Designer: Amy Buxton
Printed in United States
Last digit is the print number: 9 8 7 6 5 4 3 2 1
To the many mentors and colleagues
with whom we have collaborated.



vii
Contributors
Roberto R. Braga, DDS, MS, PhD
Professor
Department of Dental Materials
School of Dentistry
University of São Paulo
São Paulo, SP, Brazil
Chapter 5: Testing of Dental Materials and Biomechanics
Chapter 13: Materials for Adhesion and Luting
Isabelle L. Denry, DDS, PhD

Professor
Department of Prosthodontics and Dows Institute
for Dental Research
College of Dentistry
The University of Iowa
Iowa City, Iowa
Chapter 11: Restorative Materials—Ceramics
Jack L. Ferracane, PhD
Professor and Chair
Department of Restorative Dentistry
Division Director, Biomaterials and Biomechanics
School of Dentistry
Oregon Health & Science University
Portland, Oregon
Chapter 6: Biocompatibility and Tissue Reaction to
Biomaterials
Sharukh S. Khajotia, BDS, MS, PhD
Professor and Chair
Department of Restorative Dentistry
College of Dentistry
University of Oklahoma Health Sciences Center
Oklahoma City, Oklahoma
Chapter 2: The Oral Environment
David B. Mahler, PhD
Professor Emeritus
Division of Biomaterials and Biomechanics
Department of Restorative Dentistry
School of Dentistry
Oregon Health and Science University
Portland, Oregon

Chapter 10: Restorative Materials—Metals
Grayson W. Marshall, DDS, MPH, PhD
Distinguished Professor and Chair
Division of Biomaterials and Bioengineering
Vice-Chair, Department of Preventive and
Restorative Dental Sciences
School of Dentistry
University of California San Francisco
San Francisco, California
Chapter 2: The Oral Environment
Sally J. Marshall, PhD
Vice Provost, Academic Affairs
Director of the Office of Faculty Development and
Advancement
Distinguished Professor Division of Biomaterials
and Bioengineering
Department of Preventive and Restorative Dental
Sciences
School of Dentistry
University of California San Francisco
San Francisco, California
Chapter 2: The Oral Environment
John C. Mitchell, PhD
Associate Professor
Division of Biomaterials and Biomechanics
Department of Restorative Dentistry
School of Dentistry
Oregon Health and Science University
Portland, Oregon
Chapter 6: Biocompatibility and Tissue Reaction to

Biomaterials
Chapter 15: Dental and Orofacial Implants
Chapter 16: Tissue Engineering
Sumita B. Mitra, PhD
Partner
Mitra Chemical Consulting, LLC
West St. Paul, Minnesota
Chapter 9: Restorative Materials—Polymers
Chapter 13: Materials for Adhesion and Luting
Kiersten L. Muenchinger, AB, MS
Program Director and Associate Professor
Product Design
School of Architecture and Allied Arts
University of Oregon
Eugene, Oregon
Chapter 3: Design Criteria for Restorative Dental Materials
viii
CONTRIBUTORS
Carmem S. Pfeifer, DDS, PhD
Research Assistant Professor
Department of Craniofacial Biology
School of Dental Medicine
University of Colorado
Aurora, Colorado
Chapter 4: Fundamentals of Materials Science
Chapter 5: Testing of Dental Materials and Biomechanics
John M. Powers, PhD
Editor
The Dental Advisor
Dental Consultants, Inc.

Ann Arbor, Michigan
Professor of Oral Biomaterials
Department of Restorative Dentistry
and Biomaterials
UTHealth School of Dentistry
The University of Texas Health Science Center
at Houston
Houston, Texas
Chapter 12: Replicating Materials—Impression and Casting
Chapter 14: Digital Imaging and Processing for
Restorations
Ronald L. Sakaguchi, DDS, MS, PhD, MBA
Associate Dean for Research and Innovation
Professor
Division of Biomaterials and Biomechanics
Department of Restorative Dentistry
School of Dentistry
Oregon Health and Science University
Portland, Oregon
Chapter 1: Role and Significance of Restorative Dental
Materials
Chapter 3: Design Criteria for Restorative Dental Materials
Chapter 4: Fundamentals of Materials Science
Chapter 5: Testing of Dental Materials and Biomechanics
Chapter 7: General Classes of Biomaterials
Chapter 8: Preventive and Intermediary Materials
Chapter 9: Restorative Materials—Composites and Polymers
Chapter 10: Restorative Materials—Metals
Chapter 14: Digital Imaging and Processing for
Restorations

Chapter 15: Dental and Orofacial Implants
ix
Preface
The thirteenth edition of this classic textbook has
been extensively rewritten to include the many
recent developments in dental biomaterials science
and new materials for clinical use. One of our goals
for this edition is to include more clinical applica-
tions and examples, with the hope that the book will
be more useful to practicing clinicians. The book con-
tinues to be designed for predoctoral dental students
and also provides an excellent update of dental bio-
materials science and clinical applications of restor-
ative materials for students in graduate programs
and residencies.
Dr. Ronald L. Sakaguchi is the new lead editor of
the thirteenth edition. Dr. Sakaguchi earned a BS in
cybernetics from University of California Los Angeles
(UCLA), a DDS from Northwestern University, an MS
in prosthodontics from the University of Minnesota,
and a PhD in biomaterials and biomechanics from
Thames Polytechnic (London, England; now the Uni-
versity of Greenwich). He is currently Associate Dean
for Research & Innovation and a professor in the Divi-
sion of Biomaterials & Biomechanics in the Depart-
ment of Restorative Dentistry at Oregon Health &
Science University (OHSU) in Portland, Oregon.
Dr. John M. Powers is the new co-editor of the
thirteenth edition. He served as the lead editor of the
twelfth edition and contributed to the previous eight

editions. Dr. Powers earned a BS in chemistry and a
PhD in mechanical engineering and dental materials
at the University of Michigan, was a faculty member
at the School of Dentistry at the University of Michi-
gan for a number of years, and is currently a professor
of oral biomaterials in the Department of Restorative
Dentistry and Biomaterials at the UTHealth School
of Dentistry, The University of Texas Health Science
Center at Houston. He was formerly Director of the
Houston Biomaterials Research Center. Dr. Powers is
also senior vice president of Dental Consultants, Inc.,
and is co-editor of The Dental Advisor.
The team of editors and authors for the thirteenth
edition spans three generations of dental research-
ers and educators. Dr. Sakaguchi received his first
exposure to dental biomaterials science as a first-year
dental student at Northwestern University Dental
School. Drs. Bill and Sally Marshall were the instruc-
tors for those courses. After many years of men-
toring received from Drs. Bill Douglas and Ralph
DeLong, and Ms. Maria Pintado at the University
of Minnesota, Dr. Sakaguchi joined the biomaterials
research team in the School of Dentistry at OHSU with
Drs. David Mahler, Jack Mitchem and Jack Ferracane.
The OHSU laboratory benefited from the contributions
of many visiting professors, post- doctoral fellows, and
graduate students, including Dr. Carmem Pfeifer who
conducted her PhD research in our laboratory. Thanks
to the many mentors who generously contributed
directly and indirectly to this edition of the book.

We welcome the following new contributors to the
thirteenth edition and thank them for their effort and
expertise: Drs. Bill and Sally Marshall of University of
California San Francisco (UCSF); Dr. Sumita Mitra of
Mitra Chemical Consulting, LLC, and many years at
3M ESPE; Dr. Jack Ferracane of OHSU; Dr. Roberto
Braga of the University of São Paulo; Dr. Sharukh
Khajotia of the University of Oklahoma; Dr. Carmem
Pfeifer of the University of Colorado, and Professor
Kiersten Muenchinger of the University of Oregon.
We also thank the following returning authors for
their valuable contributions and refinements of con-
tent in the thirteenth edition: Dr. David Mahler of
OHSU, Dr. John Mitchell of OHSU, and Dr. Isabelle
Denry of the University of Iowa, previously at The
Ohio State University.
The organization of the thirteenth edition has been
modified extensively to reflect the sequence of content
presented to predoctoral dental students at OHSU.
Chapters are organized by major clinical procedures.
Chapter 2 presents new content on enamel, dentin,
the dentinoenamel junction, and biofilms. Chapter
3, another new chapter, describes the concepts of
product design and their applications in restorative
material selection and treatment design. Fundamen-
tals of materials science, including the presentation
of physical and mechanical properties, the concepts
of biomechanics, surface chemistry, and optical prop-
erties, are consolidated in Chapter 4. Materials test-
ing is discussed in extensively revised Chapter 5,

which has a greater emphasis on contemporary test-
ing methods and standards. Chapter 14, new to this
edition, is devoted to digital imaging and processing
techniques and the materials for those methods. All
other chapters are reorganized and updated with the
most recent science and applications.
A website accompanies this textbook. Included is
the majority of the procedural, or materials handling,
content that was in the twelfth edition. The website can
be found at />restorative/, where you will also find mindmaps of
each chapter and extensive text and graphics to sup-
plement the print version of the book.

xi
Acknowledgments
We are deeply grateful to John Dolan, Executive Edi-
tor at Elsevier, for his guidance in the initial planning
and approval of the project; to Brian Loehr, Senior
Developmental Editor at Elsevier, for his many sug-
gestions and support and prodding throughout the
design process and writing of the manuscript. Jodie
Bernard and her team at Lightbox Visuals were
amazing in their ability to create new four-color
images from the original black and white figures.
We thank Sara Alsup, Associate Project Manager
at Elsevier, and her team of copyeditors for greatly
improving the style, consistency, and readability of
the text. Thanks also to many others at Elsevier for
their behind-the-scenes work and contributions to
the book.

Lastly, we thank our colleagues in our respective
institutions for the many informal chats and sugges-
tions offered and our families who put up with us
being at our computers late in the evenings and on
many weekends. It truly does take a community to
create a work like this textbook and we thank you all.
Ronald L. Sakaguchi
John M. Powers
1
C H A P T E R
1
Role and Significance of
Restorative Dental Materials
Scope of Materials Covered in Restorative
Dentistry
Basic Sciences Applied to Restorative
Materials
Application of Various Sciences
Future Developments in Biomaterials
O U T L I N E
2
CRAIG’S RESTORATIVE DENTAL MATERIALS
Developments in materials science, robotics, and
biomechanics have dramatically changed the way we
look at the replacement of components of the human
anatomy. In the historical record, we find many
approaches to replacing missing tooth structure and
whole teeth. The replacement of tooth structure lost to
disease and injury continues to be a large part of gen-
eral dental practice. Restorative dental materials are

the foundation for the replacement of tooth structure.
Form and function are important considerations
in the replacement of lost tooth structure. Although
tooth form and appearance are aspects most easily
recognized, function of the teeth and supporting
tissues contributes greatly to the quality of life. The
links between oral and general health are widely
accepted. Proper function of the elements of the
oral cavity, including the teeth and soft tissues, is
needed for eating, speaking, swallowing, and proper
breathing.
Restorative dental materials make the reconstruc-
tion of the dental hard tissues possible. In many areas,
the development of dental materials has progressed
more rapidly than for other anatomical prostheses.
Because of their long-term success, patients often
expect dental prostheses to outperform the natural
materials they replace. The application of materials
science is unique in dentistry because of the com-
plexity of the oral cavity, which includes bacteria,
high forces, ever changing pH, and a warm, fluid
environment. The oral cavity is considered to be the
harshest environment for a material in the body. In
addition, when dental materials are placed directly
into tooth cavities as restorative materials, there are
very specific requirements for manipulation of the
material. Knowledge of materials science and biome-
chanics is very important when choosing materials
for specific dental applications and when designing
the best solution for restoration of tooth structure

and replacement of teeth.
SCOPE OF MATERIALS COVERED IN
RESTORATIVE DENTISTRY
Restorative dental materials include representa-
tives from the broad classes of materials: metals,
polymers, ceramics, and composites. Dental materi-
als include such items as resin composites, cements,
glass ionomers, ceramics, noble and base metals,
amalgam alloys, gypsum materials, casting invest-
ments, dental waxes, impression materials, denture
base resins, and other materials used in restorative
procedures. The demands for material characteristics
and performance range from high flexibility required
by impression materials to high stiffness required
in crowns and fixed dental prostheses. Materials
for dental implants require integration with bone.
Some materials are cast to achieve excellent adapta-
tion to existing tooth structure, whereas others are
machined to produce very reproducible dimensions
and structured geometries. When describing these
materials, physical and chemical characteristics are
often used as criteria for comparison. To understand
how a material works, we study its chemical struc-
ture, its physical and mechanical characteristics, and
how it should be manipulated to produce the best
performance.
Most restorative materials are characterized by
physical, chemical, and mechanical parameters that
are derived from test data. Improvements in these
characteristics might be attractive in laboratory stud-

ies, but the real test is the material’s performance
in the mouth and the ability of the material to be
manipulated properly by the dental team. In many
cases, manipulative errors can negate the techno-
logical advances for the material. It is therefore very
important for the dental team to understand funda-
mental materials science and biomechanics to select
and manipulate dental materials appropriately.
BASIC SCIENCES APPLIED TO
RESTORATIVE MATERIALS
The practice of clinical dentistry depends not only
on a complete understanding of the various clinical
techniques but also on an appreciation of the funda-
mental biological, chemical, and physical principles
that support the clinical applications. It is important
to understand the ‘how’ and ‘why’ associated with
the function of natural and synthetic dental materials.
A systems approach to assessing the chemical,
physical, and engineering aspects of dental materi-
als and oral function along with the physiological,
pathological, and other biological studies of the
tissues that support the restorative structures pro-
vides the best patient outcomes. This integrative
approach, when combined with the best available
scientific evidence, clinician experience, patient
preferences, and patient modifiers results in the best
patient-centered care.
APPLICATION OF VARIOUS
SCIENCES
In the chapters that follow, fundamental charac-

teristics of materials are presented along with numer-
ous practical examples of how the basic principles
relate to clinical applications. Test procedures and
techniques of manipulation are discussed briefly but
not emphasized. Many of the details of manipulation
have been moved to the book’s website at http://
evolve.elsevier.com/sakaguchi/restorative
3
1. ROLE AND SIGNIFICANCE OF RESTORATIVE DENTAL MATERIALS
A more complete understanding of fundamental
principles of materials and mechanics is important
for the clinician to design and provide a prognosis for
restorations. For example, the prognosis of long-span
fixed dental prostheses, or bridges, is dependent on
the stiffness and elasticity of the materials. When
considering esthetics, the hardness of the material
is an important property because it influences the
ability to polish the material. Some materials release
fluoride when exposed to water, which might be ben-
eficial in high-caries-risk patients. When selecting a
ceramic for in-office fabrication of an all-ceramic
crown, the machining characteristic of ceramics is
important. Implants have a range of bone and soft
tissue adaptation that are dependent on surface tex-
ture, coatings, and implant geometry. These are just
a few examples of the many interactions between the
clinical performance of dental materials and funda-
mental scientific principles.
The toxicity of and tissue reactions to dental mate-
rials are receiving more attention as a wider variety

of materials are being used and as federal agencies
demonstrate more concern in this area. A further
indication of the importance of the interaction of
materials and tissues is the development of recom-
mended standard practices and tests for the biologi-
cal interaction of materials through the auspices of
the American Dental Association (ADA).
After many centuries of dental practice, we con-
tinue to be confronted with the problem of replacing
tooth tissue lost by either accident or disease. In an
effort to constantly improve our restorative capa-
bilities, the dental profession will continue to draw
from materials science, product design, engineering,
biology, chemistry, and the arts to further develop an
integrated practice of dentistry.
FUTURE DEVELOPMENTS IN
BIOMATERIALS
In the United States over 60% of adults aged 35 to
44 have lost at least one permanent tooth to an acci-
dent, gum disease, a failed root canal, or tooth decay.
In the 64- to 65-year-old category, 25% of adults have
lost all of their natural teeth. For children aged 6 to 8,
26% have untreated dental caries, and 50% have been
treated for dental decay. The demand for restorative
care is tremendous. Advances in endodontology and
periodontology enable people to retain teeth longer,
shifting restorative care from replacement of teeth
to long-term restoration and maintenance. Develop-
ment of successful implant therapies has encouraged
patients to replace individual teeth with fixed, single

tooth restorations rather than with fixed or remov-
able dental prostheses. For those patients with good
access to dental care, single tooth replacements with
implants are becoming a more popular option because
they do not involve the preparation of adjacent teeth
as for a fixed, multi-unit restoration. Research into
implant coatings, surface textures, graded proper-
ties, alternative materials, and new geometries will
continue to grow. For those with less adequate access,
removable prostheses will continue to be used.
An emphasis on esthetics continues to be popu-
lar among consumers, and this will continue to drive
the development of tooth whitening systems and
esthetic restorations. There appears to be an emerg-
ing trend for a more natural looking appearance with
some individuality as opposed to the uniform, spar-
kling white dentition that was previously requested
by many patients. This will encourage manufactur-
ers to develop materials that mimic natural dentition
even more closely by providing the same depth of
color and optical characteristics of natural teeth.
With the aging of the population, restorations
for exposed root surfaces and worn dentitions will
become more common. These materials will need to
function in an environment with reduced salivary
flow and atypical salivary pH and chemistry. Adhe-
sion to these surfaces will be more challenging. This
segment of the population will be managing multi-
ple chronic diseases with many medications and will
have difficulty maintaining an adequate regimen of

oral home care. Restorative materials will be chal-
lenged in this difficult environment.
The interaction between the fields of biomaterials
and molecular biology is growing rapidly. Advances
in tissue regeneration will accelerate. The develop-
ments in nanotechnology will soon have a major
impact on materials science. The properties we cur-
rently understand at the macro and micro levels will
be very different at the nano level. Biofabrication and
bioprinting methods are creating new structures and
materials. This is a very exciting time for materials
research and clinicians will have much to look for-
ward to in the near future as this body of research
develops new materials for clinical applications.
Bibliography
American Association of Oral and Maxillofacial Surgeons:
Dental implants. />.php. Accessed August 28, 2011.
Centers for Disease Control and Prevention: National
Health and Nutrition Examination Study.
.gov/nchs/nhanes/nhanes2005-2006/nhanes05_06
.htm. Accessed August 28, 2011.
Choi CK, Breckenridge MT, Chen CS: Engineered materials
and the cellular microenvironment: a strengthening
interface between cell biology and bioengineering,
Trends Cell Biol 20(12):705, 2010.
Horowitz RA, Coelho PG: Endosseus implant: the journey
and the future, Compend Contin Educ Dent 31(7):545,
2010.
4
CRAIG’S RESTORATIVE DENTAL MATERIALS

Jones JR, Boccaccini AR: Editorial: a forecast of the future
for biomaterials, J Mater Sci: Mater Med 17:963, 2006.
Kohn DH: Current and future research trends in dental
biomaterials, Biomat Forum 19(1):23, 1997.
Nakamura M, Iwanaga S, Henmi C, et al: Biomatrices and
biomaterials for future developments of bioprinting and
biofabrication, Biofabrication 2(1):014110, 2010 Mar 10.
Epub.
National Center for Chronic Disease Prevention and Health
Promotion (CDC): Oral health, preventing cavities, gum
disease, tooth loss, and oral cancers, at a glance, 2010.
National Institute of Dental Research: National Institutes of
Health (NIH): International state-of-the-art conference on
restorative dental materials, Bethesda, MD, Sept 8-10,
1986, NIH.
National Institute of Dental and Craniofacial Research:
A plan to eliminate craniofacial, oral, and dental health dis-
parities, 2002. />54B65018-D3FE-4459-86DD-AAA0AD51C82B/0/
hdplan.pdf.
Oregon Department of Human Services, Public Health
Division: The burden of oral disease in Oregon, Nov,
2006.
U.S. Department of Health and Human Services: Oral health
in America: a report of the Surgeon General—executive
summary, Rockville, MD, 2000, U.S. Department of Health
and Human Services, National Institute of Dental and
Craniofacial Research, National Institutes of Health.
5
C H A P T E R
2

The Oral Environment
O U T L I N E
Enamel
The Mineral
Dentin
Physical and Mechanical Properties
Difficulties in Testing
The Dentin-Enamel Junction
Oral Biofilms and Restorative Dental Materials
6
CRAIG’S RESTORATIVE DENTAL MATERIALS
The tooth contains three specialized calcified
tissues: enamel, dentin, and cementum (Figure 2-1).
Enamel is unique in that it is the most highly calci-
fied tissue in the body and contains the least organic
content of any of these tissues. Enamel provides
the hard outer covering of the crown that allows
efficient mastication. Dentin and cementum, like
bone, are vital, hydrated, biological composite
structures formed mainly from a collagen type I
matrix reinforced with the calcium phosphate min-
eral called apatite. Dentin forms the bulk of the tooth
and is joined to the enamel at the dentin-enamel
junction (DEJ). The dentin of the tooth root is covered
by cementum that provides connection of the tooth
to the alveolar bone via the periodontal ligament.
Although the structure of these tissues is often
described in dental texts, the properties are often
discussed only superficially. However, these proper-
ties are important in regard to the interrelationships

of the factors that contribute to the performance
necessary for the optimum function of these tissues.
In restorative dentistry we are interested in pro-
viding preventive treatments that will maintain
tissue integrity and replace damaged tissues with
materials that ideally will mimic the natural appear-
ance and performance of those tissues when neces-
sary. Thus knowledge of the structure and properties
of these tissues is desirable both as a yardstick to
measure the properties and performance of restor-
ative materials and as a guide to the development
of materials that will mimic their structure and func-
tion. In addition, many applications, such as dental
bonding, require us to attach synthetic materials to
the calcified tissues, and these procedures rely on
detailed knowledge of the structure and properties
of the adhesive tissue substrates.
ENAMEL
Figure 2-1 shows a schematic diagram of a poste-
rior tooth sectioned to reveal the enamel and dentin
components. Enamel forms the hard outer shell of
the crown and as the most highly calcified tissue is
well suited to resisting wear due to mastication.
Enamel is formed by ameloblasts starting at the
dentin-enamel junction (DEJ) and proceeding out-
ward to the tooth surface. The ameloblasts exchange
signals with odontoblasts located on the other side
of the DEJ at the start of the enamel and dentin for-
mation, and the odontoblasts move inward from the
DEJ as the ameloblasts forming enamel move out-

ward to form the enamel of the crown. Most of the
enamel organic matrix composed of amelogenins
and enamelins is resorbed during tooth maturation
to leave a calcified tissue that is largely composed of
mineral and a sparse organic matrix. The structural
arrangement of enamel forms keyhole-shaped struc-
tures known as enamel prisms or rods that are about
5 μm across as seen in Figure 2-2.
The overall composition is about 96% mineral by
weight, with 1% lipid and protein and the remainder
being water. The organic portion and water probably
play important roles in tooth function and pathology,
and it is often more useful to describe the composition
on a volume basis. On that basis we see the organic
components make up about 3% and water 12% of
the structure. The mineral is formed and grows into
very long crystals of hexagonal shape about 40 nm
across; these have not been synthetically duplicated.
There is some evidence that the crystals may span the
whole enamel thickness, but this is difficult to prove
because most preparation procedures lead to frac-
ture of the individual crystallites. It appears that they
are at least thousands of nanometers long. If this is
true, then enamel crystals provide an extraordinary
“aspect” ratio (length to width ratio) for a nanoscale
material, and they are very different from the much
smaller dentin crystals. The crystals are packed into
enamel prisms or rods that are about 5 μm across as
shown in Figure 2-2. These prisms are revealed easily
by acid etching and extend in a closely packed array

from the DEJ to the enamel surface and lie roughly
perpendicular to the DEJ, except in cuspal areas
where the rods twist and cross, known as decussation,
which may increase fracture resistance. About 100
crystals of the mineral are needed to span the diam-
eter of a prism, and the long axes of the crystals tend
to align themselves along the prism axes, as seen in
Figure 2-2.
Enamel Dentin
Pulp
Inner
cervical
Outer
Inner
FIGURE 2.1 Schematic diagram of a tooth cut longitudi-
nally to expose the enamel, dentin, and the pulp chamber.
On the right side are illustrations of dentin tubules as
viewed from the top, which shows the variation in the
tubule number with location. At the left is an illustration of
the change in direction of the primary dentin tubules as
secondary dentin is formed. (From Marshall SJ, et al: Acta.
Mater. 46, 2529-2539, 1998.)
7
2. THE ORAL ENVIRONMENT
The crystals near the periphery of each prism
deviate somewhat from the long axis toward the
interface between prisms. The deviation in the tail
of the prism is even greater. The individual crystals
within a prism are also coated with a thin layer of
lipid and/or protein that plays important roles in

mineralization, although much still remains to be
learned about the details. Recent work suggests that
this protein coat may lead to increased toughness of
the enamel. The interfaces between prisms, or inter-
rod enamel, contain the main organic components
of the structure and act as passageways for water
and ionic movement. These areas are also known as
prism sheaths. These regions are of vital importance
in etching processes associated with bonding and
other demineralization processes, such as caries.
Etching of enamel with acids such as phosphoric
acid, commonly used in enamel bonding, eliminates
smear layers associated with cavity preparation,
dissolves persisting layers of prismless enamel in
deciduous teeth, and differentially dissolves enamel
crystals in each prism. The pattern of etched enamel
is categorized as type 1 (preferential prism core etch-
ing, Figure 2-2, A); type 2 (preferential prism periph-
ery etching, Figure 2-3, C), and type 3 (mixed or
uniform). Sometimes these patterns appear side by
side on the same tooth surface (Figure 2-3, E). No
differences in micromechanical bond strength of the
different etching patterns have been established. In a
standard cavity preparation for a composite, the ori-
entation of the enamel surfaces being etched could
be perpendicular to enamel prisms (perimeter of the
cavity outline), oblique cross section of the prisms
(beveled occlusal or proximal margins), and axial
walls of the prisms (cavity preparation walls). Dur-
ing the early stages of etching, when only a small

amount of enamel crystal dissolution occurs, it may
be difficult or impossible to detect the extent of the
Interrod
enamel
Head
Tail
A B
40.0
30.0
20.0
10.0
0
0 10.0 20.0 30.0
40.0
C
FIGURE 2.2 Enamel microstructure showing a schematic diagram of keyhole-shaped enamel prisms or rods about 5 μm
in diameter (B). Atomic force microscopy (AFM) images showing prism cross sections in A and along axes of the prisms
in C. Crystallite orientation deviates in the inter-rod and tail area, and the organic content increases in the inter-rod area.
(Modified from Habelitz S, et al: Arch. Oral Biol. 46, 173-183, 2001.)
8
CRAIG’S RESTORATIVE DENTAL MATERIALS
process. However, as the etching pattern begins to
develop, the surface etched with phosphoric acid
develops a frosty appearance (Figure 2-3, B), which
has been used as the traditional clinical indicator for
sufficient etching. This roughened surface provides
the substrate for infiltration of bonding agents that
can be polymerized after penetration of the etched
enamel structure so that they form micromechanical
bonds to the enamel when polymerized. With self-

etching bonding agents, this frosty appearance can-
not be detected.
There are two other important structural varia-
tions of enamel. Near the DEJ the enamel prism
structure is not as well developed in the very first
A
B
C
D
E
25 ␮m
FIGURE 2.3 Etching enamel. A, Gel etchant dispensed on the enamel portion of the preparation. B, Frosty appearance
after etching, rinsing and drying. C, Magnified view of etch pattern with preferential prism periphery etch (type 1).
D, Bonding agent revealed after dissolving enamel. E, Mixed etch patterns showing type 1 (light prisms with dark periphery)
and type 2 (dark cores with light periphery) etching on same surface after Marshall et al, 1975 JDR. Marshall GW, Olson
LM, Lee CV: SEM Investigation of the variability of enamel surfaces after simulated clinical acid etching for pit and fissure
sealants, J Dent Res 54:1222–1231, 1975. Part C from Marshall, Olson and Lee, JDR 1975 (same as above) and Part E from
Marshall, Marshall and Bayne, 1988: Marshall GW, Marshall SJ, Bayne SC: Restorative dental materials: scanning electron
microscopy and x-ray microanalysis, Scanning Microsc 2:2007–2028, 1988.
9
2. THE ORAL ENVIRONMENT
enamel formed, so that the enamel very close to the
DEJ may appear aprismatic or without the prism
like structure. Similarly, on the outer surface of the
enamel, at completion of the enamel surface, the
ameloblasts degenerate and leave a featureless layer,
called prismless enamel, on the outer surface of the
crown. This layer is more often observed in decidu-
ous teeth and is often worn off in permanent teeth.
However, if present, this causes some difficulty in

getting an effective etching pattern and may require
roughening of the surface or additional etching treat-
ments. The outer surface of the enamel is of great
clinical significance because it is the surface sub-
jected to daily wear and undergoes repeated cycles of
demineralization and remineralization. As a result of
these cycles, the composition of the enamel crystals
may change, for example, as a result of exposure to
fluoride. Thus the properties of the enamel might be
expected to vary from the external to the internal sur-
face. Such variations, including a thin surface veneer
of fluoride-rich apatite crystals, create differences in
the enamel properties within the enamel. Enamel is
usually harder at the occlusal and cuspal areas and
less hard nearer the DEJ. Figure 2-4 shows an exam-
ple of the difference in hardness.
THE MINERAL
The mineral of all calcified tissues is a highly
defective relative of the mineral hydroxyapatite,
or HA. The biological apatites of calcified tissues
are different than the ideal HA structure in that the
defects and chemical substitutions generally make it
weaker and more soluble in acids. Hydroxyapatite
has the simple formula Ca
10
(PO
4
)
6
(OH)

2
, with an
ideal molar ratio of calcium to phosphorus (Ca/P) of
1.67 and a hexagonal crystal structure. The apatite of
enamel and dentin has a much more variable compo-
sition that depends on its formative history and other
chemical exposures during maturity. Thus the min-
eral in enamel and dentin is a calcium-deficient, car-
bonate-rich, and highly substituted form related to
HA. Metal ions such as magnesium (Mg) and sodium
(Na) may substitute for calcium, whereas carbonate
substitutes for the phosphate and hydroxyl groups.
These substitutions distort the structure and make it
more soluble. Perhaps the most beneficial substitu-
tion is the fluorine (F) ion, which substitutes for the
hydroxyl group (OH) in the formula and makes the
structure stronger and less soluble. Complete substi-
tution of F for (OH) in hydroxyapatite yields fluo-
roapatite mineral, Ca
10
(PO
4
)
6
(F)
2
, that is much less
soluble than HA or the defective apatite of calcified
tissues. It is worth noting that HA has attracted con-
siderable attention as an implantable calcified tissue

replacement. It has the advantage of being a purified
and stronger form of the natural mineral and releases
no harmful agents during biological degradation. Its
major shortcoming is that it is extremely brittle and
sensitive to porosity or defects and therefore frac-
tures easily in load-bearing applications.
The approximate carbonate contents of the enamel
and dentin apatites are significantly different, about
3% and 5% carbonate, respectively. All other factors
being equal, this would make the dentin apatite more
soluble in acids than enamel apatite. Things are not
equal, however, and the dentin apatite crystals are
much smaller than the enamel crystals. This means
that the dentin crystals present a higher surface area
to attacking acids and contain many more defects per
unit volume and thus exhibit considerably higher
solubility. Finally, as discussed further below, the
dentin mineral occupies only about 50% of the den-
tin structure, so there is not as much apatite in the
dentin as there is in enamel. All of these factors mul-
tiply the susceptibility of dentin to acid attack and
provide insight into the rapid spread of caries when
it penetrates the DEJ.
DENTIN
Dentin is a complex hydrated biological compos-
ite structure that forms the bulk of the tooth. Fur-
thermore, dentin is modified by physiological, aging,
and disease processes that result in different forms
of dentin. These altered forms of dentin may be the
precise forms that are most important in restorative

dentistry. Some of the recognized variations include
primary, secondary, reparative or tertiary, sclerotic,
transparent, carious, demineralized, remineralized,
and hypermineralized. These terms reflect altera-
tions in the fundamental components of the struc-
ture as defined by changes in their arrangement,
Buccal
Hardness (GPa)
Lingual
6
5.5
5
4.5
4
3.5
3
2.5
B cca
B
u
cca
al
al
H
Hard
ard
FIGURE 2.4 Nanoindentation mapping of the mechani-
cal properties of human molar tooth enamel. (From Cuy JL,
et al: Arch. Oral Biol. 47(4), 281-291, 2002.)
10

CRAIG’S RESTORATIVE DENTAL MATERIALS
interrelationships, or chemistry. A number of these
may have important implications for our ability to
develop long-lasting adhesion or bonds to dentin.
Primary dentin is formed during tooth develop-
ment. Its volume and conformation, reflecting tooth
form, vary with the size and shape of the tooth. Den-
tin is composed of about 50 volume percent (vol%)
carbonate-rich, calcium-deficient apatite; 30 vol%
organic matter, which is largely type I collagen; and
about 20 vol% fluid, which is similar to plasma. Other
noncollagenous proteins are thought to be involved
in dentin mineralization and other functions such as
controlling crystallite size and orientation; however,
these functions are not discussed further in this text.
The major components are distributed into distinc-
tive morphological features to form a vital and com-
plex hydrated composite in which the morphology
varies with location and undergoes alterations with
age or disease.
The tubules, one distinct and important feature
of dentin, represent the tracks taken by the odonto-
blastic cells from the DEJ or cementum at the root to
the pulp chamber and appear as tunnels piercing the
dentin structure (Figure 2-5). The tubules converge
on the pulp chamber, and therefore tubule density
and orientation vary from location to location (see
Figure 2-1). Tubule number density is lowest at the
DEJ and highest at the predentin surface at the junc-
tion to the pulp chamber, where the odontoblastic

cell bodies lie in nearly a close-packed array. Lower
tubule densities are found in the root. The contents
of the tubules include odontoblast processes, for all
or part of their course, and fluid. The extent of the
odontoblast process is still uncertain, but evidence is
mounting that it extends to the DEJ. For most of its
course, the tubule lumen is lined by a highly min-
eralized cuff of peritubular dentin roughly 0.5 to 1
μm thick (Figure 2-6). Because the peritubular den-
tin forms after the tubule lumen has been formed,
some argue that it may be more properly termed
intratubular dentin and contains mostly apatite crys-
tals with little organic matrix. A number of studies
have concluded that the peritubular dentin does not
contain collagen, and therefore might be considered
a separate calcified tissue. The tubules are separated
by intertubular dentin composed of a matrix of type
I collagen reinforced by apatite (see Figures 2-5 and
2-6). This arrangement means that the amount of
intertubular dentin varies with location. The apatite
A
Peritubular dentin
Intertubular dentin
B
P
I
20kv
5.0kx
956
2.00␮

FIGURE 2.6 Fracture surface of the dentin viewed from the occlusal in A and longitudinally in B. Peritubular
(P) (also called intratubular) dentin forms a cuff or lining around each tubule. The tubules are separated from one another
by intertubular dentin (I). (Courtesy of G. W. Marshall.)
30kv
2.00kx
959
5.0␮
FIGURE 2.5 Scanning electron microscopy (SEM) image
of normal dentin showing its unique structure as seen
from two directions. At the top is a view of the tubules,
each of which is surrounded by peritubular dentin. Tubules
lie between the dentin-enamel junction (DEJ) and converge
on the pulp chamber. The perpendicular surface at the
bottom shows a fracture surface revealing some of the
tubules as they form tunnel-like pathways toward the pulp.
The tubule lumen normally contains fluid and processes of
the odontoblastic cells. (From Marshall GW: Quintessence Int.
24, 606-617, 1993.)
11
2. THE ORAL ENVIRONMENT
crystals are much smaller (approximately 5 × 30 ×
100 nm) than the apatite found in enamel and con-
tain 4% to 5% carbonate. The small crystallite size,
defect structure, and higher carbonate content lead
to the greater dissolution susceptibility described
above.
Estimates of the size of tubules, the thickness of
the peritubular region, and the amount of intertubu-
lar dentin have been made in a number of studies.
Calculations for occlusal dentin as a function of posi-

tion from these data show the percent tubule area
and diameter vary from about 22% and 2.5 μm near
the pulp to 1% and 0.8 μm at the DEJ. Intertubular
matrix area varies from 12% at the predentin to 96%
near the DEJ, whereas peritubular dentin ranges
from over 60% down to 3% at the DEJ. Tubule den-
sities are compared in Table 2-1 based on work by
various investigators. It is clear that the structural
components will vary considerably over their course,
and necessarily result in location-dependent varia-
tions in morphology, distribution of the structural
elements, and important properties such as perme-
ability, moisture content, and available surface area
for bonding and may also affect bond strength, hard-
ness, and other properties.
Because the odontoblasts come to rest just inside
the dentin and line the walls of the pulp chamber
after tooth formation, the dentin-pulp complex can
be considered a vital tissue. This is different than
mature enamel. Over time secondary dentin forms
and the pulp chamber gradually becomes smaller.
The border between primary and secondary dentin
is usually marked by a change in orientation of the
dentin tubules. Furthermore, the odontoblasts react
to form tertiary dentin in response to insults such as
caries or tooth preparation, and this form of dentin is
often less well organized than the primary or second-
ary dentin.
Early enamel carious lesions may be reversed
by remineralization treatments. However, effective

re mineralization treatments are not yet available for
dentin and therefore the current standard of care
dictates surgical intervention to remove highly dam-
aged tissue and then restoration as needed. Thus it is
important to understand altered forms of dentin and
the effects of such clinical interventions.
When dentin is cut or abraded by dental instru-
ments, a smear layer develops and covers the surface
and obscures the underlying structure (Figure 2-7).
The bur cutting marks are shown in Figure 2-7, A,
and at higher magnification in Figure 2-7, B. Figure
2-7, C, shows the smear layer thickness from the side
and the development of smear plugs as the cut den-
tin debris is pushed into the dentin tubule lumen.
The advantages and disadvantages of the smear
layer have been extensively discussed for several
decades. It reduces permeability and therefore aids
in maintaining a drier field and reduces infiltration
of noxious agents into the tubules and perhaps the
pulp. However, it is now generally accepted that it
is a hindrance to dentin bonding procedures and,
therefore, is normally removed or modified by some
form of acid conditioning.
Acid etching or conditioning allows for removal
of the smear layer and alteration of the superficial
dentin, opening channels for infiltration by bonding
agents. Figure 2-8 shows what happens in such an
etching treatment. The tubule lumens widen as the
peritubular dentin is preferentially removed because
it is mostly mineral with sparse protein. The widened

lumens form a funnel shape that is not very retentive.
Figure 2-9 shows these effects in a slightly differ-
ent way. Unetched dentin in Figure 2-9, A, has small
tubules and peritubular dentin, which is removed in
the treated dentin at the exposed surface after etching
(bottom). The two-dimensional network of collagen
type I fibers is shown after treatment in Figure 2-9, A.
Figure 2-9, B, shows progressive demineralization of
a dentin collagen fibril in which the external mineral
and proteins are slowly removed to reveal the typi-
cal banded pattern of type I collagen. In Figure 2-9,
C, this pattern is seen at high magnification of the
treated dentin in Figure 2-9, A.
If the demineralized dentin is dried, the remain-
ing dentin matrix shrinks and the collagen fibrils
become matted and difficult to penetrate by bonding
agents. This is shown in Figure 2-10, which compares
demineralized and dried dentin with demineralized
and hydrated dentin.
Most restorative procedures involve dentin that
has been altered in some way. Common alterations
include formation of carious lesions that form vari-
ous zones and include transparent dentin that forms
under the caries infected dentin layer. Transparent
dentin results when the dentin tubules become filled
with mineral, which changes the refractive index of
the tubules and produces a translucent or transpar-
ent zone.
Figure 2-11 shows a section through a tooth with
a carious lesion, which has been stained to reveal its

zones. The gray zone under the stained and severely
TABLE 2.1 Comparison of Mean Numerical Density
of Tubules in Occlusal Dentin
*
Outer Dentin Middle Dentin Inner Dentin
15,000/mm
2
35,000/mm
2
65,000/mm
2
20,000/mm
2
35,000/mm
2
43,000/mm
2
24,500/mm
2
40,400/mm
2
51,100/mm
2
18,000/mm
2
39,000/mm
2
52,000/mm
2
*From data reported in the literature (Marshall GW: Quintessence Int.

24, 606-617, 1993.)
12
CRAIG’S RESTORATIVE DENTAL MATERIALS
demineralized dentin is the transparent layer (Figure
2-11, A). Figure 2-11, B, shows the transparent dentin
in which most of the tubule lumens are filled with
mineral. After etching, as shown in Figure 2-11, C the
peritubular dentin is etched away, but the tubules
retain plugs of the precipitated mineral, which is
more resistant to etching. This resistance to etching
makes bonding more difficult.
Several other forms of transparent dentin are
formed as a result of different processes. A second
form of transparent dentin results from bruxism.
An additional form of transparent dentin results
from aging as the root dentin gradually becomes
transparent. In addition noncarious cervical lesions
(NCCLs), often called abfraction or notch lesions, form
at the enamel-cementum or enamel-dentin junction,
usually on facial or buccal surfaces. Their etiology
is not clear at this point; their formation has been
attributed to abrasion, tooth flexure, and erosion or
some combination of these processes. Nonetheless
these lesions occur with increasing frequency with
age, and the exposed dentin becomes transparent as
the tubules are filled. Figure 2-12 shows examples of
transparent dentin in which the tubule lumens are
completely filled.
The properties of the transparent dentin may dif-
fer from one to another depending on the processes

that lead to deposit of the mineral in the tubules.
Several studies have shown that elastic properties
of the intertubular dentin are not altered by aging,
although the structure may become more suscepti-
ble to fracture. Similarly, arrested caries will contain
transparent dentin and this has often been called scle-
rotic dentin, a term that implies it may be harder than
normal dentin. However, other studies have shown
that the elastic properties of the intertubular den-
tin may actually be unaltered or lower than normal
dentin.
Physical and Mechanical Properties
The marked variations in the structural elements
of dentin when located within the tooth imply that
the properties of dentin will vary considerably with
location. That is, variable structure leads to variable
properties.
A
B
C
FIGURE 2.7 Smear layer formation. A, Bur marks on dentin preparation B, Higher magnification showing smear layer
surface and cutting debris. C, Section showing smear layer (SL) and smear plugs (S.P.). (A and B from Marshall GW, et al:
Scanning Microsc. 2, 2007-2028, 1988; C from Pashley DH, et al: Arch. Oral Biol. 33, 265-270, 1988.)
13
2. THE ORAL ENVIRONMENT
Because one major function of tooth structure is
to resist deformation without fracture, it is useful to
have knowledge of the forces that are experienced by
teeth during mastication. Measurements have given
values on cusp tips of about 77 kg distributed over

the cusp tip area of 0.039 cm
2
, suggesting a stress of
about 200 MPa.
Difficulties in Testing
In Table 2-2, values are presented for some impor-
tant properties of enamel and dentin. The wide
spread of values reported in the literature is remark-
able. Some of the reasons for these discrepancies
should be appreciated and considered in practice or
when reading the literature.
First, human teeth are small, and therefore it is dif-
ficult to get large specimens and hold them in such a
way that you can measure properties. This makes the
use of standard mechanical testing such as tensile,
compressive, or shear tests difficult. When testing
bonded teeth, the problem is even more complicated,
and special tests have been developed to obtain
insights into these properties. From the previous dis-
cussion of structural variations, it is also clear that
testing such small inhomogeneous specimens means
that the properties will not be uniform.
Another problem is the great variation in struc-
ture in both tissues. Enamel prisms are aligned
generally perpendicular to the DEJ, whereas dentin
tubules change their number density with depth as
they course toward the pulp chamber. Preparing a
uniform sample with the structures running all in
one direction for testing is challenging. In addition,
properties generally vary with direction and location

and the material is not isotropic; therefore, the best
a single value can tell you is some average value for
the material.
Storage and time elapsed since extraction are also
important considerations. Properties that exist in a
natural situation or in situ or
in vivo are of greatest
interest. Clearly this condition is almost impossible
to achieve in most routine testing, so changes that
C
5
10
15
B
5
10
15
D
5
10
15
20 s
60 s
A
FIGURE 2.8 Stages of dentin demineralization. A, Schematic showing progressive stages of dentin demineralization.
B to D, Atomic force microscopy (AFM) images showing stages of etching. The etching leads to wider lumens as peritu-
bular dentin is dissolved and funnel-shaped openings are formed. (AFM images from Marshall GW: Quintessence Int. 24,
606-617, 1993.)