Article

Biomaterials for Dental Implants: An Overview

Abstract

The goal of modern dentistry is to restore the patient to normal contour, function, comfort, esthetics, speech and health regardless of theatrophy, disease or injury of the stomatognathic system. As a result of continued research in treatment planning, implant designs,materials and techniques, predictable success is now a reality for the rehabilitation of many challenging situations. The biocompatibilityprofiles of synthetic substances (biomaterials) used for the replacement or augmentation of biologic tissues has always been a criticalconcern within the health care disciplines. For optimal performance, implant biomaterials should have suitable mechanical strength,biocompatibility and structural biostability in physiologic environments. This article reviews the various implant biomaterials and theirsuitability of use in implant dentistry.
Biomaterials for Dental Implants: An Overview
International Journal of Oral Implantology and Clinical Research, January-April 2011;2(1):13-24 13
IJOICR
Biomaterials for Dental Implants: An Overview
1BC Muddugangadhar, 2GS Amarnath, 3Siddhi Tripathi, 3Suchismita Dikshit, 4Divya MS
1Reader, Department of Prosthodontics Including Crown, Bridge and Implantology
MR Ambedkar Dental College and Hospital, Bengaluru, Karnataka, India
2Professor and Head, Department of Prosthodontics Including Crown, Bridge and Implantology
MR Ambedkar Dental College and Hospital, Bengaluru, Karnataka, India
3Postgraduate Student, Department of Prosthodontics Including Crown, Bridge and Implantology
MR Ambedkar Dental College and Hospital, Bengaluru, Karnataka, India
4Senior Lecturer, Department of Prosthodontics Including Crown, Bridge and Implantology
MR Ambedkar Dental College and Hospital, Bengaluru, Karnataka, India
Correspondence: BC Muddugangadhar, Reader, Department of Prosthodontics Including Crown, Bridge and Implantology
MR Ambedkar Dental College and Hospital, 1/36, Cline Road, Cooke Town, Bengaluru-560005, Karnataka, India
Phone: +91-9900518069, e-mail: drbcmuddu@gmail.com
REVIEW ARTICLE
ABSTRACT
The goal of modern dentistry is to restore the patient to normal contour, function, comfort, esthetics, speech and health regardless of the
atrophy, disease or injury of the stomatognathic system. As a result of continued research in treatment planning, implant designs,
materials and techniques, predictable success is now a reality for the rehabilitation of many challenging situations. The biocompatibility
profiles of synthetic substances (biomaterials) used for the replacement or augmentation of biologic tissues has always been a critical
concern within the health care disciplines. For optimal performance, implant biomaterials should have suitable mechanical strength,
biocompatibility and structural biostability in physiologic environments. This article reviews the various implant biomaterials and their
suitability of use in implant dentistry.
Keywords: Biomaterial, Biocompatibility, Biostability, Biomimetics, Augmentation.
INTRODUCTION
Biomaterials are those materials that are compatible with
the living tissues. The physical properties of the materials,
their potential to corrode in the tissue environment, their
surface configuration, tissue induction and their potential
for eliciting inflammation or rejection response are all
important factors under this area. The biomaterial discipline
has evolved significantly over the past decades. The goal of
biomaterials research has been and continued to develop
implant materials that induce predictable, control-guided
and rapid healing of the interfacial tissues both hard and
soft.1
The most critical aspect of biocompatibility is dependent
on the basic bulk and surface properties and biomaterials.
Materials used for fabrication of dental implants can be
categorized in two different ways:
1. Chemical point—metals, ceramics
2. Biological point—biodynamic materials: biotolerant,
bioinert, bioactive
Biomaterials, regardless of use, fall into four general
categories: Metals and metallic alloys, ceramics, synthetic
polymers and natural materials. Metals and metal alloys that
utilize oral implants include titanium, tantalum and alloy of
Ti-Al-Va, Co-Cr-Mb, Fe-Cr-Ni. These materials are
generally selected on basis of their overall strength
properties.
Bioinert materials allow close approximation of bone
on their surface leading to contact osteogenesis. These
materials allow the formation of new bone on their surface
and ion exchange with the tissues leads to the formation of
a chemical bonding along the interface bonding
osteogenesis.
Biotolerant are those that are not necessarily rejected
when implanted into living tissue. They are human bone
morphogenetic protein-2 (rh BMP-2), which induces bone
formation de novo.
Biomimetics are tissue integrated engineered materials
designed to mimic specific biologic processes and help
optimize the healing/regenerative response of the host
microenvironment.
Bioinert and Bioactive materials are also called
osteoconductive, meaning that they can act as scaffolds
allowing bone growth on their surfaces.
FACTORS AFFECTING IMPLANT BIOMATERIAL
Factor affecting biocompatibility includes chemical,
mechanical, electrical and surface specific properties.2,3
10.5005/jp-journals-10012-1030
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BC Muddugangadhar et al
Chemical Factors
Corrosion may be defined as the loss of metallic ions from
the surface of a metal to the surrounding environment. There
are three basic types of corrosion: General, pitting and
crevice.
General Corrosion
General corrosion occurs when a metal is immersed in an
electrolyte solution. Positively charged ions from the metal
are transferred to the liquid electrolyte and the metal
transports the negatively charged electrons. This migration
continues until the potential difference between the metal
and electrolyte are great enough to prevent more ions from
entering solution or electrons from being transferred, at
which equilibrium point is achieved.
Pitting Corrosion
Pitting corrosion occurs in an implant with a small surface
pit placed in a solution. Such an implant exhibits two
different surface conditions. When the metal near the pit
dissolves or loses positive ions from its surface, the
associated negative charge from the liberated electrons must
be dissipated through the metal of the implant. This type of
corrosion can proceed very rapidly, actively attacking
metallic implants if proper material and surface conditions
do not exist. This corrosion type is called pitting corrosion.
Crevice Corrosion
Crevice corrosion that occurs around bone-implant interface
or an implant device where an overlay or composite type
surface exists on a metallic substrate in a tissue/fluids
environment with minimal space, little or no oxygen may
be present in the crevice. When metallic ions dissolve, they
can create a positively charged local environment in the
crevice, which may provide opportunities for crevice
corrosion. Thus, the selection of metals and alloys for
biomaterials depends on an understanding of corrosion and
biocorrosion phenomena. All metals ionize to some extent,
normally decreasing with increasing neutrality of the
metallic solution.
Surface Specific Factors
Events at the Bone-Implant Interface
The performance of biomaterials can be classified in terms
of:
1. The response of the host to the implant.
2. The behavior of the material in the host.
Material response: The event that occurs almost
immediately upon implantation of metals, as with other
biomaterials, is adsorption of proteins. These proteins come
first from blood and tissue fluids at the wound site and later
from cellular activity in the interfacial region. There is ample
literature that describes oxidation of metallic implants both
in vivo and in vitro. Although metallic implant biomaterials
were originally selected because of their stable oxide films,
it is appreciated that the oxide surfaces still undergo
electrochemical changes in the physiologic environment.
Furthermore, surface analytic studies show that the chemical
composition of the oxide film changes by incorporating
calcium, phosphorus and sulfur.
Another consequence of these events is the release of
metallic ions into tissues. These corrosion by-products
accumulate locally but may also spread systemically.
Significantly elevated metal contents have been measured
both in periprosthetic tissues in the serum and urine of
patients with orthopedic implants.
Host response: The host response to implants placed in bone
involves a series of cell and matrix events, ideally
culminating in tissue healing, leading to intimate apposition
of bone to the biomaterial, i.e. an operative definition of
osseointegration. For this intimate contact to occur, gaps
that initially exist between bone and implant at surgery must
be filled initially by a blood clot, and bone damaged during
preparation of the implant site must be repaired.
Morphologic studies have revealed the heterogeneity of
the typical bone-implant interface. One feature often
reported is the presence of an afibrillar interfacial zone,
comparable to cement lines and lamina limitans. Although
its thickness and appearance vary, this zone forms regardless
of the type of biomaterial implanted, including CpTi,
stainless steel and hydroxyapatite.
Osteoblasts, osteoid and mineralized matrix have been
observed adjacent to the lamina limitans suggesting that
bone can be deposited directly on the surface of the implant,
extending outward from the biomaterial. Thus, bone
formation in the periprosthetic region occurs in two
directions: The healing bone approaches the biomaterial,
but also bone extends from the implant towards the healing
bone. In vitro studies, bone cell culture models are employed
increasingly often to study bone-biomaterial interactions.
Most of the cultures have utilized osteoblastic cells with
only a few using osteoclastic cells. It is known that bone
from different sites, developmental ages and types show
variability. An important consideration, however, is that the
information obtained can indeed reflect in vivo events. For
example, in vitro and in vivo models have shown formation
of a cement line-like layer and appropriate organization of
mineralized matrix during culture on various substrates.
Understandably, because of the complexities of the in vivo
environment, the bone-implant interface has not yet been
fully characterized. The heterogeneity and patchy
immunolabeling observed in morphologic studies suggest
that even though several biomolecules have been identified
at the interface, they are not likely the ones present.
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International Journal of Oral Implantology and Clinical Research, January-April 2011;2(1):13-24 15
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Biomolecules also have essential roles in directing bone
response to the implant. Further work is needed to identify
them and determine their functions at the interface.
Controlling the Bone-Implant Interface by
Biomaterials Selection and Modification
Different approaches are being used in an effort to obtain
desired outcomes at the bone-implant interface. Many would
accept the promise that an ideal implant biomaterial should
present a surface that will not disrupt or even enhance the
general processes of bone healing regardless of implantation
site, bone quantity and bone quality.
Electrical Factors
Physiochemical Methods
Surface energy, surface charge and surface composition are
among the physiochemical characteristics that have been
altered with the aim of improving the bone-implant interface.
Glow discharge has been used to increase surface free
energy, so as to improve tissue adhesion. Increased surface
energy does not selectively increase the adhesion of
particular cells or tissues, it has not been shown to increase
bone-implant interfacial strength. Although short-term
clinical results have been encouraging, dissolution of
coatings as well as cracking and separation from metallic
substrates remain a concern with hydroxyapatite coatings.
Morphologic Methods
Alterations in biomaterial surface morphology and
roughness have been used to influence cells and tissue
responses to implants. Porous coatings were originally
developed with the rationale that mechanical interlocking,
bone ingrowth would increase fixation and stability of the
implant. In addition to providing mechanical interlocking,
surfaces with specially contoured grooves can induce contact
guidance whereby the direction of cell movement is affected
by the morphology of the substrate.
Concerning surface roughness and its effects, there is a
large but inconclusive literature on the biologic and clinical
effects. Using in vitro cell culture systems all the authors
have not come to the same conclusions about the role of
surface roughness. Cochran et al reported that human
fibroblast and epithelial cell attachment and proliferation
in vitro were affected by surface characteristics of titanium.
Overall, these in vitro animal and clinical studies did not
yield compelling conclusions about the role of surface
composition and texture with respect to bone response at
the interface.
Biochemical Methods
Biochemical methods of surface modification offer an
alternative or adjunct to physiochemical and morphologic
methods. Biochemical surface modification endeavors to
utilize current understanding of the biology and biochemistry
of cellular function and differentiation.
The goal of biochemical surface modification is to
immobilize proteins, enzymes or peptides on biomaterials
for the purpose of inducing specific cell and tissue responses,
or in other words to control the tissue-implant interface with
molecules delivered directly to the interface. One approach
for controlling cell-biomaterial interactions utilizes cell
adhesion molecules. Since plasma and extracellular matrix
proteins include fibronectin, vitronectin, Type-I collagen,
osteogenin and bone sialoprotein. Research has also shown
that RGD-containing peptides promote cell attachments.
A second approach to biochemical surface modification
uses biomolecules, which demonstrated osteotropic effects.
They have effects ranging from mitogenicity (interleukin
growth factor-i, FGF-2 and platelet-derived growth factor-
BB) to increasing activity of bone cells, which enhances
collagen synthesis for osteoinduction.
MECHANICAL PROPERTIES
Important mechanical properties of biomaterials that must
be considered in dental implant fabrication are:
1. Modulus of elasticity
2. Tensile strength
3. Compressive strength
4. Elongation
5. Metallurgy.
Modulus of elasticity: An important property of any
biocompatible material is its modulus of elasticity (E), which
represents elastic response to mechanical stress. The forces
(F) and stresses within bone that result from loading an
implant, balance the effect of the externally applied forces
of occlusion or muscle action. These forces may establish a
condition of static equilibrium. When these forces are not
in equilibrium, the implant and bone deform or undergo
mechanical strain. In elastic deformation, the implant and
bone regain their original dimensions after the removal of
force. In plastic deformation, the original dimension is
altered permanently after the removal of the applied force.
In this case, the properties of the material are such that a
desired extent of permanent change of original dimension
can be achieved while maintaining metallurgic and clinical
integrity.
Tensile or Compressive forces (stresses): This force when
applied to a biomaterial or bone cause a change of dimension
(strain) that is proportional to the elastic modulus.
Elongation: The magnitude of the moduli of elasticity can
provide a direct measure of the degree and relative
movement at the interface that can be expected. Both the
bone and the implant deform (strain) as a result of forces
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BC Muddugangadhar et al
applied to either one. Physiologically, this relative movement
in part determines the health or pathologic state of interface
components and influences the surrounding tissue
integration.
Metallurgy: The metals used in implant fabrication are an
important consideration. Grains often called crystals can
be of various geometric shapes. They exhibit crystallo-
graphic orientations that are a result of their formation,
geometric shape and location within the bulk structure.
Metals can be coined or squeezed into desired shapes when
sufficient ductility exists, such that relative grain
rearrangement occurs without disrupting integrity.
Coining is the process of shaping a metal in a mold or die
especially by stamping. In the early 1970s, research by
Matarese and Weiss solved this problem leading to
fabrication of first coined endosteal dental implants. The
coining process permits geometrically precise and planned
modifications of grain size and orientation. This reduces
metal fatigue over longer-term cyclic loading and promotes
ease and increased safety during insertion adjustments to
follow bone anatomy and to establish intraoral parallelism
for prosthodontic restorations.
METALS AND ALLOYS
Most of the dental implant systems are constructed from
metals or alloys. These include titanium, tantalum and alloys
of aluminum, vanadium, cobalt, chromium, molybdenum
and nickel. These materials are generally selected on the
basis of their overall strength. The precious metals often
used for restorations, such as gold, platinum and their
associated casting alloys are less frequently used for dental
implants.
Titanium
Metals as biomaterials have been increasingly used in
various devices or structures used in contact with or within
the biological system, like in orthopedics, dental and
cardiovascular applications. The evolution of titanium (Ti)
as biomaterial for medical and dental uses has dramatically
increased in the past few years because of titanium’s
excellent biocompatibility, corrosion resistance and
desirable physical and mechanical properties. Historically,
titanium was discovered in 1789 by Wilhelm Gregor. 4 The
industrial utilization of Ti, however, started only about 60
years ago when it was used for the aerospace and defense
industries, for which the metal’s high strength and light
weight offered solutions to many design problems for aircraft
engines.5 Dr Wilhelm Kroll invented useful metallurgical
processes for the commercial production of titanium metal,
therefore, he is known as the Father of Titanium Dentistry.3
He successfully developed the deoxidization process of
titanium tetrachloride through a reduction procedure with
magnesium and sodium. The result was a titanium sponge
that could be melted in an induction casting furnace into a
solid alloy and produced in long, cast solid bars. Titanium
represents only 6% of the earth’s crust.6
General Properties of Titanium
Titanium is in its metallic form at ambient temperature, it
has a hexagonal close-packed crystal lattice (α phase), which
transforms into a body-centered cubic form (β phase) at
883°C, the melting point is 1,680°C. The strength, rigidity
and ductility in pure form are comparable to those of other
noble or high noble alloys commonly used in dentistry.7,8
Commercially pure titanium is available in four grades
(1-4), according to American Society for Testing and
Materials (ASTM), which vary according to the oxygen
(0.18-0.40 wt%), iron (0.20-0.50 wt%) and other impurities.
Other impurities include nitrogen (0.03-0.05 wt%), carbon
(0.1wt%) and hydrogen (0.015wt%). Grade 1 is the purest
and softest form, which has moderately high tensile
strength.9 The environmental resistance of titanium depends
primarily on a thin, tenacious and highly protective surface
oxide film. Titanium and its alloys develop stable surface
oxides with high integrity, tenacity and good adherence.
The surface oxide of titanium, if scratched or damaged,
immediately reheal and restore itself in the presence of air
or water. The protective passive oxide film, which is mainly
TiO2 is stable over a wide range of pH, potentials and
temperatures, and is specially favored as the oxidizing
character of the environment increases.
Titanium, because of this protective coating, generally
resists mild reducing, neutral and highly oxidizing
environments up to reasonably high temperatures. It is only
under highly reducing conditions that oxide film breakdown
and resultant corrosion may occur. These conditions are not
normally found in the mouth.5 The temperature dependant
allotropic phase transformation from hexagonal close
packed α phase to body centered cubic β phase at 885°C
allows four different phase combinations of titanium alloys
to be commercially available. These are α, near α, β and
αβ. Aluminum, carbon, gallium, oxygen, nitrogen and tin
are commonly added α stabilizers and nickel, copper,
palladium, vanadium are β stabilizers added to αβ and β
phase alloys. Most commonly used alloys in dentistry are
Ti-6Al-V, Ti-30Pd, Ti-20Cu, Ti-15V and Ti-6Al-4V.10-14
Corrosion
Titanium has long been successfully used as an implant
material. Stable TiO2 surface layer with a thickness of
approximately 10 nanometers separates the reactive Ti from
the electrolyte, thus generating high corrosion resistance.
Titanium, however, is as corrosive as many other base metals
under mechanical stress, oxygen deficit or at a low pH level.
Long-term studies and clinical observations establish the
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International Journal of Oral Implantology and Clinical Research, January-April 2011;2(1):13-24 17
IJOICR
fact that titanium does not corrode when used in living tissue,
however, galvanic coupling of titanium to other metallic
restorative materials may generate corrosion.15,16 Hence,
there is a great concern regarding the material for
superstructures over the implant. Moreover, self-formed
protected oxide film on titanium can be affected by excessive
use of the commonest preventive agents in dentistry,
prophylactic polishing and topical fluoride applications.
Fluoride contained in commercial mouthwashes, toothpaste
and prophylactic gels are widely used to prevent dental caries
or relieve dental sensitivity or for proper oral cleaning after
application of normal brushes with toothpaste. The
detrimental effect of fluoride ions on the corrosion resistance
of Ti or Ti alloys has been extensively reported. Fluoride
ions are very aggressive on the protective oxide formed on
Ti and Ti alloys.17-21
Other Properties
Titanium is one of the metals that can be coupled with other
metals without fear of losing its passivity. When coupled
with metals of greater corrosion potentials it may corrode
by the mechanism of galvanic corrosion. When coupled with
metals, they remain passive and a stable combination is
produced. It would therefore be wise to avoid metals that
are not strongly passive, such as stainless steel. This should
also be taken into consideration when selecting surgical
instruments for the placement of titanium implants.
Selecting an Implant22,23
Clinical evidence documents that all six commercially
available dental implant biomaterials have exhibited
excellent biocompatibility and tissue responses. None of
the Ti-based materials have proved to be more biocompatible
than any other group. Factors such as implant design, size
and material strength should be determined in implant
selection for a particular patient. If a patient has a history of
parafunctional habits, the clinician should choose an implant
made of Ti alloy rather than Cp grade I titanium. In addition,
small diameter implants placed within thin walls indicate
the need for high strength materials.
Tissue Response
The most commonly used biomaterials for dental implants
are metals and their alloys namely commercially pure (CP)
titanium and Ti-6A-14V, which are most commonly used
as endosseous implants, whereas Co-Cr-Mo are most oftenly
used as subperiosteal implants.
CpTi and Ti alloys are low-density metals that have
chemical properties suitable for implant applications. Ti has
poor shear strength and wear resistance making it unsuitable
for articulating surface or bone screw application. Ti has
high corrosion resistance attributed to the surface oxide layer
that creates a chemically nonreactive surface to the
surrounding tissue.
Both elastic modulus and strength are important
considerations in choosing an implant material. The implant
must have sufficient strength to withstand occlusal forces
without permanent deformation and low modulus for
optimum force transfer. Clinicians can choose the most
appropriate dental implant material when they are
knowledgeable about the properties of the materials. The
surgical stainless steel alloys have a long history of use for
orthopedic and implant devices. This alloy with titanium
systems is used most often in a wrought and heat-treated
metallurgic condition, which results in high strength and
high ductility alloy.
Cobalt-Chromium-Molybdenum
Based Alloys
The cobalt-based alloys are most often used in cast or cast
and annealed metallurgic conditions.22 This permits the
fabrication of implants as custom design, such as
subperiosteal frames. The elemental composition of this
alloy includes cobalt, chromium and molybdenum as the
major elements. Cobalt provides continuous phase for basic
properties. Chromium provides corrosion resistance through
the oxide surface. Molybdenum provides strength and bulk
corrosion resistance. All these elements are critical as their
concentration emphasizes the importance of controlled
casting and fabrication technologies. Also includes minor
concentrations of nickel, manganese and carbon. Nickel has
been identified as biocorrosive product and carbon must be
precisely controlled to maintain mechanical properties, such
as ductility. In general, the cast-cobalt alloys are least ductile
of the alloy systems used for dental surgical implants and
bending of finished implants should be avoided. Properly
fabricated implants from these alloys have shown excellent
biocompatibility profiles.
Iron-Chromium-Nickel Based Alloys
The surgical stainless steel alloys have a long history of use
for orthopedic and implant devices.1 This alloy with titanium
systems is used most often in a wrought and heat-treated
metallurgic condition, which results in high strength and
high ductility alloy.
The ramus blade, ramus frame, stabilizer pins and some
mucosal insert systems have been made from iron-based
alloy. Among the implant alloys, this alloy is most subjected
to pitting corrosion and care must be taken to use and retain
the passiviated (oxide) surface condition, as this alloy
contains nickel as a major element. Its use in allergic patients
must be avoided. The iron-based alloys have galvanic
potentials and corrosion resistance that could result in
concerns about galvanic coupling and biocorrosion, if
interconnected with titanium, cobalt, zirconium or carbon
implant biomaterials. In some clinical conditions, more than
one alloy may be present within the same arch of a patient.
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Long-term device retrievals have demonstrated that
when used properly the alloy can function without significant
in vivo breakdown. Clearly, the mechanical properties and
cast characteristics of this alloy offer advantages with respect
to clinical application.
Other Metals and Alloys
Many other metals and alloys have been used for dental
implant device fabrication. Early spiral forms included
titanium, platinum, iridium, gold, palladium and alloys of
these metals. More recently, devices made from zirconium,
hafnium and tungsten have been evaluated.24 Some
significant advantages of these reactive group of metals and
their alloys have been reported. Gold, platinum and
palladium are metals with relatively low strength values,
which limit their use. These metals, especially gold, because
of nobility and availability continue to be used as surgical
implant materials.
CERAMICS
Ceramics are nonorganic, nonmetallic, nonpolymeric
materials manufactured by compacting and sintering at
elevated temperatures. They can be categorized according
to tissue response as:
Bioactive: Bioglass/Glass ceramic
Bioresorbable: Calcium phosphate
Bioinert: Alumina, zirconia and carbon.
Ceramics were introduced for surgical implant devices
because of their inertness to biodegradation, high strength
and physical characteristics, such as minimal thermal and
electrical conductivity with a wide range of material specific
elastic properties. Ceramics are chemically inert, care must
be taken in handling and replacement due to its low ductility
and inherent brittleness has resulted in its limitations.25
Aluminum, Titanium and Zirconium Oxides
High ceramics from aluminum, titanium and zirconium
oxides have been used for root form or endosteal plate form,
and pin-type dental implants. The compressive, tensile and
bending strengths exceed the strength of compact bone by
3 to 5 times. These properties combined with high moduli
of elasticity and especially with fatigue and fracture strength
have resulted in specialized design requirements for this
class of biomaterials.
Advantages
1. The Al, Ti and zinc oxide ceramics have a clear, white
cream or light gray color that is beneficial for application,
such as anterior root form devices.
2. Minimal thermal and electric conductivity, biodegra-
dation and reaction to bone, soft tissue and oral
environment are also considered as beneficial when
compared with other types of synthetic biomaterials.
3. Dental and orthopedic devices in laboratory animals and
humans, ceramics have exhibited direct interface with
bone similar to an osseointegrated condition with
titanium.
Also, characterization of gingival attachment zones
along with root form devices in laboratory animal model
has demonstrated localized bonding.
Disadvantages
1. Exposure to steam sterilization results in a measurable
decrease in strength for some ceramics.
2. Scratches or notches may introduce fracture initiation
sites.
3. Chemical solutions may leave residues.
4. Hard and rough surfaces may readily abrade other
materials thereby causing a residue in contact with the
periapical tissues.
5. Dry heat sterilization within a clean and dry atmosphere
is recommended for most ceramics.
Bioactive and Biodegradable Ceramics based
on Calcium Phosphate
The calcium phosphate (CaPO4) ceramics used in dental
reconstructive surgery includes a wide range of implant
types, and thereby a wide range of clinical applications.26
Early investigations showed that nominal compositions were
relatively similar to the mineral phase of bone (Ca5 [PO4]3
OH). The laboratory and clinical results of their particulate
were promising and led to expansions for implant
applications including larger implant shapes (such as rods,
cones, blocks, H-bars) for structural support under relatively
high-magnitude loading applications. Mixtures of particulate
with collagen and subsequently with drugs and active
organic compounds, such as bone morphogenetic protein
(BMP) increased the range of possible applications.The
coatings of metallic surfaces using flame or plasma spraying
(or other techniques) increased rapidly for CaPO4 ceramics.
The coatings have been applied to a wide range of endosteal
and subperiosteal dental implant designs with an overall
intention of improving implant surface biocompatability
profiles and implant longevity.
Advantages
1. Chemical compositions are highly pure and substances
are similar to constituents of normal biologic tissue
(calcium, phosphorous, oxygen and hydrogen).
2. Excellent biocompatibility profiles with variety of
tissues, when used.
3. Minimal thermal and electrical conductivity and
capabilities to provide a physical and chemical barrier
to ion transport (e.g. metallic ions).
4. Moduli of elasticity more similar to bone than any other
implant materials used for load-bearing implants.
5. Color similar to bone, dentin and enamel.
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IJOICR
Disadvantages
1. Variations in chemical and structural characteristics for
some currently available implant products.
2. Relatively low mechanical tensile and shear strength
under condition of fatigue loading.
3. Relatively low attachment strengths for some coating to
substrate interfaces.
4. Variable solubility depending on the product and clinical
application.
5. Alterations of substrate chemical and structural
properties related to some available coating technologies.
Bioactive Ceramic Properties
Tricalcium phosphate [Ca3(PO4)2] finds no place in this
scheme, although it is frequently employed as a starting
material in the synthesis of degradable ceramics. An
explanation for this obscene was given that presence of water
in CaPO4 yields hydroxyapatite.
H2O + 4Ca3(PO4) [Ca10(PO4)(OH)2] + 2Ca++ + 2HPO4
Apatite or more precisely hydroxyapatite is the main
constituent of hard tissues, such as bone, dentin and enamel.
Whenever a powder with Ca/P ratios in the order of 1.5 to
1.7 is sintered in atmosphere containing water at temperature
up to 1200 to 1300°C, crystallographically the end product
will be an apatite when comparing the elemental analysis.
Powder A: Commercially available is Merc W, Darmstadt,
Germany, consists of very porous agglomerates with mean
sizes of 1 to 2 mm. The specific surface area is determined
by BET analysis is 59 m2/gm. X-ray analysis of powder
shows broad peaks of the hydroxyapatite structure.
Powder B: It has been made according to the directions of
Hayek (1963). Although, it is somewhat a tedious method
due to gelatinous nature of the precipitate, it yields very finely
divided powder with high surface area (80-90 m2/gm). Trace
elements may influence biologic behavior.
Elemental Analysis
Contents Powder A Powder B
Calcium 37.5 37.2
Phosphorus 17.30 17.40
Hydrogen 0.50 0.50
Ca/P 2.167 2.138
Mol/Mol 1.68 1.66
Methods of Preparation
The powder is precompressed in a Perspex die by means of
an upper and lower punch. To prevent the powder from
sticking to the inner surface of the die, stearic acid in alcohol
is applied. After the powder compact has been pushed out,
it is placed into a rubber tube, brought under vacuum,
isostatically compressed (100 MN/rn2) in oil containing
press vessel. The samples compressed in this way have a
density of 44% (green body) and heated at temperature,
which increase at rate of 100°C/hr in wet O2 atmosphere
for 6 hours and cooled down slowly at 100°C/hr.
Preparation of Dense Apatite Crystals
Dudemans (1969) described a sintering technique called
continuous hot pressing technique. In this method, heat and
pressure are applied at same time, thus allowing
densification to take place at a much lower temperature than
in normal sintering process. First sintering occurs at 900°C,
which is far below the decomposition temperature of
hydroxyapatite. Continuous hot pressing is a fairly fast
technique compared with conventional sintering. The die is
heat punched at pressing rate of 25 mm/hr.
Forms, Microstructure and
Mechanical Properties
Hydroxyapatite (HA) is a nonporous (< 5% porosity) with
angular or spherically shaped particles, is an example of a
crystalline high pure HA biomaterial. These particles have
relatively high compressive strengths (up to 500 MPa) with
tensile strengths in the range of 50 to 70 MPa.
Nonresorbable bioinert ceramics exhibits satisfactory
load bearing capability limited to dense monocrystalline and
polycrystalline aluminum, zirconium and titanium oxide
ceramics. The coatings of CaPO4 ceramics onto metallic
(Co-and Ti-based) biomaterials have become a routine use
for dental applications by plasma spraying, which has
average thickness between 50 and 70 microns mixtures of
crystalline and amorphous phases. Concerns continue to
exist the fatigue strengths of the CaPO4 coatings to substrate
interfaces under tensile and shear loading conditions. This
has caused some clinicians and manufactures to introduce
geometric designs in which the coatings are applied to
shapes that minimize implant interface shear or tensile
loading conditions.
Density, Conductivity and Solubility
Bioactive ceramics are especially interesting for implant
dentistry because the inorganic portion of the recipient bone
is more likely to grow next to chemically similar material.
Under the bioactive categorization includes calcium
phosphate materials, such as TCP (tricalcium phosphate),
HA, calcium carbonate (cards) and calcium sulfate-type-
compounds and ceramics.
Dissolution characteristics of bioactive ceramics have
been determined for both particulate and coatings. In
general, solubility is greater for TCP than for HA. Each
increase relative to increase in surface area per unit volume
(porosity) and CaPO4 ceramic solubility profiles depend on
20 JAYPEE
BC Muddugangadhar et al
the environment. Tofe et al studied the product impacts on
the resorption rate. Greater the porosity more rapid is the
resorption of graft material.
The crystallinity of HA also affects the resorption rate
of the material. The highly crystalline structure is more
resistant to alteration and resorption. An amorphous product
has a chemical structure that is less organized with regard
to atomic structure. The hard and soft tissues of the body
are more able to degrade the components and resorb the
amorphous forms of grafting materials. Thus, the crystalline
forms of HA are found to be very stable over the long-term
under normal conditions, whereas the amorphous structures
are more likely to exhibit resorption and susceptibility to
enzyme or cell-mediated breakdown. The purity of the HA
bone substitutes may also affect the resorption rate. The
resorption of the bone substitute may be cell- or solution-
mediated. The cell-mediated resorption requires processes
associated with living cells to resorb the material, similar to
the modeling/remodeling process of the living bone.
A solution permits the dissolution of the materials by a
chemical process. Impurities or other compounds in
bioactive ceramics, such as calcium carbonate, permit more
rapid solution mediated resorption, which increases the
porosity of the bone substitutes.
The CaPO4 coatings are nonconductors of heat and
electricity. This can provide a relative benefit for coated
dental implants, where mixtures of conductive materials may
be included in the overall prosthetic reconstruction.
Hydroxyapatite-Coated Metals
The achievement of improved metallic bone implant devices
by simply coating them with HA proved to be remarkably
easy, both in concept and execution.27 From the point of
view of execution, standard methods for putting ceramic
coatings on implants are principally plasma or flame spray
technique has been around for decades. HA plasma coating
process involves first roughening the metal to be coated in
order to increase the surface area available for mechanical
bonding with HA coating. Then a stream of HA powder is
blown through a very high temperature flame that partially
melts and ionizes the powder, which emerges from the flame,
hits the metallic surface to be coated and condenses to form
a ceramic coating that is partially glossy and partially
crystalline in nature. These coatings are built up in thin layers
using robotic techniques, until the final thickness (usually
40-l00 μ) is achieved. The major shortcoming of HA
ceramics is their lack of mechanical strength. The major
strength of HA is a chemical composition, which fools living
bone tissue behaving as if the HA implant were natural
autogenous bone.
Hydroxyapatite-Tricalcium Phosphate
Bioceramics
The two calcium phosphate systems that have been most
investigated as bone implant material are HA and tricalcium
phosphate. Based on numerous in vitro and in vivo
experiments,28 it was apparent that dense or porous HA
ceramics could be considered to be long-term or permanent
bone implant materials, whereas porous TCP ceramic could
potentially serve as bioresorbable. Although TCP implant
materials were more or less comparable to HA material with
regard to biocompatability and bone bonding, achieving
predictable and reproducible bioresorption rates with
adequate mechanical properties proved to be difficult with
TCP ceramics. TCP system became eclipsed by a succession
of commercially introduced HA containing implantable
products.
HA, commonly called tribasic calcium phosphates, is a
geologic mineral that closely resembles the natural
vertebrate bone tissue. These materials must not be confused
with tricalcium phosphate (TCP), which is chemically
similar to HA but it is not a natural bone material.
Types of Ceramic Coatings
The ceramic coating available includes the bioactive type,
such as the calcium phosphates and inert ceramics, such as
aluminum oxide and zirconium oxide. The bioactive
ceramics include the bioglasses, have been documented to
produce a calcium phosphate layer on the unmodified
surface when used in vivo or in a simulated physiological
solution. Primary importance as far as response is concerned
is the amount of calcium and phosphate ions released per
given amount of time. The presence of calcium and
phosphorous ions in the area around the implant often
resulted in enhanced bone apposition as compared with the
more ceramic and metallic surfaces. It is important to realize
that all coating processes are likely to alter the composition
of the starting material to some degree and have the potential
for introducing impurities into the coating.
Plasma Spraying
It is the most common coating method for dental implants
because almost all the commercial HA coatings are produced
by this technique.29 This method involves the use of a carrier
gas, which ionizes (thus forming a plasma) and superheats
the particles of the starting material (generally HA),
undergoes partial melting as they are propelled toward the
substrates to be coated. Coatings around 50 microns are
typically produced on a roughened titanium or alloy surface
for a HA (plasma) sprayed endosseous implant. The most
stable of the plasma sprayed calcium phosphate coatings is
fluorapatite (FA), which is capable of retaining in large part
both its fluorine constituent and high crystallinity during
the high temperature plasma spray process. This process
has a crystallinity of around 60 to 70%, but higher content
can be obtained if the coated implant is heat-treated at a
suitable temperature after the deposition process. One study
showed that a low crystallinity (46% HA) plasma-sprayed
implant exhibited about three times the dissolution of Ca
ions as a higher crystallinity (75% HA) material.
Biomaterials for Dental Implants: An Overview
International Journal of Oral Implantology and Clinical Research, January-April 2011;2(1):13-24 21
IJOICR
Advantages
1. It is relatively inexpensive
2. The mechanical properties of the metallic substrate are
not compromised during the coating process.
Limitations
1. Forms mechanical bonding only with the metallic
implant surface
2. The main source of contamination appears to be copper
from the nozzle of the sprayers
Vacuum Deposition Techniques
There are several methods of placing thin coatings of
ceramics on metals, as done routinely in the electronics and
other industries. These involves bombarding a target in
vacuum chamber resulting in sputtered or ablated atoms or
particles moving through the chamber to coat on properly
positioned substrates. These techniques include ion beam
sputtering, radio frequency sputtering and pulsed laser
deposition. All are relatively expensive and capable of
depositing coatings in the order of a few micrometers.
Advantages: High quality coatings with good bonding to
either smooth or rough titanium surfaces, but usually require
a heat treatment in a controlled atmosphere to attain high
crystallinity.
Limitations
1. The efficacy of these very thin coatings is unknown
2. There is some concern that the coating may resorb in
the body before causing the desired effect.
Sol-gel and Dip Coating Methods
Studies on the use of sol-gel technology for coating dental
implants have recently been initiated. This method had been
used for depositing other types of thin coatings, such as
superconducting thin films for electronic devices. In this
technique, precursors of the final product are placed in
solution, and the metal implant to be coated is dipped into
the solution, withdrawn at the prescribed rate, and then
heated to create a more dense coating.
Technique: The coating is fired at 800 to 900°C to melt the
carrier glass to achieve bonding to the metallic substrate.
This process is repeated until a relatively thick coating (e.g.
100 microns) consisting of HA/glass mixture can be
obtained.
Advantages
1. Small crystalline size and high strength
2. Potential for applying a uniform coating to porous
substrates.
Hot Isostatic Pressing
Hot isostatic pressing (HIP) is used to develop the highest
density and strength possible in crystalline ceramic materials.
In this technique, both heat and pressure are used to enhance
ceramic density (such as alumina or HA) into a solid ceramic
of high strength. HA powder is applied to the implant
surface, an inert foil is placed over the powder to facilitate
uniform densification, both heat and pressure are applied.
Disadvantages
1. Expensive
2. The necessity of removing the inert foil or other
encapsulating material
3. The potential for contamination.
Electrolytic Process
Electrophoresis and electrolytic deposition are two processes
that deposit HA or suitable bioceramic particles out of a
bath of proper chemistry.
The advantages are that the porous surface materials can
be uniformly coated, and the original composition of the
ceramic (e.g. HA) can be maintained in most cases.
In the present state of development, none of the coating
techniques discussed produce HA coatings with both high
crystallinity and high bond strength. Heat treatment may be
used to increase crystallinity. However, they are not widely
used because of the added expense and increased possibility
of contamination of the coatings. Manufacturers can often
obtain the desired crystallinity (e.g. higher than 80%) during
the plasma spray coating operation without the need for
additional heat treatment.
Carbon and Carbon Silicon Compounds
Carbon compounds are often classified as ceramics because
of their chemical inertness and absence of ductility.
Uses
1. Extensive applications for cardiovascular devices
2. Excellent biocompatibility profiles and moduli of
elasticity close to that of bone have resulted in clinical
trails of these compounds in dental and orthopedic
prostheses.
Advantages
1. Tissue attachment
2. Can be used in the regions that serve as barrier to
elemental transfer of heat and electrical current flow
3. Control of color and provide opportunities for the
attachment of active biomolecule or synthetic
compounds.
Limitations
1. Mechanical strength properties are relatively poor.
2. Biodegradation that could adversely influence tissue
stability.
3. Time dependent changes in physical characteristics.
4. Minimal resistance to scratching or scraping procedures
associated with oral hygiene.
22 JAYPEE
BC Muddugangadhar et al
Bioactive Glass Ceramics
Bioglass (US: Biomaterials) is composed of calcium salts
and phosphates in similar proportions found in bone and
teeth.30 This graft is amorphous material, hence its
developers believed that degradation of the material by tissue
fluids and subsequent loss of the crystal would cause the
material to lose its integrity.The graft has two properties:
1. Relative quick rate of reaction with host cells
2. Ability to bond with collagen found in connective tissue.
It has been reported that the high degree of bioactivity
induces osteogenesis. Since the bioactivity index is high,
reaction develops within minutes of implantation.
Tissue Response
CaPO4 ceramics, particularly HA, have been used in
monolithic form as augmentation material for alveolar ridges
and coatings on metal devices for endosseous implantation.
The implant surface responds to the local pH changes by
releasing sodium ions in exchange for phosphorous ion.
Osteoblasts proliferate at the surface and collagen fibrils
become incorporated into the calcium phosphate rich layer.
The body’s typical response to these implanted ceramics
are:
No local or systemic toxicity
No inflammatory or foreign body response
Functional integration with bone
No alteration to natural mineralization process
Chemical bonding to bone via natural bone cementing
mechanism.
The natural bone cementing substance is amorphous in
structure, heavily mineralized and rich in polysaccharides.
Because the bond area contains the natural bone cement
substance, it is responsible for the bond between bone and
the calcium phosphate ceramic is strong.
Current Status and Developing Trends
The CaPO4 ceramics have proved to be one of the more
successful high technology based biomaterials that has
evolved within the biomaterials in the past two decades.
Their advantageous properties strongly support the
expanding clinical applications and the enhancement of the
biocompatibility profiles for surgical implant uses.
Within the overall theme for new generation biomaterials
to be chemically (bonding to tissue) and mechanically (non-
uniform, multidirectional properties) anisotropy, the CaPO4
ceramics could be the biomaterial surfaces of choice for
many device applications.
Ceramic forms of calcium phosphate, particularly HA,
had been investigated extensively and used for hard tissue
implant applications. HA ceramic still remains the most
biocompatable bone material known and posses the added
feature of becoming strongly bonded to living bone through
natural appearance bonding mechanism. A variety of new
or improved bone and tooth implant products have been
developed using HA ceramics, thus this system had lead to
overall improvement in dental hard tissue repair and
replacement.
POLYMERS AND COMPOSITES AS IMPLANT
MATERIALS
The use of synthetic polymers and composites continues to
expand for biomaterial applications. Fiber-reinforced
polymers offer advantages that they can be designed to
match tissue properties, can be coated for attachment to
tissues and can be fabricated at relatively low cost. Expanded
future applications for dental implant systems include IMZ
(Interpure Inc) and Flexiroot (Interdent Corp). Systems are
anticipated as interest continues in combination of synthetic
and biologic composites.
Biomedical Polymers
The more inert polymeric biomaterials include
polytetrafluroethylene (PTFE), polyethyleneterephthalate
(PET), polymethylmethacrylate (PMMA), ultra high
molecular weight polyethylene (UHMW-PE), polypropylene
(PP), polysulfone (PSF) and polydimethyl siloxane (PDS)
or silicone rubber (SR).
Properties
In general, the polymers have lower strengths and elastic
moduli, and higher elongation to fracture compared with
other class of biomaterials. They are thermal and electrical
insulators, and when constituted as a high molecular weight
system without plasticizers, they are relatively resistant to
biodegradation compared with bone; most polymers have
lower elastic moduli with magnitudes closer to soft tissues.
Polymers have been fabricated in porous and solid forms
for tissue attachment, replacement and augmentation as
coatings for force transfer to soft and hard tissue regions.
Cold flow characteristics, creep and fatigue strength
are relatively low for some class of polymers (e.g. SR and
PMMA) that had resulted in some limitations.
Most uses have been for internal force distribution
connectors intended to better stimulate biomechanical
conditions for normal tooth functions. The indications for
PTFE have grown exponentially for guided tissue
regeneration techniques. However, PTFE has a low
resistance to contact abrasion and wear phenomenon.
Polymers and Composites
Combinations of polymers and other categories of synthetic
biomaterials continue to be introduced. Several of the inert
polymers have been combined with particulate or fibers of
cotton, aluminum oxide, and hydroxyapatite and glass
ceramics. Some are porous whereas others are constituted
as solid composite structural forms. In some cases,
Biomaterials for Dental Implants: An Overview
International Journal of Oral Implantology and Clinical Research, January-April 2011;2(1):13-24 23
IJOICR
biodegradable polymers, such as polyvinyl alcohol (PVA),
polylactides or glycosides, cyanoacrylates or other hydrated
forms have been combined with biodegradable CaPO4
particulate of fibers. They are intended as structured
scaffolds, plates, screws or other such applications.
Biodegradation of the entire system after tissues have
adequately reformed, and remodeling has allowed the
development of significantly advantageous procedures, such
as bone augmentation and peri-implant defect repairs.
Disadvantages
1. In general, polymers and composites of polymers are
especially sensitive to sterilization and handling tech-
niques. If intended for implant use, most cannot be
sterilized by steam or ethylene oxide.
2. Most polymeric biomaterials have electrostatic surface
properties and tend to gather dust or other particulate if
exposed to semiclean oral environments.
3. Because many can be shaped by cutting or auto-
polymerizing in vivo (PMMA), extreme care must be
taken to maintain quality surface conditions of the
implant.
4. Porous polymers can be deformed elastically, which can
close open regions intended for tissue ingrowth.
5. Also, cleaning the contaminated porous polymers is not
possible without a laboratory environment.
Implications
Long-term experience, excellent biocompatibility profiles,
ability to control properties through composite structures
and properties that can alter to suit the clinical application
make polymers and composites excellent candidates for
biomaterial applications, as the constant expansion of the
applications of this class of biomaterials can verify.
FUTURE AREAS OF APPLICATION31
Synthetic substance for tissue replacements have evolved
from selected industrial grade materials, such as metals,
ceramics, polymers and composites. This situation offers
opportunities for improved control of basic properties. The
simultaneous evaluation of the biomechanical sciences also
provides optimization of design and material concepts for
surgical implants. Combinations provided are compositions
with bioactive surfaces, the addition of active biomolecules
of tissue inductive substances and a stable transgingival
attachment mechanism that could improve implant device
systems. Devices that function through bone or soft tissue
interfaces along the free transfer regions could be the
systems of choice depending on the clinical situation.
The trend for conservative treatment of oral diseases
will continue. Thus, it can be anticipated that dental implants
will frequently be a first treatment option. Implants have
rapidly moved into the mainstream of dental practice in the
last 10 years with phenomenal growth based on rapidly
expanding technology with increasing public interest.
Implants have been used to support dental prostheses for
many decades and they have always enjoyed a favorable
reputation.
CONCLUSIONS
Dental implantology is an exciting treatment concept that
includes series of surgical, prosthetic and periodontal
restorative skills. In the 1960s and early 1970s, dental
implantology was considered somewhat experimental and
basically restricted to early workers. The phenomenal
interest, clinical application, improvement in dental
materials and biomechanical understanding by dental
scientists in this field led to carefully conduct controlled
and monitored clinical trials. Implantology has become an
exciting and dynamic force within dentistry during the recent
years, from a less than well-accepted treatment option, it
has mushroomed into the current hottest issue in dentistry.
Implantology provides many new and exciting ways to help
dental patients to achieve function and social well-being,
and provide a certain amount of personal and professional
satisfaction to the dentist. Dental Implantology will become
a highly acceptable and predictable treatment modality for
the restoration of the human dental and oral apparatus.
Implants are now being targeted in predoctoral and
postdoctoral training program nationally and internationally.
Though, we have come a long way, and may be we haven’t
seen anything yet.
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... Metals and metallic alloys constitute the main material category used in dental implant systems [8], including titanium, vanadium, aluminum, cobalt, chromium, molybdenum and nickel. Also, noble metals like gold and platinum are often used restore the function, integrity and morphology of missing tooth structure. ...
... Most commonly used alloys in dentistry are Ti-30Pd (palladium), Ti-20Cu (copper), Ti-15V (vanadium) and Ti-6Al-4V (aluminum and vanadium) [8]. ...
... 8 shows an example of the resultant force for an experiment using feed per tooth of 1 µm/tooth with the positions 2 fromFig. 7.7 specified for each tool revolution. ...
Thesis
Properties like good corrosion resistance and biocompatibility as well as satisfactory mechanical resistance make titanium and its alloys a good candidate for applications in biomedical industry. Commercially pure titanium (CP-Ti) is the ideal titanium-based material to use in the manufacturing of dental implants as alloying elements can decrease its biocompatibility. However, CP-Ti shows limited mechanical properties for a few implant applications. Ti-6Al-4V is the most common titanium alloy used in biomedical implants. Machining is one of the main manufacturing process involved in producing implants and micromilling is one of the process that can be used. The proposition of this thesis is to analyze and comparethe micromilling machinability of four different titanium-based materials, indicating the better suited material regarding this manufacturing process among: standard commercially pure titanium grade 2, standard Ti-6Al-4V alloy, CP-Ti processed by equal channel angular pressing (ECAP) and Ti-6Al-4V fabricated by selective laser melting (SLM). Machinability was analyzed considering cutting forces, surface roughness, burr formation, microchips morphology as well as their mechanical properties and their influence in each factor was analyzed. It was designed a seriesof experiments varying feed per tooth and covering a wide range, from 0.5 to 4.0 µm, so a possible ploughing behavior could be identified. Despite presenting higher strength and hardness, SLM material presented the best machinability among the materials. It presented lower surface roughness, burr formation, a good microchip morphology and the cutting force was only higher than for CP-Ti, which has the worst mechanical properties values.
... Resin-based composites are extensively utilised in the dental sector (Liu et al. 2014), for example, as cavity liners, inlays, onlays, core build-ups, crowns, provisional restorations, denture teeth, cementation of crowns, bridges and orthodontic brackets, structured scaffolds, root canal sealers and posts, plates and screws (Ferracane 2011;Muddugangadhar et al. 2011;Sakaguchi & Powers 2012;Khan et al. 2017). Resin composites are the most desired restorative materials because of their superior aesthetic, moderate cost, mechanical and biocompatibility properties, simplified clinical procedures, bonding ability, developed formulations, and decreased amalgam use due to mercury hazard and toxicity (Mota & Subramani 2018;Razali et al. 2018). ...
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Resin-based composites represent a unique class of restorative dental materials; however, these composites have severe shortcomings such as low wear resistance which is mainly responsible for the short lifespan of the materials. Composites characteristics such as strength, stiffness, resistance to abrasion, polymerisation shrinkage, thermal expansion coefficients and moisture absorption depend on the filler particles and coupling agents used. Fortunately, these composites have been the focus of attention for numerous researches in recent years which aim to improve the performance of the restorations in several ways. Using several types of coupling agents, and different particle sizes and types have gained the great interest of researchers. The latter plays a critical role in the toughening mechanisms in resin-based composites. Therefore, the purpose of this review is to discuss the literature regarding the toughening mechanisms in particulate dental resin composites since these mechanisms are also crucial factors for the improvement of mechanical properties. The four main types of toughening mechanisms discussed are: crack deflection, pinning, bridging and particle-matrix interface. The current review indicates an improvement in mechanical properties of particle-filled dental composites due to the presence of various toughening mechanisms. The dental resin composites' fracture toughness is mainly contributed by crack deflection, pinning and bridging that take place in micro-and nanocomposites, in addition to the hybrid composites. Filler-matrix interphase plays an important role in improving the mechanical properties, in addition to its positive effect on crack deflection and bridging. In reality, all these mechanisms could occur simultaneously at different intensities, respectively.
... International Journal of Medical Sciences and Innovative Research (IJMSIR)© 2021 IJMSIR, All Rights Reserved years and it is expected to expand in the future due to the recent growth of the global market for dental implants and the rise in the demand for cosmetic dentistry.5 As a result of ongoing research in treatment planning, implant design, materials and techniques, unsurprising achievement is now a reality for the rehabilitation of many challenging situations.4 ...
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The objective of present day dentistry is to reestablish the patient to normal contour, function, comfort, esthetics, speech and health. What makes implant dentistry unique is the ability to achieve this goal regardless of the atrophy, disease, or injury of the stomatognathic system. However, the more teeth a patient is missing, the more challenging this task becomes. The biocompatibility profiles of synthetic substances (biomaterials) used for the replacement or augmentation of biological tissues have always been a critical concern within the health care disciplines. Therefore, the desire to positively influence tissue responses and to minimize biodegradation often places restrictions on which materials can be safely used within the oral and tissue environments.7 Improvements in both the quality and quantity of the implant biomaterial are the reasons for this treatment modality being practiced abundantly today. The development and modification of dental implants have taken place in an effort to create an optimal interaction between the body and the implanted material. The goal of achieving an optimal bone-implant interface has been approached by the alteration of implant surface topography, chemistry, energy and charge as well as bulk material composition.3 This article reviews the various implant biomaterials and their suitability of use in implant dentistry.
... e use of resins in dental applications are varied, including restorative materials, cavity liners, crowns, denture teeth, provisional restorations, root canal posts, and structured scaffolds [1,2]. ermosetting resins provide biocompatibility, a suitable environment for the part used inside the mouth, aesthetic qualities and reasonable cost, making these polymers preferred materials in various dental applications [3][4][5]. ...
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... Depending upon the bioactive material, various forms of CaPO 4 ceramics are used in medical implants but HA form of CaPO 4 ha been used as augmentation material for surface coating on metallic implants. Calcium Phosphate (CaPO 4 ) ceramics are widely used in wide range of implants and clinical surgeries preferably in dental applications [35]. The clinical results exhibited Calcium Phosphate has high fatigue strength and durability under moderately high load carrying applications thereby the ceramic has been extensively used in medical devices like blocks, cones, and rods. ...
... Polymers have excellent biocompatibility, lower strength and elastic moduli closer to soft tissues and higher elongation to fracture as compared to other biomaterials. Commonly used polymers in dentistry are polymethyl methacrylate (PMMA) and polyether ether ketone (PEEK) [42,43]. ...
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Master the use of dental materials in the clinic and dental laboratory and stay current with this ever-changing field with Craigs Restorative Dental Materials, 13th Edition. From fundamental concepts to advanced skills, this comprehensive text details everything you need to know to understand the scientific basis for selecting dental materials when designing and fabricating restorations. This practical, clinically relevant approach to the selection and use of dental materials challenges you to retain and apply your knowledge to realistic clinical scenarios, giving you an authoritative advantage in dental practice.
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Titanium, occasionally referred to as the “wonder metal”, has been utilized in a growing list of specialized applications since the Kroll process made the winning of this material from ores a commercial possibility in 1936 [1]. Titanium is the ninth most common element in the earth’s crust and is recovered from Ti02-rich deposits of rutile, ilmenite and leucoxene that are found on every continent. Since the discovery of titanium in 1794 [2], and up until Kroll’s innovative process development in 1936, there had been no practical method to recover titanium metal from these ores because of its pronounced affinity for oxygen. Modern ore extraction, beneficiation and chemical processes have since enabled the large-volume manufacturing of high-grade TiO2, an important pigment for paints and commercial products, and of titanium metal for the production of the CP (“Commercially Pure”) titanium grades, titanium-based alloys and other alloys systems.