Ebook Shafer''s textbook of oral pathology (7th edition): Part 2

Section III
Injuries and Repair

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Chapter 12

Physical
and
Chemical
Injuries of the Oral Cavity
B. Sivapathasundharam
Chapter Outline
. Injuries of Teeth Associated with Tooth Preparation
. Effect of Tooth Preparation
. Reaction To Rotary Instrumentation
. Effect of Heat
. Effect of Restorative Materials
. Physical Injuries of the Teeth
. Physical Injuries of the Bone
. Physical Injuries of Soft Tissues
. Nonallergic Reactions to Drugs and Chemicals used
Systemically
. Occupational Injuries of the Oral Cavity
. Occlusal Trauma

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Injuries of the oral cavity may be caused by physical or

chemical causes. Physical injuries may be iatrogenic,
self-inflicted, traumatic, or occupational. The most important
iatrogenic cause is the repair of tooth affected by dental caries
or other developmental defects and restoration of missing
tooth. Iatrogenic cause also includes X radiation and laser
radiation. Self-induced or factitious injuries are due to
overzealous oral hygiene practices, caused by psychotic or
neurotic condition, or habitual. Traumatic causes include a
fall, fight, road traffic accidents, and sports injuries.
Although chemical injuries are caused by environmental
elements such as toxic levels of chemicals in the water, air, or
consumables, the restorative and endodontic materials used in
the routine dental practice play an important role.

Injuries of Teeth Associated with
Tooth Preparation
The teeth, particularly the dentin and pulp, may be injured not
only by dental caries, but also from those procedures
necessary for the repair of lesions involving dental hard
tissues. Preparation of the teeth for receiving the restorations
include cutting, grinding, and etching with acids etc. These
physical and chemical methods of tooth preparation as well as
the various medicaments and filling materials which are
inserted into the prepared tooth, have their own effects.

Effect of Tooth Preparation

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The effect upon the dental pulp of restorative procedure alone
is difficult to assess except in the sound tooth, since the
carious lesion itself produces demonstrable changes in both
the dentin and the pulp. Even when a sound tooth is prepared
for experimental purpose, care must be taken in observing the
effects to separate those which are due solely to the tooth
preparation from those which are due to the restorative
materials applied.
Tooth preparation is usually done by rotary instruments such
as tungsten carbide burs and diamond burs of different sizes
and shapes. Lasers and air abrasion are also used
alternatively. Pulpal responses to these various procedures
depend on the heat generated by friction, cutting of
odontoblastic processes and drying of dentinal tubules,
thickness of remaining dentin, vibration, removal of minerals
and exposure of the organic matrix of dentin, and formation
of smear layer.

Reaction to Rotary Instrumentation
Stainless steel burs revolving at low speed were used in the
past for cavity and crown preparation. As the hardness of the
enamel is high, these burs could not abrade instead they cut or
chip away the tooth material. Also a considerable amount of
pressure is applied during the procedure, which results in
excessive heat production and evaporation of the contents of
the dentinal tubules. High speed rotary instrumentation with
tungsten carbide and diamond burs has replaced the steel burs
in recent years. Nevertheless stainless steel burs are used in
procedures involving bone.

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The reaction of the dental pulp to cutting of dentin with a
dental bur has been studied by Fish in both dogs and
monkeys. When dentin is injured, there is stasis of the
contents of the dentinal tubules, which lose their fluid
communication with the pulp because of the formation of
secondary dentin. Involved dentinal tubules are occluded by
the deposition of calcium which separates these sclerosed
dentinal tubules physiologically from the rest of the tooth.
The cavities prepared by Fish in the teeth of dogs or monkeys
were cut with steel burs which were kept wet to prevent the
complication of heat-induced damage to the pulp. In some
cases the cavities were then filled with copper oxyphosphate
cement and in other instances they were left open and
exposed to the oral fluids. The animals were sacrificed after
varying periods of time, and sections of the filled teeth were
prepared for microscopic study. Three general reactions to
cavity preparation were noted: (1) the production of
secondary dentin, (2) changes in the odontoblasts associated
with injured tubules, and (3) general changes in the pulp. Fish
carefully pointed out that the reaction of the tooth with the
formation of a calcified barrier and secondary dentin
production is always strictly confined to the pulp surface of
the injured dentinal tubules. There is never overlap of
uninjured tubules, and for this reason the changes may be
regarded as a specific reaction to injury of the dentinal
tubules.
The pulp reaction to superficial injury of the dentin varies in

degree of severity, depending partially upon the depth of the
prepared cavity and partially upon the elapsed time between
cutting the cavity and extraction of the tooth for study. In
mild reactions the odontoblasts become distorted and reduced
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in number. Small vacuoles may appear between them,
probably lymph exudate. Capillaries in the damaged area may
be prominent. In more severe injuries, there may be complete
disorganization of and hemorrhage in the odontoblastic layer
(Fig. 12-1). The bulk of the pulp tissue away from the cut
tubules may exhibit little or no reaction.

Figure 12-1
Effect on dental pulp of cavity preparation by steel bur.
Cavities were prepared in human teeth and filled with
gutta-percha. A section of pulp from an intact normal tooth is
shown in (A), while the injured area in the pulp six days after
cavity preparation is seen in (B) Courtesy of Drs David F
Mitchell and Jensen JH. J Am Dent Assoc, 55:57, 1957.
In more serious injuries there is a greater infiltration of the
injured locus by polymorphonuclear leukocytes, which
gradually become replaced by lymphocytes. The majority of
the severe pulp injuries are probably associated with irritation
brought about by the open cavities, with the sudden exposure
of large numbers of open dentinal tubules to oral fluids and
bacteria.

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Even after such severe injuries the majority of damaged pulps
undergo spontaneous healing or at least enter a quiescent
phase and produce no signs or symptoms of persisting
damage (Fig. 12-2). The factors responsible for this
phenomenon, especially from the clinical aspect, are
unknown.

Figure 12-2
Effect of cavity preparation by steel bur on dental pulp.
A calciotraumatic line (1) and reparative dentin (2) are found
beneath the cavity nine weeks after preparation Courtesy of
Drs David F Mitchell, JH Jensen. J Am Dent Assoc, 55: 57,
1957.
It appears that dentin has a heat-dissipating action which
reduces the temperature rise within the pulp to only a fraction
of the actual temperature applied to the tooth.
This is due to the low thermal conductivity of dentin, which
acts as an effective insulating medium. Nevertheless the
application of heat to a dental pulp already injured from a
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carious lesion of the dentin, but not an actual pulp exposure,
may be sufficient to affect adversely the repair or healing of
the pulp even though an apparently successful restoration is
given to the tooth.
The preparation of tooth under the constant application of
water to cool the cutting instrument and tooth will prevent

many of the serious consequences due to heat, and this
procedure is strongly recommended.
High-Speed Instrumentation

The development of high-speed dental engines and
hand-pieces necessitated investigation of the possible effects
which their use might have on pulp tissue, and numerous
reports of such studies have been published.
Bernier and Knapp reported a study on high-speed
instrumentation utilizing various speeds up to 100,000 rpm.
They found evidence of mild pulpal damage, but, in addition,
observed a new type of lesion which they termed the ‘rebound
response’. This consisted variously in: (1) an alteration in
ground substance, (2) edema, (3) fibrosis, (4) odontoblastic
disruption, and (5) reduced predentin formation in a region
directly across the pulp opposite the cavity site or at a distant
pulpal site, and thought to be caused by waves of energy
transmitted to the pulp focused into a certain region by the
pulpal walls. The significance of this phenomenon is still not
clear.
Swerdlow and Stanley in their study involving 450 human
teeth found that speeds over 50,000 rpm with coolants were

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less injurious to the pulp than lower speeds. They concluded
that the combination of high speed, controlled temperature,
and light load produced minimal pathologic pulpal alteration.
When heavy loads were used, even coolants did not minimize

inflammatory responses. Extending this investigation to 13
operative techniques, Diamond and his coworkers found that
the 300,000 rpm air-water spray—No. 35 carbide bur
technique—provided all the cutting efficiency of a high-speed
instrument without producing extended or burn lesions and
caused the highest incidence of reparative dentin formation, a
favorable protective reaction. A speed of 250,000 rpm with
water coolant was reported by Nygaard-Ostby to produce
even less pulpal reaction than the conventional (6,000 rpm)
machine without water-spray. Caviedes-Bucheli and
coworkers in their study found that substance P expression is
increased in tooth where cavity preparation is done and
concluded that it may have an important clinical significance
in terms of inflammation and pain experience.
The practicability of use of accelerated hand-piece speeds has
been accurately summarized by Stanley and Swerdlow, who
stated: ‘In principle, high speed techniques approach the ideal
but at the same time these methods can be easily abused…
properly used, ultraspeed is an extremely safe and efficient
method of reducing tooth structure’.
Effect of Air Abrasive Technique

In the air abrasive technique, aluminum oxide sprayed under
pressure is used as an abrasive for the cavity preparation and
surface treatment. The main drawback of this procedure is, it
does not allow the operators’ stereognostic ability to control

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the depth of cutting. However Ferrazzano et al, based on their
study in 60 mandibular third molar concluded that the
macroscopic size and shape of cavities is connected to
working distance, while working time is important to
determine the depth of preparation. Also the abrasive dust is a
potential health hazard to the operator and the patient.
Nowadays it is used only to clean the pit and fissures prior to
the application of sealants.
Effect of Ultrasonic Technique

The use of ultrasonic equipment for cutting cavities in teeth
has been advocated because it involves less heat, noise, and
vibration in contrast to rotary instruments. Essentially, the
technique consists in the conversion of electrical energy into
mechanical energy in the form of vibration of a tiny cutting
tip, approximately 29,000 vibrations per second with an
amplitude of about 0.0014 inch. Aluminum oxide abrasive in
a liquid carrier is washed across this tip, and the vibration of
the particles in turn results in a rapid reduction of tooth
substance.
The effects of this technique, as used in cavity preparation, on
the tooth and dental pulp have been evaluated by a number of
investigators whose results are in essential agreement. Zach
and Brown, Healey and his coworkers, and Lefkowitz among
others have found that there are no remarkable differences in
the reaction of the dental pulp to the preparation of cavities by
the steel bur, the diamond stone or the ultrasonic instrument.
This again emphasizes that only the dentinal injury itself is
important, not how this injury is produced.

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Mitchell and Jensen, studying the effect of steel bur and
ultrasonic cavity preparation on the human tooth, also
reported that no differences could be observed in the reaction
of the pulp to these two techniques. Mild hyperemia,
hemorrhage and a slight neutrophilic and lymphocytic
infiltration of the pulp tissue immediately below the cut
dentinal tubules were noted during the 6–12 day period
following cavity preparation by either means. After several
weeks the late reaction consisted in slight, irregular secondary
dentin deposition and the formation of a ‘calciotraumatic’
line, a hematoxyphilic line between the regular dentin and the
postoperative dentin apparently representing a disturbance in
dentin formation at the time of the operative procedure.
Lasers

Laser is an acronym for Light Amplification by Stimulated
Emission of Radiation. It is an electro-optical device which,
upon stimulation, can convert jumbles of light waves into an
intense, concentrated, uniform, narrow beam of
monochromatic light with an energy source of great intensity
and exceptional flexibility. The radiation may be continuous
or modulated, or the emission may occur in short pulses. This
high-intensity radiation can be focused on an extremely small
area, approximately 1 micron in diameter, because of the
small angle of divergence and coherency of the beam. Light
photons of characteristic wavelengths are produced,
amplified, and filtered to produce the laser beam. Carbon

dioxide and neodymium:yttrium-aluminum-garnet (Nd:YAG)
lasers are most commonly used. The main problem with laser
cutting of hard dental tissues is the generation of heat and
forbidden tactile control.
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Lasers are used in dental practice to coalesce pits and fissures
to eliminate retention sites for bacteria, to desensitize the
exposed root surfaces, to make the hard tissue surfaces rough
to promote bonding as an alternative to acid etching, to
vaporize the carious tissue, to vaporize the organic tissues in
the root canal in endodontic procedures, cavity preparation,
restoration removal, treatment of dentinal sensitivity, caries
prevention and bleaching.
Effects on Teeth

The effects of laser on teeth were first reported by Stern and
Sognnaes, who found that exposure of intact enamel, caused a
glass like fusion of the enamel, whereas dentin exposed to
laser exhibited a definitive charred crater. Chalky spots,
craters, or small holes in enamel may also be produced under
other conditions. Scanning electron microscopic analysis
showed the effects of laser on dentin vary from no effects to
disruption of the smeared layer to actual melting and
recrystallization of the dentin, depending on power level,
duration of exposure, and color of the dentin. Although it has
been shown that selective deep destruction of carious tooth
substance can be accomplished, the practicality of its use in
removing carious lesions is still questionable. Laser

irradiation alters the dentin structure and produces surface
layers that give the appearance of being more enamel-like.
The laser-modified surface may be more resistant to
demineralization; hence, many investigators are proposing
continued development of the laser for caries prevention.

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Open dentin surface exposed to laser results in melting and
closure of the orifices of the dentin and this property is used
to treat dentin hypersensitivity.
Bleaching of stained teeth has also been accomplished by
lasing.
Effects on Pulp

The pulps of teeth in animals subjected to laser radiation have
been described by Taylor and his associates as showing
severe pathologic changes, including hemorrhagic necrosis
with acute and chronic inflammatory cell infiltration. The
odontoblastic layer also underwent coagulation necrosis,
although the severity of the response varied with the amount
of radiation.

Effect of Heat
The reaction of the dental pulp to heat is an important clinical
problem because of the extraordinary amount of heat that may
be generated by the revolving cutting and grinding
instruments used in tooth preparation. Actually, temperatures
over 700° F have been recorded on the cutting surfaces of

stones and burs under abusive conditions.
Thermal change may be influenced by: (1) the size, shape,
and composition of the bur or stone, (2) the speed of the bur
or stone, (3) the amount and direction of pressure applied, (4)
the amount of moisture in the field of operation, (5) the length
of time that the bur or stone is in contact with the tooth, and

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(6) the type of tissue being cut, enamel or dentin. Of further
significance is the heat generated during the setting of various
restorative materials, particularly the direct resins. In in vitro
experiments, Wolcott and his associates showed that the
temperature at the dentin-resin junction may reach 212° F,
and they recorded a temperature of 133° F in the pulp
chamber.
Smear layer
Smear layer is an amorphous micro layer deposited on the
prepared tooth surfaces and consists of inorganic enamel and
dentin debris, organic pulp materials, dentinal fluid, bacteria,
and saliva. The thickness of smear layer may vary from 1μm
to 5μm. Its morphology, composition, and biological behavior
still remain controversial. Smear layer has the protective
effect by forming a physical barrier, which reduces the
permeability of dentin and prevents the exit of dentinal fluid.
On the other hand it also acts as a barrier against the
microoraganisms, which already penetrated before the
treatment, may flow back and express their pathogenicity.
Many investigators advocate the removal of smear layer as it

interferes with the bonding between the restorative material
and the tooth structure in restorative treatment and affects the
action of irrigants and disinfectants and penetration and
adhesion of sealers in endodontic treatment.

Effect of Restorative Materials
The dentist has at his/her disposal a great many materials
prepared commercially to restore the original contour of the
tooth attacked by dental caries and other lesions of the tooth

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including trauma. The dentist must be familiar with the
advantages and disadvantages of each material from the point
of view of its physical and chemical properties and its ability
to fulfil the purpose for which it is intended. In addition, he
must be acquainted with the biologic effects of the restorative
materials on the tooth, especially on the dental pulp.
A great many experimental studies have been carried out to
investigate the effects of the different restorative materials on
the dental pulp, and today such testing is routine before new
restorative materials are released by ethical manufacturers for
use by dentists. It should be obvious that a restorative
material applied to a prepared tooth is in contact with more
than just a mass of inert calcified material. The dentinal
tubules, containing odontoblastic processes which have been
freshly cut, form a series of passage ways leading directly to
the pulp through which a fluid or soluble material may reach
the pulp tissue. If this material is irritating, it may lead to

serious injury. For this reason a comparison of the effects of
the various common restorative materials is important.
Remaining dentin thickness
It is generally agreed that if the cavity depth is shallow, with
2.0 mm or more of primary dentin remaining between the
floor of the cavity preparation and the dental pulp, dentin
probably provides its own insulation against traumatic,
thermal or restorative material irritation. However, if the
remaining thickness of primary dentin is less than 2.0 mm, it
is necessary that a cement base of one type or another be
utilized.
Zinc Oxide and Eugenol

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It is used routinely as a temporary filling material or root
canal sealer. Eugenol of this cement fixes cells, depresses the
cell respiration, and reduces the neural transmission in vitro.
There is almost universal agreement that zinc oxide and
eugenol is the least injurious of all filling materials to the
dental pulp. Not only is there no irritation produced by this
substance, but actually it exerts a palliative and sedative effect
on the mildly damaged pulp, since it inhibits synthesis of
prostaglandins and leukotrienes. It seems to be such a bland
substance that it may lack even the necessary irritating
properties requisite to the stimulation of secondary dentin
formation. In view of these findings, zinc oxide and eugenol
is the material of choice for use over injured pulps or as a
base in deep cavity preparations.

Zinc Phosphate (Oxyphosphate) Cement

This particular cement is widely used in dentistry both as a
protective base in deep cavities before the insertion of the
restoration and also in cementing cast inlays, crowns, and
other similar restorations. The majority of investigators have
reported significant deleterious effects on the pulp when the
material is placed in cavities, the actual injurious agent
supposedly being the phosphoric acid.
Gurley and Van Huysen prepared cavities in teeth of young
dogs and filled them with zinc phosphate cement. After
approximately 1½ months they found hyperemia and
inflammatory cell infiltration of the pulp with disarrangement
of the odontoblastic layer. Secondary dentin had formed
under the shallower cavities. The more severe pulpal
reactions occurred under the deeper cavities.

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Studies on human teeth, such as those by Manley, by Shroff,
and by Kramer and McLean, show that hyperemia or
hemorrhage with inflammatory cell infiltration of the pulp
accompanied by reduction in the size and number of the
odontoblasts occurs after placement of this cement in
prepared cavities.
The studies generally indicate that zinc oxyphosphate cement
is an irritant when placed in the base of a deep cavity,
particularly in bulk, although the human pulp may be able to
localize this reaction in most instances. When this cement is

used in shallow cavities, it is relatively innocuous and
reportedly serves a useful function in the stimulation of
secondary dentin formation.
Polycarboxylate or polyacrylate cements have properties
comparable to those of the phosphate cements, but have a low
degree of pulpal irritation similar to that of the zinc
oxide-eugenol cements.
Silver Amalgam
Silver amalgam is used as a filling material in dentistry. It is
an innocuous material, particularly in shallow cavities.
Beneath deep cavities filled with amalgam, Manley found a
decrease in the number of odontoblasts, as well as mild
inflammatory cell infiltration of the pulp. The complication of
thermal shock transmitted by deep amalgam restorations is
difficult to evaluate, but is a source of potential damage.
In contrast, Swerdlow and Stanley studied the pulpal
responses in 73 intact human teeth with cavities prepared at

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speed of 20,000–300,000 rpm and filled with either amalgam
or zinc oxide and eugenol. They reported that the amalgam
increased the intensity of mild pulpal response to cavity
preparation and that this appeared to be due, in part at least, to
the mechanical aspects of amalgam condensation. Brännström
studied the effect of amalgam restorations on pulp tissue, and
concluded that any damage to the pulp was due to leakage
around the restoration, not to the filling material itself. Dark
colored metallic components of the silver alloy turn the dentin

dark gray and tooth may appear discolored.
Amalgam restorations when in contact with gingiva cause
inflammation because of corrosion products and dental
plaque.
Relationship between oral lichenoid reactions and silver
amalgam fillings is a matter of controversy. A number of
studies have been published with respect to amalgam filling
and lichenoid reactions. A Dunsche and coworkers suggest
the removal of amalgam fillings in all patients with
symptomatic oral lichenoid reactions associated with
amalgam fillings if no cutaneous lichen planus is present.
Glass-ionomer
Glass-ionomer cement is considered as biocompatible and is
widely used as filling and lining material and as a luting
agent. It consists of fluoroaluminosilicate glass powder and
polycarboxylic acid. Glass-ionomers are water-based, and the
set materials are composed of an inorganic-organic complex
with high molecular weight. In contrast to other cements,

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glass-ionomer has the advantages of chemically bonding to
mineralized tissues and release of fluorides.
Glass-ionomer cement bonds to the dentin by chemical and
mechanical means. The chemical bonding is based on the
exchange of ions between carboxylic groups of the substrate
and calcium ions derived from partially dissolved apatite
crystallites. The mechanical interlocking is based on the
demineralization of exposed dentin by polycarboxylic acid

treatment. Collagen fibers can be exposed and an intermediate
layer can be formed between glass-ionomer material and
undemineralized dentin.
Biocompatibility of glass-ionomer cement is due to the weak
nature of polyacrylic acid. Histologically there is minimal or
absence of inflammation in pulp after a month. Pulpal pain
may be present for a short period after the filling of cervical
cavities, and is due to the increased dentin permeability after
acid etching.
Self-polymerizing Acrylic Resin

Self-curing resins were extensively used as restorative
materials, particularly in anterior teeth. There is evidence to
indicate, however, that these resins may cause serious damage
to the dental pulp. Still, not all investigations are in complete
agreement.
Conventional Composite Resins

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These are restorative materials developed chiefly because
methyl methacrylate or unfilled acrylic resins have restrictive
characteristics such as low hardness and strength, a high
coefficient of thermal expansion and a lack of adhesion to
tooth structure. The resin matrix is a compromise between
epoxy and methacrylate resins. This resin is combined with a
filler of dispersed particles of varying types in relatively high
concentration. While most
conventional composite resins are chemically activated, some

are now marketed whose cure is based on light activation.
The biologic properties of the composite resins show the
same irritational characteristics as the unfilled acrylic resins.
For this reason, the same measures should be taken to protect
the pulp from possible injury, especially when the cavity
preparation is deep. A calcium hydroxide base is preferable to
a zinc oxide and eugenol base because of the possible
interaction of eugenol and resin.
Microfilled Composite Resins

These are a newer group of resins which contain the same
resin matrix as the conventional composite resins but differ in
that the size of the filler is much smaller than in the
conventional resin. The biologic properties of the microfilled
resins, including their irritational effects on the pulp, are
comparable to those of the conventional composite resins.
Thus, some pulpal protection is necessary under deep cavities.
Acid etching

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Resin based restorative materials are mechanically bonded to
the tooth structure by creating micropores, a procedure known
as acid etching. This process demineralizes hard tissues and
exposes the organic matrix. Phosphoric acid is the most
commonly used etchant in clinical practice.
In contrast to the scanty organic matrix of enamel which is
lost during the demineralization and subsequent washing, the
components of dentin are demineralized selectively.

Peritubular dentin demineralizes quicker than does the
intertubular matrix. Demineralization of dentin widens the
tubules, makes them funnel shaped towards the surface. It
exposes the collagen in the wall of the tubules and also
uncovers the openings of a large number of lateral branches.
The exposed collagen forms an interwoven mesh of fibers in
which the resin infiltrates. This collagen mesh infiltrated by
resin is referred to as the hybrid layer. After polymerization,
the resin-impregnated collagen, together with the resin in the
dentinal tubules and their branches, constitutes the adhesion
between the dentin and the resin. If the hybrid layer becomes
too dry, the collagen mesh will collapse and penetration of
resin will be impaired. Adequate moisture content of the
surface is a must to prevent collapse of the collagen mesh for
an optimal bonding between the resin and the hybrid layer.
The many experimental studies cited would indicate
superficially that the majority of restorative materials used in
dentistry today are dangerous because of the serious effects
on the dental pulp which they often induce. It is true that
many of these materials are potentially injurious.
Nevertheless, literally millions of restorations with these
substances are placed each year, and clinical experience has
shown that, unless actual pulp exposure has occurred, the
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death rate of dental pulps directly attributable to the
restorative material is extremely low. Even the occurrence of
clinical symptoms of pulp injury is uncommon. Although this
seems contradictory to experimental evidence, it should be

appreciated that most cavities prepared by the dentist in
which these materials are inserted are to repair a destructive
carious lesion. The presence of this carious lesion, in contrast
to the experimental cavities prepared in sound human and
animal teeth, has usually induced the deposition of secondary
dentin and has caused a certain amount of dentinal sclerosis,
and these reactions offer considerable protection to the pulp.
It is on this basis that the dentist is justified in continuing to
use these filling materials. There is a need, however, for
continued study of this general problem.
Effect of Cement Bases, Cavity Liners, Varnishes and
Primers
A variety of materials commonly used in dental practice are
inserted in a cavity preparation between the tooth and the
restoration for the following purposes:
•
To serve as a bacteriostatic agent.
•
To provide thermal insulation, particularly under metallic
restorations.
•
To provide electrical insulation under metallic restorations.
•
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To prevent discoloration of tooth structure adjacent to certain
types of restorative materials.
•
To prevent the penetration of deleterious constituents of

restorative materials into the dentin and pulp.
•
To improve the marginal seal of certain restorative materials
by preventing microleakage and the ingress of saliva and
debris along the tooth-restoration interface.
These materials are generally classified as cement bases,
cavity liners, cavity varnishes and cavity primers, and they
are important because of their possible effects on the dental
pulp.
Cement Bases

A cement base is a layer of cement commonly used beneath
the dental restoration either to encourage recovery of the
injured pulp or to protect the pulp against the injuries.
Intermediary base materials that are commonly used under
permanent restorations include zinc phosphate cement, zinc
oxide-eugenol cement, and calcium hydroxide cement.
Ideally, a cement base should be biologically compatible with
the dental pulp and such is the case with zinc oxide-eugenol
and calcium hydroxide. However, zinc phosphate cement,
when placed against dentin, acts as an irritant to the dental
pulp because of the acid content which varies between pH 3.5
and 6.6, as discussed previously.

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Cavity Liners

Cavity liners are aqueous or volatile organic liquid

suspensions or dispersions of zinc oxide or calcium hydroxide
that can be applied in a relatively thin film to the surface of a
cavity. They may also be solutions of resins in an organic
solvent to which has been added calcium hydroxide or zinc
oxide, or aqueous suspensions of calcium hydroxide in
methylcellulose. The cavity liner provides the beneficial
effects of zinc oxide and calcium hydroxide as thin films in
shallow cavities and, in addition, neutralizes the free acid of
zinc phosphate and silicate cements. The cavity liners
themselves have no effect on dental pulp and, in fact, actually
form a chemical barrier to provide reliable protection for the
pulp under certain deep restorations.
Stanley has compared the protective effect of reparative
dentin with cavity liners and bases, and generally concluded
that: (1) pulpal tissue beneath preoperatively formed
reparative dentin is safe from most subsequent procedures; (2)
cavity liners and/or bases, should be employed since the
completeness of the reparative dentin barrier cannot be
ascertained; (3) the unrestored tooth being utilized as an
abutment lacks reparative dentin and is more subject to the
damaging effects of chemical agents because of patent
dentinal tubules; (4) although 2 mm of primary dentin
between the floor of the cavity preparation and the dental pulp
is usually a sufficient protective barrier, the condensation of
amalgam or gold foil, as well as the chemical irritation of
cements and self-curing resins, may render this thickness of
protection insufficient; (5) age changes in the tooth, with the
production of reparative dentin in the involved area, are of no

2105

recognizable benefit regarding pulp protection; (6)
high-speed, water-cooled cutting techniques produce an
average incidence of reparative dentin formation of under
20%; even less reparative dentin formation is produced if
more than 1 mm of primary dentin remains beneath the cavity
preparation; (7) if reparative dentin does not form within the
first 50 days following a restorative procedure, then there will
be none; (8) nearly 20 postoperative days are required for new
odontoblasts to differentiate and produce reparative dentin,
and it has been shown that an average of 100 productive days
of matrix formation is required to produce a reparative dentin
barrier of 0.15 mm; (9) final cementation of restorations need
not be delayed in allowing time for reparative dentin to form,
since the use of cavity-lining materials is a reasonable
substitute; and (10) cavity varnish and calcium hydroxide
lining materials appear capable of protecting pulp if used
appropriately.
Cavity Varnishes

Cavity varnishes are solutions of one or more resins from
natural gums, synthetic resins, and rosin in organic solvents.
It is generally agreed that varnishes may be of aid in reducing
postoperative sensitivity, but their film thickness is
insufficient to provide thermal insulation. This film also acts
as a semipermeable membrane so that certain types of ions
penetrate it, while others do not. It has been found also that
varnishes are effective in reducing the microleakage of fluids
around the margins of restorations.

While cavity varnishes themselves appear to have no
significant effect upon a dental pulp, neither do they have a

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