Operative Dentistry
department
4TH YEAR Lecture1 ppt
WED 18-3-2020
- Protection for both dentin and pulp
- Esthetic
- Histologically: V. Imp during
cavity preparation for selection of
the most efficient cutting instrument
to provide the correct wall
directions and for giving the
gingiva cavo-surface angles their
correct angulations.
- Support from the viscoelastic dentin
- No regenerative power
- Dentinal tubules are supported by
a calcified network of collagen and
contain odontoplasts.
- Secondary dentin is the dentin formed after full
eruption of the tooth while reparative dentin is formed
due to irritation as a protective barrier to the pulp.
- Dentin is sensitive to wear, caries,
operative procedures and restorations
These insults are transmitted to the pulp
to respond.
- Provide good thermal insulation.
Dentin and pulp are closely related
structure embryologically, anatomically
and physiologically.
Dento-pulpal organ
Embryologically
Both ectomesenchymal
dental papilla.
Anatomically
Odontoblasts "Tomes
fibers" constitute
about one third
of the dentin
thickness.
Physiologically
- Dentin protect pulp
- pulp provides vitality to dentin.
- Bacteria and toxins from
restorative material can easily
pass through the dentinal tubules
by diffusion to reach the pulp
tissues.
- Dentin is permeable → fluid
interchange between enamel,
dentin and pulp
Trauma, Thermogenesis,
Speed, Pressure,
Desiccation, Vibration &
Pin drilling and insertion
1. Trauma:
During Cavity Prep.
Sharp hand
cutting instruments
Most biologically
Rotary cutting
instruments → if use
with proper cooling
If used in high speeds and
excessive pressure.
Undue over-cutting exposes
more dentinal tubules
Histological changes as hyperemia
Irritation
To protect the pulp against traumatic injury, we
should avoid:
(1) Cutting across the recessional lines of
the pulp → irritation or exposure
(2) Over cutting of enamel to expose only
minimum area of dentin.
(3) Over cutting of dentin and unnecessary
deepening of cavity to maintain proper
remaining dentin thickness
(4) Unnecessary application of pressure in
scooping out carious dentin.
2.Thermogenesis
1- Friction.
2- Increased pressure.
3- Increased speed.
4- Tissues to be cut.
5- Increased area.
6-Bur size and material.
Thermogenesis or heat generation is a highly hazardous
and damaging factor that affects the pulp vitality through
the following:-
3. Speed:
Sufficient higher speed
technique with sufficient
cooling induce the least pulpal
response.
This may be due to the more
force applied and consequently
more heat generation.
4. Pressure:
There is a Reverse relationship
between the magnitude of
pressure and the rotational speed
Pressure causes aspiration of the
odontoblastic nuclei into the
dentinal tubules.
Pressure may drive some
microorganisms from infected
dentin into the pulp leading to
pulpal inflammation.
5. Desiccation
Vital dentin is in a state
of hydration
Desiccation of dentin occur due to:
a. Overheating of dentin during
cutting.
b. Using chemicals as alcohol to
sterile the cavity.
c. Using air as a coolant or in
performing final toilet of the
cavity.
6. Vibration:
1- Patient discomfort.
2- Cracks in enamel.
3- Pulp damage.
4- Rebound response.
(it is a limited area of necrosis
at an area remote from the cut
dentinal tubules.
Vibration occurs due to eccentricity or run-
out of rotary instruments causing:
7. Pin drilling
and insertion
1. Oversized pin.
2. Improper direction of
pin insertion.
3. Luting cement.
4. Dull pin.
Factors leading to pulpal affection:
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Operative dentistry
department
4TH
YEAR LECTURES
LECTURE 1
WED 18-3-2020
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BIOLOGICAL INFLUENCES OF
RESTORATIVE MATERIALS AND
PROCEDURES ON VITAL TOOTH TISSUES
Studying the biological influences of restorative materials and procedures on the
vital tooth tissue constitutes a great and important part in restorative dentistry. The
biological bases of restorative dentistry aim to maintain the health and vitality of
the tooth structure to perform its formative, nutritive, sensory and defensive
function. As well as they aim to keep the integrity of the investing tooth structures
i.e. the gingival and periodontium.
The operator should have a thorough knowledge about the tissues which he is
going to cut. The dental tissues are vital structures and need special consideration
during cutting to get finally a cavity design which fulfills both the biological and
mechanical concepts.
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Tooth structure
I) Enamel:-
1- Enamel is the hardest tooth tissue. It provides protection for both dentin and
pulp.
2- It maintains the esthetic appearance of the tooth.
3- Enamel is formed of mushroom shaped enamel rods cemented together by the
cementing substance. These rods begin at right angle to the dentin surface at the
DEJ and ends nearly at right angle to the surface.
This histological point is very important during cavity preparation for selection of
the most efficient cutting instrument, the most rapid way of cutting, for providing
the correct wall directions and for the correct angulations of the gingival cavo-
surface angles.
4- Enamel takes its support from the viscoelastic dentin. If dentin is removed by
caries or improper cutting, the enamel will be undermined and will be chipped and
broken during biting. So, it is mandatory to remove all unsupported and friable
enamel rods to get strong cavity wall.
5- Enamel has no regenerative power, so when it is fractured or penetrated by
caries it should be mechanically replaced according to the principles of cavity
preparation.
II) Dentin: 1- Dentin is formed of dentinal tubules that are supported by a calcified network of
collagen. The tubules contain the living extensions of the odontoblasts. Whereas,
the cell body of the odontoblasts are in the periphery of the pulp. Formation of
dentin is continuous throughout life.
2- Secondary dentin is the dentin formed after full eruption of the tooth while
reparative dentin is also secondary dentin but it is formed due to irritation as a
protective barrier to the pulp.
3- Dentin is sensitive to environmental changes such as wear, caries, operative
procedures and restorations. Their insults are transmitted to the pulp to respond.
4- Dentin and pulp are closely related structure embryologically, anatomically and
physiologically. Hence, the name of dento-pulpal organ is a more preferable
biological term.
- Embryologically: both dentin and pulp are derived from ectomesenchymal dental
papilla.
- Anatomically: it is found that the protoplasmic extensions of odontoblasts
"Tomes fibers" constitute about one third of the dentin thickness.
- Physiologically: dentin is a protective tissue for the pulp; the pulp provides
vitality to the dentin. Dentin is a permeable structure, so there is constant fluid
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interchange between enamel, dentin and pulp. Bacteria and toxins from restorative
material can easily pass through the dentinal tubules by diffusion to reach the pulp
tissues.
5- Dentin, at the same time is an excellent thermal insulator. It has a thermal
conductivity less than any restorative material including the cements. It can
provide good thermal insulation for the pulp for thermal changes ranging between
85° and 130 °F, and hence care is essential to control thermogenesis when cutting
on dentin.
I.Influence of restorative procedures on dento-pulpal organ:
1. Trauma:
It has been emphasized that a degree of pulp irritation is unavoidable during cavity
preparation.
- Sharp hand cutting instruments are the most biologically accepted cutting
instruments because the energy applied during their use is completely dissipated in
the actual cutting.
- The rotary cutting instruments are also considered biologically accepted if use
with proper cooling.
- In deep cavities, rotary instruments may cause trauma to the odontoblasts leading
to their aspiration, if they are used in high speeds and excessive pressure.
- Cutting on fresh dentin causes severance of viable odontoblastic processes it is
well known that in every 1 mm2 of dentin, there are about 30.000 to 45.000
dentinal tubules. So, undue over-cutting exposes more dentinal tubules. The
opened dentinal tubules are capable of transmitting irritants from the oral cavity or
restoratives to pulp tissues.
- It may cause slight histological changes as hyperemia.
- In some cases aspiration of odontoblastic nuclei into the dentinal tubules are
reported. This was explained as cutting of the odontoblastic processes in the
dentinal tubule causes changes in the injured cytoplasm, which result in leakage of
fluids from dentinal tubules. This outward flow causes displacement of the
odontoblastic nuclei into the dentinal tubules through capillary action.
To protect the pulp against traumatic injury the operator must avoid the
following: (1) Cutting across the recessional lines of the pulp. These lines represent the lines
along which the pulp has receded during the growth of dentin. They are also lines
in which usually long pulpal extensions are found. Crossing these lines cause pulp
exposure with subsequent pulp irritation.
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(2) Over cutting of enamel to expose only minimum area of dentin.
(3) Over cutting of dentin and unnecessary deepening of cavity to maintain proper
remaining dentin thickness.
(4) Unnecessary application of pressure in scooping out carious dentin.
2. Thermogenesis:
Thermogenesis or heat generation is a highly hazardous and damaging factor that
affects the pulp vitality.
Thermogenesis can occur due to:
a) The friction between the cutting tool and the tooth.
b) Increased amount of pressure during cutting by rotary instruments.
c) Increased rotational speed.
d) Type of the tissue to be cut. Enamel needs more energy to be cut so; more heat
is generated during enamel cutting than dentin.
e) Increased area of tool to tooth contact.
f) Bur size and material.
3. Speed: It is reported that cutting at any rotational speed under dry condition cause variable
pulpal changes, due to heat generation. Yet, it is well known that sufficient higher
speed technique with sufficient cooling induce the least pulpal response. At the
same time, speeds from 3000 to 30.000 rpm even with coolant are more traumatic
when compared with the high-speed techniques at the same remaining dentin
thickness. This may be referred to the more force applied to induce cutting and
consequently more heat generation. So, for drilling a pinhole the cutting speed
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must be below 3000 rpm. Within each speed range, some factors are concerned
which may affect the pulp response.
These factors are the operating load or pressure, revolutions per minute of the
cutting tool, diameter of the bur, temperature rise on the tooth surface and type of
coolant used.
4. Pressure: There is a reverse relationship between the magnitude of pressure and the
rotational speed. So at higher speed ranges, less pressure is required. This may
explain the increased rate of pulp damage with low technique equipment.
Pressure of the instrument on exposed dentin causes aspiration of the odontoblastic
nuclei into the dentinal tubules especially at decreased effective cavity depths.
Pressure may drive some microorganisms from the infected cavity flow into the
pulp leading to pulp inflammation.
5. Desiccation: Vital dentin is in a state of hydration. Desiccation or dryness of dentin may occur
due to:
a. Overheating of dentin during cutting procedures.
b. Using chemicals as alcohol to sterile the cavity.
c. Using air as a coolant or in performing final toilet of the cavity.
Therefore efficient water-air spray should be used as coolant to avoid heat
generation and desiccation.
6. Vibration: Vibration, occur due to eccentricity or run-out of rotary instruments cause
annoyance and discomfort to the patient. It may cause cracks in enamel.
Sometimes, it shows different degrees of pulp damage. Vibrations due to increased
speeds of rotation lead to a phenomenon called rebound response. Rebound
response appears microscopically as a limited area of necrosis at an area remote
from the cut dentinal tubules. Edema, fibrosis of the pulp tissues, proper changes in
the group substance and reduction in the predentin layer are found all around the
pulp chamber.
7. Pin drilling and insertion: a. Oversized pin
b. Improper direction of pin insertion
c. Luting cement
d. Dull pin.