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:

1

Operative dentistry

department

4TH

YEAR LECTURES

LECTURE 1

WED 18-3-2020

2

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

4

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.