Microscopes 1 / orthodontic courses by Indian dental academy

INTRODUCTION

Endodontics has progressed a long way from the old toothworm theory prevalent in 16th theory

which propagated that worms burrowing in the decayed tooth was the reason for dental pain.

Treatment of diseased pulp using leech and red hot wire were the modalities followed those days.

Introduction of anesthesia has radically changed the management of pain in the medical field.

Development of antiseptics rubber dam, gutta percha, radiographs and rotary systems were

other landmarks in the progression of endodontics. Advances in the art and science of endodontics

have facilitated better understanding of disease processes and have led to development of treatment

modalities aimed at restoring health to the pulp and periradicular tissues. Technological

discoveries in instruments and materials have made it possible to achieve treatment objectives that

once were considered unattainable.

The state of art includes surgical operating microscope, which functions as the third eye for

the endodontist. The introduction of microscopes into endodontics in the early nineties brought on

a renaissance in endodontics that led to new and exciting discoveries and the blossoming of new

ideas and techniques. When the surgical operating microscope was introduced in endodontics in

USA, it was a historical landmark for advances in the filed of dentistry. The microscope proved to

be an invaluable instrument, allowing endodontists to render treatment for problems which were

previously thought to be impossible to treat.

“Modern man is seldom amazed. But there are still fascinating moments in dentistry. For

me, looking through a surgical microscope is among these. The root canal, once ruled by darkness,

is suddenly illuminated and reflects in bright light, opening its anatomical wonder of side canals,

branches, notches, furrows, colored shadows and secret passages. In many cases, the ominous

Foramen physiologicum becomes visible and can almost be touched, allowing the periapex to be

anticipated.” - Prof. Dr. Michael A. Baumann

HISTORY:

Although the first accurate lenses were not made until about the year 1300, credit for the first

microscope is usually given to Hans and Zacharias Jansen, a father and son who operated a Dutch

lens-grinding business, around 1595 (11). They produced both simple (single lens) and compound

(two lenses) microscopes.

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Using a compound microscope, in 1665, Robert Hooke coined the word cell while describing

features of plant tissue (11). Another pioneer of microscopy Anton van Leeuwenhoek produced

single lenses powerful enough to enable him to observe bacteria 2–3 mm in diameter in 1674.

Little was done to improve the microscope until the middle of the 19th century when Carl

Zeiss, Ernst Abbe, and Otto Schott devoted significant time to develop the microscope, as we

know it today. While Zeiss concentrated on the manufacturing process, Abbe and Schoot devoted

their time to the theoretical study of optical principles and conducting research on glass (12). Their

product was the genesis of the surgical operating microscope (SOM) that ultimately found its way

into the practice of medicine.

Evolution of magnification and illumination in medicine:

In 1921, Dr Carl Nylen (13) of Germany reported the use of a monocular microscope for

operations to correct chronic otitis of the ear. The unit had two magnifications of x 10 and

x 15 and a 10mm diameter view of the field. This microscope had no illumination.

In 1922, the Zeiss Company (Germany) working with Dr Gunnar Holmgren of Sweden,

introduced a binocular microscope for treating otosclerosis of the middle ear. This unit had

magnifications of x 8 – x 25 with field-of-view diameters of 6–12mm.

1953 - Carl Zeiss Company of West Germany marketed the first commercial binocular

operating microscope marked the beginning of microsurgery to literally all the surgical

disciplines. (Opton ear microscope.)

The Opton had a 5-step magnification changer, which could produce magnifications

in five steps from x 1.2 to x 40 and field-of-view diameters from 4.8 to 154 mm. Working

distances were a remarkable 200–400 mm. The Opton had built-in coaxial illumination,

which added immensely to visual acuity

Evolution of magnification and illumination in dentistry:

1977 - Dr Robert Baumann, an otolaryngologist And practicing

dentist, described the use of the otologic microscope in dentistry.

1978 – Apotheker and Jako pooled their efforts to produce a Dental

operating Microscope (DOM) first commercially available DOM in

1981, Dentiscope, Chayes Virginia Inc. The Dentiscope had a single

magnification of 8 and dual fiberoptic lights, which were directed

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toward the surgical field. The unit could be mounted on a mobile stand or could be

permanently mounted to a wall.

1982, Sep 25th – offered the first course in the clinical hands on use of the Dentiscope at

harvard dental School, Boston. - disheartening response

1986 - Chayes Virginia Inc. stopped selling the Dentiscope

1993 , March – the first symposium on microscopic endodontic surgery was held at

university of Pennsylvania School of Dental Medicine

- heralded the beginning of serious attention to the DOM

1990s – numerous commercially available microscopes were available

By 1995 – There was an obvious increase in DOM use by endodontists.

1996 January the proposal that ‘microscopy training be included in the new Accreditation

Standards for Advanced Specialty Education Programs in Endodontics’ was accepted.

One of the most important developments in conventional and surgical endodontics has been the

introduction of the surgical operating microscope.

The new standard of care in Endodontics requires:

1. Magnification

2. Illumination

3. Armamentarium

Loupes:

Historically, dental loupes have been the most common form of magnification used in

apical surgery. Loupes are essentially two monocular microscopes with lenses mounted side by

side and angled inward (convergent optics) to focus on an object. The disadvantage of this

arrangement is that the eyes must converge to view an image. This convergence over time will

create eyestrain and fatigue and, as such, loupes were never intended for lengthy procedures. Most

dental loupes used today are compound in design and contain multiple lenses with intervening air

spaces. This is a significant improvement over simple magnification eyeglasses but falls short of

the more expensive prism loupe design. Prism loupes are the most optically advanced type of

loupe magnification available today. They are actually low-power telescopes that use refractive

prisms. Prism loupes produce better magnification, larger fields of view, wider depths of field, and

longer working distances than other types of loupes. Only the SOM provides better magnification

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and optical characteristics than prism loupes. Initially, loupes seemed adequate, and emphasis was

placed on developing better loupes. Clinicians who have used surgical telescopes and surgical

headlamps have benefited from the expanded use of magnification and illumination.

Magnification range of 2X to 6X

Illumination – Fibreoptic headlamp system

Visual acuity is heavily influenced by illumination. An

improvement to using dental loupes is obtained when a fiberoptic

headlamp system is added to the visual armamentarium. Surgical

headlamps can increase light levels as much as four times that of

traditional dental operatory lights. Another advantage of the

surgical headlamp is that since the fiberoptic light is mounted in

the center of the forehead, the light path is always in the center of the visual field

Disadvantage:

The disadvantage of loupes is that x 3.5– x 4.5 is the

maximum practical magnification limit. Moderate movements

of the head resulted in total dislocation and loss of the visual

field, especially in higher magnifications. Loupes with higher

magnification are available but they are quite heavy and if

worn for a long period of time can produce significant head,

neck, and back strain. In addition, as magnification is

increased, both the field of view and depth of field decrease,

which limits visual opportunity.

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Microscopes have the capability to go to magnifications of upto 40 X and beyond.

The main advantage of the surgical microscope compared to all loupe systems is

that it is aided by coaxial illumination

Limitations in depth of field and illumination, however, make such magnifications impractical.

Magnifications in the range of 2.5 X to 30 X are recommended.

The lower magnifications (2.5 X to 8 x) are used for orientation to the surgical

field and allow a wide field of view.

Midrange magnifications (10X to 16 x) are used for operating.

Higher range magnifications (20X to 30 x) are used for observing fine detail.

Many clinicians believed the operating microscope would make highly successful operations

complicated and drawn out. Eventually, they recognized advantages such as wider fields, variable

magnification, better depth of focus, and coaxial illumination when using the microscope instead

of loupes.

In conventional endodontics the operating microscope is an invaluable tool that aids the

endodontist. The ability to visualize the root canal system in fine detail provides the opportunity to

investigate that system more thoroughly and clean and shape it more efficiently.

It also allows an assessment to be made of the dryness of the canal before obturation and of the

distribution of sealer on the wall of the root canal during obturation.

The microscope enhances the clinicians capability to diagnose fracture line in the root and crown,

locate small canal orifices in the pulpal floor, remove pulp stones in the canal orifice facilitated by

accurate placement of ultrasonic tip around it and thus preventing unnecessary removal of

radicular dentin

It also makes the diagnosis and management of perforation and patient education easy.

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The introduction of dental microscope in conventional and surgical endodontics offers a number of

advantages for improved patient care.

Areas where the surgical microscope can have great impact and consequence in clinical practice

include,

(1) Visualization the surgical field,

(2) Evaluation of surgical technique,

(3) Use of fewer radiographs,

(4) Patient education through video,

(5) Reports to referring dentists,

(6) Reports to insurance companies,

(7) Documentation for dental legal purposes,

(8) Video libraries for teaching programs,

(9) Marketing the dental practice, and

(10) Less occupational stress

The four areas to be discussed in a Surgical operating microscope are:

1. Magnification

2. Illumination

3. Documentation

4. Accessories

MAGNIFICATION:

Determined by:

1. Power of the eyepiece,

2. The focal length of the binoculars,

3. The magnification changer factor,

4. The focal length of the objective lens.

THE ANATOMY OF THE SURGICAL OPERATING MICROSCOPE

Eyepiece:

Available in powers of 6.3 X, 10 X, 12.5 X, 16 X and 20 X.

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Have adjustable diopter settings.

Diopter settings range from - 5 to + 5 and are used to adjust for

accommodation, which is the ability to focus the lens of the eyes. It

also adjust for refractive error, which is the degree to which a

person needs to wear corrective eyeglasses.

Binoculars:

FUNCTION:

To project an intermediate image into the focal plane of the eyepiece.

Hold the eyepieces.

the interpupillary distance is set by adjusting the distance between the two binocular tubes

Once the diopter setting and interpupillary distance adjustments are made, they need not be

changed unless the microscope is used by an other surgeon with different optical requirements.

Often come in different focal lengths.

Longer the focal length, the greater the magnification and the narrower the field of view.

available with straight, inclined, or inclinable tubes

Straight tube binoculars are orientated so that the tubes are parallel to the head of the

microscope. It allows the operator to look through the microscope directly at the surgical field.

This system is used by ear, nose, and throat (ENT) surgeons. The dental chair is placed below the

operator for maxillary surgery and slightly above the operator for mandibular surgery. This allows

the clinician to look down the axial plane of the root in maxillary teeth and up the axial plane of

the root in mandibular teeth. Straight tube binoculars gain even more versatility when a 135-degree

inclined coupler or variable inclined coupler is placed between the mounting arm and the

microscope. This coupler provides additional axis of rotation and aligns the microscope so that

straight tube binoculars provide direct vision whether the patient is sitting up or lying down.

Inclined binoculars are orientated so that the tubes are offset at 45

degrees to the head of the microscope. Inclined binocular tubes are used

for maxillary surgery, but the operator would have to use indirect vision

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through a mirror or position the patient's head sharply to the side while performing mandibular

surgery.

Inclinable tubes are adjustable between the straight tube and

slightly beyond the inclined tube positions up to and sometimes

beyond 180 degrees. Inclinable tube binoculars allow the surgeon to

look directly at the maxillary arches and mandibular arches and have

the advantage of the other binoculars, thus providing the operator with

additional postural comfort and flexibility during long procedures.

Most useful for endodontic surgery.

The only disadvantage of inclinable tube binoculars is that they are difficult to engineer and as

such can be quite costly.

Magnification changers:

Available in 3 or 5 step manual changers or Power zoom changers

Located within the head of the microscope

Manual step changers consist of lenses that are mounted on a turret. The

turret is connected to a dial that is located on the side of the microscope

housing. The dial positions one lens in front of the other within the changer

to produce a fixed magnification factor or value. Rotating the dial reverses

the lens positions and produces a second magnification factor. A conventional three-step changer

has one set of lenses and a blank space on the turret without a lens. When the power of the

eyepiece, the focal length of the binoculars, and the focal length of the objective lens with the

magnification changer lenses are factored in, three fixed powers of magnification are obtained: two

from each lens pair combination and one from the blank space. The blank space produces

magnification by factoring only the eyepiece, the focal length of the binoculars, and the focal

length of the objective lens.

A five-stepmanual changer has a second set of lenses mounted on the turret and produces five

fixed powers of magnification. A power zoom changer is merely a series of lenses that move back

and forth on a focusing ring to give a wide range of magnification factors.' Power zoom changers

avoid the momentary visual disruption or jump that occurs with three- or five-step manual

changers as the clinician rotates the turret and progresses up or down in magnification.

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Magnification changer functions in power zoom microscopes are controlled by either a foot control

or a manual override control knob located on the head of the microscope.

Objective lens :

The focal length of the objective lens determines the operating distance between the lens and the

surgical field. With the objective lens removed, the microscope focuses at infinity and performs as

a pair of field binoculars. A variety of objective lenses are available

with focal lengths ranging from 100 to 400 mm.

175-mm lens focuses at about 7 inches,

200-mm lens focuses at about 8 inches, and

400-mm lens focuses at about 16 inches.

A 200-mm objective lens is recommended because there is adequate

room to place surgical instruments and still be close to the patient.

TOTAL MAGNIFICATION:

MT = ft / fo x Me x Mc

MT = Total Magnification

ft = Focal length of binocular lens

fo = Focal length of objective lens

Me= Magnification of the eyepiece

Mc = Magnification factor

Charts are available that explain magnification as it relates to eyepiece power, binocular focal

lengths, magnification factors, and objective lenses. These charts contain valuable information that

helps the clinician select the appropriate optical components to satisfy his or her requirements. The

information can be summarized as follows:

1. As you increase the focal length of the objective lens, you decrease the magnification and

increase the field of view. In addition,you decrease the illumination because you are further away

from the surgical field.

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2. As you increase the focal length of the binoculars, you increase the magnification and decrease

the field of view.

3. As you increase the magnification factor, you increase the magnification and decrease the field

of view.

4. As you increase the power of the eyepiece, you increase the magnification and decrease the field

of view.

5. As you increase the magnification, you decrease the depth of field.

PARFOCALIZATION:

- Setting the operator specific focus throughout the entire range of magnification.

- Should be parfocalled once a month to keep it properly focussed even for subtly changing

eye sight.

- prevents unnecessary eye fatigue and pain.

In addition, when the microscope is parfocused, accessories such as cameras and auxiliary

binoculars are also in focus.

To parfocal a microscope, a flat object, such as a dull copper penny is placed under the microscope

and focused at the highest magnification.

The left / right eye diopter settings are unique to each person and should be written especially if

the microscope is shared.

OPTIMUM CONFIGURATION FOR ENDODONTIC MICROSURGERY

• 12.5 x eye pieces with a reticule

• 200 – 250 mm objective lens

• 180o inclinable binoculars

• 5 step manual magnification changer or power zoom magnification changer

• Working range about 8 inches from patient

• Magnification range of 3 X– 26 X

Illumination:It is important to understand the path light takes when it travels through the microscope. The light

source is a 100-watt xenon halogen bulb. The light intensity is controlled by a rheostat and cooled

by a fan. (The light is then reflected through a condensing lens to a series of prisms and then

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through the objective lens to the surgical field.) After the light

reaches the surgical field, it is reflected back through the objective

lens, through the magnification changer lenses, and through the

binoculars and then exits to the eyes as two separate beams of

light. The separation of the light beams is what produces the

stereoscopic effect that allows the clinician to see depth of field.

100 W Xenon halogen bulb in a fan cooled system

Fibre optic light (Quartz halogen bulb is focused onto the

end of the fibreoptic cable)

Xenon bulb - Brighter (comparable to day light)

- Color temp of 56000 K

- Produces a true color picture

Quartz Halogen light - Color temp of 32000 K

- Produces a yellow picture

A fan-cooled xenon halogen light system is recommended because fiberoptic cables absorb light

and have a tendency to be light deficient. In addition, xenon halogen is brighter and warmer than

quartz halogen and therefore projects a brighter and warmer light against bone and soft tissues.

Illumination of the surgical microscope is coaxial with the line of sight. This means that

light is focused between the eyepieces in such a fashion that the clinician can look into the surgical

site without seeing any shadows. This is made possible because the operating microscope uses

Galilean optics. Galilean optics are those optics that focus at infinity. This is markedly different

from Greenough optics (convergent optics), which are found in dissecting or laboratory

microscopes. Greenough-type microscopes necessitate observation with convergent eyes, resulting

in accommodation of the observer and eye fatigue. The advantage of Galilean optics is that the

light beams going to each eye are parallel. With parallel light instead of converging light, the

operator’s eyes are at rest as if he were looking off into the distance. Therefore, operations that use

the SOM and take several hours can be performed without eye fatigue.

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Beam splitter:

A beam splitter can be inserted in the optical pathway of the microscope as

it returns to the operator's eyes. The function of a beam splitter is to supply

light to an accessory such as a camera or an auxiliary observation tube.

Because the beam splitter divides each path of light separately, up to two

accessories can be added. Half of the light is always available for the operator. In addition to 50:50

beam splitters, other configurations are also available.

Documentation:Documentation is an important benefit of using the surgical microscope

- Video adapter

- Video camera

- Video printer

Purpose of documentation:

1. To communicate with the referring dentist

2. To educate patients and students

3. To maintain the required legal documentation of each case

The ability to produce quality slides and videos is proportional to the quality of the magnification

and illumination systems within the microscope. The beam splitter, which provides the

illumination for photographic and video documentation, can be connected to photo and cine

adapters.

Accessories:Many accessories are made for the operating microscope.

Pistol grips or bicycle style handles can be attached to the bottom of

the head of the microscope to facilitate movement during surgery.

Auxiliary monocular or articulating binoculars can also be added

and used by a dental assistant

Another accessory used to facilitate an assistant's viewing is the

liquid crystal display (LCD) screen. The LCD screen receives its

video signal from the video camera. When viewing the LCD

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screen, the assistant sees exactly what the surgeon sees without having to take his or her

eyes away from the surgical field.

The features of an endodontic microscope should include:

1. Excellent optics

2. Mechanical stability

3. Maneuverability

4. Modularity

The most important aspect, the quality of the optics, is very difficult

to assess. Fortunately, most microscopes on the market have excellent optics. Currently

microscopic optics are made in Brazil Seiler), Germany (Kaps, Leica, Moller, and Zeiss), Japan

(Nikon, Olympus), and the United States (Global).

Mechanical stability is the second most important criterion in selecting a microscope. Because

the microscope must be repositioned many times during a procedure to accommodate changes in

the patient's head position, it is important that the microscope stop moving immediately after being

repositioned. The stability of microscopes varies greatly. The microscope should not drift, and the

arm should not "bounce" after being moved. To test for mechanical stability, the dentist can gently

tap the end of the arm of the microscope when it is fully extended. In a good microscope, superior

suspension and balance mechanisms prevent the arm from moving or bouncing in response to

position adjustments.

Maneuverability of the microscope is essential because a patient's head moves frequently,

either to adjust position or because of involuntary muscle activity. The microscope head has to be

light for almost effortless maneuverability. For this reason it is not advisable to add an assistant

scope or any other large or heavy accessories.

Because a microscope is a life-time investment, modularity, or adaptability, is an important

factor. The requirements for the microscope will change with the user's needs, and other

sophisticated features can be added as experience dictates. For instance, manual magnification can

be changed to an automatic zoom function. Some microscopes are fully modular, whereas others

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JEDMED series

are limited in this respect. It therefore is important to check with the manufacturers about the

modularity of the microscope before it is purchased.

MISCONCEPTIONS ABOUT SURGICAL OPERATING MICROSCOPES:

1. Magnification:

‘How powerful is a particular microscope?’

Usable power is the maximum object magnification that can be used in a given clinical

situation relative to depth of field and field of view. As the magnification is increased, the depth of

field is decreased, and the field of view is narrowed.

‘How usable is the maximum power?’

Magnification in excess of 30 X, although attainable, is of little value in periapical surgery.

Working at- higher magnification is extremely difficult because slight movements by the patient

continually throw the field out of view and out of focus. The surgeon is then constantly recentering

and refocusing the microscope. This wastes a lot of time and creates unnecessary eye fatigue.

2. Illumination:

There is a limit to the amount of illumination a surgical microscope can provide. As magnification

is increased, the effective aperture of the microscope is decreased, and therefore the amount of

light that can reach the surgeon's eyes is limited. This means that as higher magnifications are

selected, the surgical field appears darker.

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Zeiss Global Seiler

3. Depth Perception:

Before surgery can be performed with an operating microscope, the clinician must feel

comfortable receiving an instrument from the assistant and placing it between the microscope and

the surgical field. Learning depth perception and orientation to the microscope takes time and

patience. Coordination and muscle memory are easily forgotten if the microscope is used

infrequently. As a general rule, the clinician should reorient himself or herself to the microscope

before beginning each surgery.

4. Access:

The surgical microscope does not improve access to the surgical field. If access is limited for

conventional surgery, it is even more limited when the microscope is placed between the surgeon

and the surgical field. Use of the microscope, however, creates a much better view of the surgical

field. Because vision is enhanced so dramatically, cases can now be treated with a higher degree of

confidence.

5. Flap Design and Suturing:

Reflecting soft tissue flaps and suturing them back in place are not high magnification procedures.

Although the microscope could be used at low magnification, little is gained from its use in these

applications. The operating microscope is recommended predominately for osteotomy, curettage,

apicectomy, apical preparation, retrofilling, and documentation.

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