Clinicians have recognized that the use of magnification can improve
the performance of dental procedures. Of the various magnification systems
available, loupes have been the most popular, yet their magnification is
limited. This article reviews and describes the function and clinical
application of the surgical operating microscope (SOM), emphasizing its
utilization in endodontic treatment. Several cases are presented to document
the clinical procedure and to illustrate the difference between operative
procedures performed without magnification and those completed using the SOM
Telescopes or loupes have been readily available in a variety
of configurations and magnifications. With the aid of a fiberoptic headlamp
system, light can be projected in the line of sight to prevent the creation of
shadows in the surgical field and render optimal visualization of the treatment
site. However, the magnification of loupes is limited (2.53 to 6.03) and their
optics are convergent, which creates eye strain and fatigue. In order to
address the limitations present in these devices, clinicians adopted new
techniques and technologies. Otologists were the first medical specialists to
utilize the operating microscope in a clinical environment. In 1921, Nylen
performed a surgical procedure with the operating microscope. When
Jannetta performed a procedure called microvascular decompression to treat
trigeminal neuralgia, the event became the subject of controversy (to use or
not to use the microscope) in the neurosurgical community. The
surgical operating microscope (SOM) has been recently introduced in dentistry,
specifically in endodontics, where increased magnification and illumination
have resulted in improved technical accuracy and performance.
The surgical operating microscope consists of three primary
components — the supporting structure, the body of the microscope, and the
It is essential that the microscope be stable while in
operation, yet remain maneuverable with ease and exceptional precision,
particularly when used at high power. The supporting structure can be mounted on
the floor, ceiling, or wall. As the distance between the fixation point and the
body of the microscope is decreased, the stability of the setup is increased.
In clinical settings with high ceilings or distant walls, the floor mount is
preferable. Careful attention should be given to the precise setting of the
arms. The built-in springs should be tightened according to the weight of the
body of the microscope to establish perfect balance in any position. This
permits precise visualization and renders the fine focus unnecessary in the
majority of clinical circumstances.
Body of the Microscope
Eyepieces are used in the overall magnification. They are
available in various powers, ranging from 6.33 to 203; the two most commonly
used are 103 and 12.53. The end of each eyepiece has a rubber cup that can be
lowered for clinicians who wear glasses. Eyepieces also have adjustable diopter
The binoculars contain the eyepieces and allow the
adjustment of the interpupillary distance; they are aligned manually or with a
small knob until the two divergent circles of light combine to effect a single
focus. Binoculars are available with straight, inclined, or inclinable tubes.
Straight tubes are generally used in otology and are not well suited for
dentistry. Inclined or inclinable tubes are preferred to allow the clinician to
establish a comfortable working position. Inclined tubes are fixed at a 45°
angle to the line of sight of the microscope; inclinable tubes are infinitely
adjustable. The microscope is positioned over the patient’s mouth, and the
binoculars are inclined in such a manner that the head and neck of the operator
can be held at an angle where comfort can be sustained throughout the entire
procedure. Indirect vision is a characteristic of clinical diagnosis
and treatment that is specific to dentistry. In conventional endodontics, it is
impossible to examine a root canal with straight line access. With the
microscope, use of the mirror is essential and allows multiple angles of vision
without moving the body of the microscope.
Magnification changers are available as 3-, 5-, or 6-step
manual changers, or a power-zoom changer. They consist of lenses mounted on a
turret that is connected to a dial located on the side of the microscope. The
magnification is altered by rotating the dial.
The objective lens is the final optical element, and its
focal length determines the working distance between the microscope and the
surgical field. The range of the focal length varies from 100 mm to 400 mm. A
200-mm focal length allows approximately 20 cm of working distance, which is
generally adequate for utilization in intraoral procedures.
The range in magnification from 2.53 to 83 is used for an
intraoral surgical site. For example, the wide-field view allows a better
evaluation of the root position in surgical endodontics. Magnifications in the
range of 103 to 163 are used for operating; 90% of the use of the microscope is
at this power. The higher magnifications (203 to 303) are used to examine fine
A typical microscope setup should have the following
features to be properly equipped for application in dentistry:
changer, ranging from 43 to 283.
Surgical operating microscopes possess the additional
benefit of Galilean Optics. As opposed to loupes, which have convergent optics,
Galilean Optics focus at infinity and send parallel beams of light to each eye.
With parallel light, the operator’s eyes are at rest, as though looking off
into the distance, permitting performance of time-consuming procedures without
inducing eye fatigue.
The light source is one of the most important features of an
operating microscope. For the first time in dentistry, the illumination is
coaxial with the line of sight, which eliminates the presence of any shadow.
The light source is generally powered by a 100- to 150-watt halogen light bulb
that is connected to the microscope with a high-efficiency fiberoptic cable.
The light passes through a condensing lens, a series of prisms, and then
through the objective lens to the surgical site. The intensity of light is
controlled by a rheostat.
In order to deflect a certain percentage of the light from
the eyepiece towards the accessories, a beam splitter can be placed between the
binoculars and the magnification changer. The beam is generally split at a
50:50 ratio (ie, half of the light is always available to the operator). A
photo or video adapter can be connected to the beam splitter. The video camera
is a useful adjunct and serves two additional purposes: it allows the
assistants to follow the procedure precisely and assist efficiently, and it can
also be used for documentation using video prints or recordings.
Use of the Surgical
Operating Microscope in Endodontic Therapy
The surgical operating microscope was introduced to
endodontic therapy only a decade ago. At the time, only a few clinicians in the
United States and Europe believed in its utility. The SOM has gained wide
acceptance during the past 10 years and is now considered to be an important
tool in endodontic practice. Since 1997, microscopic techniques in endodontics
have been instituted in the curricula of all graduate dental schools in the
United States. All graduate students must be proficient in clinical application
of the SOM and knowledgeable of all aspects of its usefulness in endodontic