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Case Study
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Magnification in Endodontic Therapy

Four Applications of the Surgical Operating Microscope

Bertrand G. Khayat, DDS, MSD

Learning Objectives:
After reviewing this case study, the reader should have an increased knowledge of:
  • The advantages of the operating microscope
  • The clinical application of these magnification devices

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 with micromirrors.

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

The surgical operating microscope consists of three primary components — the supporting structure, the body of the microscope, and the light source.

The Supporting Structure

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 settings.

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 details.

A typical microscope setup should have the following features to be properly equipped for application in dentistry:

  • 12.53 eyepiece power.
  • 125-mm inclined binoculars.
  • 5-step changer, ranging from 43 to 283.
  • 200-mm objective lens.

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.

 

Light Source

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.


Accessories

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 therapy.


Conclusion

The introduction of the surgical operating microscope in dentistry, particularly in endodontics, has been a significant addition to the profession’s armamentarium. The increased magnification and illumination have enhanced the treatment possibilities in surgical and nonsurgical procedures. Treatment modalities that were not possible in the past have become reliable and predictable. The SOM has enabled the clinician to work in a more comfortable ergonomic position, for longer durations, and with increased precision. Improved visibility has enhanced the performance of various endodontic procedures, and numerous endodontists have already incorporated the use of the SOM in their practice. Based on the clinical experience of the author and the results of preliminary studies, the use of magnification and the SOM in partic­ular indicate promise as essential adjuncts in the dental practice of the 21st century.


*Assistant Professor of Endodontics, University of Pennsylvania, Philadelphia, Pennsylvania. Private practice, Paris, France.


Related Reading:

 

  1. Nylen CO. The microscope in aural surgery: Its first use and later development. Acta Otolaryngol 1921;116:226.
  2. Shelton M. Working in a Very Small Place: The Making of a Neurosurgeon. 1st ed. New York, NY: Vintage; 1989.
  3. Carr G. Microscopes in endodontics. J Calif Dent Assoc 1992;20(11):55-61.
  4. Rubinstein RA. New horizons in endodontic surgery. Part 1. The operating microscope. Oak Country Dent Rev 1991;12:7.
  5. Rubinstein RA. Endodontic microsurgery and the surgical operating microscope. Compend Cont Educ Dent 1997;18(7):659-672.
  6. Hess W, Zurder E. The Anatomy of the Root Canals of the Teeth of the Permanent and Deciduous Dentitions. New York, NY: William Wood, 1925.
  7. Neaverth EJ, Kotler LM, Kaltenbach RF. Clinical investigation (in vivo) of endodontically treated maxillary first molars. J Endodont 1987;13(10):506-512.
  8. Kulild JC, Peters DD. Incidence and configuration of canal systems in the mesiobuccal root of maxillary first and second molars. J Endodont 1990;16(7):311-317.
  9. Weller N, Niemczyk S, Kim S. Incidence and position of the canal isthmus. Part 1. The mesiobuccal root of the maxillary first molar. J Endodont 1995;21(7):380-383.
  10. Rubinstein R, Kim S. Results of 94 endodontic microsurgeries using SuperEBA retrofill. J Endodont 1996;22:188(Abstract).
 

 

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