The Role of the Surgical Operating Microscope in Endodontics

Ahmad Tehrani, DDS

Nearly 20 years have passed since Dr. Gary Carr started using a surgical operating microscope (SOM) in his office. His teaching facility, known as PERF (Pacific Endodontic Research Foundation), has trained and been visited by many pioneers in endodontics, including past and present endodontic graduate program directors, current endodontic residents, and faculties. It is undisputed that endodontics has greatly benefited from use of SOMs; after all, one can only treat what one can see. With the advent of its use, Stropko reported that incidence of a second mesial canal system in mesial-buccal roots of maxillary molars is greater than 90%.¹ SOM also revolutionized the endodontic apical surgery into micro-endodontics surgery.²

The incision line, tissue reflection, bone cut-out, and hemostasis are all controlled with extreme visual acuity under the scope.³ When hemostasis is achieved, the periapical region and the root are both isolated to remove the lesion while resecting the root end, if needed, under the scope. Before the endodontic microscope era, all of these steps were crude in nature because no one could see with certainty.⁴

With the advent of new microsurgical instruments—such as small sapphire- and rhodium-coated mirrors and diamond-coated ultrasonic tips for root end resection, preparation, and isthmus cleaning—and the full-time use of SOMs, endodontic surgery has transformed into a microsurgical era where the surgeon can visualize the entire bony crypt, lesion, and the root end without guesswork.

Yet even today, there are dentists who still argue about the necessity of a scope during endodontic procedures and only use it when they see a crack or fracture with the naked eye. The "I only need it when I need it" opinion equates with wearing seatbelts only when someone suspects he or she might be in a car accident.

This article will focus on the use of the SOM during the entire endodontic procedure and postendodontic restorative phase. The SOM allows the operator to sit in an upright position to decrease the backache and neck fatigue usually associated with incorrect posture. The use of a rubber dam is mandatory to isolate the tooth or the quadrant of teeth under treatment. The light source of most microscopes is focused on the operating field without loss of light. The different magnification settings enable the dentist to focus in on a fracture line, study the pulpal floor anatomy for locating the entrance of calcified canals, remove hidden decay, and prepare a deep gingival margin for a Class II preparation with precise control.⁵ The SOM has enabled clinicians to discover usual and aberrant canal anatomy to aid in endodontic treatment and revision of previously failing root canal treatment.⁶

With the aid of an assistant’s scope attached to the beam splitter of most microscopes, the assistant can be fully involved with the treatment while he or she observes the operating field with the same acuity as the dentist. An experienced assistant can anticipate what the next step will be and be ready without interrupting the flow of the procedure. In short, the SOM provides precise visualization needed to deliver optimum dentistry.

To deliver the best possible care, it is undeniable that dentists should be able to accurately diagnose the etiology of the patient’s complaint and treat the problem. A surgical microscope allows clinicians to focus on a tooth or a quadrant of teeth with unparalleled sharpness and a focused beam of light illuminating the operating field.⁷

The attention of the operator is focused on the tooth undergoing treatment. The scope is positioned so that the dentist’s spine is in an upright position, eliminating back and neck pain. The visual acuity of the scope is unrivaled because the magnification can be easily adjusted by dialing up or down to a higher or lower magnification. The concentrated halogen and xenon light beam is not scattered, but focused on the field.

The full use of a operating microscope during dental procedures requires practice and patience.⁸ Most new users make the mistake of starting on the highest magnification setting instead of the lower settings, which help to familiarize the clinician with the depth of field and finger rest positioning while not blocking the view of the tooth; facilitating finger and arm movements for the pass and delivery of instruments to and from the assistant; and optimizing patient positioning, which is of utmost importance for proper ergonomics.

Once the operator is comfortable with small procedures, such as routine operations, rubber dam placement, occlusal preparation, and finishing and polishing, then more advanced procedures can be done without experiencing frustration with the new equipment. The use of typodonts and stone models is extremely helpful in the beginning to ease into the use of the scope.

It is very helpful to outline every step during each procedure and make a goal of accomplishing each step under a SOM before moving to the next step. It is best to take small steps to try and eliminate disappointment and the feeling of being overwhelmed. The microscope can be very in-timidating in the beginning, but we all should remember that our first pair of magnification loupes was not comfortable either. It was a total departure from "naked-eye dentistry," which we were comfortable with. The leap to "microscope-enhanced dentistry" can be easily accomplished if the clinician believes that he or she can perform better dentistry because he or she can see better. This notion is the most difficult to accept, because it is hard to admit what we could not see or do before the scope was available. The best parameter is preparing the very best cavity preparation and visualizing it under a scope.

The strongest argument for using a SOM is going through documented cases obtained during treatment. The use of a SOM is facilitated when the operatory design and ergonomics of the workspace is conducive for efficiency. Having a properly trained assistant using his or her own scope attached to the beam splitter can simplify the task at hand. The assistant can see if the mirror needs to be changed, if a stream of air is needed to clear the field, how much precurving is required in the endodontic file, or if the tooth needs to be cleared of debris. It is a rehearsed concert between the assistant and the dentist to work harmoniously together under a scope. Basically, using the SOM requires a departure from what one has learned in dental school if the dentist was never trained to use one.

CASE STUDIES

The following cases were all treated from the start of diagnosis to the final restorative phase under the microscope.

Case Presentation 1
The patient was experiencing throbbing pain with sensitivity to cold, which was confirmed with ice testing. The molar was decayed under the existing composite filling (Figure 1 and Figure 2). There was an existing gap from the previous treatment between the composite and the dentin. During careful removal of the decay, a thick layer of pulp stone was uncovered with the use of an ultrasonic tip. The canals were located and routine cleaning and shaping continued in all canals. The operating field was so crystal clear that meticulous removal of all decay and the existing restoration was not a laborious task. The SOM was invaluable in the postendodontic restoration to complete the coronal seal of canal orifices (Figure 3) and core build-up (Figure 4 and Figure 5) for the permanent crown.

Case Presentation 2
The SOM enables the operator to virtually address all aspects of the tooth, from the coronal restoration to the pulpal floor, as well as the location of canals, fractures, impediments, pulp stones, caries control, etc. The discipline of endodontists and general dentists using microscopes enhances the treatment outcome. When the caries is controlled, and all of the canal systems are identified and cleaned, the success rate is also increased, which is illustrated in this case.

The patient was having localized pain, which was confirmed through responsive tests to the upper right first premolar. Tooth No. 5 responded with a lingering pain when subjected to ice stimulus, duplicating the pain she had experienced days ago. The patient also mentioned that the porcelain crown on this tooth felt loose, even though it appeared to be seated and stable at the clinical examination.

After administration of anesthesia and rubber dam placement, an access was prepared through the porcelain-fused-to-metal crown. However, the crown sheared off shortly after the pulp was accessed. After the crown came off it was obvious why the tooth was symptomatic and the crown was dislodged: There was no core under the crown and the tooth had minimal crown exposure (Figure 6). The rubber dam was changed and a suitable clamp was selected (Figure 7).

The calcified pulpal floor and extensive decay was easily managed when the operating field was visibly illuminated and magnified enough to address a relatively difficult situation. The remaining tooth was isolated with a block-out resin to complete the endodontic treatment (Figure 8).

The endodontic access was refined to find the orifice of the canals (Figure 9). Radiographically, the canal was almost not visible, but by following the dentinal map under high magnification and bright xenon light, the location of the canal’s orifice was easily accessed to begin pulp extirpation.

In this case, the white calcified dentin was followed in the usual location of the canal with a thin ultrasonic tip for about 2 mm to 3 mm below the osseous height of the bone before the orifice of the canals was located. Using proper magnification, at no point was the operator unsure or suspicious of where the canals were. After completion of the endodontic procedure, a fiber post was placed in the canal with a bonded core build-up (Figure 10). The crown preparation was completed under the scope and a temporary crown was fabricated for the patient (Figure 11 and Figure 12).

Case Presentation 3
The following case illustrates an extensive Class V caries that was delicately managed without incident under SOM. This patient presented complaining of erratic sharp shooting pain on tooth No. 31.

Even though there was also a sinus tract associated with tooth No. 30, since the pain was coming from the irreversible pulpitis in tooth No. 31, the patient elected to treat the source of his current pain and address the first molar at a later time.

The Class V lesion was well below his gum line (Figure 13 and Figure 14). The tooth was clamped on the gingival to access the lesion with ease (Figure 15). Never be afraid to apply the tines of a sterilized clamp to the gingival to place a rubber dam. The gum tissue will heal; a contaminated root canal will not. After cleaning out the decay, the carious defect was isolated with block-out resin as a temporary wall to contain the irrigant during the endodontic procedure (Figure 16 and Figure 17).

The use of a rubber dam facilitated the endodontic procedure. Isolating the entire quadrant provided optical orientation for the long axis, allowed access for the opening preparation, and kept the field in plain view. The SOM enabled the endodontist to visualize and easily remove the small tissue tags, debris, and contaminants in and around the canals. After the endodontic objectives were accomplished, the canals were obturated with gutta-percha and a sealer. The core buildup was accomplished with bonded resin after endodontic treatment while the tooth was still isolated with a rubber dam (Figure 18 and Figure 19).

Case Presentation 4
The fourth case exemplifies the power of high magnification and visualization needed in endodontics. The patient presented with irreversible pulpitis and severe pain radiating from tooth No. 14. Evaluating from the radiographs it was obvious that the pulp chamber was calcified (Figure 19) and the access had to be dissected through a thick layer of pulp stone to expose the canal’s orifice. The use of a caries indicator, an ophthalmic solvent, and a surgical microscope was instrumental in locating the elusive calcified canals. Ophthalmic dyes (eg, fluorescein sodium, rose bengal) are currently being used in ophthalmic diagnostic procedures and for locating damaged areas of the cornea due to injury or disease.⁹ When these dyes come into contact with vital or non-vital pulp tissue, they are readily absorbed by the connective tissue elements of the pulp in the chamber and root canal system (Figure 20). When exposed to blue light, these dyes dramatically fluoresce, showing scattered tissue segments that contrast with the surrounding monochromatic dentin. It is this quality that makes them useful in the location of pulp tissue in root canals (Figure 21).¹⁰ Of course, thorough knowledge of pulpal anatomy and tooth anatomy is mandatory for undertaking such a difficult task. Figure 22; Figure 25; Figure 24 demonstrate the dissection of the canals and completion of the case subsequent to location of the pulp tissues with the ophthalmic dye.

CONCLUSION

Training in the use of a SOM is now a mandatory requirement in most postgraduate endodontic residency programs. Endodontists today are familiar with the use of microscopes; however, many are not efficient with its use. It is incumbent upon endodontists and general dentists alike to seek out mentors and colleagues to help them master the microscope to its full potential.

Endodontics remains the forefront specialty dedicated to salvaging the natural tooth. With the increasing popularity of implants, patients need to be educated about the options available to them. Implants have a solid place in dentistry today; however, they are not a replacement for a natural tooth that could be saved through endodontics. Endodontists can enjoy the multitude of new advancements and technological tools that were not available decades ago. Through these advancements, the otherwise condemned tooth can be saved. Conversely, patients also benefit from avoiding unneeded treatment if the tooth is not salvageable, such as internal cracks extending down the canals, massive perforation, or inadequate coronal structure for definitive restoration. SOMs enable the clinician to see vertical root fractures and pulpal floor perforations, and discover the extra canal systems that are present in most teeth. Patients deserve the extra care taken with the visual acuity that microscopes provide; our professional obligations demand that we be and remain the "physicians of the mouth." The question is: to see or not to see.

RESOURCES

For additional help mastering the SOM, there are many centers for microscope training throughout the United States including:
• www.globalsurgical.com/dental/dental_training.asp
• www.microscopetraining.com
• www.dental.upenn.edu/depts/microscopecenter/endo.html
• www.ncofi.com/microscopy.htm

ACKNOWLEDGMENT

Case Presentation 4 is courtesy of Dr. Sashi Nallapti, Ocho Rios, Jamaica.

References

1. Stropko JJ. Canal morphology of maxillary molars: clinical observations of canal configurations. J Endod. 1999;25(6):446-450.

2. Rubinstein R. Endodontic microsurgery and the surgical operating microscope. Compend Contin Educ Dent. 1997;18(7):659-674.

3. Burkhardt R. Hurzeler MB. Utilization of the surgical microscope for advanced plastic periodontal surgery. Pract Periodontics Aesthet Dent. 2000:12(2): 171-180.

4. Kim S. Principles of endodontic microsurgery. Dent Clin North Am. 1997;41(3): 481-497.

5. Gester V. The microscopy on dental medicine: gadget or necessity? Rev Belge Med Dent. 2004;59(1):62-76. [Article in French.]

6. Carr GB. Retreatment. In: Pathways of the Pulp. 7th ed. 1998;810,832.

7. van As G. Magnification and the alternatives for microdentistry. Compend Contin Educ Dent. 2001;22(11A):1008-1116.

8. Friedman MJ, Landesman HM. Microscope-assisted precision (MAP) dentistry. A challenge for new knowledge. J Calif Dent Assoc. 1998;26(12):900-905.

9. Newell FW. Ophthalmology: Principles and Concepts. 6th ed. 1986; St. Louis, Mo, CV Mosby:124.

10. Niemczyk S. Intrinsic and extrinsic aids in root canal location. Endo Therapy. 1976;2(1):7.

Figure 1 Preoperative radiograph for Case 1.		Figure 2 Appearance of the composite. Note the dark areas of decay visible through the composite.
Figure 3 Obturation of the canals with guttapercha and sealer.		Figure 4 Closure of the chamber with bonded composite before definitive build-up.
Figure 5 Postoperative radiograph of completed endodontic treatment.		Figure 6 Preoperative view of tooth No. 5 in Case 2.
Figure 7 Preparation for crown removal.		Figure 8 Appearance of tooth No. 5 following crown removal. Note the calcified pulp chamber.
Figure 9 Canals were located, shaped, and cleaned.		Figure 10 Obturated canals with post space created.
Figure 11 Buildup of tooth No. 5.		Figure 12 Postoperative radiograph.
Figure 13 Preoperative radiograph of tooth No. 31 in Case 3. Note the appearance of extensive caries.		Figure 14 Gutta-percha point traced in the sinus tract of tooth No. 30.
Figure 15 Clinical view of Class V lesion in tooth No. 31.		Figure 16 View of shaped and cleaned mesial canals in tooth No. 31.
Figure 17 Gutta-percha obturation of mesial canals, tooth No. 31.		Figure 18 Postoperative radiograph of tooth No. 31 showing the abrupt curvature of the distal root.
Figure 19 Preoperative clinical view of Case 4. Note the extreme calcification of tooth No. 14.		Figure 20 Application of opthalmic dye.
Figure 21 Ultraviolet light illuminating the organic tissue location for chasing the orifice of the canals.		Figure 22 Dissection of the calcified dentin to locate the canals.
Figure 23 Identifying and instrumenting the existing canals under the calcification.		Figure 24 The completed case.
About the Author
Ahmad Tehrani, DDS Private Practice Plano, Texas