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The Use of Magnification in Endodontic Therapy

The Operating Microscope

The surgical operating microscope (SOM) was introduced to endodontic therapy only recently but has gained wide acceptance during the past 10 years and is now considered to be an important tool in endodontic practice. Not only is the SOM beneficial for its magnification abilities, but it also eliminates eye fatigue and improves operator ergonomics. The SOM possesses Galilean Optics, which focus at infinity and send parallel beams of light to each eye, permitting the operator to perform time-consuming procedures without inducing eye fatigue. Loupes, however, have convergent optics. Likewise, the SOM and its binoculars are adjustable, ensuring that the operator’s head and neck are held at an angle comfortably sustainable throughout an entire procedure (Figure 1).

           

Use of the SOM in Endodontic Therapy

Diagnosis

The SOM enables the endodontist to assess the marginal integrity of restorations and to detect cracks or fractures. The cracks can be coronal and may be found following the removal of a restoration. Once the tooth has been accessed, cracks can also be detected on the floor of the pulp chamber. For optimal visibility, it is important to control the dryness of the dentin with an irrigator when using the microscope.

The SOM is also an efficacious method for detecting radicular cracks. Undetected root fractures in large fixed restorations can initiate significant complications. In such cases, the gingiva is carefully retracted, and the root surface is gently dried with an irrigator. In numerous instances, the width of the crack would go unnoticed without the use of the operating microscope. In addition, utilization of the microscope allows a video print to be recorded and presented to the patient and the referring clinician.

Nonsurgical Endodontics

Accessing the pulp chamber and locating the canals constitute important visual phases of endodontic therapy. Errors at this level will compromise the entire treatment. The SOM identifies calcified and additional canals with ease. The initial step mandates complete removal of the roof of the pulp chamber. Using round burs under the microscope, smooth and regular surfaces are created on the walls and floor of the access cavity. The floor of the pulp chamber can then be carefully explored with a DG 16 explorer. Smaller instruments are used under the microscope to localize the canal orifices. A round bur and ultrasonic tips are used in combination in a brush-cutting action to safely eliminate the secondary dentin overlying the orifices. Pulpstones can be readily detected and eliminated.

One of the advancements in canal location with the operating microscope is the routine identification of the second mesiobuccal canal of maxillary first and second molars (Figures 2 and 3). Clinically, the mesiobuccal root contains a second root canal system1 that can be identified and treated more than 75% of the time.2 Histologically, it has been demonstrated that mesiobuccal roots contain 2 systems almost 100% of the time.3 Kulild et al also found that almost 10% of the canals could be detected only with the microscope.3 One of the determining features is the “dentin map,” a fine line on the pulp chamber floor that connects all orifices. The dentin map can be traced and will invariably lead to the locations of the remaining canals.

Retreatment

Utilization of the SOM in endodontic retreatment has brought significant advantages and has expanded the scope of indications using a nonsurgical approach. Procedures such as bypassing a ledge, removing a broken instrument, or repairing a perforation have become considerably more reliable.

Surgical Endodontics

Surgical endodontics is likely the area of endodontic therapy that has experienced the greatest degree of change during the past decade. Introduction of the SOM and ultrasonic tips for root-end preparation are the two primary reasons for the change. Every step of the surgical procedure benefits from enhanced magnification and illumination. Periapical curettage is facilitated, since bone margins can be scrutinized for completeness of tissue removal. The apicoectomy is performed with a high-speed handpiece perpendicularly to the long axis of the root, which ensures preservation of root length. The resected surface is examined carefully with micromirrors for the presence of an isthmus.

In recent studies, a complete or partial isthmus was found at the 4-mm level of the mesiobuccal root of the maxillary first molar 100% of the time, and a complete isthmus was found 90% of the time at the 3-mm level of the mesial root of the mandibular first molar.4 Apical preparation is achieved with ultrasonic tips, which are available in shapes to suit all clinical circumstances. For sufficient energy, the tips must be used on piezoelectric units, which allow a conservative preparation in the long access of the canal. The preparation is dried with an irrigator and carefully examined under the microscope at high power, using micromirrors. The cavity is subsequently filled with retrofilling materials. The margins are finished, and the retrofill is inspected. A video print should be recorded and forwarded to the referring clinician with the definitive radiograph.

(Continued from page 1 )

Case Presentations

Case 1

A 45-year-old male patient presented with mild symptoms and a sinus tract in the mandibular right quadrant. The first molar had been extracted, and a fixed prosthesis had been used to replace the tooth using the second molar and the second premolar as abutments. The sinus tract was traced with a gutta-percha point, and a radiograph was taken (Figure 4). At the completion of diagnosis, the presence of a lateral lesion was established on the distal aspect of the second premolar at the junction of the middle and apical third of the root, perhaps due to the existence of a lateral canal. The treatment plan was designed as follows: If the bridge required reconstruction, nonsurgical endodontic retreatment would be attempted; if the prosthesis was to be retained, endodontic surgery would be performed.

Upon periodontal probing on the facial aspect of the second premolar, a narrow sulcular defect was detected; however, no crack was visible at the margin of the restoration. The gingiva was retracted, the surface dried, and the microscope was used to enhance visibility. The crack was clearly visible, even though its coronal extension was not complete (Figure 5). Prognosis for tooth survival was deemed to be poor, and no endodontic therapy was scheduled.

Case 2

A 32-year-old female patient presented with a lesion of endodontic origin on the maxillary right central incisor. The tooth had a suitable crown and a post that extended beyond the midroot level. Use of the surgical approach was selected. Prior to magnification, the treatment required appeared to be a straightforward anterior surgery (Figure 6). At high magnification (16x), however, 3 portals of exit were readily discerned (Figure 7). If not treated, each portal could be responsible for the persistence of the lesion. The 3 apical foramina were prepared with the ultrasonic tips and filled (Figure 8).

Case 3

A 42-year-old female patient presented with recurrent symptoms in the region of the maxillary first left premolar. A previous surgery had been performed, but the symptoms were still present. The preoperative radiograph revealed an inadequately placed amalgam retrofill (Figure 9). In view of the previous surgery, the surgical approach was selected to treat the condition. The bevel of the root revealed a more complex anatomy than expected; the premolar had 3 canals and an isthmus joining them (Figure 10). The apical preparation was performed with the ultrasonic tips (Figure 11), and a retrofilling material was subsequently placed (Figure 12). The immediate postoperative radiograph revealed an unusual appearance of the retrofill (Figure 13). Six months postoperatively, a radiograph confirmed complete healing at the site of the treatment (Figure 14).

Case 4

A 55-year-old female patient presented with a lesion of endodontic origin at the apex of the mesial root of the mandibular left first molar (Figure 15). A complete root canal treatment of the 2 mesial canals appeared to be present in the radiograph. The etiology of the lesion was not evident. The surgical approach was selected, and the root end was beveled. Using the microscope at high power, a third canal responsible for the lesion was detected between the two treated canals (Figure 16). All 3 canals and the isthmus joining them were prepared apically and obturated (Figure 17).

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. 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, PA; Private practice, Paris, France.

 

References

  1. 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.
  2. Neaverth EJ, Kotler LM, Kaltenbach RF. Clinical investigation (in vivo) of endodontically treated maxillary first molars. J Endodont 1987;13(10):506-512.
  3. 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.
  4. 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.
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