Operating Microscope

The typical OM (Operating Microscope) head has three main parts -- body tube optics, an eyepiece and an objective lens. Working together, these pieces magnify small objects in the surgical area by powers of approximately 5, 8 and 12. This system also is available in an upgraded five-step version that adds approximately 4 and 16 powers. By changing the eyepiece from 10 power to 12.5 power, overall magnification can be increased by 25 percent. Typically the 200mm or 225mm objective lens provides the correct working distance in the dental setting.

The OM is adaptable to various office environments, since the head portion of the microscope, supported by a counterbalanced arm, can be attached to a floor stand, wall mount or ceiling mount. Additional installation options also are available, and many OM systems accommodate modular expansion and upgrades. One example is the multi-axial binocular observer system, which enables an assistant or second operator to view the procedure. Another example, the inclinable binocular, allows the binoculars to be adjusted for added flexibility and operator comfort.

Illumination is a key feature of the OM. Procedures can be viewed with a high level of clarity and depth of focus. Fiberoptic or integral halogen light sources equip current OMs to deliver approximately 20,000 foot candles of light to the operating field. Optional xenon fiber optic light sources offer about 50,000 candle power.

OM documentation systems require the addition of a beamsplitter so that video cameras and/or 35mm photographic cameras can be attached for high resolution imaging. Video monitors, video recorders, computer disk storage and retrieval systems and video printers for OM systems also are available. The video data created by the printer can be stored in the printer's internal micro-computer for later optimization and printing, or printed at the time of capture for viewing in about a minute.

Uses of the Operating Microscope in Dentistry
The OM has revolutionized both nonsurgical and surgical endodontics, and is likely to have a significant impact in other fields of dentistry in coming years. Applications of the OM in endodontics are outlined below.

Routine Cases:

The OM is an asset in examining the pulp chamber and root canal system. It helps assess the completeness of cleansing and the existence of fractures. An OM also enables users to see if the chamber roof has been adequately removed, especially in cases where calcification has narrowed the vertical height of the chamber in a crown-root direction. Before the OM was available, removal of the chamber roof could more easily result in inadvertent perforation of the chamber floor due to lack of visualization. Enhanced visualization through the OM also reduces fatigue and eye strain, which facilitates more efficient biomechanical instrumentation. The eyeglass type loops available for improved magnification help in this regard as well, but are limited by lack of focused lighting, restricted depth of focus, and the availability of only one power of magnification per pair.

Complex Cases

Difficult endodontic cases may involve calcified root canal and/or chamber systems; internal resorptive lesions with or without external complications; crown and root fractures; caries; and cases with limited or restricted access.

Calcified Teeth:

This condition poses difficult challenges because the coronal and radicular pulp are obliterated. Although calcifications do occur in healthy uninflammed pulp, they tend to increase in dimension and frequency with irritation and age. The OM allows the operator to discern differences in the color of primary and other dentin types, which facilitates location of root canal orifices. An explorer being used to locate the softer dentin typically found at the orifice in a calcified chamber system can actually gouge the dentin at different depths depending on the density of the dentin. By contrast, the OM allows the user safely to explore the dentin visually rather than invasively. When an explorer is inserted into a necrotic root canal orifice, an exudate may become instantly visible, marking the site as the correct location for further instrumentation. This allows immediate inspection of each explored site to determine if a perforation of the chamber floor is made before instrumentation causes extensive erroneous enlargement.

Removal of overlying dentin can be accomplished safely and precisely with direct vision through the OM, using high speed instrumentation or ultrasonic tips. Actual penetration of the root to locate buried root canal systems is visible through the dental mirror provided by the OM while operating the handpiece.

Lesions:

Among the most difficult endodontic lesions to treat are pathologic external root resorption and the rarer progressive type of internal resorption. When the resorptive lesion is in the middle or coronal third of the root canal system, it often is possible to view using the OM and better gauge the prognosis of these teeth without relying solely on radiographic interpretation. Calcium hydroxide can be applied directly to the lesion, and prognosis for other treatment modalities such as root extrusion can be assessed with the aid of the OM.

Crown and Root Fractures:

Fractured amalgams and tooth structure can be viewed and documented with excellent quality results using both 35mm and video OM technology. The video images can be displayed to the patient instantly via the freeze frame mode, or saved as a video print either on disk or on any computer equipped with a video capture board. This level of documentation is a valuable tool for educating patients. In addition, the images, once transcribed to hard copy, can be used to communicate the exact location and extent of the fractures to other treating dentists.

Ordinarily, the size and extent of a fracture determines the prognosis for a tooth. A dark fracture that extends from the crown cavo-surface margin of a molar into the distal root and down the root to the apical third would be more likely to fail than a fracture that extends only to the orifice or slightly beyond. The use of methylene blue dye is a superb marker of fractures and aids visualization.

Caries:

Especially under full crown restorations, caries removal is more accurate and complete using the OM because the carious defect can be viewed while the dental handpiece is being used. The OM is helpful in sealing a carious perforation because it makes the site visible and illuminates the application of appropriate filling material.

Limited or Restricted Access:

Locating canals and examining the chamber and root canal system for fractures in difficult access situations also is easier with the OM. For instance, third molars and distally tipped second molars present fewer visibility problems with the intense light of the OM. Minor color changes in the dentin are more easily discernible, providing clues for locating calcified canals and facilitating caries removal.

Retreatments:

Endodontic retreatments pose some of the most difficult challenges to the clinician. The nonsurgical retreatment of endodontic failures is the preferred treatment when feasible.

Non-Surgical:

When retreatment is necessary, whether due to radiographic periapical pathosis, discomfort or prosthetic problems, the OM again enhances visualization. Inadequate cleansing and obturation are principal contributors to endodontic failure. The enhanced visibility afforded by the illumination and magnification of the OM aid in the accurate removal of the material in the chamber without undue risk of perforation. It becomes a simple matter to remove most cements, amalgam and cast metallic cores because the material can be viewed almost simultaneously with removal. Canal orifices can be identified accurately; removal of canal filling material can be accomplished using a solvent (or heat) for gutta-percha and ultrasonics for non-soluble cements, silver cones and broken instruments.

Ultrasonic instrumentation is valuable in removing the cements frequently used in endodontic therapy performed overseas. Ultrasonic retroprep tips and files often can remove non-soluble cements quickly and accurately, thereby greatly reducing the chances of perforation associated with high and low speed dental handpiece burs. This procedure can be monitored with the OM at critical intervals to enhance control of the removal process.

Separated endodontic instruments in the root canal system may result in endodontic failure. The OM is helpful in illuminating the handling of these iatrogenic problems. Once the canal is widened with ultrasonic tips, the fractured instrument blocking the canal often can be visualized using the OM. The instrument can be vibrated free using ultrasonic tips if it is in the coronal one third of the root, or similarly freed with ultrasonic file tips if in the middle or apical third. With the OM, this process can be monitored at critical points to ensure accurate placement of the tips or files. Occasional use of the Masserann and Roydent trephines and pinch-pressure devices may prove successful, but their large size makes them impractical for many radicular situations.

Similarly, the OM is useful in removing silver cones. Even silver cones lodged in the middle and apical third can be manipulated with retrieval instruments and more accurately vibrated ultrasonically with the increased visibility provided by the OM. Intra-radicular post removal has been a difficult treatment issue for anyone attempting nonsurgical retreatment of an endodontic failure or post fracture. While there is no general agreement among endodontists about the best methods of post removal, ultrasonics play a significant role. With the OM, placement of ultrasonic post removal tips on the non-cast and cast posts becomes more precise, and the vibratory forces are better directed until the post loosens in its preparation. Also, removal of the cement and/or composite or glass ionomer resins in the chamber around the post become easier. Most cemented non-cast posts can be removed in less than 20 minutes using the ultrasonic and the OM.

Surgical:

The surgical approach is necessary when orthograde endodontic treatment is impossible or ineffective in resolving endodontic pathosis . The OM is especially well suited to endodontic surgery because of its superior ability to magnify and illuminate the surgical site. When directed under the OM, microsurgical scalpels can be used to make accurate, precise incisions. While lighting the site with much higher intensity than an overhead light or headlamp, the OM is used at low power for the initial incision to afford an overview of the entire surgical area. Atraumatic flap management, using the microsurgical scalpel to preserve the sulcular epithelium in sulcular incisions and the Ruddle curette to "reverse elevate" the flap, is best accomplished under relatively low magnification. The magnification can be increased for assessment of the osseous tissue. Slight changes in the color of the cortical plate can help to locate the site of the periapical pathosis. Curettage of the periapical tissue then can be accomplished, and the crypt and root visualized.

Beveling of the root tip can be performed with the Impact Air high speed handpiece, using its specially designed 45 degree angled head and water-only delivery. This avoids the chance of an air embolism due to introduction of air into tissue spaces. Finally, in order to examine the exposed root for fractures, a small applicator brush can be used to apply methylene blue stain.

Retropreparation of the root apex or large lateral canals then can be performed using the ultrasonic retroprep tips. These tips seem to afford much better handling characteristics than the mini-handpieces now in general use for the low speed handpiece. The tips allow a true Class I preparation down the long axis of the root, and accurate preparation of the isthmus between canal apices, if necessary. Other advantages of the retrotips include minimum root bevel and minimum bone removal because these tips are approximately 1/10 the size of the traditional mini-handpiece. The OM allows detailed examination of the apical micro-preparation during the entire procedure.

After the apical retroprep is performed, a thorough examination can be made using the extremely high quality reflective surfaces of small sapphire mirrors. Retro views of the apical preparation are necessary to ensure that angulation of the retrotips is correct and that at least three millimeters of clean dentin are prepared for retrofilling. Using the OM, tags of gutta-percha, cement and involved dentin can be visualized and removed even on the buccal or facial prep wall. Retrofilling of the prep can be accomplished with a series of micro-condensers, burnishers and carvers.

The spectacular clarity of the OM provides a definite benefit in the placement of bone augmentation material, guided tissue regeneration procedures, and routine suturing. Because suturing is critical to the success of these membrane placements and routine surgery, the OM is an invaluable device. Even in routine endodontic surgery, where accuracy of needle placement and tissue edge approximation for primary wound healing are critical, the OM is extremely effective.