General Information

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.

Medical grade digital cameras (which produce an image as a series of "1"s and 0"s) are available from several manufacturers. Attached to dental microscopes, the cameras produce VL (visible light or photographic) images. These high-tech cameras provide single frame capture as well as motion digital video from the operating microscope directly to the computer via the USB (Universal Serial Bus), the serial port or a memory card.

Digital Radiography:

There are three methods of producing digital images: CCD/CID/CMOS sensors, phosphorus plates and scanning of conventional film. All three systems are available in periapical, panoramic and cephalometric sizes. This digital radiography equipment uses conventional generation devices to produce x-ray energy. Direct digital radiography and phosphorus plates have many advantages over silver halide film, such as speed, reduced radiation, environmental waste reduction, elimination of darkroom costs, lossless e-mail image transfer and enhanced practice image.

The value of instant digital imaging in the modern dental office, especially for endodontic and implant procedures is well known. "Several phosphorus and CCD/CMOS digital systems have good-to-very-good image quality, plus ease of use, and image enhancement capabilities that make them competitive with conventional film in overall usefulness." However, according to the CRA Associates, the image quality of digital radiographs still does not measure up to the sharpness and detail of silver halide film. Conventional film provides a finer grade of detail through continuous shades of black-and-white images, rather than discrete shades of gray used by digital systems. Advances are being made (digital subtraction radiography , improved resolution), though, and digital image quality may equal or surpass that of film in the future. As Dunn and Kantor stated in their review of the subject, "digital imaging has many potential benefits yet to be fully explored or demonstrated."

Resolution:

One of the most critical - and most misunderstood - issues concerning digital representation of image data is resolution. While computer screen selection, ambient lighting and image compression all affect resolution, the most compelling issue is the image quality of dental structures as viewed by the clinician. According to a study by Clinical Research Associates on dental imaging quality, some currently available systems were ranked using a scale of 1-10. Film ranked highest at 8.7. The second highest ranking was a film scanner that achieved an image quality score of 7.0, but is dependent on the quality of the original film-based image. The digital radiography systems ranked slightly lower for image quality in dental applications with scores ranging between 6.5 and 3.0.

The quality of many film-based images, on the other hand, is compromised by operational problems such as chemical and film freshness, developing inconsistencies, light leaks, and shipment handling. Detection of gross and moderate caries can be performed with both conventional film and digital imaging systems with a great degree of surety. For incipient caries detection, film sharpness and detail are still helpful adjuncts to digital systems. Unfortunately, the presence of caries are always more extensive than depicted by either digital or film systems. Incipient caries and some periapical lesions continue to present a challenge for both film and digitally based systems.

In the detection of periapical bone lesions created in cortical and trabecular bone, no difference was detected by Paurazas, et al. between E-speed film, CCD and CMOS sensors. Furthermore, cortical bone lesions were detected with significantly higher accuracy once the junction of the cortical plate was involved or perforated.

Radiation:

Digital imaging generally requires less radiation than film-based systems. According to the CRA Newsletter, CCD/CID/CMOS sensors can reduce exposure by up to 82 percent. Phosphorous plates reduce radiation by up to 22 percent compared with conventional film . Foroughi et al. noted reduced radiation averaging 55% when compared to Kodak D speed film and an average of 45% reduction when compared to E speed film. Film scanning provides no dose savings because a conventional film image must first be produced.

Time-to-image and time-to-retake: Conventional film and phosphorous plates takes at least a minute to process after the film is transported to the developing site and unwrapped, while CCD/CID/CMOS sensors are virtually instant, with paint times usually completed in less than four seconds. If the image is unsatisfactory or a second view is required, a second image can be generated using the CCD/CID/CMOS sensor by simply repositioning the x-ray tube head and/or sensor and exposing another image. Phosphor plates and films require considerably more time to produce the first image; time-to-retake is thereby increased, with less assurance that the second image will be at the desired angle. This improved workflow pattern using CCD/CID/CMOS sensors will enhance staff utilization and reduce patient waiting time for retakes. Dedicated film scanners generally take ten seconds to process a developed film.

Optimization:

All digital radiographic systems allow for image optimization. Most feature the ability to change contrast/brightness to view images that are under or over exposed, create an inverse image, equalize density, magnify and allow for image rotation and mirror imaging. Image annotation is another advantage of digital radiography. Some programs allow creation of markers or notes that will place descriptive annotation with numbered pointers, to call attention to specific details in the image. Algorithms that can sharpen and enhance caries are also present in a number of systems, holding promise for even more future improvements. Another enhancement, pseudo coloring ascribes false colors based on brightness of pixels and can help with patient visualization of images.

Measurement: Three types of measurement available with digital images: linear measurement, which allows the practitioner to measure the distance between two points in millimeters; angle measurement, which measures the angle between to lines; and area measurement, which measures the area of the image or a segment of the image. Since magnification and distortion error play a significant role in all radiographic measurement accuracy, both film and digital systems subject to error. A recent study by Eikenberg and Vandre demonstrated that „measurement error was significantly less for the digital images than the film-based images when comparing images of human skulls taken with a custom jig. However, the authors point out that in clinical situations, these measurement differences may not be clinically significant. Measurements are based on magnification and distortion error, so there is no statistical significance between conventional film and direct digital radiography. Sophisticated calibration algorithms are under development, so that accurate measurement of parallel images should be more feasible in the future.

Security:

While film based images can easily be produced in duplicate, each subsequent rendition of the image will be reduced in quality. Digital images, on the other hand, can be reproduced in unlimited quantity because the images are stored and produced without loss of any detail. Furthermore, digital images can be stored on and off site, on many types of media, thereby helping to mitigate theft, fire or other damage to records.

Paradoxically, the ease of reproduction and storage of digital images allows for the alteration of radiographs without a trace. The ease of producing an altered image is controversial, but improved safeguards are under development. Archiving radiographs in the form of write-once, read-many formats, such as the now ubiquitous multi-session CD-ROM recorder are among the current solutions to this issue. These CD-ROMs can be stored off site by a third party archivist. When sent through the Internet, this data is also vulnerable. The two technologies available today to encrypt this data, either SSL (Secure Socket Layer) or digital certificates, can provide at least 128 bit encryption and virtually eliminates the chance of alteration or fraud. SSL connections to Internet servers can be recognized by the prefix "https://" in the address line.

Markers:

Occasionally, radiographs and VL images warrant a tag so that you can return to them later to assemble teaching or patient education materials. Most software today allows markers to be placed so that a computer search can call up the images efficiently. In addition, readily available software enables you to create notes and diagrammatic annotation of important features of an image.

Computer Interface:

While each of the intraoral direct or wired digital radiography systems requires connection to the computer, only Schick Technologies&Mac226; system connects directly to the USB port of the CCW, thereby eliminating the input board and simplifying installation and maintenance. Laptop configurations add flexibility if the practitioner wants to move the equipment between different operatories and office locations, or use it for off-site procedures at hospitals and nursing homes. They also benefit from the elimination of special cards for sensor connection.
 

Ultrasonics

Root Apex Locators

System B

Electronic Handpiece

• American Academy of Cosmetic Dentistry
• American Academy of Implant Dentistry
• American Academy of Orthodontists
• American Academy of Pediatric Dentistry
• American Academy of Periodontology
• American Academy of Prosthodontists
• American Association of Dental Schools (AADS)
• American Association of Endodontists
• American College of Prosthodontists
• American Dental Association
• British Endodontic Society
• British Dental Association
• Canadian Dental Association
• F.D.I. World Dental Federation
• International and American Association for Dental Research (I.A.D.R.)
• Sociedad Italiana de Endodoncia