1
The Dental Operating Microscope

Frank Setzer

Key Concepts

• Parts and functions of the dental operating microscope.
• Advancements in dental microscopy.
• Applications of the dental operating microscope in endodontic microsurgery.
• Individual adaptation of the dental operating microscope (parfocaling).

Endodontic therapy is performed in a naturally dark and confined working space. Operating microscopes were introduced into Endodontics in the early 1990s, and then into endodontic specialty programs in the United States. Since then, operating microscopes have become widely accepted by endodontists and are also increasingly being used by other specialists. The American Association of Endodontists made teaching the operating microscope a required standard for postgraduate endodontic education in 1998. The standard now requires the instruction in using magnification devices "beyond the scope of head worn magnification devices", at an in-depth level, which is the highest of the levels of knowledge described by CODA.

Higher magnification was demonstrated to significantly increase the successful outcome of endodontic surgery. Both the operating microscope and endo-scope provide appropriate magnification and illumination that is required to perform surgical and non-surgical endodontic procedures with high success rates. Moreover, from an ergonomic perspective, a microscope can allow the clinician to maintain an upright position, which can help avoid long-term back and neck problems that may range from general discomfort to disability (see Chapter 22).

1.1 Benefits of the Operating Microscope

Loupes and microscopes offer different ranges of magnification (Figure 1.1). An increase in magnification decreases the focal depth. Wearing loupes, especially at magnifications higher than ×4, requires the practitioner to stay in a narrow range from the object to stay in focus. In contrast, even at high magnifications, a microscope remains stable and the practitioner can work in an upright and ergonomically non-stressful position. Moreover, microscope use reduces strain on eye muscles, fatigue, and soreness compared to loupes. Through a microscope the light reaching the left and right eyes appears to be essentially parallel, achieving the effect of far distance observation (Figure 1.2) and avoiding short accommodation stress as with the naked eye. Binoculars of loupes and thus the viewing direction are convergent, resulting in similar eye strain. In addition, microscopes provide imaging virtually free of shadows, allowing excellent image quality for clinical operations and documentation.

Figure 1.1 Comparison of magnification ranges: loupes versus microscopes.

Figure 1.2 Comparison of ocular angles and viewing directions of loupes and microscope.

Figure 1.3 Key microscope features (Penn Dental Endodontic Clinic).

1.2 Key Features of Operating Microscopes

Basic components of an operating microscope are binoculars, microscope body with magnification and fine focus adjustments, and a light source (Figure 1.3). Depending on usage and preferences of the practitioner, a microscope can be further configured to individual specifications. For non-surgical and surgical endodontics, different magnification ranges are required (Table 1.1). In addition, surgical procedures will require more angulations to view resected root surfaces and other anatomical details. At a minimum, a microscope being used for surgical endodontics should be equipped with 180°-tiltable binoculars to address the angulation requirements and an eyepiece with a reticle. A reticle is a set of fine lines that provide proper centering on the object in focus and allows for individual calibration (parfocaling) of the microscope, most commonly in the shape of cross-hairs or concentric rings.

Table 1.1 Recommended magnification ranges for different stages of non-surgical and surgical endodontic treatment.

Orientation

Inspection of surgical site

Initial osteotomy

Ultrasonic tip alignment

Suturing (6.0+)

Suture removal

Access

Orifice identification

Fracture identification

Obturation

Hemostasis

Tissue removal

Root tip identification

Root tip resection

Root surface inspection

Root end preparation

Root end filling

Root amputation

Orifice identification

Fracture identification

Calcified canal location

Identification of fine anatomical details

Documentation

Root surface inspection

Root end preparation inspection

Root end filling inspection

Identification of fine anatomical details

Documentation

1.3 Customizing a Microscope

Microscopes are available as floor-standing, wall- or ceiling-mounted units, depending on personal preferences and possible locations in the operatory. Modern microscope innovations allow for upgrades or modifications of standard microscopes. For example, in the past, a microscope was delivered with a fixed focal distance, typically 200 mm, 250 mm, or 300 mm, depending on the height of the practitioner and his or her most comfortable and appropriate working position. However, top of the line microscopes today include a variable focal distance that can be adjusted to practitioner and patient, often in conjunction with electrical zoom and fine focus options that allow smooth and step-less adjustments of both magnification and focus. Recently, mechanical focal distance adjusters were introduced to upgrade microscopes with a fixed focal distance (Figure 1.4).

Figure 1.4 Variable focal distance adjuster (ZEISS Varioskop®; Penn Dental Endodontic Clinic).

Optional ergonomic upgrades allow a left/right swivel of the main body of the microscope. This will allow the practitioner to tilt the microscope in a vertical angulation without changing the horizontal level of the eyepieces. In particular, for endodontic surgery, this is a valuable feature to observe root tips and resected root surfaces in the posterior arches. Other major potential upgrades include extendable (foldable) binoculars for better visualization and ergonomics (Figure 1.3), magnetic arrest functions (clutch) for increased stability, as well as different light sources and documentation options, which are described in greater detail in Figure 1.5).

Figure 1.5 Top of the line microscope with electrical zoom, fine focus, and magnetic arrest functions, 3-chip HD video camera (TRIO 610) attached to right documentation port (ZEISS PROergo; Penn Dental Endodontic Clinic, Surgical Suite).

1.3.1 Light Source

Halogen lighting was the first dental microscope light source introduced. It is still available for standard applications and basic microscopes and displays a yellowish hue. Xenon and the more recent LED light sources were developed to deploy better illumination to the operating field. All three light sources differ from each other in light intensity, peak wavelengths, color temperature, heat emission, and lifetime.

Xenon light sources appear almost as natural as daylight while providing the highest light intensity. This ensures the best illumination for fine anatomical details and allows shorter documentation exposure times, which will provide sharper images.

LED light sources are similar to xenon in color temperature and appear close to natural daylight. In comparison to xenon and halogen the heat emission from LED radiates from the back of the light source, resulting in a greatly reduced temperature surrounding the microscope. Table 1.2 provides an overview of the light spectra, appearance, color temperatures, intensities, and average lifetimes of the three light sources. Most microscopes provide additional orange and green filters for restorative work or surgical procedures with increased blood flow. Recent developments include depolarization and daylight UV filters, as well as fluorescence for caries detection.

Table 1.2 Comparison of microscope light sources.