Magnification Systems

A variety ol simple and complex magnification systems are available to dentists, ranging from simple loupes to prism telescopic loupes and surgical microscopes, liach magnification system has its sped lit advantages and limitations. Although magnification improves the accuracy ol clinical and diagnostic skills, it requires an understanding of optical principles that govern all magnification systems lhe assumption that more magnification is better must always be weighed against a decrease in field of view and depth of focus that can occur as magnification increases. Ibis is a problem more common with dental loops than with surgical operating microscopes.

Magnifying Loupes

Dental loupes tire by tar the most common system ol optical magnification used in periodontics. Loupes are fundamentally two monocular telescopes with side-by-side lenses converged to focus on the operative field. The magnified image they form has stereoscopic properties by virtue of their convergence. A convergent lens optical system is also called a Kcplcrian optical system.

Although dental loupes are widely used, they have a considerable disadvantage. Ihe clinician's eyes must converge to view the operative field. Ibis may result in eyestrain, fatigue, and even pathologic vision changes, especially alter prolonged use of poorly fitted loupes.

I hree types of Keplerian loupes are commonly used in periodontics: simple or single-element loupes, compound loupes, and prism telescopic loupes, l-.ach type may differ widely in optical sophistication and individual design.

Simple Loupes. Simple loupes consist of a pair of single meniscus lenses (lig. 67-1). Simple loupes are primitive magnifiers with limited capabilities. I acli lens is limited to just two refolding surfaces. Only increasing their lens diameter or thickness can increase their magnification. Size and weight limitations make simple loupes impractical for magnification beyond 1.5 diameters. Another disadvantage of simple loupes is that they are highly affected by spherical and chromatic aberration, which distorts the shape and color of, objec ts being viewed.

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Fig. 67-1 Simple loupes.
Fig. 67-2 Compound loupes.

Compound Loupes. Compound loupes use multielement lenses with intervening air spaces to gain additional retracting surfaces (Fig. 67-2). This allows increased magnification with more favorable working distance and depth of field. Compound loupes can be adjusted to some clinical needs without excessive increase in size or weight.

In addition to ottering improved optical performance, compound lenses can be achromatic. This is an optical feature that c link lans should always choose when selecting magnifying loupes. Achromatic lenses consist of two glass lenses, joined together with clear resin. I be specific density of each lens counteracts the chromatic aberration of its paired lens to produce a color-correct image. Multi-element compound loupes become optically inefficient at magnifications above 3.0 diameters.

Prism telescopic Loupes. Ihe most advanced type of loupe magnification currently available is the prism telescopic loupe. Such loupes employ Schmidt or rooftop prisms to lengthen the light path through a series of switchback mirror reflec tions within the Jens elements. I his arrangement literally folds light so that the barrel of the telescopic loupes can be shortened. Prism loupes produce better magnification, wider depths of field, longer working distances, and larger fields ot view than other types of loupes. I he barrels of prism loupes are short enough to be mounted on either eyeglass frames (Fig. 67-3) or headbands. However, the increased weight ot prism telescopic loupes with magnification above • makes headband mounting more comfortable and stable than eyeglass frame mounting. Recent inno-

Fig. 67-3 Eyeglass-mounted prism loupes.
Prism Telescopic Dental Loupes
Fig. 67 4 Coaxial lighted prism loupes.

vat ions in prism telescopic loupes include coaxial fiberoptic lighting incorporated in the lens elements to improve illumination (I'ig. 67-4).

Magnification Range of Surgical Loupes

Dental loupes provide a limited range ot magnification (1.5> to l()x). Those delivering magnification ol less than 2.5x are usually inadecpiate for the visual acuity necessary tor periodontal microsurgery. Those providing magnification of more than 4.5x are awkward to use because ol their small field of view, shallow depth of focus, and excessive weight. I he latter makes it quite difficult for «i surgeon to maintain a stable visual field.

For some periodontal procedures, prism telescopic loupes with magnification ot 4x provide an adequate combination of magnification, field ol view, and depth of focus. However, the surgical operating microscope provides much higher magnification and superior optical properties than any of the loupe optical systems previously discussed.

The Operating Microscope

The surgical operating microscope provides superior magnification and better optical performance compared with dental loupes (Fig. 67-5). Although the microscope is expensive, it is durable and can withstand an entire clinical career. \n operating microscope requires a period of adjustment to reach clinical proficiency, but it offers far better clinical performance and versatility than loupes. Operating microscopes designed for use in dentistry

878 PAR I S ■ hcatmciit of Paioilontol Diseuse employ Galilean optical principles1 and have binocular eyepieces joined by offsetting prisms with parallel optical axes. Galilean optics allows stereoscopic viewing of the operative field without eye convergence. I bis positions the eyes as il they were focused on infinity to permit a relaxed viewing of the operative field without eyestrain or fatigue. I he operating microscope incorporates fully coated optics with achromatic lenses to provide the highest optical resolution with the most efficient illumination.

Perhaps the greatest advantage of the surgical operating microscope is its ability allow the dentist to easily change working magnification to a level appropriate lor the clinical task at hand.* Operating microscopes have a rotating variable magnification element that easily varies magnification to match the immediate surgical demands. Some operating microscopes incorporate electronic loot-controlled locus and magnification for further convenience. Because Ihe optical elements of surgical microscopes are more sophisticated than those found in loupes, depth-of-focus and field-of-vievv characteristics are qtiite enhanced.

I lie periodontal surgeon must establish adequate working distance between the surgical field and the microscope objective lens. I bis permits the surgical assistant to retract tissues and to irrigate or evacuate the surgical site. Such assistant aided control of surgical access is essential for microsurgical visibility. Assistant eyepiece attachments are available lor .ill surgical microscopes and can greatly aid the progress of microsurgical procedures. Surgical microscopes are available with objective lenses with various working distances. The useful range in dentistry is 250 to .*50 mm. Because operating with indirect mirror vision adds 100 to 150 mm to the working distance, a ready means of changing working distances is valuable. Quick-change objective lenses are available for many surgical microscopes.

for practical use in periodontics, the surgical microscope must have both maneuverability and stability. Microscope mountings «ire available for ceiling, wall, or floor. Inclining eyepieces also lend flexibility to the clinical use of the surgical microscope in periodontics. Maneuverability must always be sufficient to meet the c linical requirements for visual access to the various posterior regions of the oral cavilv and Ihe anatomic tissues dealt with during periodontal microsurgery. Optical performance of most microscope lenses is almost identical. Maneuverability is, therefore, more important than optical configuration in choosing an appropriate microscope tor periodontal microsurgery procedures.

Illumination of the microsurgical field is an extremely important consideration. Periodontists are accustomed to lateral illumination from side-mounted dental lights. ( Hnicians who work with loupes often require a headlamp to compensate for the decreased light-gathering ability of loupes compared with normal vision. ( oaxial fiberoptic illumination had been a major advantage of the operating microscope over surgical loupes, ( oaxial lighting positions the light source exactly parallel to the microscope's optical axis. With coaxial lighting, no shadows are produced. The surgeon can view perfectly the deepest reaches of the oral cavity, including into subgingival pockets and angular bony defects. Definitive visualization of root surface deposits and irregularities is only possible at magnification levels provided by a surgical microscope. Through the microscope, surgeons can view normal and abnormal periodontal anatomy never before possible. Clinical decisions can be made based on certain visual knowledge of altered or normal anatomy rather than based on blind educated guesses.

Documentation of periodontal procedures has become increasingly important for dental-legal reasons as well as for patient and professional education. The surgical operating microscope is Ideal for documenting periodontal pathology and procedures of all types; TS-mni slides can easily be produced using a beam splitter camera attachment dig. 67-6). With a foot-operated shutter control, the surgeon can compose the photographic field as the procedure unfolds without interrupting the surgery. In addition, the photographic slide represents the surgical field exactly as seen by the surgeon, as opposed to a photographer's view produced over the surgeon's shoulder as he or she works. Excellent video documentation is also available through the operating microscope using a video beam splitter attachment. High-resolution cameras with video and slide printers are currently replacing TS-mm camera photography In many microsurgical disciplines. High-resolution digital video cameras bring new capabilities for live or recorded video of periodontal procedures for educational purposes.

Continous Beam Diagram
Fiq. 67-5 Surgical operating microscope.

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