Magnification in Dentistry Stuart A. Caplan, D.D.S.
The use of today’s highly sophisticated dental materials has required a corresponding increase in the technical skills of the operator. Surgical telescopes with high resolution and contrast are replacing plastic lenses of somewhat lesser quality. Moreover, depending on their frame mounting, these ground glass magnifiers are also offering the operator additional comfort and safety. The problem for the dentist, however, is to assess properly the products currently being presented by manufacturers. A detailed description of each device offered by four major suppliers is given relative to true field width and depth, working distance or range, “down time” during prescription changes, usefulness with correction, operator positioning, light admittance, degrees of magnification available, and expense. Photographs of the operator practicing without magnification and then using each of three devices is shown and analyzed. With some exceptions, those instruments providing the most flexibility as regards the above factors are most worthy of the dentist’s consideration.
There is a long list of professional advantages in using magnification. Diagnosis tends. to be more thorough since the dentist is able to easily detect marginal breakdown, invisible cracks in both enamel and restorations, porosity in bonding materials, and caries penetration. (In this regard, it might be noted that magnification may be particularly valuable when used in combination with a fiberoptic system.) Reading and analysis of radiographs could also be more accurate with the use of magnification. In the specialties, periodontists likely value magnification when treating trifurcation areas of maxillary molars and when checking for complete calculus removal. Likewise, oral surgeons and endodontists performing apicoectomies, for example, may feel more confident about their treatment when they have better acuity. In fixed prosthetics, finish lines are more easily defined as are paralleling tooth preparations. Before crown, bridge, or inlay cementation, margins and subgingival fit can be readily analyzed. In operative procedures and especially cosmetic dentistry, magnification seems essential in differentiating the restorative material from tooth structure. Finishing of bonding materials is critical, but it seems that the attention paid to usually difficult subgingival areas might be made easier by the use of magnification. “All right,” you say, “I can see the value of magnification. But what will the patients think? Will they think I’m losing my eyesight? Will I become so dependent on the device that I won’t be able to practice without it? How long does it take to get used to magnification? What is available for dentists, how expensive are they, and which one is best for me?” First, while no one can predict what patients may think, the addition of a magnification device to a dentist already encumbered with gloves, mask, and protective
ention the subject of “magnification” to non-using dentists and you are likely to get a number of replies. “What will the patients think?”, “I haven’t gotten to that stage yet,” “I have good eyes,” and “I’m afraid I’ll become dependent on it” are typical answers. But, rationalizations aside, it appears that dentists (and all human beings for that matter) exist in a dynamic state. Their requirements, both physically and professionally, are changing as the years pass. As the aging process occurs, it is generally accepted that muscular strength diminishes.’ This is particularly noticeable when one who previously had excellent eyesight experiences difficulty reading small print. Failure of the lens to be accommodative in near vision leads to eyestrain, which together with yet another physical demand results in chronic fatigue. The deep back muscles and particularly the paraspinals can be severely taxed as the operator struggles to maintain awkward positions for extended periods.2 Magnification located in the lower third of the lens and with sufficient downward working angle may help relieve back and shoulder stress while eliminating the compulsion to lean over the patient for better vision.3 But postural problems do not seem to be limited to just aging practitioners.4 Even students, with their youthful ability to accommodate, try to increase image size with awkward positions. New York University School of Dentistry has responded to this problem by requiring that a magnification system be included in the sophomore kit. Consultant, Florida Board of Dentistry and Florida Departmenr of Professional Regulatio-Legd. Address reprint requests to Stuart A. Caplan, D.D.S., 1175 Coconut Road, Boca Rnton, FL 33432 O 1330 B. C. Decker Inc.
JOURNAL OF ESTHETIC DENTISTRY/VOLUME 2, NUMBER 1Junuary/February I990
that the manufacturer must beware of in order to deliver a consistent product.’ Design of single lens magnifiers can also be problematic. Limited depth of field as well as the requirement that the operator be either very close to the patient or distance himself with an extension rod off a headband are factors that may have led to the development of surgical telescopes. Optics’ designers must deal with several problems such as the weight of the telescope and light admittance. In the case of surgical telescopes, the designer must coordinate the point of focus with the placement of the scope in front of the eye. The farther away from the eye and the higher the angle off the frame, the more forward is the scope’s center of gravity. The resulting torque manifests itself most noticeably to the operator as discomfort on the bridge of the nose. The more downward the angle and the closer it is to the midline of the body, the more comfortable is the device. Another problem for designers is that of light admittance. Galilean (double lens) systems can only be used up to a certain magnification after which adequate illumination becomes insufficient. So as magnification increases, more light must be obtained by using prisms or mirrors. But the length of the telescope barrel that is necessary to accommodate these additions takes the designer back to the problem of excessive weight. Selective wavelength antireflective coatings, approximating different materials, quality of glass, shrinkage of plastics during processing, borings, material strength, effective seals, and corrosion resistance to infection control solutions are additional problems facing optics’ designers. Unlike surgeons, dentists require special consideration. For example, while the surgeon’s patient is unconscious, the dentist must be able to see over the device in order to maintain eye contact when talking to the patient. Additionally, a dentist’s surgical telescopes must allow him to see over the device in order to monitor the passing of instruments and the activities of personnel. Of particular interest to the dentist concerned with operator positioning is the effect of certain types of surgical telescopes on one’s posture. Performance logic devotees who study stress resulting from faulty operator positioning find that telescopes mounted in the lower third of the lens and with sufficient downward angle allow the head to remain more in line with the long axis between shoulder and hip. The center of body mass is balanced when the use of anti-gravity muscles is minimized.8 Currently, there are several telescopic magnification systems available to dentists. Naturally the choice is influenced by the operator’s age, physical condition, operatory arrangement, type of practice, personal habits, and demeanor. Selecting the proper amount of magnification depends largely on the situation in which it is used. Preparing and paralleling multiple abutments across two quadrants or even comparing anatomic relationships during cosmetic procedures means the scope
eyewear should come as no surprise. Further, the worry that patients might think you’ve acquired some form of eye impairment may be replaced by the attitude, “my dentist is very particular about how he treats me and wants to see every detail.”3 Secondly, there is the question of whether the operator will become completely dependent on magnification. At least one researcher studying perception feels that there is no physiologic dependence associated with the use of magnification and that the operator can always return to practicing with the unaided eye.5 Moreover, just as in the use of the fiberoptic light, the dentist may have become mentally more self-assured once having used magnification. As far as getting used to the device is concerned, it is obviously subject to individual variation. It may be wise to begin in the laboratory by trimming dies, checking impressions and models, or waxing up a cast restoration. Initial patient contact might begin with an oral examination or prophylaxis check. You are establishing a frame of reference in this surreallstic environment into which a mirror, explorer, or handpiece of unusually large size will suddenly appear. Gradually progress to more complex procedures should be made. Should the widely used 2 - 2 Y 2 X magnification be chosen, the operator can expect to use magnification comfortably within a week. Higher power may require correspondingly longer adjustment time. Finally, the questions regarding which magnification systems are best suited to dentists, what their cost is, and how is an appropriate magnifier selected must be addressed. Although there are no pat answers, some principles can be used in order to make prudent judgments. Single plane, flip-down loupes have been used by dentists for a number of years. But while these plastic devices are lighter and less expensive than the ground glass alternatives, they nonetheless present a number of s i g d c a n t problems. Plastics soften at relatively low temperatures, thus producing a far greater index of refraction than glass. They are much more easily scratched than glass. Because of thermal limits and chemical reactions, antireflective coatings are extremely diilicult to apply.6 For the dentist, these physical properties translate to less image resolution and definition when compared to glass. To the manufacturer, the high cost of tooling means that these devices must be mass produced in order to be cost-effective. Finally, there are few materials from which to choose and data on optical grade plastics is rarely supplied by the producers. In contrast, the physical properties of glass are well documented and easily controlled by the manufacturer. The qualities ofglass lenses are centered on the ABBE number (a measure of a medium’sability to bend light relative to the dispersion) and index of refraction. Lead monoxide (PbO)increases the index of refraction as do boron oxide, dunha, fluorides, etc. Scratch and stain resistance as well as chemical, climatic, and thermal ernpansion and conductivity and attenuation are factors 18
Magnification in Dentistry
Table 1. Worklng Distance Options Manufacturer & ??OO No.
Advanced Dental Concepts 369-3698
$569 2x(Gal.) $589 2,35x[Gal.)
Yes 1 day Yes Yes 1 day yes
Designs For Vision 345-4009
$1295 $695 $745 $745
25x(exp.) 3 . 5 (exp.) ~ 2 . 5 (std.) ~ 3.5x[std.) 4.5x (std.)
3.4" 5 3.5 2.5"
4w 3Y4" 3Y2" 2 1%''
Yesf Yest Yest Yest Yest
Yes Yes Yes Yes Yes
Yesf Yest Yesf Yesf Yesf
Yes Yes Yes Yes Yes
Yes Yes Yes Yes Yes
Yes Yes Yes Yes Yes
No No No No No
5wkg days reg. 7for bifoc.
Yes Yes Yes Yes Yes
Keeler Instruments 523-5620
$395 2Sx(Gal.) $895 2.5x(Prsm.) $895 3x(Prsm.)
3" 4" 23"
~Yz",4Yz"§ by req. only Yesx No ~Yz",3W by req. only Yes' No 2.4" Yes" No
No" No" No"
Yes Yes Yes
Yes 1 day Yes 1 day Yes 1 day
Yes Yes Yes
Carl Zeiss Inc. 442-4020
~ $1400 3 . 6[Prsm.)
IYz" @ 14
Yes 1 day
Prot. Side Ergon. Head Lens Nip BChg. Cr Lens Shields Mtng. Strap Coat Up Time Cs
"$20 additional charge t$30 charge added to base price *$19.95extra §Thefirst numbers given apply to a 13Yz" working distance; the second to a 1 6 point. *Additional $55 'While the 2 . 5 ~is double-hinged, the scope does not drop low enough for erect seating. ttSlngle hinge assembly does not allow scope Into lower 3rd of lens.
must encompass the entire oral cavity. The 2-21/2~ surgical telescopes would serve these requirements. Bearing in mind that, as magnification increases, depth and width of field decrease, the dentist may wish to use higher power for single surface procedures or spot checking a margin. Eye and body fatigue are important so it is best to try any device in an operatory setting in order to evaluate body positioning better. Imagine how the operator feels after 2 hours of continuous use. The following is an analysis of four major suppliers of optical instruments to the dental profession. For purposes of comparison and illustration it is presumed that the operator prefers to sit as upright as possible and at the 12 o'clock position. Keeler Instruments Inc. manufactures both a Galilean and prismatic magnification system. The Galilean is a 2.5 x and has a 3" depth of field and a 3%'' width. The company calls attention to a peripheral fade or "halo" included in the width measurement. A recent addition to this model is a clear plastic cap to protect the lens. Its price is currently $395. The "panoramic-wide field" offering comes in a 2.5 x or 3 x and has a 4" field depth in the former, while the latter has a 2-3" depth. Working distance options are shown in Table 1. The width of field of the 3 X is 2.4" and it is priced at $895. Both models come in small, medium, or large metal frames with a choice of silver or gold colors. All models are interchangeable with the frame, may be flipped up out of the way, and are mounted on a stationary PD (interpupillary) bar. The buyer is responsible for placement of any correction, bifocal, or safety lens. Designs For Vision Inc. offers dentists a standard 3Y4" wide 2.5x for $695 and a 2" wide 3.5x priced at
Figure 1. No magnification used. 19
JOURNAL OF ESTHETIC DENTISTRYNOLUME 2, NUMBER 1 JanuurylFebruary 1990
Figure 3. With Designs for Vision surgical telescope, a more relaxed working angle is possible.
Figure 2. Use of prismatic system is demonstrated.
5745 (each without a prescription). A $30 additional charge is made for those operators requiring correction. These prices also apply to the 4.5X, which has a 1%“ width. Designs also supplies a 2.5X and a 3.5X expanded field unit for $1295 (see Table 1).In all cases, their representatives measure the individual for working distance, angle, and interpupillary dimension. It is up to the denast needing correction to provide the company with the ophthalmologist’s prescription. Should a change in the prescription be required, additional charges are incurred. Den-Mat Inc. represents Carl Zeiss optics. Magnificacion of these prismatic lenses begins with 3 . 2 ~and increases to 3-3,3.5,3.6,4.0, and 4.5 X . With 14“being the most popular focal length for dentists, the operator can depend on a 60 mm or 2%’’ width of field in the 3.6X, for example. However, focal length can be set anywhere along a 10-20” range while the depth of field will measure %tU on either side of the selected point. The weight of the unit is 1.3 02, and it comes either on a headband or spectacle mount. Dentists appear to prefm the spectade mount that has a single hinge for iiip up and click stops for returning to the same working angle. Light transmittance is 8596, the dentist provides his own cortection, a carrying case is inchded, and the price is $1400.
Finally, there are 2 x and 2.35X magnifying telescopes produced by Advanced Dental Concepts Inc. This company offers a 5” depth of field beginning at 12” from the operator and extending to a 17” distance for the 2~ with a decrease of 1%”in field depth for the 2.35X. Its double hinge assembly allows the operator to sit erect since they may be tilted into a severe downward angle in the lower 3rd of the lens. Field width is greater than 5”, making observation of the entire oral cavity possible without having to change head position. The dentist is responsible for having the prescription placed in the frame, which includes a counterbalancing elastic head strap and soft silicon nose support. The ground glass lenses are coated in order to eliminate shadows while enhancing brightness and definition. Gold or silver stainless steel frames are available in several sizes and the price for the 2X is $569, while the 2.35X costs $589. Lateral adjusting knobs allow the convergence angle of the left scope to be set slightly less acutely than the right so that when the operator turns the center interpupillary knob and the right and left images superimpose, the result is a stereoscopic effect.9 The ability to increase the width of field quickly, exchanging scopes, same-day prescription mounting, use with bifocal cor20
Magnification in Dentistry
neck and lower back following an extended appointment. Figure 3 shows a more relaxed working angle in the Designs For Vision surgical telescopes. However, the telescopes are fixed to the lens and consequently the entire spectacle must be removed when not in use. Permanent cementation to the lens usually requires 8 working days for prescription changes and subsequent “down time.” Finally, Figure 4 shows the Orascoptic Telescopes by Advanced Dental Concepts. The double hinge assembly allows the operator to sit fairly upright when looking down but still see over the top of the scopes without changing head position.
CONCLUSION If, indeed, dentists and dentistry exist in a dynamic state, then their physical and professional requirements are ever changing. With this in mind, a prudent choice in magnification would be the system that is most flexible. The device should allow for standing or sitting procedures, preparing teeth or taking impressions, slight patient or operator movements, distance from contaminating aerosols, and as wide and deep a field as possible.
1. Friedman LW. Freedom from backaches. New York: Simon and Schuster, 1983:4445, 6243. 2. Shugars D, Miller D, Williams D. Musculoskeletal pain among general dentists. Gen Dent 1987;35:272-276. 3. Strassler HE, Kaim JM, Ibsen RL. Magnification in dentistry. Academy of General Dentistry Transcript, March 1988:7,6. 4. Goldman HS, et al. Occupational hazards in dentisty. Chicago: Year Book Medical Publishers, 1984133-150. 5. Coren S. Human perception. Lecture, Fourth Annual International Symposium on Performance Logic and Performance Simulation Training In Dentistry, University of British Columbia, July 25-28, 1988. 6. Palmer CH. Optics experiments and demonstrations. Baltimore, MD: The Johns Hopkins Press, 1969:99-103. 7. Musikant S. Optical materials; an introduction to selection and application. New York and Basel: Marcel Dekker, 1985:152. 8. Beach DR. 0 Concept for Health and Health Care. Monograph, 4th Annual International Symposium on Performance Logic and Performance Simulation Training in Dentistry, University of British Columbia, July 25-28, 1988. 9. Welford WT. Optics. 3rd. Ed. London: Oxford University Press, 1988.
The Orascoptic Telescopes.
rection, flip up capacity, and instant change of working angle are additional features. Selection of an appropriate optical device depends on the operator’s physiologic requirements. If the operator is seated, the mounting of the telescopes must allow him to both sit as upright as possible while looking down as well as be able to see instruments, the patient, and office personnel when looking over the top of the scopes. Figure 1 shows the dentist working without magnification. This typical posture held over an extended treatment time may produce muscular strain in the neck, shoulders, and lower back. In comparison, Figure 2 represents the use of prismatic systems produced by both Keeler and Zeiss. Notice the “chin on chest” working angle. Again, tension could result in the