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Authors: Dr. S Sai Swethaa, Dr. Subashani, Dr. K Lokesh Kumar

Abstract

The intent of this article is to give a panorama of the use of surgical loupes in the field of Prosthodontics. It is a known fact that magnification in Dentistry improves the accuracy and quality of works in various ways. The precise fit of laboratory completed restorations can also be more easily controlled. Meticulous tasks such as caries excavation, the bonding technique, restorations, periodontics and surgical procedures are all greatly improved by clearer and better vision. Especially in the relatively new field of restorative cosmetic dentistry, with the adhesive technique, a high level of precise work is required. Caries excavation, enamel etching, bond application, as well as the finishing of restorations with special attention being paid to the enamel area and adjacent teeth are all difficult procedures, and are all greatly simplified by using magnifying loupes.The use of microscope-level magnification allows a dentist to see microscopic amounts of elevation of FPD marginal ridges or FPD seating and to identify which adjustments result in microscopic incremental improvements in seating the Fixed dental prosthesis.

Keywords: Loupes, microscopes, Prosthodontics, magnification, cementation.

Introduction

Magnification in general is considered one of the great revolutions in science, and specifically in dentistry. This revolution allowed scientists to undertake precise studies in the natural world and accelerate progress in the fields of medicine and dentistry. The idea of enhanced magnification was introduced to dentistry in the form of an operating microscope in the late 1970s. The Dental Operating Microscope (DOM) was introduced to endodontics in the late 1980s by Dr. Gary Carr. He established that magnification and illumination could be helpful in increasing the success rate of endodontic apical surgeries 1. Regular use of a DOM in various dental specialties was advocated for caries diagnosis and excavation 2, crown margins and post placement 3, surgical incisions, bone and soft tissue grafting procedures 4, and furcation and perforation repairs.
 
FIG 1 Loupes and operator position with loupes FIG 1 Loupes and operator position with loupes
FIG 1 Loupes and operator position with loupes
The surgical operating microscope was introduced in the early 1920s, but it was largely ignored until 1950, when it was reintroduced by Richard A. Perritt for use in microsurgical operations in opthamology5. The magnification and illumination provided by the microscope has resulted in its acceptance as an essential part of the surgical armamentarium. Microsurgical techniques gained widespread acceptance, primarily in otolaryngology, ophthalmology, neurology, and urology, and they play a critical role in surgery to reattach severed extremities.6The application of the operating microscope in clinical dentistry can be traced to Apotheker in 1981.

He converted a medical operating microscope for use in endodontics. Reports by Carr, Arens, Buchanan, Kim, Ruddle, and othersled to the routine use of the microscope in the 1990s for both surgical and standard endodontic therapy. During that time, specifically designed dental operating microscopes became an accepted part of endodontic therapy. Since 1998, competency in the use of a surgical microscope is required for all postdoctoral students in endodontics who complete an accredited training program.

The microscope provided clinicians with improved precision during delicate surgical procedures and resulted in reduced postoperative discomfort. Until recently, the role of the operating microscope in general dental practice has been very limited, involving practitioners who performed a significant number of endodontic or periodontic procedures.7, 8
General dentists have found that it allows for significant enhancement in the precision of restorative and prosthodontic care. Martignoni, in his textbook on prosthodontics published in 1990, was among the first to discuss how the microscope might be useful in operative dentistry. Since that time, several clinicians have suggested that this device can be used to improve tooth preparation and the final restoration in fixed prosthodontics. 9

Magnification systems and surgical loupes

Loupes are the most common form of magnification used in dentistry. Fundamentally, loupes are two monocular microscopes with side by-side lenses that are angled to focus on an object. The magnified image that is formed by the convergent lens system has stereoscopic properties. The disadvantage of loupes is that the eyes must converge to view an image, which can result in eyestrain, fatigue, and even vision changes with prolonged use of poorly fitted loupes.

Magnifying loupes may be wornsuccessfully by most dental practitioners buta period of adaptation is required. There are anumber of different systems available in the market, some more costly than others. It is important that the loupes are correctly fitted, in order to minimize eyestrain.Three basic types of magnification systems havehistorically been used in operating loupes: simpleloupes, compound (Galilean) loupes, and prismaticloupes.

Single-lens loupe: The single-lens loupe is the simplest and most cost-efficient type of loupe. For optical reasons, the distance to the object decreases with increasing magnification. From factor 2× on, this results in ergonomic problems in dentistry.

Galilean loupe: Galilean loupes are the most common type of loupe in dentistry. They have a typical conical shape. The optical system consists of a combination of convex and concave lenses, the working distance of which can be adjusted to the given ergonomic needs. Although the magnification factor is physically limited to 2.5×, it is possible to reach a higher magnification of up to 3.5×, albeit with optical compromises (limited field of vision, blurring around the edges).

(FIG 1)To gain refracting power, magnification, workingdistance, and depth of field, compound loupes use converging multiple lenses with intervening air spaces. Such lenses can be adjusted to clinical needs without excessive increase in size or weight. Compound lenses can be achromatic. The lenses consist of two glass pieces bonded together with clear resin. The specific density of each piece counteracts the chromatic aberration of the adjacent piece, making such lenses a desired feature by dentists. Compound loupes are commonly mounted in or on eyeglasses.

Keplerian (prismatic) loupes: These are characterized by their cylindrical shape. Keplerian loupes consist of a complex convex optic system of lenses and prisms. This system allows various magnifications and working distances. The preferred range of magnification in dentistry is between 3.5× and 6×, in order to minimize the influence of the limited depth of focus. The considerable optical advantage over Galilean loupes is offset by greater weight and higher price.

Prism loupes contain Schmidt or rooftop prisms that lengthen the light path through a series of mirror reflections within the loupes, virtually folding the light so that the barrel of the loupe can be shortened. These loupes are the most optically advanced type of loupe magnification presently obtainable. Prism loupes produce better magnification, wider depths of field, longer working distances, and larger fields of view than other types of loupes.

The barrels of prism loupes are short enough to be mounted on either eyeglasses or a headband, but at magnifications of 3.0 diameters or greater the increased weight often results in headband-mounted loupes being more comfortable and stable than those mounted on glasses. To obtain better optical characteristics and magnification than those achievable with prism loupes requires the use of the surgical microscope.

Typically, dentists will initially use loupes with a magnification of 2.5 x, and employ them for difficult procedures requiring enhanced vision such as endodontic therapy or veneer cementation. After an initial adjustment period, the dentist will begin to use the loupes for all procedures.
 
Fig 2: Explorer and premolar crownduring try-in.
Fig 2: Explorer and premolar crownduring try-in.
 
Fig 3Precise adjustment of a small
Fig 3Precise adjustment of a small


Operating microscope:

The surgical microscope consists of acomplicated system of lenses that allows stereoscopic vision at a magnification of approximately 4–40×. The optical unit of the microscope includes the following components:
  1. Magnification charger
  2. Objective lenses
  3. Binocular tubes
  4. Eyepieces
  5. Lightning unit
  6. Additional attachments
Operating microscopes are designed on Galilean principles. When using themicroscope, there must be an adequate working distance between the microscope and the object being viewed for instruments to be used. The addition of inclinable binocular eyepieces gives a microscope great improvement in manoeuvrability

Loupes versus operating microscope:


Advantages of loupes:
 
  • Ergonomic benefits of an increased working distance from the viewing object as well as increased visual acuity.
  • Loupes are less expensive and initially easier to use.
  • They are also less cumbersome in the operating field and less likely to breech a clean operating field.



  •  
  • Disadvantages of Loupes:
     
    • Include fixed magnification or a lack of magnification variability.
    • Potential need for additional light for magnification levels of 4.0 or greater.
    • Eyes must converge to view an image, which can result in eyestrain, fatigue and even vision changes with prolonged use of poorly fitted loupes.
    • As the length of the loupe increases to provide for more magnification, the weight of the lens also increases which becomes more uncomfortable.


    Advantages of Operating Microscope:
     
    • It offers versatility due to an extended range of variable magnification from 2.5 to 20 and to excellent coaxial fibre-optic, shadow-free illumination.
    • Availability of numerous accessories for digital still and video images for case documentation


    Disadvantages of Operating Microscope:
     
    • Can be more cumbersome to use.
    • More expensive
    • Both the loupes and the operating microscope allow clinicians to perform tasks with improved visual acuity; however, loupes cannot compare to the comfort, versatility, illumination, and visual acuity offered by the microscope.


    Illumination:

    .When using loupes, the surface refraction that occurs through the lens results in a 4% loss of transmitted light and 50% reduction in brightness unless antireflective coatings are used. Several sources of fibre optic light can be attached to hand pieces, instruments, or loupes .10-13

    Role of surgical loupes in Prosthodontics:

    The main objectives of using loupes is to use microscope-level magnification and head mounted coaxial illumination to obtain optimal seating of crowns and bridges and to use magnification and coaxial illumination to properly adjust the occlusion of crowns and bridges.

    The most commonly preferred and used magnification level is 2.5 X for all prosthodontic procedures such as, seating crowns (fig 1), preparing crowns and evaluating the fit of a long span fixed prostheses. However for more detailed procedures such as finishing of single crown preparations the use of clinical microscope has been shown to be a significant aid in quality treatment. When first using the microscope for crown and bridge procedures, the clinician will find that it takes longer to prepare teeth for crowns as compared to conventional technique. It takes time to develop the motor skills necessary to work at higher magnification. Shanelec has observed that with time, the clinician can learn to make movements in the range of 10 to 20 μm (10 to 20/1000ths of an mm). In addition, higher magnification will reveal rough and irregular margins, which causes the clinician to spend more time trying to finish these margins to the ideal. Once the learning curve for positioning the microscope is mastered, the actual time required for tooth preparation is equal to or less than what it was prior to using the microscope.

    The microscope helps the clinician see when the margin is satisfactory. There is no need to indirectly assess (with a dental explorer) whether the margin is on solid tooth structure or if caries or restorative material is on the finish line. The margin is visualized at 10x power and above. After the final margins have been completed, another benefit of the operating microscope is improved tissue management. Whether retraction cord, a laser, or electrosurgery is used, it is easier to determine precisely whether the margin of tooth structure is visible prior to taking the impression. It is of paramount importance to be able to circumferentially view the margins so that a clear impression is obtained. The impression can then be viewed under the microscope and then checked at high magnification for voids, tears, or other discrepancies prior to being sent to the laboratory. The provisional restoration can be trimmed under the microscope, ensuring that the restoration is well adapted and will allow for the healing of the tissues during the provisional stage

    One of the primary reasons crowns may be difficult to seat properly is tight interproximal contacts. Patients will remark that a crown feels tight and return to the office complaining of food entrapment. Interproximal contacts involving gold crowns can be sandblasted. The actual contact can then be viewed at high magnification as a shiny spot on the sandblasted surface. (Fig 2) For porcelain crowns, waxed floss will often leave a remnant of wax at the contact, which again will be visible under high magnification and easily and specifically adjusted. The specificity of adjustments reduces the risk for an open contact after cementation.

    CONCLUSION

    Like any technology there is a learning curve and training and applications are essential. The popularity on the use of loupes and microscopes will likely increase in the future for prosthodontic procedures. Dentists willderive benefits frommagnification, primarily during the preparation and insertion stages of fabricating indirect restorations. The enhanced visual acuity andillumination simplifies many technically difficult tasks. In addition, the clinician is able to practice in a balanced ergonomic position and candocument the procedure with still or video photography.

    Acknowledgement:

    The author likes to acknowledge Dr. Snehal Kadge for her insights in the preparation of this manuscript.

    References:
     
    1. Carr GB, Murgel CA. The use of the operating microscope in endodontics.
    2. Dent Clin North Am. 2010;54:191–214.
    3. Malterud MI. Magnification: you can’t effectively practice minimally invasivebiomimetic dentistry without it. Gen Dent. 2013;61:14–7.
    4. Leknius C, Geissberger M. The effect of magnification on the performance of fixed prosthodontic procedures. J Calif Dent Assoc. 1995;23:66–70.
    5. Shanelec DA. Periodontal microsurgery. J Esthet Restor Dent. 2003;15:402–7.1. Schultheiss D, Denil J. History of the microscope and development of microsurgery: a revolution for reproductive tract surgery. Andrologia. 2002;34:234-241.
    6. van As GA. The use of extreme magnification in fixed prosthodontics. Dentistry today. 2003 Jun;22(6):93-9.
    7. Belcher JM. A perspective on periodontal microsurgery. Int J Periodontics Restor Dent. 2001;21:191-196.
    8. Pecora G, Andreana S. Use of dental operating microscope in endodontic surgery. Oral Surg Oral Med Oral Pathol. 1993;75:751-758.
    9. Martignoni M, Schonenberger A. Precision Fixed Prosthodontics: Clinical and Laboratory Aspects. Chicago, Ill: Quintessence PublishingCo Inc; 1990.
    10. Magnifying loupes in modern dental practice:an updateArticle in Dental update • November 2010.

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