Endodontics Instruments and Armamentarium: Visual Enhancement - JAMES K. BAHCALL
Visualization during surgical and conventional endodontic treatment has historically been limited to two-dimensional dental radiography representative of a three-dimensional biologic system and what could be seen with the naked eye (perhaps enhanced by loupes). Today, endodontic treatment is to a large extent viewed as a microsurgical procedure. The principle upon which all microsurgery is based is the observation that the hand can perform remarkably intricate micromanipulations as long as the eye can see a magnified field and it can be interpreted by the mind.1 Magnification affects vision by increasing the size of an image on the retina. "Visual image" is the basic parameter used to describe how large something appears, and is expressed in units of degree or cycles/degree.2 The use of optical magnification instruments such as loupes, microscopes, endoscopes, and orascopes enables the endodontist to magnify a specified treatment field beyond that perceived by the naked eye.
Working Distance: The distance measured from the dentist's eye to the treatment field being viewed.
Depth of Field: The amount of distance between the nearest and furthest objects that appear in acceptably sharp focus.
Convergence Angle: The aligning of two oculars to be sure they are pointing at the identical distance and angle to the object or treatment field.
Field of View: The area that is visible through optical magnification.
Viewing Angle: The angular position of the optics allowing for a comfortable viewing position for the operator.
Dental loupes are the most common magnification system used in dentistry. All loupes use convergent lenses to form a magnified image.3 The simplest form of optical magnification is single-lens loupes (ie, jeweler's flip-down magnifiers). Single lenses have a fixed focal length and working distance.4 The advantages of these types of loupes are low cost and light weight as they are made of plastic. The disadvantage of single-lens loupes is poor image resolution compared with multi-lens glass optics (telescopic loupes and microscopes).5 Because single-lens loupes provide a set working distance, the dentist may find the ergonomics incorrect and may need to compensate with poor body posture, causing the possible neck and back strain.
In order to overcome the disadvantages of single-lens loupe optics, the use of multi-lens optic system is recommended. This type of glass multi-lens configuration is known as a Galilean optical system (Figure 1). It provides a higher level of magnification, improved depth of field and working distance, and higher optical resolution compared with single-lens optics.4 Telescopic loupes use Galilean optics. Ideal magnification with telescopic loupes is ×2.5. This offers a good compromise between weight, optical performance, and cost. Galilean lens systems cannot offer magnification much greater than ×2.5 without incurring weight, size, and image resolution problems.5 Silber recommends the use of ×2.5 operating loupes because magnification of loupes greater than ×2.5 limits the depth of field and working distance during treatment.1 Any head movement of the operator, while using loupes with magnification greater than ×2.5, will move a treatment field in and out of focus, very distracting and irritating to the clinician. When need for higher magnification is required (up to ×6), prism optics are
[Figure 1. Diagram of Galilean optics.]
available. This optical system is based on the Keplarian astronomic telescope, which uses five lenses and two prisms. The advantages of this optical system are superior optical clarity and a flatter view from edge to edge. However, the disadvantages are expense and added weight to loupes.5 And as the magnification in loupes increases, the need for more illumination is required.6 Loupe manufacturers have designed portable clip-on light sources to accommodate demand for increased light.
Figure 1. Diagram of Galilean optics. Illustration courtesy of Designs for Vision, Inc., Ronkonkoma, NY.0
Baumann7 was the first to report the use and benefits of an operating microscope for conventional endodontics. Since then, the use of the surgical operating microscope (SOM) has evolved in the field of endodontics as an invaluable optical magnification instrument8-10 (Figure 2). Today, this visual evolution in endodontics, from using loupes and headlamps to the use of the microscope, parallels a similar transition in medical specialties, such as ophthalmology and neurosurgery.11 On January 1, 1998, the American Dental Association Accreditation Standards for Advanced Specialty Education Programs in Endodontics were revised; formal microscope training must be included in surgical and nonsurgical endodontic treatment.11
The magnification needs in endodontic treatment range from ×3 to ×30.12 A SOM accommodates these magnification requirements. Although loupes can have a magnification as high as ×6, they are not able to provide the same depth of field at ×6 magnification compared with the microscope,1 and fiber optic light source of the SOM provides two to three times the light emitted from a surgical headlamp.13
Similar to loupes, microscopes use the Galilean lens system. The magnification of the SOM is
[Figure 2. Clinical use of surgical operating microscope.]
[Figure 3. A schematic diagram of the surgical operating microscope. The eyepiece connected to binocular field glasses allows adequate focal length. The objective lens increases the magnification. The magnification changer adds to the flexibility of the microscope.]
determined by the magnification power of the eyepiece, the focal length of the binoculars, the magnification changer factor, and the focal length of the objective lens (Figure 3).12,14 The eyepiece has adjustable diopter settings ranging from -5 to +5. Diopter settings help the clinician focus the lens of the eyes and adjust for refractive error, which is the degree to which a person needs to wear corrective eyeglasses.12
The benefits of using an SOM for optical magnification in conventional endodontic treatment are well documented in the literature.15-19 They are increased visualization of the treatment field, enhanced visualization in locating canals, aid in the removal of separated instruments, diagnosis of micro fractures, perforation repair, and case documentation.
The advantages of using an SOM during surgical endodontic treatment are enhanced view of the surgical treatment field, need for taking fewer radiographs during the surgical procedure, and the ability to document the treatment.20
When viewing an endodontic treatment field through a microscope, the use of a standard dental mirror or micromirror is usually required, in conjunction with the microscope, to overcome the angulation difficulties of certain tooth positions in the mouth. Saunders and Saunders15 have stated that the most common reasons for endodontists not using the SOM during treatment: positional difficulties, inconvenience, and increased treatment time.
Figure 2. Clinical use of surgical operating microscope. Photo courtesy of Jedmed, St. Louis, MO.0
Figure 3. A schematic diagram of the surgical operating microscope. The eyepiece connected to binocular field glasses allows adequate focal length. The objective lens increases the magnification. The magnification changer adds to the flexibility of the microscope.0
The use of a rod-lens endoscope in endodontics was first reported in 1979.21 In 1996, the rod-lens endoscope was recommended as a magnification instrument for conventional and surgical endodontic procedures.22,23 The rod-lens endoscope (Figure 4) is made up of rods of glass working in junction with a camera, light source, and monitor (Figure 5). The option of a digital recorder (either streaming video or still capture) may be added to the system for documentation.
The rod-lens endoscope allows clinicians' greater magnification than that achieved with loupes or a microscope, with optical resolution comparable with that of microscopes and/or loupes. Although the endoscope can be used as a visualization instrument for conventional endodontic treatment, it can be bulky and difficult to maintain a fixed field of vision compared with a microscope. A fixed field of vision is defined as "viewing a treatment field from one single angle and distance."24 The use of the endoscope is therefore recommended for visualization of surgical endodontic treatment.22-27 The
[Figure 4. A rod-lens endoscope (Jedmed, St. Louis, MO).]
[Figure 5. Endoscope visual system (EVS) (Jedmed, St. Louis, MO).]
visualization advantage, in surgical endodontic treatment, the endoscope provides over the microscope, is the ability to view a surgical treatment field in a nonfixed field of vision. This is defined as the ability to view a treatment field at various angles and distances without losing depth of field and focus.24
The recommended rod-lens endoscope sizes, for endodontic surgical application, are a 2.7 mm lens diameter, 70° angulation, 3 cm length rod-lens, and a 4 mm lens diameter, 30° angulation, and 4 cm length rod-lens.24 A pair of ×2 to ×2.5 loupes should be used for visualization prior to the use of the endoscope.1,24 Loupes aid the endodontist during surgery when reflecting gingival tissue, removing cortical and medullary bone, and isolating root ends. The clinician should hold the endoscope while the assistant retracts gingival tissue and suctions.24 This maintains good eye-hand coordination during examination or treatment. The clinician and the assistant(s) view the magnified image on the monitor.
Hemostasis of the surgical field must be obtained before the endoscope is used because the scope cannot provide a discernible image when placed in blood. The warmth of the blood can also create lens condensation and a blurred image. If this occurs, the use of suction and irrigation, or an antifogging agent, will eliminate the fogging effect. The tips of the endoscope should be placed on bone around the surgical crypt in order to stabilize the scope. Prior to usage, a protective metal sheath is placed over the endoscope to add rigidity and allow the endoscope to be held in a stable position. It is not recommended to use the endoscope to also retract gingival tissue while viewing a surgical treatment field. This will not allow free movement of the scope by the operator while also having difficulty keeping the gingival tissue out of the line of sight.
Figure 4. A rod-lens endoscope (Jedmed, St. Louis, MO).0
Figure 5. Endoscope visual system (EVS) (Jedmed, St. Louis, MO).0
An orascope is a fiber optic endoscope and like the rod-lens endoscope works in injunction with a camera, light source, and monitor. Fiber optics are made of plastics and therefore are small, lightweight, and flexible. It is important to note that image quality from fiber optic magnification has a direct correlation with the number of fibers and size of the lens used. The fiber optic endoscope is designed for intracanal visualization.28 The orascope has a 0.8 mm tip diameter and 0° lens and the working portion is 15 mm in length (Figure 6). The orascope is
[Figure 6. An orascope (Jedmed, St. Louis, MO).]
[Figure 7. Cross-section of orascope probe showing the distribution of fiber optic image bundle and the light transmission fibers.]
made up of 10,000 parallel visual fibers. Each visual fiber is between 3.7 and 5.0 μm in diameter. A ring of much larger light transmitting fibers surrounds the visual fibers for illumination of a treatment field (Figure 7).
Prior to the placement of the 0.8 mm fiber optic scope, it is recommended that ×2 to ×2.5 loupes or a SOM be used for conventional endodontic visualization during access to the canal(s). A canal must be prepared to a minimum size of a 90 file in the coronal 15 mm of the canal. If the canal is under-instrumented, a wedging of the orascope may damage some of the fiber optic bundles within the scope. The proper canal enlargement also allows the full 15 mm of the scope to penetrate within the canal. The canal must also be dried before the 0.8 mm fiber optic scope is placed. Although the scope will see through sodium hypochlorite, this solution has a high light-refractory index. This will cause greater amounts of light that will be reflected, thus making it difficult to see details of the canal.
The focus and depth of field of an orascope is from 0 mm to infinity. This allows the orascope to provide imaging of the apical third of the root without actually having to be placed in this region of the canal.
Similar to the endoscope, the endodontist holds the orascope while viewing the image from the monitor.28 Temperature and humidity difference between the dental operatory and the canal can cause moisture to condense on the fiber optic lens, causing fogging. The use of a lens antifog solution helps eliminate lens condensation build-up.
Figure 6. An orascope (Jedmed, St. Louis, MO).0
Figure 7. Cross-section of orascope probe showing the distribution of fiber optic image bundle and the light transmission fibers.0
In conventional and surgical endodontic treatment, there are different visualization parameters for each type of treatment, when magnification beyond loupes is required. Although both the microscope and rod-lens endoscope can be used for magnification for either type of endodontic treatment, the advantages for using a microscope for conventional endodontic treatment and a rod-lens endoscope for surgical visualization led to the development of a microscope coupler (Jedmed, St. Louis, MO) that enables the endodontists to combine both technologies (Figure 8). The combination unit also allows for the use of the orascope and digital documentation.
Figure 8. Combination microscope-endoscope visualization system (Jedmed, St. Louis, MO).0
Magnification versus Differentiation
Magnification is defined as making an object or treatment field greater in size. Differentiation is defined as making something distinct or specialized.29 The need to differentiate a magnified treatment field, when looking for a fracture in conventional endodontic therapy, or in surgical endodontic therapy when trying to identify the periodontal ligament space, an isthmus, or marginal leakage around a previous root-end filling, is important. Methylene blue, a nontoxic, biocompatible dye, can be used in conjunction with endodontic visualization instruments to help differentiate a treatment field in order to aid the endodontist in identifying etiology30 (Figure 9).
[Figure 8. Combination microscope-endoscope visualization system (Jedmed, St. Louis, MO).]
[Figure 9. A, Magnification of a root end without differentiation. B, Magnification of a root end with methylene blue added for differentiation.]
Figure 9. A, Magnification of a root end without differentiation. B, Magnification of a root end with methylene blue added for differentiation.0.015625
The ability to enhance vision during endodontic procedures has significantly increased the comfort level of endodontists in terms of identifying fracture lines, locating minuscule canal orifices, and confidently determining anatomic variations in teeth and supporting structures. Technological advances are continuously being made in advanced vision equipment, promising an even brighter future.
1. Silber S. Microsurgery. Baltimore: William & Wilkins Co; 1979. p. 1.
2. Kagan J, Gehly J, Wilson H. The effect of vibration on vision during microsurgery. Microsurgery 1983;4:209-14.
3. Shanelec DA. Optical principles of loupes. J Can Dent Assoc 1992;20:25-32.
4. Kanca J, Jordan PG. Magnification systems in clinical dentistry. J Can Dent Assoc 1995;61:851-6.
5. Millar BJ. Focus on loupes. Br Dent J 1998;185:504-8.
6. Caplan SA. Magnification in dentistry. J Esthet Dent 1990;2:17-21.
7. Baumann RR. How may the dentist benefit from the operating microscope? Quintessence Int 1977;5:17-18.
8. Selden HS. The Role of the dental operating microscope in endodontics. Penn Dent J 1986;53:36-7.
9. Selden HS. The role of a dental operating microscope in improved nonsurgical treatment of "calcified" canals. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1989;68:93-8.
10. Carr GB. Microscopes in endodontics. J Calif Dent Assoc 1992;20:55-61.
11. Mines P, Loushine R, West L, et al. Use of the microscope in endodontics: a report based on a questionnaire. J Endod 1999;25:755-8.
12. Rubinstein R. The anatomy of the surgical operating microscope and operating positions. Dent Clin North Am 1997;41:391-4.
13. Mounce R. Surgical operating microscopes in endodontics: the quantum leap. Dent Today 1993;12:88-91.
14. Nunley JA. Microscopes and microinstruments. Hand Clinics 1985;1(2):197-204.
15. Saunders WP, Saunders EM. Conventional endodontics and the operating microscope. Dent Clin North Am 1997;41:415-27.
16. Coelho de Carvalho MC, Zuolo ML. Orifice locating with a microscope. J Endod 2000;26:532-4.
17. Gorduysus MO, Gorduysus M, Friedman S. Operating Microscope improves negotiation of second mesiobuccal canals in maxillary molars. J Endod 2001;27:683-6.
18. Buhrley LJ, Barrows MJ, BeGole EA, Wenkus CS. Effect of magnification on locating the MB2 canal in maxillary molars. J Endod 2002;28:324-7.
19. Kim S. The microscope and endodontics. Dent Clin North Am 2004;48:11-18.
20. Rubinstein R. Endodontic microsurgery and the surgical operating microscope. Compendium 1997;18:659-72.
21. Detsch S, Cunningham W, Langloss J. Endoscopy as an aid to endodontic diagnosis. J Endod 1979;5:60-2.
22. Held S, Kao Y, Well D. Endoscope-an endodontic application. J Endod 1996;22:327-9.
23. Shulman B, Leung B. Endoscopic surgery: an alternative technique. Dent Today 1996;15:42-5.
24. Bahcall J, Barss J. Orascopic visualization technique for conventional and surgical endodontics. Int Endod J 2003;27:128-9.
25. von Arx T, Montagne D, Zwinggi C, Lussi A. Diagnostic accuracy of endoscopy in periradicular surgery—a comparison with scanning electron microscopy. Int Endod J 2003;36:691-9.
26. Taschieri S, Del Fabbro M, Testori T, et al. Endodontic surgery using 2 different magnification devices: preliminary results of a randomized controlled study. J Oral Maxillofac Surg 2006;64:235-42.
27. Bahcall J, Di Fiore P, Poulakidas T. An endoscopic technique for endodontic surgery. J Endod 1999;25:132-5.
28. Bahcall J, Barss J. Fiberoptic endoscope usage for intracanal visualization. J Endod 2001;27:128-9.
29. Bahcall J, Barss J. Orascopy: a vision for the new millennium, Part 2. Dent Today 1999;18:82-4.
30. Cambruzzi J. Methylene blue dye: an aid to endodontic surgery. J Endod 1985;11:311-14.